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 O-1, 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.
L-6
A band saw steel that is very tough and holds an edge well, but rusts easily. It is, like O-1, 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.
5160
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.
52100
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.
CPM 10V
Crucible's somewhat-stain-resistant 10V provides incredible wear resistance with D-2-class toughness. It is an outstanding choice when maximum wear resistance is desired, but not super toughness.
CPM 3V
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
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 D-2, or even better), incredibly tough for a high-alloy ingot steel, and with extremely good wear resistance.
Vascowear
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:
420and 420Jrepresent 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.
440Aand its relative peers, 425M, 420HC, 12C27, and 6Aare 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 440Ccomprise 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 S60Vare 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 S30Vconstitute 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.