The use of magnets to identify stainless steel is not acceptable. It is better to use copper sulfate and a grinder.
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For example, the use of magnets can only basically distinguish between two types of stainless steel. Because the chromium stainless steel can be attracted by the magnet in any state; the chromium nickel stainless steel is generally non-magnetic in the annealed state, and after the cold working, some are magnetic. However, manganese-rich steels with higher manganese content are non-magnetic; chromium-nickel-nitrogen-based stainless steels have more complex magnetic properties: some are non-magnetic, some are magnetic, and some have a non-magnetic vertical surface and a magnetic surface. Therefore, although magnets can basically distinguish between chromium stainless steel and chromium-nickel stainless steel, they cannot correctly differentiate some special-purpose steel grades, let alone distinguish specific steel grades.
If you identify with copper sulfate, the method is more convenient and the effect is more obvious. "Remove some of the oxide layer on the steel, put a drop of water, rub with copper sulfate, and if it does not change color after rubbing, it is usually stainless steel; if it becomes purple, non-magnetic is high manganese steel."
“While grinding the stainless steel on a grinder, observe the sparks that appear. If the spark is streamlined and there are more dense knots, it is a high manganese or manganese nitrogen steel with higher manganese content; Steel or chromium-nickel stainless steel.†Industry insiders said that the method of using the grinder is also intuitive and fast.