Macroscopic lack-of-fusion chain
A series of planar lack-of-fusion defects over a longer length of the weld leads to a macroscopically visible lack-of-fusion chain, impairing strength and toughness.
Physical-Chemical Mechanism of Action
A chain of lack-of-fusion defects forms when several minor lack-of-fusion spots line up along a longer stretch of the weld. These can come from too short melting time, too high voltage, or missing deoxidizer.
Metallurgical Relevance & Welding Risks
A chain of lack-of-fusion defects cuts the strength and toughness of the weld. It can cause hot cracks, stress cracks, or overall worse mechanical properties. These defects can lead to fracture or failure of the part in service.
Shop Practice & Procedures
To avoid chains of lack-of-fusion defects, make sure you have enough melting time (at least 10-15 seconds per millimeter of steel thickness). Also use a stable deoxidizer and check the voltage setting. In severe cases, you might need to do a repair pass or reweld.