On hot deformation behavior and workability characteristic of 42CrMo4 steel based on microstructure and processing map

In order to determine the safe region of 42CrMo4 steel during hot working and obtain excellent workability, the hot deformation behavior at the temperatures of 850–1150 °C and the strain rates of 0.01–10 s⁻¹ was investigated through single-pass compression test of thermo-simulation. Through observing and analyzing the true stress–strain curves, the conclusion may be drawn that the flow stress value increases with the decrease in deformation temperature and the increase in strain rate. Raising temperature and reducing strain rate are conductive to dynamic recrystallization (DRX) nucleating and growing, but adiabatic heating caused by higher strain rate can also promote it. Since the Zener–Hollomon (Z) value and dynamic recrystallized grain size (D_DRX) have completely opposite trends with deformation condition parameters, the expression of Z value and D_DRX can be determined as: \(D_{{{\text{DRX}}}} = 15,567.645Z^{ - 0.2174}\). The processing map and instability map constructed at a strain of 0.9 show that the suitable window for hot working with a true strain of 0.9 is in the temperature range of 970–1150 °C and strain rate range of 0.01–0.25 s⁻¹, as well as at the temperature of 1150 °C and strain rate range of 0.25–10 s⁻¹. The instability phenomenon appears in the process interval of 850–1096 °C and 0.22–10 s⁻¹.