Simulation and Experimental Study on Stress–Strain Behavior and Microstructure Evolution of 38MnVS6 Steel Piston During Hot Forging

To reveal the stress–strain response and microstructure evolution of 38MnVS6 non-quenching and non-tempering steel pistons during hot forging, this study combines finite element simulation with experimental validation to investigate the effects of deformation temperature and strain rate on equivalent stress, true stress–true strain curves, and grain evolution. The results show that the deformation resistance of 38MnVS6 steel decreases with increasing temperature and increases with higher strain rates. Under 1000–1050 °C and a strain rate of approximately 1 s−1, the stress distribution in the forging is relatively uniform, and stress concentration is effectively relieved. An Arrhenius-type high-temperature constitutive equation is established based on peak stress data, yielding a deformation activation energy Q of 335.99 kJ·mol−1, which accurately represents the flow stress variation under different hot deformation conditions. Grain evolution simulated using the CAFE model indicates that 50% deformation promotes dynamic recrystallization and refines the grains. Experimental results show that water cooling increases the tensile strength by approximately 35% compared with air cooling, although the plasticity slightly decreases. In contrast to existing studies on general operating conditions, this paper establishes a coupled correlation mechanism linking the thermal deformation parameters–cooling regime–microstructure–mechanical properties. The findings provide important theoretical foundations and engineering references for the optimization of precision forging processes for non-quenched and tempered steels, the precise control of the microstructure and properties, and the quality control of forgings.