Stainless Steel (Stainless Steel) refers to air, steam, water resistance and weak corrosive medium and acid, alkali, salt, chemical corrosion of Steel of erosion medium, also called Stainless Steel acid. In practical application, often be weak corrosive medium corrosion resistance of steel called stainless steel, and chemical resistance of medium corrosion of steel called acid steel. Because both in chemical composition, the gap between the former not resistant to corrosion medium chemistry, and the latter is normally has no rust sex. Stainless steel corrosion resistance depends on steel contain alloy element. Stainless steel alloy elements and basic nickel and molybdenum, titanium, niobium, copper, nitrogen etc, in order to meet various USES of the stainless steel organization and performance requirements.
The chemical composition of the stainless steel corrosion resistance with the increase of the carbon content and reduce, therefore, most of the carbon content of stainless steel were lower, some steel the wC (carbon) and even less than 0.03% (such as 00 Cr12). Stainless steel alloy element is the main, Cr, only when Cr content to a certain value, steel have corrosion resistance. Therefore, stainless steel general wCr were above 13%. Stainless steel with Ni, Ti, Mn, N, Nb the element.
Stainless steel used to the organization state is divided into: martensite steel, ferritic steel, austenitic steel, etc. In addition, the composition is divided into: chromium stainless steel, chromium nickel stainless steel and chromium manganese nitrogen stainless steel, etc.
1, ferritic stainless steel: including chromium 12% ~ 30%. The corrosion resistance and toughness and weldability with containing cr increases with the increasing of quantity, chloride stress corrosion resistance performance is better than other types of stainless steel.
Belong to this category of Crl7, Cr17Mo2Ti, have Cr25, Cr25Mo3Ti, Cr28, etc. Ferritic stainless steel because contain chromium volume is high, corrosion resistance and oxidation resistance are relatively good, but the mechanical properties and the process performance is poorer, more for stress of acid structure and as little antioxidant use steel. This kind of steel can resist the atmosphere, nitric acid and brine solution of the corrosion, and has high temperature oxidation resistance, good thermal expansion coefficient characteristics such as small, used to nitric acid and food factory equipment, also can make in the high temperature parts, such as gas turbine parts, etc.
2, austenitic stainless steel: including chromium greater than 18%, still contain 8% of nickel and a few molybdenum, titanium, nitrogen element. Comprehensive performance is good, resistant to a variety of medium corrosion. Austenitic stainless steel grades of commonly used one Cr18Ni9, 0 Cr19Ni9, etc. 0 Cr19Ni9 steel the wC < 0.08%, GangHao marked as "0". This kind of steel contain a lot of Ni and Cr, make steel at room temperature is austenitic state. This kind of steel has good plasticity and toughness, weldability and corrosion resistance, in oxidizing and reducing medium corrosion resistance were well, used to make acid equipment, such as corrosion resistant containers and equipment, pipeline, resistant to the lining of the equipment parts nitric acid. Austenitic stainless steel generally USES solid solution processing, steel is heated to a 1050 ~ 1150 ℃, and water, for single-phase austenitic organization.
3, austenitic-ferritic duplex stainless steel: with austenitic stainless steel and the advantages of ferrite, and has the plastic.
Austenitic and ferritic organization about half of the stainless steel. Containing C in the situation of low, Cr content at 18% ~ 28%, 3% ~ 10% in Ni content. Some steel also contain Mo, Cu, Si, Nb, Ti, N, alloy element. This kind of steel with austenitic stainless steel and the characteristics of ferrite, compared with ferrite, plastic, higher toughness, no room temperature brittleness, intergranular corrosion resistant performance and welding properties are improved significantly and also maintain a ferritic stainless steel 475 ℃ brittle and high thermal conductivity, and has the characteristics such as plastic. Compared with austenitic stainless steel, high strength and corrosion resistance and intergranular corrosion resistant to chloride stress have increased significantly. Duplex stainless steel has excellent resistance to corrosion resistance hole, is also a kind of festival nickel stainless steel.
4, martensite stainless steel, high strength, but plastic and solderability is poorer.
Martensite stainless steel grades of commonly used one Cr13, 3 Cr13 and so on, because it contains carbon is higher, it has high strength, hardness and wear resistance, corrosion resistance is a bit poor, mechanical performance requirements for higher, corrosion resistance performance of some parts of the general requirements, such as spring, turbine blade, hydraulic press valves, etc. This kind of steel is quenching and tempering treatment in use.
