Rehardening a grade 5 or 8 bolt after annealed

Orange-ish (1400-1600°F), quench in oil or water (depends on steel type... I don't know, someone else?), and draw temper to.. 400-600°F in the oven, is the general advice. But if it needs the strength, I personally wouldn't trust it after treating it by hand. ;)

Tim

-- "That's for the courts to decide." - Homer Simpson Website @

Not knowing what kind of steel was in it, I'd have to say you either need to experiment (which you may or may not be set up for), or buy another bolt. Different steels have quite different hardening and tempering requirements. You can probably make it hard, but will have no way to tell if you have tempered it correctly.

Steve Smith

Tim Williams wrote:

If yu actually need the hardness (strength) for some application, then I wouldn't do this in the first place. I have never found the slightest problem machining bolts of any grade, including SAE, AN, SHCS, etc, cold.

The only thing that is a pain is drilling SHCS for lockwire. The heads seem to get pretty hard, probably from work-hardening.

Brian

That bolt was originally case-hardened after it was manufactured, and in machining it you have removed some or all of the case-hardened material and exposed the softer, lower-carbon metal beneath it. It won't harden to the same strength or hardness as before, and if strength is critical, it could be risky.

Dan

Just use carbide tooling for the machining. No problem.

Ted

Thanks for all the help guys. What I used was a Allen Head 3/4" X 4" shoulder bolt. Maybe this is very hard on the surface. Not using any threads, just the ground part. It is not going to be used to secure anything. David

I just wanted to reharden to where it was.