Drill rod, oil vs water hardening

I know drill rod can be purchased in oil or water hardening types. What is the difference? What happens if I try to harden oil rod in water or vs versus.
i assume oil quenches faster and it may add or replace carbon to the surface.
Bill D

Bill D said:

i assume oil quenches faster and it may add or replace carbon to the surface.
Bill D

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Oil quenches slower than water. Water quenching oil hardening rod may cause it to crack. Oil quenching water hardening rod may not get to full hardness.

From what I know, the two tool steel types you mentioned are at opposite ends of the distortion after heat treating spectrum. Water-hard prone to distortion and oil-hard much less so. Though I do think water-hard has properties in the unhardened state that can be useful as is for some projects.

Thing about water hard is you can heat it up with a torch and throw it out in a snow bank for quenching. At least that's what an old timey machinist friend of mine used to say.

Dave

I thought oil had a higher specific heat and so it would quench faster. I guess water is at the boiling point at much lower temperatures so the heat of vaporization is involved with water but not oil at the temperatures involved after a fraction of a second.
Bill D.

How does air hardening compare with these two's.
Bob

piedmontg said:

How does air hardening compare with these two's.
Bob

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I was also thinking about this, I'm not sure but I would think air is slower than oil.

Air quench is much slower than either oil or water. Air hardening steels tend to very low distortion and comprehensively through hardening. It's very convenient to leave the tools enclosed in a stainless foil envelope through the heat and quench.

Oil quench is slower than water quench.
Water quench is slower than brine quench.

While there are certainly exceptions (like huge thick sections of air hardening steel needing some directed oil or water during quench, it's usually not a good idea to quench X-hardening steel in anything but X.

sfriedberg said:

Air quench is much slower than either oil or water.
Oil quench is slower than water quench.
Water quench is slower than brine quench.

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Yep, and all of those are slower than brine containing a surfactant.

As an explanation, the dissolved salt increases the mass of the water, so it requires more energy to boil it. The surfactant keeps more of the water in contact with the quenched item instead of inside a protective bubble of steam, increasing the rate at which this happens. Agitating the item can also accomplish this, but risks inducing thermal strains due to differential cooling rates, i.e. warp.

Edit to add: I don't think there are any actual steels that need surfactant brine. It's mostly used by idiot hobbyist blacksmiths to eke some hardness out of railroad spikes and the like (30-35 points carbon, barely enough to harden at all). Ask me how I know

13engines said:

Thing about water hard is you can heat it up with a torch and throw it out in a snow bank for quenching. At least that's what an old timey machinist friend of mine used to say.

Dave

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Snow!?! Whats that? I think I have seen that stuff if calendar photos. Carpenter's book said to use water hard wherever possible. Change to something else if needs such as hardness, warping, or wear resistance dictated. W1 machines a little faster and nicer than O1. Carpenter also said you could oil quench small sections W1 in oil for less warping.