Steel is your Friend

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:

420 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.

420HC 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-1aka 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.

ATS-55

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.

VG-10

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.

BG-42

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.

CPM S30V
The newest stainless steel from Crucible, purpose-designed as a cutlery steel. This steel gives A-2-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 Steel

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, . 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.

The following steels will provide bright lines:

L-6 and 15N20 (the Swedish version of L-6) -- nickel content
O-1 -- chromium content
ASTM 203 E -- nickel content
Nickel

The following steels will provide dark lines:

1095
1084
5160
52100
W-2

D. Non-steels used for cutlery

Talonite- Stellite 6K- Boye Dendritic Cobalt

(BDC)
These cobalt alloys have incredible wear resistance, and are practically corrosion resistant. Stellite 6K has been around for years, but was expensive and very difficult to work, and so is only rarely seen. Talonite is easier to work, and as a result has been gaining in popularity, especially among web-based knife buyers. .

Titanium

Newer titanium alloys can be hardened near 50 Rc, and at that hardness seem to take something approaching a useful edge. It is extremely rust-resistant, and is non-magnetic. Popular as expensive dive knives these days, because the SEALs use it as their knife when working around magnetic-detonated mines. Mission knives uses titanium.