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What is Stainless Steel?

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Another interesting development occurred in India in the 1980s. India has no indigenous
supply of nickel and imported nickel was very expensive. So, to develop the market for stainless steel, local producers turned to the 200-series. Grades such as J1 and J4,
developed by Jindal Stainless Limited, became widely used.

These grades were mainly used in India for cookware, and very successfully. Ferritic grades such as grade 430 could also have been used to avoid the cost of nickel but CrMn grades were chosen because they are not magnetic. Indian consumers who were buying cookware had already associated quality with nonmagnetic stainless steel, since high quality products had been mainly made from grade 304. Lower quality, cheaper items had been made from grade 430, which is magnetic, so the belief arose among consumers that highquality stainless steel was non-magnetic. CrMn grades, which are austenitic and therefore nonmagnetic, fit that requirement.

However, it should be noted that magnetism has absolutely nothing to do with corrosion resistance – this was a consumer perception only. This decade has seen a significant rise in stainless steel use, particularly in Asia. This has been accompanied by high nickel prices. As a consequence, the market share enjoyed by 200-series grades has doubled from about 5% to about 10%. And this growth has occurred in grades such as J1 and J4, which are 4% and 1% Ni grades respectively. Because of the desire for cost saving, the 1% Ni grade became particularly popular. It should be noted that these grades, such as J1 and J4, are proprietary alloys – they are company specific and not covered by international codes and specifications, unlike the traditional 200-series grades such as grade 201. So their composition is at the discretion of the manufacturer and there are now many small producers of grades such as these in China.

Differences between 200-Series and 300-Series Stainless Steels

The differences between these two series of stainless steels may be summarized as follows:

Corrosion resistance

In all of these stainless steels, Cr is trying to form ferrite while the austenitising elements, Ni, N, Mn and Cu, are trying to form austenite. The higher the Cr content, the more austenitising elements are needed to change all the ferrite to austenite. J4 is a good example – in order to get the Ni level down to 1% Ni, and so minimize the price, it has been necessary to reduce the Cr content to 15-16%. This is much lower than the 18.0 – 20.0% Cr specified for grade 304 and it is Cr which makes the greatest contribution towards corrosion resistance. This means that such 200-series grades have lower corrosion resistance and are suitable for a much narrower range of applications than grade 304. This has not been well understood and there are many instances where 200-series grades have failed due to corrosion, such as when they have been used for components like handrails or  in exterior applications.

Recycling

The positive image which stainless steel enjoys is enhanced by its very high level of recycling. Little stainless steel is lost to landfill because it is an inherently valuable material, and it is the nickel content which represents most of the scrap value. But because both 200-series and 300-series grades are non-magnetic, it is not possible to separate them except by sophisticated analysis. As the amount of 200- series material in the community increases, so too does the likelihood of this material getting into the established 300-series scrap circuit and causing contamination with manganese, copper and possibly other impurities. This is an issue of concern to the entire stainless steel industry since anything which disrupts the efficient recycling of stainless steel has the potential to damage the whole industry.

Conclusion

CrMn grades of stainless steel have been in existence for many decades and have been
successfully used in numbers of applications. But there have also been many failures and
unsatisfied customers. This has particularly been the case over recent years with the rapid
growth of these materials in China and South East Asia. Because they are non-magnetic,they cannot be easily distinguished from grade 304 and this has led to their misuse in somecases.

Even when 200-series material is identified as such, it must be recognized that it may not have the same level of corrosion resistance, formability and weldability as a 300-series
grade. Consequently, it is most important that anyone considering using these grades
should have all relevant mechanical, physical and corrosion data in order to be satisfied that the material will be suitable for the intended purpose. Ideally, case histories should be
available to verify the satisfactory performance of the material in applications similar to that
being considered.

Additional Information

If you are seriously considering the use of a 200-series grade, it is recommended that you
also visit the ISSF website www.worldstainless.org and read their article: “New 200-series steels: An opportunity or a threat to the image of stainless steel?"

 

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