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MetalsResearcher (Materials) (OP)
5 Mar 11 18:09
I have been told that copper contamination can be the cause of cracks in welds. Is this true? Is this specific to a type of metal? If it does cause cracks why is copper used so commonly around welded components? I.e., GTAW collets, GMAW contact tips and nozzles, pipeline backup shoes for the root-pass. Is there any type of copper alloy that is better to use than another to stop the cracking?
Helpful Member!  unclesyd (Materials)
5 Mar 11 21:00
There are no specific answers to your OP as each application is different depending on specific requirements such as strength, wear, conductivity, etc..

Generally OFHC (Oxygen Free High Conductivity} Copper is better for use around electrical systems. Oxygen is one of the primary causes of cracking in Copper.

so you have a specific application in mind?
MetalsResearcher (Materials) (OP)
6 Mar 11 0:29
Thanks "unclesyd" but I must not have been clear. We weld all types of material, i.e., carbon steel (A106, A53...), stainless steel (304, 316...), chrome-moly (P11, P22, P91). Generally they are welded to the same type of material, i.e., A106 to A106. I was told that copper can contaminate the bevel of a weld and cause it to crack when welded. And so my questions:

Is this true? Is this (cracking) specific to a type of metal (only carbon steel or only stainless steel)? If it does cause cracks why is copper used so commonly around welded components? I.e., GTAW collets, GMAW contact tips and nozzles, pipeline backup shoes for the root-pass. Is there any type of copper alloy that is better to use than another to stop the (copper contamination of the bevel) cracking?
Helpful Member!  metengr (Materials)
6 Mar 11 8:12
This is true, copper that becomes liquid can cause a hot short condition (cracking) in ferrous materials during welding. However, the copper must become liquid for this to happen during welding and penetrate the surface of the material being welded. If the copper remains solid, there is no issue. The reason high OFHC copper is used is because it is an excellent conductor of heat and ferrous materials do not weld directly to it.

A common problem is copper plated, SAW weld wire that was used to prevent light rusting and binding in welding machines but created problems with copper contamination in welds.
 
unclesyd (Materials)
6 Mar 11 9:53
Adding a little to the above post.  Cracked coupons for Magnaflux testing are made by melting a piece of Copper wire in the weld metal.
meteng will remember when the use of Copper coater wire, both Tig and Mig, was prohibited due to concern of this type cracking.  
a couple of reasons that Copper coatings don't cause cracking is due to ammount present and Copper's affinity for O2. If a metal has a tendency to crack a little O2 can be added to the shielding gases to take care of any possible Copper cracking. It all ends up in the typical light scale on the weld metal are in the dust.  

Copper will also cause cracking in SS.

 
Helpful Member!  blacksmith37 (Materials)
6 Mar 11 11:56
Adding a little more: Copper cracking of steel is in the general catagory of LME (liquid metal embrittlement). Bacause of the high melt temp of copper, it usually involves welding of steel or fires. Saw it in auto MIG welding a large dia pipeline; the tips of the torches were being melted; weld parameters needed adjustment. Radiography can reveal Cu in the weld deposit.
EdStainless (Materials)
7 Mar 11 8:41
I have seen microscopic amounts of Cu on the surface of SS result in cracks when the parts were latter annealed.
We do use Cu containing tooling, we are just very careful with all contact points.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

arunmrao (Materials)
7 Mar 11 10:02
" A survey of factors affecting the use of copper in steels"

Author Morrison .J.D

NCRA REP; PP 58; REPORT NO INCRA PROJECT NO. 84; 1966

Copper Data Centre.

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

brimstoner (Materials)
7 Mar 11 10:37
The copper components in your welding gun won't cause any problem (any pickup will be miniscule).  Copper backing and shoes can safely be used for a variety of applications including electroslag.  

There are grades such as weathering steels that contain up to about 0.5% copper without cracking issues.  I am not sure what your concern is, but obviously you want clean, bright bevel surfaces before all welding, but particularly on the less forgiving, more exotic grades such as P-91.  

Heat treatment and high temperature service conditions (e.g., copper contamination in boilers) are a different matter.   

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