welding treated/hardened steel

I have a customer that has a 4wd bobcat truck/ loader. The front axel spline to differential is stripped and will need all new parts at a cost of a few thousand dollars. He wants me to weld the spline to the differential, of course we do not know what the steel is but it is either case hardened or something like a 4140 steel. I am thinking to use either some 309 stainless or 7018 to weld it. He feels the correct repairs would cost more than the thing is worth and if welding does not work all the parts need changing anyway so there is no big loss. Any thoughts?

I would not touch it. That could come back to haunt you and you end up being responsible for the repair.

First I would figure out if it is heat treated or case hardened, and get a rough idea of the carbon content. (spark test would probably be good enough) I'm not sure if you are talking about welding up the splines to remachine them, or are you talking about welding the spline coupling solid. The former is no big deal, I would use ER80S-D2, re-machine, and heat treat or case harden. If it's the latter, I wouldn't do it as there will be nothing to allow any movement in the joint. This sounds like the kind of job you should probably run far away from. Of course because he is trying to go cheap, nothing will be taken apart as it should be. If this was something super rare, of course you could do a weld repair. But that would almost certainly cost more than just buying new parts. Another option is to cut off the bad spline and weld on a new one. Again not a big deal for a restoration job, but you would have to pull everything apart and turn a registration in a lathe. Is it just an axle and the spider gear that are bad? The spider can't be that much and the axle can probably be repaired. Of course the metal bits in the diff may have trashed a lot more by now. You could just lock the diff and let the other axle do all the work, until it fails.

I would bail on it. Unless a real good friend that knows it might not work or last (not a customer). RAMs idea on cut and weld it is a lot of work/time and you have to turn it (unless you get lucky). What are the RPMs on it? You can weld it solid too, cheaper and a lot less work, wear on tires and other things.

I think you got both sides. One said walk away other said run and far. It is weld/machine rebuild, weld on another piece (if you not find the part cheap), weld solid or find a part on the net. 4K is a lot of money, just make sure it is "as is" which ever way you go.

The wire pushing the gun back would mean too high wire speed or too low amps/voltage.
What does welding on 50 volts mean ?

.

Too low of volts or too high of wire speed. The units don't weld on 50 volts. Not sure what that means.