Metallurgical properties of UNS S32750 weld joints: effects of nickel addition and post weld heat treatment

In this study the effects of both the addition of nickel powder and the application of a short time post weld heat treatment (PWHT) on UNS S32750 weld joints were investigated. Microstructural analysis, phase percentage measurements by manual points counting, microhardness tests and tensile tests were performed on all the joints. The results showed that the microstructure was deeply influenced by the addition of nickel powder, but the best performance of the joints was obtained after PWHT at 1100 °C for 10 min followed by water quenching. Both methods were able to restore the equal percentage of austenite and ferrite phases. Hardness profiles were performed on the cross sections of all the joints in order to evaluate the evolution of hardness from the base metal to the fusion zone across the heat-affected zone: a narrow decrease in hardness was found in the fusion zone with respect to the base metal and the heat-affected zone. The results of tensile tests showed that addition of nickel and PWHT leads to improve the strength of the joints and fracture fracture mainly occurred in the base metal.