During continuous casting, welding and thermal processing, if the stress of the material can not bear the stress and strain, forming hot cracks will. Here, you must distinguish between two different types of thermal crack. In the first thermal cracking is crystal cracks, when liquid thin film layers into grain boundary under tensile load, no plastic deformation occurs, grain microstructure on internal tearing occurs. Second thermal cracking is on the contrary, without regard to liquid phase. About below its recrystallization temperature, material ductility has decreased, so this hot crack called " ductility reduces crack ".
