Numerical Simulation Of Carbon Concentration Field And Structure Field In Carburizing-quenching Process

Carburizing-quenching,a most employed case hardening technique,can keep well obdurability of the center and improve wear resistance and fatigue strength.It has been widely used in mechanical parts with excellent surface properties,such as heavy-duty gear and high-speed bearing.With the development of computer technology,studies on the mathematical models of the process of carburizing and quenching are making more and more progress.However,there are still several significant explorations such as the universality of computational model,reliability of boundary condition parameters and connection of carburizing-quenching model.In this work,the model of carburizing-quenching process and the key parameters in the simulation have been studied,and the carbon concentration field and structure field of carburizing-quenching process are expected to be predicted accurately by modeling the whole technical process.Thus,reasonable references for the process design,parameter selection and field controlling in actual carburizing and quenching treatment can be provided,and the carburizing level,carburized parts lifespan can be improved to develop the intelligent heat treatment.A method of calculating the carbon transfer coefficient during gas carburizing was put forward.Moreover,the carbon transfer coefficient was accurately measured by the carburizing tests of steel foil.In addition,the rationality of the empirical formulas for carbon diffusivity was evaluated.The results indicate that the carbon transfer coefficient during carburizing is a function of the surface carbon content,and it decreases with the increase of the surface carbon content.Meanwhile,the carbon diffusivity is a function of carburizing temperature and carbon concentration.The carbon concentration distribution of G20CrNi2 Mo steel after carburizing was predicted by using the Thermal Prophet heat treatment simulation software.The carburizing experiment was carried out to verify the rationality of the model and parameters.On the basis of considering the effects of carbon gradient caused by carburizing on the temperature field and phase transformation field in the subsequent quenching process,the effective connection between carburizing model and quenching model was achieved by the linear interpolation of transformation kinetic and thermophysical parameters.The carbon concentration distribution,hardness distribution and structure distribution of 20 CrMo steel after carburizingquenching were predicted.Finally,the simulation results were verified with carburizing-quenching experiment.