Need help: stainless steel and carbides
Need help: stainless steel and carbides
(OP)
I'm busy with some testing for temp repairs.
While I'm pretty versed in high-C steel, I don't know a whole lot about austenitic stainless steels.
I've got a specific question, and an open one.
1): If you encounter sensitization (depletion of Chrome) in stainless, I know this enables corrosion to develop faster than normal. But does it also enable mechanical malfunctions (cracking, flaking, ...) ? For a temp repair, corrosion resistance is not important (we're talking days/weeks here, not months/years). Mechanical strength however, is.
The repair gets quite hot, and stays for some time in the critical zone where carbides are formed. And there's no lack of carbon here.
2): Attached, you'll find some micros from a weld made with 18-8-6 Cr-Ni-Mn (AISI 307) on high-C steel (pearlitic structure).
What does this micro tell you, or what info do you need in order to evaluate these pictures?

While I'm pretty versed in high-C steel, I don't know a whole lot about austenitic stainless steels.
I've got a specific question, and an open one.
1): If you encounter sensitization (depletion of Chrome) in stainless, I know this enables corrosion to develop faster than normal. But does it also enable mechanical malfunctions (cracking, flaking, ...) ? For a temp repair, corrosion resistance is not important (we're talking days/weeks here, not months/years). Mechanical strength however, is.
The repair gets quite hot, and stays for some time in the critical zone where carbides are formed. And there's no lack of carbon here.
2): Attached, you'll find some micros from a weld made with 18-8-6 Cr-Ni-Mn (AISI 307) on high-C steel (pearlitic structure).
What does this micro tell you, or what info do you need in order to evaluate these pictures?

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RE: Need help: stainless steel and carbides
For the dissimilar metal weld I assume the fillee meral used is 309. The microstructure reveals nothing out of the ordinary.
RE: Need help: stainless steel and carbides
Thx for your reply!
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RE: Need help: stainless steel and carbides
What are you welding to? I would also use 309 instead of 307 if possible, Mn is a very weak austenite stabilizer.
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P.E. Metallurgy, Plymouth Tube
RE: Need help: stainless steel and carbides
Choice of 307 is made due to availibility. Our welders always carry 307 with them, and hardfacing rods that are not suitable for joining. This repair needs to be executed fast if it happens (a once in 10 years event), so this is the only practical solution.
Would etching with a particular agent be more helpful or would that tell you more? At this point, everything is still possible.
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RE: Need help: stainless steel and carbides
Other than that there isn't much to say.
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P.E. Metallurgy, Plymouth Tube
RE: Need help: stainless steel and carbides
I was only afraid that I'd have severe sensitization here, because of the large weld (time), and high hemperatures. I would've thought that this would be shown by a large amount on carbides as one comes from the other.
So Ideally, I was hoping for someone to comment particularly on this.
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RE: Need help: stainless steel and carbides
You should be able to clearly see grain boundaries, and if there is pronounced (and nearly continuous) ditching then it is sensitized.
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P.E. Metallurgy, Plymouth Tube
RE: Need help: stainless steel and carbides
RE: Need help: stainless steel and carbides
http://www.fusionpoint.be
http://be.linkedin.com/in/fusionpoint
RE: Need help: stainless steel and carbides
RE: Need help: stainless steel and carbides
It might work, but it is the wrong filler.
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P.E. Metallurgy, Plymouth Tube
RE: Need help: stainless steel and carbides
It is not feasable to hand out other rods to all of our welding teams (field welders, not plant based welders) for an event that might happen again in 10 or 20 years, and expect that they will still even find those rods, and/or that they will be in good shape.
If the repair holds for a few days, awaiting proper replacement, that's already a succes.
Thanks for your insights.
A picture of the stainless steel, etched as suggested will arrive soon.
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RE: Need help: stainless steel and carbides
Could someone please post a picture with sensitization, for my education and to compare the (non-)severity of what I should be able to see here?
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RE: Need help: stainless steel and carbides
The concern with sensitization is not the formation of the carbides, but the Cr depleted region adjacent to them, this area would then have relatively low corrosion resistance.
When welding to steel the corrosion resistance of the welds is not a real concern, since the steel will corrode first anyway.
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P.E. Metallurgy, Plymouth Tube
RE: Need help: stainless steel and carbides
Corrosion resistance does not really matter for this application, but thanks for confirming this.
Could sensitization also have mechanical consequences, like a greater likelyhood for cracking or similar failure modes?
Thanks for your continued remarks!
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RE: Need help: stainless steel and carbides
RE: Need help: stainless steel and carbides
http://www.fusionpoint.be
http://be.linkedin.com/in/fusionpoint
RE: Need help: stainless steel and carbides
RE: Need help: stainless steel and carbides
http://www.fusionpoint.be
http://be.linkedin.com/in/fusionpoint