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.

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.

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.

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.

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.

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.

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.

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.