1. Bubbles
Bubbles mostly occur in the center of the weld, and hydrogen is still hidden in the weld metal in the form of bubbles. The main reason is that the welding wire and flux have moisture on the surface and are used directly without drying. In addition, the current is small during welding, the welding speed is too fast, and the accelerated solidification of the metal will also cause this situation.
2. Undercut
The undercut is a V-shaped groove along the center line of the weld at the edge of the weld. The main reason is that the welding speed, current, voltage, and other conditions are not appropriate. Among them, too high a welding speed is more likely to cause undercut defects than an inappropriate current.
3. Thermal cracks
The reason for thermal cracks is when the weld stress is very large or the SI silicon element in the weld metal is very high, there is also a sulfur crack. The billet is a plate with a strong sulfur segregation zone (belonging to soft boiling steel). During the welding process, sulfides enter the weld metal and cause cracks.
4. Insufficient penetration
The overlap of the internal and external weld metals is not enough, and sometimes it is not fully welded.

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