selective weld seam corrosion
selective weld seam corrosion
(OP)
What is the mechanism behind selective weld seam corrosion? In a low-carbon steel, why is a ferrite-enriched zone more susceptible to corrosion? Is acicular ferrite more susceptible than ferrite, if so, why?





RE: selective weld seam corrosion
RE: selective weld seam corrosion
RE: selective weld seam corrosion
RE: selective weld seam corrosion
Thanks
RE: selective weld seam corrosion
Now, what I suspect you have is a heat-affected-zone (HAZ) problem rather than a weld metal one. You appear to have martensite or bainite in tne HAZ (acicular/needle-like structure). Such areas are anodic to the normal pearlitic microstructure, meaning they will preferrentially corrode.
If you know or can determine the base metal actual composition, it will help identify how likely these anodic areas would form while being welded (preheat-related). Just because it's "low-carbon steel" doesn't mean you can weld it with no preheat, assuming you want high quality welds and HAZ'z.
RE: selective weld seam corrosion
I am sure the corrosion is in the seam. The vicinity surrounding the seam has some pitting and general corrosion but it is outside the HAZ. Metallographic examination revealed a weld seam that appears to be almost all ferrite. The ferrite in the seam is needle shaped and, no, it does not appear to be martensite or bainite. This is a semi-killed, low-carbon steel manufactured in the 1950's.
However, you raise an interesting point. What is it about the bainite and martensite that makes it anodic to the pearlitic structure?
RE: selective weld seam corrosion
Many ERW and continuous forge welded pipe steels in the '50s had superior corrosion resistance in buried service than subsequent "clean" BOF melted products. However, the galvanic mismatch at the ERW seam in these steels was sometimes severe enough to cause rapid pitting along the seam.