Plastic properties and constitutive equations of 42CrMo steel during warm forming process

In order to obtain the practical warm forming process parameters of 42CrMo steel in manufacturing, the plastic properties and constitutive equations of 42CrMo steel during the warm forming process are investigated through the isothermal compression tests. The results show that the true stress of 42CrMo steel increases as the forming temperature decreases and the strain rate increases; the strain rate sensitivity increases as the forming temperature increases, but decreases when the forming temperature is >750°C; the maximum strain rate sensitivity exponent 0·0988 appears at 700°C and the true strain of 0·65; the temperature sensitivity decreases as the strain rate and true strain increase; the strain hardening exponent decreases slowly as the true strain increases under the strain rates of 0·01, 0·1 and 1 s −1 , but it decreases sharply under the strain rate of 10 s −1 , especially the strain hardening exponent increases when the true strain is >0·55 under 750°C and the strain rate is 0·01s −1 . Furthermore, the developed constitutive equations represented by a Zener–Hollomon parameter could give a precise estimate (correlation coefficient: R = 0·99) for the plastic flow behaviour of 42CrMo steel during the warm forming process.