Effect of heat treatment on mechanical properties of low-alloy steel/nickel-based welding material dissimilar welded joint

The 15CrMoR heat-resistant steel/nickel-based welding material dissimilar welded joint is widely used in the pressure vessel engineering field, and understanding its distributions of mechanical properties is highly important for the reliable application. Since the microstructure and mechanical properties of dissimilar welded joint are not matched well, the appropriate heat treatment is needed to balance their differences. In this paper, based on microstructure analysis, digital image correlation technology (DIC), hardness test, and small punch test (SPT), the effect of tempering temperature on the distributions of microstructure and mechanical properties for the dissimilar welded joint are discussed. The DIC test reveals that the tempering heat treatment improves the uniformity of mechanical properties in weld fusion zone (WFZ), and all specimens fracture in base metal (BM) area. Through SPT, the tempering heat treatment at 600 °C significantly improves the strength in all three zones of welded joint. From the fracture analyses of SPT tested specimens, the BM exhibits ductile fracture, while the heat affected zone (HAZ) and WFZ exhibit mixed cleavage and ductile fracture features. From microstructure analyses, the tempering heat treatment at 600 °C not only makes the dendrite more uniform and more orderliness in the WFZ, but also makes the pearlite and ferrite distribution more uniform in the HAZ, resulting in the better ductility and uniformity. This paper gives an optimized heat treatment method with the tempering heat treatment of 600 °C for the welded joint with heat-resistant steel and nickel-based welding material, and provide basic mechanical property support for the engineering application of the dissimilar welded joint.