Tempering is final process used in heat treatment of steel components.It is important to improve the toughness and ductility of the quenched steel without a great loss of the hardness and strength.However,the traditional tempering process is hard to satisfy requirements of combination mechanical properties with low cost.A quantitative model is developed to simulate the micro-structural evolution during tempering process of carbon steel by modifying the previous Ju and Inoue’s model.The model takes into account tempering parameters,carbon content and morphology for iron-carbon phases.Segregation of carbon atoms,precipitation of transition carbides(ε-carbide),decomposition of retained austenite and precipitation of cementite can be predicted respectively.The precipitation of carbides is modeled by considering the competitive precipitations ofε-carbide and cementite.The kinetics of decomposition of retained austenite into ferrite and cementite is depicted by the modified Avrami equation.To validate the model,it is applied to simulate the tempering process of the as-quenched plain carbon steel.The volume fractions of iron-carbon phase are calculated at different tempering temperature and time.It is indicated that tempering time has greater effect on the volume fraction of carbides at high temperature stage.The calculated results are reasonable consistent with the theoretical descriptions. Tempering is final process used in heat treatment of steel components. It is important to improve the toughness and ductility of the quenched steel without a great loss of the hardness and strength. However the traditional tempering process is hard to meet the requirements of combination mechanical properties with low cost. A quantitative model is developed to simulate the micro-structural evolution during tempering process of carbon steel by modifying the previous Ju and Inoue’s model. model takes into account tempering parameters, carbon content and morphology for iron-carbon phases. Segregation of carbon atoms, precipitation of transition carbides (ε-carbide), decomposition of retained austenite and precipitation of cementite can be predicted respectively. The precipitation of carbides is modeled by considering the competitive precipitations of ε-carbide and cementite. kinetics of decomposition retained austenite into ferrite and cementite is depicted by the modified Avrami equation .To validate the model, it is applied to simulate the tempering process of the as-quenched plain carbon steel. The volume fractions of iron-carbon phases are calculated at different tempering temperatures and time. It is indicated that tempering time has greater effect on the volume fraction of carbides at high temperature stage. The calculated results are reasonable consistent with the theoretical descriptions.