he solidification structure of an autogenous, low–carbon 7Cr–1Mo–12Ni–0·2Nb steel weld and the transformation behaviour of δ-ferrite during cooling of the weld and subsequent elevated-temperature aging have been examined. Regions of both primary ferritic and primary austenitic solidification were exhibited by the weld. The concentration profiles, determined by scanning transmission electron microscopic/energy dispersive X-ray analyses, and the calculated diffusion distances, indicate that the transformation of δ-errite to austenite occurred by a diffusional process during cooling. Niobium stabilization appears to restrict M23C6 formation and to promote the transformation of retained δ–ferrite to intermetallic phases, including σ-, χ,Laves,and R;amp;#x2013;phase.
MST/227
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