Optimization of quenching process for BS960E high strength steel based on orthogonal experimental method
Based on the orthogonal experimental method,the effects of heating rate,holding temperature,holding time and cooling rate during the quenching process on microstructure and mechanical properties of BS960E bainitic high-strength steel were studied.The results show that the microstructure of quenched BS960E steel is lath martensite.The optimal parameter combination for obtaining the minimum average grain size through orthogonal experimental design of the quenching process is:heating rate of 50 ℃/s,holding temperature of 920 ℃,holding time of 2 min and cooling rate of 100 ℃/s.The optimal parameter combination for obtaining the maximum Vickers hardness is:heating rate of 50 ℃/s,holding temperature of 1010 ℃,holding time of 2 min and cooling rate of 100 ℃/s.The correctness of the orthogonal experimental method is verified by adding a control experimental group.The minimum average grain size of the sample designed by the orthogonal experiment is 6.36 μm,and the packets,blocks and laths of lath martensite are 5.2 μm,1.24 μm and 336.3 nm,respectively.The maximum hardness of the sample designed by orthogonal experiment is 424.3 HV,and the packets,blocks and laths of lath martensite are 8.5 μm,1.65 μm and 333.5 nm,respectively.Compared to the former,the latter decreases from a higher temperature(1010 ℃)to room temperature at the same cooling rate(100 ℃/s),resulting in greater undercooling,the increase in martensitic transformation driving force leads to an increase in dislocation density,and the proportion of large angle grain boundaries increases from 70.5％to 83.3％,resulting in higher hardness.
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