Effect of aging on interfacial structures of nickel-based transition joints

Abstract

The interfacial structures between 2·25Cr–1 Mo steel and Inconel 182 weld metal have been studied in the as-welded condition and after aging at temperatures between 630 and 700°C for times up to 6000 h. Examination of the as-welded specimens revealed a band of martensite ∼0·5 to ∼50 μm wide between the steel and the weld metal. During aging, precipitates developed in this band and led to arrays of interfacial carbides which showed two morphologies, depending on the initial width of the martensite band. Single lines of coarse carbides were associated with narrow bands, and finer precipitates were distributed within the wider martensite bands. Initially, the interfacial precipitates formed readily between 630 and 700°C, but on further aging at temperatures >675°C the precipitates dissolved. The effects of changing the welding conditions and weld metal composition on the development of the interfacial precipitates are considered. In comparison with nickel-based transition joints examined after longterm service in a power station at temperatures of ∼565°C, the optimum laboratory heat treatment for accelerating precipitate development and simulating long-term structures is established.