A B S T R A C T Dissimilar steels welded joints, between ferritic steel and austenitic stainless steel, are always encountered in high-temperature components in power plants. As two new grade ferritic steel and austenitic stainless steel, T92 (9Cr0.5Mo2WVNb) and HR3C (TP310HCbN), exhibit superior heat strength at elevated temperatures and are increasingly applied in ultra-supercritical (USC) plants around the world, a complete assessment of the properties for T92/HR3C dissimilar steels welded joints is urgently required. In this paper, metallographic microstructures across the joint were inspected by optical microscope. Particularly, the creep rupture test was conducted on joints under different load stresses at 625 • C to analyse creep strength and predict their service lives, while their fractograph were observed under scanning electron microscope. Additionally, finite element method was employed to investigate residual stress distribution of joints. Results showed that the joints were qualified under USC conditions, and T92 base material was commonly the weakest part of them.

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The microstructure of as-supplied, as-aged and as-crept S30432 at 650°C (=923 K) was examined to study the strengthening mechanism, especially the precipitation behavior and the contribution of precipitated particles to the creep rupture strength were emphasized. Results show that Nb(C,N) precipitates in the as-supplied microstructure, while aging and creep result in the precipitation of ε-Cu and M23Q. High creep rupture strength of S30432 steel is attributed to the precipitation hardening of ε-Cu, Nb(C,N) and M 23 C6. Extremely, ε-Cu plays an important role in improving the creep rupture strength of S30432, and at least 61% of the creep rupture strength of S30432 at 650°C results from the precipitation hardening of ε-Cu particles.