Hot Deformation Characteristics and Processing Map of FV520B Martensitic Precipitation-Hardened Stainless Steel

Abstract

Hot deformation characteristics of FV520B martensitic precipitation-hardened stainless steel were investigated in the temperature range of 850-1150 °C and strain rate range of 0.005-0.5 s−1 with true strain 0.8 by using Gleeble-3500 thermo-mechanical simulator. Critical stress and corresponding critical strain for dynamic recrystallization initiation were calculated. The constitutive equation was developed by employing Arrhenius constitutive model to represent the nonlinear relationship of true stress and deformation parameters including temperature, strain rate and strain. The correlation coefficient and average absolute relative error are 0.9979 and 2.225%, which indicates the good predictive accuracy of the established constitutive equations. Processing maps were constructed at different plastic strains levels based on dynamic material model (DMM) and established constitutive equation. Combining the processing map with microstructure, the optimum region for good workability is designated as the temperature range of 1050-1125 °C and strain rate range of 0.027-0.23 s−1 with peak efficiency of 0.32. Homogeneous fine and equiaxed dynamic recrystallization (DRX) grains can be found in this optimum according to the microstructure metallographic pictures.