Lack of root fusion
Lack-of-fusion defects in the weld root occur due to insufficient penetration, leading to lack of fusion between the flanks and reducing the weld cross-section.
Physico-chemical mechanism of action
The weld root consists of the unmelted metal base and the molten weld pool. With insufficient penetration, part of the metal remains in its solid phase, leading to lack of fusion between the flanks.
Metallurgical relevance & risks in welding
A lack-of-fusion defect can lead to reduced strength and toughness of the weld. This increases the risk of cracks and fractures, especially under mechanical stress. The service life of the weld is reduced.
Workshop practice & instructions
To avoid lack-of-fusion defects, sufficient penetration is essential. This means the metal flanks must be melted at least 2-3 mm deep. The welding temperature should be set so that the metal in the entire root area is melted. Too fast cooling can also lead to lack-of-fusion defects, so a controlled cooling method is required.