The main alloying element in stainless steel is chromium. The content of chromium is usually between 10% and 20%. Stainless steel is popular for its high corrosion resistance. The corrosion resistance of stainless steel is 200 times that of mild steel.
Stainless steel can be divided into five groups:
1. Austenite:
Austenitic steels account for the largest segment of the global stainless steel market. Its functional uses are mostly food processing equipment, kitchen utensils and medical equipment. Austenitic stainless steels are weldable stainless steels. It can be roughly divided into three categories: ordinary chromium nickel (300 series), manganese chromium nickel nickel nitrogen (200 series) and special alloys. These metals are non-magnetic and not heat treatable.
2. Ferrite:
Ferritic steels contain trace amounts of nickel, 12-17% chromium, less than 0.1% carbon and other alloying elements such as molybdenum, aluminium or titanium. They have good ductility and formability, but relatively poor high temperature strength compared to austenitic grades. Certain ferritic stainless steels are priced lower than others, such as 409 and 405. These metals are magnetic but cannot be heat treated and can be strengthened by cold working.
3. Martensite:
Martensitic steels contain 11-17% chromium, less than 0.4% nickel and up to 1.2% carbon. The carbon content of this hardenable steel affects forming and welding. To obtain practical properties and prevent cracking, preheating and post-weld heat treatment are required.
4. Duplex steel:
Duplex steels are mainly used in chemical plants and pipeline applications. Duplex stainless steels typically contain about 22-25% chromium, 5% nickel, and molybdenum and nitrogen. Compared with austenitic stainless steels, duplex steels have higher yield strength and greater resistance to chloride stress corrosion cracking.
5. Precipitation hardening steel:
Precipitation hardening steel is a chromium-nickel stainless steel that contains other alloying components such as aluminum, copper or titanium. These alloys allow stainless steel to be hardened by solution and aging heat treatments. In the aged state, they can be austenitic steels or martensitic steels.
