Which of the following is not considered ferrous?

316L stainless steel is an austenitic stainless steel that is not considered ferrous. This type of stainless steel contains nickel and chromium, which provide corrosion resistance and make it non-magnetic or only very weakly magnetic compared to ferrous materials. Ferrous materials are primarily composed of iron and exhibit significant magnetic properties.

In contrast, cobalt is a ferromagnetic material and has ferrous properties. Ferritic stainless steel and 405 stainless steel also contain iron and have magnetic characteristics, classifying them as ferrous. The distinction lies in the composition and magnetic properties, where austenitic stainless steels, like 316L, are recognized for their non-ferrous characteristics and suitability for MR environments due to their reduced risk of magnetic attraction.