Metallurgy Question

[PVF1799]

I'm working on dismantling the hydraulic drive motor from a skid-steer.

There are A LOT of socket-head cap screws that are hardened and unremovable. We had to cut the heads off with my torch. Now for the question.

Does hardened steel get harder, softer or stay the same when you get it red-hot?

Ken

[tst]

I would have heated the metal the bolt was in to expand it to loosen the bolt, you can still do that but now use vise grips or what ever to grab whats left of the bolt, if you cut it flush they might have to drill and tap, just hacking them off should not change the temper much

[Jim Reid]

I have a friend who does my welding and helping free rusty bolts and pieces he says as long as you let it cool naturally it don't change the hardness.

Jim

[Urbish]

I'm a mechanical engineer. If you heat them up to glowing red hot, then let them cool slowly, you will anneal them.

[PVF1799]

I'm a mechanical engineer. If you heat them up to glowing red hot, then let them cool slowly, you will anneal them.

Jim - it was 1974 when I took metal shop in HS. Annealling is not one of the things I remember. I know it alters the chemical properties - question is harder or softer? I'm asking because I need to drill them out?

Thanks for your help, Ken

[Don McCombs]

anneal = heat (metal or glass) and allow it to cool slowly, in order to remove internal stresses and toughen it.

[Bill Hudson]

Ken,

Basically softer. Here is a quick read http://en.wikipedia.org/wiki/Annealing_(metallurgy).

Bill

[bob in CT]

If the cap screw was in a casting, you had a heat sink and a temperature gradient, so the entire screw did not get to the same temperature. I doubt that you had sufficient time at temperature(important) or the right cooling rate to anneal the screw, which is probably around RC40 which is fairly hard. You will need cobalt steel bits at a minimum.