Longitudinal hot cracking
A longitudinal hot crack is a fracture in the weld metal or HAZ parallel to the welding direction. It forms due to thermal stresses when the material is prone to grain boundary segregation.
Physico-Chemical Mechanism of Action
A longitudinal hot crack forms when thermal stresses occur during cooling of the weld metal or heat-affected zone. These stresses can arise from uneven cooling diffusion or grain boundary segregation.
Metallurgical Relevance & Risks in Welding
A longitudinal hot crack can lead to brittleness and cracking, especially if the material is prone to grain boundary segregation. This can significantly impair the mechanical strength of the weld and cause early failure of the component.
Workshop Practice & Instructions
To avoid longitudinal hot cracks, it is important to ensure even cooling diffusion. This can be achieved by using cooling water or cooling gas. The weld should not be cooled too quickly to minimize thermal stresses. Recommended cooling times vary depending on the material and welding process, but generally they should be between 10 and 30 seconds.