Answer

Not a dumb question if you don’t know. Oil hardening steel is steel that is hardened when it is heated red hot and quenched in oil. Water hardening steel is steel that gets hard when it is heated red and quenched in water. There are also air-hardening steels. If you heat oil hardening steel red and quench it in water it will OFTEN break into many pieces or crack, the water shocks it and hardens it too fast. If you heat water hardening steel red hot and quench it in oil it will not harden or will just harden the surface slightly. So you have to know what you have before you make a part from a piece of steel so you can temper it correctly, or the first time you use the gun (or whatever it is you just fixed) will break.

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One more time. What is the benefit between oil and/or water. I can only think that the oil would not cool as rapidly as water and might allow the metal to flex slightly more then water cooled steel before breaking.

Answer:

They BOTH harden all the way thru when they are hardened so they are brittle. They are just different metals that need the different quench solution to harden.