Investigation on grinding-induced dynamic recrystallization behavior of 40Cr alloy steel

Highlights: • The dynamic mechanical properties of 40Cr alloy steel under high temperature and high strain rate is obtained. • The dynamic recrystallization behavior of 40Cr alloy steel in the grinding was simulated by cellular automaton. • Grinding strengthening (GS) is superior to heat treatment and grain refinement for exhibiting strength. • The GS provides a probability for developing of competitive and low-cost surface strengthening technology. -- Abstract: This study aims to investigate the metallurgical behavior of high strength alloy steel 40Cr during the grinding strengthening (GS) process. The grinding heat can cause phase transformation, which increases surface hardness during the GS process. It is worthwhile mentioning that the severe plastic deformation can easily lead to dynamic recrystallization (DRX) under the high temperature on the grinding strengthening layer (GSL). It can improve the mechanical properties of metal components significantly. Firstly, the relations between true stress and strain of 40Cr alloy steel are obtained by the split Hopkinson pressure bar (SHPB) experiment under high temperature and high strain rate. The critical conditions and key simulation parameters of DRX are determined. Secondly, the temperature field and plastic strain field of the GSL are solved with the analytical method and finite element method, respectively. The results show that there is a large temperature gradient in GSL. The maximum temperature of the ground surface can reach 1060 °C. And the austenite transformation occurs within 150 µm. The severe plastic deformations generated within 60 µm in the grinding subsurface can reach the critical conditions of DRX. Thirdly, a cellular automaton (CA) model is established to simulate DRX of the microstructure evolution of the grinding enhancement layer. The comparison between simulation and experimental indicates that the plastic strain of the strengthening layer increases and the degree of refinement of the microstructure becomes higher with the increase of the grinding depth.