this post was submitted on 21 Apr 2025
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Comment from imgur:
Never underestimate thermal strain. So if that's the reason, yeah.
Pulling from memory here, but doesn't the oil also add carbon to the steel? Or affect the outer chemistry somehow? Aside from just cooling at a different rate
It could add a little but not significant. Not enough to counteract the decarburization from annealing in an air fired oven.
Carburizing surrounds the metal with a carbon source and heats it for hours to get sufficient hard layer thickness. That typically is done in the anneal cycle before the quench shown in the video. High temperature austenitic steel has higher solubility of carbon and a proper quench will produce a fine mix of martensite and carbides. Tempering will precipitate more fine carbides in the martensite and reduce hardness a bit to prevent brittle failure. Sometimes the surface is then peened to build a thin surface layer of compressive stress to prevent crack initiation.
Neat! So much knowledge exists, but you don't know what you don't know. It's crazy. Thanks!
So the slower the cooling, the less stress damags, but I’m sure there’s a curve where something like air cooling would damage it in a different way? I wonder what the best rate of cooling and medium is to facilitate it.
I think air cooling would give the material time to anneal and become softer as a result.