Influence of Thermo-mechanical Control Process for Duplex Stainless Steel on Low-Temperature Toughness

The microstructure dependence of the low-temperature toughness of a 2205 duplex stainless steel produced by a thermo-mechanical control process was investigated in the temperature range from − 147 °C to − 60 °C. In order to compare the influence of the thermo-mechanical control process on toughness, specimens with two different microstructures were prepared by using different thermal processing histories. The heat treatment process was carried out by high temperature heating to induce grain growth. The conventional process and the thermo-mechanical control process were applied with different cooling rates of 0.1 and 30.0 °C/s from the heating temperature of 1300 °C to the hot working temperature of 1000 °C. Coarse microstructures were observed with the heat treatment and the conventional process, while the microstructure achieved by the thermo-mechanical control process consisted of fine austenite grains with a single μm size. The thermo-mechanical control process resulted in a higher low-temperature toughness and a decrease of 26 °C to 33 °C in the ductile–brittle transition temperature. Based on an investigation of the relationship between the fractography and instrumentation Charpy test results, it was concluded that the fine austenite grains produced by the thermo-mechanical control process have the function of preventing crack initiation.