Hot Deformation Studies and Optimization of Hot Working Parameters in Custom 465® Martensitic Precipitation Hardenable Stainless Steel

Abstract Hot deformation studies and optimization of hot working parameters and corresponding microstructure control were explored in Custom 465® ultrahigh-strength precipitation hardenable martensitic stainless steel. Hot compression tests were carried out in the temperature range of 800°C–1,100°C and at five different strain rates (0.001–10 s−1). Processing maps were developed based on the results of hot compression tests, employing principles of the Dynamic Materials Model, and various domains of microstructure evolution (in the austenite phase) were identified. The stable and unstable domains as well as domains indicating dynamic recrystallization (DRx) were identified from the processing map. The domain for DRx was confirmed by detailed microstructural investigations (prior austenite grains) of the respective water-quenched specimens, as well as from the inflections in hardening curves. The optimum conditions for processing Custom 465 steel were suggested as T = 1,075°C and ε˙=10−3s−1 and can be used for initial ingot breakdown (cogging) operations and T = 925°C and ε˙=10−3s−1 for finish forging operations to obtain grain size control. The value of the activation energy for hot deformation was calculated to be 543.88 kJ/mol for this steel.