Controlling Grain Sizes of 42CrMo Steel by Pre-Stress Hardening Grinding

The dynamic recrystallization behavior of 42CrMo steel during the pre-stress hardening grinding (PSHG) process was investigated at temperatures ranging from 850-1150 °C and pre-stress from 0 MPa to 167 MPa. A coupled grain size model considering different grinding conditions was constructed to research the grinding process. Microstructure analyses showed that the hardening layer exhibits the typical features of dynamic recrystallization (DRX), and the evolution process of microstructure and grain size can be predicted properly by the model. The volume fraction of DRX grains increases with increasing pre-stress and grinding temperature. The critical condition for DRX grains occurring is that with a grinding depth of 150 µm, pre-stress is larger than 67 MPa, while most of the DRX grains occurred when pre-stress is larger than 100 MPa. Furthermore, the relationship between pre-stress and flow stress has been derived. The result shows that flow stress shows a linearly increasing trend, with the increase of pre-stress at the stage of lower strain.