TCF -- Knives and Steel

Our Thoughts on Knives and Steel

Contents

Opinions and Facts

Everybody's got an opinion. We recognize that you probably have some. We certainly do. We'll share some of ours along with some facts about knives and steel.

If you find our opinion differs strongly from yours, we're more than willing to listen to yours. Opinions are, after all, formed through experience and your experience is almost certainly different from ours.

Facts are facts and if you find something here that appears to be stated as a fact and that you believe to be incorrect we'd certainly like to hear about that too.

Having said all of that, we will give you our take on Knives and Steel.

Context -- Pragmatism and Hard Reality

Life is full of trade-offs. Knives and steel are not exceptions to this. A knife is both a tool and a work of art (if you think of a knife only as a work of art you might have come to the wrong place, but we'll nevertheless try to convince you otherwise). These can but need not imply a competing set of priorities with regard to materials. We believe that first and foremost a knife, like any tool, must be useful and secondarily it's really nice if it is also pleasing to look at and doesn't take much care and feeding to keep it that way.

As regards "care and feeding" you need to understand that we, tools and firearms go back a long way and we're accustomed to occasionally cleaning and applying a preservative to our tools (firearms and knives are tools too). If you really like a tool it can be an enjoyable experience. If the last two sentences seem weird to you, again, you may have come to the wrong place.

In our opinion a good knife has (at least) the following characteristics:

Primarily, it's a cutting tool and to be a good one it must
1. feel comfortable in the hand of the user
2. retain its sharpness long enough to get a reasonable amount of work done before needing to be resharpened
3. accept a sharp enough edge to cut what it is intended to cut without undue force being needed
4. be durable enough to stand up to its intended use for a long time
5. not weigh more than necessary to satisfy the preceding requirements
Secondarily, it's a work of art and to be a good one it must look like one to the person who owns it.

Feeling comfortable in the hand of the user boils down to proper balance and thoughtful design within the limits imposed by the dimensions of the user's hand. We need to know what the dimensions of yours are and something about what feels comfortable, in the general sense, to you in order to make a knife for you (see Custom Work).

We usually make knives as light in weight as possible. Keeping the weight down, along with other concerns and issues, has led us to our choices in steels. It's rare for a knife to actually need much weight to do its job. A lighter knife is quicker and generally less tiring to use and carry. Even really big blades, used for chopping, don't need to be very heavy because sharpness, the right edge geometry and thinness of the blade can add up to a really good big honking camp knife that won't result in your needing suspenders to keep your pants up. The same characteristics with a somewhat different edge geometry can add up to a really good hunting knife that doesn't weigh a lot more than its sheath. We don't know how you feel about it but we find that when a knife's weight with its sheath approaches a pound it stops being unnoticed when carried.

Now we come to some other important trade-offs in good knife design. Namely, sharpness and edge retention in the intended use. There are a number of factors. One is the composition of the steel and the method used to shape a blade from it. Another is the heat treatment process used to bring the steel to the right hardness in the right places. Last, but certainly not the least important, is choosing the right kind of edge for the work to be done. We'll get to the steel composition issues last because it's important to understand something about the design issues (and a few more of our opinions) first.

Shaping the Blade

There is a very good reason to forge steel to shape rather than simply machining or grinding it. It's the reason that the best rifle receivers and knives and many other things are made this way. A forged steel product can be lighter in weight than one produced by just machining and grinding from a cast or rolled steel. This is because forging alters the structure of the steel.

Steel has structure which is composed of "grains". The grains are composed, usually, of one crystaline phase of the steel. While it isn't practically possible to align the crystals or grains in any particular way, it is possible to produce an overall pattern of grains that is oriented to, or "flows" with, the shape of the object being produced. This is what forging does.

The grains in steel are much stronger than the boundaries between them. Obtaining a small grain size with an overall grain structure that is oriented to the shape of the blade results in a much stronger blade than otherwise. Careful forging and heat treatment are required to produce this result.

For the steels we have chosen to use, forging the blade always produces a better result than stock reduction. The heat treatment process we use always produces a better result for these steels than can be obtained from commercial heat treatment establishements.

Hardness

There is, from our point of view, a two-fold concern here. The issue isn't just edge hardness. If the whole blade is "edge-hard" then the cross-section of the blade must be thicker to make the knife sufficiently durable. The steels we prefer to use are actually remarkably flexible in thin sections; when edge-hard, however, there are limits. In our opinion it's better to have only the edge (1/3 to 1/2 of the blade's depth) edge-hard with the remainder of the blade at more of a "spring-like" hardness (see Quenching Methods and Steels. This makes it possible for the blade to be much thinner and lighter than it would need to be if all of it were edge-hard.

Actual edge hardness is another issue about which folks will have their own opinions. These are often quite strongly held. Our opinion is that for the steels we use (and paraphrasing Albert Einstein) the hardness should be as close to 60RC as possible without compromising durability or sharpenability but no closer. This works out, in practice, to an edge hardness of 57-59RC which is plenty hard. All of the steels we use will hold an edge well at this hardness and are reasonably easy to sharpen.

Sharpness

How sharp is plenty sharp? Well, a razor blade or a surgical scalpel is certainly plenty sharp but they have a narrow range of practical uses. Working knives are designed for ranges of uses as well and their ranges are relatively broader. Steel composition, blade design (especially edge geometry), hardness and the grit to which the edge is polished are characteristics that directly affect how well a knife performs as a tool.

Edge Geometry

The right edge geometry is essential for a knife to perform well in its intended use. At one extreme you have fine, flat edges and at the other you have "sabre-ground" (markedly convex) edges. The key to good cutting performance is to pick a point between the two. Razor blades and surgical scalpels have a very fine flat-ground or stoned edge. They're terrific on fairly unresistant materials. Axes, sabres and other chopping tools have a pronounced convex edge. The convex geometry of the edge produces a very thick cross section right behind the cutting edge which greatly decreases the tendency of the edge to chip from impact shock. Axes can be very sharp but they don't make good slicers because they need a good deal of force behind them to cut very deeply. Most working knives need some combination of a razor-like (thin) edge and an axe-like (heavier and convex) edge . A fine convex edge geometry where the edge bevel is fairly shallow relative to the blade thickness and the last 1/8-1/4 inch of the bevel has a slight convex contour is a good compromise for general use. This kind of an edge is retained better on tough materials like wood, cardboard, leather and hide and is less likely to chip when you take a whack at something with it than a thin flat edge while sacrificing a bit of the thin flat edge's cutting ability on unresistant materials.

You may have noticed an important (and intentional) omission in the previous paragraph. The term "hollow-ground" or "concave edge" does not appear anywhere in it. There are two reasons for that. The fact is that hollow-ground edges tend to "wedge up" when you attempt to slice deeply into something or "dive" into the work when you attempt to shave the edge of something with them. Our take on the whole hollow-ground thing is that it's a symptom of the use of the stock removal method to produce a very fine razor-blade-like edge without needing to flat-grind a really thin blade -- and the fact that some people seem to think the pronounced grind-line is really cool. As we've noted elsewhere (see Forging, Heat Treatment and Finishing) we don't "grind in" any of the blade geometry. We also don't put hollow-ground edges on anything. In our opinion, the hollow-ground/concave edge is a solution to a production, materials or aesthetics problem and has no place on a working knife.

Knife Steels

To state the immediately obvious, knives are cutting tools. So a good knife steel needs to take a good edge and hold it well. However, most knives are not highly specialized cutting tools like drill bits, chisels, taps, reamers, etc. Most knives get used for a variety of chores. Even hunting knives (or perhaps especially hunting knives) get used this way because many hunters carry only one knife and many are as likely to use it for whatever cutting needs to be done as they are to use it only for field dressing, quartering and skinning. Generally speaking, knives need more shock strength than most specialized cutting tools. So it's important to consider more than just maximum hardness, sharpness and edge retention when choosing a steel for making knives. We're certainly not alone in having thought about this, though it's surprising how many knife makers nowadays appear to have discarded the toughness consideration in favor of obtaining greater hardness. Finally, we do not think that most tool steels are particularly good knife steels because most of the currently available tool steels that can be used to make really good knife-like tools are notably lacking in shock strength and toughness.

Finding the right balance of characteristics (always a compromise) for a given knife design is the first step in making a good knife. To this end we have settled primarily on two steels, 5160 and 52100; we also sometimes use 1084. There are many more possibilities than just those but we like to stick with a few steels that are good choices for the kinds of knives that we make. We also think it's a truism that one can be very good at a few things or mediocre at a lot of things. We prefer to be very good at a few.

Non-Damascus Knife Steels

5160, 52100 Steels

The vast majority of the non-damascus knives we make are made from new H-grade 5160 (a relatively clean chrome alloy spring steel) or E52100 (an aircraft-grade bearing steel). 5160 is also commonly used for automotive suspension springs, bumpers and floor pans. 52100 is frequently used to make cutting tools for non-ferrous materials. Good ball bearings are almost all made from 52100 while the not-so-good cheaper ones are frequently made from stainless steel.

One might, at this point, ask the question: Why aren't these steels used in making mass-produced knives whether by forging or stock-reduction? The reason 5160 and 52100 aren't (or at least shouldn't be) is that these steels only become superior knife steels when hammer-forged to shape. You can't just jam the stuff in a drop-forge or for that matter simply grind a blade from them and produce a really good quality knife. The steels only exhibit their truly outstanding qualities when forged to shape through multiple heat and forging cycles followed by multiple normalization cycles prior to differential heat treatment with three hardening and tempering cycles along with some sub-zero chilling at appropriate points in the process. The bottom line is that all of this is too labor-intensive for mass production to be practical.

Mass producers of knives don't have bladesmiths on their payrolls and stock removal doesn't involve forging and heat-cycling of the steel. The simple fact is that if you're going to mass-produce a product you want relatively few steps and little or no individual attention to each object being produced. Additionally, a desired result of mass production is relatively low product price. The process required to produce a really good knife from 5160 or 52100 is labor-intensive and not conducive to a low price.

We also make some knives using 1084. It's a carbon spring steel and has many of the good qualities of 5160 and 52100 with a carbon content that approaches that of 52100. On the down-side, being a straight carbon steel, 1084 has little or no chromium in it. Because of that it isn't as tough as 5160 or 52100 and is more susceptible to staining and corrosion. It's still a good compromise for a working knife used by people who take good care of their tools. It's a little easier to forge than 5160, much easier to forge than 52100 and requires a simpler heat treatment process than either of them. 1084 is not as tough as 5160 or 52100 and because of that a blade made with it must be a little thicker/heavier than it would need to be with 5160 or 52100. The "as-quenched" hardness of 1084 is several points higher than 5160 but practically speaking the maximum working hardness of a blade made with it is about the same

Availability of 1084 is becoming a problem due to the last mill that was producing it going bankrupt in 2002. Because of this we've begun using 1075 and 1080 instead. The slightly lower carbon content of 1075 is essentially a non-issue; it's between 5160 and 52100.

Typical Analyses for 5160, 52100, 1084

Note that 1075, 1080, and 1095 are, like 1084, "straight carbon steels" with nominal carbon content of .75%, .80% and .95% respectively (see Steel Information). There are some differences in the additives, however. Notably, there is usually less manganese in 1095 than in any of the others. This has an effect on how deeply the steel hardens when quenched but the effect of this is only seen in cross-sectional thicknesses greater than approximately one inch which results in the effect being absent when using the steel for knife blades.

	5160	52100	1084
Carbon	.55-.65%	.98-1.1%	.8-.94%
Chromium	.60-1.00%	1.3-1.6%
Manganese	.65-1.10%	.25-.45%	.6-.9%
Silicon	.15-.35%	.15-.35%	.15-.30%

Some of the ranges for the alloying elements have widely varying ranges due to the fact that different steel manufacturers use different process control limits and some of them add stuff that others don't. Additionally, all steel has some level of impurities (e.g. sulfur) and some of the alloying elements are there to "scavenge" those impurities so that they don't interfere with the functional quality and forgability of the steel. Manganese is usually added to promote deep hardening and to prevent the formation of iron sulfides from small amounts of sulfur in the steel.

Iron isn't listed because it's the principal constituent of steel and amounts to the percentage other than the alloying elements.

The primary alloying element in all steel is carbon. The amount of it present has more of an affect on the steel than any of the other alloying elements.

The general effects of the other alloying elements present in these steels are:

chromium
promotes deep hardening and air-hardening
1-4% - increases toughness, hardenability, and corrosion resistence
>= 5% - weakens grain boundaries
>= 10% - greatly increases corrosion resistence: manganese
promotes deep hardening
deoxidizes the steel and prevents the formation of sulfides
decreases weldability

Characteristics and Uses for 5160 and 52100

As can be seen from the analyses above, the steels are similar in composition with 52100 having markedly more carbon and chromium. Both of them are excellent knife steels but because of the differences in composition they have different characteristics.

5160 is primarily used in industrial applications for the manufacture of springs and automotive bumpers and sometimes floor pans. In these applications the toughness and ductility of the steel are important and the steel is typically heat treated for a hardness of 38-44RC. In using this steel to make knives we differentially heat treat it for a body hardness of low- to mid-forties RC and an edge hardness of 57-59RC.

52100 is primarily used in the manufacture of balls, rollers and races for bearings, cam rollers and the like. In these applications it is usually heat treated for a hardness of 60-61RC. For knives we heat treat it (essentially) the same as we do with 5160 and usually with the same target hardnesses.

It's hard to say enough good things about 5160. Its a wonderfully versitile steel when differentially heat treated to be good and hard at the edge and springy everywhere else. It will take a very good edge, hold it well and be easy to hone or re-sharpen. Bend it (within reason) and it not only returns to straight but the edge doesn't chip or crack during the proceedings. 52100 shares these characteristics to a great extent, but it holds an edge noticably longer while being a bit less tough.

Speaking of bending, we don't suggest that you bend any knife intentionally just to see how far it will bend, but sometimes knives do get flexed a bit in normal use. We think that it's important that you not have to take a kink out of it afterwards. We also think that the ability to flex in this way provides the user with feedback that is useful in helping them avoid unintentional excesses (abuse).

Characteristics and Uses for 1084

1084 is a carbon steel. The only alloying element in it (other than carbon) is manganese which is added to scavenge impurities and promote hardenability. 1084 is used by industry in the manufacture of automotive bumpers and springs and is an excellent knife steel. It lacks the toughness of 5160 and 52100 and is not as strong in thin sections.

Knives we make from 1084 are a bit heavier (have a somewhat thicker cross-section) than the same knife would be if made from 5160 or 52100.

Sharpness and Edge Retention

Both 5160, 52100 and 1084 all take an excellent edge at 57-59RC. They'll get as sharp as anyone really needs a knife to be.

Given proper forging, heat treatment and identical blade geometry, a knife made of 52100 has noticeably better edge retention than one made of 5160 or 1084. It's also more expensive, taking nearly twice as long to forge, requiring more careful attention to heating and more heats than 5160. It's the best choice if you want a knife that will hold an edge longer, isn't likely to be flexed greatly in use and, the higher price isn't an issue.

For bigger knives and knives that are going to be used for chopping, 5160 usually is the best choice with 1084 being a good second choice, sacrificing a bit of lightness. Don't take this to mean that 5160 can't be used to make a really good small knife. It can be forged and finished very thin, takes a very good edge and is frequently the best choice for a thin lightweight knife (whether small or large) that might see some rather hard use. We frequently make hunting/utility knives using 5160.

Corrosion/Rust and How to Easily Avoid It

In our experience neither 5160 nor 52100 is particulary rust-prone but we do live in a relatively dry climate where the humidity is rarely above 20-30%. Like all steels, these will rust. Some are just more prone to it than others. Even stainless steels will rust, they are just less prone to it than non-stainless steels. 1084 is more prone to staining and corrosion than 5160 or 52100. All you need do with a blade made with any of these steels to keep it from rusting in the worst of climates (continuous salt-spray poses another less preventable corrosion problem) is to treat it like a blued firearm using a good preservative oil, grease or wax. Note that products like WD40 (which is a water displacer but not a preservative) 3-in-1 Oil, motor oil or any simple lubricant oils are not adequate for this. You need to use something that displaces moisture, provides a vapor barrier, and adheres strongly to prevent moisture from getting to the steel for a useful length of time following application (see Knife-Care). This is important and isn't hard to do or expensive. We've seen a lot of firearms, knives and other tools that rusted because the owner did nothing or used a lubricant oil or WD-40 on them thinking that those products would provide adequate protection.

With proper care, a 5160 or 52100 blade won't rust. Even 1084 blades won't rust if properly maintained, though you've got to be more diligent about preservation with them than with 5160 and 52100. Depending on how well they are kept coated with a preservative they may develop a patina over time varying from light to dark gray. If you use a good preservative product on them often enough they will keep most of their "new" appearance indefinitely. Of course, the surface of any knife that actually gets used (no matter what steel it's made from) will get scratched and burnished whether by what it's used to cut, stuff it gets dropped on (or dirt and grunge in its sheath if you put the knife in there dirty).

Tool Steels

Yes, knives are certainly tools but their requirements are usually broader than those of other tools. For instance, most other (knife-like) cutting tools don't need to flex without breaking or taking a set (i.e. staying bent) and they don't need the shock resistence in very thin sections that a knife needs. For strictly rigid cutting tools (drill bits, files, engraving tools, taps, broaches and a zillion others), tool steels are a good choice. Some marking stamps are made using O1 but it's about the only steel you'll see in good ones other than S5 (which is the hands-down winner for that application). In our opinion and because we prefer to avoid excess weight in a knife, they are a good choice for only a very small set of knife designs.

In our opinion, L6 and O1 are the two best knife-steel candidates among currently available the tool steels.

L6 is similar to 5160. It has .1-.2% more carbon and around 1.75% nickel. It is also notoriously finicky about heat treatment, difficult to anneal and needs a salt pot setup for the best results in heat treatment. If we could have 5170 or 5180 (neither of which is apparently being made anymore) we'd probably use them instead of 5160.

O1 is similar in carbon content to 52100 but it has less chromium than 5160 making it less tough than those steels. It usually has some molybdenum in it which increases wear-resistence a bit. The tungsten in O1 is essentially useless in a knife steel. Having said that, the greater carbon content of O1 and the presence of molybdenum in it (adding up to increased edge retention) make it a somewhat better choice than 5160 and 1084 for a limited set of knife designs.

Sharpness and Edge Retention

O1 is the apparent best logical alternative to 52100 among tool steels that can be used for knives and in our experience it does not perform as well as 52100. 52100 has a little more carbon and much more chromium than O1. It holds a better fine convex edge and when heat treated properly outperforms O1. 52100 is probably the overall best knife steel of them all. The only disadvantage 52100 has is that it is a bear to forge and requires much more careful heat control in forging and heat treatment, resulting in a somewhat higher price for knives made from it.

Strength/Toughness

If you need the toughness and springiness obtainable with 5160 or 52100 in a knife the answer is that you simply can't have it in tool steel (with the possible exception of L6). You can optain the same usable strength with a tool steel but you'll pay in weight or a tendency to take a set if flexed. This is because there are two ways to deal with a tool steel's tendency toward brittleness. Make the blade thicker (and heavier), or leave everything but the edge unhardened, or both. Most tool steel blades need to be made heavy enough to not flex in anything like normal use in order to avoid being bent or broken.

Again, life and knives are full of trade-offs and the world is full of opinions. It is our opinion, given the characteristics that a good knife steel should have, that the advantages of tool steels over 5160, 52100 and 1084 as knife steels are insignificant while the disadvantages of all of them (with the exception of L6 and perhaps O1) are show-stoppers. None of the tool steels will perform as well in a knife as 52100. O1 has only somewhat better edge retention than 5160 and 1084 and lacks the toughness of 5160 in all cases. Having said all of that one characteristic of L6 is better resistence to brittleness in extreme sub-zero conditions than just about anything else so if you're planning a trip to Antarctica in mid-winter (or the Moon and plan on being in the shade a lot) L6 just might be the best choice

Why We Don't Use Stainless Steel

We have nothing against stainless steel in general. It is good stuff for a lot of things and a good serviceable knife can be made using some types of it but a stainless steel blade will not perform as well as a 52100, 5160, or 1084 blade assuming the blade and edge cross-sectional geometry are chosen correctly for each steel and the best processes are used in the creation of each.

Stainless steel has one clear advantage and that is, obviously, corrosion resistence. In all other respects the stainless steels that we could use to forge knives aren't as good as 5160, 52100 or 1084 when correctly chosen by application. The only reason for stainless steel knives is that there are applications where it makes sense to sacrifice performance in order to gain corrosion resistence.

Furthermore, it is a simple fact that all stainless steels we could use are inherently weaker than the steels we use because all of those stainless steels have too much chromium in them. Chromium has very beneficial effects in steel when present in the range of 1-4%. However, amounts of it greater than that weaken the grain boundaries which were already the weakest part of the steel. Stainless steels have 10-16% chromium and are inarguably weaker than steels with 0-4% chromium. A stainless steel blade (like a tool steel blade but for different reasons) needs to be thicker (and thus heavier) to be as strong as a blade made from a good non-stainless knife steel.

Some stainless steels are forgeable outside an industrial setting but many (including some of the best of them) aren't. All of them need to be forged hotter than non-stainless steels in order to avoid cracking. This poses problems, particularly in winter, in getting (and keeping) an anvil warm enough to forge stainless steel for more than a blow or two. All steels with chrome in them air-harden to some extent. Stainless steels suitable for forging blades in our setting (elevation 7800ft and a bit chilly at times to say the least), which typically have at least 12% chromium, air-harden to the extent that they are much harder to forge (red hard) than non-stainless steel and are prone to cracking while being forged. Our opinion again, stainless steels have a real advantage in corrosion resistence but that's about the end of the advantages they have for the kinds of knives that we make over the steels we have chosen to use. There are some smiths who forge stainless (some very good and some who just forge a bar out of round stock and then grind from it) but we don't.

You may still think that stainless is necessary. Perhaps you have a really good reason. Whatever the reason, if you really need or simply want a stainless steel knife, we wish you well. Ed Caffrey has been making noise about the potential of S30V and may well be forging with it as you read this. A couple of other makers that come immediately to mind for stainless steel knives are Don Cowles and Gene Osborne. The Custom Knife Directory is a site where you can see the work of and find links to many knife-makers.

page last modified Sat, 06 Mar 2004 09:11:57 -0700 (MST);