Hot Compression Deformation Behavior and Microstructure Evolution of 18CrNiMo7-6 Gear Steel

The thermal simulation method was used to study the hot compression deformation behavior of 18CrNiMo7-6 gear steel at temperatures of 900-1 150 °C and strain rates of 0.01-5 s^-1. The full strain constitutive equations based on the Arrhenius model were established, and the flow stress curves were predicted by the equations. The hot working maps were drawn according to the dynamic material model and the microstructure evolution characteristics was systematically studied in conjunction with the hot working maps. The results show that the peak stress of the test steel increased with the increase of strain rate or the decrease of deformation temperature. Dynamic recovery and dynamic recrystallization were the main softening mechanisms in hot deformation. The flow stress curves predicted by the established full-strain constitutive equation were basically consistent with the test results, and the relative error between predicted true stresses and test results was less than 4.715%, indicating that the equation could accurately simulate the hot compression deformation behavior of 18CrNiMo7-6 gear steel. The suitable hot working parameters for the test steel were deformation temperatures of 1 050-1 150 ℃ and strain rates of 0.1-1 s^-1, and the microstructure was uniform and fine recrystallized grains with grain size of 5-15 μm. With the increase of deformation temperature or the decrease of strain rate, the original austenite grains were replaced by dynamic recrystallization grains, and the degree of dynamic recrystallization and the size of recrystallization grains increased.