technical insight MYTH OR TRUTH: MAGNETIC STAINLESS STEEL IS LESS CORROSION RESISTANT THAN NON-MAGNETIC GRADES? All stainless steel grades are usually in a clean and shiny condition in a warehouse and once they are mixed up, it becomes hard to identify them as individual grades.
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ne of the basic tests would be to test for magnetism. The magnetic grades would likely be ferritic grades with a magnetic crystal structure. The others might be the nonmagnetic austenitic grades due to the nickel content. The lack of magnetism in certain grades would normally 17
be caused by nickel content that is added to the alloy to make the material more workable. However, some people would also like to contribute certain levels of corrosion resistance to the specific grades based on the material’s level of magnetism. And then there’s the old saying that if it is magnetic, it is not
suitable for corrosive conditions. This is false, but also true. There is no correlation between magnetic permeability and resistance to corrosion, but there is a sound reason for this mistake. The magnetism/corrosion myth is based on the fact the less noble ferritic (magnetic) grades of stainless steel, such as grades 409 and 430, do not resist corrosion as well as the nobler and nickelcontaining austenitic (nonmagnetic grades) such as 304 and 316. Stainless steel is an alloy of iron and chrome. At least 50% iron is required to make the mixture MAY
