Effect of aging on impact properties of ASTM A890 Grade 1C super duplex stainless steel

Super duplex stainless steels in the solution annealed condition are thermodynamically metastable systems which, when exposed to heat, present a strong tendency to “seek” the most favorable thermodynamic condition.The main purpose of this study was to characterize the microstructure of a super duplex stainless steel in the as cast and solution annealed conditions, and to determine the influence of aging heat treatments on its impact strength, based on Charpy impact tests applied to V-notched test specimens.The sigma phase was found to begin precipitating at heat treatment temperatures above 760 °C and to dissolve completely only above 1040 °C, with the highest peak concentration of this phase appearing at close to 850 °C. Heat treatments conducted at temperatures of 580 °C to 740 °C led to a reduction of the energy absorbed in the Charpy impact test in response to the precipitation of a particulate phase with particle sizes ranging from 0.5 μm to 1.0 μm, with a chromium and iron-rich chemical composition.