Welding Operation and Interpass Control
Electrode Manipulation
For flat welding, use straight or small oscillations (oscillation amplitude ≤ 3× electrode diameter) to avoid excessive exposure of the molten pool.
For vertical or overhead welding, use short arcs and narrow passes with slightly faster travel speeds to prevent pool sagging or dripping. Typically, "zigzag" or triangular oscillations ensure uniform pool temperature.
Fill the crater during arc termination (using backstep technique) to avoid crater cracks.
Interpass Temperature Control
For multi-pass welding, interpass temperature must be controlled between 150~300℃ (adjusted based on base metal strength grade):
Excessively high interpass temperature (＞300℃): Coarse weld metal grains and significantly reduced toughness, especially harmful for structures requiring low-temperature toughness (e.g., below -20℃).
Excessively low interpass temperature (＜150℃): Inadequate stress relief from the previous pass and poor hydrogen diffusion, increasing the risk of delayed cracks.
Use an infrared thermometer for real-time monitoring. Pause welding to cool if overheating; reheat locally to target temperature if underheating.
Slag Removal and Root Cleaning
Thoroughly remove slag after each pass (using a chipping hammer or wire brush), especially in groove corners, to avoid slag inclusion.
Root passes in multi-pass welding require root cleaning (using carbon arc gouging or angle grinders) to remove potential defects (incomplete fusion, porosity, etc.). After cleaning, grind to metallic luster and re-preheat.
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