Heat treating of wheel nuts

[Skelly]

Hello All
I could use some advice on a current project. I am making some wheel nut assemblies for a Ralt RT4 i was told to make them out of 4340 steel and have them heat treated. What hardness do they need to be after heat treat?

Thanks
Sean

[mark elder]

Why would you want to harden them
and what sort of hardening were you thinking of anyway.
Its 4340.
Do you want a surface hardening to stop the rattle gun beating them to death?

[Skelly]

I forgot to add that I made mine from 4140 not 4340 like they recommended. ( I could not get that in hex) so would you think 4140 would still need some type of hardening?
Thanks
Sean

[R. Pare]

If you are going to harden them, 4140 can be hardened up to somewhere around RC52 or so, but will still have a small percentage of retained austenite, which decreases its toughness. For use as a wheel nut, I would guess that drawing it to somewhere around RC 40-45 would be more than sufficient for both strength and toughness - that is about where lathe tool holders are hardened to.

[patman]

I wouldn't make them any harder than you have to, you don't want them to be brittle and potentially crack.

I am not familiar with the Ralt and don't know what these look like, so hard to judge.

Just to give you some ideas, a Grade 5 bolt is 25-34 HRc through hardened. Grade 8 is 33-39. Both are similar chemistry to 4140.

[stownsen914]

Would it be worth knowing the hardness of the mating axles/spindles to which the nut will be fitted? I'm thinking I'd rather the nut be softer to act as the sacrificial part, as they are obviously the easier one to replace.