Structure- Property relationships in low c weld metal

A study was made of the effects of microalloy elements Cb and V on weld metal structure and impact properties. The results of this study have emphasized the importance of microstructure in determining low temperature impact properties. A number of correlation techniques have been used to account for observed toughness trends in terms of microstructure change and the accompanying alteration in the brittle fracture surface. Two categories of microstructure are described which are commonly observed in low C weld metal, namely, grain boundary ferrite plus intragranular acicular ferrite which is denoted as Category I and the lath structure which is called Category II. Category II is shown to emanate from prior austenite grain boundaries in the form of parallel side plates with similar orientation. Cb is shown to promote the Category II structure which results in decreased low temperature Charpy properties.