I sometimes watch machinists and blacksmiths on youtube.

One of the things I've become more aware of lately is the fact that hardened steel eats through cutting tools like candy, so the solution is to anneal the steel, do most of the shaping, harden it again (temper it for as much as 24 hours in a very smart oven that slowly slowly drops the temps), and then finish the piece with sanding and grinding tools instead of cutting tools.

I wonder if this treatment survives annealing and hardening cycles or if that just destroys the structure.

Dan Gelbert with his micron accuracy milling machine and lathe. He has stuff on air bearings, positive pressure rooms with pH and humidity control measures.

https://youtu.be/HWPYoE1SNnA

You've got the heat cycles for annealing, hardening, and tempering confused. The slow cooling is for annealing, hardening requires a fast cool from rather hot and is a very different process from tempering, which is a short soak at a comparatively low but tightly controlled temperature.

> very smart oven

They just have PID temperature controllers with ramp/soak timers. They're really cheap these days.