Microstructure and Mechanical Behavior Study of the GTAW Joint of AISI 310 and Modified 9Cr-1Mo (P91) Steel

This study investigates the impact of varying Ni-based filler compositions on the microstructure-mechanical property relationship of AISI 310 austenitic stainless steel and modified 9Cr-1Mo (P91) ferritic/martensitic steel dissimilar welded joint, aimed at applications in ultra-supercritical boilers. To fabricate the dissimilar weld joints, three types of Ni-based fillers were used: Inconel 617, Inconel 625, and Inconel 82 and joint was fabricated using the gas tungsten arc welding (GTAW) process. The interface characterization revealed macrosegregation near the interface, and this is represented by features such as peninsulas, islands, and an unmixed zone. The weld metal exhibited a typical austenitic microstructure with a high weight percentage of Ni. The Ni-based fillers had minimal impact on the ultimate tensile strength (UTS), and all the joints were failed in the AISI 310 steel at room temperature and in the P91 steel at high temperatures. The UTS was measured as 581 +/- 8 MPa for Inconel 617, 574 +/- 4 MPa for Inconel 625, and 571 +/- 3 MPa for Inconel 82 filler welds. At 550 degrees C, the UTS was measured in the range of 388-415 MPa, while at 650 degrees C, it ranged from 247 to 331 MPa. Among all the fillers, the maximum hardness of the weld metal, 422 HV, was recorded for the Inconel 625 filler weld. However, during impact testing, the highest Charpy toughness was observed for the Inconel 82 filler weld, while the lowest was noted for the Inconel 617 filler weld. Based on the microstructure-mechanical property relationship, it can be concluded that Inconel 82 filler is the best choice for making dissimilar joints between P91 and AISI 310 steels.