What is silicon island in the welding process?
The MIG welding of 304 stainless steel usually uses ER308LSi wire, and the high content of silicon is added to the wire, which can provide good molten iron fluidity, easy to spread and obtain high-quality welding seam morphology, as shown below. It can reduce the stress concentration of the welding seam and improve the surface quality of the product. But the process easily forms oxides and is difficult to clean up, that’s black “silicon islands” in welds.
ER308 welding wires
ER308LSi welding wires
Silicon island is generally an oxide of silicon, which is formed by the interaction between silicon, manganese, iron and other trace elements and oxygen. It affects the appearance of the weld but does not impair the performance of the welded joint. Some customers regard the appearance of the weld as a part to be improved, so the operator must pay attention to it. The best way to solve the residual silicide in the welding seam is to reduce the oxidation tendency in the welding process. The oxidation source should also come from protective gases, air and pollution (including oil, grease, rust, dust, etc.) near the welding area. So how do you avoid and reduce silicon islands?
- Select welding protective gas with low oxidation, 98% argon mixed with 2% oxygen has stable arc jet transition.
- Optimize welding process parameters, especially arc voltage (arc length) and welding speed. The high arc length increases the formation of “silicon islands” by exposing droplets and pools to an excessive oxidizing atmosphere. Therefore, it is necessary to reduce arc voltage and arc length appropriately. In addition, the appropriate welding speed also helps to reduce the exposure time of the molten metal, thus reducing the silicide.
- Provide necessary protection for welding. adding a protective cover to the welding gun or gas protection after welding, and the exhaust hood should also be shielded with high-temperature resistant materials to achieve welding joints with good appearance. The high gas flow rate will disturb the gas, but the low gas flow rate will not provide sufficient protection and will drain the air out of the welding area.
In general, reducing the oxidation of welding gas; Keeping the welding area clean; Keeping the arc stable; avoiding the interference of air and other measures, to have done the tips, the black spots on the stainless steel welding joints, namely silicon island will be greatly reduced.