22CrMnMo, 20CrMnMoH, and 20CrMoH steel with high hardenability and used medium car gear. This type of steel can be direct quenching after carburizing. Due to chromium-manganese-molybdenum steel and chromium molybdenum steel containing chromium and molybdenum form carbides of elements in carburizing process will lead to tooth surface carbon content increased, easier in carburized layer of a large number of carbide, deterioration of the carburized layer properties. Therefore, the gears during carburizing of chromium-manganese-molybdenum steel and chromium molybdenum steel, weak carburizing atmosphere should be adopted in order to prevent the formation of excessive carbon. 22CrMnMo and 20CrMnMoH forged gear blanks in 650~670℃ high temperature tempering treatment after the fire, fine lamellar Pearlite microstructure + small amount of ferrite, hardness 171~229HB.