Unexpected Charpy Impact Toughness Spike of 1.25Cr-0.5Mo Steel After Simulated Postweld Heat Treatment

The present study elaborates on the effect of simulated postweld heat treatment (SPWHT) on microstructure and mechanical property variations of 1.25Cr-0.5Mo steel. With the increase in SPWHT holding time, lath ferrite tends to morph into blocky ferrite, and carbides aggregate along grain boundaries. Although tensile strength keeps decreasing, Charpy impact toughness undergoes a spike, followed by a sharp decrease. Such an interesting phenomenon is explained by the competition between high-angle grain boundary population and carbide segregation, and bodes well to the pressure vessel industry for optimized PWHT.