Influence of nickel-based interlayers on mechanical, corrosion, and thermal fatigue performance of functionally graded weld joints between P91 steel and SS304

Abstract

This study introduces a novel methodology for fabricating functionally graded weld joints (FGWJ). This method employs the activated gas tungsten arc welding process (A-TIG), incorporating nickel-based interlayers. This study aims to enhance the weld joints' mechanical integrity, corrosion resistance, and thermal stability. FGWJs address key challenges like uneven thermal expansion, accelerated degradation at high temperatures, and high corrosion rate at the weld joint between P91 and SS304. The distinct transition zones of FGWJ ensure smooth property gradation, enhancing toughness, thermal fatigue life and electrochemical stability. The dilution of nickel-based interlayers yielded a predominantly austenitic microstructure across all three fusion zones, with trace amounts of δ-ferrite confined to FZ II. This led to a gradual increase in both impact toughness (FZ I: 40.5 J, FZ II: 46 J, FZ III: 59 J) and corrosion resistance (FZ I: 0.75 mpy, FZ II: 0.55 mpy, FZ III: 0.15 mpy), without compromising tensile strength (550 MPa, 84.6 % joint efficiency, 35 % elongation). Furthermore, this microstructural transformation achieved a 110 % improvement in thermal fatigue life compared to the direct joining of a conventional P91–SS304 weld without any filler metal. Ni-based interlayers in FGWJs improve the mechanical properties, thermal fatigue life and corrosion resistance of dissimilar steel welds for power generation and chemical industry applications.