Oil Tempering

T

tattooedfreak

Steel mutilater is more like it.
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Ok, don't laugh right away, I'm just thinking out loud (well, in writing). Is there any drawback or inherent problem with tempering in oil? What I mean is after hardening and quenching an oil steel like O1, does anyone know of a reason not to then temper in oil? Yes, #50 or AAA has a upper working temp of about 120-180f but using a deep fryer and veg oil you can get temps of 300-500f and they are sustainable for long periods. Since deep frying is a dry cooking method, does it translate to tempering like an oven? For that matter, is it comparable to salt pot tempering which is also a dry cooking liquid? So, harden, quench in oil, grind off any scale/decarb (even take to high grits like salt pots) place in 400f veg oil for 1-2 hours for tempering? Depending on the answer, if the wife leaves the house for a bit, I may give it a try. :p
 
The one major downside is that you'll be keeping a large volume of flammable liquid near it's flash point and over a heat source. Tempering temps are higher than deep fry temperatures and put you really pretty close to the flash point of most oils. Oh, and then there's the smoke. Once you hit 400F or so with most oils you start smoking...the wife won't like that, trust me ;)

If you MUST try this, do it outside, away from the house, never look away from it, and keep an extinguisher handy. Oh, and from what I understand of what happens in tempering, this won't speed it up any, it will still need 2 passes of an hour each. Personally I don't see much benefit to it.

-d
 
If you did it safely, outside sounds like a good idea, I think it could work out pretty well. The advantages would be more even heating and much more efficient thermal transfer. Liquids like oils or salts conduct heat much more efficiently than air, I can often get results in my preliminary tempers within 20 minutes in my salts, a blade in an oven would barely be to temp in that time, in the tempering range. I wouldn't want to steer anybody in the direction of a safety hazard, but if folks could do it safely most makers could do themselves a favor by tossing their toaster ovens and going with your idea.

But then propane is a bit more dangerous than hot oil and we don't hear of bladesmiths snuffing themselves out at the rate we should considering the number of cobbled together abominations I have been frightened to see in use by too many smiths. It has always been a mystery in a field full of folks too cheap to spring for basics, or for more than a roll of duct tape for holding things together, that serious accidents are relatively rare. :confused:
 
FWIW, I just did a quick search and found this on Wikipedia. It looks like Safflower would be your safest bet with a smoke point of 510F.

-d
 
I'm using Canola oil to hold my blades until the Evenheat oven drops down from 1500 to the 400 or so needed for tempering. Seems like it takes FOREVER for that oven to drop down. So, I decided to put the blades in 300 degree oil until the oven decides to get to temp.
 
Well, I currently use safflower oil to cook with and I always have my fryer on its hottest setting (400-425f). Using a good deep fryer (albeit used) is a cheaper (for me) alternative than trying to make a propane salt pot. For the amount of blades I do, heating up the oven (I dont have a toaster oven, I do have a fryer) for long periods seems a waste. As for flashover, with a tight fitting lid and handy fire extinguisher (both should be available no matter what your HT set up) there is no more danger than forges or salt pots.
 
I say batter in flour it first and it will sell. Add bacon and you may never be able to keep up with orders.
 
I didn't know it would work quicker. I have often wondered if I could just use the French Fry fryer at the diner next door. Knowing that the temperature would remain constant and not waste energy because they are running all day anyway. Just drop the knife in and come get them an hour later. Cool off and drop for another hour.
 
I did a course with Howard Clark and Owen bush in the UK last year, and we used 'marquenching oil' for the tempering cycles on the swords we made, it worked a treat :) - did smoke a bit even well within its recommended operating temperatures. (gotta love the smell of marquenching oil in the mornings..... kinda smells like victory...!)

I got the impression it was a fairly standard HT method?
 
My friend does his tempering in the deep fat fryer at his restaurant. Theoretically, it is a far better system, as heat conduction and temperature regulation are far superior to the radiant heat in an air filled oven.
 
Most fryers these days have fairly accurate temperature controls but if you were worried, a good thermometer and some experimentation should get your controls pretty much dialed in and you can adjust accordingly. It might take a little more space than a toaster oven but it might be more efficient. More importantly, my wife has given me permission to try hehe.
 
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Hold, on! Time out! There seems to be some confusion between quenching and tempering here. Concerns of flashing, make it seem as if we may be thinking of quenching, I give no recommendations whatsoever about quenching into hot oil, unless it is an actual martempering/marquenching oil engineered specifically for that purpose, in fact I wholeheartedly discourage it!

Mr. tattooedfreak, were you talking about quenching into overheated cooking oil, or were talking about using it to heat a blade already properly quenched in order to temper it back? My advice for tempering still stands, but I would never offer advice on the idea of quenching into 400F cooking oil.

Once again, there are martempering oils designed to do this, but Crisco, Wesson, peanut, canola, etc... are not suitable to safely do this.
 
Danbo said:
I'm using Canola oil to hold my blades until the Evenheat oven drops down from 1500 to the 400 or so needed for tempering. Seems like it takes FOREVER for that oven to drop down. So, I decided to put the blades in 300 degree oil until the oven decides to get to temp.
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Danbo,
Do you allow your blades to drop down to ambient (or atleast 120F or so) before tempering. It is my understanding that this is an important step in heat treat. There is still quite a bit of transformation happening below 300F.


Kevin,
I didn't see where anyone was mentioning quenching in hot oil. Marquenching oil was suggested for the temper. Breath in, breath out.... lol.
 
Yes I gathered that in the marquenching oil post, but I see a lot of concern for flashing. The only threat there should be of flashing is if open flame is used to heat the oil, the blades should be "hand warm" or less before going into the oil, and thus should pose no flashing threat at all.

You just need to remember that a very large number of people still use the terms "tempering" and "hardening" interchangeably, causing endless confusion in our field.
 
Putting a hardened blade already quenched into preheated oil in order to temper it. Visions of putting a red hot blade into oil already at high temps make me shiver. My wife and I are professional cooks and have been working with hot oils for many years now and understand well the dangers of hot oil. My question was based on my wondering if(after reading many of your posts Kevin) hot oil would work the same, or approximate the results of, a tempering salt pot. Maybe my post was worded incorrectly and led some to misunderstand. I apologize if that was the case. I do intend to try this as it does seem that it will work. Also, just to clarify to anyone else who wants to try it, the smoke point of an oil is not the flash point; the flash point is usually (but not always) 20-30 f higher than the smoke point and in some cases even higher. Prolonged heating will reduce the smoke and flash point, as will any additives. I intend on using safflower or sunflower oil which have high flash points (up to 525f) and have no flavours or colours added. I don't recommend peanut or corn oil for this but canola might be ok if you stayed at temps below 400-425f. Sunflower and Safflower should be good up to 450-475 and soybean around 450, so it will depend on what temps you need to get the hardness you desire. I will let you know how it turns out, I just wish I had a rockwell tester for when I finish. :-)
 
So, twenty minutes in oil as opposed to two hours in the toaster oven? Cool and repeat. Same temps just a faster medium? Open the rolls of pop'n'fresh biscuit dough and make some donuts while you're waiting.
 
zaph1 said:
So, twenty minutes in oil as opposed to two hours in the toaster oven? Cool and repeat. Same temps just a faster medium? Open the rolls of pop'n'fresh biscuit dough and make some donuts while you're waiting.
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Not quite.... don't let yer stomach get the best of you, bud:p
Kevin R. Cashen said:
... I can often get results in my preliminary tempers within 20 minutes in my salts, a blade in an oven would barely be to temp in that time, in the tempering range.
Click to expand...

Kevin R. Cashen said:
I wouldn't want to steer anybody in the direction of a safety hazard, but if folks could do it safely most makers could do themselves a favor by tossing their toaster ovens and going with your idea.
Click to expand...

I think Kevin is just pointing out that the low-tech guys may benefit from the even heat dsitribution and liquid conductivity of the oil temper as opposed to the quirks in most toaster ovens.

Rick
 
Yes, I would still keep the blade(s) in the oil for 1 or 2 hours depending on the blade, I just wouldn't have the house heating up and be wasting a ton of electricity (unless I was baking potatoes at the same time :-)
 
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