Why is it So Difficult to Produce an Equiaxed Microstructure During Welding?

It is well established that the solidification microstructure has an important influence on the mechanical properties of a welded zone. This is especially true, when one considers cold cracking and hot tearing during the process. In the past, several authors have reported that grain boundaries, mainly of columnar grains, are particularly sensitive to cracking. Equiaxed microstructures, on the other hand, showed a better resistance to crack formation and propagation. Therefore a theoretical approach which shows the influence of solidification conditions on the weld microstructure has been developed and will be presented. Conclusions will be drawn about the reasons for the predominance of columnar structures with possible methods of promoting the columnar to equiaxed transition (CET).