Cu in stainless
Cu in stainless
(OP)
Guys,
we recently did some PMI work on 316 stainless, and found that there was an amount of Cu in it (<1% in all samples). We didnt make a big deal, but the client queried it saying that there is not supposed to be Cu in 316 stainless and that it could causes poor surface finishes.
I know there is a similar thread on this subject from a couple of years ago, but it was obviously the first time this situation had presented itself, and there wasn't a definitive answer as to whether it is ok or not.
I would like to know if anyone has a definitive yeah or nay now?
Declan
we recently did some PMI work on 316 stainless, and found that there was an amount of Cu in it (<1% in all samples). We didnt make a big deal, but the client queried it saying that there is not supposed to be Cu in 316 stainless and that it could causes poor surface finishes.
I know there is a similar thread on this subject from a couple of years ago, but it was obviously the first time this situation had presented itself, and there wasn't a definitive answer as to whether it is ok or not.
I would like to know if anyone has a definitive yeah or nay now?
Declan





RE: Cu in stainless
Mark
RE: Cu in stainless
Just being curious, filling in self-training hours 8<)
RE: Cu in stainless
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RE: Cu in stainless
PMI stands for Positive Material Identification, in other words, spectrometric test evaluating metals chemical composition.
But I prefer - Pardon Mine Ignorance
RE: Cu in stainless
I knew it wouldn't really cause a problem, but just couldn't come up with what I considered myself to be a satisfactory answer...
Declan
RE: Cu in stainless
- poorly sorted scrap that is supposed to be all ferrous but has some Cu, brass, or bronze mixed in.
- the use of structural steel as a source of iron, since much of this is weathering steels that contain Cu
- naturally occurring Cu in the Mo or Ni that is added.
There is no way to remove the Cu in the melting process, it is too similar to Ni. If you need low Cu you either by metal in Europe (where the scrap streams have been kept sorted better) or you pay to have a heat melted from virgin materials ($$$$).
Cu is a weak austenite stabilizer. In higher amounts (~2%, Alloy 20) it helps resistance to some acids (H2SO4). It can contribute to discoloration in welds, it looks like you have bad shielding but it is from the Cu.
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Plymouth Tube
RE: Cu in stainless
RE: Cu in stainless
RE: Cu in stainless
Yes, Cu comes into the ferrous stream due to the sources that you mentioned. This is why Ed mentioned "poorly sorted scrap". While it may be considered acceptable to have this type of contamination in carbon steels that have relatively low quality requirements (rebar, flat rolled products w/ no real formability requirements, etc.), it certainly isn't considered acceptable for carbon/alloy steels with high quality requirements (cold heading quality, bearing or axle grades, flat rolled products for auto & appliance sheet, etc.) or for stainless steel production. I have been through a number of steel mill scrap yards, and it is always disappointing/frustrating to see automotive alternators and electric motors mixed in with the shredded steel panels, etc. It's not so much the copper that is concerning, but the Sn, Sb, Pb, and other deleterious elements that come along with the copper and brass.
RE: Cu in stainless
You can also find low grade ferro nickel produced in China,which is being used for stainless steels. This is more a cottage industry ( hugely popular),but the ferro nickel reaches major manufacturers. Just for reference I am providing a link, I hope it is fine,.
http:
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RE: Cu in stainless
RE: Cu in stainless
One thing to watch is that there are SS grades that require Cu. If there is enough that the alloy qualifies for one of them then it is no longer usable as the 'base' grade. The only exceptions to this are C and N, sometimes.
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Plymouth Tube