Effect of heat treatments on Charpy impact properties of 15Cr12MoVWN ferritic/martensitic steel

The Charpy impact properties of 15Cr12MoVWN ferritic/martensitic steel for sodium-cooled reactors with variation in heat treatment factors and parameters are reported. The results show that the ductile-to-brittle transition temperature (DBTT) increased and the upper shelf energy (USE) decreased with increase in normalizing temperature. However, the variation tendency of DBTT and USE was the opposite with increase in tempering temperature. The tempering temperature showed a greater influence on USE than the normalizing temperature, and normalizing and tempering temperatures had the equally significant effects on DBTT, but the cooling method was not a significant factor for DBTT and USE. The prior austenite grain and M23C6 size were the main influences on DBTT, and the dislocation density was the main factor affecting the variation of USE. The heat-treatment regime recommended for 15Cr12MoVWN steel was composed of normalizing at 1000–1050 °C for 0.5 h followed by water quenching or air cooling and tempering at 760 °C for 1.5 h.