Effect of Isothermal Treatment on Microstructure and Performance of Micro/Nanostructure 2205 Duplex Stainless Steel Prepared by Aluminothermic Reaction

Abstract

Using an appropriate heat treatment process to control the precipitation of the σ phase, while regulating the alloy structure and grain size, is one of the effective ways to obtain good comprehensive properties of duplex stainless steel (DSS). Herein, the feasibility and preparation parameters of micro/nanostructure 2205 DSS prepared by the aluminothermic reaction are explored. The microstructure and properties are further controlled by isothermal treatment at 1000 °C for a different time. The results show that the volume percentages of α and γ phases in the 1.0 h isothermal treated steel obtain a maximum value and a minimum value, corresponding to 60% and 36%, respectively. The evolution of microstructure with isothermal treatment also affects the content and morphology of the precipitated σ phase, which changes from continuous precipitation to granular precipitation at the α/γ phase boundaries, and its volume percentage obtains a minimum value when the isothermal treatment is performed for 1.0 h. With the increase of heat treatment time, the average grain size and volume fraction of nanocrystals increase gradually. Corresponding to the changes in microstructure and grain size, the maximum values of Vickers hardness and tensile properties of the alloy are obtained after 1.0 h isothermal treatment.