Precipitation of very fine particles has been observed by transmission electron microscopy in a C–Mn weld metal containing small amounts of chromium, niobium, and molybdenum. The precipitates were found in the bead from the first pass of a two–pass weld. The hardness of the bead from the first pass was found to be greater than that from the second pass. Precipitation had occurred from a supersaturated ferritic matrix as a result of the heat treatment of the first pass imposed during the second pass. The precipitates were analysed by atom–probe field–ion microscopy and found to be of the M2X type, where M = Cr, Mo, Ni, and X=C, N.
MST/173
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