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Welding deformation and stress formation Welding deformation and stress are caused by many factors colleagues. The most important factors are: uneven temperature distribution on the weld; shrinkage of the deposited metal; metal structure transformation of the welded joint and rigid constraint of the workpiece.
The temperature distribution on the weldment is uneven. Due to the action of the arc, the weldment is locally heated to the melting temperature, and a large temperature gradient is formed between the weld and the base metal. According to the principle of thermal expansion and contraction, the object is heated to be elongated, and the elongation at different temperatures is different. The high temperature region of the joint requires a large amount of elongation and is hindered to form a compressive stress; and the elongation at a lower temperature region is small. The part forms a tensile stress due to resistance to elongation in the high temperature region.
During the cooling process, the volume of the molten metal shrinks, and the base metal other than the joint restricts its shrinkage to form a tensile stress in the weld zone, and the base material is subjected to compressive stress adjacent to the weld zone.
The weld seam and the adjacent weld zone almost lose the yield strength at high temperature, and plastic deformation occurs under the action of stress. After cooling, residual stress and residual deformation are formed in the weldment.
The shrinkage weld metal of the deposited metal shrinks in volume during solidification and subsequent cooling. Deformation and stress are caused in the weldment, and the magnitude of the deformation and stress depends on the amount of shrinkage of the deposited metal pair, and the amount of shrinkage of the deposited metal depends on the amount of molten metal. For example, the angular deformation of the V-shaped groove is due to the large amount of deposited metal in the upper part of the weld, the large amount of shrinkage, and the small section of the lower part of the weld is small, the amount of deposited metal is small, the amount of shrinkage is small, and the up and down shrinkage is inconsistent. Caused.
Due to the form of the welded joint, the thickness and shape of the workpiece, the length of the weld and its position, various forms of deformation occur during welding. Generally, it can be divided into: longitudinal deformation, lateral deformation, bending deformation, angular deformation, wave deformation, distortion and the like.