I was first introduced to materials science during the Chemical and Environmental Technology program at the British Columbia Institute of Technology (BCIT). Upon graduation, I began a job as a Corrosion and Materials Engineering Technologist. The information I utilized to make my own knife, I will pass along to you in this article. It is my hope that it may prove useful to you the next time you wish to purchase a blade.
I often hear the question, “what is the best steel to make a knife out of”? With so many options on the market, and so many manufacturers claiming to have the best possible steel, it is a very confusing consumer landscape. So here is what you need to know to help you make an informed decision.
I can tell you right now, there is no such thing as the steel, to make a blade from. There are a huge number of options, most of which are indiscernible to the average user. A few do stand out above the crowd, but in all of those cases you will pay dearly for the honor of owning one.
To understand what would make a particular knife blade material superior to another, you must understand materials science. Some say you must understand steel, but in reality, steel is not the only material to make a knife from. As such, you have to increase the scope of your knowledge. Steel is required as a primary component of a blade in order to achieve a crystal structure known as Martensite. This structure is our ideal general purpose blade making material. However, as in the case of a purpose-specific blade (like a skinning knife), there are materials that will perform vastly better, at the expense of utility and usually a much higher cost. In this case, I am referring to a ceramic blade which will hold an edge easily ten times longer than a steel edge, will never corrode, and will break the moment you do anything that attempts to bend it sideways, or drop it on a hard surface.
We must keep in mind, there are factors to steel composition that go beyond just what a material is made out of. Two identical pieces of steel, alloy-wise, can have considerably different properties based upon their heat treating, and post-production processing. It is a simple thing to take two identical pieces of carbon steel and quench one into a Martensitic phase structure (which is almost as brittle as glass), and anneal the other into a ferritic phase structure (which would bend and stretch considerably before ever breaking).
These structures can also be achieved in most stainless steel alloys, some requiring much more effort than others, by the addition of various elements into the alloy. This is where terms like air hardening, oil quenched, quenched and tempered come into play. These names are referring to processes performed on the steel, usually once it’s been shaped, and the majority of any grinding has been finished on it. Each manufacturer will have their own way of achieving the proper alloy crystal structure within their steel, and some are better than others. This is why proper heat treating is essential to a good blade.
With that said, we can narrow down the properties most important to a blade rather quickly. Each of these properties will be more or less desirable depending on what you want your knife to do (will it be a utility knife, a skinning knife, or a combat knife). Those properties are: strength, toughness, hardness, and wear resistance.
*In a study of materials, strength and toughness are very different things and must be considered each on their own merit*
Strength pertains to the ability of a material to literally hold itself together under load. For steel, we typically look at two things- Ultimate Tensile Strength (UTS), and Yield Strength (YS). Strength is determined by placing a piece of material into a machine that can pull in opposite directions with incredible force (thousands of kilograms worth in order to test steel). The UTS test typically involves placing a piece of steel into the machine and pulling on it until it literally snaps in half. The amount of force required to achieve this is the UTS. The information more pertinent (in my opinion) to a blade is the YS. This value tells us how much force can be applied (again, in opposing directions) before the material undergoes plastic deformation. As in, how much force can it take before it cannot return to its original shape. The higher the YS, the more stress that can be applied to the edge of your knife before the thin, sharp, edge will bend under that applied force.
Toughness of a material indicates its ability to withstand a force without fracturing. Something with high toughness will absorb an impact from a hammer and deform under the blow, but not crack. Toughness is the opposite quality to brittleness. A knife of high toughness will not chip along the blade when you strike a bone, or rock with it. When undergoing tensile testing, a tough material will stretch before severing into two pieces, which provides insight into a blade’s likelihood of bending before snapping.
Hardness of your blade will determine its resistance to bending. The harder something is, the harder it is to get it to flex, and the more likely it will fail under a laterally applied load (think of putting your knife in vice and bending it over sideways). The harder your knife is, the harder it will be for you to sharpen it to a good edge, but the better it will hold that edge once applied. It will also most likely be susceptible to chipping along that edge if it is overly hard. Hardness in steel is initially due to the formation of the Martensitic phase structure and is then typically increased as the result of hard ceramic carbides formed in the metal matrix of your blade, due to the addition of appropriate alloys.
These carbides are very hard, and very brittle, so a good knife will have lots of very small carbide structures dispersed throughout the steel of your blade (like raisins in a loaf of raisin bread on a microscopic scale).
Wear resistance is the primary property involved in edge retention of a sharp knife, and is dependent on all three of the previously noted properties. This arises from a blade’s need to withstand a variety of forces acting upon it (mainly friction), while you force it through any matter of substances. The ability to hold very tightly to a thin segment of metal as it encounters bone, sand, or other grit, comes from a combination of strength, toughness, and hardness. A significant contributing factor here is (again), the presence of ceramic carbides. Chromium carbide, and vanadium carbide are typically seen well dispersed in the matrix of a good blade. This requires an excess of carbon, and chromium\vanadium in the metal alloy, without there being too much of any one. Too much carbon can lead to a host of issues including sensitization, or problems like spheroidization. Too much chromium or vanadium typically causes issues with regards to grain structure or brittleness. Balance here is key.
There are a number of factors that a knife maker has to take into consideration on top of these four properties that you won’t be privy to. The heat treatment of a blade can, and will, drastically affect the properties of the material. Grain size of the crystal structure in the metal will be very important in determining the blades ability to react to stress. Inclusions, or impurities in the steel, will create weak spots that are prone to failure\fracture. Chinese steel is a great place to find sulphur in steel that doesn’t belong there. Unfortunately, you have no access to that information unless you’re inclined to purchase a blade, then take it your materials analysis lab, and do a metallographic examination utilizing etching acids and metallographic analysis techniques.
Typically, you get what you pay for, but are required to take it on faith. There have been a great deal of examples over the years of companies producing less-than ideal blades with the consumer none the wiser. Other than wondering why their knife needs to be sharpened so often, or why it snapped so easily under stress.
Having read through all of that, I hate to say, you’re really no closer to knowing what an ideal blade would be made out of. As I said earlier I don’t believer there is one. Most of the knife steel alloys are so similar in their properties, the regular user of a general purpose knife will not be able to tell much of a difference. Unless they encounter a very poor material, and a very good material to compare directly. It all comes down to personal preference, and what you intend on doing with your knife.
An expensive S30V blade will typically satisfy the most discerning of consumer, as this material was developed specifically for the cutlery market. Although chopping through dirty blocks of wood to make a fire probably wouldn’t be the best use of this investment. High carbon stainless steels meet the listed properties in most categories, but in some cases fail rather spectacularly due to a number of factors. Tool steels is another place to find hard, wear resistant blades, with desirable properties. However, they can be very difficult to sharpen well, due to the significant amount of carbide throughout the material. The very same thing making them so effective at cutting through other steels. Brittle failure can be a concern with tool steels, as they are more likely to snap than bend.
For those that pay keen attention to their blades, and sharpen them themselves on a regular basis, I would imagine you have a favorite for any number of good reasons. For the rest of you, I believe the best blade you can get when considering overall quality of a knife, against price, is a carbon steel blade. Ask any Marine about their Ka-Bar for a good reference, as those knives have a very significant following amongst their users going back to the second great war (WWII). I personally use a 1018 carbon steel knife (that I made) as my general purpose blade. My skinning knife is currently a CRKT Bez Tine, and I pair those two with a Browning 814 as my backup blade.
Should you choose to purchase a carbon steel knife, you have to keep in mind that carbon steel rusts. So use it, and then dry it as soon as possible, also it won’t like salt water or acidic foods. If exposed, a quick rinse (in your own spit if necessary) followed by a quick dry, is really all that’s required. Carbon steel has been used since the Iron Age. Every old knife, and sword you read about in the history books will have been a poor comparison to the quality of carbon steel blades available today. The best part? Aside from having very high marks in the four categories listed above, carbon steel blades are cheaper than an equivalent stainless option. You get a lot more than you pay for with one of these, and you really just need to look at your knife once a day while in the field to ensure you are maintaining it.
This was a lot of information. Feel free to ask any questions in the comment section below.
Thomas James served with the 1st Battalion Princess Patricia’s Canadian Light Infantry from 2003 to 2007, including deploying to Kandahar, Afghanistan in February of 2006 in support of Operation Archer. He graduated from the Chemical and Environmental Technology program at the British Columbia Institute of Technology in 2012. Currently he is working as a Corrosion and Materials Engineering Technologist in British Columbia. Outside of work hours he enjoys hunting, fishing, skiing, and science.