Mechanical Properties and Microstructure Evolution of PWHT of Dissimilar Joints of SS304 and P92 Steels for Power Plant Applications

Abstract

This study investigates the effect of post-weld heat treatment (PWHT) on the dissimilar welding joint of AA304 and P92 steels with filler ER90S-B9. The PWHT was conducted at three distinct temperatures, 780 °C, 810 °C, and 840 °C, on the welded specimens. The heterogeneity in mechanical behavior and grain structure was evident, particularly in the HAZ of the P92 side, which experienced more pronounced changes than the SS304 side. The Coarse-grained HAZ (CGHAZ) exhibited an average grain size of 72 ± 8 µm post-PWHT, while the fine-grained HAZ retained finer prior-austenite grain boundaries. Microstructural analysis revealed a higher presence of δ-ferrite and martensite in the as-welded state, accompanied by a coarser grain structure in the HAZ, rendering the sample more susceptible to failure in this region. The hardness values decreased with increasing PWHT temperature, with the CGHAZ recording 276.52 HV, 268 HV, and 245 HV under PWHT_780 °C, PWHT_810 °C, and PWHT_840 °C, respectively. The HAZ and WFZ of the P92 side observed tempered martensite, while the HAZ of SS304 did not respond to PWHT. The UTS of the welded joints without PWHT was observed as 511.27 MPa, while after PWHT at 780 °C, 810 °C, and 840 °C the UTS of the welded joints were increased as 534.14 MPa, 545.96 MPa, and 569.38 MPa respectively.