In this work, a numerical model was developed to simulate the continuous cooling of steel. The model was employed for simulation of the cooling process of the plain carbon steel AISI 1045 and the low alloy steel AISI 4140. In the case of AISI 1045, modeling was performed on the cylinders with diameters of 25, 50 and 75mm and gears. In addition, the cooling process of Jominy bars as well as steel gears of AISI 4140 was simulated. Still water and still oil were considered as quenching mediums. A cylindrical probe of AISI 304 stainless steel was used to evaluate the quench severity of the mediums and various methods were employed to calculate the convective heat transfer coefficients during quenching process. Furthermore, the effects of latent heat releases during phase transformations, temperature and phase fractions on the variation of thermo-physical properties were considered. In order to simulate the kinetics of diffusional phase transformations, JMA equation and additivity rule were employed and a novel approach was applied for computing the actual phase fractions in the off-eutectoid steel. In the case of martensitic transformation, the model of Koinstinen and Marburger was used for AISI 1045 plain carbon steel, while a new model was applied for AISI 4140 low alloy steel. Moreover, the empirical model of Maynier et al. was used for hardness predictions. The present model was validated against cooling curve measurements, metallographic analysis, and hardness tests, and good agreement was found between the experimental and simulation results. This model is able to simulate the continuous cooling and kinetics of phase transformation and to predict the final distribution of microstructures and mechanical properties in steels. Key Words Steel, Phase transformation, Continuous cooling, Quenching, Numerical simulation
