The Making & Shaping of Steel
Steel is essentially a combination of iron and carbon. All steels contain certain other elements in small controlled amounts, like Manganese, Sulfur, Silicon, and Phosphorus. If nothing else is present, the steel is referred to as plain carbon steel. Steels used for knife blades are enhanced with additional elements and are called alloy steels. It is these additions that give different types of steel their special properties. Alloy steels that have additions to make them corrosion-resistant are labeled stainless steels, and these are the steels most frequently used in making knife blades.
The making of stainless steel begins by melting steel in a furnace. Alloying elements are added to the melt, and the molten steel is poured into molds called ingots. Once the ingots have solidified, they are processed in a mill to make usable shapes and sizes (plates, coils, etc.). Buck Knives uses plates and coils, depending on the type of steel and its thickness. Plates are turned into knife components by laser cutting and coils are shaped into components using a fine blanking press.
Properties of Steel
The selection of steel for specific applications is based on the properties of the steel and other factors like manufacturability—if the steel is difficult to fabricate, then it is not practical for use in a manufacturing environment. These properties are established by the alloys added to steel and by the methods used in its manufacture. Some of the important properties of blade steel are:
· Hardness : A measure of the steel's ability to resist permanent deformation (measured on a Rockwell Scale)
· Hardenability : The ability of a steel to be hardened (through the heat-treating process)
· Strength : The steel’s ability to resist applied forces
· Ductility : The steel's ability to flex or bend without fracturing
· Toughness : The steel’s ability to absorb energy prior to fracturing
· Initial Sharpness : The sharpness of the blade "out of the box"
· Edge Retention : The ability of the steel blade to hold an edge without frequent resharpening
· Corrosion Resistance: The ability of the steel to resist deterioration as a result of reaction with its environment
· Wear Resistance: The ability to resist wear and abrasion during use
· Manufacturability : The ease with which steel can be machined, blanked, ground, and heat-treated
The nomenclature used to describe the types of steel and their properties is often derived from the internal structure of metals. As steel is heated and cooled, its internal structure undergoes changes. The structures formed during these changes are given names like Austenite and Martensite. Martensite is a very hard structure that can be formed by rapidly cooling certain types of steel during heat-treating. Steels that are capable of forming Martensite are called martensitic steels, and it is this type of steel that is of most interest to the cutlery industry. S30V, BG-42, 154CM, 420HC and 420J2 are all martensitic stainless steels.
The properties of steel can be altered by the addition of certain elements to the steel during the melting process. The alloying elements that are important to knife-making are listed with a brief description of how they affect the steel's properties.
Carbon - is not an alloying element since it is present in plain carbon steels. Nonetheless, increasing carbon increases hardness.
Chromium - improves hardenability, wear resistance, and corrosion resistance. It is a major element in martensitic stainless steels, which are most commonly used for sports cutlery applications.
Molybdenum - improves hardenability, tensile strength, and corrosion resistance, particularly pitting.
Nickel - improves toughness, hardenability and corrosion resistance. Nickel is a major element in Austenitic stainless steel that is sometimes used for dive knives.
Vanadium - improves hardenability and promotes fine grains. Grain structure in steels is another important factor in wear resistance and strength. Generally, fine grain structures are desirable.
Difference between carbon steel and stainless steel
There are two main differences between carbon knife steel and stainless knife steel. The first is that stainless steels have much higher corrosion resistance, due to the protective chromium oxide layer that covers the steel surface after heat treatment. The second difference relates to the alloying elements that form carbides. Stainless steels contain at least 10.5% by weight of chromium. The carbide particles provide the steel with significant wear resistance. The carbides are bonded together by the steel matrix.
Types of Steel
Steel makers follow a precise recipe to ensure that each time they make a particular alloy it has correct properties. The recipes are known as Specifications, and they specify the amount of each alloy. Each alloy recipe or type is named according to a number convention. Martensitic stainless steels, for example, have numbers like Types 410, 420, and 425.
Blade Steels used:
S30V - Developed primarily for the cutlery industry by Crucible Steel, S30V contains noticeably higher amounts of Carbon and Vanadium than does BG-42. This increase in Carbon and Vanadium provides superior edge-holding and abrasion resistance. S30V is the best blade steel available today.
· Superior edge holding
· Improved ductility
· Good hardness- ideal range Rc 59.5-61
· Good corrosion resistance
· Very high amounts of Carbon and Vanadium
Chromium - 14.0%
Vanadium - 4.0%
Molybdenum - 2.0%
BG-42 - A proprietary alloy of Timken Latrobe Steel, BG-42 is a high-performance, bearing-grade martensitic stainless steel used in the aerospace industry. Because of its high strength and ability to reach high Rockwell hardness (Rc 61-62), BG-42 is well suited for blades that are subjected to extreme use.
· Very good edge holding ability
· High strength
· Rockwell Rc 61-62
· Fair corrosion resistance
· Contains Vanadium, improving hardenability and a fine grain structure
Silicon - .3
Chromium - 13.50 - 14.50
Molybdenum - 4.0
Vanadium - 1.20
154CM – 154CM is a very high carbon stainless steel with the addition of Molybdenum. Because 154CM provides better edge retention than standard cutlery (stainless) steels, it is a good choice for blades that require heavier cutting applications.
· Very good edge holding ability
· Rockwell Rc 60-61
· Good toughness when double tempered
· Fair corrosion resistance
· Less expensive than BG-42 and S30V
Silicon - .35
Chromium - 13.50 - 14.00
Molybdenum - 4.0
420HC - A higher carbon version of standard Type 420 martensitic stainless steel. The Carbon content, combined with the high Chromium content, provides good abrasion resistance and edge-holding. This steel is not to be confused with standard 420 stainless steel. 420HC is an excellent general purpose knife steel when heat-treated with our proprietary Paul Bos heat-treat process.
· Good edge holding ability
· Resharpens well
· Rockwell Rc 58
· Good toughness
· Very good corrosion resistance
· Excellent standard knife steel
Nickel - .50
Silicon - .60
Chromium - 12.00 - 14.00
Manganese - 1.0
420J2 - A lower carbon content, general-purpose stainless steel. 420J2 has fair hardness and corrosion resistance and high ease of resharpening. 420J2 is suited for knife blades with light to medium use and routine applications.
· Resharpens well
· Rockwell Rc 56-58
· Good manufacturability
· Good corrosion resistance
Carbon - .36 - .45
Nickel - .60
Silicon - .60
Chromium - 12.00 -14.00
Manganese - 0.80
17-7 PH - A Chromium/Nickel/Aluminum, precipitation-hardening, stainless steel. The alloy is used for high-strength applications requiring resistance to salt-water corrosion. 17-7PH offers a good compromise between Martensitic stainless steels (heat-treatable) and Austenitic (300 series) stainless steels (non heat-treatable). This is due to the high Chromium/Nickel/Aluminum content.
· Moderate edge holding
· Very good toughness
· Excellent corrosion resistance
· Rockwell Rc 54-56
Carbon - .07
Chromium - 17.00
Nickel - 7.0
Aluminum - 1.25
OTHER BLADE STEELS
AUS-8 - The words "stainless steel" are misleading, because, in fact all steel will stain or show discoloration if left in adverse conditions for a sufficient time. Steel is made "stainless" by adding Chromium and reducing its Carbon content during the smelting process. Some authorities claim that there is a serious performance trade off with stainless steel: As the Chrome increases and the Carbon decreases, the steel becomes more "stainless". But it also becomes more and more difficult to sharpen and, some claim, the edge-holding potential is seriously impaired. We have found that most stainless steel blades are as sharp as other material blades and hold the edge longer. AUS 8A is a high carbon, low chromium stainless steel that has proven, over time, to be a very good compromise between toughness, strength, edge holding and resistance to corrosion.
ATS-34 - premium grade of stainless steel used by most custom knifemakers and upper echelon factory knives. It is Japanese steel, owned by Hitachi Steels. The American made equivalent of ATS-34 is 154CM, a steel popularized by renowned maker Bob Loveless.
0-1 - is perhaps the most forgiving of any knife quality steel other than the very simple alloy types, and produces a blade of excellent quality for most normal use. It can be heat treated very easily. Further references? Well, the ole' master, Cooper, used it for many years and folks do love his blades because they're tough. Awhile back, one of the best of the blade smiths said that well treated 0-1 would out cut any Damascus, and no one argued with him. Edge holding is exceptional. 0-1 is precision ground unless you're lucky enough to stumble across some mill bar. Goof up the heat treat and 0-1 will let you try again as often as you like, as long as you don't overheat the metal. Tough on grinding belts.
0-6 - is the next step up from 0-1 easy heat treat but pure hell to grind. It's significantly tougher, with finer crystalline structure and hard graphitic particles that resist wear. Stock is both hot rolled and precision ground. Hot rolled prices are reasonable. Very tough to grind. Edges are incredible, lasting even longer than the best Damascus and even 0-1. Has an odd, rather orange spark.
W-1 W-2 - and the series of 10-- steels from 1045 through 1095 are the ultimate in simplicity and very shallow hardening so they may be used to make a selectively hardened edge as one sees on old Japanese swords. Toughness is outstanding, with these alloys being used for grader blade edges, truck springs and files. Uses up grinding belts at quite a rapid rate. Edges are acceptable with 1045, good with 1060, nice with 1084, and excellent with 1095, W-1 or W-2. Those last two are often referred to as O-F, old file. It is very easy to get the higher carbon end of this series way too hard to make a good knife.
5160 - is a common spring steel, basically 1060 with one per-cent of chromium added to make it deep hardening. (It may still be selectively drawn with a softer back, if desired.) An excellent steel for swords, or any other blade that will have to take some battering. The choice of Jim Hrisoulas who makes some of the finest working swords in the business. Long blades are best around the mid 50's on the Rockwell scale, while small, working blades can be put into service at a full 60 RC. Forged blades with a well packed edge seem to cut forever! Rough on grinding belts. Jokingly called O-C-S, Old Chevy Spring.
52100 - is a ball bearing steel, generally not found in useful grinding sizes, but terrific in edge holding and toughness. 52100 is 5160 with an attitude, more alloy and more carbon that makes it harder and tougher. Like 5160, throws a brilliant yellow spark. Ed Fowler has developed a superior heat treating technique for this steel.
L-6 - is the band or circular saw blade steel used in most lumber mills and downright hard to find in any other form. Hardens in oil to about RC 57 and takes a fine edge for most cutting, particularly where the edge might be steeled back into shape. Outstanding where flexibility is needed but rusts easily, like virtually all of the simple carbon steels. L-7 is the same stuff with a little more carbon.
A-2 - is an exceptional steel, with fine wear-resisting qualities plus excellent resistance to annealing and warping. Grinding is noticeably harder than 0-1 but not extremely difficult. Sawing is tougher and relates to the five percent of chrome in this steels chemical make up. Really nice to finish with the grinder and very little grain appearing in buffing. Excellent flexibility. Phil Hartsfield get incredible cutting ability out of this steel. Several other of the A series will also make fine blades.
D-2 - offers another air hardening tool steel, but with 12% chrome and excellent, if not superb, wear resistance. The resistance also holds true in both sawing and grinding, even while the steel is fully annealed. While using belts up at a faster rate than average, D-2 is not particularly hard to grind with fresh belts. Using old belts causes enough heat to work harden the steel. D-2 anneals at somewhat higher temperature than A-2 and will not take a true, mirror polish. Definitely a steel for the advanced craftsman. It's major drawback is the orange peel appearance of the surface when finished to a high gloss. One knife maker is often quoted as saying that D-2 takes a lousy edge and holds it forever. Often found as surplus wood plainer blades. D-4 and D-7 are also good cutlery alloys, but darn hard to find in the right sizes. Air hardening steels can work harden while you're grinding them if you get the stock too hot. This doesn't mean much on the grinder, but when you try to file a guard notch, the file will just slide.
M-2 - is a high temperature steel made for lath cutting tools, which has darn little to do with knives, but allows you to really cook the blade in finishing after heat treat without annealing it. M-2 is perhaps a bit better in edge holding than D-2. It is also rather brittle and not recommended for large knives.
440C - was the first generally accepted knife makers' stainless and remains quite popular, particularly since the sub-zero process was developed to add toughness. On the grinder, it's gummy and gets hot fast, but it cuts a lot faster and easier than any of the carbon steels. Your belts will cut about 2 to 3 times as much 440-C than 0-1. Using hand hacksaws on it will wear out a lot of blades in a hurry. But with the proper care, good heat treating and finishing, 440C produces an excellent, serviceable and durable knife, even for the new knife maker. Anneals at very low temperature. Please note that 440A and 440B are similar alloys, often confused with 440C, but not worth a damn for knife making use. Commercial knife companies often mark blades 440 when they're one of the less desirable versions, giving the real stuff a bad name. 440C is also available in more sizes and in more places than just about any stainless alloy suitable for knives. It is also essential to remember that collectors hate to see one of their prizes turn brown in the sheath, and 440C handles corrosion resistance very well. While the variation, 440-V doesn't seem to get quite as hard, but holds an edge for much longer and is much more difficult to grind.
GIN-1 (formerly known as G2) - another low cost steel, but slightly softer than AUS-8.
CPM-T440V - sometimes touted as the "super steel", it outlasts all stainless steels on the market today. It is, however, harder to resharpen (due to its unprecedented edge retention). But the tradeoff is that you do not have to sharpen as frequently.
CPM-T440V is widely used by custom knifemakers and is slowly finding its way into high-end factory knives.
420J2 - Due to its low carbon high chromium content this steel is an excellent choice for making tough (bends instead of breaking), shock absorbing knife blades with excel lent resistance to corrosion and moderate edge holding ability. It is an ideal candidate for knife blades that will be subject to a wide variety of environmental conditions including high temperature, humidity, and airborne corrosives such as salt in a marine environment. This extreme resistance to corrosion via its high chrome content also makes it a perfect choice for knife blades which are carried close to the body or in a pocket and blades which will receive little or no care or maintenance
San Mai III® (Cold Steel products) San Mai means "three layers". It's the term given to the traditional laminated blades used by the Japanese for swords and daggers. Laminated construction is important because it allows different grades of steel to be combined in a single blade. A simple way to think of this type of construction is to imagine a sandwich: The meat center is hard, high carbon steel and the pieces of bread on either side are the lower-carbon, tough side panels. The edge of the blade should be hard to maximize edge holding ability, but if the entire blade was hard it could be damaged during the rigors of battle. For ultimate toughness the body of the blade must be able to withstand impact and lateral stresses. Toughness is generally associated with "softness" and "flexibility" in steel, so that, surprisingly, if a blade is made "tough" the edge won't be hard enough to offer superior edge holding. San Mai III® provides a blade with hard (higher carbon) steel in the middle for a keen, long lasting edge and tougher (lower-carbon) steel along the sides for flexibility.
VG-1 Stainless Steel Physical testing for sharpness, edge retention, point strength, shock, and ultimate blade strength showed that VG-1, showed the greatest performance increases in ability to retain an edge and proven strength in point and blade tests, VG-1 will provide Cold Steel® customers with superior performance previously unavailable in a stainless steel blade.
4116 Krupp Stainless Steel 4116 is a fine grained, stainless steel made by ThyssenKrupp in Germany and is used for hygienic applications (medical devices and the pharmaceutical industry) and food processing which make it a superb material for kitchen cutlery. The balance of carbon and chromium content give it a high degree of corrosion resistance and also impressive physical characteristics of strength and edge holding. Edge retention in actual cutting tests exceeded blades made of the 420 and 440 series of stainless steels. Other alloying elements contribute to grain refinement which increase blade strength and edge toughness and also allow for a finer, sharper edge.
1055 Carbon Steel 1055 steel is right on the border between a medium and a high carbon steel, with a carbon content between 0.50%-0.60% and with manganese between 0.60%-0.90% as the only other component. The carbon content and lean alloy make this a shallow hardening steel with a quenched hardness between Rc 60-64 depending on exact carbon content. These combination of factors make this one of the toughest steels available because, when quenched, it produces a near saturated lathe martensite with no excess carbides, avoiding the brittleness of higher carbon materials. This steel is particularly suited to applications where strength and impact resistance is valued above all other considerations and will produce blades of almost legendary toughness.
SK-5 High Carbon Steel
SK-5 is the Japanese equivalent of American 1080, a high carbon steel with carbon between 0.75%-0.85% and 0.60%-0.90% manganese. As quenched, it has a hardness near Rc 65 and produces a mixture of carbon rich martensite with some small un-dissolved carbides. The excess carbide increases abrasion resistance and allows the steel to achieve an ideal balance of very good blade toughness with superior edge holding ability. Due to these characteristics, this grade of steel has been used traditionally for making a variety of hand tools, including chisels and woodcutting saws, and has stood the test of time and use over many years in many countries.
VASCO WEAR is rather expensive but very, very good in edge holding. Resists grinding very well too! You'll swear your belts have all gone dull when you try it. Do everything you have to before heat treating, cause you sure aren't going to be able to do much afterward. Priced like lobster tails, when you can find it. Try Vasco-Pacific in the Los Angeles area. Vasco - Pacific uses their own series of names for their alloys.
DAMASCUS steel is such a widely made product that it is impossible to make too many general statements about it, other than it seems to catch collectors better than any other type. Each smith does his in a slightly different way, ranging from the fellow who toughs it out, starting with three layers, to the guy who welds a 300 layer sandwich of shim stock into a billet with one hit in a 40 ton press. They're all pretty. Reese Weiland suggests that the last etch of a Damascus blade be done with phosphoric acid, which will sort of, parkerize the metal and help protect it. He said that you have to play around with the concentration of the acid and immersion times a bit, depending on the steel you're using. This will also work on most carbon steel blades. If a Damascus blade has been hardened with a softer section at the spine or guard, you will get a much better looking etch if you use muriatic acid first, to get the depth you want, and then ferric chloride for adding color.
STELLITE 6-K fits into the same category as Vasco Wear in the wear resistance area, but doesn't need heat treating since there is no iron in it at all. The trick is exceptionally hard particles embedded in a rather soft alloy. Very flexible and easy to bend. Virtually cannot be brought to a mirror finish. Stellite blades are very much in demand by some collectors. The alloy best suited for knives now must be ordered from Canada and costs about a hundred bucks a pound. Part of Stellite's toughness comes from the rolling process used to form the bars. Cast Stellite is not nearly as tough.
TITANIUM is only a marginally acceptable metal for a knife blade. It cannot be hardened much past the mid 40's of the Rockwell C scale, and that's spring, or throwing knife territory. Aside from that, I'm sure that there will soon be collectible titanium knives on many custom makers tables, designed to catch collectors, and not for cutting
Refrence from Blades 'N' Stuff | Buck Knives | Cold Steel | Sandvik materials Technology and Jake DeBaud (Bladesmith) www.DEBAUDBLADES.COM