About to take the plunge - my first knife and heat treatment!!!

L

LarryE

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Sep 21, 2009
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I just got to the stage of heat treating my first knife. I have a lot of time and sweat already in it and I'm a little nervous about heat treating. It is and old file I bought at a flee market. I annealed it (cherry red and slow cool down) and ground the shape I want. It is 9" overall and a 4-1/4" drop point blade. I got it beveled just right (I think so anyway). Got it sanded down to 600 grit and now the next step is going to force me to heat it all up again. I plan to do it with oxy/actylene and magnet and warm oil to quench.

My concern is that it will warp and after all the work I have in it, that would not be good. I know you guys can tell me how to minimize this from happening. Thanks for the help everyone. Larry
 
I don't know about the torch as a heat treating method. I built my oven complete with temperature control. But I've seen many articles on this subject and method your attempting. A cryogenic soak would help. Good luck. DM
 
Thanks David, any tips on warping while heat treating?

I have read that a lot of knife makers use a torch and heat until a magnet will not hold. I think this is pretty common. However, an oven and temp gauge would be the best way to go. I'm just starting out in this and this is my first knife. Some day maybe I will have all the proper equipment. My first investment is going to be a good belt grinder. Larry
 
The non-magnetic part only works with certain steels who upper critical temp is just above non magnetic like 1084
 
I think for your first shot this should be alright, I did my first one out of a piece of 01 in my dads wood stove many years ago. He didn't think it would get hot enough but eventually it wouldn't pick up the magnet anymore. Just my 2 cents but I would do my best to get the blade at as even a temperature as possible from side to side and across its length before quenching and then either stab the knife into the oil as fast as your can or take it in edge first as if you were slicing, depending on the size/shape/set-up of your oil tank.
 
i heat treat with a torch and i have good luck. i only do the edge though and leave the rest of the blade soft. i do my heat treat in a dark room with a really dim light in the background that is just enough to see what you are doing till the torch is lit.

i hold the blade edge up while a buddy runs the torch the length of the blade staying away from the cutting edge by more than 1/4". remember to have the edge flat and even better rounded and sanded smooth. this will help eliminate any chances of cracking the blade during heat treat. i leave my edges a little thicker than a dime but no thinner than a dime.

when heating the blade, make sure you never let the steel get yellow colored since that is way too hot. quite a few sparks with the yellow color are also a bad sign.

i'm using 1075 and i heat to a really bright orange and hold that temp for a few minutes. when i quench i put the knife in tip down and go straight down into the oil. once i get the blade in the oil i move the blade in line to help cool the blade.

test the blade with a file and see if it skates. if not the hardness is not high enough.
 
To minimize warping during quench, make sure you heat the blade as evenly as possible. When quenching, I usually plunge the blade point first into my quench and then move back and forth "edge wise" to help cool things down faster. I.E., pretend you're cutting the quenching oil. Moving back and forth laterally may cool one side faster than the other and cause warping.

If there is still any warping, it can usually be straightened out in the tempering process by clamping the blade to a straight piece of steel while tempering. You may have to "over correct" any bending, but after 2 or 3 tempering cycles you should be ok.
 
First of all, let me thank you all, David M, xmtgx, call to arms, richard j and knife to a gunfight. You guys have given a new knife maker all the information needed to proceed, but more than that, the motivation to go ahead and "get 'er done"! I need to blunt the edge of my knife and round it over. Make the thickness of a dime. Then get my oxy/actylene torch and warm oil and I'm going for it. I'm going to normalize the steel first. Probably do that 3 times and then heat until the magnet no longer holds. Put the blade tip in first into oil and use a slicing action while in the oil to cool the blade (not side to side). I'll probably do this in a day or two and I will let you guys know how it comes out. Thanks again for the great help. Larry
 
There's a fair chance you will get the blade hard that way, assuming it was a decent file to start with and not just case-hardened low-carbon steel.

Pre-heat your kitchen oven, toaster oven, whatever you have to 400 degrees or so, so it's ready when your blade is quenched and cooled down to room temperature. Temper the hardened blade in there for an hour or two, let it cool, then repeat the tempering. This will draw back the hardness somewhat so it's not so brittle.

This is not the most "sciency" way to do things, but it doesn't hurt to give it a shot :)
 
The magnet trick is only good to tell you that you need another 50° to 75° of heat, which is from one, to two shades of red hotter. Non-magnetic occurs at 1414°, and you need about 1475°/ 1485°. If you would take another similar piece of steel, and lay a line of table salt on it, heat from the underside, you can then see the color of 1474°/1475°, when the salt melts.
 
Pure salt melts at 1474°. You might want to use sea salt, or non-iodized salt. It's easy to find nowadays, but you need to use the same light as you would when you go for quench heat. If you are color blind, this may not work. All carbon steels I know of, are best quenched at 1475°, or a little above. If you are a tad off in judgement, a tad more heat beats a tad less, in most cases.
 
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