Characterization of GMAW processed AISI 304L-P92 dissimilar steel joints: microstructure-property correlation
摘要
This study investigates the microstructural evolution and mechanical performance of dissimilar welded joints between AISI 304L austenitic stainless steel and P92 ferritic-martensitic steel, fabricated using gas metal arc welding (GMAW). ERNiCrCoMo-1 (Inconel 617) and ERNiCr-3 (Inconel 82), two different Ni-based filler metals, were used to assess their impact on weld integrity. To achieve thorough microstructural characterisation, optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were employed. The non-destructive testing and liquid penetrant testing results indicated that both filler welds were sound and defect-free. The columnar dendritic structures were observed near the weld interfaces, transitioning to equiaxed and columnar dendrites at the weld center, reflecting thermal gradients during solidification. The variation in heat input during each welding pass, as well as the variation in cooling rate, has a significant impact on the weld microstructure for both the filler welds. The microstructure varies from the top region (capping pass) to the bottom region (backing pass), which results in significant variation in the mechanical properties associated with each welding pass. The SEM/EDS point studies and area elemental mapping showed the presence of NbC, TiC, and M23C6 type carbides in Inconel 82 filler weld and M23C6 and Mo6C type carbides in Inconel 617 filler weld. The loacalized inter-dendritic precipitation of eh carbide precipitates have seen a significant impact on mechanical behaviour. Charpy impact toughness, room and high-temperature tensile testing, and hardness profiling were done for the mechanical assessment. The room-temperature tensile testing showed that the Inconel 617 filler weld had a tensile strength of ~ 664 MPa with ~ 51% elongation, while the Inconel 82 filler weld had a tensile strength of ~ 658 MPa with ~ 50% elongation. In both cases, failure occurred in the weaker AISI 304L base metal. The percentage elongation, the appearance of the fracture surface tip, and SEM characterization of the fracture surfaces confirmed ductile fracture for both filler welds. The high-temperature tensile test results showed failure in the P92 base metal at 600 and 650 °C. The tensile strengths were 323 MPa and 229 MPa at 600 and 650 °C, respectively, for the Inconel 82 filler welds, and 285 MPa and 205 MPa at 600 and 650 °C, respectively, for the Inconel 617 filler welds. The presence of solid solution strengthening elements such as Mo, Co, and Cr in the Inconel 617 filler welds, along with a high density of coarse carbide precipitates M23C6 and Mo6C, resulted in higher hardness in the Inconel 617 filler weld compared to the Inconel 82 filler weld, with values of 238 ± 10 HV and 225 ± 7 HV, respectively. Significant hardness variation was measured in the P92 heat-affected zones (HAZs), with the maximum hardness in the coarse-grained HAZ and the minimum in the intercritical HAZ for both filler welds. Variation in hardness within the weld region from the capping pass to the backing pass and from the weld center toward the weld interface region was also observed and attributed to microstructural variations. The Charpy impact toughness values of 172 ± 14 J for the IN82 filler weld and 144 ± 7 J for the IN617 filler weld were measured. These values were lower than those of the base metals but met the minimum requirements of 80 J for fast breeder applications and 47 J for ultra-supercritical (USC) boiler systems. The findings demonstrate that direct GMAW of AISI 304L and P92 steels can achieve reliable mechanical performance, and the choice of filler metal plays a critical role in tailoring microstructure and property optimization for power generation and high-temperature applications. Based on the present investigation, Inconel 82 filler was recommended for producing the dissimilar joint between P92 and AISI 304L steels for USC boiler applications.