This is just an introduction to help take the 'mystery' out of the big, thirteen dollar words you see concerning heat treating of steel. It'll also establish the steps you need to take before the actual quenching operation.

I'll keep it basic and understandable, but it's important that you know what's actually going on inside the piece of steel you're working with. And also, that you know the most important terms so you'll know what you're reading when you look at books on the subject.

The steel I'll use for this intro is plain, low alloy carbon steel; 1084. There are many reasons why this is a good steel to use for forging blades and it brings up the first funky word: Eutechtoid. The big heads in metallurgy say that the Euthchtoid, or the balance point for carbon/iron content in steel is .85% or 85 points of carbon. All that means to me and you is that there's not much of a reason to use steel with more carbon than that for knife blades unless you're dealing with high alloy, high carbon steels. Higher carbon content would be referred to as 'hyper-eutechtoid'. Lower carbon content would be referred to as 'hypo-eutechtoid'. Enough about that.

If you don't get anything else out of this tutorial, get this. Don't trust your eyes to determine when the steel is ready to normalize, anneal, or quench. You just won't get good, consistent results. (Ask me how I know). Use a magnet to determine when the steel is at a nonmagnetic state.

Now, it's important that you know that steel behaves differently with a magnet during the heating/cooling process. When you're heating your blade up in the forge, the steel will get progressively hotter and change colors continuously starting from the first hint of dull red all the way through the spectrum. ON THE WAY UP, your magnet will not lie to you. On the way down however, the steel will remain nonmagnetic for a long period of time. I kind of started in the middle there, but you'll see why in a minute.

When you start out with a piece of steel, it's in the 'Alpha' state or at room temperature. As you heat it up, it will change structure to 'Gamma' at the critical temp or nonmagnetic Gamma simply refers to the changed state of the steel known as 'Austenite'. The point at which the steel becomes Austenite is very important. Several things happen at this stage. I know you've all seen what's referred to as the shadow in hot steel. Well, that shadow is the dividing line between the Austenite or Gamma structure (higher temp) of the steel and the Alpha structure (lower temp) of the steel. So, as the steel heats up, the shadow moves through the steel from the higher temp area toward the low temp area or from the end of the bar/blade towards the handle. (Scratching my head here, how to get the point across?)

This shadow is your visual cue that you need to check with the magnet. So, when you see the shadow in the steel as you're heating it up, start checking it with the magnet for critical temp in the steel. In the completely forged blade, the shadow will travel up from the edge toward the spine. From the thinner to thicker sections of the blade. It will follow any curves in your blade as well. Pay close attention the next time you're heating up a finished blade and you'll see what I mean. Don't get it too hot and then wait for the magnet test to work because it won't work on the way back down. I can't stress this point enough. If you get the steel too hot it will cause grain growth and you'll have to stop and normalize the steel in order to get this under control. That brings up normalizing.

Normalizing is the slow, even heating and cooling of the steel to get all the carbon and iron in a stress free state and ready for annealing. This is done after forging the blade to shape. To do this, simply heat the steel evenly to nonmagnetic and let it air cool down to a black heat or where all 'visible' color has left the steel. Lay the blade spine down to avoid overheating the edge. Do this three times. I usually just heat up the steel and then walk around the smithy with the bar till it's at a black heat and then repeat the process.

If you're going to anneal the steel, you do this on the third normalizing sequence. So, instead of heating it up and letting it cool in the air, heat it up and put it in ashes or vermiculite or what have you. In order to anneal properly, don't leave any steel exposed from the ashes. Hot cut your blade off of the bar you're forging from before annealing it so it can be totally covered with ashes during annealing. If you're using tongs, you won't need to hot cut anything as long as the entire blade will fit in the annealing bucket. This slow cooling should take 8 - 12 hours. Don't be impatient and pull it out to check on it. That will only undermine an otherwise great anneal. Now is the time to start on another forging project or work on other knives.

I've had the best luck with fine hardwood ashes. The only bad thing about this is that the ashes will melt onto your blade and make a mess. Just soak it in white vinegar overnight and it comes off clean as a whistle. If you don't want to wait, just heat the vinegar to below boiling and put the blade in that. It will clean up pretty fast. Save the vinegar for this and it will get stronger and faster each time as the water is boiled out of it.

Why anneal at this point? Well, I'm assuming that we just normalized a fully forged blade, ready for hand working. I always anneal at this point because I want the steel at it's softest so it's easier to file, stamp and so on.

Now, I mentioned grain growth earlier and I'll explain it now. When you get the steel too hot during forging, the grain gradually gets larger and larger. It's most critical at the normalizing, annealing and heat treating phase. So, all the heating/cooling, heating/cooling that went on during the forging process has the steel in a very uneven state and it most likely is stressed from cooling unevenly on the anvil and from hammer blows, etc... I don't know exactly why the grain grows, it just does. And it will kill an otherwise good blade deader than a door nail. To avoid grain growth, use the magnet in all phases of normalizing, annealing and quenching! It's that simple.

If you do everything else right all the way up to the quench and then overheat the steel for quenching, all that work was for nothing and you have to start over with the normalizing process. The grain size will be large and sandy looking if you break the blade at this point. It will still get hard, but it won't hold an edge and the steel will be weak. That's what happened to my test blade in the intro class. I did everything else right all the way up to the quench and overheated the steel before quenching. When the blade broke in the vise, it had large grain. DUH! I didn't use a magnet. I resisted that little trick until then. I guess a hard head like me just has to learn the hard way. That's all it took. Seeing is believing and now I'm a firm believer in the magnet trick.

So, to recap this part of heat treating - USE THE MAGNET! It's just that simple. There are probably some of you guys out there that are saying 'Oh, BS, I can judge the color of the steel'. You're probably right. Experience is the key to your success. But, for the majority of us blade bangers, the magnet is the key.

In the next part, I'll go over some more thirteen dollars words and get to the meat of the matter - What happens when you quench the blade and how to get the most out of your techniques. Thanks for looking in on me and please ask all the questions you can think of. I know I'm a little disjointed with my presentation, but I think I got all of my points across to get you primed for the next part of heat treating.

Oh, thanks Ron. I was thinking about it, I just forgot to write it down clearly. If you get grain growth from overheating your steel, it's a simple matter to 'normalize' the grain structure again by normalizing it. Up to a certain point, anyway. If you really overheat your steel several times, there is a point of no return with the carbon in the steel. Burn your steel just once and your total carbon content in the burned section is reduced. I've been told that if you burn a piece, even slightly, just cut it off and start over. I don't believe you can do anything to restore the carbon or reduce the grain size at that point. How do you reduce the grain size and keep it there? Quench the properly normalized blade at nonmagnetic!

So, you've done whatever grinding, filing, stamping and sanding you intend to do on the blade. By the way, how fine a finish should you take your blade to before the quench? There are lots of opinions about it. I used to get silly and forget that my blade wasn't ready for final finishing just about the time I finished it. Hmmm..... If you're quenching in oil, there's not much reason to go any finer than 220 grit prior to the quench. You want to get all the surface irregularities out of the steel before the quench. If you don't there's a good possibility that you can get heat risers or stress risers that will crack and ruin all your hard work. After the quench, you'll want to grind off at least a little of the surface, especially on the edge because of decarburization. That's why it's important to leave the edge thick for the quench. So you can get down into the hardened steel and have a good, high carbon edge on the finished blade. Also, it's a good idea to wait until after the heat treating is finished to grind your ricasso shoulders on a hidden tang blade. If you file the shoulders to a sharp 90 degree angle, it might crack during the quench. You'll have to draw the tang and ricasso back in order to do that. Just suspend the blade in a pan of water and heat the ricasso and tang to a purple heat and let it cool. It's best to radius the shoulders anyway. If you radius the shoulders, it won't make any difference when you quench.

In the past, when I forged a tribal piece I left the surface 'as forged' and just cleaned the scale off by soaking it in vinegar overnight. Then, I'd do some hand sanding to highlight the texture and make it look good (to me anyway). Now however, I take the surface of the blade to a fully finished, flat surface to avoid the cracking and warping that can occur on an irregular blade surface with hammer dings and scale pitting during quenching. I still forge tribal blades, I just take a lot more time during the finishing heats to flatten the blade surface as close to finished as possible for minimal cleanup. Keeping the face of your anvil clean will help tremendously with that process.

Now, I'm not saying that tribal, 'as forged' pieces are necessarily going to fail. It's just a lot more likely that they will given the nature of most of the steels we work with. Take 5160, for example. I was working with a piece of 5160 yesterday that I brought home from school. They let us have the short scraps to bring home and play with. Well, that particular batch of 5160 was full of inclusions, or tiny cracks from the manufacturing process. You won't know those cracks are there unless you clean up the surface down to bare, shiny metal. That's the point I'm trying to make here. You won't know the cracks are there unless you can see them. So, when it's an important blade, finish it accordingly for the best quality.

So, we have a blade that's been normalized, annealed and otherwise finished up ready for the quench. There are several ways to heat the blade up for the quench. You can use the coal or gas forge, an oxy/acetylene torch, an electric heat treat oven or whatever will allow you to heat the steel slowly and evenly to a uniform critical or nonmagnetic heat. There are several quenching methods as well. We're quenching a blade forged from 1084, so we'll use oil.

There's a lot of controversy over which oil to use. I learned so much about different quenching mediums at school that it got kind of confusing at times. Here are some key elements to think about when you're selecting your quenching oil. First and foremost, choose a light oil with a high flash point. Some folks say to use organic oils like vegetable oil, linseed oil, transmission fluid, bear grease.... the list goes on and on. I think the vast majority of us use old motor oil. That's what I've used for years because it's what I learned to use. It's not the best, but it works. I'm still using it because that's what I have. I do intend to get myself some Chevron quench oil, I just haven't done it yet. The oil you use isn't nearly as important as your technique.

Probably the most important thing to do with whatever oil you're using is to preheat it before the quench. I never preheated my oil in the past because it didn't seem important with my limited knowledge. It's very important! You should always preheat your oil to around 150 F. A good way to do it is to heat up a big hunk of junk steel and quench it until the oil is at a temp that is 'almost' uncomfortable to put your finger in. You can use a candy thermometer if your wife don't find it out

The reason it's important to preheat your oil is because of the vapor barrier that forms around the steel immediately at the time of quenching. It really has very little to do with the temp of the oil. Actually, it has more to do with the viscosity or thinness of the oil. When you heat the oil up, it gets thinner. That means less of a vapor barrier around the steel when you quench. Lets look at that vapor barrier a little closer.

When you quench a blade, very little oil actually contacts the surface of the steel initially because the oil vaporizes on the surface and puts a vapor jacket or barrier around the steel. Now, this all happens pretty fast and is usually accompanied by a flame that jumps up and catches your beard on fire and blinds you with thick, white smoke. As the steel cools down to below the flash point of the oil, the oil finally comes into contact with the steel and cools it down quickly. But, right at first, the oil is doing very little cooling to the steel. It's the oil vapor that's cooling it. You can begin to see that it's not as simple as you once thought it was. It's really quite complicated and bears considerable thought to really understand what's going on in your quench tank.

Water is even worse. Most oils have a flash or boiling point of around 450 F. Water doesn't have a flash point, but it boils at 212 F at sea level. So, the steel has to get down to 212 F before the water actually comes into contact with the steel. All the way from 1550 F to 212 F, the steel is surrounded by a vapor barrier. The water is actually boiling just off the surface of the steel! That makes for a very poor quench medium.

Time for some more thirteen dollar words. A bunch of 'ites'. We talked about Austenite yesterday. That's the gamma state of the steel during the heating up process. Austenite is the beginning of the transformation of the steel into a useable blade. When the steel has been transformed into austenite at the nonmagnetic target temp, it's time to quench. Now, 1084 steel is considered a very fast quenching steel. In other words, you have approximately 3/4 of a second to get the temp down from nonmagnetic to around 400 F in order to get the best conversion to Martensite, which is most desirable form of steel to the knifemaker. Martensite is very crystalline in structure. It looks like a bunch of needles in a pile going every which a way. Martensite gives steel its hardness. But, it's very unstable and is under a tremendous amount of stress. Because, what you've just done is cause the steel to be in a state that it doesn't want to be in. You tricked it by freezing it's structure at a determined point.

Now, if you don't have the right oil, or it's not preheated correctly, the quench won't be rapid enough and you will most likely transform the steel into Pearlite. Pearlite is still fairly hard, but it's not as fine or hard as Martensite. This gets very confusing, but try and stay with me. There is coarse Pearlite and fine Pearlite. If you miss the quench time by a second or two, you will most likely get fine Pearlite. If you miss it by more than a few seconds, you'll most likely get coarse Pearlite. Fine Pearlite is acceptable, but coarse Pearlite is bad news.
So, a rapid quench is necessary to produce Martensite, which is what you want in your blade.

Now lets look at a few quenching techniques. Edge quenching is very popular and I use it myself. There are a few ways to do it. First, you can just heat up the edge to nonmagnetic and quench the entire blade edge down until the oil stops bubbling. That's pretty tricky to get right. You have to be very precise with your heat so you don't overheat the edge and especially the point. Then, you have to be extremely fast on the quench because the edge won't hold the temp for long. The other way to edge quench is to heat the entire blade up all the way into the ricasso and then quench edge down for at least 1/3 the width of the blade. Rock it back and forth along the edge until all the color leaves the spine. Then, dip the blade in the oil until it's cool enough to handle. If you take it out of the oil, the heat in the spine may draw the hardness out of your edge. Some folks use a brick or hunk of steel to set the quench depth in the oil. I just use the edge of the pan as a guide. It works for me.

The full quench is easier, but can cause warping if not done correctly. Heat the entire blade to nonmagnetic and quench the entire blade edge first. Just put it straight into the oil and leave it there. Don't move it around until the most violent bubbling and gurgling is gone. This is a good time to bring up Mar-Quenching or 'Quenchus Interuptus' as Kevin Cashen likes to call it. It's a new technique he's developed that makes a lot of sense to me. After the oil stops bubbling and smoking, take the blade out and look at it quickly. If the oil is smoking, but not burning off, you're at right around 450 F. This is where you interrupt the quench. Leave the blade out of the oil and let it cool to room temp. According to Kevin, this will result in a better transformation to Martensite.

I had been doing that in a different way. It just seemed to make sense to me. I would quench the blade until it quit burning the oil, then put it in the ashes until it cooled. What I was trying to do was shortcut the tempering process which I'll cover next. I told Kevin about what I had been doing and he wasn't sure that was a good thing or necessarily a bad thing. The jury is still out on it for now.

Anyway, after the blade is cool enough to handle, clean off the oil residue with a scotch brite pad or sandpaper so you can see the tempering colors later on. Actually, the easiest way to get the oil crud off is to use a scotch brite pad as soon as you remove it from the oil. It will come right off when the blade is still hot.

Now, place the blade immediately in your tempering oven. Don't delay the tempering of your blade. If left even for a few hours, it could begin to crack as the Martensite starts to form. Martensite expands as it forms which is why the blade cracks if not tempered right away. I use a toaster oven because they have a smaller variation of temperature in most cases. A kitchen oven can fluctuate as much as 100 F during the tempering process. That's not good for the tempering process. Use whatever you have available that will maintain a nice, even temp. For 1084, 400 F is about right for a good hard blade that's tough as well. I don't know the Rockwell scales, but if I remember right 400 F for one hour will give you somewhere in the neighborhood of 56 - 59 RC. Some folks do a triple temper. I haven't tried it yet but intend to. The main thing to remember with tempering is that you're taking the stress out of the steel and allowing the Martensite to finish forming in a stable environment. No sudden temperature changes during tempering. If you triple temper, let the blade cool down all the way to room temp before you put it back in the oven. The tempering color I mentioned earlier is a light straw color. If you cleaned the blade well enough you should be able to see it before you take it out of the oven.

Now, for the full quenched blade, you may want to draw the spine to make it more flexible and less likely to break during hard use. That's especially important on a large blade. Just hold the blade by the tang and lay the edge in a pan of water and gently heat up the spine to a nice blue color down to the water line. Be very careful not to overheat the spine or it will make the knife weak. Draw the spine three times being careful not to quench the blade. Let it cool slowly with the edge in the water.

Finish up your blade and there you go. Probably the most important thing to remember when heat treating your blade is being careful with temperature variations. The only violent temperature shift you want is with the quench. Be patient, take your time and you should wind up with a nice, sharp, tough blade.
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