Hot Deformation Behavior and Flow Stress Prediction of Ultra Purified 17% Cr Ferritc Stainless Steel Stabilized with Nb and Ti

Abstract

The hot deformation behavior of ultra purified 17% Cr ferritic stainless steel stabilized with Nb and Ti was investigated using axisymmetric hot compression tests on a thermomechanical simulator. The deformation was carried out at the temperatures ranging from 700 to 1100 °C and strain rates from 1 to 10 s−1. The microstructure was investigated using electron backscattering diffraction. The effects of temperature and strain rate on deformation behavior were represented by Zener-Hollomon parameter in an exponent type equation. The effect of strain was incorporated in the constitutive equation by establishing polynomial relationship between the material constants and strain. A sixth order polynomial was suitable to represent the effect of strain. The modified constitutive equation considering the effect of strain was developed and could predict the flow stress throughout the deformation conditions except at 800 °C in 1 s−1 and at 700 °C in 5 and 10 s−1. Losing the reliability of the modified constitutive equation was possibly ascribed to the increase in average Taylor factor at 800 °C in 1 s−1 and the increase in temperature at 700 °C in 5 and 10 s−1 during hot deformation. The optimum window for improving product quality of the ferritic stainless steels was identified as hot rolling at a low finisher entry temperature of 700 °C, which can be achieved in practical production.