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05-10-2008, 08:27 PM #1
Heat Treatment - Quenching in motor oil?
I heard that if one quenches in used motor oil, mild steel will absorb carbon and improve its hardening properties. Does this work?
I have also seen a reference that states that motor oil is NOT good to quench in as it yields unpredictable results.
05-10-2008, 08:44 PM #2Does this work?
Carbon takes high heat (about 1650° F) and lots of time to "get in"
There are better oils for quenching - in fact there are quenching oils.
05-10-2008, 08:59 PM #3
Chris, to add to what John said, it sounds like you're thinking of case-hardening, where you dunk (or pack) the metal in a carbon-rich dust (bone charcoal, or a commercial product like Kasenit), and heat it up to 1100° F. The skin (or case) of base metal absorbs the carbon, and when you quench it, can get quite hard, while the center remains soft.
05-10-2008, 08:59 PM #4
Quenchants are quenchants. Motor oil is a bit hygroscopic and the water it may have in suspension increases the cooling rate. If your material will stand a little quicker quench go for it.
As for carbon uptake from the quenchant there may be some but it's likely to be in the 4th decimal place and then a molecules thick surface film. Carbon takes hours to diffuse into 1600 degree steel from a carbon rich environment. I hardly think a few second exposure to the carbon in an oil quench would have significant effect. Ignorant rubes will insist that motor oil adds carbon to steel quenched in it but it wont.
I don't know why some regard motor oil as a panecea for the home shop owner's lubrication requirements. It's motor oil; compounded for internal combustion engines running at elevated temperatures. It requires elevated temperatures to work correctly - that is evaporate out condensed water from combustion gas blowby. It's not intended for machine shop and general lubrication because the application is at or near room pemperature.
ATF and hypoid oil work well where compatible in general lubrication of gearing and mechanism and worm gears respectively but motor oil should be used for internal combustion engines.
That said any oil is better than no oil but the reccommended oil for an application is best of all. Use way oil for ways. Use gear oil for gearing. Use spindle oil for plain bearing spindles. Use motor oil in your car engine and no where else.
Getting back to quenchants. Yeah, use motor oil if you have it. A medium hydraulic oil or a vegetable oil might be better but any oil will do. It's the cooling rate that's important in a quenchant and not much else.
05-10-2008, 10:13 PM #5
For forged knives and tomahawks my brother in law and I
use Olive Oil for the quench.
Does great and smells like cookies baking.
Dino oils stink.
05-10-2008, 11:06 PM #6
Quench with motor oil
I have had good results with motor oil, but it smokes & stinks. I don't recommend it for the basement. The motor oil leaves a black skin on the part and sometimes for non contact surfaces it provides a nice contrast with a ground or polished surface.
For the basement and small work old cooking oil seems a good bet.
Watch out while putting a large piece of steel in a small recipient, it might ignite on you. An ample lid for the bucket will quickly extinguish flames if spontaneous combustion takes place. For small parts I dip using a colander or deep fryer basket.
05-10-2008, 11:19 PM #7
Along with everyones else's good quenchants that they've mentioned ATF works well also.
The used motor oil thing is an urban steel workers myth that has been around in the custom knife world for awhile.
05-10-2008, 11:58 PM #8
Thanks, I certainly will get a quenching oil. I did suspect that the used-motor-oil was a myth of sorts. Interesting to see that one can actually get carbon back into steel (but obviously over extended periods under heat).
05-11-2008, 12:05 AM #9
If it is truly "mild" which is .20% carbon or less IIRC, it does not matter what liquid you quench it in!
Normally the quench process is used to artificially "freeze" another microstructure either with a higher carbon content or more alloy that could not exist in equilibrium at room temperature.
Other posts talk of carburizing which is an appropriate way of case-hardening the mild steel.
However, the easiest way to produce something "hard" IMHO is to use O-1, heat with a torch, quench in oil and temper in a kitchen oven when SWMBO is out
05-11-2008, 12:08 AM #10
05-11-2008, 12:13 AM #11
One maddening thing about this is there are several references on line and in the literature (including Machinery's Handbook) that describe various carburizing methods and all of them include oil quench as a carburizing method. Further reading showed that carburizing takes place at certain temperatures over time along with other critical components like a carbon source. Somewhere out there is the definitive treatise on this subject - anyone know where?
My take on it now is that hardening takes place but carburizing does not. Now how to prove it?
05-11-2008, 12:25 AM #12
05-11-2008, 01:28 PM #13
You can get lower carbon steel to harden somewhat by using "Super Quench"; a saturated salt and surfactant soap solution developed buy Rob Gunther at Sandia labs. Blacksmith's use it for quick and simple tooling, etc. Typical recipe is 1 pound of plain salt and 8 ounces of Dawn liquid dish washing detergent to 1 gallon of water. Horse shoes and most railroad spikes have too little carbon (A-36) to harden in oil, or even plain water quench, but will show moderate hardness after heating above the Curie point (no longer magnetic) and quenched in super quench with rapid agitation. No need to temper. The cooling rate is very fast and typically you will hear a loud screeching noise.
05-11-2008, 01:48 PM #14
How about the often quoted benefit for hand tapping with used motor oil, that it actually contains some sulfur and this makes it work better for tapping ??
I have heard that from a couple sources, myself I prefer black sulfur oil from Brownells, a compound they call "Do-drill" but it is probably just a common sulfur oil like is used in pipe threaders I bet, works nice however :-)
05-11-2008, 05:07 PM #15
The liquid you use determens the speed of the cooldown The faster the cooldown the harder up to a certain maximum for the steel So with water you can get a harder result as with oil when the steel allows it With some steels quenching in water may result in so much internal stress the steel breaks up in several pieces Others work perfectly in water and it has the bennifit of less odeur
05-11-2008, 05:36 PM #16
I used to mess around trying to heat treat bits and pieces I would make but now days I don't bother, I just send my stuff to Winston heat treating in Dayton Oh. 937 226 1061 They know more about heat treating than I will ever know. you send your parts,they do the work, its always right when it comes back and its cheap as well. bonus... they are fast too.....
05-11-2008, 07:47 PM #17
Brine water is preferred for water quenching it seems. The salt slows down the formation of the steam blanket around the work and allows cooling at a quicker rate (sometimes double). I am not sure what is recommended in industry but 10% salt/water is considered a good solution. Oil is better to help keep parts accuracy and avoids cracking and distorting.
What type of salt do most use and where does one buy it?
05-14-2008, 02:59 AM #18
Quench in salt
I believe the best salt is plain sodium chloride un-iodized pickling salt; 1 pound per gallon of water - a saturated solution. The Dawn detergent acts as a sufactant and help prevent the formation of a steam blanket on the part.
05-14-2008, 10:17 PM #19
I watched the owner try and save time by heat treating in house,set the can of oil on fire,fire dept. came, next week we all got a 1 hour break while the fire dept. taught us fire saftey,plus the hour for standing in the parking lot,them goll darn owners,eh?
05-14-2008, 10:58 PM #20
I suppose if the smell is what many object to they could use baby oil. Baby oil is nothing other than pure mineral oil with a little perfume added. Difficult to get used though
I use unscented mineral oil because it was handy and I had a whole gallon left over from another project that got cancelled. Nice and clear and doesn't seem to burn or smoke as easy as other oils I have tried. Most of the O-1 I heat treat is smaller than a fist.