1) Black overburned inclusions: This type of defect is formed on the surface of the molten metal at the V-shaped mouth by the metal oxide not being clamped on the molten surface with the extrusion of the molten metal.If the approach speed of the strip edge is less than the melting speed, the melting speed is higher than the discharge speed of the molten metal, after the apex of the V-shaped mouth, a narrow sector containing molten metal and metal oxides is formed.These molten metals and metal oxides cannot be completely discharged through normal extrusion, thus forming an inclusion zone.
2) White peroxide inclusions: In fact, the fusion is insufficient due to the pre-arc, and no foreign matter is clamped on the fusion surface. Under normal circumstances, burrs or rust form a bridge before falling to the apex of the V-shaped mouth, resulting in a short circuit and a pre-arc phenomenon caused by current jumping.
2. Insufficient fusion
1) Crack: The edges of the two steel strips are not completely fused to form a good weld, and the cracked edge is blue, indicating that the steel strip has been heated. However, the edge of the steel strip is flat and smooth, indicating that the weld is not fully fused. The most direct main reason for this type of defect is insufficient welding heating.
2) Edge waves: The reason is that there is no metal on the fusion surface. Such defects often appear on the outside or inside of the edge of the strip, similar to peroxide defects.Preventive measures for insufficient edge fusion: ① The edges of the steel strip are flat and parallel to butt; ② Use a better extrusion amount; ③ If the fracture of the defect caused by the bulge is silver-gray, use a larger welding heat input
3) Internal cold welding: After the weld with insufficient fusion is damaged, the section in the middle of the wall thickness is a flat silver-gray strip, and the edge is fibrous. This welding defect is caused by the fact that the power required by the welding speed exceeds the rated power amplifier of the welding machine, and the entire end edge of the steel strip does not have sufficient time to heat to the optimum temperature and heating depth required by the weld. In addition, the molten metal that is not fully discharged and the joint surface is not completely discharged correctly may also cause internal cold welding.
3. Cast welding
Casting welding means that the molten metal on the joint surface is not fully discharged, and the as-cast metal on the fusion surface contains metal oxides like peroxidation, and the fracture morphology changes according to the residual as-cast metal content.Most of them have a flat, brittle morphology, and metallographic examination shows that there is as-cast metal on the joint surface.Preventive measures for casting welding: ① Increase welding discharge. ② Increase strip width.
The pores on the welded joint surface are caused by high temperature welding but insufficient discharge. The fracture morphology is fibrous, and the spherical bright white spots are randomly distributed on the entire fracture. When the white spots appear on the outer wall, the surface phenomenon of the white spots is black due to oxidation. Small pores can be seen before the outer burr is removed, and pores can also be seen on the fusion line after the outer burr is removed.Preventive measures for blowholes: ①Reduce welding input; ②Increase extrusion
5. Jump welding
There are many forms of jump welding. Usually, such defects have a regular and continuous distribution, and the outer defects of the wall thickness are similar to wavy defects, and the spacing is generally equidistant. Preventive measures for jump welding: ① Increase the filtering equipment of welding current. ② Check the input voltage. ③ Check the roller and shaft