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 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

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	-
	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	-
	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	-
	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
				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
		BS	En	No	Name
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.

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.