Strength-Toughness Improvement of 15-5PH Stainless Steel by Double Aging Treatment

To obtain better strength-toughness balance of 15-5PH stainless steel,a double aging treatment is proposed to investigate the mechanical properties and microstructure evolution.In this study,Cu precipitates and reversed austenite played a determining role to improve strength-toughness combination.The microstructure was observed using electron backscattered diffraction,transmission electron microscopy and scanning transmission electron microscopy.The volume fractions of Cu precipitates and reversed austenite were calculated with Thermo-Calc software and measured by X-ray diffraction.The results showed that the reversed austenite is formed at the martensitic lath boundaries and its volume fraction also increases with the increase of the aging temperature.At the same time,the size of the Cu precipitates gradually increases.Compared with the traditional single aging and double aging treatment,double aging treatment of 15-5PH stainless steel can increase the toughness while retaining the necessary strength.During double aging of 550℃×4 h+580℃×1 h,15-5PH stainless steel has the best strength and low-temperature(-40℃)toughness match.Its yield strength,ultimate tensile strength and the Charpy impact energy are 1.037 GPa,1.086 GPa and 179 J,respectively.