Prediction of high temperature flow stress in 9Cr–1Mo ferritic steel during hot compression

Constitutive analysis was performed on the experimental true stress-true strain data obtained from hot isothermal compression tests on 9Cr–1Mo steel in a wide range of temperatures (1173–1373 K, i.e. 900–1100 °C) and strain rates (0.01–100 s−1). The constitutive equation for hot deformation is represented by a hyperbolic–sine Arrhenius type equation relating flow stress, strain rate and temperature, and could be described by the Zener–Hollomon parameter in an exponential type equation. The influence of strain was incorporated in the constitutive equation by considering the variation of material constants as a function of strain. It is observed that the compensation for strain could not accurately predict the flow stress for the entire strain rate and temperature regime. The constitutive equation was revised incorporating compensation for both strain and strain rate by suitably modifying the Zener–Hollomon parameter and the modified constitutive equation is found to give good prediction of flow stresses for most strain rate and temperature combinations.

► Constitutive analysis is performed on hot compression flow data on 9Cr–1Mo steel.
► The influence of strain was incorporated in hyperbolic–sine constitutive equation.
► The material constants in constitutive equation were found to vary with strain.
► Constitutive equation was revised by suitably modifying the Zener–Hollomon parameter.
► The modified constitutive equation gave good prediction of the flow stress.