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

Abstract

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 °C × 4h + 580 °C × 1h, 15-5PH stainless steel has the best strength and low-temperature (−40°C) toughness match. Its yield strength, ultimate tensile strength and the Charpy impact energy are 1.037 GPa, 1.086 GPa and 179 J, respectively.

摘要

为了获得15-5PH不锈钢更好的强度-韧性匹配，采用双时效处理方法研究了15-5PH不锈钢的力学性能和组织演变。在本研究中，Cu析出相和逆变奥氏体对强度-韧性匹配的改善起着决定性作用。采用电子背散射衍射、透射电镜术和扫描透射电镜术对其微观结构进行了观察。分别采用Thermo-Calc软件和X射线衍射计算并测量Cu析出相和逆变奥氏体的体积分数。结果表明，逆变奥氏体在马氏体板条边界处形成，其体积分数也随着时效温度的增加而增加，同时，Cu析出相的尺寸也逐渐增大。双时效处理与传统的单时效处理相比，15-5PH不锈钢的双时效处理可以在保持必要强度的同时提高韧性。15-5PH不锈钢在550 ℃ × 4 h + 580 ℃ × 1 h的双时效处理中，具有最佳的强度和低温（− 40 ℃）韧性匹配，其屈服强度为1.037 GPa，抗拉强度为1.086 GPa，低温（− 40 ℃）冲击功为179 J。