Dark Areas of Stainless Steel Welds
Dark Areas of Stainless Steel Welds
(OP)
Hello,
I am looking at a fillet on 304ss material that was welded with GMAW pulse. Some welds appear to have dark discoloration - see attached picture. Is this normal?
Thanks,
I am looking at a fillet on 304ss material that was welded with GMAW pulse. Some welds appear to have dark discoloration - see attached picture. Is this normal?
Thanks,





RE: Dark Areas of Stainless Steel Welds
RE: Dark Areas of Stainless Steel Welds
Short of removing the weld, is there any way to correct the issue?
RE: Dark Areas of Stainless Steel Welds
RE: Dark Areas of Stainless Steel Welds
RE: Dark Areas of Stainless Steel Welds
RE: Dark Areas of Stainless Steel Welds
Dik
RE: Dark Areas of Stainless Steel Welds
Grinding the surface will only embed this material into the weld metal, and buffing will not remove the Cr depleted metal under these oxides.
Since these are in the weld the could be pools of oxide that formed on the weld puddle and then got trapped.
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P.E. Metallurgy, Plymouth Tube
RE: Dark Areas of Stainless Steel Welds
Dik
RE: Dark Areas of Stainless Steel Welds
RE: Dark Areas of Stainless Steel Welds
Nitric acid is fine after the material has been cleaned, but you need HF to strip the oxides.
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P.E. Metallurgy, Plymouth Tube
RE: Dark Areas of Stainless Steel Welds
RE: Dark Areas of Stainless Steel Welds
B.E.
You are judged not by what you know, but by what you can do.
RE: Dark Areas of Stainless Steel Welds
Dik
RE: Dark Areas of Stainless Steel Welds
I suspect simple oxidation from insufficient shielding would be more consistent over the entire surface of the weld. Stainless filler metals can contain increased amounts of silicon (ER308Si, ER316Si for example)) that can produce more silicon oxide on the surface of the weld if a CO2 base shielding gas is used. The silicon acts as a deoxidizer, but it also changes the fluidity of the weld pool and helps reduce the amount of undercut along the toes of the weld.
The attached photograph depicts some porosity, but it also depicts some of the silicon islands I mentioned. Granted, the base metal is carbon steel, but the silicon islands can appear on stainless welds as well. Once the islands are chipped and removed, there is a slight difference in color under the silicon oxide islands.
Best regards - Al
RE: Dark Areas of Stainless Steel Welds
RE: Dark Areas of Stainless Steel Welds
RE: Dark Areas of Stainless Steel Welds
The problem with grinding or blasting is that you are re-embedding the surface material and leaving the problem.
Nitric acid (or citric) will remove free Fe, but it will not break down oxides.
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P.E. Metallurgy, Plymouth Tube
RE: Dark Areas of Stainless Steel Welds
As previous posters have made clear, diagnose what it is before attempting treatment.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."