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I have done a lot of metals heat treating, things like connecting rods in an oven at 450? for 8 hours. Then we left them in there until they cooled slowly to room temperature which usually took another 3-4 hours or so.

The process hardened steel connecting rods or I should say we thought so. We did that to reharden the beams after grinding off all flashings and polishing them. Connecting rods are shot peened to about .125 ARC which work hardens them, grinding removes that.


Correct me if I'm wrong (probably am), but I thought the long cooldown softened the metal, whereas quenching it in cold water made it hard, but brittle. I recall in high school engineering class (welding/drafting) the teacher talking about modifying something in their cars transmissions back in the 60s that was a hardened piece. He said they'd heat it red hot, and then pack it in oiled sawdust to slow the cooldown. It was soft enough then to drill/cut/whatever they did, and afterwards it would get re-heated and quenched to re-harden it.

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