Modeling of the high temperature flow behavior of stabilized 12-27Â wt% Cr ferritic stainless steels

Constitutive equations and a flow stress model for the hot deformation of stabilized ferritic stainless steels with Cr contents between 12 and 27 wt% have been developed. The equations are based on compression tests in a Gleeble thermomechanical simulator to the strain of 0.4 at temperatures of 950-1050 °C at the strain rates of 0.01, 0.1 and 1 s−1. A pronounced influence of dynamic recovery on the flow curves of all steels was evident. In the constitutive equations, the activation energy for deformation decreased systemically from 359 kJ/mol to 329 kJ/mol as the Cr content increased from 12 to 27 wt%, and the interpretation of this peculiarity is discussed. A flow stress model developed, based on dislocation density, was found to predict quite accurately the experimental flow curves at the deformation temperatures and strain rates applied. Also reasonable values for dislocation densities could be evaluated from the model. The strain independent work-hardening parameter, U, which is a measure of the rate of dislocation immobilization, and the initial flow stress σ0 were found to be dependent on the deformation conditions and the Cr content. In contrast, the recovery parameter, Ω, which represents the remobilization of immobile dislocations, was found to be independent of the Cr content.