Study on the Variation in Mechanical Properties along the Dissimilar Weldments of P22 and P91 Steel

The aim of the present work was to examine the microstructure and mechanical aspects of the Gas Tungsten Arc Welded dissimilar joint of P22 and P91 steel in as-welded (AW) and post-weld heat-treatment (PWHT) conditions. The weldments' optical and scanning electron microscopy characterization showed the heterogeneous microstructure formation along the weldments, which led to the variation in mechanical properties. After the PWHT, a carbon depleted soft and carbon enriched hard zone was observed near the interface of P22 steel and weld metal (WM) due to the diffusion of the carbon elements across the interface. A variation in hardness was observed along the weldments, and maximum was measured in WM (430 HV) and CGHAZ (408 HV) and reduced as move from the WM to base metal. A significant reduction in hardness of WM (333 HV) and CGHAZ (308 HV) was measured after the PWHT. Tensile strength of AW and PWHT conditions was measured 611 ± 9 MPa and 650 ± 13 MPa, respectively, which was higher than the tensile strength of P22 steel. The tensile test of the welded joint showed the failure in P22 steel base metal in AW and in P22 HAZ after PWHT, which indicates that welded joint is stronger than the base material. The impact toughness results also showed that the variation along the weldments and minimum impact toughness was measured 41 J in WM, which was lower than the impact toughness of the P22 and P91 base metal. The poor impact toughness of the WM was attributed to the untempered martensitic microstructure present in WM. In AW condition, maximum impact toughness of 184 J was measured in P22 HAZ; however, it was lower than the P22 base metal. The PWHT showed a significant increase in impact toughness of the WM and HAZ of P22 and P91 steel.