Weld Cracking -
Introduction
A crack is a fissure produced in a metal by tearing action. Only brittle microconstituents tend to crack following welding. When martensite is formed in the weld region, cracking is prevalent; but when martensite formation is prevented, cracks are usually avoided. Cracking, generally, does not occur if the weld metal and the surrounding base metal remain ductile after welding because ductile constituents are able to deform plastically prior to cracking, thus distributing the applied stresses more uniformly.
Besides brittle microconstituents, another important factor that promotes cracking is the tensile stresses, in the welded joint, set up due to the contraction of the weld metal during cooling. The main reason for cracking is that the material has insufficient strength or ductility at the relevant stage to tolerate the welding stresses which exceed the fracture stresses.
