Mechanical Properties And Dynamic Constitutive Model Of 42CrMo Steel

42CrMo steel is strong and tough and is mainly used for manufacturing axles and other components of high-speed trains;in addition,after the quenching and tempering process,it has a higher fatigue limit and resistance to repeated impact.Since axles are essential components,in addition to the consideration of normal design loads,the effect of impact loading needs to be considered more specifically.Therefore,studies on the mechanical properties of 42CrMo steel,especially dynamic mechanical properties,are receiving increased attention.In this study,the quasi-static compression of 42CrMo steel at three different strain rates was studied by RPL100 and the quasi-static tension at three different strain rates was studied by MTS-858.Dynamic compression experiments at three different strain rates are using the split-Hopkinson pressure bar(SHPB)set-up and dynamic tension experiments at three different strain rates are using the split-Hopkinson tension bar(SHTB)set-up.metallographic observation was performed using Zeiss Axio Scope.Al.The results show that,42CrMo steel,which belongs to typical BCC metal,has high sensitivity of strain rates and temperature under a wide range of strain rates.Particularly,adiabatic shear has been found to be prevalent in high-speed deformation and impact damage.According to the dynamic experiments,a strain-rate effect is evident in the yield behavior and the strain hardening.The dislocation theory explains the deformation mechanism of 42CrMo steel.Furthermore,a new constitutive model,which includes the thermal softening effect,based on the Zerilli-Armstrong constitutive model,is proposed to describe the dynamic mechanical behavior of 42CrMo steel.The model results are in good agreement with the experimental data,demonstrating that the proposed constitutive model describes the mechanical behavior of 42CrMo steel at various strain rates very well.Based on the typical properties of BCC metals and the experimental results,the thermal activation theory was used to explain the deformation mechanism of 42CrMo steel.In addition,the high temperature and strain-rate sensitivity of the Peierls stress are the main causes of the strain-rate and softening effects on the macroscopic properties of 42CrMo steel.A modified model based on the crystal plasticity theory is proposed to account for the macroscopic strain rate of 42CrMo steel and the softening caused by adiabatic temperature rise.We verified that the model describes the quasi-static and dynamic mechanical behavior of 42CrMo steel very well,particularly the effects of strain hardening and thermal softening.The results of this study demonstrate that the new constitutive model can predict the deformation trends of 42CrMo steel well over a wide range of strain rates.