1. Manifestation of slag inclusion defect
Slag inclusion defects are formed by the slag remaining in the weld during welding. Slag inclusion defects generally exist in a single small area, and linear defects are generally formed at the welding defect groove. The cross section is generally small area or single point during sampling, as shown in Figure 1. The place where slag inclusion defects gather is easy to cause stress concentration, which not only reduces the mechanical properties of the weld, but also produces crack defects seriously, which is potentially harmful in the use of castings.
2. Main measures to prevent slag inclusion defects
Slag inclusion defects are mostly caused by serious lack of fusion or non cleaning of welding slag and weld bead. For large steel castings, slag inclusion defects are mainly caused by unreasonable groove angle, incomplete slag removal during multi-layer welding and improper use of welding process parameters. Some positions that are not conducive to welding, such as overhead welding position and welding dead corner, are not handled in time, which are also easy to produce linear slag inclusion and incomplete fusion defects at the welding groove. Prevention measures for slag inclusion defects include:
① Groove angle control: during defect excavation, the groove angle shall be strictly controlled, and the openings on both sides of the defect shall be inclined upward by 10 ° ~ 15 °, in the shape of a ship, so as to ensure circular arc transition and avoid vertical upward defects;
② The slag shall be removed in time during the welding process of defects. The slag shall be removed immediately after each layer is welded. If necessary, the flashlight shall be used for close inspection. The places with weld beading or dead corners need to be polished in time to ensure that they are qualified before welding;
③ During welding operation, the arc should not be too long, the thickness of welding layer should be controlled at about 3 mm ~ 5 mm, the welding speed should be controlled at 12 cm / min ~ 15 cm / min, and the swing of electrode should not be too wide;
④ Place the defect in a position conducive to welding. For large steel castings, the casting structure is complex and the defect distribution positions are different. Reasonably adjust the placement position of castings to make the defects in a position conducive to welding. If conditions permit, try to ensure vertical welding or flat welding, avoid horizontal welding, and effectively avoid slag inclusion defects.