Can kunifer tubing be annealed?

[Mike TilbyParticipant @miketilby23489]

I am making a flash steam boiler out of kunifer brake tubing. (i.e. copper alloy with 10% nickel and about 1.8% iron). As expected, this is harder to bend than copper tubing and became more difficult to bend as it work hardened. However, I was dissappointed that, unlike pure copper tubing, heating to red heat did not make much difference to its ductility.

Does anyone know how to anneal work hardened kunifer so as to regain the original slightly softer condition?

Regards

Mike

[Mike TilbyParticipant @miketilby23489]

[Clive FosterParticipant @clivefoster55965]

Mike

My understanding is that kunifer can be annealed in the same way as copper. Heat to bright cherry red then quench in cold water. It is said that kunifer is less tolerant than copper over not quite being up to temperature and, unlike copper, you can't get away with air cooling.

Have to say I've never done it myself. Merely looked the procedure up before starting a job just in case.

Clive

[duncan webster 1Participant @duncanwebster1]

according to Copper Development Association you might have to get up to 950C to anneal Kunifer, depending on how much cold work you've put into it. This is a lot hotter tan copper, but I don't see any need to quench, apart from it gets the oxide off.

[Clive FosterParticipant @clivefoster55965]

Duncan

Sounds like the advice I found ages back is about right.

Depending on which authority you choose to quote 950°C is up at the top end off the cherry red shading towards orange region.

Fair bit higher than copper needs in my experience. I find it generally anneals quite well when merely at the higher end of darkish red. Especially if quenched. If leaving to air cool it seems to like a bit more heat and you have to shift the oxide so air cool is too much faff for me.

Clive.

[FulmenParticipant @fulmen]

With most alloys annealing is a matter of time and temperature, so the hotter you go the faster it anneals. If you don't want it soft as clay you should work your way up. I haven't found any reason for a quench either, except to limit the amount of heat you put into the part.

Some special CuNi-alloys can be age hardened, but that usually means holding the part at elevated temperatures for hours.

[Mike TilbyParticipant @miketilby23489]

Many thanks Clive and the others who responded.

I just went out and did a quick test (before the household guests all woke up). I had previously heated to bright red/yellow and let air cool without success. This time I did the same heating and quenched from that temperature in a bucket of water. The tubing definitely became malleable again, whereas prior to this treatment it had behaved like a piece of spring steel.

Mike

[FulmenParticipant @fulmen]

Huh, that is interesting. None of the sources I've seen mention this, and no other common Cu-alloy behaves like that. But you can't argue with empirical evidence.

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