Martensitic stainless steels are chromium alloys (about 11 to 18%) with relatively high carbon (up to 1.1% by weight), containing small quantities of other elements, they are mainly known by the American nomenclature AISI 400 series.

Typical elements present in alloys are: Manganese, Silicon, Chromium and Molybdenum; sulphur may also be added to improve machinability with metal-removing machines, but with partial detriment to the mechanical properties.

Martensitic stainless steel has very high mechanical properties and is well machinable with machine tools; it is the only stainless steel that can undergo heat treatment to increase its mechanical properties (tensile strength, yield strength, hardness).

They have a crystalline structure with a body-centred cubic lattice (CCC) which, like the ferritic family, makes them magnetic.