Welding to nitride-coated shafts

[jerofen]

We have some nitride coated shafts that we need to weld end collars to. The shaft sizes are 1.00 and 1.25 in. dia.
The surface is Rockwell 64-70C and the core is 50C, the steel is AISI 1045. Please advise to correct procedure.
Thank you
Jerofen

 

[jackboot]

If I was doing this- and I would test this with samples first:

The nitriding will have to be ground off at the weld joint and adjacent areas (say 3/4 inch from weld).

Second use a low hydrogen welding rod. You might be better off using GTAW process as you have a smaller HAZ.

With that high hardness you will have to have a high-preheat - my guess; 500 F minimum. You will need to limit your heat input so - use many small passes instead of a few big ones.

A stress relief should be conducted as well. If your part has been tempered, but sure to stay 50-100F below that temperature for at least 1 hour per inch thickness. If no temper you can take the part into the 1000-1100F degree range. However, I don't know how the nitride coating will handle this temperature- test before trying.

I would caution you with the suggestions I have put here as welding on any material with a Rockwell C of 50 will be very tricky. If you have any other means for attaching this collar besides welding you will probably be much better off. Somebody with experience in brazing could have some better suggestions.

If you have the option in the future:
Fabricated this assembly in the annealed condition and then send the assembly out for heat treatment and then nitriding. In other words, weld it up before heat treating and nitriding. This situation would be best if your situation allows for it.

Jackboot

 

[CoryPad]

I would try solid-state welding like friction welding and friction stir welding to avoid the major problems associated with high hardness, dissimilar coating, etc. The suggestion to remove coating near the welding area is a good one, as is the suggestion to look for non-welding assembly methods.

 

[tomwalz]

You can braze to the coating if you mean TiN. a 49% braze alloy with manganese can give you 60,000 to 100,000 psi tensile.

Tom