Mechanical and corrosion behaviors of 25Cr–5.3Ni–2.8Mo–0.15N duplex stainless steel castings affected by annealing process

Abstract

Stress relief annealing treatment is generally applied to keep the dimension stability and tolerance during machining process for casting. However, this process might depress properties of duplex stainless steel (DSS) castings used for sea water circulating pumps in power plants. In this paper, the microstructure and composition analysis of the 25Cr–5.3Ni–2.8Mo–0.15N DSS cast samples affected by stress relief annealing treatment were investigated by SEM and EDS. Meanwhile, uniaxial tensile test, Charpy impact test, and Brinell hardness test were also applied to research the strength, impact toughness, and hardness. Furthermore, the corrosion resistance of 25Cr–5.3Ni–2.8Mo–0.15N cast DSS was also determined by potentiodynamics polarization curves and cyclic voltammety. Brittle sigma phase precipitation has been observed in stress relief annealed samples by SEM and domain elements distribution, especially for samples annealed at 650 °C, comparing to the solidification solution treated sample. The strength and hardness of DSS sample stress relief annealed increased significantly, however, the elongation and toughness is depressed comparing to the solidification solution treated samples. Furthermore, the results of electrochemical measurements showed that annealing treatment at 650 °C significantly depresses the corrosion resistance of DSS. Therefore, stress relief annealing process of casting samples shall be considered especially due to its brittle transformation and depression of corrosion resistance.