copper contamination vs bronze contamination when welding brviouls brazed maerial

[Tmoose]

thread330-293785 talked some about copper contamination.

I've damaged some mild steel parts by welding, when the parts were previously bronze welded using commercilly available oxy acetylen brazing rod. It seemed like the old bronze diffused into the steel, and after oxy acetylene welding the steel became quite brittle and sometimes even cracked when cooling.
I think I'd read something long ago about "not welding previoiusl brazed parts" perhaps in one of the late great Carrol Smith "X to win" books
I was thinking that since OA rods are often copper plated it is probably NOT the copper that gave me the problem, but something else in the bronze recipe.
Articles like this one seem to focus on copper as a problem.

http://files.aws.org/wj/supplement/WJ_1982_03_s075.pdf

 

[swall]

Tmoose--that looks like a good article and I will read it later. I have had the same experience as you in oxyacetylene welding low carbon steel that was previously brazed with brass filler rod. As for the copper plating on OA welding rods, consider the amount of copper--it is pretty small compared to the volume of steel. Most of it probably turns into copper oxide and floats on top of the weld pool. Copper is known to cause hot shortness cracking in steel in amounts approaching 3% if I recall. I would not expect the amount from a copper plated rod to be problematic.

 

[blacksmith37]

Copper can crack steel by Liquid Metal Embrittlement . It is usually a situation when a steel with copper contamination is welded. I have seen it in pipeline welds when the copper nozzle of an automated MIG torch was partially melted into the puddle.

 

[EdStainless]

Any low melting point contaminant can be an issues, Cu, Sn, Zn, Pb, and so on.
Depending on the alloys involved the problem may not be in the weld itself, but in the HAZ where it got hot enough to melt the second alloy. This is often where LME cracking will show up.

I have seen this in miss-handled SS tubes where they had some surface Cu (or brass) contamination prior to annealing. After annealing there were small through wall cracks.

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