Characterization of hot workability of a Cu containing high strength low alloy steel using processing map

Abstract

Hot workability of an experimental Cu containing martensitic high strength low alloy (HSLA) steel was characterized by conducting isothermal hot compression tests at different temperatures (900–1100 °C) and strain rates (0.0003–1 s−1). Flow curves exhibits predominantly single peak behaviour at temperatures for a strain rate > 0.01 s−1. At temperature > 950 °C and for low strain rates of 0.0003 and/or 0.001 s−1, multiple peaks characterised by oscillations in flow stress was observed. The strain rate sensitivity (m), temperature sensitivity (S) of the material was calculated and the processing map was developed to identify optimum condition for thermo-mechanical processing. The material exhibits three suitable processing windows in temperature – strain rate space viz., (1) 1050–1100 °C; 0.1–0.01 s−1 (2) 980–1020 °C; 0.1–1 s−1 and (3) 980–1020 °C; 0.001–0.0003 s−1. The microstructure of the material deformed under all the above mentioned processing conditions exhibited defect free equiaxed dynamically recrystallized grains with an average grain size of 30–40 μm. Any or combination of these processing conditions can be used by the industry for designing suitable forging process (roughing, finishing etc.) based on the infrastructure available. Further, using Avrami approach, the effect of strain, strain rate and temperature on the kinetics of dynamic recrystallization (DRX) was also evaluated. The results obtained are presented and discussed.