TIL my old boss was right about letting steel cool on its own

I was talking to a retired guy at the hardware store last week, and he said he never quenches his mild steel right after forging. He just lets it sit on the anvil until it's black. I always thought that was a waste of time, but I tried it on a set of hooks yesterday. The metal was way less stressed and way easier to file smooth. I mean, it adds maybe 15 minutes to the job, but the finish is so much better. Has anyone else switched to just air cooling for simple stuff?

4 comments

4 Comments

elliotjenkins1mo ago

That part about stress showing up later during machining is spot on. I've seen it with brackets we made that looked fine until we drilled the mounting holes. The bit would wander or the part would shift in the vise because of hidden tension. Letting it cool slow just gives the metal time to settle into its final shape before you start cutting into it. It's not about the finish right then, it's about the part holding true for the next step.

benlewis2mo ago

Yeah but @kim_martin, I find air cooling makes the finish way easier to work with.

schmidt.eva1mo ago

A welding instructor told me rapid quenching can lock in stresses that show up later during machining. Air cooling takes longer but lets the metal relax more evenly. That extra time on the rack really does make a difference for parts that need precise fits later. I’ve seen air-cooled pieces come off the lathe with a cleaner surface. It’s one of those things you don’t notice until you’ve had a part warp on you mid-cut. What kind of projects are you working on where the finish matters most?

kim_martin2mo ago

My old shop teacher always said to quench mild steel right away to save time. I still do it for most projects and haven't had any problems with stress cracks.