Cold cracks are cracks formed during the cooling stage of the welded joint during welding. The thermal stress generated during welding will remain in the joint after the weld pool solidifies. As the joint cools, the thermal stress will gradually release. When the thermal stress exceeds the tensile strength of the material, cracks will occur.
Cold cracks are mainly divided into the following three categories:
1. Intergranular cracks: Intergranular cracks mainly occur in certain alloy materials, such as stainless steel, nickel alloys, etc. This type of crack occurs between grains because the welding thermal cycle and changes in material composition lead to intergranular corrosion and brittleness.
2. Penetration cracks: Penetration cracks occur in the weld pool of the weld, usually due to excessive heat input during welding, resulting in excessive amounts of dissolved metal, causing the weld pool to solidify excessively, thus forming cracks.
3. Heat-affected zone cracks: Heat-affected zone cracks occur in the weld heat-affected zone, that is, the area around the weld joint. The heat input during welding changes the structure and properties of the material, resulting in increased brittleness in these areas, thus forming cracks.

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