Heat treating in oil

[Ed Tipton]

My "tehcnique" for doing the HT on carbon steel is to raise the temp in the forge to slightly over the non-magnetic temp and then quench as rapidly as possible in 140 degree heated oil. I then remove from the quench, and test with a file to verify that the hardening is as it should be. I then clean off the blade sufficiently to allow the oxidation colors to show and go directly into my toaster oven for the tempering. What I'm wondering is if I quench, test, and clean and then once again put the blade back into the oil and increase the heat to 400 degrees, would this change in my process give me better control and more uniform treatment of the blade than using the toaster oven for the tempering. I am doing very well with the toaster oven, but I am concerned that the temp inside the oven is not uniform. I don't know how to determine if the blade was uniform in it's tempering, but I do feel than having the blade totally immersed in the oil would have to be more uniform. Comments please.

[Eli Jensen]

How do you then heat and monitor the oil temp? Could you use the oil in the toaster oven? A little voice tells me that could end badly though . . .

[Doug Lester]

Ed, what you might do is to get an electric roaster. I use one to austemper 52100 in. They are a little slow to heat up any volume of oil in-ok, they're real slow, like3-4 hours- but they hold temperature well. I got a thermometer from MSC Direct to moniter the heat with.

Cpt-Jens, what I use is a turkey frier as a quench tank. This allows me to heat the oil in the container over the burner. You could also use a deep pot to heat the oil on the stove top and then take out of doors to do the heat treating. You could also heat the oil in a pot and then transfer it to a taller, narrower tank if you have to, or a shallow pan if you are edge quenching. Trust your instincts on using oil in a toaster oven. Not only does it sound like a recipe for disaster, it is a recipe for disaster.

Doug

[Ed Tipton]

Follow-up....Well, I tried it and it puked on me. I do use a small roaster oven for a quench tand, and my thoughts were to just simply increase the temp up to the tempering temp and have at it. Well....scrap that idea. The oil got up to about 250 degrees and ERUPTED in a shower of boiling oil. Luckily, no damage was done to me or my shop...just a clean-up.
BAD IDEA! Actually, I still think the idea is a sound one, but the physics just won't get out of the way. In any event....if you're interested...don't try it unless you're prepared to clean up lots of oil spill. I guess for the time being I'm just stuck with the toaster oven...and by the way...putting oil into the toaster oven never entered my mind. I can only imagine......

[Doug Lester]

I don't quite follow what happened, Ed. I heat my oil up to 470 degrees in my roaster and have heated my oil up to 510 degrees in my turkey firer for marquenching. I"ve never had any type of oil eruption, though I did note that the oil in my frier will rise by about 3". I've been using peanut oil for the high smoke point. What oil did you use? Is there any way that you got water in the oil?

Doug

[ARCustomKnives]

Sounds like you had some water in your oil.... Glad to hear noone was hurt or nothing burned down.

As far as toaster ovens go, I recommend getting an analog oven thermometer (should cost 5 bucks or less) and a toaster oven with 4 internal heating elements (2 on top and 2 on bottom). Monitoring my toaster oven (I think I paid about 30 bucks for it at walmart... black and decker brand) with the analog oven thermometer, I really don't notice any fluctuations in temperature unless I open the door for a while. I usually do 2 full cycles as well to ensure a full temper.

Hope this helps.

[Ed Tipton]

Well...the oil is actually an oil that is one of those used by Caterpiller in their heat treating shop. It was purchased from a local distributor (Morgan) in Decatur, Il. and at the time he bought it, my friend asked for a good HT oil that would be best suited for general HT. I don't know the number or mfg. of the oil, but I can get it. I have been using a garden variety oven thermometer in my toaster oven, and I used that for determining the actual temp. I had the temp control set on 300 degrees, and I felt that I was being conservative in my approach. It was my intention to gradually and cautiously sneak up on about 350 degrees, but 250 was as far as I got. Prior to the eruption, the oil had reached an active boiling state, but then it suddenly erupted and started overflowing the roaster and spewing on the surrounding area. The oil was clean, and had not been contaminated by anything. I used the approach mentioned because I had been for-warned that the oil could possibly ignite at about 325 degrees. Because I was trying to do something even after being warned, I was being very careful and was watching the entire thing ....especially after the oil began to boil. Once the eruption happened...things went really quick... and I used a three pound "ice cube" in the form of a chunk of steel to help in cooling things back down, since removing the power didn't seem to help in slowing things down much. Once the overflowing started, I immediately pulled the plug, but it actually seemed to increase in activity until I introduced the steel into the oil. At that point, things got back under control, and I had some time to reflect upon my stupidity.
This whole thing happened in a 6 quart roaster that was new. Apparently, the roaster was pretty well insulated since the whole thing remained hot for quite a while after being shut down.
All in all, it was a scary moment...but little damage resulted.Today, I'll finish cleaning up the oil-dry and wiping down where it spewed over things. Messy...but nothing really hurt.
Once again, this craft has found another way to humble me. With all the mistakes I've made, one would think I should know it all by now....but somehow I don't think so.......

[Doug Lester]

I must have dumped my post into nothingness earlier today. It looks like the oil that you used was a fast oil on the order of Parks 50. That oil is not ment to be used at high temperature. You could try something like peanut oil in the roaster.

Doug

[ARCustomKnives]

Just a suggestion for future endeavors (and to anyone else you might read this)....

If you're using any type of chemical, oil, solvent, etc... that you are not completely familiar with, ALWAYS consult the MSDS (Material Safety Data Sheet)... heck, even if you've used a product for years, this doesn't hurt.

It will tell you just about all you need to know about operating temps/flamability, suggested uses, ihherent hazards, proper disposal, etc....

[Ed Tipton]

For the time being, I've abandoned the idea and simply filed it away under the "failures" category. As stated earlier, I wasn't even really having a problem. This whole episode came about just because I thought that maybe I could get a better and more uniform tempering from an oil bath than I was getting from the toaster oven....but I am not really having a problem with the oven.
The whole thing occurred because I was attempting to gain what I thought might have been a better level of control over my process.
The blades that I am making have not had any problems with hard or soft spots, but in the pursuit of excellence, I was simply wondering if there was improvement to be found.
Now I know....lesson learned.
After re-playing the entire episode, I thing the problem was that the oil in the roaster was nearly 6inches deep, and it was being heated from a heating element in the bottom of the roaster. The thermometer which was near the surface was reading 250 degrees, but on the bottom it was probably closer to the 300 degree setting. I think the temp gradient in the oil caused the oil in the bottom to simply rise in a violent manner causing the overflow.