Intergranular embrittlement in CrMoV steels: an assessment of the effects of residual impurity elements on high temperature ductility and crack growth

Abstract
Examination of the causes of cracking in the heat-affected zones of welded joints in CrMoV steels during stress relief or operation at elevated temperature has shown that the presence of certain residual impurity elements is an important contributory factor. A detailed study of the effects of the elements P, As, Sn, Sb and Cu on the high temperature ductility and crack propagation behaviour of heat-affected zone microstructures in $\frac{1}{2}$Cr$\frac{1}{2}$Mo$\frac{1}{4}$V steel has been carried out to provide information on the role of these elements in the formation of cracks during stress relief and their growth in service. Work on experimental alloys has identified the relative importance of individual elements in promoting intergranular embrittlement; comparison is made with the behaviour of commercial steels. The results are discussed in terms of a possible embrittlement mechanism and consideration is given to the practical measures available for preventing cracking, both in terms of residual element and microstructure control.

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