Rehardening a grade 5 or 8 bolt after annealed

I heated a grade 5 or 8 bolt up to dull red so I could machine it easier and
now I would like to reharden.
What temps do I quench and heat treat back?
Thanks, David
Reply to
David Seidel
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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
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Reply to
Tim Williams
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:
Reply to
Steve Smith
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
Reply to
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
Reply to
Dan Thomas
Just use carbide tooling for the machining. No problem.
Ted
Reply to
Ted Edwards
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.
Reply to
David Seidel

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