Effect of Secondary-Phase Precipitation on Mechanical Properties and Corrosion Resistance of 00Cr27Ni7Mo5N Hyper-Duplex Stainless Steel during Solution Treatment

In this work, the effect of secondary-phase precipitation on the microstructure, mechanical properties, and corrosion resistance of 00Cr27Ni7Mo5N hyper-duplex stainless steel (HDSS) during solution treatment was investigated. The results reveal that σ-phase precipitates at the interface between the α and γ phase when the solution treatment temperature is lower than 1070 °C. It is not only brittle, but also prone to create a Cr-depleted zone, which significantly deteriorates the mechanical properties and corrosion resistance. With the increase in the solution treatment temperature, the volume fraction of ferrite gradually increases. The yield strength and tensile strength increase slightly, but the elongation decreases. At the same time, the impact toughness shows a trend of first increasing and then decreasing. When the solution treatment temperature is higher than 1130 °C, Cr2N precipitates in the ferrite. The precipitation of Cr2N causes a decrease in the plastic toughness, but it does not deteriorate the mechanical properties as significantly as the σ phase. However, it can also cause the formation of a Cr-depleted zone that significantly decreases the corrosion resistance. There is no secondary-phase precipitation in the sample after solution treatment at 1100 °C, which shows the best mechanical properties and corrosion resistance.