Fusion boundary hydrogen cracking

Rowe, M.D., Nelson, T.W., and Lippold, J.C., Hydrogen-induced cracking along the fusion boundary of dissimilar metal welds, Welding Res., February, 1999, p. 31. 

The identification of hydrogen cracks is not simple, as they can occur in a variety of locations and orientations, and can be trans-granular or intergranular, the latter being more likely if the steel or weld metal is of the alloyed type, or exceptionally hard. In the HAZ, hydrogen cracks are usually longitudinal to the weld (unless they are extensions of transverse weld metal cracks) and usually have a portion close to the fusion boundary. However, the cracks may divert into the fine-grained HAZ, as in Fig. 1.2(b), or into the weld metal. 

The partial fusion of minute regions rich in impurity elements (particularly sulphur) in the HAZ close to the fusion boundary. When liquation leads to cracking, the cracks are very small, but they can initiate hydrogen cracking. 

---