Hot Deformation Behavior and Processing Map of As-Cast 40CrNiMo Alloy Steel

The as-cast 40CrNiMo alloy steel with uniform microstructure is obtained through vacuum casting by using metal mold. The hot deformation behavior of as-cast 40CrNiMo alloy steel is investigated by isothermal compression tests. The Arrhenius constitutive model and processing maps of as-cast 40CrNiMo alloy steel are constructed. The results indicate that the true stress–strain curves present typical dynamic recovery type under low deformation temperature and high strain rate. With the increases in deformation temperature or the decreases in strain rate, the true stress–strain curves gradually transform to dynamic recrystallization type. Through the analysis of processing maps and microstructures, it can be found that the area of plastic instability increases with the increase in the strain and gradually expands to the region of high deformation temperature and low strain rate. The deformation temperature range of 850-1050  °C and strain rate range of 0.001-0.01 s−1 are recommended as the reasonable hot-working process conditions. Results of this research can provide references for the selection of process parameters in casting–forging combination forming of 40CrNiMo alloy steel.