Stainless steel is often divided into martensitic steel, ferritic steel, austenitic steel, austenitic ferrite (duplex) stainless steel, and precipitation hardening stainless steel according to their structural state. Stainless steel is the abbreviation for stainless steel and acid resistant steel. Steel that is resistant to weak corrosive media such as air, steam, water, or has rust resistance is called stainless steel.