Thermal Contraction
Thermal contraction is the shortening and narrowing of a material upon cooling, which creates internal stresses. Non-uniform cooling leads to welding defects.
Physical-chemical mechanism of action
During cooling, the material shrinks because the atoms have less energy and pack closer together. This leads to a shortening of the material.
Metallurgical relevance & risks in welding
Non-uniform cooling can lead to stress concentrations that cause cracking or fracture points in the material. In the weld, these stresses can accumulate, leading to hot cracks or distortion.
Workshop practice & instructions
To minimize thermal contraction, the material should be cooled uniformly. This can be achieved by selecting the right welding process and cooling techniques. For steel, for example, a cooling time of 10-15 seconds after welding is specified to ensure uniform cooling.