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Reheat cracking in 2¼CrMo weld metal: the influence of residual elements and microstructure

Although the incidence has been low, reheat cracking has led to major problems in welded creep resistant steam power plant. Circumferential cracks have formed in the heat-affected zones of CrMoV pipe-like joints and transverse cracks in the 2¼%CrMo weld metal (Schüller et al. 1974). The alloy content and the stress relief heat treatment conditions have been shown to determine the underlying reheat cracking characteristics of low alloy steel types (Vougioukas et al. 1974), but residual element content and the type of microstructure determine whether or not the problem is of practical significance. Reheat cracking susceptibility in weld metals, measured by the notch bend relaxation test (Batte et al. 1976), has been shown to be generally independent of specimen orientation. The extent of cracking in multipass welds, however, has been found to depend on the type of microstructure present. Cracking occurs more readily in the coarse grained unrefined regions, clearly delineated by smooth grain boundaries, than in the partly or fully refined regions formed in the deposited weld metal by subsequent weld passes