Introduction of Stainless Steel

The steel resistant to air, steam, water and other weak corrosive media and acid, alkali, salt and other chemical corrosive media corrosion steel also known as stainless acid resistant steel. In practical applications, we often called weak corrosive medium corrosion steel as stainless steel, and chemical corrosion steel known as acid-resistant steel. Due to the difference in the chemical composition of this two kind of steel, the former is not necessarily resistant to chemical corrosion, while the latter are generally have a stainless properties. The corrosion resistance of stainless steel depends on the alloying elements. Cr is the basic element to obtain the corrosion resistance of stainless steel. When the Cr content achieved about 12%, Cr and the oxygen in the corrosive medium forms a thin layer of oxide film (self-passivation film) on the steel surface to prevent further corrosion of the steel substrate. In addition to Cr, the commonly used alloying elements also contains nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., to meet the various application of stainless steel structure and performance requirements.
Stainless steel based on matrix usually divided into : ① ferritic stainless steel. Contains 12％～30％Cr. Its corrosion resistance, toughness and weldability will be increased while the chromium content increased,  and the resistance of chloride stress corrosion is better than other types of stainless steel. ② austenitic stainless steel. Containing more than 18% Cr, also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Comprehensive performance is good, it can also withstand a variety of media corrosion. ③ austenite - ferrite duplex stainless steel. It owns both the advantages of austenitic and ferritic stainless steel, it also has good superplasticity. ④ martensitic stainless steel. High strength, but poor plasticity and weldability.
The common stainless steel grade is 301, 304, 304L, 304H, 309S, 310S, 316, 316L, 316Ti, 321, 347, 410, 904L.