Development of the matching filler metal for MARBN—new advanced creep resisting alloys for thermal power plant

Abstract

MARBN alloys, which are anticipated an estimated 25 °C increase in advanced ultra-super critical (A-USC) power plant operating temperature, are expected to be commercially available soon and will partially displace some older materials and lead the market. Two examples are the Japanese alloy, 9Cr-3W-3Co-Nd-B material, which is considered a strong contender in wrought pipework, and the UK’s IBN-1 alloy which currently leads the development in cast steels. Through the courses of two consecutive UK collaborative projects IMPEL and IMPULSE, a matching composition filler metal for welding MARBN alloys in the form of shielded metal arc SMAW electrode has been developed. The design of this filler metal was aimed to optimize the deposit chemical composition hence to provide creep resistance properties matching the base alloys. The weld metal was specifically intended for high integrity structural service at expected temperatures. Accordingly, the minor alloy additions responsible for its creep properties were kept at the middle of the base alloys or at least above the minimum considered necessary to ensure a satisfactory performance. This paper introduces the design, investigation and test results of the matching filler metal. Findings relevant to the microstructure, mechanical properties at ambient and elevated temperatures, including creep properties of the all-weld metal and weld joint made with IBN-1 base alloy, are presented.