How do I heat treat a knife, simply and cheaply?

C

Calaustria

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Sep 5, 2009
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I've been trying to figure out how I'm going to go about heat treating my first knife. I don't have, and don't plan on buying some $1000 furnace. I do have an acetylene torch though. The problem is, I have no clue what I have to do to harden, then temper the knife. Every time I try to do some research, I get huge words and chemistry that makes my head hurt, lol... Could somebody please explain to me in simple terms what I need to do to my blade to heat treat it, and how I can do that cheaply? Thanks in advance.

I'm using 01 steel. Forgot to include that.
 
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the easest by far is send it off to a smith adn pay them a little to do it for you
or maybe find a nice mom and pop tool and die shop (thats where i got my first 3 blades done )
 
I was thinking about doing that, but I'd really like to do it all myself. I saw some homemade "forges" with a pot and pan full of charcoal, but if I made something like that, what exactly would I do with the knife...?
 
Using your torch, heat the blade till it reaches a nice even orange color and the steel no longer sticks to a magnet. Try to maintain that temperature or a little above for a minute or two and then immediately quench the blade horizontally into a pan of motor oil or vegetable oil. It should get hard enough that you cannot file it. Clean all the oil residue and black scale off the blade and stick it into your kitchen oven at 350 deg for an hour. After the first hour has elapsed, let the blade air cool, then stick it back in the oven for another hour. Do this for a total of three times. This is very simple and maybe not the most ideal method, but it works.
 
Thank you. Unless I get any other suggestions, that's gonna be my plan. Do I have to torch/quence it 3 times as well, or just the oven part?
 
Calaustria said:
Thank you. Unless I get any other suggestions, that's gonna be my plan. Do I have to torch/quence it 3 times as well, or just the oven part?
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No, that's not really necessary, I would just do the oven part (tempering) 3 times. You don't want your knife to be glass hard. Always test it afterwards by doing some cutting and chopping. Use caution when heating the blade with the torch though because it is really easy to get the blade too hot, white hot, especially the point...this ruins the steel.
 
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If it's 01, you need to send it out. You'll do it no justice using a torch. 01 requires a couple of controlled temp soaks before quench. Non-magnetic heat is not enough for 01, or acually any other knife steel if you want a decent hardness. 01 has to considered a complicated simple steel, and does not respond well to makeshift heat treats.
 
Oh pooh. I think it will work okay. Not perfect, but okay. And if you send it out, they may not do it perfect either (I know from first hand experience).

O1 likes a nice long soak. 15 min is great. I soak at temp 20 min with O1.

It is actually fairly tolerant of being somewhat overheated. If you can hold it a nice orange heat for a few minutes without over heating the tip or very edge, you might get 80% of the steels potential which is actually pretty good and I'll bet will put a big grin on your face.

I haven't looked at the temps specs in a while, but I remember tempering in the mid 400s

The nice thing about O1 is it isn't picky about quench oil at all. I used to use chainsaw bar oil because of the flame retardants in it (doesn't burn and smoke, but otherwise a terrible quench oil). Literally any oil will do for an O1 blade.

You can pull it out after about 10 seconds to finish cooling in the air. You'll be well under the nose by then and it will warp less. Don't fool around too much - get it into temper once your can comfortably handle it bare handed. Your uneven heating and quenching can lead to cracking. I've cracked O1 before temper on a tool before.
 
It will likely harden....*some*. As LRB pointed out, O1 likes a soak at temp. I soak for a full 20 minutes. A few minutes at temp with an oxy/acet torch is hard to do without overheating, and while it may get you some hardness, it will probably be a mediocre result. And as was also pointed out, non magnetic will get you in the same town, but not necessarily in the neighborhood unless you're working with 1084. I harden O1 at 1475F and non-magnetic (curie point) occurs around 1414F.

I admit I made a number of knives when first starting out using O1 and a one-brick forge with no real temperature control using a magnet to get an idea of the steel temperature. If you watch closely, you'll see the point where the steel goes above it's critical temperature as a series of "shadows" dance through the blade followed by an increase in brilliance. That should be close to the appropriate temperature once all the blade is above the shadowy decalescent state. That being said, these were all "learning" blades and experimentation blades. You shouldn't have the expectation of making a blade you can sell from O1 without better temperature control.

--nathan

--nathan
 
LRB said:
If it's 01, you need to send it out. You'll do it no justice using a torch. 01 requires a couple of controlled temp soaks before quench. Non-magnetic heat is not enough for 01, or acually any other knife steel if you want a decent hardness. 01 has to considered a complicated simple steel, and does not respond well to makeshift heat treats.
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That is true and I agree, but you can still get a functional knife from O1 with a simple heat treat. I made a bushcraft type knife from O1 and treated it exactly the way I described. The person who later used my knife said it cut really well and held it's edge really well. Point is, it is not the "proper way", nor is it ideal, but for simplicity sake, it will work. Now if you are expecting professional grade cutlery from a sub-par heat treatment, not likely. Functional yes, top quality no. Being that O1 is not cheap, if you were to do more knives from this steel then yes, I would say send them out for proper treatment unless you can find a way to do it properly yourself.
 
Calaustria said:
I was thinking about doing that, but I'd really like to do it all myself. I saw some homemade "forges" with a pot and pan full of charcoal, but if I made something like that, what exactly would I do with the knife...?
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Get a coffe can and line it with durablanket, cut a hole in the side and stick a MAPP gas torch in the hole, put a firebrick inside the can where you set the blade.
Whenever the blade gets hot enough and loses it magnitism stick it in some warm olive oil.
I ain't scientific and im sure it ain't right but it does harden o-1 as hard as a file.

But like the others said, if i ever wanted to start selling knives id ship 'em to Paul Bos and be done with it!
 
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For these reasons, I am really liking 1075/1080. These steels seem to respond better to a simplistic heat treatment. With the O1, just make sure you test your blade and see if you are happy with the performance of it. You learn great deals more from tial and error doing it yourself than simply "sending it out" to get it done. If I would have sent out all my blades that I made, I probably would not have learned much.
 
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R C. You raised a point I have been wondering about. You indicated the blade should be quenched horizontally versus vertically. Somewhere I got it in my head that I should quench horizontally, sharp edge down and making the first contact with the oil....something to do with making the cutting edge harder than the spine ??? Yet I noticed on the forum that some use a quenching tank that can only accept a blade going in vertically, knife tip first. Can you or anyone else comment on this ? Thanks.:jerkit:
 
drlozier said:
R C. You raised a point I have been wondering about. You indicated the blade should be quenched horizontally versus vertically. Somewhere I got it in my head that I should quench horizontally, sharp edge down and making the first contact with the oil....something to do with making the cutting edge harder than the spine ??? Yet I noticed on the forum that some use a quenching tank that can only accept a blade going in vertically, knife tip first. Can you or anyone else comment on this ? Thanks.:jerkit:
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From trial and error, the main thing I found was to not swish it back and forth side to side. That will cause warping. As for horizontal versus vertical quench, I just do horizonatal because my quench tank is long and narrow and sits horizontal like.
 
drlozier said:
R C.

You indicated the blade should be quenched horizontally versus vertically. Somewhere I got it in my head that I should quench horizontally, sharp edge down and making the first contact with the oil....something to do with making the cutting edge harder than the spine ??? Yet I noticed on the forum that some use a quenching tank that can only accept a blade going in vertically, knife tip first. Can you or anyone else comment on this ? Thanks.:jerkit:
Click to expand...

I always quench tip first. I quickly submerge and I wisk the blade edge to spine quickly to disrupt vapor jackets.

Some very knowledgeable people quench spine first because that it the area with the greatest heat mass. This allows the entire blade to reach the point where martensite if forming a little more evenly. As the blade hardens during the quench (martensite is forming) it grows because martensite takes up more space. First the edge falls through Ms because it is the thinnest. Then the spine, which then bends the blade forward, possibly putting waves in the edge. Quenching spine first will even the temp gradient a little.

I quench point first and agitate like crazy. Not stirring though, you don't want more heat transfer on one side than the other - again it causes warping.
 
I did my first few heat treatments using a good hot camp fire, building a deep bed of coals, burying that sucker in there, and testing with magnet. Test with file and temper in the oven. I would think a nice deep bed of coals would give you a more even heat than a torch.
 
Yeah, I might even do it with a fire, seeing as it would probably heat the knife more evenly than I could with a torch. What do the rest of you think?

I'd also need to rotate and flip the knife in the oven every 15 minutes since its not a convection oven.
 
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