Hi Simon

Heck, this takes me back a few years.....when I was working we made many, many halfshafts. As you say, En24 is a common material used for halfshfts and, depending on the section, can be taken above "T" condition (V or W). Though this may need an intermediate stress relieving operation.

Also En24 is often induction hardened. Either the whole length or just the splines. Whether you do the whole length or not depends on the torque and likelyhood of breakage. As above, if you induction harden the whole, a stress relieve op may be necessary to reduce the amount of bending.

In my opinion case hardening is unusual on halfshafts, I can't see it's benefit.

My other option is to use something like EN36b and have the shafts case hardened but I'm concerned about warpage unless I grind them and machine the splines after heat treatment but I'm reluctant to do that.
I don't follow the logic here.....surely you are worried about the splines resistance to wear. If you are removing the case to enable the splines to be milled/hobbed, then you have a spline surface no better than En24 for wear resistance. (not to mention bend and grinding through the case.)



It comes back to what you want:

a)Will En24T (or "V") carry the torque? (unless there are any sharp changes in section, the shaft will fail at the point where the spline leaves the hub)

b)Will the spline wear excessively?

If you are worried about a) then push the En24 to "V" or above or/and add induction hardening

If you are worried about b) then induction harden the splines (En24 will take nitriding. Not as good as En40B. Worth thinking about)

Hope this helps

Martin

PS, it might be cheaper to machine two sets of shafts and depending on how long the first ones last, the spares can be used "as is", or hardened.