Microstructure and mechanical properties of weld fusion zones in modified 9Cr-1Mo steel

Modified 9Cr-1Mo steel finds increasing application in power plant construc tion because of its excellent high-temperature properties. While it has bee n shown to be weldable and resistant to all types of cracking in the weld m etal and heat-affected zone (HAZ), the achievement of optimum weld metal pr operties has often caused concern. The design of appropriate welding consum ables is important in this regard. In the present work, plates of modified 9Cr-1Mo steel were welded with three different filler materials: standard 9 Cr-1Mo steel, modified 9Cr-1Mo, and nickel-base alloy Inconel 182, Post-wel d heat treatment (PWHT) was carried out at 730 and 760 degreesC for periods of 2 and 6 h, The joints were characterized in detail by metallography, Ha rdness, tensile properties, and Charpy toughness were evaluated. Among the three filler materials used, although Inconel 182 resulted in high weld met al toughness, the strength properties were too ion: Between modified and st andard 9Cr-1Mo, the former led to superior hardness and strength in all con ditions. However, with modified 9Cr-1Mo, fusion zone toughness was low and an acceptable value could be obtained only after PWHT for 6 h at 760 degree sC, The relatively poor toughness was correlated to the occurrence of local regions of untransformed ferrite in the microstructure.