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Comment from imgur:
Hardening the gears... pretty awesome. Oil cools the metal slightly slower than water so it helps avoid stress damage from the cooling process, but ends up a little bit less hard overall. The fire looks dramatic but it's actually safer than steam from a water quench. We don't have such good footage but the same technique was used for tanks in world war 2, which just looks bananas.
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.
Gifsthatendtoosoon
No audio? :((
Word cannot describe the awe I am in but I will try:
dat's cwazy
Why doesn’t the weight of the part cause the hook to distort the red hot metal?
Just because it's red hot does not mean it's near molten. The material still has sufficient proprieties to support its weight.
And may be much cooler on the interior
It should be. If you heat it all the way through, you get more heat-stress. Ideally, you only want the outside hot (and then cold again) to surface-harden it. You don't need the middle bits hardened, after all.
lol, there are like 10 fire extinguishers in various places nearby in the background
That's unbelievably gnarly. Heavy-duty manufacturing is awe-inspiring and scares the crap outta me. I can't even imagine the range of safety regulations that go with all of this.
This kills the crab
Heavy metal af