It is possible to divide stainless steel into three macro categories: martensitic, ferritic, and austenitic. But what are their characteristics? Are they all subject to magnetism?
3 steels, many differences
Usually, austenitic steels are not born ferromagnetic. That is, they fail to attract a magnet. In contrast, ferritic and martensitic ones turn out to be ferromagnetic. These, in fact, are capable of attracting magnets. But what is their chemical composition?
- Martensitic and ferritic: with chromium content (AISI 400 series)
- Austenitics: with chromium and nickel content (AISI 300 series)
Steels and magnetic behavior
As mentioned earlier, usually austenitic type steels are non-magnetic. However, there is a possibility that their magnetic permeability may be changed. How? This type of steels remains nonmagnetic when in the annealed state. After undergoing cold plastic deformation (or nitrogen addition), however, there may be an increase in magnetic permeability. In these cases, the mechanical strength increases, “work-hardening” the material, thus increasing its hardness and magnetism.
Some examples
When molding washers, strong magnetism is transmitted to them. Work hardening allows the partial transformation of austenite into martensite, with a significant increase in magnetic permeability. This aspect, in no way affects the corrosion resistance of the resulting artifact. Thus, a part obtained by cold deformation processing (in AISI 304 and/or AISI 316) and subsequently pickled, manages to maintain the corrosion resistance characteristics. Regardless of the increase in magnetic permeability.
Magnetism and austenitic steel: calamine pollution
But in what other ways can austenitic steel take on magnetism? Also by calamine pollution. How can this happen? This happens when both carbon and magnetic stainless steel are simultaneously processed in the same environment. In this case, there will also be effects on corrosion resistance. These, however, can be resolved by pickling the article at the end of processing.
Freely excerpted and translated from https://bloginoxtirrenica.it/