Strain Modified Constitutive Equation and Processing Maps of High Quality 20MnCr5(SH) Gear Steel

Abstract

In order to develop the high-temperature forging process of high-quality 20MnCr5(SH) gear steel, according to the physical characteristics of high-temperature hot deformation of 20MnCr5(SH), the single pass hot pressing test was carried out in the temperature range of 930–123 °C and the strain rate range of 0.002–2 s−1 by using a Gleeble-1500D thermal simulator. The stress-strain curve of 20MnCr5(SH) was analyzed and confirmed by microstructure analysis. The dynamic recrystallization occurred, and the constitutive equation of 20MnCr5(SH) high temperature flow stress was established. Considering that the traditional Arrhenius constitutive equation does not consider the effect of strain on the constitutive equation, a strain modified Arrhenius constitutive equation is proposed. The results show that the correlation is 0.9895 and the average relative error is 8.048%, which verifies the stress prediction ability of the strain modified constitutive equation. According to the dynamic material theory and instability criterion, the processing maps of 20MnCr5(SH) are obtained. It is therefore considered that 20MnCr5(SH) is most suitable for thermoplastic processing at strain rate of 0.05–1 s−1 and temperature of 1030–1100 °C.