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Copper Contamination Cracking (CCC) of Austenitic Stainless Steels
 
Copper contamination can cause CCC on austenitic stainless steels weldment when the surface at or near HAZ get contaminated and the cracks will be resulted from Liquid Metal Embrittlement) LME and intergarnular cracking

Cu as an alloying element improves the corrosion resistant of stainless steels in reducing acids like sulfuric and phosphoric acids.

*The issue of CCC can result from surface contamination where the temperature at the HAZ or during the application of annealing heat treatment where the temperature exceeds the melting temperature of Cu (~1083 C) while 304L stainless melts over a temperature range of about 1400° to 1450°C.

*The usual scenario when this occurs is that copper is rubbed on the stainless surface, as, for example, by sliding the stainless against a copper chill bar on a seamer. Microscopic bits of copper rub off and adhere to the surface of the stainless.

*A copper backing bar is often used when welding sheet material. It is important to avoid rubbing the stainless steel against the Cu which can transfer Cu to the SS surface.
 
The surface of austenitic stainless steels such as 304L and 316L should be protected against having copper rubbed on the surface.

Direct contact, such as with a chill bar or backup bar or alignment clamp, is acceptable so long as rubbing is avoided.