Step 5: Heat Treating--for the little pyro in all of us

Here's probably the most technical part of the entire project--heat-treating the blade. You can use either a coal forge (as I did), a gas forge, or a torch. The last should only be used on small knives--maintaining high heat on a big blade would be hard with just a torch. See picture one below to see me starting the fire.

Heat-treating consists of two steps, hardening and tempering. In hardening, you heat the blade to a critical temperature and then quench it. This changes the structure of the steel so it's extremely hard but also pretty brittle. A knife in this stage, if dropped, can crack or shatter like glass. The next step, tempering, is done by heating the knife to a lower temperature, around four hundred degrees. This makes the knife less brittle, while still keeping a relative amount of strength.

Now, You'll need a hardening bath. For 01 steel, you should use oil. Different types of steel require different methods of quenching--oil quench, water quench, air quench, etc... again, I recommend 01 steel because it's easy to heat treat and doesn't require anything more complicated than a bucket of motor oil. See picture two. You should be able to immerse the blade completely. The second thing you'll need for hardening is a magnet. This will help you determine the hardening temperature, because at that point the steel becomes non-magnetic. See picture three--I keep the magnet on the hood of my forge, specifically for this purpose.

Now to start. Make a fire on your coal or gas forge or light up your torch--heat the blade by the spine, so as not to burn off the edge. Steel will burn off or melt into an unusable foam-like metal mousse if it's heated too high.
So, you're going to heat the metal to a medium-high orange heat, until the steel becomes non-magnetic. Just tap it against the magnet while it's glowing, and if it doesn't stick, it's ready. At this point you'll want to let the steel cool slowly in the open air, a couple times. This is called annealing, and relieves stresses in the steel cause by the rolling and milling process. After you've annealed (three times is a good round number), heat it to the same temperature you have been, but instead of annealing it, plunge it into the oil bath. Wear gloves because there's going to be some fire here. See picture eight. When you take the knife out it'll be smoking and the entire room should smell like the French fry tent at the county fair. To test the edge, run a sharp file over it. If it's hard, the file should skitter over the edge without making a mark, as in picture ten. You've hardened the blade at this point, so be careful. It'll break if you drop it.

Now, there's not much you can do with the blade until you temper it. Put out your fire, go inside, and preheat the oven. Your steel might have come with tempering information on it. If it did, chose your hardness from the sheet and use that temperature. You'll want a medium hardness for a knife. The eleventh picture of this step is an illustration of the tempering colors--these are a visual aids for measuring the temper of the blade. The higher the temperature, the softer and springier the blade will be. Try to shoot for a brown or purplish color, which will usually show up at about 400-450 degrees. If you don't know exactly what temperature to use, go for 425 degrees fahrenheit. Put the blade on the middle rack and let it cook for one hour. When the hour's up, the knife is ready. Congratulations. You've officially made a blade--though to turn the blade into a fine piece of cutlery, you'll need to do a little more work.
<p>nice instruction!</p><p>Informative and entertaining read.</p><p>thanks</p>
I have made several Knives. I like A2 or O1 tool steels. the biggest thing to remember is keep the steel HOT when you are working it. But if you hit wielding heat (2500&deg;) you can also ruin the blade by having too course of a grain structure. Here are some of my knives. I don't cut the blanks I Forge them out from stock. mainly because I don't have a bandsaw yet. the biggest thing is don't get frustrated if you mess up be willing to adapt your design if you need to. and if you find a good steel provider see if you can get cheaper rates for scrap instead of paying for cuts. <br>
<p>Is regular charcoal okay to use to heat treat the steel? does it have to be blacksmithing coal?</p>
I used lump charcoal. brickets will not get hot enough. if you are going to forge the knife instead of cutting the blank you really need to use the smithing coal.
<p>Charcoal works fine, all you really need is a fire with some sort of blower to make it hotter, wood can work, but I don't recomend it.</p>
<p>Yes, the important thing is the right temperature. I find using charcoal just burns faster than coal.</p>
<p>I screwed up because I forgot the sock, no sock thing. Im sorry I have disobeyed you.</p>
<p>Do you have to put oil on the sharpeing stone?</p>
How long was the overall length of the knife (handle and blade)
Hello, can i use my BBQ with some blowers next to it for more air as forge? Can i make the knife hot enough?
<p>beautiful knife, I did one of a old saw blade is not so handsome but it is very practical </p><p><a href="https://www.patriotdirect.org/step-by-step-instructions-to-make-a-knife-from-an-old-saw-cutting-edge/" rel="nofollow">https://www.patriotdirect.org/step-by-step-instructions-to-make-a-knife-from-an-old-saw-cutting-edge/</a></p>
I know that using motor oil is most common but can you use olive oil instead or is the whole point to let the carbon from the motor oil soak into the blade as it is changing state? <br>great instructible by the way!
I've used canola oil before, so yes. I've heard people talk about carbon leeching during the quench, but I really don't see a difference. With the correct steel gaining or losing a little carbon (if this even occurs, which I'm not sure of) will not noticeably change the blade's properties. Using oil is more about controlling the speed of the quench than altering the chemical properties of the steel.
What do you use to save the blade from rusting? Does the polish prevent it?
I don't think polishing will help. Blueing the steel with polish or keeping it lightly coated with oil is definitely better. My friend uses petroleum jelly on his blades.
You are correct when you say the quench is more about controlling the rate of cool down. The carbon leeching is negligible. Peanut oil, motor oil, transmission fluid, those are all good quenchants. On a side note, most of these oils should be preheated to around 120 degrees so they are thin enough to release the vapor that is created by the work piece, this allows the fresh quenchant to stay in contact with the piece to cool it down at the rate needed. If you start off with a good steel and control your heat you shouldn't lose enough carbon during forging to decrease the stability of the steel. Msg me for more info.
<p>Great instructable :)</p>
<p> <br> <br> <br> <br>This article gives <br> the light in which we can observe the reality. This is very nice one and <br> gives indepth information. Thanks for this nice article.</p><p><a href="http://www.monacopropertylistings.com" rel="nofollow">immobili monaco</a></p>
So I know this guys says to use carbon steel over stainless, but carbon steel doesn't have a lot of tensile strength, and can be snapped with somee pressure. It would still work, but I would suggest 400c stainless to make a knife.
Stainless is crap, it doesn't hold a edge. There is a reason high carbon steel has been used for centuries in knife and sword making.
<p>Hey, just to drop a note on this for anyone reading, carbon steel (or rather high carbon steel, since all steel has carbon to some degree) is ideal for knifes. Yes it can snap, but that's if you don't do some tempering on it. Quench the blade once the shapes done and then clean it off a bit. Drop in in the oven on 400-450 for 45-90 minutes. Allow to cool and that should do it.</p>
<p>Problem with that is a) 400c is really not a good knife steel, but I'll presume you meant 440c, and b) stainless steels require a very complex heat treat process which is, generally speaking, not doable at home.</p>
<p>Nice job! And hey, you're local! :) Nifty! I'm going to make some knives down at the Open Bench Project (at Thompson's Point) this spring and summer! </p>
ok.... I've made knives swords tools, I'm an engineer... if you want a usable blade to chop skin dig etc use a leaf spring... work it.... aneal it, quench it....
<p>Anyone thinking about making a knife should view this hands down the best tutorial I have found. Thank you! </p>
used th is ible as a guideline and got this.
<p>Please check this link:</p><p><a href="http://www.terasrenki.com/en/prod-cate/knife-steels-blank-blades-materials-for-knives/carbon-steels/" rel="nofollow">http://www.terasrenki.com/en/prod-cate/knife-steel...</a></p><p>I'm from finland and I'm gonna make a knife, can you tell me which of those steels in that site would be the best? Is any of them the 01?</p>
<p>very nice, and an excellent finished project</p>
<p>Wait a second. IS THAT HOMEMADE I CAN'T BELIEVE IT!!! that is awesome. if i saw that at a knife shop i would think it was made by a very large company like Olson Knives. wow just amazing. :)</p>
<p>Not bad. It seems easy enough. I have got a few throwing knife sets but I think making my own is the way forward. I guess I can make <a href="http://deadbullseye.com/reviews/bladesusa-throwing-knife-reviews/" rel="nofollow">something like this</a>, doesn't seem very complicated.</p>
<p>hi! im just about to finish my knife,</p><p>i made it from an old car's suspension and used your guide as reference</p><p>its not as good as yours but im really happy with the outcome!</p><p>(the pic is badly taken srry for that)</p>
<p>Awesome job, man! It looks really good.</p>
<p>Thanks!</p><p>there are certain parts that could be better but for my first knife using terrible steel i think its pretty good..</p><p>im glad the master aproves!:D</p>
<p>very nice, im making one from a steel cable (forge welded into Damascus steel) with a bloodwood handle.</p>
<p>I sometime make my own throwing knife. It is pretty easy because my throwing knives are<a href="http://deadbullseye.com/reviews/gil-hibben-throwing-knives-review/" rel="nofollow"> full-tang structure</a>, meaning the blade and the handle are made with one single piece of metal. The important thing is the steel. Spend a bit more on a better quality steel and your knife will last long.</p>
purple heart aint cheap 9.80 a board foot
Where did you find the carbon steel sheet?
<p>Really nice article. I just found out that you can build a knife with a 3D printer as well. Maybe the next <a href="http://www.bestmultitoolreview.net/best-folding-knife-guide/" rel="nofollow">best folding knife</a> will be done by a 3D Printer. :P</p>
This is definitely one of my favorite instructables. And I've been looking around for an 01 stock still but I was just going to ask, about how much should I look to play for the steel?
<p>We got a 2&quot; x 36&quot; length of the 1/8&quot; O1. We got quite a few knives out of it. </p>
truly a god amongst men
<p>Something I would like to tell you, and I am a complete knife knut :) is that you have really nailed the concept of the &quot;organic&quot; handle. So many VERY EXPENSIVE knives have the worst handles, some with protrusions that are ridiculous, that I would imagine &quot;look&quot; good but in actual use are worse that useless :( In my opinion, and I have used and owned MANY knives, the handle should be simple, as you have done. Now, you have also made it beautiful, but someone could use your knife for hours of hard work and not have any &quot;hot spots&quot;!!!</p><p>Well done</p>
How long did u make your knife
im trying to build a throwing knife and could realy use some tips you can get me at facebook or at yahoo look me up at wisephillip@yahoo.com. I've drawn up alot of designs and have constantly tryed to build knife after knife i could realy use the tips so if anybody has any ideas could u please get ahold of me.
socks very important to making a good blade
Thank you. I purchased a knife blade recently at a gun show and have been looking for a decent set of instructions for how to grind ans shape it, This instructable has a lot of good information.
Erm.. so... I'm gonna be making a karambit using this idea... and I only have a few of the tools mentioned... please help. Any advice would be appreciated. <br>
It's hard to give good advice without the details...which tools don't you have? It's possible to make a (maybe not beautiful) knife with as little as as a rough file, sandpaper, a hot wood fire, oil, a conventional oven, and carbon steel. Filing a large primary bevel by hand will take some time, though.

About This Instructable


1,771 favorites


More by Basta: A Simple Hollow Grinding Jig Wetshaving for the Common Man How to Build a Sheath
Add instructable to: