The Ultimate Guide to Knife Steel
There are a number of different determining factors that go into denoting the qualities of a folding knife. From handle materials, to deployment, to size and shape, to locking mechanism, the margin for description is tremendous. Perhaps the greatest and most confusing metric regarding pocket knives is, however, blade steel. The type of steel is widely though of as one of the most important factors that goes into a knife's makeup, but it's also one of the least well identified. And there is good reason for this. For starters, blade steel denotations follow no standardized pattern. That means, regardless of the composition, HRC rating, or otherwise, the name of the steel does not actually have to represent anything at all. It just has to be distinct from the names of other steels.
And that causes problems. If you aren't an expert on the vast number of knife materials, chances are the random combinations of numbers and letters aren't going to mean anything to you at all. Based on name alone, you likely would not be able to tell the difference between, say, AUS-8 and 8Cr13MoV. But don't feel bad about that, because those designations don't really say anything about the qualities of those steels. In fact, they might as well be called George and Philip.
Sometimes, parts of the steel names do hold meaning, but because there is no industry standard for how those meanings should be incorporated into the name of the steel, the point is moot. Though one blade material may be a literal acronym for the parts that go into it, the next could just be named after the person or company who created it, and the next might just be a random number. To be perfectly clear - when looking for an everyday carry knife, you're far better off looking at the other metrics that describe the material itself.
Metrics
Hardness: A measurement of the Rockwell Scale, this is the only metric with a true numerical value. This is determined via a standardized machine test that uses pressure to forcefully indent the material in question. The indent depth is then measured and assigned a corresponding rating. Knife steel hardness is, most often, measured in the Rockwell "C" Scale (HRC, alternatively). This number designates the overall strength of the blade steel in regards to its resistance to pressure deformation. It is important to note that higher rated steels are harder to apply an edge to and tend to be more brittle.
Edge Retention: How well a blade resists becoming dull through repeated use. Softer materials do not hold edges very well and they can dent, but they are very easy to sharpen. Harder materials can hold their edge through more, but they are much more difficult to get sharp again and are prone to chipping - which is harder to fix than denting.
Durability: This includes both general toughness and resistance to wear. Toughness can refer to a blade's resistance to chipping or cracking under heavy use, as well as the ability of the blade to flex without breaking. Resistance to wear refers to a blade's ability to withstand abrasion and/or adhesion over time. Abrasion occurs when a hard rough material rubs against a softer smoother material causing a loss of mass. Adhesion occurs when friction between two surfaces causes displacement of material from one surface to the other.
Corrosion Resistance: A blade's ability to resist chemical or elemental breakdown, such as rust, which can be caused by prolonged exposure to salt, water, abrasive/acidic chemicals, general humidity, or any combination of these things over time. Though the name would suggest otherwise, stainless steel is not actually stain-proof, just resistant. So, even a stainless steel blade can - and will - corrode if the conditions are right.
As things are, there is no such thing as a steel which rates as high as possible throughout all of these categories, no matter how much money you are willing to spend. Unfortunately, these metrics require a trade off, on some level. A knife whose blade rates extremely high on the Rockwell Scale isn't going to have a high level of overall durability. Though the steel may be hard, it will also be brittle, prone to cracking and/or chipping, and be difficult to sharpen. Conversely, a softer metal will not hold an edge as well and might dent, but it can be sharpened easily. And, as a general rule, a higher corrosion resistance means worse edge retention. Unfortunately, until leaps and bounds are made in the world of knife steel, this is the way things are.
Elements
Don't let anyone fool you; in order for something to be considered steel, there are two elements that must absolutely always go into it: iron and carbon. Other things can be added to it to create a number of various alloys with different benefits - and drawbacks - but both of those elements must exist within a material's makeup in order for it to actually be designated as a steel. It's quite literally the definition.
An alloy, by contrast, simply means a substance made by combining and fusing a metallic element with at least one other element. No pure metal can be considered an alloy. Alloys are a great way to add together the benefits of two - or more - elements, but you inevitably also combine some portion of the drawbacks. It is important to note that the small amounts of these elements added to the blade steel does not necessarily alter the color or look of the blade. The following is a list of common elements and terminology that goes into making knife steel and steel alloys, their definitions, and some of their benefits and drawbacks.
Alloying Element: Any element added in specified amounts to a base metal.
Iron: a strong, hard, magnetic metal and the base necessary element in the creation of steel.
Carbon: An organic nonmetal, the key component for life on Earth, and the second necessary element in the creation of steel. All steels, by definition, are carbon steel on some level, although they are not necessarily called carbon steel unless the carbon content is high enough and/or the other alloying elements do not exceed a certain amount - this depends both on the other elements, as well as the percent of which they make up the steel.
Chromium: A hard white metal which is corrosion-resistant and adds to toughness. The primary alloying element in stainless steel. A steel alloy requires a minimum 10.5% chromium content in order to be considered truly stainless, but most knife makers set their threshold around 14%.
Cobalt: A hard, shiny, silver-white metal. Increases strength of the blade.
Copper: A reddish brown metal. Adds to corrosion resistance and durability.
Manganese: A hard gray transitional metal. Adds to overall hardness. Can cause additional brittleness.
Molybdenum: a brittle silver-gray metal. Adds to overall hardness. Can reduce durability.
Nickel: A silver-white metal. Adds to overall toughness and can increase corrosion resistance.
Niobium: A silver-gray transitional metal. Adds to strength and toughness.
Phosphorus: A poisonous combustible non-metal. Can increase strength, but also increases brittleness.
Silicon: A semiconducting nonmetal. Contributes to strength.
Sulphur: A yellow combustible nonmetal. Increases machinability of the blade, but lowers overall toughness.
Tungsten: A hard gray transitional metal. Increases durability.
Vanadium: A hard gray transitional metal. Increases hardness and durability.
Common Varieties
There are quite literally hundreds of different kinds of steels and, as we mentioned before, there's no real system to the way that they are designated. The numbers and letters - upper or lower case - don't necessarily have to be in any specified order. They don't even have to mean anything. The only necessity is that they cannot be named the same thing as a previously existing designation. Many apparently related designations are simply the result of a company's decision to have a formulaic process by which they name their steels.
There are, however, a few across-the-board constants in regards to the prefixes and suffixes of different kinds of steel. For example, stainless steel - surgical steel, alternatively - must always meet the minimum of 10.5% chromium content. Inox is simply the international term for stainless steel. Damascus steel - another term that floats around the knife world - is a type of blade metal made by layering, forge welding, and folding together different steels. It has a distinct "oil slick" swirling patterned look to it and is used primarily for aesthetic purposes in collector knives.
Powder metallurgy is a name for a number of different processes by which materials that are otherwise impossible to melt down or otherwise form are turned into a powder for use in metalworking. It is widely used in the tool industry, as it drastically lowers manufacturing losses.
Keep in mind that, at the end of the day, there's not really a comprehensive guide to knife steels. New ones are always being created and added to the list and different versions of previously existing steels are being developed therein. The premium "super steels" of today could be considered low-end a few years from now, so it's impossible to create a comprehensive list without it being exhaustive, as well. As always, it's good to do a little research into the specific type of steel from which a knife you may want is constructed. The following is a list of currently popular knife steel varieties, grouped by set, which you may run into when looking for everyday carry folding knives:
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400 & AUS Series
Generally speaking, the higher the first three digits in the 400 series, the greater the overall toughness to the steel. 420, probably the most common, is on the lower end of the spectrum in regards to hardness, but it is more corrosion resistant and easy to sharpen that some of its higher numbered counterparts. 420j is, for all intents and purposes, pretty much the same as 420. 420HC is the high carbon variety, which still has corrosion-resistant properties, but also has an increase in hardness. Versions with a letter after the number indicate an added element, but the letter is not necessarily representative of the element. For example, 420F has added chromium. 440 - A, B, and C (which have increasing carbon content, respectively) - is a generally tougher variety of stainless steel, but does not exhibit the same corrosion resistance. None of them are company specific.
The AUS series is basically the Japanese-made version - owned by Aichi Steel - of the 400 series, with just a few slight differences. AUS-6 is equivalent to 420, whereas AUS-8 is similar to 440B. Overall, both series varieties of steels are very popular for their wide availability, low cost, and relative quality, but their differences are nominal to all but the most stringent of knife experts.
10-Series
The 10-series variety of steels are the most popular line of carbon steels and do not belong to any specific company, each named for the carbon content of the steel - for example, 1095 has a carbon content of 0.95% carbon. 1095 is the industry standard for combat knives, 1060 is common for swords, and 1070/1075 can typically be found in machetes and large cutting blades. These carbon steels tend to be very wear- and chip- resistant, but do not ward off corrosion very well. Still, they are great for more heavy-duty use.
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Sandvik
Sandvik steels are one of the proprietary varieties that somewhat follows a denominational theme. Most of the knife steels owned by Swedish company Sandvik are laid out as follows: one or two digits, a letter, two more digits, and then - sometimes - another letter. 12C27 stainless steel is their main knife steel and is very well rounded, offering a good balance between quality and value. 13C26 is their version of 440A, but sacrifices some corrosion resistance as a trade-off for greater toughness. They then improved upon that version and created the more popular and higher end 14C28N, which is more corrosion-resistant thanks to the addition of nitrogen.
Cr/MoV Series
Essentially the Chinese version of the 400- and AUS-series steels, but with slight variations. The most popular version of this steel is 8Cr13MoV. It is comparable with AUS-8, but has a higher carbon content and, therefore, greater strength. These steels are owned by a company called Ahonest. They offer good quality at low cost.
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CPM
CPM - which stands for Crucible Particle Metallurgy - is a proprietary method - owned by Crucible Industries - of making very high quality tool steel that is both durable and tough. It is also very expensive and, therefore, impractical for your average EDC folding knife. This family includes - in order of best-judged ascending quality and price - S30V, S35VN, M4, 20CV, and S90V. As these steels vary on almost molecular levels, your average knife user will not be able to tell much difference between them, honestly.
Other Notable Steels
D2: A non-company specific "semi-stainless" steel. Contains 13% chromium for corrosion-resistance and is a very hard steel with great edge retention. It is, however, fairly difficult to sharpen.
H1: Owned by Japanese company Myodo Metal, H1 offers excellent resistance to corrosion and is essentially rust-proof, making it extremely popular for diving knives. However, it does not have great edge retention.
Elmax: Originally a product of Uddeholm, a Sweden-based company that has merged with Bohler, Elmax is an ultra-premium powdered steel alloy made with chromium, vanadium, and molybdenum. It offers great wear- and corrosion-resistance and high edge retention.
Niolox: A high-quality stainless steel alloy made with vanadium, molybdenum, and niobium. Offers great hardness and edge-retention whilst still remaining corrosion-resistant.
Sleipner: A high alloyed stainless tool steel, made by Uddeholm, which offers high hardness, wear and chipping resistance, and is easily machined. It's made with silicon, manganese, molybdenum, and vanadium.
M390: Made by Bohler, of Bohler-Uddeholm, this stainless "super-steel" offers excellent corrosion resistance, hardness, and wear resistance. This alloy is made from vanadium, molybdenum, and tungsten.
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The Final Word
The steel world is ever-evolving and new alloys, procedures, and versions of previously existing steels emerge all the time. Though it can seem a daunting task, you can usually find some kind of information regarding the make-up and common usage of these steels on their respective company's website. If you aren't certain of the qualities of a steel, just look it up. There are also dozens of message boards from which you can garner advice, if you still aren't convinced.
Just keep in mind that quality of steel is just a single measurement in the overall value of any given knife. And, if you're looking for a good EDC pocket knife, you don't necessarily need the ultimate custom treated and tempered steel in order to have the best knife - or knives - for you. Technology has advanced to the point where, if you're buying from a reputable source, the differences between decent and uber-high quality steels will likely not matter as much as some of the other factors that make up your ideal knife. Even claiming that there is a "best steel" is incorrect, as all existing steels require some kind of trade-off - whether that be hardness vs. longevity, corrosion-resistance vs. edge retention, or simply cost vs. budget. Find the compromise that works best for your needs.
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