The main types of "stainless steel" is not merely the term refers to a stainless steel, but rather that more than one hundred kinds of industrial stainless steel are developed each in their specific fields of application with good performance. The first key to success is to understand the purpose, and then determine the correct steel. Building construction and steel-related applications usually only six of them. They contain 17 to 22% chromium, preferably steel further contains nickel. Add molybdenum can be further improved atmospheric corrosion, especially in chloride-containing atmospheric corrosion resistance. Stainless often by organized state is divided into: martensitic steels, ferritic steels, austenitic steels, austenitic - ferritic (duplex) stainless steel and precipitation hardening stainless steel. In addition, according to the composition is divided into: chrome stainless steel, chrome-nickel stainless steel and chrome-manganese nitrogen stainless steel. Ferritic stainless steel containing chromium 15% to 30%. Its corrosion resistance, toughness and weldability with the increase of chromium content increased resistance to chloride stress corrosion better than other types of stainless steel, fall into this category are Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 like. Ferritic stainless steel because of the high chromium content, corrosion and oxidation resistance are better, but the mechanical properties and process performance is poor, and more for large discontinuity acid structure and as anti-oxidation steel. This kind of steel resistant to corrosive atmosphere, nitric acid and saline solution, and has good oxidation resistance, thermal expansion coefficient, etc., for the nitric acid and food factory equipment, parts can also be produced at high temperatures, such as gas turbine parts, etc. . Austenitic stainless steel title chromium greater than 18%, also contains about 8% of the nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Good overall performance, corrosion resistant to many media. Common austenitic stainless steel grades are 1Cr18Ni9,0Cr19Ni9 like. Wc 0Cr19Ni9 steel <0.08%, steel marked "0." Such steel contains a large amount of Ni and Cr, the steel austenitic state at room temperature.. Such steel has good ductility, toughness, weldability, corrosion resistance and non-magnetic or weakly magnetic, corrosion resistance are good in oxidizing and reducing media, the equipment used to produce acid, such as corrosion resistant containers and equipment liner, pipeline, nitric acid-resistant parts and other equipment, also used as the main material of stainless steel watches jewelry. Austenitic stainless steels commonly used solution treatment, is about steel heated to 1050 ~ 1150 ℃, then cooled or air-cooled, in order to obtain a single phase austenite