July 7, 2014
Q: We fabricate 401 stainless steel components and have considered using metal-cored stainless steel consumables. One of the issues with metal-cored consumables is the dull appearance of the weld compared to the appearance achieved with a solid wire. What can we do to maintain a clean or shiny appearance?
A: Very good inquiry! What you’re experiencing is the downside to stainless steel metal-cored electrodes. The dull appearance you describe is the result of oxidation. Because metal-cored electrodes increase travel speed, the weld bead is exposed to the atmosphere much faster than if you were welding with a solid electrode.
If you are using a stainless steel shielding gas mix that is optimized for solid wire, the weld bead surface is exposed to the atmosphere at a considerably higher temperature than it would be if you were using a solid wire. The result is a higher level of oxidation, or a dull weld appearance.
How can you solve this dilemma? If cosmetic requirements call for a shiny weld bead surface, your only option is to incorporate a trailing shield. You can do this by using a gas dam or by attaching a secondary shielding gas line to your nozzle. This displaces the atmosphere in the weld area until it cools, leaving you with less oxidation on the weld surface.
Additionally, you could explore using a shielding gas designed especially for stainless steel metal-cored wires. These gas blends are proprietary, so talk with your gas supplier if you choose to pursue this.
Using a pulse-spray transfer mode could also reduce oxidation levels because of the lower average amperage output. Depending on the material thickness, this could reduce the maximum travel speed you could achieve with a conventional spray mode of transfer.
Remember, metal-cored electrodes are designed to increase travel speeds compared with solid wires, so research whether the travel speed gains offset any additional costs associated with metal-cored electrodes. A relatively simple cost comparison can determine if your cost per pound deposited with metal-cored electrodes is lower than the cost per pound with solid electrodes.
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