Shrinkage Stresses
Shrinkage stresses occur when metals cannot grow freely during cooling and thus shrink. This leads to tensile stresses that can cause cracks or deformations.
Physical-Chemical Mechanism of Action
When metals cool, the material contracts and shrinks. If this shrinkage is hindered by obstacles such as material boundaries or weld surfaces, internal tensile stresses develop. These stresses store energy and can lead to cracks under the right load.
Metallurgical Relevance & Welding Risks
Shrinkage stresses are particularly dangerous in weld areas because they increase hardness and coarsen the microstructure. This can lead to hot cracks, distortion, or even material failure. It is crucial to control these stresses through appropriate countermeasures.
Workshop Practice & Instructions
To minimize shrinkage stresses, the following measures should be taken:
• Material pretreatment: Remove surface imperfections and use protective coatings.
• Set welding parameters: Regulate cooling steps to ensure even cooling. Avoid rapid cooling directly at the weld edge.
• Post-treatment: Apply temperature curves or mechanical methods for stress relief after welding.