Stainless alloys are divided into four basic groups: martensitic stainless steels, ferritic stainless steels, austenitic stainless steels, and precipitation hardening stainless steels.

When nickel is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels virtually non-magnetic and less brittle at low temperatures. For greater hardness and strength, more carbon is added, and these grades are defined as ferritic or martensitic alloys. The ferritic types achieve moderate increases in strength by cold working. The martensitic types become martensitic during heat treatment and achieve excellent strength.