Cu in stainless 5

[deco0404]

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

 

[mw1st]

Generally 316 doesn't have any Cu in its composition. AMS 5360D or 5361D designations may have .75 Max. However in my opinion less than 1% will not cause poor surface finish. And it is not uncommon to have traces of Cu in 316, usually gets "contaminated" from ferro alloys additions for chemistry adjustments, for example Ferro Molybdenum. I don't know what type of products you manufacturing and process you using. If this presents problem for your customer, and you casting your parts, you can dilute - refine metal with virgin metal addition, i.e. certified ingots (that should have no Cu) to your melt.

Mark

 

[racookpe1978]

What does your PMI abbreviation mean?

Just being curious, filling in self-training hours 8<)

 

[unclesyd]

Checkout this abstract on Cu in Stainless Steel. This and one other article mention the increase in the area and number of oxides which is probably where your client is coming from.

http://www.sciencedirect.com/scienc...2eeadb462b4d3b2b6b80551ba4d468be&searchtype=a

 

[mw1st]

racookpe1978

PMI stands for Positive Material Identification, in other words, spectrometric test evaluating metals chemical composition.

But I prefer - Pardon Mine Ignorance

 

[deco0404]

Thanks guys,

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

 

[EdStainless]

The Cu comes from a number of sources;
- 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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[metengr]

thread330-161183

 

[racookpe1978]

Wouldn't Cu also come into the ferrous stream whenever cars or motors or appliances (with their wiring intact) are melted down as scrap?

 

[TVP]

Mr. Cook,

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.

 

[arunmrao]

Induction furnace processors of castings,always use prime select quality scrap and do not entertain such mixed scrap of varying origin and content. Critical parts have upper limits set for trace elements like Cu,Sn,Pb, etc individually and also a cumulative one.

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://ferroalloy.metalfirst.com/subsites/news_detail.php?id=1651

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[blacksmith37]

And , monel (non-magnetic (mostly) and not rusted), looks like ss scrap.

 

[EdStainless]

Yes, the pig Ni guys are putting a lot of crap into the alloy stream.

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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