Microstructure and Vickers-hardness of 20CrMnTiH steel during hot compression testing

The isothermal hot compression tests of 20CrMnTiH steel were carried out by using Gleeble-3500 thermo-simulation-machine at deformation temperatures ranging from 1123 to 1423 K and at strain rates ranging from 0.01 to 1 s−1. The microstructural characteristics after hot compression under various deformation conditions were described with optical microscope and EBSD method, meanwhile the Vickers-hardness (HV) corresponding to the samples was measured. The strain-induced fine and uniform recrystallised grains instead of the original coarse microstructure and higher hardness were obtained with increasing strain rate and decreasing deformation temperature. The average misorientation angle got increased and an intense α-fibre texture was dominated with increasing temperature, and then the angle decreased when the temperature increase to 1423 K. By introducing Zener–Hollomon (Z) parameter, the relationship of recrystallised grain size (D) and HV under different Z values were generated. The relationship of 20CrMnTiH steel recrystallised grain size (D) and HV was formulated based on the analysis of the experimental data, which is in agreement with Hall–Petch relationship.