Precipitation Strengthening Behavior of 15-5PH Stainless Steel During Aging at 500 °C

The mechanical property and microstructures of the 15-5PH stainless steel aged at 500 degrees C for different times have been studied in detail by using transmission electron microscopy and atom probe tomography. The precipitation-hardening effect is significant during aging and the peak hardness occurs at 2 h, but prolonged aging decreases the hardness significantly. The peak hardness is attributed to the formation of a large number of Cu-rich precipitates of 3-6 nm in diameter, with the Ni and Mn atoms segregating around the Cu-rich precipitates and forming a core-shell structure. The over-aging process increases the size of Cu-rich precipitates and causes Si and Nb atoms to segregate to the vicinity of Ni and Mn atoms, forming Nb-rich and NbN-rich particles. The formation of various phase precipitates, including possible G-phase particles, and their effects on mechanical property are discussed.