Knife Blade Steel: A Primer
There is a plethora of information about knives and knife blade steel available on the web and elsewhere, written by experts far more knowledgeable than I. My intent here is to provide some basic, perhaps rudimentary, information on what qualities you, as a prospective purchaser, ought to look for in a knife.
It goes without saying, although I’ll say it anyway, that the prices of knives are as diverse as the number of knife models and styles available. Do not let price alone be a deciding factor … there are as many great values available for a quality knife as there are overpriced knives of undesirable quality.
There are many factors that influence a knife’s overall quality, and many of those factors are inter-related with other elements of the knife. A well crafted knife, made of good materials, properly utilized and maintained, can last a lifetime, without costing a fortune.
So as a prospective buyer, you must ask yourself what are you going to use the knife for? No knife will do everything; some knives are extremely specialized, while others are great choices for all-around duties. So your first task is to ask what purpose(s) will the knife be used for? Then, when looking at a knife, ask: for what purpose is this knife best suited?
Our task here is to clarify the elements of a knife, and to describe the different options of those elements, and why certain characteristics – especially the knife blade steel – lend themselves better to specific applications.
We will need to isolate the components of a knife, and describe the varieties of options for each of them. We’ll begin with the Knife Blade Steel itself. Future articles will speak to other important considerations such as Knife Geometry, Blade Shapes and Styles, Blade Edge Styles, Folders and Fixed-Blades, etc.
Knife Blade Steel Is the Elemental Building Block
In its simplest form, a knife is a hunk of metal, with a non-sharpened end (tang) that you grasp, and a sharpened end (blade edge) that you use for slicing, sawing, striking, chopping or piercing. We can add a handle to the tang, for more comfortable gripping; we can modify he shape of the knife for more effective handling; and we can add (or more appropriately, not remove from the original stock) areas of flat steel to protect our hands and fingers from sharp edges. And of course, we can shape the blade (ending in a point, or not) and add an edge (or two).
So what makes one hunk of metal better than another hunk of metal? Well, it depends on what you’re going to use it for. Generally speaking, we want a knife to be strong, hard, tough and corrosion resistant. Oh yeah, and sharp too.
Unfortunately, in the world of knife blade steel, you can’t have it all. Mom used to say, “You can’t have your cake and eat it too.” (Which never made any sense whatsoever to me; if I have my cake, I most certainly can eat it. And I will!) But I digress …
Certain properties of steel dictate certain trade-offs: If a piece of steel is extremely hard, it will also be brittle (not tough). If its edge is extremely sharp, it won’t also be strong. If it’s extremely strong, it’s very difficult to sharpen. And all steel (even stainless) is susceptible to corrosion. And so on.
Many thousands of years of research and development have gone into learning how to create better steels. And how to apply that learning into better knife blade steel.
Since the stone age*, we have been “tampering with the tempering” of that amazing stuff we have come to call “steel.” Is it alchemy, is it magic, or is it pure science? Well, methinks it’s a bit of all three!
*For the purists among you, I realize the stone age predated man’s use of metal as ‘tools.’ However, stone-age man used flint and obsidian as tools for cutting, slicing, sawing and piercing, sometimes using the stone as a tip on wood handle, sometimes using the stone as the whole tool.
Why did we choose those particular kinds of stone over other rocks? (Obsidian is actually glass, but back then if I had found it just laying on the ground and picked it up, I would probably have considered it a stone). Because, when chipped and formed into an edge, they are devastatingly sharp — although brittle.
Then we came to learn that some rocks that were harder could be used to hone or sharpen rocks that were softer … and thus the beginning of “knife-ology” as we knife knuts know it today!
A Magical Mystery Tour of Knife Blade Steel
Give It a Name
In the simplest terms, steel is iron, with carbon added to it. Different steels have other elements added in various proportions, but all steel has some carbon in it. Although the amount of carbon in steel is minimal (0.05% to 1.5% typically; sometimes as high as 2%), it is the most important hardening element, and it also increases the strength of the steel. (Note that there is a difference between strength and hardness; more on that later).
Other elements are added to the iron/carbon matrix to produce specific steels with specific qualities. Broadly speaking, we can break these down into Carbon Steel, High Carbon Steel, Alloy Steel and Stainless Steel.
These steels are identified by names designated according to AISI or SAE standards. In the AISI Steel designation system, steels named with “10xx” are carbon steels; any others are alloy steel. In the SAE designation system, steels with letter designations (A-2, W-2 etc) are tool steels. Often, the last numbers in the name closely approximate the carbon content. Thus, 1095 Steel has about 0.95% carbon; 5160 Steel has about 0.60% carbon.
CHROMIUM: Added for wear resistance, hardenability, and most importantly, corrosion resistance. Steels with 13% or more chromium are designated “Stainless Steel,” although no steel is truly “stainless.” All steel will rust and corrode if not properly maintained.
MANGANESE: Contributes to hardenability, strength and wear resistance. Also aids the grain structure; increases deoxidization during the steel’s manufacturing process.
MOLYBDENUM: Prevents brittleness; maintains strength, especially in high temperature applications.
NICKEL: Adds strength, toughness and corrosion resistance.
SILICON: Contributes to strength, and increases the steel’s soundness during manufacture.
TUNGSTEN: Increases wear resistance.
VANADIUM: Contributes to wear resistance and hardenability. Helps to produce fine-grained steel.
Common Knife Blade Steel by Name
Carbon, High Carbon and Alloy Steels:
O-1: A popular steel among forgers (iron-workers, not counterfeiters), as it is considered “forgiving.” An excellent steel, will take and hold an edge well, and is very tough. However, it will rust easily.
W-1, W-2: Reasonably tough, holds an edge well.
W-1 has no vanadium; W-2 has 0.2% vanadium, which helps it hold an edge. Most files are made from W-1.
1095 (and others in the 10xx Series): Among these, 1095 Steel is the most popular for knives. 1095 has the most carbon, and better edge retention.
However, as you progress down from 1095 to 1050, you’ll go from tough to tougher to toughest. So a knife made from 1095 is the least tough (of the 10 series), but its other qualities make up for that.
Also of interest is the fact that swords tend to be made of 1060 and 1050 – sacrificing edge holding for superior toughness. 1095 is a reasonably priced, well-performing steel; it contains only two alloying elements: 0.95% carbon and 0.40% manganese. As such, it rusts easily, but it can be a perfectly good knife if properly maintained. Ka-Bar knives were usually 1095 Steel with a black coating.
A-2: A2 Steel is well-known for its great toughness and good edge retention. Its toughness lends it to being a great choice for combat knives.
L-6: Used for bandsaws, L-6 is a very tough steel that holds an edge well, but rusts easily. If well maintained, L-6 may be one of the best steels for knives, especially if toughness is a concern.
M-2: Considered a “high-speed” steel, M-2 is used in industry for high-heat cutting jobs. It holds its edge extremely well. It is tough, but not as tough as some of the tougher steels in this section. But it is still tougher than stainless steels, and it holds an edge better. Of course, it rusts easily. As always, maintenance is key.
5160: Known for its outstanding toughness (like L-6), it is often used in swords. Its added chromium contributes to its hardenability. When used for swords, where toughness is desired, the steel will be hardened only into the low 50s on a Rockwell scale (Rc). But if intended for use as hard-working knives, the steel will be hardened to near 60 Rc: thus harder, but less tough. Its versatility in this regard may explain why it is such a popular steel, especially among forgers.
52100: Similar to 5160, but with a higher carbon content, it will hold an edge better. But is is less tough than 5160. 52100 is popular for hunting knives where the user is willing to sacrifice a bit of toughness for better edge holding ability.
D-2: With its fairly high chromium content (12%), D-2 is referred to as “semi-stainless.” It is more stain-resistant than other carbon steels, but does not have the 13% chromium needed for the official accepted stainless designation. It is not as tough as some of the other carbon steels; however it has excellent edge retention.
The following steels are considered “Stainless Steel” because they have at least 13% chromium. Bear in mind, that all steels can rust. “Stainless” does not mean stain-resistant or stain-free; think stain-less as opposed to stain-more.
There is no true consensus on exactly what percentage of chromium constitutes “Stainless.” The standard in the knife world is 13% or greater; but ASM Metals Handbook says “greater than 10%.” Other sources cite different percentages.
Additionally, the alloying elements included in the melt influence the amount of chromium necessary to achieve “stainless” results. A lower chromium percentage can, with the right mixture of other elements, produce a steel that is as “stainless” as one with higher chromium without the alloying elements. The magic of alchemy …
420: Because 420 contains less than 0.5% carbon, it is extremely soft, and will not hold an edge well. It is, however, very stain resistant, and so is frequently used for diving knives or other uses in and around salt water. It is also used for very cheap knives, as it is too soft to be a good choice for a utilitarian knife. (Late night TV, anyone?)
440A, 440B, 440C: The carbon content of the 440 series rises in order, from A (0.75%) to B (0.9%) to C (1.2%). All three resist rust well; 440A is the most rust resistant and 440C the least. 440C is considered an excellent, high-end stainless steel, and is usually hardened to 56 to 58 on the Rockwell scale (Rc). The 440 series is quite common in everyday knives, and the general consensus is that 440A is just good enough for everyday use, 440B is very good, and 440C is excellent.
AUS-6, AUS-8, AUS-10: These are Japanese steels, and quite comparable to the 440 Series (see above). AUS-8 has become quite popular, but will not hold an edge like ATS-34. It is, however, a bit softer and may be a bit tougher. AUS-10’s carbon content is just about the same as 440C, but has less chromium so it will be a bit less rust-resitant; on the other hand, it’s apt to be a bit tougher than 440C. All 3 of the AUS Series have added vanadium, which will improve wear resistance over the 440 Series.
ATS-34, 154-CM: Both of these are exceptional steels — perhaps the premier stainless. ATS-34 is a Hitachi product; 154-CM is American made. Both can be hardened to about 60Rc, still hold an edge and be very tough even at that hardness. Neither are quite as rust resistant as the 400 Series, so again, maintain your knife and you’ll be a happy camper.
ATS-55: This is very similar to ATS-34, but the molybdenum has been drastically reduced, and other elements added. Moly is very expensive, and actually not essential to knife steel, so ATS-55 may be a steel that performs as well as ATS-34, and yet be significantly less expensive.
BG-42: Similar to ATS-34, but with twice the manganese, and 1.2% vanadium. These additions will provide better edge-retention than ATS-34.
GIN-1, G-2 A: A very good stainless steel, contains slightly less carbon, slightly more chromium and much less molybdenum than ATS-34.
Knife Blade Steel Composition Tables
Stainless Steel Composition
(Carbon Steel, High Carbon Steel, Alloy Steel)
Non-Stainless Steel Composition
|Hitachi Super Blue Steel||1.40-1.50||0.20-0.30||0.30-0.50||—||0.50||0.30-0.50||2.00-2.50||—||62-64|
Our sincere thanks to AG Russel for his meticulous work on the data presented in these tables.