How To Heat treating with electric furnace?

M

Mstrick96

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Mar 6, 2018
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I'm about to do my first heat treat and wanted to get a review of my planned process to make sure I'm not making any mistakes or overlooking anything.

I designed and have built a 220 VAC electric-powered heat treat furnace with a programmable PID controller. I've had it up to over 2000F in testing, so it has more than enough power. I'm ready to try using it for real!

I've been nervous about quenching in oil because of potential fire danger. I have a 2 1/2 gallon galvanized oval bucket for the quench oil. I plan to place it inside a larger galvanized tub for fire safety to contain spills. I have a couple of fire extinguishers and a fire blanket as well.

I've ground out a knife from O1 tool steel. Here is how I plan to conduct my heat treat:

1 Put the knife in the furnace at room temperature and then ramp the temperature to 1500F and then hold there for 10 minutes.
2 Quench in room temperature canola oil. (OR should I preheat the oil to 125F or so? Does it make a big difference?)
3 Temper at 400F for two hours and let air cool to room temp. Repeat so that I have two tempering cycles. (I can use a toaster oven or I can use the heat treat furnace once it has cooled to 400F. Recommendations?)
 
Submerse entire blade in the oil and it won’t flash.

Preheat the furnace before placing knife in the chamber. You’ll need gloves and tongs for safety.

Oil should be heated slightly, O1 will do fine with that oil.

Hoss
 
Do you have something to hold the blade upright in the furnace? Since this is your first time, practice getting the blade in and out while the oven is cold using whatever tongs or pliers you intend to use wearing the gloves you plan to use. Make sure you get a good grip on the blade with your tongs.

I always preheat the oven and then wait for at least half an hour before I put the blade in. After you put the blade in, it might take a few minutes for the blade to reach temperature.

I'd use the toaster oven for tempering, it takes really long for my oven to cool down, and there is no room to clamp the blade to a piece of angle iron in case it needs straightening. Preheat the toaster oven a good while before you need it, especially if you don't have a PID controller for it. They can overshoot the set temperature by a lot. You can use an oven thermometer to verify the temperature.

You can definitely do this without any fireball at all. Like Hoss said, submerse the blade in the oil and don't pull it out until it has cooled down enough. Ten seconds is long enough for the knives I typically do.
 
To hold the blade upright, I plan to use a piece of firebrick with a slot cut in it. I was going to rest the tang of the blade in the slot. I'll make the slot just deep enough to keep the blade upright.

Good idea to practice first! Also good to hear about the fireball!

I'll use the toaster oven for sure. I'm not allowed in the kitchen anymore since I cleaned a big flathead catfish there the other day!!!
 
You gotta practice making a big fireball for your future performance on Forged in Fire! :D
 
Just to clarify a couple of previous points:

Preheating kiln: Make sure you let your oven soak at setpoint for a bit before putting your knife in. I normally let it reach setpoint and then soak for anywhere from 30 minutes to even an hour before putting any blades in. It may not really need quite that long, but normally there's plenty to do around the shop in the mean time anyhow. This allows your oven to stabilize/equalize and reach a more even temperature throughout. There won't be as wide of a swing when you open the door either.
Also realize that it takes a couple of minutes for your blade to reach the internal temp of your oven. Make sure you factor that in to your soak time.

I'm not sure what your shop's room temperature is, but I'd preheat your oil. Right now, my quench tank is sitting around 60 degrees, which is a bit too cold for canola (and almost too cool for my parks 50). Heat it to 110F or 120F, and that way it'll be consistent no matter what your shop's temperature is throughout the year.

Fully submerging your blade for a few seconds should prevent any flareups, but if you do have one, don't panic. Just pull your blade out and back away from the flame. It'll likely extinguish itself, but a lid over the bucket will make short work of it too.

After your first 2 hour temper, you can cool the blade to room temp by dunking into some water. That way you don't have to wait around for 15 or 20 minutes for the blade to cool. Dunk it, and pop it back in the oven for two more hours.
 
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