Here are some of the articles I have written in the past. Feel free to use this information in any way you would like.
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Question and Answer Articles - Mostly from Knives Illustrated
Several Years ago I bought a knife from a fellow named _______________, who had, just turned pro. He made very pretty Damascus knives at very reasonable prices. The one I bought had an 8" x 1 1/4" blade and a dessert ironwood handle. Yesterday I decided to see how well it would work. It had very short, chisel like bevels so I filed them a little higher. Then I tried to sharpen the thing on a water stone. I have no trouble getting near razor edges on my Swiss army and Cold Steel knives, but I just couldn't get _______'s knife sharper than an axe edge.
Knowing that the American Bladesmith Society tests knives on 2 x 4's I decided to try it. It must have taken 50 whacks to cut half way through! I turned the 2 x 4 over and started whacking and the pretty desert ironwood handle split and came off! Imagine if I had been stuck in the deep woods and relying on _______'s knife!
I do a little amateur knife making. So far I've mostly forged Scottish dirk blades for the people in my living history group. I use auto body rasps and leave the blades a little rough. Since they didn't have belt sanders in the 17th century, I don't either.
But, if you want to make knives for using rather than as costume pieces, how do I avoid having them be pretty and useless like _______'s? Do wood and horn handles need steel ferrules? Do knives need convex edges, and do I need a belt sander to produce them? If I do Damascus, what do I put in it? My O-1 knives seem to hold edges pretty well, but they're small and I don't attack 2 x 4's with them.
I would appreciate any suggestions.
I'm sorry to hear you've had such a hard time with ________'s knife. Poor quality work from one maker reflects badly on the trade as a whole. It used to be that a Damascus knife was seen as a sign of quality. But then, very few of those knives were ever tested or used. Now that more Damascus knives are being used, it has become apparent that just because a knife is made of Damascus it doesn't necessarily mean that the knife is any good. Actually, it is a good idea to be more skeptical of Damascus bladed knives than straight tool steel ones.
The most important consideration in determining the tool quality of a knife is the heat-treating. Any steel that will harden can be made in to a serviceable knife. The great variation one sees in the cutting and strength qualities of a knife is influenced by the heat-treating. Try to find someone who is really good to show you how. Or, failing that, read a lot of basic heat-treating books and ask a lot of questions.
What to put in to Damascus is a "loaded" question. There are so many variables and each one effects the other. For simple forging and heat treating set-ups, I prefer to use 85% W2 and 15% ASTM 203E. It makes a good blade that etches easily. With gas forges and salt bath heat treating furnaces I prefer 75% O1 and 25% L6. This mix is capable of out cutting the W2/203E mix by 100%. But, it is more difficult to get just right.
Wood and horn handles don't really need steel ferrules. They can help strengthen the handle, but are not necessary. A band or collar around each end of the handle can greatly strengthen the handle, but are a lot of trouble to make. The best thing you can do to strengthen the handle of a hidden or stick tang knife is to keep the tang as wide as possible where it enters the handle material, not just the guard. A great number of knives break just behind the guard not on the blade. Japanese swords are a good example of how this should be done.
Convex edges are not needed to have a sharp knife. Check out straight razors. Yet, convex edges do help greatly in the strength department. In general, you should try to make both the blade and cutting edge as thin as possible for the intended use or abuse of the knife. A thinner blade will always cut better than a thick one, all else being equal. But, a slightly convex edge will add support to the edge and help keep it from chipping out. For chopping purposes, a convex knife side can add great strength at the expense of some cutting ability. It all depends on the use of the knife.
You can make convex edges and knife sides without a belt sander. It is just faster and easier with one. Just use your files, before heat-treating, and stones, after heat treating to blend convex surfaces in with your flat surfaces.
An economical way to learn a lot of this information is to attend a quality seminar or conference and ask a lot of questions. The two best I've found are Jim Batson's Alabama Hammer-in (spring), 205-971-6860 and The New England Bladesmith's Guild Ashokan conference (late September) 914-657-8333.
(Was that an echo?)
HI! I've been dreaming about making knives for 5 years before finally being able to do something about it. I started three months ago, and have put in about 100 hours total, including setting up my shop., whenever I can steal time from my day job (CAD building design and drafting).
I'm willing to do whatever it takes to learn. Without being falsely modest, I'm good at what I choose to do and learn real fast. Even so, I expect to spend at least two to three years working through knives and up to swords (my real interest). I've done a lot of machine shop work and technical welding (TIG, MIG, titanium, alum, stainless, bronze, etc in the marine field), and feel at home with metal. I've used everything except a helical mill, and have some CAD/CAM experience as well. I'd rather work by hand though, just because that's what turns me on.
So, the first two knives I made were file steel (Nicholson with the teeth ground off after annealing but before forging), and I quenched them in room-temperature water (about 85 degrees F here), then eyeball tempered them (until my intuition said take them out of the forge and stick them back in the water) . I whacked them HARD on the edge of the anvil and they didn't break or bend and a new file just skated off the edge of the blade. I made handles for them and velvet-lined scabbards. They made a couple of well-appreciated gifts for my two best friends.
The next knife I made was out of a Toyota leaf spring and following the same process half of it just went ping! Off the edge of the anvil and stuck in the anvil stump. Totally depressed but determined to figure it out, I reread everything I had and talked to a friend who had some experience forging wrought iron fancywork. Three hours later I had a 24" long oil quenching bath "thing" welded up and sitting next to the forge. I was going to try cold oil first, then warm, then hot, if the darn thing kept breaking. The first try on cold oil (85 degrees F new 30-weight motor oil), my leaf spring knife acted like the file knives- no ping and the file skated off it. It seemed a little tougher than the file knives, so I put 1-1/2" of it in the vise and pounded on it with a 2-lb hammer until it bent 30 degrees and finally went ping and flew off across the shop. I figured this was pretty good as I wasn't planning on using it as a pry bar or chisel.
I got inspired and pounded out an 18" wakizashi blade from a 3-lb chunk of the leaf spring (I thought I should use pieces out of the same leaf spring until I knew more). After way more grinding than anyone with experience would have needed to do, it was ready for heat treating, and I was sweating when I popped the edge of the anvil with it, hard, at arm's length. It bent slightly, and then the file skated off it, and I relaxed and bent it back to straight in the vise. I had made a (piece-of-shit, full-of-scratches, wrong-grind, funny-looking-tsuba-and-habaki) sword. I did get a hold of some sugi pine (some call this Japanese cypress- a very aromatic hard cypress with dramatic grain) for the handle and scabbard, and presented it to my kendo sensei for teaching me for 3-1/2 years at no charge. I was a little embarassed that it wasn't a good blade I was giving him. I wanted to do better so badly I could taste it, but I was just OK with that and figured I had to be patient.
That's the little I "know" so far. I've included these questions in case you're inclined to help a rank beginner out. I'll start out with what I have in the shop so you can tell me if I need different tools or am using the ones I have the wrong way.
· Coal forge is a steel can lined with fire brick- inside it's 14" dia by 12" high with a hole out the opposite side from the anvil side so I can run long stuff through. I'm using Australian coal. Size is from grit up to about 1" max. A 2" dia tuyere driven by a 2-speed cold-air hair dryer pointing straight up in the center of the forge creates a hot spot I can get about 6-8" of blade yellow hot in 3 to 5 minute heats. It lets me do a lot of forging in a short time, consumption- burned about Ÿ of a 5-gal bucket of coal for the wakizashi blade over 1-1/2 hours of forging.
· A 2" x 72" Grizzly (I'm on a budget! Who isn't?) belt sander/buffer, 1" x 42" Grizzly belt sander, 6" wheel sander, a 6" vise I can pound on, 6" x 80" Grizzly horizontal belt sander, Grizzly 10" x 2" wet wheel grinder w/ 6" x 5/8" dry wheel, Ÿ" chuck Delta 14-speed drill press, œ" chuck Grizzly drill press, 120 amp MIG welder, oxy-acetylene setup, a Beaudry 1896 model 150-lb power hammer that weighs about three tons (this needs 50-100 hours of work to get running again- but I got it for $100 and a 10-horse 3-phase motor for another $100), and lots of power and plain hand tools- grinders, sanders, routers, everything left over from my boat shop that employed 12 people.
1. Should I stick with the files and springs, or buy something of known qualities such as D2, D1, 1095, or? I hate stainless steel knives (although I never could afford a $400 ATS 34 boat knife), and even during my fishing days carried a carbon steel blade because it stayed sharp and cut. I considered making stainless laminated with a good thin carbon core when I get to that skill level. I prefer carbon steel. What should I try first and what skills and knowledge am I trying to develop here?
I'm including the full text of your letter here. It is a good reminder of what we all have gone through. After making knives for twenty years it is easy to forget about the things that used to drive me crazy. Thank you for refreshing my memories by relaying your experiences.
Material selection can be thought of in many ways. Many knife makers find a great deal of satisfaction in recycling used material. The most commonly used are: old springs, files and ball bearings. All of these materials can be used to make a good, serviceable knife. It is quite gratifying to know that you were able to take a piece of junk and make a beautiful tool from it.
The problem in using scrap steel lies in the identification of your material and whether it fits in to the plans and equipment you have. When 5160 was the new "hot steel" I had to try it. John Smith got a Timken bearing race for me to play with. I forged it, ground it and heat treated it, and nothin'. It wouldn't even harden! John called Timken, they assured him it was 52100. A few tests and phone calls later, Timken finally admitted that "well, maybe it wasn't 52100 after all". Sometimes they would substitute other materials when 52100 wasn't available. It pays to know what you are working with.
I will usually use new steel bought directly from the manufacturer. I always request an analysis for that particular batch. Even new steel, of the same type, from the same manufacturer, will vary in analysis. On rare occasions, I will use some scrap steel. Especially if it has some sentimental value for myself or the customer. But mostly, I use new steel.
Even though it isn't as popular as it used to be, I recommend starting with plain old O-1. It is inexpensive, easy to work and readily available. O-1 is a good steel to use while learning the basics of forging and heat treating, It doesn't have any quirks or require special techniques. As your requirements, skills and equipment increase, you can then branch to other grades.
Should I invest in pyrometers/tempering ovens/gas forge/fancy oil bath equipment/cryo equipment or anything else I don't even know about yet, in order to make heat treating more predictable? Or just keep developing my intuition? Or both? Should I try charcoal instead of coal? (I have a local source of mesquite charcoal fairly cheap here).
It is possible to make excellent knives with very simple equipment. The "learning curve" is just much steeper. To see how simple it can be, check out Tai Goo and the Neo-tribal Metalsmiths.
If having the highest quality, most consistent work is a priority, buy at least a kiln. You can "fake" everything else, for now. The heat-treating is the "soul of the blade". If you mess it up, even if everything else is perfect, your knife will be a pretty, yet useless, tool. This is not to say that you can't get good results without a kiln. It is just easier with one.
Getting the steel to its critical temperature, accurately, is the most tedious and frustrating part of heat-treating. You can learn to do it by eye. See the XXXXXXX issue of KI for a simple experiment on how to see the right temperature. This experiment also shows how important it is to get it right. Yet, if you miss the correct temperature by as little as 50F, you can really mess things up. A kiln is one of those investments you won't regret.
For forging, you really don't need anything fancy. The forging range for most steel is pretty wide. Your eyes are a good enough pyrometer here.
Compared to coal, charcoal is wonderful to forge in. It doesn't have all those nasty things that make coal a pain. I'm referring to sulfur and clinkers. As your experience and budget increase, you may want to build or buy a gas forge. They are cleaner and more efficient than any hard fuel forge. But, a charcoal forge is a wonderful way to learn about fire and heating steel.
That is all we have room for this month. Next issue, we will get to the rest of your questions.
Lately it seems like a lot of knife makers are trying to become armchair metallurgists. They are throwing around a lot of big words. What do words like cementite, austenite and pearlite mean?
It is good that more knife makers are getting interested in metallurgy. It can only help the quality of their knives and increase the level of the entire craft. Although there are many more than this, these are the terms you will see used most often in knife making:
Soft or annieled states:
1. Ferrite - Iron
2. Cementite - Iron Carbide or Fe3C.
3. Pearlite - A equilibrium mixture of ferrite and cementite that occurs at .83% Carbon.
1. Austenite - A heated state of steel where the carbon is in solution with the iron and free to move around. This state is non-magnetic.
1. Martensite - The standard hardened state of steel.
2. Banite - Another hardened state of steel formed by inturrupted quenching called austempering. Banite is not as hard as martensite, but it is very tough.
Heat Treating :
1. Austenizing - Heating the steel to the point where it contains austenite. Also called the critical temperature.
2. Quenching - Cooling the steel, from the critical temperature, at a prescribed rate so that the structure will be martensite or banite. Quenching can be done in water, oil, molten salt or air depending on the type of steel used.
3. Hardening - Both steps 1 and 2 above.
4. Tempering - A secondary heating of the hardened piece. This removes excess hardness and/or stress formed during hardening. Some people incorrectly call steps 1, 2, and 4 "tempering".
5. Martempering - A type of quenching where the cooling is interrupted slightly above the temperature that martensite starts to form. This is usually around 400F. The steel is held there for a minute or so and then allowed to cool in air to room temperature. The resulting structure is martensite with much lower internal stress than a standard quenched piece.
6. Austempering - Similar to martempering in that the quench is interrupted slightly above the temperature that martensite starts to form. The difference is in the time that the steel is held there, instead of a few minutes it can be several hours. The resulting structure is banite.
7. Annieling - Softening steel by heating it to , or near , the austenizing temperature and cooling very slowly.
8.Spherodize Annieling - A special type of annieling that leaves the cementite in the shape of spheres. Steel in this state machines easier and builds up less internal stress than those that are full annieled. Most new steels come from the mill spherodize annieled.
I recently read an article in Blade magazine re: Damascus steel. One maker of pattern welded steel indicated that there were really only four types: random, twist, ladder and a fourth that I forgot (I don't have the article in front of me). In my reading I have seen other types referred to: wootz, watered, 8-bar composite, wire, 1000 layered, etc. How many different types of Damascus are there in your opinion?
The term Damascus steel generally refers to steels having a visible pattern on the surface. Commonly, two very different procedures are used to make Damascus: Pattern welding and Wootz.
Pattern welded Damascus is formed using two or more different types of steel that are forge welded together. These layers are often folded several times to multiply the number of layers. Then the layers are manipulated in various ways to achieve different surface patterns.
It is not necessary to use flat bars for pattern welding. . Round and square bars are often bundled and welded together to achieve various surface patterns. Even EDM machinery is used to cut different shapes out of the parent materials which are then forge welded together. These more advanced welding and patterning techniques are commonly referred to as "mosaic Damascus". Mosaic Damascus can mean many things to many people. It is best to ask the maker about the specifics of the patterning..
The visual patterns available in pattern welded Damascus are endless. Your list above is a list of visual patterns formed by manipulating the layers in pattern welded Damascus.
Wootz is formed by melting iron in a crucible. Carbon is then added to the melted iron. Temperature and time control are critical. Careful forging of the resulting product will yield bars of steel where the cementite, iron carbide, has segregated out into visible layers.
I have been enjoying your articles in Knives Illustrated. It is refreshing to get a perspective on knife making that isn't filtered through "party lines". Keep up the good work.
I've been reading quite a bit about the making of Damascus steel. I was wondering, what is the purpose of the flux in welding? I have heard several opinions as to the reasons for its use and for different formulas. Can I make it myself?
Thank you for your kind words. I'm just a guy who makes knives, and wants to help others see that it isn't that hard to do.
Flux is used during the welding process to clean and protect the surface of the steel. It isn't magic and it isn't glue. When steel is heated into the forging range, a surface oxide forms. This is commonly known as "scale". In the steels used by knife makers, it is usually iron oxide or a combination of iron and nickel oxides. These oxides can build in thickness over time and completely prevent successful welding.
The flux is put on the surfaces of the steel being welded. It is usually applied just before the "welding heat". The flux will then combine with and dissolve the oxides already on the surface of the steel, forming a runny liquid. This liquid coating protects the surface of the steel from further oxidation.
The steel is then brought to welding temperature. A slightly reducing atmosphere in the forge will also help prevent further oxidation. At the proper welding temperature the flux, will flow over the surface of the billet and sort of "shimmer". The best description I have heard of how this looks was by Bill Moran, "It looks like butter starting to melt under the sun". The steel is then removed from the forge and the weld is closed with a hammer or press. If the welded surfaces were prepared properly, the flux and dissolved oxides will be forced out of the weld seam as the weld is closed.
Some oxides are particularly difficult to deal with. They stick to the surface of the steel and are quite resistant to the flux. The worst of these seems to be nickel. If you weld L6, A203E, 15N20, Nickel 200 or meteorite you will have more problems getting the welds to "stick". The easiest method of removing the scale from these alloys is to grind it off. I prefer to do the grinding hot, right after the billet is creased for folding. This conserves the heat in the steel, saving re-heating time.
My procedure looks like this:
1. Heat to 1700F in slightly oxidizing flame.
2. Sprinkle flux on surfaces to be welded.
3. Heat to 2100F in slightly reducing flame.
4. Close weld, forge billet to double length.
5. Cut through center of billet to create a "hinge" for next fold.
6. Grind off scale from next weld surfaces
7. Fold billet in half.
Notice that the only heating is at steps #1 and #3. This method is very efficient since everything is done hot. A 160 layer billet usually takes about 50 minutes.
There are several formulas for welding fluxes. In the past some of them were closely guarded secrets. I guess that some still are. Several years ago a well-known knife maker offered a substantial cash prize to any one who could guess his "secret" liquid welding flux. I guess too many people got a little too close because nothing more was ever said.
Most fluxes used today have borax as their primary ingredient. This is sometimes mixed with sand, iron filings, florspar and other materials to meet the needs or desires of the blacksmith. Some smiths prefer anhydrous borax to the regular stuff. It will flow better on the steel at lower temperatures.
I find that I mostly stick with plain old 20 Mule Team Borax from the grocery store. It is inexpensive and easy to find. Some of the commercial or anhydrous borax/florspar mixes do work better. They flow at lower temperatures and protect the billet better. But, I have a lot of practice and am used to 20 Mule Team's quirks. If you use straight 20 Mule Team Borax, apply the flux in the bright orange or 1700F range. Otherwise it will foam, froth and fall off your billet. Maybe I am just too lazy (or cheap) to use something better.
I hope this helps.
I was very glad to see you now have a column in KI.
Question for your next article:
I have heated knife up really hot to forge to shape... grains are big and
fat sluggish and slow
What various techniques are there to make-um small sharp eyed and fast. Pros and cons.... your preferrences... why? Hope things are going well for you in the land of ice and snow
Thank you for your question. I'm glad to see that someone is reading my column. A small grain structure us usually desirable in a blade to increase its strength. If the grain size of the blade is too large the edge will tend to crumble as it is used. Conversely, if the grain size is too small you can lose wear resistance. The edges may also tend to wear to a smooth polished one rather than a fine micro tooth. Finding a happy medium is important.
A lot of different things go on inside a blade that has been forged. These will all relate to the variables of: temperature, atmosphere and how you forged it. The internal structure of a blade forged at 2000F and one forged at 1600F will be quite different. Areas of the blade that receive more forging will have a different structure than little forged areas. Fortunately, it is possible to straighten out almost every forging problem by proper thermal processing.
First, after forging, the blade should be normalized. I am assuming you are working with a water or oil hardening steel. Normalizing is not usually recommended for air hardening steels. Normalizing will break up non uniform structures, relieve residual stresses and produce greater uniformity in grain size. A great deal of distortion or warping during heat treating can be traced back to skipping, or poorly performing, this step.
To normalize, slowly and evenly heat the blade to above its transformation range, then cool in still air. The temperatures for normalizing simple steels usually falls in the 1550F - 1650F range.
After normalizing, the blade should be annealed. This will soften the steel, allowing it to be drilled and cut. Typically the blade is held at a temperature at or near its transformation range for an hour, and then cooled at a rate of 30 to 50 degrees per hour. The actual temperatures and cooling rate depend on which alloy you are using.
After grinding and finish shaping the blade is ready for hardening.
The heating for hardening, or austenizing, is the most critical part of keeping the grain size small. Overheating a piece of simple steel by as little as 100F can turn an otherwise good blade in to junk. The pictures here tell the story. Even though these pictures are of M2, the same thing happens with steels like 1095 or O1. If you have a kiln or controlled furnace available, use it. It takes a great deal of practice to get the temperatures right with a forge or torch. I'm not saying that you can't get good results with a forge or torch. It is just easier and more consistent to take the human factor out of the equation.
Here is a simple exercise to demonstrate what the critical temperature should look like and the importance of getting it right.
1. Take an old file and grind grooves across it. Use a large and good quality file such as Nicholsen. The grooves should be about one inch apart and go half way through the file.
2. In a dark shop heat one end to yellow while leaving the other end cold. What you are doing is setting up a temperature gradient, just like on the wall charts. You will notice that, starting from the cold end, the bar will get brighter. Then, there will be a definite "shadow" that goes across the bar. This is not a cold spot. It is the area where the steel is transforming into Austenite. Just to the hot side of that shadow is the correct critical temperature.
3. After doing step 2 a couple of times, just to get used to it, quench the file in water. Note which groove the shadow is at.
4. Put the file in a vice at the first, hottest, groove and break it off. Use safety glasses and gloves. A gentle tap with a hammer will be all it takes. The grain will be very coarse and weak.
5. Continue down the bar noting how the grain gets finer and stronger as you go. Pay special attention to the groove where the shadow was at and the one just above it. This will illustrate a temperature difference of about 100F. Also, try to remember how subtle the color difference was between those last two pieces. You will see how difficult it is to get it "just right" in a forge or with a torch.
Holding the blade at the critical temperature for too long will also promote grain growth. For simple steels the standard rule is five minutes per inch of thickness. So for a 3/16" blade you would want to soak it at temperature for about a minute.
There are special techniques to further reduce the grain size. The most common is the use of multiple quenches. This involves hardening the blade, then repeating the austenizing and quenching process one or several times. Done properly, the subsequent austenizing must take place in less than 45 seconds, with no soak at temperature and have a temperature control capability of less than ten degrees. Usually, this needs to be done is salt bath furnaces with a contact thermocouple on the blade. Slower heating or overshooting the critical temperature will give little or no grain size reduction.
Remember, with the grain too small you may be giving up both sharpness and edge holding for increased strength. Overly large grain size is always bad. Techniques such as martempering and cryogenic treatment can give greater strength increases than an ultra fine grain structure. Usually, if you hit the critical temperature just right, the grain will be the right size for both edge holding and strength.
For more information see:
Metals Handbook, Vol. II 8th ed., ASM
Tool Steel Simplified, ISBN: 0137558056, pp. 331-335
The Rapid Treatment of Steel, R.A. Grange Metallurgical Transactions, Volume 2 - January 1971
The ISBN numbers have changed for two of my reference books. They are:
Tool Steel Simplified - ISBN: 0137558056
Metallurgy Fundamentals - ISBN: 0870069225
Thank you Matt for bringing this to my attention.
I have been messing around with old tiller blades, files and various "scrap" stuff. I am going to order some 0-1 to seriously forge some blades. My question is this- In my situation of not having a heat treat oven what would you do to harden and temper blades in 0-1?
I was considering a simple edge quench, and temper in my conventional oven. What would method would you use in my situation. What's the best oven temp for 0-1, how many temper cycles, how long per cycle?
Also, when I'm forging the blades how do I know when to stop forging?
Thanks for your questions. The nice thing about O1 is that it is adaptable to many different techniques, to suit your equipment and desires for the finished blade. Since you forge before heat-treating I'll cover that first.
The blade should be forged in a temperature range from 1550F to 1950F. So on the hot side of the forging range it should look bright orange in a dimly lit room. Avoid yellow and white colors as this is definitely overheating the steel. O1 is one of those steels that if you get it too hot it will crumble when you hit it. Below the point where the steel crumbles you can still do some damage so it is safer to forge on the cool side.
On the cool side of the forging range it is a good idea to stop forging at 1550F or so. Forging below the critical temperature can cause fractures in the steel lattice. These won't be visible cracks in the blade but they do weaken it considerably. A dependable indication is to look for "shadows" starting to form as the blade cools. When you see these shadows, quit forging.
Remember to allow for decarberization during forging. Forge everything at least 0.020" oversize. Normalize and anneal the blade after forging.
For heat treating, I recommend that you harden the whole blade. Then soften the back if you desire.
In heating the blade for hardening, it is very easy to overheat the edge, if you are trying to heat just the edge using a torch. Overheating by as little as 100F can turn an otherwise good blade into junk. It is better to heat the entire blade in the controlled environment of a forge or kiln. Heat the blade slowly and evenly watching for those telltale transformation shadows to disappear. When the shadows disappear the blade will also become non-magnetic. When this happens, it is time to immediately quench the blade.
I prefer to quench the entire blade. It results in a knife with higher tensile strength than a blade that is only edge quenched. The edge-quenched blade would have higher impact strength, but that relates mostly to swords. If your desire is to do a sword or have a temper line, then I suggest that you consider using the Japanese clay technique. It gives much better and more beautiful results than edge quenching.
Quench the blade tip down into warm oil. The type of oil doesn't matter much with O1 as you have seven seconds to get the blade below 1000F. Warm (150F) oil usually works better than cold. As the blade enters the oil begin moving it from edge to back. This further speeds the cooling. After several seconds, remove the blade from the oil. The blade should be smoking but not flash. You are trying to interrupt the quench at about 400F. After the blade has cooled to room temperature it is time to temper.
Tempering is easiest to control in an oven. Just be sure that your oven control is accurate. Buying a quality candy thermometer is a good investment. Tempering is usually done two or three times for 45 minutes to one hour. With Carpenter O1, 425F should result in a hardness of 60HRC. If you prefer a softer back on your blade, heat the back of the blade to a blue color with a torch after oven tempering. Be careful to not allow the edge of the blade to get hot.
I hope this helps.
I'm new to knife collecting. I have noticed that both custom and factory knife makers seem to have a favorite steel. Some go as far as to say that no one can make a knife as good as theirs if they don't have their special steel. The most notable are Cold Steel with their Carbon V and Busse Combat with their INFI. What do you know about these steels and their relative merits?
Thank you for your question. I need to start out by saying that due to confidentiality concerns there is a lot that I can't say. One thing I won't say is which is one better. I'll leave that one for the companies to fight out. Both are excellent steels made specially for the individual companies and both make great knives. When buying a factory made knife the real issue usually comes down to quality control and heat treating, not the steel that the knife is made from.
Cold Steel's Carbon V is a high carbon tool steel. I had the privilege of using some of it several years ago. It forges well, heat treats easily and is an all around wonderful steel for forging. It seems to take the best properties of my favorite forging steels (O1, W2, and L6) and combines them into one.
Because it is so forgiving in the heat treat it is especially suited for large production runs, or a guy with just a forge and a torch. When you heat treat it with more advanced equipment, it makes some of the best knives I have ever seen. It will tarnish with use, but so will Purdy shotguns. Just keep it clean. My only regret is that I can't buy it. I would use it for most of my carbon steel forging.
Busse Combat's INFI is a steel that is beginning to unravel all my theories about high chromium steels. Jerry Busse sent me some recently to test its' suitability for forging by custom makers. At this point I have only done preliminary testing, but the results are very intriguing.
While this isn't truly a stainless steel INFI does resist staining about like ATS-34. It is stronger than any stainless steel I have ever seen. I think it will rival O1 in tensile strength and L6 in impact strength. After shaving a lot of cardboard it will easily keep up with, and probably surpass most carbon steels on edge holding. Finally, there is a rust resistant steel that really cuts and cuts and cuts�
One of the weird things I noticed was how the hardness test marks looked under the microscope. In many carbon steels the dent crater will have cracks around the edge. This is especially true if the steel is not martempered. Even at a hardness of 62HRC INFI just seems to mush out of the way like putty.
INFI is an air hardening steel. It is also difficult to forge. You really have to hit it to get it to move. For heat treating, kilns and liquid nitrogen are required. But, if you have access to the equipment this could be one of the best all around knife steels ever. Hopefully, Jerry will make it available to custom makers.
I have spoken with several knife makers who say that all knives should be put in liquid nitrogen as part of the tempering process. Others say it is a waste of time and money, that "it is just propping up a poor heat treat" or "you can't get any further improvement". What, if any, are the advantages to the cryogenic treatment of knife blades?
Rapid City, SD
Thank you for your question. You may be aware that this is a rather hot topic among knife makers lately. As always, there are many different opinions and explanations to back them up.
Let's start with what most makers seem to agree on. Cryogenic treatment does help stainless and high alloy blades. The reason is that there is retained austenite in the steel after the quenching of the blade. This retained austenite weakens and reduces the hardness of the steel. Freezing the blade in liquid nitrogen transforms the retained austenite in to martensite. This will greatly improve the cutting and strength qualities of the knife.
An example of M2 tool steel can be seen in the transformation diagram below. Note that at 0F the blade still has only 80% martensite. 20% is retained austenite. You need to get the blade way below 0F to get the retained austenite out.
The controversy begins when you start talking about the simple carbon steels. Since carbon steels will convert essentially all of their austenite in to martensite with normal quenching techniques, many makers feel that freezing them doesn't do any additional good. The transformation chart below shows that O1 has 99% martensite at 100F. So, if you don't have any retained austenite, what is the point of freezing simple steels?
Here is where we get in to my opinion. I believe that the deep freezing of steels not only converts retained austenite, but it also acts like a super stress relief.
In the simple steels you aren't after, and don't get, higher hardness from converting retained austenite in to martensite. What you do get is less residual stress after hardening and more strength in both bending and impact.
The mental picture I have is; if you have a room full of balls that are in random arrangement and then shrink that room by freezing it, the balls will be forced in to a more orderly arrangement. Then, as the room grows bigger again, the balls will hold their relative positions. This will result in more regular and stronger bonds. This might not be anything like how it really works. But, for right now, it seems to be a good way to think about it.
A few years ago I did some simple testing to see if freezing had any use at all. I had the testing done at a real metallurgy lab to keep my biases out of it. The results are in the chart below. The samples were Starrett O1. The sizes are non standard so please don't compare these values to those printed elsewhere. They were either oil quenched or martempered to the hardness stated. The frozen piece was simply thrown in to a bucket of liquid nitrogen after the final temper. After twenty minutes it was removed and allowed to come back to room temperature slowly.
As you can see, the results are very encouraging. The frozen piece was stronger than all the other pieces at all hardneses. Failure in bending, energy to max. load and total energy are all higher than the other samples. It is interesting to see that it is possible to make a knife at 60HRC, with its' high tensile strength, that has the impact strength of a non frozen knife at 53HRC. See sample C.
There are several other interesting things to note from this chart. Notice how poorly samples A and B do on the impact test. They were tested immediately after quenching and were not tempered. That is why you want to temper your blades right away and be careful not to drop them. Yet, samples A and B also clearly show the advantages of martempering at high hardness.
For now, I am putting all my knives in liquid nitrogen after the first temper. The blades are simply immersed in the dewar and held there for œ hour after they reach the temperature of the nitrogen. They are then removed and allowed to reach room temperature slowly. Two standard tempers follow.
I understand that there are others who will disagree with me on this one. I would love to see their test results and learn from them. The search for better methods to produce a better product is one of the things that helps keep knife making interesting.
Quecnhing & Salts
Thanks for the great information. I'm writing to get more information and the address of Park Metalurgical. To clay temper 1084 steel do I use a fast quench oil or a meduim oil?
Sometimes when I etch my blades they come out with light and dark blotches. Is there a reason?
Dennis P. Tingle
The address for Park Metallurgical is:
8074 Military Ave.
Detroit, MI 48204
They are an excellent source for heat treating salts and oils. You can also click on the link above to look at their website.
To completely harden 1084 steel you have to cool it from the critical temperature to below 1000F in less than one second. That takes a pretty fast oil as it is. When you add clay to the back of the blade it acts as a heat sink and further slows the cooling of the edge. So just about the only way to go is water or a very fast oil.
The water, although it will work, can be quite severe and lead to edge cracking and warpage. The boiling water forms a vapor jacket around the blade. This vapor jacket contributes to uneven cooling which, in turn, can cause cracking of the edge and warpage.
The very fast oils are usually a better alternative. They will cool the blade quickly enough to get full hardness, without the problems mentioned above. My favorite fast oil is Park Metallurgical #50. It is very fast and approaches water in speed.
The reason for the light and dark blotches is usually decarberization of the steel at the surface. These blotches are usually seen at the ricasso and along the spine of the knife. This is where the least amount of grinding is done after forging. If you pay attention you will notice that the blotches usually occur where the last few forging pits disappeared while you were grinding.
It is good practice to leave all surfaces at least 0.010" oversize after forging. This means that a blade you want to finish at Œ" (0.250") thick should be forged to a minimum of 0.270". Forging in a slightly oxidizing atmosphere will also help cut down on the decarberization.
Blotches can also be caused by poor etching technique. Most commonly it is oily fingerprints on the blade. Be sure to clean your blades with acetone or laquer thinner before putting them in your etching solution. Changing your etching solution once and a while doesn't hurt either.
I'm setting up a high temperature salt bath system for hardening my blades and have a few questions.
How big a container do I need for the salts?
Does it only have to be big enough to accept the steel I am heating? Or should it be slightly larger?
Should it be made from stainless steel?
Is there a cheap way to make a heater for the quenching salts? (I can't afford another kiln right now.)
Since I have to quench in oil, is there any advantage to heating the oil to 300+ as opposed to 150 degrees?
Thanks for all the help. As you can tell, I need all the help I can get.
In setting up a high temperature salt bath your salt container can be fairly simple. Schedule 60 or 80 steel pipe is all that is needed. Have a thick bottom welded on by an expert welder. BE SURE IT DOESN'T LEAK! The salts will destroy the elements and brick in your kiln.
The container for high temperature use only needs to be big enough to get your blade in. But, a bigger pot doesn't hurt as it and the salts will have more thermal mass and get your blades up to temperature faster.
A container for quenching, low temperature, salts should be larger to allow for agitating the blade as it cools. I use 6 inch diameter pipe in both my salt pots.
Stainless pipe is not necessary, as the high temperature salt, Nu-Sal, is not corrosive to steel. The outside of the pot will oxidize whether it is stainless or not. In very high temperature applications (1900F) inconel or ceramic salt pots are recommended.
Some knife makers have made low temperature, quenching, systems using old electric water heaters, I have only seen one. It was slow in melting the salts, but it worked. This might be a better question to ask Al Pendray.
When you quench in oil use the temperature recommended by the oil manufacturer. Different oils cool best at different temperatures. If you are using waste or mystery oil a good guess is to keep it in the 150F to 200F range.
Some makers are trying to martemper using oils instead of salts for the quench medium. While this works ok for air hardening steels, it is simply to slow of quench to work well with oil and water hardening steels. Also, sticking a hot blade in 300-400F oil is only asking for problems. You are dangerously close to the flash point of the oil and are very likely to have a fire on your hands literally! The salts aren't expensive, about $00.60 per pound for Thermo Quench. Try to use the real thing if you can.
If you want to approximate martempering using oil, try interrupting the quench. Use the best and fastest oil you can get. Pre-heat it to the temperature recommended by the manufacturer. Then, as you quench the blade try to give it your best guess of when the blade has cooled to 400F. This is usually only a few seconds. Pull the blade out of the quench oil. It should be smoking lightly but not flash. Let the blade cool to room temperature in still air and temper as usual. It isn't quite martempering, but it works pretty good.
I would like to get your opinion on different sharpening stones. I need to buy a set and want to get the best that I can.
The options that I know of are:
1- Japanese water stones
2- Arkansas stones (I found a good supply of large [3-1/2" x 14"] best quality Arkansas stones)
3- Norton stones
I like the water stones, as they are very clean. I am leaning toward the water stones and getting a black (surgical) Arkansas stone for finishing the edge prior to stropping.
I am also thinking about getting a 2" x 72" leather belt for finish honing (using 10,000 grit "powder" supplied with belt).
Thank you for your question. The subject of sharpening and stones is one where you will find many different opinions. The tools and techniques used will vary depending on the type, steel, hardness and edge geometry of the knife. This is really a subject better covered with an entire article. Here, I will just stick to my preferences for sharpening stones.
For most uses, I generally prefer Spyderco ceramic stones. The three available grits are useful in everything from repairing a badly damaged edge, to fine finish work. Spyderco calls their three stones medium, fine and ultra fine. I'm not sure why this is. The medium stone is really quite aggressive. The fine grit stone still removes metal quite well, while leaving a fine micro tooth. The ultra fine stone puts a very fine micro tooth on carbon steels.
Which stone you finish with will depend on the specifics of the knife. For many stainless steels you are best to finish on the medium grit. Simple steels, such as 1095 will benefit from the ultra fine.
The ceramic stones last quite well. My set has never needed flattening. That is probably due to the fact that I put the initial edge on my knives with a belt sander. These stones are used dry. When they need cleaning you simply scrub them with detergent and a Scotch Brite pad.
I still use my Japanese water stones, once in a while. They work and cut very well. My only complaint is the hassle of using them. Since the stones are porous. They should be soaked in water before use. You work in the slurry of material that develops as the stone wears. Since the stone wears so quickly you will need to flatten them frequently. This isn't hard to do; it is just a pain. I find that I mostly use the 6000 and 8000 grit stones for very fine work after using the Spyderco ultra fine stone.
I haven't used Arkansas stones in years. I'm sure they would work fine. I just don't have any recent experience with them. I do remember that the black hard stone seemed to polish the metal rather than cut it. I would avoid that one in favor of the Spyderco ultra fine stone or 6000-grit water stone.
I don't have much experience with Norton stones either. Many knife makers tout the India stone as one of the very best finishing stones ever. Rumor has it that Norton is coming out with a line of water stones. I look forward to trying them.
These days, I rarely use a strop in sharpening. A strop is wonderful for developing a polished edge. Yet, my experience is that a finely polished edge is best for shearing type cuts. Since knives are mostly used with a slicing type action, I prefer to leave most of my knives with a very fine micro tooth on the edge.
I hope this helps. Remember that there are as many different ideas on sharpening, as there are knife makers. These are just my current preferences. They are bound to change as I learn more.