American Welding Society Forum
During welding Carbon steel to Copper-Nickel I have been faced to cracking problem.I used E Ni Cu 7 for joining two parts .The weld joint is used to prevent leak not strength weld.
I would be please to receive any suggestion/experience .
You may need to post a little more information about the parameters that was used when this joint was made. Include such things as welding process/shielding gasses(if any) used and preheat/interpass temperatures and any post heat that may have been applied and any holding times. Thicknesses and joint configuration, cleaning methods are some more things to mention.
Try inconel 182 . E NiCrFe. A search for various nickel alloy manufacturers should produce some results that prevent trial and error. Another option is to butter the carbon steel with another alloy.
This link will take you to a site with electrode selection. If you click on a particular reference, it takes you to a page with a description, application, weld metal chemical analysis, as welded mechanical properties, current, sizes, and amperage.
I don't know if this is related to your problem, but copper-nickel alloys are susceptible to lead or sulfur embrittlement. For welding, the phosphorus and sulfur levels in these alloys are normally held to a maximum of 0.02 percent. Another thing worth mentioning is that contamination from sulfur bearing marking crayons or cutting lubricants will cause cracking during welding. Also, if the material is above 3mm thick, you may want to use a v groove, with an included angle of 70 degrees or above, because the molten weld metal is not as fluid as with carbon steels and needs manipulation of the electrode to ensure fusion of the side walls. Also, welding with covered electrodes should be done in the flat position, although small sizes can be used in all positions. As John said, a little more information is needed. I'm just throwing out a few things for consideration.
Not to seem a boor about this, but the base and weld filler metals must be ABSOLUTELY CLEAN (the ONLY thing on the metal should be the metal itself). Use similarly clean gloves to handle the filler metal. Use new wire wheels and grinding media. Keep in mind that a wire wheel immediately become contaminated when used, and then spread the contamination to subsequent joints. Chemically clean the metals (with a non residue solvent) until a white cloth shows no more discoloration after any abrasive preparation and immediately prior to welding. Watch for burrs or rough surfaces that could hold contamination, and do not touch the surface with your bare fingers once it is chemically cleaned. And remember, do not breath while welding .... (hey, just kidding there).
You may want to look at this problem from a design standpoint. If what you have here is Cu/Ni piping going through a carbon steel penetration sleeve at a bulkhead, generally a better option is to use flanged connections on either side of the bulkhead with an insulation gasket kit. This may include the need for increasing the thickness of the carbon steel penetration for corrosion allowances.
I have done a lot of welding of carbon steel to copper nickel (90-10). RN67 Weld wire is what I always used. It can be bought from a company called Arcos. It welds nicely with a gtaw process with argon gas. Although you want it to get penetration on both metals, traveling too hot or too slow can result in a weaker weld that may crack.
For gmaw, you can use EN67, which I think can also be bought from Acros. For this, you can use 75% argon /25% helium gas.
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