Investigation Of Heat-Treatment Process For 20CrMoH Steel Using As Gear

In the present study, the effect of pre-heat treatment of isothermal normalizing on the structure and performance of 20CrMoH gear steel were studied, and the effects of the parameters of different carburizing on the microstructure in carburized layers of the steel were also investigated. According to the results of tension, impact and bench tests, the optimal carburizing-quenching parameters of the 20CrMoH gear steel were determined. For using the normal normalizing, because the continues cooling transformation takes place within a wide range of temperature and also because of the different cooling rate in different parts of the steel pieces, it is difficult for the obtained microstructure and hardness to fit for the engineering standard. However, when using isothermal normalizing, the optimal microstructure and hardness can be obtained, which also reduces quenching deformation. The effect of processing parameters such as carbon potential, carbonizing temperature, quenching temperature on the rules of effective harden layer, microstructure, interior rigidity, distribution of hardness and carbon concentration were studied. Based on the above analysis, the optimal parameters of carburizing processing are determined as follows: the temperature in the zones of I, II, III, IV, and V is 880℃, 900℃, 920℃, 900℃and 835℃, respectively. The carbon potential in zones of II, III, IV and V is 1.00%, 1.15%, 0.90% and 0.90%, respectively. The temping temperature is 190 ℃, and the cycle of feed is 25min. The bench tests was carried out in the CA7-100 gearbox assembled with 20CrMoH gear steel treated at the optimization condition parameters, which proofs the technique proposed in the study to be excellent. The optimization technique has been adopted in automotive truck, and a great benefit is gained.