Strain dependent constitutive analysis of hot deformation behaviour in 9Cr–1Mo ferritic steel

Abstract

Following the sine - hyperbolic Arrhenius equation, constitutive analysis has been performed on true stress - strain data obtained from hot compression tests on plain 9Cr - 1Mo steel over a wide range of temperatures (1223 - 1373 K) and strain rates (0.01 - 100 s^-1). On incorporating the correction for shear modulus and diffusivity into this equation, the power-law plot exhibited a distinct deviation at higher stresses and was accounted for by considering the contribution from dislocation pipe diffusion. The correlation between stress, strain rate and temperature was found to follow the rate equation of the form ε/D_L = constant[sinh(αLσ/G)]^nh, where D_L is lattice diffusivity, G is the shear modulus and, α_L and n_h are constants. The material constants were observed to be strain dependent and this was incorporated into the constitutive equation for predicting flow stress. The higher correlation coefficient (R = 0.996) and a lower average absolute relative error (3.264%) associated with prediction revealed that the developed strain dependent constitutive equation could predict flow stress over the investigated hot working domain.