U-groove joint geometry
U-groove geometry has a rounded root and steep faces. It minimizes weld metal volume and reduces shrinkage distance, which is especially useful for large component thicknesses.
Physical-chemical mechanism of action
The U-groove geometry has a rounded root and steep flanks. This minimizes weld metal volume compared to a V-groove, since less metal goes into the joint. A smaller weld metal volume leads to less shrinkage after cooling.
Metallurgical relevance & risks when welding
Reducing shrinkage prevents stress buildup and minimizes the risk of cracks and distortion. However, too fast a cooling rate after welding can lead to glass-hard martensite, which increases hardness and reduces toughness.
Workshop practice & instructions
For U-grooves in thick sections:
• Use a slow cooling rate after welding (t8/5 > 25 s) to coarsen the structure and lower hardness.
• Make sure the joint diameter is correct to ensure even weld metal volume.