Influence of post-weld heat treatment on tensile properties of modified 9Cr–1Mo ferritic steel base metal

Abstract

The paper presents the influence of post-weld heat treatment (PWHT) on tensile properties of modified 9Cr–1Mo ferritic steel base metal. Tensile tests at room and elevated temperatures (300–873 K) were performed on specimens in normalised and tempered condition as well as with additional PWHT (993 K for 1 h; 1013 K for 1 h and 1033 K for 1 h). The yield and ultimate tensile strengths decrease gradually up to intermediate temperatures followed by a rapid fall at high temperatures in all heat treatment conditions. At intermediate temperatures, the steel exhibited ductility minima, serrated flow, negative strain rate sensitivity on flow stress and peak in the average work hardening rate. The influence of additional PWHT is reflected in a systematic and gradual decrease in both the yield and tensile strength values with increasing PWHT temperature from 993 to 1033 K for 1 h. However, there has been no appreciable change in ductility values as well as the fracture mode in PWHT conditions compared with those observed in normalised and tempered condition. Comparison of strength values in PWHT conditions suggested that the strength values remained higher than the average values specified in the French Nuclear Design Code, RCC-MR.