Hot tensile deformation behaviors and constitutive model of 42CrMo steel

• Hot tensile deformation and fracture behavior of 42CrMo steel were studied.
• Localized necking is dominant under strain rate range of 0.1–0.001 s−1.
• The gage segments of specimens maintain the uniform macroscopic deformation under 0.0001 s−1.
• The elongation to fracture is affected by the coupled effects of deformation temperature and strain rate.

The hot tensile deformation behaviors of 42CrMo steel are studied by uniaxial tensile tests with the temperature range of 850–1100 °C and strain rate range of 0.1–0.0001 s−1. The effects of hot forming process parameters (strain rate and deformation temperature) on the elongation to fracture, strain rate sensitivity and fracture characteristics are analyzed. The constitutive equation is established to predict the peak stress under elevated temperatures. It is found that the flow stress firstly increases to a peak value and then decreases, showing a dynamic flow softening. This is mainly attributed to the dynamic recrystallization and material damage during the hot tensile deformation. The deformation temperature corresponding to the maximum elongation to fracture increases with the increase of strain rate within the studied strain rate range. Under the strain rate range of 0.1–0.001 s−1, the localized necking causes the final fracture of specimens. While when the strain rate is 0.0001 s−1, the gage segment of specimens maintains the uniform macroscopic deformation. The damage degree induced by cavities becomes more and more serious with the increase of the deformation temperature. Additionally, the peak stresses predicted by the proposed model well agree with the measured results.