Stainless steels are usually grouped into 5 types:

A．Ferritic: Ferritic stainless steels are based on Chromium with small amounts of carbon less than 0.1%.That means ferritic stainless steels are plain chromium steels (12 to 27 percent chromium) with no significant nickel content which results in lower corrosion resistant than austenitic stainless steels.But, they have slightly higher yield strengths and much lower strain hardening than austenitics.

B．Austenitic: Austenitic stainless steels are containing high amounts of chromium and nickel and are designated as 300 series (such as type 304 and type 316).They are the most common .Austenitic stainless steels have high ductility, low yield stress and relatively high ultimate tensile strength, when compare to typical carbon steel.

C．Martensitic: Martensitic stainless steels are similar to ferritic steels in being based on Chromium but have higher Carbon levels up as high as 1%.However, due the addition of carbon, they can be hardened and strengthened by heat treatment, in a similar way to carbon steels.

D.Duplex: Duplex stainless steels are called “duplex” because they have a two-phase micro structure consisting of grains of ferritic and austenitic stainless steel. Duplex stainless steels have a microstructure which is approximately 50% ferritic and 50% austenitic. This gives them a higher strength than either ferritic or austenitic steels.

E.Precipitation hardening (PH)PH stainless steels can develop very high strength by adding elements such as Copper, Niobium and Aluminium to the steel.