View Full Version : hardening solutions

10-22-2005, 01:51 AM
Reading some of the latest posts regarding material selection and hardening has me wondering what role the materials in solution might play in the hardening process. In particular, oil has been mentioned. Most oils have a blend of additives, and some are unwanted for use in hardening parts. Makes me wonder what effect the different additives have on the process. Someone stated a preference to use american oils and not mid eastern oils. Can a person blend up their own mix to achieve certain properties?

I would tend to think that since the material being quenched is cooled so quickly in the medium that it won't pick up much if anything from the solution, except maybe some color.

Any thoughts?

Your Old Dog
10-22-2005, 07:46 AM
Darryl, I only mentioned the parafin versus sulphur based oil because that's the way someone told me to do it years ago. I took it on faith they knew something I didn't! It's possible I'm wrong. I'm just pretty sure that the self-annealing quench works well for "back yard machinist" if parafin based oils are used. I'd be surprised to hear that it wouldn't work with vegetable oil also but I got nothing to base that on.

Wonder if K-Y Jelly would work on boring tools? http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

Paul F
10-22-2005, 11:22 AM

My understanding from metallurgy classes is that it really almost doesn't matter WHAT you're quenching in as long as it cools your part at the correct rate...
If your quenching medium cools it too fast, you'll get cracks or at least heavy warping and stresses.
If you quenching medium cools it too slow, it won't harden.

All the exotic brews are just ways to modify the cooling rate of a dunked piece.

In blacksmithing, I've used a variety of salvaged scrap steels, and had to harden 'em. I've been fairly sucessful hardening in vegetable oil. Those that won't harden in vegetable oil I quench in plain water.
I will admit that plain water is too severe a quench (too fast a cooling) for many steels.. I've had a lot of cracked pieces.
I'm too lazy to mix up a bucket of brine http://bbs.homeshopmachinist.net//smile.gif

I've read automatic transmission fluid recommended as a "light" quenching oil also... but prefer a medium with as few additives as possible.

Hope this helps!
Paul F.

10-22-2005, 01:27 PM

That's what I'd have said, but I expected that someone would have a Metalurgy Class, or Degree to disagree! http://bbs.homeshopmachinist.net//smile.gif

I would expect the Rate of cooling to be most important. Your question about "absorbtion" is interesting though. have to wonder if any carbon is absorbed into surface layer of the steel(like in case hardening, except that tool steels already have a lot of carbon campared to mild steel).

Or hydrogen, which must be bad? Anyway, I'm sure there are many Optimum fluids superior to motor oil, but it should work for most home projects.

My 2 cents, and you've been overcharged. http://bbs.homeshopmachinist.net//smile.gif

10-22-2005, 03:33 PM
Overcharged? I don't think so. Everyone's advice is worth hearing and considering.

I figured the rate of cooling to be the most important thing. I was thinking about how the 'coolant' will react. Water will turn to steam instantly where it's in contact with the hot metal, oil must 'burn' somewhat in that thin area of contact. I'm just wondering if there isn't some additive that would more or less get baked onto the surface of the part, and which could be left behind as a protective layer, unreactive to oils, greases, and water. My little U-joint is a typical part that would benefit from a protective coating, and though it sort of gets one from hardening in oil, it does polish off quite easily. That's fine for the areas where the bare metal is a bearing surface or similar, but it would be nice not to have to spend more time to protect the rest of the part. Maybe quenching in Rustoleum would work- then there's varnishes, urethanes, shellac, pasta water-

YOD, yeah, I suppose K Y is the quenching medium of choice for boring tools http://bbs.homeshopmachinist.net//smile.gif

[This message has been edited by darryl (edited 10-22-2005).]

10-23-2005, 10:04 AM
I'm not sure if i'm thinking of metalurgy class or something else from physics class. But I thought there was something about when the metal is really hot there is a void or gap between the metal and the quenching medium until it gets to a cooler temperature. Again I could be totally wrong metalurgy was't my best class, and that was a couple of years ago.

10-23-2005, 04:56 PM
Yeah, the void is the vaporized quench medium. Steam, oil vapor, smoke-

Davis In SC
10-23-2005, 06:08 PM
The vaporized quench, is why I try to agitate the part in the oil, until oil stops boiling...

10-23-2005, 06:37 PM
Ya, that's it, that's why you're not supposed to just let the part sit there.

Your Old Dog
10-23-2005, 08:20 PM
It must be the vapor barrier that allowed my S-5 engraving chisels to self anneal. I didn't have to go thru the bother of drawing them back at and they hold up as well as commercial. It might be worth the simple effort of a test to see if it doesn't work for you too. Will save you some time and one less step to go wrong.

I used a 16oz can filled with 10weight non-detergent and held the chisel so that when the pliers were resting on the cans edge, the tip would be immobile in the center and about two thirds of the way down into the oil. I held it very still for about 2 minutes. My engraving chisel faces are about 1/8th inch in width. I only did 3 chisels one at a time in the oil bath and then it became to warm to work as well.

If I were doing your cutter I'd use a container maybe 32oz because you have more mass there then I do with my 1/4 - 3/8th chisels.

[This message has been edited by Your Old Dog (edited 10-23-2005).]

10-24-2005, 05:48 AM
You put viagra pills in a brine solution and that is supposed to get the tool hard.. http://bbs.homeshopmachinist.net//biggrin.gif

But yea my book tells me a brine solution cools steel fastest...

With bigger pieces that you want thoroughly hardened right through you need to cool it fast as possible as it takes awhile for the centre to cool and if it takes too long the carbon transforms to a softer metal and not get locked into a harder metal(yea I can't remember the correct terms pearlite, carbide and all them)

Of course then you have the problem of cracking and warpage when you cool too fast..

It has been mentioned to me that a fellow who knew what to do used cutting oil that had sulphur in it but I am sure everyone has their brew that they like...

When you are cooling the piece you are supposed to move it in an up and down motion vertically..This strips the bubbles off the piece as it is cooling as steam vapour sitting on the piece in question will create soft spots as it cools slower than the rest of the piece....

Hope that helps...