Microstructure characteristics in weld zone of the novel thick 08Cr9W3Co3VNbCuBN heat-resistant steel welded joint by fusion welding

One of the primary candidate materials used in 650°C ultra-supercritical (USC) thermal power plant units is a novel thick grade of heat-resistant steel, 08Cr9W3Co3VNbCuBN (G115), for which China has complete intellectual property rights. In this study, G115 steel with a 115 mm thick wall was successfully welded using gas tungsten arc welding (GTAW) + shielded metal arc welding (SWAM), which was a significant step toward achieving its application in large-diameter boiler tubes. The influence of the welding process on the microstructure and mechanical properties of the G115 welded joint after post-weld heat treatment (PWHT) at 770°C for 11 h was investigated. The findings demonstrate that the weld zone (WZ) after PWHT was composed of martensite and ferrite, and M23C6 was the precipitate. The average hardness of WZ was 273.1 HV, and the average impact toughness was above 39J, which was sufficient for actual production applications. It offered the necessary theoretical foundation for the practical development of thick-walled G115 heat-resistant alloy steel during welding.