Knife Blade Steel
There are two general categories of steel that knife blades are made of- Carbon Steel and Stainless steel. Both of these categories of steel are widely used today due to their unique characteristics. Generally, carbon steel can hold a better edge than stainless steel, but stainless steel has better corrosion resistant properties. There is a tradeoff between corrosion resistance and edge retention.
Carbon Steel is made of iron and a very small amount of carbon. Carbon steel is categorized into four classifications- low carbon (or mild) steel, medium carbon steel, high carbon steel and very high carbon steel. Low carbon steel contains .05% to .3% carbon. Medium Steel contains .3% to .5% carbon, high carbon steel contains .5% to .95% carbon, and very high carbon steel contains .96% to 2.1% carbon. High carbon steels are the most widely used carbon steel for making blades, because once heat treated, they can maintain a good balance between high toughness and the ability to harden.
Stainless Steel is made of iron, a very small amount of carbon and a very small amount of other elements such as chromium, vanadium, molybdenum, tungsten and nickel. When these other elements are added to iron and carbon, the metals’ resistance to corrosion is increased. Varying amounts of carbon and these other elements are added to iron to form different types of stainless steel, called alloys. High carbon stainless steels are widely used for making blades because high carbon content is needed to increase the blades’ edge holding ability.
Powder Metallurgy Steel was developed to allow high wear resistant steel to also have a high toughness. The steel is rapidly solidified into a powder rather than slowly cooled in a large ingot. It is then formed to shape under high pressure and heat. This process decreases the average carbide and grain size, and raises the toughness, edge retention, and grindability compared to steels produced by conventional processes.
Edge Retention: the degree in which a blade can hold a sharp edge.
Corrosion Resistance: the degree in which a steel can resist rusting (oxidation).
Hardness: the degree in which a steel will resist permanent deformation. Blade steels are measured on a Rockwell Scale (example: Rc 56-58).
Hardenability: the degree in which a steel can be hardened by a heat-treating process.
Strength: the degree in which a steel can resist applied forces.
Ductility: the degree in which a steel can flex or bend without fracturing.
Manufacturability/Machinability: the degree in which a steel can be machined, ground, and heat-treated.
Chromium: improves corrosion resistance, wear resistance and hardenability. Steel with at least 13% chromium is generally deemed "stainless" steel. Adding chromium in high amounts decreases toughness.
Cobalt: improves strength and hardness, and permits quenching in higher temperatures.
Copper: improves corrosion resistance.
Manganese: improves hardenability, strength and wear resistance. It also improves the steel during the manufacturing process.
Molybdenum: improves hardenability, tensile strength and corrosion resistance (particularly pitting). It also helps to maintain the steels strength at high temperatures.
Nickel: improves toughness, hardenability and possibly corrosion resistance.
Nitrogen: improves corrosion resistance when used in place of carbon. Nitrogen can function in a similar manner to carbon but offers unusual advantages in corrosion resistance.
Tungsten: improves wear resistance. It is a carbide former. When combined properly with chromium or molybdenum, tungsten will make the steel become a high-speed steel.
Vanadium: improves wear resistance and hardenability by promoting a fine grain structure, which improves toughness and allows the blade to take a very sharp edge. It is a carbide former. Vandium carbides are the hardest carbides.
Common Blade Steels
0170-6 : 0170-6 is the steel makers classification for 50100-B steel.
1045, 1050, 1055, 1060, 1084, 1095 : From 1045 up to 1095 there is an increase in carbon content. The higher the number, the more wear resistant, but the less tough (more brittle) the steel is. 1050 and 1060 are often used for swords. 1095 is the most popular of the 10 series steels for making knives. When properly heat treated, it is a reasonably tough steel, holds an edge well and it is easy to sharpen. It does, however, rust easily. It is a simple steel, which contains only carbon and manganese.
12C27 : Similar to 440A. 12C27 is a Scandanavian Sandvik stainless steel often used in Finish and Norwegian knives. It is a high purity steel that performs very well when properly heat treated. It has good hardenability and wear resistance. It has a higher toughness and corrosion resistance than 13C26 and AEB-L. It has less wear resistance, but higher edge retention than 440C.
13C26 : Similar to AEB-L. It is a Scandinavian Sandvik stainless steel. It has better hardenability and wear resistance, but lower toughness and corrosion resistance than 12C27.
154CM : An American made Crucible steel that has similar machining and grinding qualities of 440C, but has a definite advantage in both hardness and toughness over 440C. Can be somewhat hard to sharpen. Normally hardened to around Rc 60, it holds an edge very well, often better than S60V, and is tough even at high hardness. Not as stain resistant as the 400 series. Because of its excellent edge retention, it is suitable for blades that will endure extreme use.
17-7 PH : - A high corrosion resistant precipitation-hardening, stainless steel. It has a high chromium, nickel and aluminum content. It is used for applications requiring high strength and resistance to corrosion, including salt water corrosion. It offers a good compromise between martensitic stainless steels (heat-treatable) and austenitic stainless steels (non heat-treatable).
4116 Krupp : A fine grained, stainless steel made by ThyssenKrupp in Germany. Due to its high chromium content, it is often used for hygienic and food processing applications, including kitchen cutlery. Its high carbon content gives it a high strength and an edge retention ability that outperforms the 420 and 440 series stainless steels. Other alloying elements contribute to grain refinement. This increases blade strength and edge toughness in order to allow for a finer, sharper edge.
420, 420HC, 420J, 420J2 : The 420 series performs at the low end of the stainless steels. They are tough, due to being soft, and they are very stain resistant, but they are not very wear resistant. They do not have very good edge retention. They are a low cost stainless steel and they machine easily. The 420 series steels are often used on inexpensive and fantasy knives. 420J2 is often used as knife liners and due to its corrosion resistance, is also used for dive knives and fillet knives. 420HC, also referred to as modified stainless, due to its increased carbon, is roughly comparable to 440A. It has a relatively high edge retention compared to the other 420 stainless steels, but it still has a low wear resistance.
425M : Very similar characteristic to 440A.
440A, 440B : The 440A and 440B stainless steels can be hardened more than the 420 series, for better strength. They are also more wear resistant, with proper heat treating, although wear resistance is just getting to the point of acceptability for knife blades. 440B has a higher carbon content and hardenability than 440A. They both have a higher corrosion resistance than 440C.
440C : A very good, high-end stainless steel, usually hardened to around Rc 56-58. It is very tough and has good edge retention, compared to the other 440 series stainless steels, due to its higher carbon content. But it is not as stain resistant as the other 440 stainless steels. It is tougher and more stain resistant than ATS-34 but has less edge retention. Its toughness can be increased with a sub-zero quench process. It was the first widely accepted stainless steel by knife makers. Until the ‘high-tech’ stainless steels came along, it was the most popular stainless steel in the knife industry. It cuts easier than carbon steels, and it grinds much easier than O-1. It also anneals at very low temperature.
440V : Similar to 440C, but does not get quite as hard. It does, however, have better edge retention and is much more difficult to grind.
50100-B : Also known by the AISI designation as 0170-6 steel. It is a good chrome-vanadium steel that has many similarities to O-1, but is much less expensive. It has approximately one third the chromium of 52100 steel. The ‘B’ indicates that the steel has been modified with vanadium, making this a chrome-vanadium steel.
5160 : A spring steel that is similar to 1060, but with one percent chromium to increase hardenability. It is often used for swords and large knives. It has excellent edge retention, wear resistance and toughness, but it is difficult to grind. It performs well over a wide range of hardness. It is a popular forging steel.
52100 : A ball bearing steel with similar characteristics to 0170-6 but with three times the amount of chromium. It has similar characteristics as 5160, but it holds a better edge. With the proper heat treating, it can be as tough as 5160.
6A, 8A, 10A : See AUS Series.
A-2 : An exceptional air-hardening, cold worked tool steel. It has an excellent resistance to annealing and warping, but is difficult to differentially temper. It is tougher than D-2 and M-2, but is less wear resistant. It is just slightly harder to grind than 0-1. It has excellent flexibility and finishes nicely.
AEB-L : Similar to 13C26. Most popular for kitchen knives. It has similar characteristic as 440B. It heat treats like 440C and has good edge retention when cryogenically heat treated. It grinds easy, but can have unusual grinding characteristics. It is very easy to polish and buff.
ATS-34 : Very similar to 154CM, but it has slightly less manganese and slightly more phosphorus, silicon and sulfur. It is made in Japan by the Hitachi Corporation. It is a very tough steel. It has very good edge retention, even when hardened to Rc 60. Although, it is not as rust resistant as the 400 series stainless steels. It is a very clean steel, but it comes with a hard, black outer coating that must be removed before grinding. One method of removing the coating is to soak it in vinegar.
ATS-55 : Similar to ATS-34, but with reduced molybdenum, phosphorus and sulfur removed, and cobalt and copper added. It is a good steel, but does not hold an edge as well as ATS-34. It is also less rust resistant. It is comparable in performance to AUS-8.
AUS-6, AUS-8, AUS-10 : Sometimes referred to as 6A, 8A and 10A stainless steel. AUS-6 is roughly comparable to 440A, and competes with 420J. AUS-8 is roughly comparable to 440B and competes with ATS-55 and Gin-1. AUS-10 is roughly comparable to 440C, but slightly tougher and slightly less corrosion resistant. It competes with ATS-34 and 154CM. The AUS series stainless steel contains vanadium, unlike the 440 series, which increases its wear resistance and edge retention. The vanadium allows a sharper edge to be put on the blade.
AUS-8A : A high carbon, low chromium stainless steel that is tougher, but less corrosion resistant than AUS-8. It has better edge retention than AUS-8, but less edge retention than 440C.
BG-42 : A high performance, bearing-grade, martensitic, proprietary stainless steel made by Timken Latrobe Steel. It is often used in the aerospace industry. It is similar, but tougher and more stain resistant than ATS-34. It has more manganese than ATS-34 and it contains vanadium, unlike ATS-34. This gives it better edge retention than ATS-34. It has a high wear resistance, which can make it difficult to sharpen. It can also be difficult to manufacture. Because of its high strength and hardenability, it is well suited for extreme use.
Boye Dendritic Cobalt (BDC) : A stainless steel containing cobalt that has excellent wear resistance and corrosion resistance. It has good toughness, but a low strength. It is produced by David Boye using a casting process.
Carbon V : A proprietary carbon steel that is trademarked by Cold Steel. It is unclear exactly what type of steel it is, but it has characteristics similar to 50100-B.
Cowry X : Similar to ZDP-189.
CPM 10V : A very high vanadium tool steel made by Crucible. It was designed to provide superior wear resistance while maintaining toughness and fabrication characteristics comparable to D2 and M2. It has excellent wear resistance, but low corrosion resistance.
CPM 3V : A vanadium tool steel made by Crucible. It was designed to provide maximum resistance to breakage and chipping in a highly wear-resistant steel. It has excellent wear resistance and toughness. It also has good corrosion resistance. However, when this steel does corrode, it tends to pit rather than surface rust.
CPM S30V : A high carbon, high vanadium martensitic stainless steel made by Crucible. This stainless steel was created by Dick Barber of Crucible Materials Corporation specifically for the cutlery industry. It was designed to offer the best combination of toughness, wear resistance and corrosion resistance. It is tougher than D-2 and 440C and compares in toughness to A-2. It has excellent wear resistance and hardenability. It has a corrosion resistance comparable to 440C. It is comparable to D-2 for grinding and machining and much easier to grind than S60V or S90V. It has superior edge retention and wear resistance to BG-42, due to higher carbon and much higher vanadium. This is an all around excellent cutlery steel.
CPM S60V : A high carbon, high vanadium stainless steel. It is made from Crucible’s particle metallurgy process. It has outstanding wear resistance and edge retention. But it can be difficult to grind and sharpen. It can also be difficult to heat treat. The hardness can be reduced, in order to keep toughness acceptable.
CPM S90V : Similar to S60V, but packed with more carbon and vanadium. This results in extremely high wear resistance and edge retention- possibly better than any other stainless steel used in the cutlery industry. It is tougher and more wear resistant than S60V. It is has some comparable characteristics to BG-42. It is very difficult to grind, sharpen and heat treat.
D-2 : An excellent air hardened, cold worked tool steel. It has increased carbon and chromium over A-2, which results in very high wear resistance. For a tool steel, it has very good corrosion resistance. D-2 is often referred to as a semi-stainless, due to its high chromium content and very good corrosion resistance. D-2 is much tougher than the premium stainless steel, including ATS-34 and 154CM. But, it can be difficult to grind, due to its tendency to work harden easily. It also will not take a mirror polish, due to its ‘orange peel’ appearance.
GIN-1 : A very good stainless steel, sometimes referred to as G-2. It has slightly less wear resistance and strength than ATS-34. It is more wear resistant than ATS-55. It is often used as a low cost alternative to ATS-34 or 154CM.
INFI : A proprietary tool steel used only by Busse Combat. Some of the carbon is replaced with nitrogen. It is comparable to D-2 in corrosion resistance. It has very high toughness for a high-alloy ingot steel. It has extremely good wear resistance. It is a good overall tool steel with an excellent balance of corrosion resistance, toughness and edge retention. It is good for large blades and blades that need to endure extreme use.
L-6 : A carbon steel that is used for band saw and circular saw blades. It is a medium carbon steel that can be oil hardened. It has slightly better wear resistance than plain carbon steels. It is similar to the Swedish band saw blade steel 15n20. It has very good toughness, but extremely low hardenability and corrosion resistance.
M-2 : A high speed tool steel (HSS), which means it will not loose its temper during high heat cutting jobs. This quality is mostly irrelevant for the cutlery industry. M-2 is most commonly used for lathe cutting tools. It has very high wear resistance and a fine grain structure for toughness. It has a high hardenability and slightly better corrosion resistance than most tool steels.
O-1 : An good oil hardening, cold worked tool steel. It has excellent edge retention and toughness. But it is hard to grind and has very low corrosion resistance. It is popular among forgers because it is very forgiving and can be heat treated repeatedly if a mistake is made.
O-6 : Slightly outperforms O-1. It is tougher and holds a better edge than O-1. It has very good wear resistance. It is very easy to heat treat, but very difficult to grind.
San Mai III : A proprietary premium layered steel used by Cold Steel. It is made with three layers- a high carbon center, surrounded by lower carbon outer layers. This allows for good edge retention in the high carbon center layer, while maintaining toughness with the outer layers. The exact steels used are a trade secret.
SK-5 : A high carbon steel made in Japan. It is the Japanese equivalent of 1080. It has a high hardenability. It has a mixture of carbon-rich martensite and small un-dissolved carbides. The carbides increase wear resistance. This helps to create a good balance between toughness and edge retention. This steel is often used for making hand tools.
Stellite 6-K : Contains no iron, so it does not need heat treating. It has exceptionally hard particles contained in a softer alloy. It has a low strength, but very good wear resistance. It is difficult to work.
Talonite : A cobalt super-alloy. It is very soft, Rc 42-47, and has a very low strength, but it is very easy to work.
Vasco Wear : This steel is no longer produced. It contains a high amount of vanadium. The vanadium gives it very good edge retention and wear resistance. But it is very hard to grind.
VG-1 : A proprietary stainless steel used by Cold Steel. Its contents are a trade secret. It is a lower cost alternative to their San Mai III steel.
W-1, W-2 : Similar to 1095. It is a moderately tough steel with very good edge retention, but low wear resistance. W-2 contains vanadium, which allows it to hold a better edge than W-1. They both have a high hardenability. W-1 is often used to make files.