These steels are the steels most often forged. Stainless steels can be forged (guys like Sean McWilliams do forge stainless), but it is very difficult. In addition, carbon steels can be differentially tempered, to give a hard edge-holding edge and a tough springy back. Stainless steels are not differentially tempered. Of course, carbon steels will rust faster than stainless steels, to varying degrees. Carbon steels are also often a little bit less of a crap shoot than stainless steels -- I believe all the steels named below are fine performers when heat treated properly.
In the AISI steel designation system, 10xx is carbon steel, any other steels are alloy steels. For example, the 50xx series are chromium steels.
In the SAE designation system, steels with letter designations (e.g., W-2, A2) are tool steels.
There is an ASM classification system as well, but it isn't seen often in the discussion of cutlery steels, so I'll ignore it for now. Often, the last numbers in the name of a steel are fairly close to the steel's carbon content. So 1095 is ~.95% carbon. 52100 is ~1.0% carbon. 5160 is ~.60% carbon.
D2 is sometimes called a "semi-stainless". It has a fairly high chrome content (12%), but not high enough to classify it as stainless. It is more stain resistant than the carbon steels mentioned above, however. It has excellent wear resistance. D2 is much tougher than the premium stainless steels like ATS-34, but not as tough as many of the other non-stainless steels mentioned here. The combination of great wear resistance, almost-stainlessness, and good toughness make it a great choice for a number of knife styles. Bob Dozier is one maker who uses D2. Benchmade has begun using D2 in its Axis AFCK.
A "high-speed steel", it can hold its temper even at very high temperatures, and as such is used in industry for high-heat cutting jobs. It is slightly tougher, and is slightly more wear resistant, than D2. However, M2 rusts easily. Benchmade has started using M2 in one of their AFCK 710 variations.
An excellent air-hardening tool steel, it is tougher than D2 and M2, with less wear resistance . As an air-hardening steel, don't expect it to be differentially tempered. Its good toughness makes it a frequent choice for combat knives. Chris Reeve and Phil Hartsfield both use A2.
This is a steel very popular with forgers, as it has the reputation for being "forgiving". It is an excellent steel, that takes and holds an edge superbly, and is tough (although not as tough as, say, 5160). It rusts easily, however. Randall Knives uses O1, so does Mad Dog Knives.
Reasonably tough and holds an edge well, due to its .2% vanadium content. Most files are made from W-1, which is the same as W-2 except for the vanadium content (W-1 has no vanadium).
1095 (and 1084, 1070, 1060, 1050, etc.) Many of the 10-series steels for cutlery, though 1095 is the most popular for knives. When you go in order from 1095-1050, you generally go from more carbon to less, from more wear resistance to less wear resistance, and tough to tougher to toughest. As such, you'll see 1060 and 1050, used often for swords. For knives, 1095 is sort of the "standard" carbon steel, not too expensive and performs well. It is reasonably tough and holds an edge well, and is easy to sharpen. It rusts easily. This is a simple steel, which contains only two alloying elements: .95% carbon and .4% manganese. The various Kabars are usually 1095 with a black coating.
Carbon V is a trademarked term by Cold Steel, and as such is not necessarily one particular kind of steel; rather, it describes whatever steel Cold Steel happens to be using, and there is an indication they do change steels from time to time. Carbon V performs roughly between 1095-ish and O1-ish, in my opinion, and rusts like O1 as well. I've heard rumors that Carbon V is O1 (which I think is unlikely) or 1095. Numerous industry insiders insist it is 0170-6. Some spark tests done by a rec.knives reader seem to point the finger at 50100-B. Since 50100-B and 0170-6 are the same steel (see below), this is likely the current Carbon V.
0170-6 - 50100-B
These are different designations for the same steel: 0170-6 is the steel makers classification, 50100-B is the AISI designation. A good chrome-vanadium steel that is somewhat similar to O1, but much less expensive. The now-defunct Blackjack made several knives from O170-6, and Carbon V may be 0170-6. 50100 is basically 52100 with about 1/3 the chromium of 52100, and the B in 50100-B indicates that the steel has been modified with vanadium, making this a chrome-vanadium steel.
A band saw steel that is very tough and holds an edge well, but rusts easily. It is, like O1, a forgiving steel for the forger. If you're willing to put up with the maintenance, this may be one of the very best steels available for cutlery, especially where toughness is desired. In a poll on the knifemakers email list back in the 1990s, when asked what the makers would use for their personal knife, L-6 emerged as the top choice.
A steel popular with forgers, it is popular now for a variety of knife styles, but usually bigger blades that need more toughness. It is essentially a simple spring steel with chromium added for hardenability. It has good wear resistance, but is known especially for its outstanding toughness. This steel performs well over a wide range of hardnesses, showing great toughness when hardened in the low 50s Rc for swords, and hardened up near the 60s for knives needing more edge holding.
Formerly a ball-bearing steel, and as such previously only used by forgers, it's available in bar stock now. It is similar to 5160 (though it has around 1% carbon vs. 5160 ~.60%), but holds an edge better. It is less tough than 5160. It is used often for hunting knives and other knives where the user is willing to trade off a little of 5160's toughness for better wear resistance. However, with the continued improvement of 52100 heat treat, this steel is starting to show up in larger knives and showing excellent toughness. A modified 52100 is being used by Jerry Busse in his lower-cost production line, and such high-performance knife luminaries as Ed Fowler strongly favor 52100.
Crucible's somewhat-stain-resistant 10V provides incredible wear resistance with D2-class toughness. It is an outstanding choice when maximum wear resistance is desired, but not super toughness.
CPM's incredibly tough 3V gives excellent wear resistance and good stain resistance as well, although when it does stain, it is said to pit rather than surface rust. When maximum toughness is desired, with very good wear resistance, 3V is a great choice.
INFI is currently only used by Jerry Busse. In place of some of the carbon (INFI contains .5% carbon), INFI has nitrogen. The result is a non-stainless steel that is nevertheless extremely stain resistant (informally reported at close to D2, or even better), incredibly tough for a high-alloy ingot steel, and with extremely good wear resistance.
A very hard-to-find steel, with a high vanadium content. It is extremely difficult to work and very wear-resistant. It is out of production.
B. Stainless Steels
Remember that all steels can rust. But the following steels, by virtue of their > 13% chromium, have much more rust resistance than the above steels. I should point out that there doesn't appear to be consensus on what percent of chromium is needed for a steel to be considered stainless. In the cutlery industry, the de-facto standard is 13%, but the ASM Metals Handbooks says "greater than 10%", and other books cite other numbers. It probably makes more sense to measure stainlessness by the amount of free chromium (chromium not tied up in carbides), because free chromium is what forms the chromium oxide on the blade surface that offers stain resistance. The alloying elements have a strong influence on the amount of chromium needed; lower chromium with the right alloying elements can still have "stainless" performance.
Because any particular stainless steel is often heat treated to around the same hardness (i.e., 440C is usually around 57 Rc, ATS-34 is 59-61 Rc, S60V is getting consensus at around 56 Rc, etc.) even by different manufacturers, it's a bit easier to give a general feeling of the performance you'll get from different classes of stainless steels, without introducing too many inaccuracies. Please note, though, that the act of grouping differing steels in classes definitely does oversimplify, and some of these steels might more properly fit between the class it's in, and the following (or previous) one. In addition, better heat treat can move a steel up in performance significantly. Last disclaimer: not everyone will agree with the groupings I have here. Whew, all that said, here is a general categorization of stainless steels:
420 and 420J
represent the low end of stainless steels. They are very stain resistant, and are tough due to being very soft. However, they are also very weak, and not very wear resistant. Generally speaking, expect these steels to lose their edge quickly through abrasion and impaction. They are used in less-expensive knives due to their ease of machining.
440A and its relative peers, 425M, 420HC, 12C27 and 6A
are the next group. They can be hardened more than the previous group, for better strength, and they are more wear resistant, though wear resistance is just getting to the point of acceptability. 440A and 12C27 are the leaders of this group, with solid heat treat both perform okay. 12C27 is said to be particularly pure and can perform very well when heat treated properly. 6A trails those two steels, though with its vanadium content, can take a razor edge. 425M and 420HC trail the rest.
Gin-1, ATS-55, 8A and 440C
comprise the next group. These steels will usually be stronger than the previous group, and more wear-resistant. Generally speaking, they retain excellent stain resistance properties, though ATS-55 sticks out here as not particularly stain resistant. 8A is also worth a mention, with some vanadium content, it can take an extremely sharp edge very easily, but is also the weakest and least wear-resistant of this group.
ATS-34/154CM, VG-10 and S60V
are the next group up. It's difficult to make generalizations about ATS-34 and 154-CM -- they are in such widespread use that heat treat varies widely. These steels provide a high-end performance benchmark for stainless steels, and hold an edge well, and are tough enough for many uses (though not on par with good non-stainlesses). They aren't very stain resistant, however. VG-10 can be thought of as being like ATS-34 and 154-CM, but doing just about everything a hair better. It's a little more stain resistant, tougher, holds an edge a little better. And VG-10 has vanadium in it, it's fine-grained and takes the best edge of this group. S60V has by far the best wear resistance of the group, though consensus is becoming that it should be left around the same hardness as 440C (56ish Rc), which means it will be relatively weak compared to ATS-34, 154-CM, and VG-10, and so it will indent and lose its edge quickly when strength is required. S60V is the winner here when pure abrasion resistance is much more important than edge strength.
BG-42,S90V and S30V
constitute the next group. BG-42 has better wear resistance than all the previous steels except for S60V. It is tougher than ATS-34, and more stain resistant. It is wear resistant to the point where it can be difficult to sharpen. S90V represents the ultimate in wear resistance in the steels discussed so far. Also tougher than ATS-34, and more stain resistant. It can be very difficult to put an edge on. It is difficult enough to machine than it is used almost exclusively in custom knives, not production knives. In your buying decisions, you might want to take into account the difficulty of sharpening these steels. S30V backs off on the wear resistance of S90V, but is significantly tougher and easier to sharpen. It is more wear resistant than BG-42. The jury is still out, but it may end up this week's ultimate high-end all-around stainless steel, due to high performance coupled with easier machinability and sharpenability than the other steels in this class.
Okay, on to the steels in more detail:
Lower carbon content (<.5%) than the 440 series makes this steel extremely soft, and it doesn't hold an edge well. It is used often for diving knives, as it is extremely stain resistant. Also used often for very inexpensive knives. Outside salt water use, it is too soft to be a good choice for a utility knife.
420 modified with more carbon, to be roughly comparable to 440A.
440 A - 440 B - 440C
The carbon content (and hardenability) of this stainless steel goes up in order from A (.75%) to B (.9%) to C (1.2%). 440C is an excellent, high-end stainless steel, usually hardened to around 56-58 Rc, very tough and with good edge-holding at that hardness. 440C was the king of stainless cutlery steels in the 1980s, before ATS-34 took the title in the 1990s. All three resist rust well, with 440A being the most rust resistant, and 440C the least. The SOG Seal 2000 is 440A, and Randall uses 440B for their stainless knives. 440C is fairly ubiquitous, and is generally considered a very good general-use stainless, tougher and more stain resistant than ATS-34 but with less edge-holding and weaker. If your knife is marked with just "440", it is probably the less expensive 440A; if a manufacturer had used the more expensive 440C, he'd want to advertise that. The general feeling is that 440A (and similar steels, see below) is just good enough for everyday use, especially with a good heat treat (we've heard good reports on the heat treat of SOG's 440A blades, don't know who does the work for them). 440-B is a very solid performer and 440-C is excellent.
425M - 12C27
Both are very similar to 440A. 425M (.5% carbon) is used by Buck knives. 12C27 (.6% carbon) is a Scandanavian steel used often in Finish puukkos and Norwegian knives. 12C27 is said to perform very well when carefully heat treated, due to its high purity. When done right, it may be a slighter better choice than 440A and its ilk.
AUS-6 - AUS-8 - AUS-10(aka 6A 8A 10A)
Japanese stainless steels, roughly comparable in carbon content to 440A (AUS-6, .65% carbon) and 440B (AUS-8, .75% carbon) and 440C (AUS-10, 1.1% carbon). AUS-6 is used by Al Mar, and is a competitor to low-end steels like 420J. Cold Steel's use of AUS-8 has made it pretty popular, as heat treated by CS it won't hold an edge like ATS-34, but is a bit softer (and therefore weaker) and tougher. 8A is a competitor of middle-tier steels like ATS-55 and Gin-1. AUS-10 has roughly the same carbon content as 440C but with slightly less chromium, so it should be a bit less rust resistant but perhaps a bit tougher than 440C. It competes with higher-end steels, like ATS-34 and above. All 3 steels have some vanadium added (which the 440 series lacks), which will improve wear resistance and refines the grain for both good toughness, and the ability to sharpen to a very keen edge. Many people have reported that they are able to get knives using steels that include vanadium, like 8A, sharper than they can get non-vanadium steels like ATS-34.
GIN-1 aka G-2
A steel with slightly less carbon, slightly more chromium, and much less moly than ATS-34, it used to be used often by Spyderco in their less-expensive knives. Spyderco has since switched to ATS-55 and 8A, but Benchmade is now using Gin-1 in their less-expensive knives. A very good stainless steel, with a bit less wear resistance and strength than ATS-34.
ATS-34 - 154-CM
ATS-34 was the hottest high-end stainless in the 1990s. 154-CM is the original American version, but for a long time was not manufactured to the high quality standards knifemakers expect, so knifemakers switched over to ATS-34. CPM is again making high-quality 154-CM, and some companies seeking to stick with American-made products (like Microtech) are using it. ATS-34 is a Hitachi product that is very, very similar to 154-CM. Normally hardened to around 60 Rc, it holds an edge very well and is tough enough even at that high hardness. Not as rust resistant as the 400 series above. Many custom makers use ATS-34, and Spyderco (in their high-end knives) and Benchmade are among the production companies that use it. Contrary to popular belief, both steels are manufactured through the Argon/Oxygen/Decarburization process (AOD), not vacuum remelted.
Similar to ATS-34, but with the moly removed and some other elements added. This steel is a good cutlery steel but a tier behind ATS-34 and its closest competitors (other steels in ATS-55's class might be Gin-1 and AUS-8). With the molybdenum removed, ATS-55 does not seem to hold an edge quite like ATS-34, and reports are that it's less rust-resistant. My guess is that with the moly gone, more chromium is tied up in carbides -- which means less free chromium for rust resistance, and softer chromium carbides replacing moly carbides for less wear resistance.
Another vanadium-containing high-end stainless steel. Due to the vanadium content, VG-10 takes a killer edge, just like other vanadium steels like BG-42 and AUS-8. VG-10 is also tougher and more rust-resistant than ATS-34, and seems to hold an edge better.
Bob Loveless announced a while back that he's switching from ATS-34 to this steel. Keep an eye out for it, it's bound to catch on, although the higher cost, limited stock-size availability, and added difficulty of manufacturing are holding BG-42's popularity back. BG-42 is somewhat similar to ATS-34, with two major differences: It has twice as much manganese as ATS-34, and has 1.2% vanadium (ATS-34 has no vanadium), so look for significantly better edge-holding than ATS-34. The addition of vanadium and the clean manufacturing process (VIM/VAR) also gives BG-42 better toughness than ATS-34. Chris Reeve has switched from ATS-34 to BG-42 in his Sebenzas.
S60V(CPM T440V) - S90V(CPM T420V)
Two steels that hold an edge superbly, world class type edge holding, but it can be difficult to get the edge there in the first place. These steels are made with Crucible's particle metallurgy process, and that process allows these steels to be packed with more alloying elements than traditional steel manufacturing methods would allow. Both steels are very high in vanadium, which accounts for their incredible wear resistance. Spyderco offers at least one model in CPM S60V. Spyderco, one major user of S60V, has cut back hardness down to 55-56Rc, in order to keep toughness acceptable, but that sacrifices strength so there is a tradeoff. S90V is CPM's follow-on to 440V, and with less chromium and almost double the vanadium, is more wear-resistant and tougher than S60V -- and, in fact, is probably more wear-resistant than any other stainless steel used in the cutlery industry. As such, S90V is in the running with steels like BG-42 as among the best general-purpose stainless steels; however, S90V is even more expensive and difficult to work than BG-42, so it's strictly in the realm of custom makers currently.
The newest stainless steel from Crucible, purpose-designed as a cutlery steel. This steel gives A2-class toughness and almost-S90V class wear resistance, at reasonable hardness (~59-60 Rc). This mix of attributes is making S30V one of the hottest stainless steels going, with makes such as Chris Reeve switching from BG-42 to S30V. Will this be the new king of general-purpose stainless cutlery steels? We'll know over the next couple of years.
400 Series Stainless
Before Cold Steel switched to AUS-8, many of their stainless products were marketed as being of "400 Series Stainless". Other knife companies are beginning to use the same term. What exactly *is* 400 Series Stainless? I always imagined it was 440-A, but there's nothing to keep a company from using any 4xx steel, like 420 or 425M, and calling it 400 Series Stainless.
Damascus steels are made by forge-welding two or more different metals (usually steels). The billets are heated and welded; to get an idea of the process, see Don Fogg's URL listed in the bibliography. The Damascus is then acid-etched. The different metals etch at different rates, and depth and color contrast are revealed.
Damascus can be made with performance and/or aesthetic objectives in mind. Aesthetically, the choice of materials is important. One shiny steel and one darker steel etch out to show the most striking pattern. If the maker is going more for beauty than performance, he might even go with nickel, which is bright but does not perform as well as steel for cutlery applications. The other factor affecting beauty is of course the welding pattern. Many patterns of Damascus are available today, from random to star to ladder, and a whole lot more.