Microstructure transformation of high strength steel automobile steering knuckle during quenching
In order to simulate the microstructure and hardness distribution of high strength steel steering knuckle after quenching,the thermophysical parameters and isothermal transformation curves of 42CrMo steel were calculated using Jmatpro software,and the kinetic model parameters of pearlite,bainite and martensite transformation of the 42CrMo steel were obtained.A multi field coupled finite element analysis model for heat transfer and phase transformation during the quenching process of the 42CrMo steel was established based on Comsol software.The quenching and cooling process of the steering knuckle in PAG(poly alkylene glycol aqueous solution)was simulated,and the temperature,microstructure and hardness distribution were obtained.The hardness and microstructure of the forged rod after quenching were analyzed and compared with the simulation results.The simulation results show that the surface of the forged rod is mainly composed of 82.1%martensite and 17.9%bainite,with a hardness of 31.9 HRC.The center is mainly composed of 15.9%martensite,72.5%bainite,9.1%ferrite and 2.5%pearlite,with a hardness of 26.8 HRC.The maximum surface hardness of the forgings measured by the experiments is 32.0 HRC,and the minimum hardness of the center is 26.4 HRC.The surface microstructure is short lath martensite and some granular lower bainite,and the center is needle martensite,feathery upper bainite and ferrite.The simulation results are basically consistent with the test results,indicating that the established multi field coupled finite element analysis model can accurately predict the quenching microstructure and hardness distribution of high strength steel steering knuckle forgings.