Deformation characteristics and microstructure evolution during hot deformation of 18Cr–12Ni–4Si stainless steel

The effect of hot deformation parameters on the flow behavior of newly developed 18Cr–12Ni–4Si has been studied. Hot compression tests were carried out in temperatures 1173–1473 K with varying strain rates from 0.01 to 10 s−1. The flow curves exhibited strain-hardening, strain-softening, and steady-state characteristics at different thermomechanical processing conditions. Constitutive modeling of the flow behavior has been carried out using a hyperbolic sinusoidal Arrhenius equation-based kinetic model to correlate the changes in the flow stress with temperature and strain rate. Due to low values of strain rate sensitivity, the proposed constitutive equation was less accurate at the lowest temperature and highest strain rate conditions. The dynamic materials model approach was adopted to identify the stable hot workability regimes using the processing maps. The regimes for optimum hot workability were found at 1222–1473 K/0.01–0.04 s−1; 1173–1473 K/0.04–0.36 s−1; and 1383–1473 K/3.89–10 s−1. Subsequently, the microstructural characterization using EBSD confirmed the occurrence of dynamic recrystallization (DRX) and was found to be the dominant recrystallization mechanism. The microstructures were segmented using the grain orientation spread analysis to distinguish between the deformed grains and the recrystallized grains. Avrami equation for DRX has been utilized for elucidating the DRX kinetics and prediction of recrystallized grains volume fraction at different strain rates and temperatures. The percentage of recrystallized grains that was obtained experimentally was in good agreement with the predicted results. It was discovered that, at a given strain, the recrystallization kinetics accelerates with the increasing temperature, while the reverse trend was observed with increasing strain rate.