Steel Markets Steel Alloys

Refractories for The Iron and Steel Industry from Shinagawa Refractories Including Castables, Bricks, Gunning Mixes and Taphole Clays

2007-02-27T23:44:00.001-08:00

Shinagawa Refractories Australasia (Shinagawa) has established an enviable reputation for the manufacture and supply of quality refractory and insulating materials to the Australasian, South East Asian and Pacific Rim markets.
Refractories for The Iron and Steel Industry

This iron and steel industry is a primary consumer of refractory worldwide. It has historically been a key market for Shinagawa in Australasia, and also for Shinagawa in Japan. From blast furnace stoves, BOS vessels and steel ladles to torpedo ladles, troughs and electric arc furnaces, the company produces refractories suitable for the most arduous of steel making environments. SHIRAMAG, AIRMAG and RESICAL basic brick, SHIRAL high alumina and firecaly brick and SHIRACRETE low cement castables are just some products that have proven performances within this field. Commitment to continual improvements are evident in record achievements in steel ladle life with 80% alumina SHIRAL brick and also in expert production of intricate shape brick for coke oven chequers. Special developments such as the SHIRAGUN range of low cement gunning mixes are used in a number of applications within the iron and steel industry such as blast furnace trough covers and hot metal ladle pouring spouts. The product range also includes CASTON blast furnace trough castable and AIRTAP® tap hole clay for use on the blast furnace. An extensive range of state-of-the-art steel flow control refractories is offered from Shinagawa’s plants in Japan.

SHIRAMAG – Basic Monolithic Refractories

Shinagawa manufactures a range of basic refractories including magnesia, chrome magnesia and magnesia alumina spinel monolithics based on high purity magnesite and chrome ores. Magnesia contents range to 95%. Installation is by casting, gunning or ramming. With high strength and a unique bonding system they provide excellent resistance to molten metals (steel, copper, lead, alloys etc.) and slags. This family of refractories is marketed under the name SHIRAMAG.
AIRMAG – Magnesia-Carbon Bricks

Shinagawa offer a complete range of Magnesia-Carbon bricks. These products are marketed under the AIRMAG trade name and range from 7% to 20% Carbon content. With proven performance in Steel making vessels, Electric Arc furnaces and Steel Ladles throughout Australasia, the AIRMAG range of products are manufactured from very high grade raw materials and pressed to exacting specifications as required of such demanding applications. AIRMAG products are divided into three main classifications, premium, X and Y, according to process and technology and then are further classified based on Raw Material Quality (H/J/K) and anti-oxidation additions. Premium Magnesia-Carbon bricks - these represent the tried and tested materials used in all facets of Steel-making. Manufactured using premium grade materials, these product focus on security of production for our customers. X-Grade Magnesia-Carbon bricks – this range of bricks features a blend of materials aimed at meeting the stringent cost demands of our customers while still providing a high level of security and performance. Y-Grade Magnesia-Carbon bricks – these products maintain product consistency and a high quality standard for customers where pricing is a primary factor.
RESICAL – Alumina-Silicon Carbide-Carbon Bricks

The range of RESICAL bricks are alumina-silicon carbide-carbon products designed for use in molten iron handling applications. Typical use is in torpedo ladles and hot metal pots in integrated steel mills.
SHIRAL - Alumina Refractory Bricks

Shinagawa offers a complete range of high quality dry pressed alumina bricks, ranging from 35% to 95% in alumina content. These materials are manufactured with state of the art equipment, including computer controlled hydraulic presses that tightly regulate brick sizing and compaction pressure.

Firing is accomplished in multi-stage kilns to ensure even and accurate burning and consistent properties. Strict quality control standards control brick appearance and inherent variables such as strength, density and porosity. This quality approach serves three product groups in the SHIRAL dry pressed brick line:

· Fired High Alumina Bricks – these are produced from premium grades of alumina’s and bauxite’s and include brick with very low porosity, high strength, high thermal shock resistance and metal slag resistance. Some special grades are manufactured with phosphate bonds or andalusite aggregate for specific applications.

· Chemically bonded High Alumina Bricks – these high alumina, phosphate bonded brick are ideally suited to steel ladle or molten aluminium furnace applications due to their unique chemistry, including special aggregates and additives.

· Superduty and Fireclay Bricks – these lower alumina grades of brick are produced to the same exacting standards as the high alumina grades. These brick exhibit good strength and spall resistance over a range of service conditions and find use in a variety of applications.
SHIRACRETE – Low Cement Castables

The SHIRACRETE range of low cement, high technology monolithics is based on ‘state-of-the-art’ refractory castable technology using the highest quality aggregates, cements and additives. These products vary in alumina content from as much as 90% down to 45%. Superior physical properties are evident throughout the range. Low porosity plus outstanding strength and abrasion resistance are standard features of the SHIRACRETE low cement castable line.
SHIRAGUN – Low Cement Gunning Refractory

SHIRAGUN is a revolutionary range of low cement gunning products. SHIRAGUN low cement gunning materials combine the excellent physical properties of low cement castables with the speed and ease of installation by gunning. These materials were developed through an extensive research and development program over a number of years. The technical advantages of SHIRAGUN products over conventional gunning products include improved strength at all temperatures, excellent abrasion resistance, very good hot properties such as creep and hot MOR and very low porosity. SHIRAGUN low cement materials also show low dust and rebound characteristics and installs overhead with no slumping due to its excellent adhesion. The patented Shinagawa Inline Preform Mixer installation system can be used to further enhance the installation characteristics and physical properties of this product range.

CASTON – Castables for Blast Furnace Cast House Floors

The CASTON range of castable materials are used in blast furnace cast house floor applications. The range of CASTON products are based around high alumina aggregates with varying amounts of silicon carbide and carbon additions and contain no pitch or fume. These materials are excellent performers in metal and slag zones of main iron runners in blast furnace troughs as well as in slag runners, skimmer blocks, slag noses and other applications in the cast house floor. CASTON products have also found uses in non-ferrous applications where the non wetting abilities of silicon carbide and carbon provide benefits such as in molten copper handling and ferro-alloy production.
AIRTAP – Clays Specifically Designed for Metal Taphole Applications

AIRTAP is a range of clays specifically developed and manufactured for molten metal taphole applications. Typical applications include tapholes on iron blast furnaces, non-ferrous flash furnaces and electric arc furnaces. The clays are designed to ensure ease of application whether through manual or automatic means, the ability to fully fill the taphole and displace all liquids as well as high degree of security for taphole operations. The clays are also designed for simple removal through either mechanical drilling or other removal mechanisms.

High Tensile Steel for Tyres

2007-02-27T23:42:00.002-08:00

A full set of tyres is a major constituent of any car or truck because it has the exclusivity of contact with the road. Progress in automotive technology is impossible without synchronous improvement in tyre developments.

Types of Tyres

Although the tyre appears to be a simple thing, it is, in fact, a complex composite with as demanding a combination of requirements as any part of the vehicle structure. Since the introduction of the first steel-reinforced tyres, a continuing series of innovations has enabled cold drawn 0.8% C steel cord to remain the most economical and efficient way to manufacture high performance tyres in mass production. Consequently the market share for textile and glass fibres has been reduced or reserved for specific niches.

Factors Leading to Increased Life of Tyres

The aims have been to reduce the unsprung mass of the vehicle, with consequential improvements in fuel economy and reduced emissions, and to increase the lifetime of tyres. These have been achieved by increasing the strength of steel cord filaments by 15%, with a corresponding increase in fatigue performance as well as maintaining the level of ductility of individual filaments and optimising manufacturing methods to control costs. A change in the design of the cord assembly was made in order to improve the reinforcement functionalism of the tyre.

Why use Steel?

Steel is the only material available to reinforce tyres which has a stabilised endurance limit, i.e. below a characteristic stress level no fatigue crack propagation will occur with infinite fatigue life. Above this threshold stress level, the higher strength steel cord gives between 10 and 30% longer life and enables truck tyres to be safely retreaded twice, giving lives of 500,000 km.

Steel Developments

A new high strength steel has been developed through the adoption of continuously casting with low segregation levels and high surface quality. Modifications and improvements to the drawing and heat treatment equipment have enabled steels with higher carbon contents to be drawn. The cold work deformation ψ increased from 3.2 to 3.5. The availability of the higher strength steel has facilitated the use of more productive stranding equipment. New strand and cable assemblies have been developed to make it possible to transmit an increased shear stress from the reduced cord surface to the surrounding rubber.

The strength of steel cord filaments is related to the logarithmic value of the filament size, table 1.

Table 1. Strength of steel cord filaments in relation to filament size.

Diameter (mm)	Regular tensile (N/mm²)	High tensile (N/mm²)
0.15	2950	3400
0.20	2815	3240
0.25	2720	3130
0.30	2650	3000
0.35	2580	2960

The amount of cold work is limited to levels that assure an acceptable ductility, and this is size dependent.

Load Transfer

As far as tyre design is concerned, the increase in the ultimate strength of the filaments must be effectively transferred to the functional surroundings of the reinforcement. To increase its efficiency the coated cord ply must have a lower weight for the same strength or a higher strength for the same weight. Higher strength cord also requires less special rubber providing adherence to the brass-coated cord.
Implications of High Tensile Cords

Because the wall thickness of the tyre body is decreased with the higher strength steel cord the hysteresis loss of deformation energy is also reduced, leading to lower fuel consumption and lower running temperature. The overall benefits include the following:

· Reduced weight tyres

· Reduced unsprung mass

· Longer life tyres

· Reduced fuel consumption

· Reduced vehicle emissions

· Reduced running costs

· Lower consumption of natural resources.

Galvanised Steel - Underground Corrosion

2007-02-27T23:42:00.001-08:00

Buried steel items are subjected to a range of corrosive forces quite unlike those experienced in atmospheric exposure conditions, and the performance of both steel and galvanized steel in-ground is not as well understood as is the durability of these materials in above-ground applications.

Considerable research into the management of underground corrosion has been done, particularly with pipelines and related services.
Corrosion Factors In-Ground

Both steel and zinc react in different ways when in contact with soil and an understanding of the performance of each material when in contact with soil allows structure service life to be determined with reasonable accuracy.

Steel requires oxygen, moisture and the presence of dissolved salts to corrode. If any one of these is absent, the corrosion reaction will cease or proceed very slowly. Steel corrodes quickly in acidic environments and slowly or not at all as alkalinity is increased.

Zinc requires the presence of stable oxide films on its surface to provide its corrosion resistance. It performs best in neutral pH environments although it can tolerate exposures in the range from pH 5.5 to pH 12. In the absence of air, the stable oxide films do not form on the zinc surface, and corrosion can be accelerated if moisture is present under these conditions.

For this reason, galvanized steel is the best combination where structures are partly buried and partly exposed to the atmosphere, as the zinc provides the durability above ground while the steel performs predictably in-ground.
Soil Types and Corrosion

Corrosion of metals in soil is extremely variable and while the soil environment is complex, it is possible to make some generalizations about soil types and corrosion. Any given soil is a very heterogeneous material consisting of three phases:

The solid phase is made up of the soil particles that will vary in size and will vary in chemical composition and the level of entrained organic material.

The aqueous phase which is the soil moisture – the vehicle that will allow corrosion to proceed.

The gaseous phase, which consists of air entrained in the soil’s pores. Some of this air may dissolve in the aqueous phase.
The Solid Phase

Soils are classified according to their average particle size and their chemistry. Convention classifies particles over 0.07 mm to around 2 mm as sands, particles from 0.005 mm to 0.07 mm as silts and 0.005 mm and smaller as clays. Soils rarely exist with only one of these components present. Clay soils are characterized by their ability to absorb water readily. For this reason, clay soils present a significantly higher corrosion risk than sandy soils.
The Aqueous Phase

There are three types of soil moisture. These are free ground water, gravitational water and capillary water.
Free Ground Water

This is determined by the water table, which may range from ground level in swampy areas to many metres below the surface. This is the least important factor in determining corrosion as most buried structures are above the water table. High water tables will result in the buried structures behaving as if they were in an immersed environment.
Gravitational Water

This arises from rainfall, irrigation or condensation and will soak into the soil at a rate determined by its permeability. The frequency of contact will determine the period of wetness of the metal surface. In areas of regular heavy rainfall, most soluble salts may have been leached from the soil. Desert areas of low rainfall may have very high salt levels and can thus be more corrosive to buried metals than tropical environments.
Capillary Water

This is water entrained in the pores and on the surfaces of the soil particles. The ability of soil to retain moisture is vital to plant growth but it is the capillary water that is the prime source of moisture in determining corrosion rates of metals in soil.
The Gaseous Phase

Access of gas (air) into the soil depends on the soil’s permeability. Drier soils or coarser grained soils will allow more oxygen access to the sub-surface and increase the rate of steel corrosion relative to the oxygen deficient areas.
Corrosion Rates And Australian Standards

AS/NZS 2041-1998 –Standard for buried corrugated metal structures contains much useful information in table for to allow product life in-ground to be determined. These tables take into account resistivity of the soil (which factors in related issues such as levels of dissolved salts), pH and soil characteristics. This information is then related to in-ground corrosion rates for both zinc and steel.

Steel Plant Developments

2007-02-27T23:41:00.001-08:00

Although world steel production has grown at a relatively slow rate since the mid 1970s, the process by which the steel is produced has changed, with a continuing shift from open hearth to oxygen steelmaking and more recently an increasing emphasis on EAF production, figure 1. The timescale for the deployment of such new process technology is measured in decades owing to slow growth, long life of existing plant and the low variable cost of current blast furnace and basic oxygen steelmaking (BOS) plant. The cost factor is crucial, as it is not economically viable to replace existing BF/BOS plant with new technologies such as electric arc furnaces, direct reduction or smelting reduction until the plant reaches the end of its life.

As a result, the strategy in areas where there is little or no growth is to maximise the profitability and competitiveness of existing plants, prior to replacing them at the end of their life in a cost effective way. In areas where there are growth opportunities, there is a wide range of process technologies that can be tailored to match local market demand, feedstock and energy availability. This article gives examples from within British Steel of developments to increase the competitiveness of existing plants and summarises the new process technologies available.
Improving Profitability

British Steel seeks improvements to profitability through cost reductions, extending plant life, higher quality and higher value products. The company has made cost reductions in the area of ironmaking through advances in blast furnace performance. Productivity has increased thanks to operational improvements and also by reducing the number of furnaces, removing the older, most inefficient units. Equivalent coke rate in the furnace has reduced from 540 kg.thm-1 in 1980 to 480 kg.thm-1 in 1997. In addition, coal injection has increased and now is installed on most furnaces in British Steel. Developments in other fuel injection technologies, such as oil and natural gas, have also continued, and the use of fuel injection will increase. Consequently, coke consumption will continue to fall, minimising imports.
Extending Plant Life

Maximising asset life to defer expenditure on plant replacement is also key to maintaining competitive plants. Cokemaking developments in the areas of coal blend selection, control and monitoring, improved maintenance and inspection are geared to achieving a 40 year campaign life on current coke oven batteries. Blast furnace productivity has, over the past six years or so, levelled off and in recent times decreased. This is owing to the emphasis being placed on extending plant life as much as possible. As an example, Redcar blast furnace has reduced its daily production capacity from more than 10 ktpd to 9.2 ktpd. Key developments in ironmaking on life extension include:

· operator guidance systems for improved operation and reduced fuel rates

· liquid management systems using EMI's

· plant condition monitoring

· a stability task team

· a long life hearth group

· shell cooling improvements.
Control Systems

Blast furnace stability and control are important for maximising plant life. There have been developments in instrumentation, probes, expert systems and process control. Systems are now available that supply the operator with advance warning of furnace instability. Several key process variables are monitored and correlated, such as off-take temperatures, bosh and stack differential pressure, Eta CO and stock rod monitoring.
Higher Quality Steels

For producing higher value added products, higher quality steel must be produced in the first place. Over the past two decades, quality improvements have been developing, particularly with the introduction of secondary steelmaking. With the recent improvements in computing power and information technology, several examples of secondary steelmaking process control developments can be highlighted. These include ladle thermal tracking, ladle additions modelling, ladle power input modelling and process route timing. Other process and engineering developments include the smart lance, sub lance, tank degasser and a reduction in slag carryover. These have all led to substantial improvements in steel grade quality that can now be produced.
Improved Casting Technology

British Steel has invested substantially in casting technology, with many projects for either new casters or caster enhancements since 1994. Retrofitting new technology into existing plant is a key means of enhancing performance and the installation of a heat removal device to achieve near liquidous casting is an example of this. This process development has provided better quality in terms of improved segregation ratios.
Higher Value Added Products

Partly owing to improved steel quality being available and partly owing to process and engineering developments, the capability to produce higher value added products has increased. Current examples within British Steel are Slimdek (based on the asymmetric beam), the jumbo column, Bisteel and Lasersure. Indeed, Slimdek has been chosen by the Design Council as one of only six construction related products to be nominated as a ‘millennium product’. This scheme was proposed to identify and encourage the UK’s most innovative products and services.
Finite Element Analysis

Important to rolling development is finite element analysis, figure 2. This enables accurate simulations of the rolling process to optimise shape development through the process within the capability of the mill. This can lead to faster development and lower development costs of new products, the ability to optimise product quality, improved process understanding and input into design of new rolling equipment. Future development in this area includes metallurgical modelling to predict product properties.

New Process Technologies

New process technologies are being developed, with the aim of achieving:

· lower capital costs

· economic viability at small scale

· lower operating costs

· raw material flexibility

· environmental benefits.

The main areas for new process technology are alternative ironmaking, EAF steelmaking and casting technologies.

Alternative ironmaking can be split into two parts:

· direct reduction (scrap substitute)

· smelting reduction (hot metal replacement).

World direct reduced iron (DRI) production has increased markedly in the past 6 years, as the product is predominantly used in the EAF and therefore demand has increased with increasing global EAT steelmaking. Current world DRI production stands at 36 Mtpa.

There are several DRI processes but the Midrex process is by far the most prevalent. Newer fines based processes are being built, such as Finmet and Circored, and these should provide even lower operating costs. The only commercially available smelting reduction process currently available is Corex, with two operating plants worldwide and three other projects under development. Corex uses agglomerated ores as the feedstock and currently has a maximum capacity for a C3000 unit of 1.08 Mtpa. The next generation of fines-based smelting reduction processes are still several years away from fully being developed and include Hismelt, CCF and DIOS.
Electric Arc Furnaces

Electric arc furnaces have comparatively low capital costs at a capacity of 1 Mtpa, when compared to conventional ironmaking. The viability at small scale and the ability to feed regional markets with product from greenfield site developments has led to this technology being the first choice for new growth. To make the process even more attractive there are ongoing improvements to the EAF design concept, such as twin DC electrodes, oxy-fuel energy, scrap preheat, high furnace aspect ratio, twin shell and DC furnace.
Casting Developments

Casting developments have aimed to reduce the number of process steps involved in producing the final product. Conventional casting machines may be up to 800m in length, containing repeating furnace, roughers and finishers. With the advent of thin slab casting the number of stages is reduced, typically reducing machine length to 250m. Figure 6 shows a thin slab caster, commercialised in 1989, with more than 30 installations to date, including British Steel's investment in two US-based mills, Tuscaloosa and Trico.

Another development in casting is direct strip casting at much thinner gauges. Worldwide there are 15 developments underway, mainly for stainless product, with an NSC plant scheduled to be commence operation later this year.

Stainless Steel - Sorting and Identification Tests

2007-02-27T23:40:00.001-08:00

These tests are intended for rapid, inexpensive and usually non-destructive and on-site sorting of grades of stainless steel. They are particularly useful for sorting products when, for example, bars of grades 304 and 303 have been accidentally stored together, or grade 304 and 316 sheet offcuts mixed.

These tests are extremely useful, but it is important to realise that they have limitations; they cannot sort one heat from another of the same grade, and there is no easy way of sorting certain grades from each other. For instance, it is not possible to readily sort 304 from 321, 316 from 316L or 304 from 304L. The Molybdenum spot test therefore indicates that a piece of steel contains Mo, but does not alone indicate 316. In the absence of other knowledge the steel could be 316L, 2205 or 904L etc.

The simple tests described may assist in grade identification and product sorting. Other, more complex tests can also be carried out; these can involve several chemical reagents, hardness tests or checking response to heat treatment. In most cases, however, if these simple tests are not sufficient to identify the product it is best to have a full spectrometric analysis carried out by a competent laboratory.

The need for these sorting tests can be reduced if original product identification is retained. Product colour codes, tags and stickers and stamped or stencilled Heat/Grade/Specification markings should be retained as much as possible.

Tests

Table 1. Tests for the identification and sorting of stainless steel

Test	What Can Be Sorted	Method	Precautions
Magnetic Response	Austenitic (300 Series) stainless steels from other steels. All other steels are attracted to a magnet, including the ferritic, duplex, martensitic and precipitation hardening stainless steels. The only other non-magnetic steels are the austenitic manganese steels (eg “P8”).	Note response, if any, when a permanent magnet is brought close to the steel.	Some austenitic grades, particularly 304, are attracted when cold worked, eg by bending, forming or rolling. Stress relieving at cherry-red heat will remove this response due to cold work. This stress relief may sensitise the steel and should not be performed on an item which is later to be used in a corrosive environment. A full anneal is acceptable, however.
Nitric Acid Reaction	Stainless steels from non-stainless steels.	1. Place a piece of the steel in strong nitric acid (20% to 50%) at room temperature, or a drop of the acid on a cleaned surface of the steel. 2. Test standard samples in the same way, ie stainless and non-stainless steel samples. 3. Non-stainless steels will quickly be attacked, a pungent brown fume is produced. Stainless steels are not affected. Compare result with standards. 4. Wash samples thoroughly afterwards.	Wear safety glasses. Strong nitric acid attacks skin and is very corrosive. Handle carefully. Use minimum quantities. Wash off immediately if skin contact occurs. Do not breathe brown fume.
Molybdenum Spot Test (Mo)	Stainless steels which contain significant Molybdenum from those which do not. The most common use is to sort 404 from 316, but the following grades also contain sufficient Mo to give a positive response to this test: 316, 316L, 317, 317L, 444, 904L, 2205, "6-Mo" grades, 4565S and all “super duplex” grades (e.g. S32760 / Zeron 100 / S32750 / 2507 / S32550 / Alloy 255 / S32520 / UR52N+). Other similar grades with deliberate Molybdenum additions will also respond.	1. Clean the steel surface; use abrasive paper, and if necessary degrease and dry. 2. Use "Decapoli 304/316" solution – shake well, then place one drop on the steel. 3. Place similar drops on standard 304 and 316 samples. 4. Darkening of the yellow drop in 2 to 4 minutes indicates significant Mo. Compare with indications on standard samples. 5. Wash or wipe samples clean.	Avoid contact of test solution on skin, and particularly eyes. Wash off immediately if contacted. Reliable results only obtained if samples all the same temperature and freshly cleaned. Avoid very low sample temperatures. Some Heats of "Mo-free" stainless steels, such as 304, contain enough Mo to give a slight reaction. Standard comparison samples must be used.
Sulphur Spot Test (S)	Steels (stainless and plain carbon) containing at least 0.1% Sulphur, ie free machining grades. (eg S1214, S12L14, 303, 416, 430F), from non-free machining steels. Ugima 303 contains high sulphur (the same as standard Type 303) so will give a positive reaction, but Ugima 304 and Ugima 316 have the same low sulphur contents as their standard (non-Ugima) equivalents, so will not give positive reactions.	1. Clean the steel surface; use abrasive paper, and if necessary degrease. A flat area is preferred. 2. Prepare standard samples in the same way, eg known CS1020 and S1214, or 304 and 303. 3. Soak photographic paper in 3% sulphuric acid for about 3 minutes. 4. Press the prepared steel surfaces on the face of the photographic paper for 5 sec. 5. A dark brown stain indicates significant sulphur. Compare with indications from standard samples. 6. Wash samples thoroughly.

Caburising 9310 Steels – Control of Carbon Profiles in a Fluidised Bed Furnace

2007-02-23T20:57:00.001-08:00

For many years, carburising has been amongst the most widely used processes for developing a hard, wear resistant layer on steel components. Fluidised bed furnaces have proven themselves to be very effective in carrying out the carburising process. Whilst conventional atmosphere carburising can be carried out in the fluidised bed, the boost/diffuse technique is the preferred option, with cycles carried out between 920°C and 1000°C. During the boost period, enriching hydrocarbon gas in excess of the desired carbon potential is passed through the furnace. This enriching hydrocarbon is generally natural gas or propane and is mixed with a carrier gas such as nitrogen to dilute the hydrocarbon, Following this boost period in which the surface of the material is saturated with carbon, the component then undergoes the diffuse period, whereby only nitrogen is present and the absorbed carbon diffuses towards the core of the material. The rate of carbon absorption is controlled by the carbon potential present in the furnace, as well as the surface activity and solubility limit of the steel, whilst diffusion is controlled by Ficks Law. As with vacuum and plasma carburising the surface carbon and effective case depth can be calculated by a computer program to give optimum times.

Advantages of Using a Fluidised Bed Furnace

There are a number of advantages gained by using fluidised beds. The major difference between carburising in fluid beds and conventional furnaces is the extremely high carbon potentials produced in the fluid bed during the boost period. Research has shown that within minutes of passing the hydrocarbon gas into the furnace it has broken down to produce free carbon particles causing the bed to reach a high carbon potential. For this reason treatment times in fluid beds can be significantly shorter than in conventional furnaces. Other advantages of the fluid bed include good temperature uniformity and excellent heat transfer properties which translates to better process control and uniformity.

The Importance of Controlling the Carbon Profile

However, even with the latest furnace technology, manufacturers are often unsure as to what are optimal case properties. It is clear that the carbon profile is crucial in producing optimal properties and performance on a case hardened component. In fact it is the carbon profile that generally determines the microstructure and hardness profile of the final treated component. For example, if the carbon content at the surface is too low then the resultant hardness and wear resistance will be subsequently poor. Conversely, too high levels of carbon leads to excessive retained austenite and the formation of carbide networks at grain boundaries which can lead to premature fatigue failure.

The Hardness Profile and Carbon Gradient

What is considered particularly desirable is a relatively high surface hardness that extends into the steel producing what is referred to as a flat hardness profile. This type of hardness profile can provide a number of advantages. Firstly, in comparison with standard hardness profiles, the flatter profile will have higher hardness values at similar depths, and therefore improved wear resistance over the life of the component. Furthermore it has been shown that higher carbon levels can result in small spheroidal carbides forming within grains which have been shown to improve wear resistance. Secondly, a great number of carburised components are machined or ground after case hardening in order to bring them back to within operating tolerances. It is common for up to 0.2 mm of material to be removed from the component in the final machining or grinding process. The problem with this practice is that in typical case depths of up to 1.00mm, this is removing 20% of your hardened zone, and once removed the underlying surface has considerably less carbon and therefore lower hardness and wear resistance. Considering these points it is therefore important to establish the correct ratio between boost and diffuse times to obtain a carbon gradient that will produce the desired transformation sequence and case depths upon quenching.

The Pulsed Boost Diffuse Technique

Tests have indicated that merely increasing the boost period to obtain higher carbon levels leads to excessive retained austenite and/or carbide networks. There is however, an alternative to the standard carburising cycle, which gives greater control over the final carbon profile. This technique is known as the Pulse Boost Diffuse technique (PBD). The key is to shorten the boost and diffuse periods but repeat them a number of times during the one cycle at the same temperature. This ensures that high levels of carbon are maintained at increased depths, hence producing a flat hardness profile. An additional advantage of this technique is that small spheroidal carbides can nucleate within the microstructure as a result of the higher carbon levels.

Case Study – Pulse Diffuse Boost Treating of 9310 Steel

A series of experimental trials was therefore conducted to evaluate the effectiveness of the Pulse Boost Diffuse treatment and determine if indeed a superior carbon and hardness profile could be obtained. The sample material was 9310, a commonly used carburising steel and one which can provide difficulties when attempting to achieve higher carbon levels due to the high nickel content (up to 3.55%) acting as a retained austenite stabiliser and causing excessive carbide networking.

Experimental Procedure

All tests were conducted in a fluidised bed furnace at 950°C using natural gas as the enriching gas and high purity nitrogen as the carrier gas. All samples were machined from 93 10 barstock.

Standard Boost and Diffuse Carburising Cycle

The first test (cycle 1) involved performing a standard boost and diffuse carburising cycle to obtain an effective case depth of 1.00mm. A computer program based upon the Harris Equation was used to determine the boost and diffuse times. It was calculated that a boost period of 47 minutes was required, followed by a diffuse period of 113 minutes. On completion of the carburising cycle the samples were direct oil quenched followed by a temper at 180°C. Finally, each sample was cryogenically treated in liquid nitrogen to transform any retained austenite and a second temper carried out. This standard cycle was performed not only to evaluate results but also to act as a standard against which the Pulse Boost Diffuse cycles could be compared.

Pulse Boost Diffuse Carburising Treatment Cycle

The second stage of the experiment was to carry out the Pulse Boost Diffuse treatments. This initially involved dividing up the standard cycle into shorter boost and diffuse periods and repeating these a number of times. The first Pulse Boost Diffuse cycle was 15 minutes boost and 25 minutes diffuse repeated four times, producing a total cycle time the same as the standard cycle. A second FBI) cycle reduced the boost period to 10 minutes and extended the diffuse period to 30 minutes also repeated four times. As with the standard cycle these samples underwent an initial temper followed by subzero treatment and final temper after carburising. It is important to note that the total treatment time was kept constant in order to keep the effective case depth to 1.00mm. All other variables such as quench rates were kept constant. After the trails each specimen was cut, mounted in epoxy resin, etched and the microstructure examined. Finally, each sample underwent a traverse hardness test to determine the hardness profile. This was carried out on a Vickers microhardness tester using a 100g load. A summary of the cycles carried out is given in Table 1.

Cycle	Carburising Temp (°C)	Boost Period (min)	Diffuse Period (min)	Repet-itions	Quench	Post Carb. Treat
1	950	47	113	1	Oil	Temper, Subzero, Temper
2	950	15	25	4	Oil	Temper, Subzero, Temper
3	950	10	30	4	Oil	Temper, Subzero, Temper

Results

Plotting hardness versus depth clearly demonstrates the difference between the cycles and ultimately provides an indication of the final carbon profile produced. Graphical representation of results for the various cycles is shown in Figure 1.

Figure 1. Hardness profiles of 9310 steel after the various carburising treatments.

Hardness Profile for the Boost and Diffuse Treatment

The standard carburising cycle (cycle 1) resulted in a surface hardness of 700HV that begins to taper off after only 100 microns down to a core hardness of 380HV The effective case depth was approximately 0.9mm (determined at 500Hv. The microstructure for the standard cycle was predominantly tempered martensite with a very few scattered carbides.

Hardness Profile for the Pulse Boost Diffuse Treatment

The hardness profiles produced by the two Pulse Boost Diffuse cycles were similar, however both of which were considerably different to that produced by the standard cycle. Both cycle 2 and cycle 3 had a high surface hardness (760Hv) as compared to the standard treatment. This higher hardness has been maintained to a depth of 0.3mm hence producing a flat hardness profile, At approximately 0.8mm all three profiles come together to give an effective case depth of between 0.9mm and 1.00mm. In all cases core hardness was between 360 and 400HV.

Microstructural Differences

The main difference between the two Pulse Boost Diffuse cycles was in the case microstructure. In both cases the matrix was composed of tempered martensite, but cycle 2 produced a microstructure with strong grain boundary carbide networks. Cycle 3 however, produced a marked improvement in microstructure. Although some large carbides are present, they are evenly dispersed and there is no carbide networking at grain boundaries. Figure 2 indicates the microstructures produced by each cycle.

Figure 2. Microstructures of 9310 steel after the various carburising treatments.

Discussion

Modifications to the standard carburising cycle in order to alter carbon levels and nucleate spherical carbides is not new technology. In fact, carbide dispersed carburising was first proposed by O.E. Cullen in 1961, and has been covered in a number of papers since. However, these methods have required that a second furnace be available in order to nucleate carbides at a lower temperature once the boost period is complete. This technique, whilst successful in producing higher hardness values and intergranular carbides, is not practical in the heat treatment industry. Therefore, a major advantage of the Pulse Boost Diffuse cycle is that it can be carried out in a single furnace at one temperature without interruption, and with modern programmable controllers the cycle can be carried out with a minimum of supervision.

Effect of Treatment Cycle on Hardness

In comparing the results obtained from the experiments, it is clear that the Pulse Boost Diffuse technique has the capability to produce a superior carbon profile, and subsequently an improved hardness profile. This is illustrated in Figure 1, as both cycle 2 and cycle 3 have achieved a greater surface hardness and a considerably flatter profile whereby hardness has been maintained at increased depths. In fact the Pulse Boost Diffuse cycles have both maintained 700HV or above, up to 0.3mm within the case. This type of profile would provide excellent wear resistance on the component and extend service life considerably. It would also mean that any grinding or machining after carburising would have less of a detrimental effect on the case. It should be noted that the effective case depths produced by all three cycles were very similar, and beyond 0.7mm all hardness values are approximately the same. This means the Pulse Boost Diffuse cycle can be carried out without having to extend standard treatment times, and that controlled case depths can be achieved on critical components.

The Effect of Microstructure on Materials Properties

The effect of microstructure on the final properties of 9310 is also of considerable importance. Again the microstructure is strongly dependant on carbon content and achieving an optimum gradient. Lower levels of carbon are not easily detectable, but will result in reduced hardenability and wear resistance. Excessive carbon has a much more pronounced effect. Excessive carbon can firstly lead to unacceptable levels of retained austenite. In the trials conducted all samples were subjected to a subzero treatment in order to minimise retained austenite, but the effects of retained austenite must be considered. Retained austenite is generally not considered harmful when present in amounts less than 30%, particularly if finely dispersed, and in some instances a small amount of retained austenite is desirable.

However, in other applications such as heavily loaded gears, retained austenite is limited to less than 5%, given that austenite is unstable and can cause lower hardness, reduced wear resistance and premature failure.

Excessive Carbon

Excessive carbon has the additional problem of creating grain boundary carbides. As carbon levels increase, carbides begin to outline prior austenite grain boundaries. If these levels continue to increase the carbides will not only grow in size but network along the grain boundaries. Large particle carbide precipitates at grain boundaries are detrimental to impact toughness and contact fatigue properties. This situation has occurred in cycle 2 and it appears that the longer boost periods have lead to an acceptable carbon level. It is likely that a component with this microstructure would fail in service. It should also be noted that 9310’s high concentration of nickel acts as a carbide stabiliser, and is the likely reason that carbides were present in all cycles conducted. An additional factor to consider is the concept of the corner effect. Most components have a sharp edge of some description, which can also enhance the problem of having excessive carbon levels as a result of carbon diffusing from both sides of the corner. However, in sensitive components where this may pose problems copper plating or stop off paints may be utilised to minimise the problem.

Controlled Carbide Formation

Controlled carbide formation, can however, provide benefits. The volume, size and distribution of carbides in a case microstructure all have a distinct influence on wear resistance. Generally, wear resistance improves as the volume of carbides increase at the wear surface due to the very high hardness levels obtained by alloy carbides. It is therefore important to be able to produce finely dispersed carbides within the microstructure of a case hardened component, such as those produced by cycle 3.

Stainless Steels - Formability, Fabrication and Finishing, Supplier Data by Aalco

2007-02-23T20:56:00.004-08:00

The single most important thing to remember when fabricating a product from stainless steel is to ensure that the fabrication processes retain and do not compromise the intrinsic properties of stainless steel.

Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials. Tooling and work surfaces must be thoroughly cleaned before use. These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

Tools and blades must be kept sharp and clearances, for example between guillotine blades, must be tighter than for carbon steels.

Advantages

Apart from the commercial reasons for choosing stainless steel as a material, like heat and corrosion resistance, another advantage is its fabrication properties. The austenitic grades in particular can be fabricated by all standard fabrication methods. Some techniques are more suited to particular stainless grades than normal carbon steels. This is well demonstrated for severe deformation procedures such as deep drawing.

Due to stainless steel tending to have higher strength and work hardening rates than carbon steel, some alteration to tooling and equipment may be required:

· A more robust machine may be required due to the high strength of stainless steel.

· For the same reason the capacity of a machine, such as a guillotine may be only 60% of its carbon steel capacity.

· Greater deformation than used for carbon steels may often be necessary due to spring-back after forming. For example in tube making a different roll set design to that used for carbon steel will be required as a higher degree of over-bending is necessary.

Fabrication Methods

Drawing

Cold drawing can produce components in 301, 302 and 304 with tensile strengths in excess of 2000 MPa due to work hardening. Producing components at these strengths is limited to very thin sections and fine wires.

With increasing section thickness the amount of cold work required to produce these strengths also increases to the point that it cannot be done practically. This is due to the surface of stainless steel work hardening more rapidly than the interior of the material. Work hardening the entire cross section of larger diameters requires exceptional and impractical forces.

Austenitic stainless steel can be used to produce deep drawn components that require very high elongations and thus stainless steel is widely specified for the production of hollowware.

Forming Speeds

Unlike carbon steels, work hardening rates for stainless steels mean that more severe deformation is possible at slower forming speeds. For forming operations normally performed at high speed, like cold heading, it is recommended that the process is slowed.

Cutting

Most grades of stainless steel can be cut using standard cutting methods employed for other metals. The work hardening rate of stainless steels sometimes means heavier equipment and specialist blades or cutting edges are required. Consideration must also be given to changes in the heat affected zone when the cutting method generates high heats along the cut.

Common cutting methods include:

· Plasma cutting

· Laser cutting

· Water jet cutting

· Bandsawing

· Slitting

· Guillotining

· Abrasive disc cutting

Bending

Like many other fabrication methods for stainless steel, bending can be done using the same equipment used to bend other metals. A difference is that working hardening rates may mean a need for more rigid equipment and higher power levels. Equally, equipment capacity will be much lower than for Carbon steels.

Bar and Flat Bending

Round bar, flat bar, sheet and plate can be bent using a press brake, bending machine or ring-rolling. Due to work hardening, bending should be done quickly. Some over-bending will be required to counteract spring-back of the bend. The inside bend radius should not be smaller than the thickness of the material being bent.

Tube Bending

Tube bending is often done for architectural and other applications. Bending of stainless tube can be difficult unless done by persons experienced in the field. Rotary bending and hydraulic press bending can both be employed to bend stainless steel tube.

Centre line bend radii should not be smaller than twice the tube diameter.

Welding

Most grades of stainless steel can be welded by all traditional welding methods. However, the weldability of different grades can vary considerably. Some austenitic grades are considered to be the most readily welded metals. Weldability is generally low for ferritic and martensitic grades. For some grades, such as 416, welding is not recommended at all.

Recommended filler rods and electrodes vary depending on the grade being welded.

Machining

A commonly held belief is that stainless steel is difficult to machine. Machining can be enhanced by correct grade selection and using the following rules:

· Cutting edges must be kept sharp. Dull edges cause excess work hardening.

· Cuts should be light but deep enough to prevent work hardening by riding on the surface of the material.

· Chip breakers should be employed to assist in ensuring swarf remains clear of the work

· Use lubricants in large quantities.

Stainless steels like 303 and free machining grades have Sulphur included in the composition. This produces a marked increase in machinability but reduces both corrosion resistance and weldability. Over the years manufacturers of stainless steel bar have greatly improved the machinability of standard 304 and 316 grades. This has been achieved by careful control of compositions and production process variables that avoid the detrimental effect seen with Sulphur-bearing grades. This means the point has now been reached where many specifiers and machine shops have switched away from 303.

Finishing

Although stainless steels have excellent corrosion resistance, and are often selected for this property, proper finishing is required to maintain it. After any fabrication process that alters the surface condition of the material, the stainless steel needs to be degreased, cleaned and finished appropriately.

Finishing methods may include one or more of the following:

· Pickling

· Passivation

· Grinding

· Electropolishing

· Mechanical Polishing

· Blackening

· Colouring

Pickling

Pickling uses an acid or mixture of acids to remove scale produced in high temperature operations like welding, heat treatment or hot working. Acids and procedures depend upon the grade of stainless steel being treated. A great deal of care must be taken during the pickling process and with disposal of the waste as the acids used include sulphuric acid, nitric acid and hydrofluoric acid.

Pickling also removes rust due to corrosion of the stainless steel or corrosion of contaminant iron and steel particles.

The scale is removed as it retards the corrosion resistance of the underlying stainless steel.

Pickling is commonly done using baths or “Pickling Paste”. Pickling paste is a specially prepared stiff paste of strong acids. In this form it can be applied to vertical or overhanging surfaces and localised areas. Pickling paste is often employed to remove post-weld discolouration.

These are strong acids and appropriate caution must be taken when handling them. The same applies with acids used in passivation.

Passivation

Passivation is a process used to remove any free iron contamination of the stainless surface. Iron in the form of elemental iron, cast iron, carbon steel, mild steel or other non-stainless alloys can cause problems with stainless steels. This material is normally deposited from tools or work surfaces during fabrication. The iron particles promote corrosion on the surface of the stainless steel. At it’s mildest form, the discolouration caused can be unsightly. More serious corrosion is isolated pitting corrosion at the point of contamination.

Passivation involves treatment of the stainless steel with nitric acid or a nitric acid and sodium dichromate combination to remove the iron contaminants.

Grinding

Stainless steels are readily polished and ground if standard techniques are slightly modified. A build up of material on abrasive media occurs due to the high strength of stainless steels. Low thermal conductivity means that there is also a build up of heat. The result can be heat tinting of the surface of the material.

Using low grinding and feed speeds combined with specifically selected lubricants and grinding media can alleviate these complications.

Corrosion resistance of stainless steels tends to increase with the extent of surface polishing.

Electropolishing

The reverse of electroplating is electropolishing. This is an electrochemical process that removes the peaks of the rough surface of a metal. Electropolishing smooths the material surface making it brighter.

The resultant finish is very corrosion resistant, hygienic and attractive. On some stainless steels the surface finish appears frosted rather than smooth and reflective.

Mechanical Polishing

Any mechanical polishing procedures must be carefully done to ensure contamination by iron based materials doesn’t occur.

Sand blasting must be done with clean silica or garnet sand. Shot, grit and cut wire blasting must use stainless steel media of equal or greater corrosion resistance than the metal being cleaned. Barrel and vibratory finishing are often used to polish fittings and small parts.

Light heat tint can be removed by wire brushing but the brushes must be stainless steel and never be used on other materials.

Mechanically cleaned parts are not as corrosion resistant as pickled stainless steel. This is due to mechanical cleaning not removing all the chromium depleted material from the surface and the retention of some scale residue. Mechanical cleaning is often used to prepare the surface of stainless steel before pickling.

Blackening

Occasionally a highly polished surface is not wanted for stainless steel. In this case blackening is used to produce a non-reflective black oxide surface. Several methods can be used to achieve this finish.

Some treatments are proprietary but two common methods are immersion in a solution of sulphuric acid and potassium dichromate solutions or immersion in a molten salt bath of sodium dichromate.

Colouring

Stainless steels can be given a range of surface colours for architectural applications. These colours include bronze, blue, gold, red, purple, black and green. A range of shades can also be produced.

The colouring is done by a proprietary process that involves immersing the stainless steel in a hot chromic/sulphuric acid solution. This is followed by a cathodic hardening treatment in another acidic solution. The base material reacting with the hot acid produces a transparent film. Although the film is colourless, light interference imparts a colour to the layer. If the underlying metal surface is highly polished the effect will be a strong metallic lustre. For matt and satin finished stainless steel, the result will be a matt finish.

Car Recycling under way According to New European Union Directives

2007-02-23T20:56:00.003-08:00

The old breakers’ yards, going for a long time, are soon to disappear. The future is now in recycling components from these vehicles and all as a consequence of a new Directive approved by the European Union. The new law came into being in the Spanish State in December 2002. From February of this year the Royal Decree for the Direction General of Traffic obliges owners of vehicles to obtain a certificate of destruction in order to be legally free of contractual ownership of the vehicle. Here, in the Basque Country, the Sestao-based Car Recycling company is the first of its kind.

The new European Union-approved Directive on non-useable vehicles prohibits forthwith the leaving of vehicles without them having previously undergone special. It is prohibited to accumulate vehicles in any place and, before breaking them up for scrap metal, any contaminant parts, liquids and gases have to be removed.

The European body has proposed the goal of recycling 85 % of vehicle components and converting 5 % into energy by the year 2006. In most European scrap yards, cars are piled up in fields with no kind of care or control. With this new legislation the idea is to avoid contamination of the Earth and the environment but also to make savings on raw materials and energy.

In the Basque Autonomous Community some 50,000 vehicles are taken out of use annually. In Europe, a total of some 150 million every year. The company Car Recycling of Sestao has already started to operate with the new legislation. Last year they processed 2,000 vehicles; this year they propose to treat some 6,000 and, from 2005 on, they hope to deal with about 9,000 vehicles a year.

Car Recycling receives automobiles from car dealers, from local council and also from individual members of the public. The cranes move some 40.000 kilos of scrap metal a year which are fed into the breaker and subsequently end up in the steelworks. Car Recycling has sited its plant next door to the Sestao ACB (compact steelworks).

Decontaminate and classify

Once the vehicles arrive at the recycling plant, the technicians begin to decontaminate and classify them, before being sent to be broken up. They are directed to one of three zones, depending on which market they are destined for. Pieces of plastic and rubber wheels are, for the time being, taken to the rubbish tip but. In the future, they will be elements in an integrated recycling process. The vehicle is weighed and this is when the process begins. First the vehicle must be decontaminated, i.e. the wheels, plastic parts and the battery must be removed; the oil is collected and the anti-freeze and brake liquids and then the fuel; finally the gases – the air conditioning and airbag gases – are extracted. All these contaminants are stored and distributed to the authorised companies for the treatment of waste.

The vehicles are subsequently taken apart, part by part, and classified for re-use. All the engine parts, gear change components, and so on, are re-bored – a practice widely used in Central Europe – and these recycled parts used in new cars.

According to Santiago Perea, Director-General of Car Recycling, every part recovered has one an end-market or another. There is a local market of mechanical parts or exterior accessories for old or antique cars. These are local workshops, the breakers’ yards; another market takes the bodywork, large parts for re-manufacturers which reconstruct them to be sold as spare parts; a third market are the third world countries which consume both second-hand cars and spare parts, starter motors, alternators, etc. of nearly all models.

When the parts are taken out, the rest is broken up for scrap. The crane takes the cars, one by one, and introduces them into the crushing machine. The vehicle is crushed again and again until it forms a compact packet. Once the volume is small enough, it is placed alongside the rest of the crushed vehicles, and from here they are taken to the steelworks as furnace scrap.

Car Recycling will soon be opening centres, not only in Alava and Gipuzkoa (the other two provinces within the Basque Autonomous Community), but also in other places within the Spanish State and Portugal – a total of 40 plants will be opened.

In order to facilitate the recycling process, in several zones in Europa, car manufacturers have begun to make parts in a diffferent way. If, up to now, some 22 types of plastic have been used, the idea is to make to with just 2 or 3 in the production of vehicles. Changes in design are also being undertaken in order to facilitate taking the vehicle apart.

Hardening of Steels – Surface Hardening, Nitriding, Flame Hardening and Induction Hardening

2007-02-23T20:56:00.001-08:00

Hardenability is the term used to describe the effect of various elements on the transformation characteristics of steels and the resultant microstructure after cooling from the austenitising (or hardening) temperature.

Depth of Hardening

In plain carbon steels the depth of hardening will be shallow, even for small sections given a relatively fast quench rate. As the alloying element content increases so does the depth of hardening. This means that the alloy steels can be hardened in many cases right through sections to the desired microstructures and give optimum service life.

It is at the design stage that these basic considerations should be made and the right steel grade chosen for the application.

Specifying Heat Treatments

In the final analysis, it is the heat treater who is asked to transform an expensive shape into a serviceable product. Remember, it is not the heat treaters function to guess the steel grade or required heat treatment. Full details of the steel grade must be given together with a property specification sheet. By far the most commonly specified property is hardness and it is normally given as a range in either Brinell, Rockwell or Vickers scale. It is normal for the heat treater to hardness test sample components and the area of the component which can be treated for a hardness test should be indicated.

Tensile Strength and Hardness

For heat treated steels a relationship exists between tensile strength and hardness. By referring to published figures the hardness values can be converted to tensile strength usually measured in N/mm² or MPa.

Properties That Can be Affected by Heat Treatment

When service conditions demand higher hardness areas on components to resist wear, abrasion, erosion, indentation or increase fatigue resistance, various treatments can be specified.

Surface Hardening

Case carburisation followed by quench hardening is a process which is well documented and has occupied a leadership role in surface hardening technology for decades. It is still the major surface hardening treatment with wide application in the gear industry and automotive components manufacturing.

Nitriding

Nitriding and various related processes are lower temperature solid state reactions which as a consequence are very valuable for surface hardening items requiring minimal distortion during processing.

By using special steel grades the surface hardness of nitrided components can be very high, say 1100 Vickers compared to 750-800 Vickers for a carburised and quenched structure.

It is important to note that for nitriding to be successful, the steel used should be hardened and tempered or the components should be rough machined then hardened and tempered, usually to a hardness range of HRc 30 - HRc 35. Nitriding must be carded out on a correct microstructure of tempered martensite to minimise the occurrence of spalling.

Flame Hardening

This process consists of hardening the surface of an object by heating it above the transformation temperature using a high intensity flame from a specially designed burner and then progressively quenching it in water, oil or suitable synthetic quenchant. The depth of hardened layer can range from 1 to 10 mm.

A considerable level of skill and understanding is required for the process and depending upon the complexity of the part to be hardened, a large number of variables need to be examined before the job should proceed.

Induction Hardening

This process is capable of a high degree of automation and as such can be used for high volume production. It involves heating the component by an induced eddy current to temperatures at which the rate of formation of austenite is rapid and then quenching to transform austenite to martensite. Induced currents are generated in the metal surface using specially designed inductors which suit the surface shape and using an alternating current in the inductors at frequencies from 50Hz to 1000kHz, depending upon the depth of hardening required. The advantage of induction hardening is that the process is quick, efficient and surface degradation is minimal. The disadvantage is that capital and set up costs are high.

Concrete Reinforced with Fibre Reinforced Plastic

2007-02-23T20:55:00.001-08:00

Concrete is a very durable material. Fine examples of its first structural use by the Romans are still standing, and concrete is now probably the most widely used building material in the world. During Roman times and for many centuries after, its use was limited to compression structures, because of its poor tensile strength. But in the 19th century, the introduction of iron rods into the material led to reinforced concrete as we know it today, with its incredibly wide range of uses.

Iron and Steel Reinforcing in Concrete

Iron and steel rods cause potential corrosion and durability problems, however. Embedded steel is generally very durable, as it is protected from corrosion by the alkaline environment of the concrete. But in highly aggressive environments, the protection given by the concrete is often insufficient. The protective layer is broken down and corrosion begins, the initial signs being cracking and spalling of the concrete. Expensive remedial work is needed to repair this damage if the structure is to achieve its intended service life. Such repairs form a major part of the workload of the construction industry.

Tackling the Problem of Steel Corrosion in Reinforced Concrete

Tackling the problem of steel reinforcement corrosion has usually meant improving the quality of the concrete itself, but this approach has had only limited success. More recently, the construction industry has considered alternative steels for reinforcement, replacing carbon steel with stainless steel or using bars with an epoxy coating. In extreme cases cathodic protection is installed, although this is usually as part of a repair system and not for new structures.

Fibre Reinforced Plastic Reinforced Concrete

Now, the latest idea is to replace the steel with fibre reinforced plastics (FRPs). These materials, which consist of glass, carbon or aramid fibres set in a suitable resin to form a rod or grid, are well accepted in the aerospace and automotive industries and should provide highly durable concrete reinforcement. The durability is a function of both the resin and the fibre, while the amount and type of fibre are keys to determining the mechanical properties of FRPs. The strength of FRP reinforcement tends to be between that of high yield reinforcing steel and prestressing strand - about 1000 MNm^-2 for glass fibres and 1500 MNm^-2 for carbon fibres. However, the stiffness is generally much lower - about 45 GNm^-2 for glass fibres and 150 GNm^-2 for carbon fibres. All FRP materials have a straight line response to failure with no plasticity.

Manufacturing and Limitations of FRP Reinforcing Elements

FRP reinforcing rods are normally made by pultrusion. One limitation of this method is that thermoset resins are generally used and so once the material is fully cured, the rods cannot be bent into the range of shapes currently possible with steel. New manufacturing techniques are being developed to make such ‘specials’. Spiral reinforcement, both circular and rectangular, is being produced by several Japanese manufacturers, as are two- and three-dimensional grids. Other techniques are being developed in which resin-impregnated fibres are wound onto mandrels to produce closed shapes, such as shear links. As an alternative, thermoplastic resins are being developed that would allow the fully cured material to be warmed and bent to shape. However this is likely to give weaker reinforcement where the bar is bent due to misalignment of the fibres.

History of FRP Concrete Structures

The potential of FRP concrete reinforcement has already been shown around the world by the construction of many demonstration structures. Initially, owing to concerns about the lower stiffness of FRPs compared to steel, most structures were pre-stressed, with conventional steel being used as secondary reinforcement. A number of footbridges and highway bridges have been built, mainly in Japan and North America.

Highway Bridge

The first major European structure was built in Dusseldorf in 1987 - a highway bridge with glass FRP pre-stressing cables. Later demonstration structures formed an important part of the Eurocrete project, which was the first co-ordinated European programme of development work on FRP reinforcement. Eurocrete was a collaborative research project between partners in the UK, France, the Netherlands and Norway funded partly under the Eureka scheme. It was probably the first project of its kind in the world to bring together all the disciplines involved with FRPs, including materials suppliers, processors, research organisations and designers.

Footbridges and Non-Magnetic Fencing

Two footbridges were built during the Eurocrete project, one at Chalgrove near Oxford, and the other in Oslo. Part of a berthing facility at docks in Qatar was also constructed using FRP reinforcement, and another application was as reinforcement for the concrete fencing around a test facility for sensitive electrical equipment where conventional steel bars would have caused magnetic interference, (figure 1). Many applications were tested in the laboratory and may move into practice shortly, including retaining wall units and cladding panels. Meanwhile, other programmes are developing larger structures fully reinforced with FRPs, such as an 80 metre-long footbridge in Denmark.

Figure 1. Non-magnetic concrete security fencing erected around a test facility for sensitive electrical equipment.

FRP Concrete Standards

As FRP-reinforced concrete is being developed, design standards for its use are also being drawn up around the world. When introducing a new type of reinforcement with very different properties, there are two approaches - adapt the existing approach, or go back to square one and write completely new rules. The second is obviously more technically correct, but is a costly and time consuming process. As real applications are the only way to get good experience of the behaviour of a new material, modifying existing standards is the only feasible option.

The current standards for the design of reinforced concrete structures have developed over the last 100 years or so. They combine methods based on sound scientific principles and certain rules of thumb. For example, as reinforced concrete is a composite material, some aspects of its behaviour, such as shear, are still not well understood and so empirical approaches are used. FRP-reinforced concrete will follow similar rules to steel-reinforced concrete, but will differ in a number of ways.

Much experimental work has been carried out using FRP-reinforced concrete, mainly on simple beams and slabs, and basic design methods are being developed in a number of countries. The Japanese Ministry of Construction has published draft guidelines for design, the Canadian Bridge Code will shortly have a chapter dealing with FRPs and the American Concrete Institute is preparing guidance. Proposed modifications to British Standards covering the design of reinforced concrete structures were developed under the Eurocrete project and are now being validated by the Institution of Structural Engineers. They will provide a document for use by design engineers in the absence of a formal code of practice. These design approaches will lead to safe structures, but are unlikely to lead to the most economic use of the relatively expensive FRP materials. The cost of FRP rods is expected to be between that of epoxy-coated steel and stainless steel, two to eight times as expensive as normal steel bar. Such a high initial cost can only be justified by looking at ‘whole life’ costs for structures in aggressive environments. Potential users need to consider the total costs for their structures, including repairs, and not just the material costs. In the future, such savings should become obvious as design approaches are developed which take account of the enhanced properties of FRP-reinforced materials.

Differences between FRP and Steel Reinforced Concrete

· Because of the high strength and relatively low stiffness of FRPs, failure is likely to occur by compression of the concrete and not rupture of the reinforcement.

· Crack widths in steel-reinforced concrete are controlled to prevent aggressive substances reaching the steel, so improving durability. For FRP-reinforced concrete, aesthetics and possibly watertightness will be the only criteria for crack width control.

· Deflections are likely to be higher than for equivalent steel-reinforced units.

· FRP rods have low compressive strengths in comparison to their tensile capacities, so the traditional design approaches for columns are no longer valid. Studies looking at the effect of wrapping FRP around circular columns have found that the confinement leads to increases in the failure load and the failure strain.

· Fire will be a design consideration for some types of structures. The main concern is to limit the temperature rise at the surface of the FRP bar, so that it stays below the glass transition temperature of the resin. Above this temperature, the material stops acting as a composite, and so weakens.

Problems Associated with FRP Concrete

Durability

The major cause for concern in the use of FRPs as reinforcement is probably the durability of the material when embedded in concrete. The highly alkaline environment degrades glass fibres and some resins, and manufacturers are reluctant to disclose the details of the materials they use for commercial reasons. Work has concentrated on developing alkali-resistant glass and on using carbon and aramid fibres, but little attention has been paid to the resin. Ways of assessing the durability of the materials are urgently needed, but considerable work still needs to be done to develop acceptance criteria.

A major assessment of durability was carried out in Eurocrete, which included work on the materials themselves and on FRPs embedded in concrete. The latter samples were stored in laboratories under various environmental conditions and also on exposure sites in Europe and the Middle East. The results, which apply to the particular resin and fibre combinations studied, show that the composite rods resist the alkaline environment well, with no significant degradation during the test period.

Industry Acceptance

Despite its excellent properties and durability, FRP reinforcement is unlikely to replace steel for the vast majority of structures in the foreseeable future. Experiments and demonstration projects around the world have shown that FRP reinforcement is a viable and cost effective alternative to steel in special circumstances, for example as an alternative to stainless steel. But the construction industry is extremely conservative, and so the most likely development route is the use of the new materials in non-structural applications or in ones where the consequences of failure are not too severe. More highly loaded and critical applications will follow later as confidence in the materials grows.

Stainless Steel Fibre Filled Compounds for Electrostatic Discharge Applications

2007-02-14T22:06:00.001-08:00

LNP Engineering Plastics have produced a range of stainless steel fibre filled compounds for electrostatic discharge (ESD) applications. These materials can be made in virtually any base polymer including PEEK, PPS and other high temperature resins.

The new stainless steel fibre filled products are marketed under the name Stat-Kon electrically active compounds. Use of these compounds is expected to yield significant performance benefits in applications requiring non-sloughing electrostatic discharge protection and high temperature performance.

This new range of compounds extends the range of previously available stainless fibre filled compounds which could only be made from base resins compatible with commercially available stainless steel concentrates.

Where electrostatic discharge, high temperature performance and non-sloughing are required, the Stat-Kon range of compounds are the materials of choice. Compared to carbon filled compounds for electrostatic discharge applications, the stainless steel fibre filled compounds can be produced in nearly any colour and offer superior dimensional stability.

The Stat-Kon range also incorporates:

· Impact modifiers

· Internal lubricants

· Other performance enhancing additives

They can also be moulded using almost any injection moulding machine.

Potential applications for these materials include hard disk drive components and applications where FDA approval is required.

Microtex HT – Stainless Steel Fibre Products for Use in Automotive Exhausts and Mufflers – Supplier Data by Fibretech

2007-02-14T22:05:00.002-08:00

Microtex HT is Fibretech’s lightweight acoustic absorption material for automotive exhaust silencers. Made from semi-continuous stainless steel filaments using Fibretech’s unique Rapid Solidification (RS) technology, HT outperforms conventional glass, basalt and steel alternatives at high temperature.

Figure 1. Microtex HT in automotive exhausts and mufflers.

Unique Benefits of Microtex HT

· RS metallurgy

· No impurities

· Robust steel matrix

· “As-cast” ductility

· Enhanced sound absorption

· Homologation

· Customising

· Low cost

· Innovative, new alloy thermally stable to 1100°C

· Resistant to chemical corrosion

· Will not compact under gas pressure.

· Easy component manufacture.

· Can be combined with basalt or E-glass.

· Proven and accepted by vehicle and exhaust manufacturers.

· Optional “tailored” alloys possible.

· Suits all models.

Quality Guarantee

Microtex exhaust system fibres are made to ISO 9002 standards, conform to current safety and environmental standards, and are supported by a full in-house Technical Support Team.

Compositional and Design Flexibility

Other RS alloys can be manufactured on request to provide exhaust system designers with infinite variations for optimising performance and cost objectives

Stainless Steel - Grade 316 – Properties, Fabrication and Application

2007-02-14T22:05:00.001-08:00

Grade 316 is the standard molybdenum-bearing grade, second in importance to 304 amongst the austenitic stainless steels. The molybdenum gives 316 better overall corrosion resistant properties than Grade 304, particularly higher resistance to pitting and crevice corrosion in chloride environments. It has excellent forming and welding characteristics. It is readily brake or roll formed into a variety of parts for applications in the industrial, architectural, and transportation fields. Grade 316 also has outstanding welding characteristics. Post-weld annealing is not required when welding thin sections.

Grade 316L, the low carbon version of 316 and is immune from sensitisation (grain boundary carbide precipitation). Thus it is extensively used in heavy gauge welded components (over about 6mm). Grade 316H, with its higher carbon content has application at elevated temperatures, as does stabilised grade 316Ti.

The austenitic structure also gives these grades excellent toughness, even down to cryogenic temperatures.

Key Properties

These properties are specified for flat rolled product (plate, sheet and coil) in ASTM A240/A240M. Similar but not necessarily identical properties are specified for other products such as pipe and bar in their respective specifications.

Composition

Table 1. Composition ranges for 316 grade of stainless steels.

Grade		C	Mn	Si	P	S	Cr	Mo	Ni	N
316	Min	-	-	-	0	-	16.0	2.00	10.0	-
316	Max	0.08	2.0	0.75	0.045	0.03	18.0	3.00	14.0	0.10
316L	Min	-	-	-	-	-	16.0	2.00	10.0	-
316L	Max	0.03	2.0	0.75	0.045	0.03	18.0	3.00	14.0	0.10
316H	Min	0.04	0.04	0	-	-	16.0	2.00	10.0	-
316H	max	0.10	0.10	0.75	0.045	0.03	18.0	3.00	14.0	-

Mechanical Properties

Table 2. Mechanical properties of 316 grade stainless steels.

Grade	Tensile Str (MPa) min	Yield Str 0.2% Proof (MPa) min	Elong (% in 50mm) min	Hardness
Grade	Tensile Str (MPa) min	Yield Str 0.2% Proof (MPa) min	Elong (% in 50mm) min	Rockwell B (HR B) max	Brinell (HB) max
316	515	205	40	95	217
316L	485	170	40	95	217
316H	515	205	40	95	217

Note: 316H also has a requirement for a grain size of ASTM no. 7 or coarser.

Physical Properties

Table 3. Typical physical properties for 316 grade stainless steels.

Grade	Density (kg/m³)	Elastic Modulus (GPa)	Mean Co-eff of Thermal Expansion (µm/m/°C)			Thermal Conductivity (W/m.K)		Specific Heat 0-100°C (J/kg.K)	Elec Resistivity (nΩ.m)
			0-100°C	0-315°C	0-538°C	At 100°C	At 500°C
316/L/H	8000	193	15.9	16.2	17.5	16.3	21.5	500	740

Grade Specification Comparison

Table 4. Grade specifications for 316 grade stainless steels.

Grade	UNS No	Old British		Euronorm		Swedish SS	Japanese JIS
Grade	UNS No	BS	En	No	Name	Swedish SS	Japanese JIS
316	S31600	316S31	58H, 58J	1.4401	X5CrNiMo17-12-2	2347	SUS 316
316L	S31603	316S11	-	1.4404	X2CrNiMo17-12-2	2348	SUS 316L
316H	S31609	316S51	-	-	-	-	-

Note: These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted.

Possible Alternative Grades

Table 5. Possible alternative grades to 316 stainless steel.

Grade	Why it might be chosen instead of 316?
316Ti	Better resistance to temperatures of around 600-900°C is needed.
316N	Higher strength than standard 316.
317L	Higher resistance to chlorides than 316L, but with similar resistance to stress corrosion cracking.
904L	Much higher resistance to chlorides at elevated temperatures, with good formability
2205	Much higher resistance to chlorides at elevated temperatures, and higher strength than 316

Corrosion Resistance

Excellent in a range of atmospheric environments and many corrosive media - generally more resistant than 304. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. Considered resistant to potable water with up to about 1000mg/L chlorides at ambient temperatures, reducing to about 500mg/L at 60°C.

316 is usually regarded as the standard “marine grade stainless steel”, but it is not resistant to warm sea water. In many marine environments 316 does exhibit surface corrosion, usually visible as brown staining. This is particularly associated with crevices and rough surface finish.

Heat Resistance

Good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C. Continuous use of 316 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 316L is more resistant to carbide precipitation and can be used in the above temperature range. Grade 316H has higher strength at elevated temperatures and is sometimes used for structural and pressure-containing applications at temperatures above about 500°C.

Heat Treatment

Solution Treatment (Annealing) - Heat to 1010-1120°C and cool rapidly. These grades cannot be hardened by thermal treatment.

Welding

Excellent weldability by all standard fusion methods, both with and without filler metals. AS 1554.6 pre-qualifies welding of 316 with Grade 316 and 316L with Grade 316L rods or electrodes (or their high silicon equivalents). Heavy welded sections in Grade 316 require post-weld annealing for maximum corrosion resistance. This is not required for 316L. Grade 316Ti may also be used as an alternative to 316 for heavy section welding.

Machining

A “Ugima” improved machinability version of grade 316 is available in round and hollow bar products. This machines significantly better than standard 316 or 316L, giving higher machining rates and lower tool wear in many operations.

Dual Certification

It is common for 316 and 316L to be stocked in "Dual Certified" form - mainly in plate and pipe. These items have chemical and mechanical properties complying with both 316 and 316L specifications. Such dual certified product does not meet 316H specification and may be unacceptable for high temperature applications.

Applications

Typical applications include:

· Food preparation equipment particularly in chloride environments.

· Laboratory benches & equipment.

· Coastal architectural panelling, railings & trim.

· Boat fittings.

· Chemical containers, including for transport.

· Heat Exchangers.

· Woven or welded screens for mining, quarrying & water filtration.

· Threaded fasteners.

· Springs.

Stainless Steel - Life Cycle Costing

2007-02-14T22:04:00.002-08:00

Life Cycle Cost (LCC) analysis is a means of quantifying the choice of materials for a product or construction, with the aim of selection of the most economic alternative.

Traditionally the selection of a material for a given application has been on the basis of the cheapest purchase price. It is now recognised that the cheapest purchase price may not be the most economic choice if account is taken of the very real additional costs due to installation, regular maintenance and for periodic replacement should the material's life be less than that required for the product or construction. In the case of equipment installed in factories or processing plants a further cost which must be included for each possible alternative material is that caused by lost time - the time for which production is lost because of unscheduled down-time of the equipment. In many industries this lost time cost far outweighs all other costs, and must certainly be included in estimates of life cycle cost.

Life Cycle Cost Components

In general terms the total LCC can be broken down into components:

LCC=

Acquisition Cost

Fabrication and Installation

Cost

Maintenance Costs (periodic)

Replacement Costs (periodic)

Cost of Lost Production (periodic)

Residual (Scrap) Value

Each of these terms must be known if a realistic result is to be calculated.

Evaluation of Life Cycle Cost

The calculation of LCC relies upon the concept of the "time value of money" - the notion that a dollar spent next year costs less than a dollar spent today, because the money could in the interim be invested and hence be generating income of its own. Future expenditures can therefore be discounted by a factor which depends upon several inputs, including the cost of funds to the organisation, the prevailing inflation rate and the time period for which the expenditure is delayed. Calculation by manual methods is quite complex, so in the past this valuable tool has been left to the accounting specialists. With the wide availability of PC spreadsheets the calculation of LCC has become much easier, but a further step towards ease of use has been made with the implementation of a personal computer program specifically for this task.

LCC Calculation by Computer Program

A PC program has been produced by the International Chromium Development Association and is available in Australia from the Australian Stainless Steel Development Association (ASSDA). Copies can also be obtained free of charge from stainless steel suppliers. The program is designed to run on any IBM-compatible PC.

The LCC computer program has been written to ensure ease of use; all inputs are keyed into appropriate simple screens, and the resulting changes are reflected immediately in the calculated LCC, giving comparative costs for up to three alternative materials.

An Example Life Cycle Cost Analysis

An example of the use of LCC analysis using the ICDA LCC software is for a simple rectangular mixing tank. The requirement is for a 20 year tank life, to coincide with the requirement for other components of the water treatment plant.

The design brief requested evaluation of three alternative materials:

1. Mild steel with applied fibreglass lining

2. Stainless steel - austenitic Type 304

3. Stainless steel - duplex Type 2205

As the 2205 was not readily available in the angle and channel products required for reinforcement of the tank, these were substituted by Type 304 in the 2205 design; these components were not to be in regular contact with the corrosive environment, so no corrosion problem was anticipated.

Experience suggested that both the 304 and 2205 would survive without replacement for the full twenty years, whereas the mild steel was expected to last for only eight years before replacement. In addition both the stainless steels were expected to require only minimal inspection and cleaning as regular maintenance, in comparison with regular fairly extensive patching of the mild steel and its lining.

The "Summation of Present Value Costs" in Table 1 shows the resulting LCC analysis - the Type 304 stainless steel is lowest cost, closely followed by the 2205 and with mild steel substantially more expensive due to its higher maintenance and replacement costs. The Material Cost (acquisition cost) of the mild steel construction is of course by far the cheapest.

The negative Replacement Costs for the two stainless steel alternatives reflect the expected significant residual scrap value of the metal at the end of 20 years, discounted from the initial material costs because it is a deferred income.

The "Value of Lost Production" in the summary table is shown as zero - this implies all maintenance and replacement is carried out in scheduled shut-downs for other plant maintenance. Unexpected shut-downs causing lost production could substantially add to the Total Operating Cost of the option requiring this unscheduled maintenance.

Sensitivity Analysis

A very powerful feature of the ICDA software is its ability to give a "sensitivity analysis" of the output. This is an estimate of the effect on the output if each of the inputs is independently varied by some given amount - usually ±20%. From examination of these values it is clear which inputs must be very precisely known if a realistic output is to be obtained, and which inputs have very little influence over the calculated cost. Further efforts might then need to be made to gain further precision in some of the more critical inputs. A sensitivity analysis of the water treatment plant mixing tank showed that the most critical data is the time before replacement becomes necessary. The assumption was that the 304 and 2205 would both survive for the full twenty years; from the sensitivity analysis it is apparent that if the 304 fails before this time (possibly due to its lower pitting corrosion resistance compared to the 2205), the 2205 duplex stainless steel becomes by far the cheapest option. Clearly a good knowledge of the actual operating conditions to be encountered is crucial to the correct selection.

Example Summary

The Mixing Tank example may be included with other examples on copies of the LCC program floppy disc. This example can be retrieved, modified if desired, and the results printed. Standard printed output includes the summary table (as below), a more detailed breakdown of inputs and outputs, and a table showing the sensitivity analysis.

Stainless Steel - Grade 3CR12

2007-02-14T22:04:00.001-08:00

This "utility stainless steel" is a proprietary modification of Grade 409 chromium stainless steel. It has been developed as a readily fabricated, low cost grade, exhibiting good resistance to wet abrasion and mildly corrosive environments. National specifications cover this grade by designations 1.4003 and UNS S40977 / S41003.

The designation "3CR12" is a registered trade mark of Columbus Stainless, the original developers of the grade, and who are still active in research into its production, fabrication and application. Proprietary 3CR12 conforms to EN 10088.2 grade 1.4003, ASTM A240/A240M grades UNS S40977 and S41003 and ASME SA240 grades UNS S40977 and S41003. 1.4003 is also included in EN 10028.7 covering stainless steels for pressure purposes.

Key Properties

These properties are specified for flat rolled product (plate, sheet and coil) in Euronorm EN 10088.2 1.4003 and ASTM A240/A240M S40977 and S41003. Similar but not necessarily identical properties are specified for other products such as pipe and bar in their respective specifications.

Composition

Typical compositional ranges for grade 3CR12 stainless steels are given in table 1.

Table 1. Composition ranges for 3CR12 grade stainless steel

Grade

1.4003

S40977

min.

max.

0.030

1.50

1.00

0.040

0.015

10.50

12.50

0.30

1.00

0.030

S41003

min.

max.

0.03

1.50

1.00

0.040

0.030

10.5

12.5

1.50

0.030

Mechanical Properties

Typical mechanical properties for grade 3CR12 stainless steels are given in table 2.

Table 2. Mechanical properties of 3CR12 grade stainless steel

Grade	Tensile Strength (MPa) min	Yield Strength 0.2% Proof Stress (MPa) min	Elongation (% in 50mm) min	Hardness
Grade	Tensile Strength (MPa) min	Yield Strength 0.2% Proof Stress (MPa) min	Elongation (% in 50mm) min	Rockwell (HR) max	Brinell (HB) max
1.4003	450 650	280 (long.) 320 (trans.)	20	-	-
S40977	450	280	18	HR B88	180
S41003	455	275	18	HR C20	223

Physical Properties

Typical physical properties for annealed grade 3CR12 stainless steels are given in table 3.

Table 3. Physical properties of 3CR12 grade stainless steel in the annealed condition

Grade

Density (kg/m³)

Elastic Modulus (GPa)

Mean Coefficient of Thermal Expansion (mm/m/°C)

Thermal Conductivity (W/m.K)

Specific Heat

0-100^°C (J/kg.K)

Electrical Resistivity (nW.m)

0-100°C

0-300°C)

0-700°C

at 100°C

at 500°C

3CR12

7740

200

10.8

11.3

12.5

30.5

480

570

Grade Specification Comparison

Approximate grade comparisons for 3CR12 stainless steels are given in table 4.

Table 4. Grade specifications for 3CR12 grade stainless steel

Grade	UNS No	Old British		Euronorm		Swedish SS	Japanese JIS
Grade	UNS No	BS	En	No	Name	Swedish SS	Japanese JIS
3CR12	S40977	-	-	1.4003	X2CrNi12	-	-
These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted.

Possible Alternative Grades

Possible alternative grades to grade 3CR12 stainless steels are given in table 5.

Table 5. Possible alternative grades to 3CR12 grade stainless steel

Grade	Why it might be chosen instead of 3CR12
304	Better corrosion resistance and fabrication properties are required.
430	Better corrosion resistance and appearance is required. Weldability not needed.
Galvanised steel	A lower cost is required, and the reduced corrosion resistance and fabrication characteristics of galvanised steel are acceptable.
Weathering steel	A lower cost is required, and the reduced corrosion resistance and fabrication characteristics of weathering steel are acceptable.

Corrosion Resistance

3CR12 is effective in many applications where carbon steel, galvanised, aluminised or painted steel or aluminium give unsatisfactory life. It is not attacked by strong alkalies, and often gives adequate resistance in acidic conditions.

3CR12 strongly resists chloride stress corrosion cracking, but is less resistant than 304 to pitting and crevice corrosion in chloride environments. 3CR12 is likely to resist water with chloride contents of up to 150 to 200 mg/L at ambient temperatures. The presence of sulphate or nitrate ions will reduce the corrosivity of chlorides. Light surface rust can form in many atmospheres, making the material unsuitable for decorative applications.

Heat Resistance

In air 3CR12 offers scaling resistance to 600°C continuous or 750°C intermittent, but if under stress the temperature should be limited to 450°C continuous or 600°C intermittent. 3CR12 suffers negligible embrittlement after extended exposure at temperatures of 450-550°C; it can be used safely at these temperatures without loss of room temperature impact resistance.

Heat Treatment

Annealing - heat to 700-750°C, soak for 1½ hours per 25mm section. Air cool. The maximum temperature of 750°C should not be exceeded. Annealing should usually be followed by pickling and passivating.

This grade should not be hardened by heat treatment; quenching treatments may reduce the corrosion resistance and mechanical properties.

Welding

3CR12 can be readily welded using similar techniques to austenitic stainless steels. Low heat input processes are preferred - particularly GTAW (TIG) and GMAW (MIG). Filler wire pre-qualified by AS 1554.6 (3CR12 referred to as "4003") is grade 309, but 309L, 309Mo, 316L and 308L have been successfully used. Argon plus 1-2% oxygen shielding gases are recommended. Discolouration of the weld should be removed by pickling, except possibly in wear applications; effective purging and use of backing gases is often a better option.

Machining

3CR12 has a machinability similar to that of grade 430, ie about 60% of that of mild steel. The work hardening rate is lower than that of austenitic stainless steels, so reducing the need for special machining techniques.

Finishes

3CR12 is available in standard HRAP (Hot Rolled Annealed and Pickled) finish in plate, and 2B or 2D in coil. "Black" finish is also produced; this is hot rolled and with the high temperature scale left on the steel. The resulting dark oxidised surface has good low friction characteristics and a corrosion resistance that is useful for many wear applications, even although slightly less resistant than the "white" pickled finish.

Applications

Typical applications include:

· Mining and mineral processing and transport equipment

· Rail wagons for coal and iron ore

· Sugar processing equipment

· Furnace and oven parts

Environmental Scanning Electron Microscopy - ESEM

2007-02-08T21:27:00.001-08:00

Scanning electron microscopy (SEM) has long played a central role in structural characterisation for material scientists. Bombarding the surface of a material with a beam of electrons and detecting those that are emitted or backscattered allows microscopists to see down to resolutions of 10 nanometres or so, giving them intricate details of the material’s structure. However, the requirements of SEM, such as a high vacuum and the need for a thin coating if an insulator is being analysed, mean that certain types of materials have always proved difficult or impossible to image straightforwardly.
Limitations of Conventional SEM

For example, the coating can obscure the fine surface detail on some insulators - although SEMs equipped with field emission guns have made such samples easier to image. Another difficulty arises with wet and damp samples such as paints, inks, emulsions and biological tissue - these materials prove particularly challenging for SEM. The high vacuum requirements in the chamber mean lengthy specimen preparation techniques are required to remove or fix the water before imaging, raising the risk of artefacts being introduced.
Overcoming These Limitations Using ESEM

These problems can now be overcome, thanks to the new environmental scanning electron microscope (ESEM), which permits the imaging of wet systems with no prior specimen preparation. The development of this instrument means that whole new classes of materials, previously undreamed of, can be imaged in their natural state. But the potential of ESEM is even greater than. this. Because the sample environment can be dynamically altered, hydration and dehydration processes can be followed as they happen in the sample chamber.
How Are These Limitations Overcome?

So how is this all achieved? Two basic developments have made it possible for this new generation of SEMs to hit the market. Firstly there was the recognition that by using a system of differential pumping, the electron gun can be maintained at high vacuum while the sample chamber can be kept at a constant pressure of 10-20 torr (1 torr ~ 133 N.m-2).
Pressure Limiting Apertures

In the ESEM instrument, a series of pressure limiting apertures (PLAs) are placed down the column, across each of which a pressure differential is maintained. Figure 1 shows the column and highlights the pressures in the different zones. Consequently, despite the relatively high pressure in the chamber, this design allows ESEMs to operate with LaB6 filaments as well as tungsten, and field emission guns are also becoming available to give superior quality imaging.

Detectors

Having a vapour in the sample chamber presents another problem - the conventional Everhardt-Thornley detector used to pick up the electrons emitted from the sample surface in standard SEM cannot be used for ESEM. So the second crucial development needed was a new type of detector that can operate at a pressure of tens of torrs. The enlarged section in figure 1 shows the environmental secondary detector, which was the first successful detector to operate under these conditions. As its development has been only fairly recent, detector design is still being modified and optimised.
Electron Beam Scattering and Resolution

Scattering of the electron beam between the gun and the sample is an obvious concern, given that there are many atoms/molecules of vapour in the ESEM’s chambers. The question is: if such scattering occurs, can a decent resolution be achieved? The answer is yes, as long as the gap between the final PLA and the sample is kept reasonably small, say 510 mm, and the pressure is kept quite modest, say less than 12 torr.

Under these circumstances, with a mean free path for 20 KeV electrons of a few millimetres, the majority of incident electrons from the gun are not scattered at all. A well defined electron ‘probe’ is still incident on the sample, but with an accompanying ‘skirt’ of scattered electrons which can extend for tens of microns from the central probe. Fortunately, the intensity distribution of the skirt is quite flat and so it can essentially be treated as a background signal, above which the central probe still gives a strong signal. In fact, the probe signal is strong enough to give a resolution of down to 5nm with a LaB6 filament, if the pressure in the sample chamber is kept sufficiently low.
Backscattered Electrons

Of greater importance is what happens to the electrons - both those ‘backscattered’ from the sample surface and ‘secondaries’ produced by the surface bombardment - after they leave the sample and move towards the detector. Owing to the presence of the vapour, these electrons also undergo collisions, many of which lead to ionisation of a gas molecule (particularly in the case of the low energy ‘secondaries’). Each ionisation produces a daughter electron, which can then itself ionise further gas molecules, creating a cascade in the gap between sample and detector, figure 2. The overall effect is considerable signal amplification the extent of this depends on parameters such as gas pressure and type, detector bias and of course the population of electrons leaving the sample.

Wet Imaging

As vapour is tolerated in the sample chamber, ESEM makes it possible to carry out ‘wet imaging’ of samples. In order to view a wet sample such as a colloidal dispersion, the atmosphere in the sample chamber must be carefully controlled at all stages. After the sample is placed in the chamber, air at atmospheric pressure must be replaced by water vapour at a few torr It is important to carry out the pump-down carefully so that premature dehydration of the dispersion does not occur. If done correctly, no accidental aggregation of the particles occurs, and a truly dispersed state will be imaged.
Evaporation and Condensation

During imaging it is also important to ensure that neither water evaporation nor condensation occur. This is achieved by using an atmosphere at the saturated vapour pressure (SVP) of water. However, this raises an additional difficulty in imaging samples at room temperature, because the SVP of water is relatively high at this temperature compared to the modest pressures of a few torr that are acceptable in the sample chamber. The trick is to use a Peltier stage to drop the temperature by a few degrees so that SVP is easily maintained without undue loss of image quality and resolution.
Real Time Hydration/Dehydration Studies

However, for certain experiments it is desirable to move away from these SVP equilibrium conditions to allow deliberate hydration or dehydration of a sample. In principle, changes in structure or state of a wet sample can be dynamically followed as water condenses on to or evaporates from the sample. In practice though, beam damage - always a bugbear for electron microscopists and a particular problem when examining organic materials - may well prevent real time studies being carried out.

It may therefore be necessary to examine the structure by viewing different samples at different times during the hydration or dehydration process. Dropping the temperature to cause water to condense onto a sample surface can be just as useful an experiment. Chemical reactions taking place in water can be followed in this way.
Case Study – Hydration of Cement

The hydration of cement is one important example of a chemical reaction in water that can be followed using the ESEM. Cement is an extremely important and complex commercial material. Controlling the reaction of the grains of material with water is vital in ensuring that the cement sets at the right rate - too fast and it could, say, plug a deep sea oil well, too slow and it holds up construction. Despite its importance, there are still uncertainties about the precise mechanisms involved in the setting process and about how subtle changes in cement composition may affect it. ESEM can look at the developing structure in the cement at different times during the setting reaction.

Cement has a number of different inorganic ingredients, including tricalcium silicate (C3S), tricalcium aluminate, dicalcium silicate, tetracalcium aluminoferrite and gypsum. Within the limited field of view of the microscope it is difficult to examine the individual reactions of each component, and so it is easier to follow the reactions of the components separately.

Initially, water is condensed onto a dry grain by dropping the sample temperature, and the reaction is then allowed to proceed for the required length of time. ESEM cannot produce an image through a significant thickness of water, however, so after this time the sample temperature is raised slightly to evaporate most of the surface water. Only a thin, electron-transparent layer remains, to keep the grain hydrated. By repeating this process, the evolving structure can be followed and related to measurements made by other techniques, such as calorimetry.

Applications of ESEM

ESEM has a number of different applications already, but there is plenty of opportunity to extend this range of uses. ESEMs have been around for a number of years, with more in the US than elsewhere, yet as a technique it appears to be substantially underexploited. This is perhaps especially true of its application to studying wet systems. In part this can be attributed to an early failure to appreciate the careful control of chamber pressure required at all times. With improving awareness of this, ESEM will find a key role in an increasing number of materials characterisation laboratories.

Environmental Analysis and Related Services Offered by Bodycote Testing Group

2007-02-08T21:25:00.002-08:00

Bodycote Testing Group is the world’s leading supplier of independent sub-contract testing. In the environmental field, we have two established laboratories in the U.K. and are now offering commercial testing from our laboratory in Shotton, North Wales. The Shotton Laboratory currently supports Corus Colors, the UK’s largest coated steel strip processor and has the experienced staff and equipment to undertake a wide range of environmental tests.
Testing Equipment Available at the Shotton Laboratory

The equipment inventory includes: -

· ICP Optical Emission Spectrometers

· Industrial Microwave

· Photometric COD Analyser

· BOD Analyser

· Photometric Ammoniacal Nitrogen Analyser

· pH Meters

· Conductivity Meters

· Gravimetric and Titrimetric Methods

· Infra-Red Oil in Water Analyser
Testing Procedures Available at the Shotton Laboratory

This enables the Bodycote laboratory to carry out a wide range of commonly required tests including environmental effluent monitoring, groundwater and borehole analysis. The range of specific tests available includes: -

· Metals in Solution

· COD

· BOD

· Ammoniacal Nitrogen

· pH

· Conductivity

· Suspended Solids

· Moisture Content

In addition to the above, a wide range of classical wet chemistry techniques are available within the laboratory enabling the testing of, for example, Nitrates and Sulphates.
Ananlytical / Environmental Laboratories at Glasgow

The existing Bodycote Analytical (Environmental) laboratory in Glasgow offers a vast range of testing and consultancy services, and clients who may have a requirement for services not offered by the local laboratory will be contacted by an expert and guided through the testing process.
Bodycote’s Accredited Testing Facilities

Bodycote’s laboratories are accredited by the United Kingdom Accreditation Service (UKAS), which provides assurance of the quality systems in place. The assessment standard is ISO 17025, which is an internationally recognised quality assurance standard, compatible with the ISO 9000 series.
Additional Services to Customers

Bodycote management and technical staff alike pride ourselves on our customer service ethic, and our belief is that understanding and satisfying our customer’s needs is paramount. Routine samples are typically processed and reported within 48 hours of receipt. Also, our laboratory management computer system ensures standardised and efficient reporting, and allows the transmission of certificates by e-mail if required.

Elemental Analysis Of Metals Using The ARC-MET8000 Optical Emission Analyser From Oxford Instruments

2007-02-08T21:25:00.001-08:00

Optical Emission analyser designed to identify all the key elements in metals - especially where highest accuracy and/or the analysis of light elements like C, Al, S, P, Mg, Si is needed and when sorting low alloys and aluminum. Ideal, for example, for separation of 316 H (>0.04% C) and 316 L (<0.03% C).

Production Cycle Applications

Use one unit throughout the whole production cycle including:

· Classification of raw material (recycling metal)

· QC of semimanufactured products

· QC of final product
Carbon Analysis Of Steels

Recognising that carbon analysis in steels is of primary concern in many material verification functions, and e.g. in welding work, ARC-MET8000 has the unique capability of measuring carbon in both air and argon modes.
ARC-MET8000 Features

ARC-MET8000 offers:

· Accurate results using Air or Argon measurements

· Fast grade identification and assay

· Only one probe with an integrated display

· Low level carbon analysis using Air burn in a few seconds

· Battery operation, long cable between main unit and probe, and convenient mobility

· Unique to ARC-MET8000: the probe is the heart of the system
Suitable Materials

· Ideal for ferrous and non-ferrous metals.

· Low alloy steels

· Stainless steels

· Tool steels

· Low alloy (white) cast iron

· Aluminum alloys

· Titanium alloys

· Nickel alloys

· Cobalt alloys

· Copper alloys

· Zinc alloys

· Magnesium alloys

Effect Of Titanium in Cu-Hf Based Bulk Metallic Glasses

2007-02-08T21:24:00.000-08:00

Abstract

Alloys of composition Cu100-xHfx with 50 ≥ x ≥ 25 at.% and Cu55Hf45-xTix with 5 £ x £ 45 at.% have been investigated. All alloys investigated in both series were fully vitrified when melt spun to ribbon of thickness ~25 mm, except the binary alloy Cu75Hf25 that showed a crystalline + amorphous structure. The critical size for the binary alloys was limited to ribbons, while the critical diameter is 3 mm for the Cu55Hf25Ti20 and Cu55Hf20Ti25 alloys. On the other hand, 2 mm fully glassy diameter was found for the Cu55Hf30Ti15 and Cu55Hf15Ti30 alloys. The substitution of Hf by Ti causes an increase in the glass-forming ability (GFA). As the Ti content increases, the glass transition temperature (Tg) and crystallization temperature (Tx) decrease for both Cu100-xHfx and Cu55Hf45-xTix alloys. In contrast, the liquidus temperature (Tl) has a minimum value of 1163 K for the Cu55Hf20Ti25 alloy, resulting in a maximum Tg/Tl of 0.61. The alloys with the highest Tg/Tl value showed the best GFA in this Cu-based alloys series.
Keywords

Bulk Metallic Glasses, Suction Casting, XRD, DSC, Critical Glassy Diameter
Introduction

Metallic glasses are non-crystalline alloys formed by continuous cooling from the liquid state. Up until recently [1], such materials could only be formed in thin sections at cooling rates typically in the range 104-106 Ks-1. Such alloys, based on iron, nickel and/or cobalt have established numerous applications as ultra soft magnetic materials in power and high frequency cores for transformers, chokes, inductors and other similar devices [2]. In the past decade, researchers had paid more attention to the metallic glasses not only due to their superior chemical and physical properties, but because they can now be fabricated in bulk form. They are therefore considered as real practical engineering materials and open up new application opportunities. For instance, glassy alloy can be used for making magnetic tapes [3, 4] as it exhibits better wear resistance. Extensive experimental investigations have demonstrated that many compositions in these systems can be formed into the glassy state by using suction casting to form cylindrical or slab-shaped ingots. Maximum section diameters or thicknesses of fully glassy phase range up to 72mm [5], depending on the combination of constituent elements and their precise concentrations. Recently, Inoue et al. [6, 7] reported Cu-based alloys with high glass forming abilities, high tensile strength of over 2000 MPa and lower material cost bulk metallic glasses which can be prepared by copper mould casting. Their excellent mechanical properties and glass forming ability (GFA) make the production of precision mechanical parts possible such as high precision gears [6]. Driven partially by interest in engineering applications, there has been an ongoing effort to identify amorphous alloys with greater strength, elastic modulus, hardness, and ductility. Of particular interest are alloys based on such common metals such as Cu, Al, Co, Fe, Ni, etc. However, the information of a glassy phase in Cu-Hf-Ti alloys is based on 60 at.% Cu. The aims of this investigation are to produce bulk amorphous rods of Cu-Hf and Cu-Hf-Ti and determine the critical glassy diameter of these alloy families.
Experimental

Alloy ingots of nominal compositions Cu100-xHfx (x = 50, 45, 40, 35, 30 and 25 at.%) and Cu55Hf45-xTix (x = 5, 10, 15, 20, 25, 30 , 35 and 40 at.%) were prepared by arc melting mixtures of Hf (crystal bar), Cu (sheet) and Ti (Rod) having purities of 99.5 at.%, 99.99 at.% and 99.8 at.%, respectively. The arc melting was performed in a Ti-gettered high purity Argon atmosphere. Each ingot was re-melted at least four times in the arc melter in order to obtain good chemical homogeneity. Ribbon samples of mean thicknesses ~ 25 mm and width ~ 2 mm were prepared by melt spinning in a controlled Ar atmosphere. Copper die suction casting was employed to produce rods with a stepped profile having diameters decreasing from 4 to 3 to 2 mm, each with a total length of 50 mm. The phase constitutions of the rods were studied by X-ray diffraction (XRD). The thermal stability, defined by the glass transition temperature (Tg) and the crystallization temperature (Tx), was studied by differential scanning calorimetry (DSC) at a heating rate of 20 K/min. The solidus temperature (Tm) and liquidus temperatures (Tl) were determined by differential thermal analysis (DTA) at a heating rate of 20 K/min. Thermal characterization was performed using melt spun ribbons.
Results

The average thickness of the ribbon produced was 25 mm and almost all the ribbons produced were of uniform width. All the alloy ribbons formed, except for one sample, the binary alloy Cu75Hf25, were found to be nominally fully amorphous by XRD analysis. They showed high metallic lustre and could easily be bent through 1800 without fracture, thus showing very good ductility to a high strain and indicating a fully amorphous or almost fully amorphous thickness. However, the Cu75Hf25 alloy ribbon had very poor ductility and it was shown to be crystalline by the XRD analysis. Stepped rods were produced of diameters 2, 3 and 4 mm with a length of 50 mm. Figure 1 shows a photograph of a 2/3/4 mm diameter stepped rod produced by suction casting. The rods produced by suction casting showed good metallic lustre and a low incidence of fabrication defects.

The structure results by X- ray diffraction for all the ribbon and rod samples of the Cu100-xHfx alloy series with x = 25 – 50 are summarised in Table 1. All rods were crystalline or largely crystalline as several distinct peaks can be seen for all these traces with no clear evidence of a diffuse halo corresponding to a glassy phase. The ribbon samples are clearly fully amorphous in each case, with the exception of the composition Cu75Hf25 which shows a small fraction of crystalline structure, with one peak at ~ 43o 2 q corresponding to the phase Cu8Hf3 (111). Figure 2 shows DSC curves for the melt-spun ribbons of this alloy series and values of Tg and Tx are plotted as functions of Hf content in Figure 3. Although no clear glass transition is observed for 30 at.% Hf, the alloys containing 50 at.% to 35 at.% Hf exhibit distinct glass transitions, followed by the glass transitions region before crystallisation, however, the alloy containing 25 at.% Hf was found to be partially crystalline, giving a DSC curve with amorphous + crystalline structure. The Tg and Tx decrease with increasing Hf content from 35 at.% to 45 at.%, despite the fact that the Hf has a much higher cohesive energy than Cu. It is also seen that the supercooled liquid region defined by the temperature interval between Tg and Tx, DTx (=Tx − Tg), shows a relative constant value of ~ 30 K over the range 35 – 50 at.% Hf, but appears to narrow considerably for 50 at.% Hf. The substitution of Hf for Cu in the range 25 – 35 at.% Hf decreases the liquidus temperature, but increasing the Hf content beyond 35 at.% Hf then leads to an increasing Tl. The values of the reduced glass temperature (Trg=Tg/Tl) are plotted as a function of Hf content in Figure 4. Trg increases when decreasing Hf content from 0.55 up to 0.61 for x = 50 and 35 respectively, then decreasing to the value of 0.59 for x = 30. Table 2 shows the thermal analysis results for this alloy series.

Ecoflex - Sustainable Construction Solutions from Recycled Tyres

2007-02-08T21:20:00.000-08:00

Ecoflex is a multi purpose technology that enables a wide range of building solutions to be cost effectively constructed using recycled raw materials. The technology has been proven effective in important applications for four major industries:

· Civil Construction

· Mining

· Commercial Construction

· Agriculture & Aquaculture
Applications
Civil Construction

Retaining walls, sealed and unsealed roads and hard stands, drainage and water flow systems
Mining

Underground roads and retaining walls
Commercial Construction

Concrete slabs and sealed pavement
Agriculture & Aquaculture

Dams, ponds, creek crossings, access roads, wave barriers
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Ecoflex technology has been proven by through the construction of over 450 construction projects, all of which have been independently certified and have demonstrated both the engineering values and the commercial advantages of the technology. Ecoflex enables construction companies and recycling companies to manufacture and supply proven building products and gain competitive advantage in their market place.

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Enables recycled waste tyres and recycled aggregate to be used for high value purposes rather than disposed of via land fill. Ecoflex can make a major contribution to construction project waste reduction, can be reused and eliminates waste. Ecoflex meets a pressing need world wide for a high volume, sustainable means of recycling used tyres.
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Ecoflex technology is patented in most of the industrialised world. International business development potential is enormous.
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