Effect of one step isothermal treatment and two step isothermal treatment on mechanical properties of 30CrMnSiA steel
A one-step isothermal and two-step isothermal Q&P treatment was designed,and the multiphase microstructure of 30CrMnSiA steel with different contents of primary martensite(PM),retained austenite(RA),secondary martensite(FM)and bainite(BF)was obtained by changing the quenching temperature and isothermal temperature.The effects of Q&P treatment on microstructure and mechanical properties of the experimental steel were analyzed by means of X-ray diffraction(XRD),electron backscatter diffraction(EBSD)technique and transmission electron microscopy(TEM).The micro mechanisms by which the heat treatment process affects the RA content,morphology and C concentration were also analyzed.The results show that the quenching temperature and isothermal temperature in the Q&P process determine the content and characteristics of each phase.A high isothermal temperature is beneficial for improving the tensile plasticity of the experimental steel,while the content of retained austenite and carbon concentration can significantly affect the elongation,product of strength and elongation,and yield strength of the experimental steel.330℃is the optimal quenching temperature for one-step and two-step isothermal treatment.At this temperature,high RA content and C concentration can significantly improve the elongation,product of strength and elongation,and yield strength of the 30CrMnSiA steel.Compared with one-step isothermal Q&P treatment,two-step isothermal Q&P treatment can increase the RA content in the microstructure and significantly reduce the FM content,which helps to improve the mechanical properties of the 30CrMnSiA steel.
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