Weld evaluation: cracking on the surface of 304 stainless steel during MAG welding
Thread Content
This post was last edited by The surging river waters_FHMG on 2018-1-2 at 19:42. I am currently working on the development of MAG welding for austenitic stainless steel, and I have encountered some problems: cracks appear in the center of the weld seam. The diameter of the weld zone is 2t. I have conducted many tests, with some yielding no issues while others do have problems. The shielding gas used is a mixture of argon and carbon dioxide, and the welding wire is Sandvik 19.9LSi. TIG welding is used for the root pass, followed by MAG welding for the cover pass. The heat input for MAG welding is 0.725 KJ/mm, with a current of 100 A and a voltage of 20.5 V. I suspect that the composition of the gas might be the cause, but I’m not sure yet. Please help me figure this out
The shielding gas is 98% argon + 2% carbon dioxide
How is the flaw detection? Is the welding wire flux-cored or solid?
I originally wanted to carry out this assessment as well, but I didn’t in the end; two plans were drawn up at that time. 1. Solid wire, 98% argon + 2% oxygen. 2. Flux-cored wire, 100% CO2. But in the end I didn’t use it either. I also want to know which of these two options is better.
Hello! I tried using 98% argon + 2% oxygen, and the surface oxidation was extremely severe, making it impossible to perform PT
1. Use solid welding wire as recommended by SANDVIK, with a gas mixture of 98% argon + 2% oxygen. 2. The gas might not be the problem; it could be an issue with the operation method (insufficient cleaning between channels, poor welding). Sometimes there is also a difference between the left welding method and the right welding method. 3. Flux-cored wire, 100% CO2. It might be a mixed gas. Flux-cored wires enjoy dual protection in the form of a slag shell and gas, which significantly reduces oxidation of the weld bead; the color of such weld beads is usually golden or slightly blue-violet. Flux-cored wires are more expensive, but they result in a higher RT qualification rate.
Thank you! I’ll check Sandvik’s welding recommendations later
Perhaps the voltage is a bit high, causing the dry elongation to be a bit long
Clean with alcohol before welding, and clean between layers with a wire brush
Using a wire brush for cleaning is not sufficient; generally, a wire brush can only remove minor oxidation. However, during the welding process, the oxides of Si or Mn that are oxidized in the molten pool get tightly trapped in the shallow grooves after solidification. A wire brush can only polish the surface of metal oxides; it cannot remove them (an obvious sign of this is that more spatter occurs during welding subsequent weld passes, and the arc stability deteriorates). To remove oxides, only grinding can be used.