In this study, dissimilar welds between HP heat-resistant steel and AISI 310 stainless steel were made with four different filler materials including: 309 stainless steel, Thermanit 25/35 R and nickel-based INCONEL 182 and 617. The microstructure of the base metals, weld metals and their interfaces were characterized by utilizing optical and scanning electron microscopy. Moreover, mechanical properties such as notch toughness, microhardness measurement, and transverse tensile testing was carried. Evaluation of the weld metal specimens was done at room temperature befor and after subjecting them to an embrittling heat treatment at 1000 °C for 120 hours. Furthermore, comparative evaluation was carried based on hot-cracking tests (Varestraint test) for all filler metals. The microstructure of the all weld metals revealed a nearly fully austenitic structure with a dendritic morphology. No crack was found in the weldments corresponding to thermanit 25/35 R and INCONEL 182 weld metal while some cracks such as solidification, reheat and ductility deep cracks was observed in the weldments corresponding to 309 and INCONEL 617 weld metals. Exposure of dissimilar weldments corresponding to Thermanit filler metal to elevated temperature results in the formation of carbide rich precipitates in the HAZ of the 310 base metal. The microhardness measurements exhibited that the highest and lowest hardness values is related to 309 and INCONEL 182 weld metals, respectively. During tensile test, all weldments failed in the weaker parent metals (i.e., HP heat resistant) except specimen corresponding to 309 weld metal that failed in the interface of the weld metal with HP base metal. The INCONEL 182 weld metal showed higher impact energy in notch toughness test befor and after heat treatment. According to Varestraint tests, Thermanit 25/35 R showed the least susceptibility to hot cracking. At last it can be concluded that INCONEL 182 and thermanit 25/35 R are the best compromise, respectively for this dissimilar weld. Key Words: HP heat resistant, AISI 310 stainless steel, dissimilar welding, varestraint.
