Effect of Post-Weld Heat Treatment Temperatures on Microstructure, Intergranular Corrosion Resistance, and Mechanical Properties of 4130 Steel with Inconel 625 Weld Overlay

The effect of post-weld heat treatment (PWHT) temperatures (650, 750, 850, and 950°C with a 2-h hold time on the microstructure, intergranular corrosion resistance, and mechanical properties of Inconel 625/AISI 4130 steel bimetal plates, which was manufactured through pulsed tungsten inert gas, was investigated. The results showed that the as-welded Inconel 625 overlay is mainly composed of equiaxed dendrites and columnar dendrites. With an increase in PWHT temperatures, equiaxed dendrites transfer into columnar dendrites, and columnar dendrites transfer into cellular dendrites. It is observed that there are seldom residual equiaxed dendrites distributed in the heat-treated Inconel 625 overlay at 750°C, and the Inconel 625 overlay heat treated at 850 and 950°C consisted of columnar dendrites and cellular dendrites. The intergranular corrosion tests indicated that heat treatment at 650°C is beneficial to improve the intergranular corrosion resistance of the Inconel 625 overlay, but the corrosion rates increase sharply with the rise of PWHT temperatures. In addition, the tensile tests demonstrated that the PWHT has detrimental effect on the yield strength (YS) and tensile strength (TS) of the substrate; however, it is beneficial to the elongation. It is found that the heat-treated substrate at 650°C features relatively good YS, TS, and elongation compared with those of heat treated at higher temperatures. Therefore, considering the intergranular corrosion resistance and mechanical properties, 650°C is recommended as the optimal PWHT temperature for the Inconel 625/AISI 4130 steel bimetal plates.