Influence of thermal deformation conditions on the microstructure and mechanical properties of boron steel

The influence of thermal deformation conditions on the microstructure and mechanical properties of B1500HS boron steel was investigated based on a series of isothermal uniaxial tensile tests. The relationship model between work hardening rate and temperature and strain rate was established on the basis of Johnson Cook constitutive model. Moreover, the equation of the temperature rise caused by plastic deformation was modified by introducing the conversion efficiency of deformation work to heat. Next, the effects of deformation conditions (temperature and strain rate) on the volume fraction of martensite and ferrite were studied by metallographic observation. It was found that a higher strain rate brought out the martensite lath with a shorter length and thus a better ductility, and the ferrite transformation was restrained at the higher strain rate. Finally, the hardness and dislocation densities of the boron steel were detected by Vickers micro-hardness and X-ray diffraction (XRD) tests, respectively. The dislocation densities of the boron steel were quantitatively characterized by analyzing the XRD peak profiles according to the Williamson-Hall (WH) method. The results show that deformation temperature and strain rate have a similar influence on the dislocation density and micro-hardness, and hence the relationship of dislocation density and micro-hardness was deduced.