Heat resistant steel
Heat-resistant steel refers to the special alloy steel with good chemical stability and high strength at high temperature, and can better adapt to the high temperature conditions. Mainly used for the manufacture of industrial heating furnace, internal combustion engine, petroleum and chemical machinery and equipment and other high temperature conditions working parts.
(1) The concept of heat resistance
The heat resistance of steel includes both thermochemical stability and high temperature strength.
Thermochemical stability refers to the ability of steel to resist the chemical corrosion of various media at high temperature, among which the most basic and the most important is the oxidation resistance. The thermochemical stability is mainly determined by the chemical composition of the steel. Adding human Cr, Al and Si to the antioxidant capacity, because Cr, Al and Si can form a compact and protective Cr with oxygen when oxidized at high temperature2O3，A12O3perhaps SiO2film. Cr is the preferred alloy element. when the steel WCr 15%, the antioxidant temperature of steel can reach 900℃; when WCr 20%~25%, the antioxidant temperature of steel can reach 1100℃. Rare earth (a small amount of yttrium, cerium, etc.) elements can also improve the heat resistance steel oxidation. This is mainly due to the improvement of the antioxidant performance of the oxide film, but also can improve the binding force of the oxide film and the metal surface. In the surface of steel seepage aluminum, silicon or chromium aluminum, chromium and silicon co-seepage have significant antioxidant capacity.
High temperature strength refers to the ability of steel to resist plastic deformation and fracture at high temperature. The creep limit and persistent strength are commonly used to assess. By adding Cr, Ni, W, Mo and other elements, strengthening the matrix, improve the recrystallization temperature and increase the stability of the matrix; adding V, Ti, Nb, Al and other elements, forming the carbide with high hardness and good thermal stability, prevent the development of creep and dispersion; trace B and rare earth (RE) elements and enhance the high temperature strength of steel.
