High temperature deformation of 316L stainless steel

Abstract

A constitutive description for AISI 316L stainless steel deformed at elevated temperatures in a wide range of strain rates is proposed. The strain dependence is introduced by means of the exponential­saturation evolution law proposed by Sah et al., and the temperature and strain rate dependence of the saturation stress are introduced by means of the kinetic model advanced by Kocks. The derivation of this formulation is conducted in a sequential manner: first, by fitting of the Sah et al. evolution law to the stress–strain data under conditions of constant temperature and strain rate; second, by correlating the extrapolated values of the saturation stress with temperature and strain rate by means of the kinetic model advanced by Kocks; third, by imposing the condition that the initial work hardening rate of the material at the beginning of plastic flow should be a constant independent of temperature and strain rate. The overall constitutive description proposed in this manner requires only four material parameters besides an expression for the temperature dependent shear modulus of the alloy. The results indicate that the equation derived in this way is able to describe satisfactorily both the flow stress and work hardening rate of the material under most of the conditions of strain, strain rate, and temperature that have been analysed. At deformation temperatures in the range 850–900°C and strain rates in the interval 10–100 s-1, it has been observed that the extrapolated values of the saturation stress are overestimated, which is thought to be due, in part, to the proximity to the upper temperature limit where dynamic strain aging effects are present in this material. The kinetic analysis that has been conducted, emphasises the need to employ appropriate scaling parameters in order to compute the correct value of the activation energy for deformation.