It is often thought that any stainless steel is non-magnetic and the magnet test will differentiate stainless steel from carbon steel but that is not true. Stainless steel bearings made from 440 grade steel are strongly magnetic. 316 stainless steel bearings are very slightly magnetic.
400 grade stainless steels are martensitic steels so can be hardened by heat treatment to give good load capacity which is why most stainless steel bearings are made from 440 grade steel. 316 stainless steel is an austenitic steel. It is not hardenable by heat treatment so can only support much lower loads than 400 grade steel.
It is easy to test austenitic steels against martensitic steels with a magnet. For example a 440 grade stainless steel bearing will be attracted almost as much as standard steel. A 316 grade bearing will have an almost no attraction.
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