Investigations of dissimilar welds of the high temperature steels P91 and PM2000

Abstract Compared to present reactors, modern nuclear power plant as well as fusion power plant concepts are based on materials which can be operated at higher temperatures and up to higher fuel burn-up. Oxide dispersion strengthened (ODS) steels – produced by mechanical alloying – with chromium contents of 9 and 14 wt.% (or even more) are the typical candidate materials. Preliminary studies have shown that these ODS steels have superior thermal creep strength and they are more resistant to irradiation damage than standard 9Cr ferritic/martensitic steels. Irradiation swelling, helium embrittlement, and irradiation hardening were observed on a much lower level [1] . Joining of high temperature steels is an important aspect for modern power plant concepts. Therefore investigations on joining the ferritic ODS steel PM2000 and the ferritic/martensitic nuclear standard steel P91 were made [2] . After welding by electron beam (EB) several heat treatments were performed and investigated. First, the samples were annealing at 1050 °C for 1 h and then tempered at 770 °C for 2 h. To characterize the joints, creep and Charpy tests were performed. The microstructure was analyzed using optical microscopes, SEM and TEM. This paper presents and discusses the results of the mechanical tests focusing on the microstructure of the dissimilar welds. A comparison of Charpy and creep tests of dissimilar with similar welds shows that the later are much easier to produce. Therefore, further investigations of dissimilar welds are necessary for a full characterization, understanding, and possible optimization.