Knife Steel Composition

You can learn a lot from just studying the amounts of the various alloying elements in knife steels. Basic steel is just iron and carbon. Once you add at least 13 percent Chromium you have "stainless" steel.

I am no metallurgist. I don't play one on TV or on any of the various knife forums. Much of this data comes from the table in the back of the 2017 Spyderco catalog. Valuable though this table is, I find it hard to stay on the same row when reading it. I made various errors transcribing information into this page and may not have caught them all! At any event, I find it useful to group steels into small related groups and think about them in that way. These categories are my own invention, and the criteria have been chosen in whatever way suits me, though I hope the divisions are useful in spite of being artificial.

And if you are looking for the "best" knife steel, forget it. There are a few old dogs, but in general each steel has its virtues and areas of best application. You have to consider cost, edge holding, ease of sharpening, toughness, resistance to corrosion, difficulty of manufacture and heat treating, and other things I am surely overlooking. And the point is that you don't get all these things together. A steel that gives you one virtue generally gives ground in another area. A good point of view is to view the world of knife steels like "fine wines". Enjoy the differences and appreciate the nuances of each.

It is important to keep in mind that composition is just one variable. How a given steel is heat treated can make all the difference in the world.

Carbon Steel

This is where steel began. By adding carbon to iron you get iron with some content of iron carbides, which is basic steel. There is a whole series of steels with numbers like 10xx where the "xx" denotes the amount of carbon. These carbon steels typically also include Manganese. 1095 steel is commonly used for large blades like machetes and tomahawks.

element 1095 5160 9260 52100
Carbon 0.95 0.60 0.60 1.00
Chromium -- 0.80 -- 1.50
Manganese 0.40 0.80 0.80 0.40
Silicon -- 0.20 2.00 0.20

5160 and 9260 are "spring steels" and are often used for big blades like swords. Note that none of these steels are stainless and will definitely rust if given the chance.

52100 is an interesting steel. It is sometimes mentioned along with VG10 and Aogami Super Blue as a steel that can be sharpened easily to a very fine edge.

Stainless Steel

Steel with 13 percent or more of Chromium is stainless steel. The "440" steel group is used for many inexpensive knives these days, with 440C being perhaps the best of the bunch. In the day when a Buck knife was the holy grail, you got a 440C blade. These days there are many better choices.

element 1095 440c AUS-8 8Cr13MoV VG-10 Super Blue
Carbon 0.95 1.00 0.70 0.75 1.00 1.50
Chromium -- 17.0 14.0 13.0 15.0 0.4
Nickel -- -- 0.49 0.20 -- --
Cobalt -- -- -- -- 1.40 --
Manganese 0.40 1.00 0.50 0.40 0.50 0.30
Molybdenum -- 0.75 0.20 0.15 1.20 0.50
Silicon -- 1.00 1.00 0.50 0.60 0.20
Tungsten -- -- -- -- 2.50
Vanadium -- -- 0.20 0.10 0.20 0.50

AUS-8 was a fine steel in its time; a step up from plain 440C, but with the advent of 154CM and other steels with significant Molybdenum it is no longer in use except for budget knives. The Ontario "RAT" series are notable knives using AUS-8 that are great bargains. AUS-8 is or was made in Japan by Aichi.

The 8Cr13MoV steel is being produced in China and is used by Spyderco and others in their less expensive knives. The tiny amount of Molybdenum and Vanadium aren't enough to merit moving it out of this category. Superior to plain old 440C. In some ways is a Chinese version of AUS-8, but true AUS-8 has a more uniform and finer grain. It does especially well in knives like the Spyderco Tenacious and the Byrd series. Apparently Spyderco has the heat treat for this steel nicely dialed in and the 8Cr13MoV in their knives may be significantly harder than what you get from other knife makers. One fellow said:

8Cr13MoV is an excellent steel, especially in Spyderco's Tenacious folder. It is very tough for a stainless and if reprofiled and sharpened with a medium grit stone (eg. Lansky diamond hones) and then stropped to remove the burr, it takes a superb long lasting edge. Out of the box from Spyderco it isn't sharpened very well, but if reprofiled and stropped, it is one hell of a knife.
And Sal Glesser said (in 2008):
In CATRA lab tests at Spyderco, 8Cr13MoV edge retention was in the area of AUS-8. The steel held thin edge angles quite well and would perform at a fairly hard Rc. Corrosion resistance was not as good as AUS-8. AUS-8 will get sharper as the steel has a very homogenous grain structure and the foundry, Aichi in Japan, does a very good job at refinining.
And from Sal again, in 2009 (see the forum link below):
Spyderco was the first production company to regularly mark the steel used on almost all of their blades (early 80's). Spyderco was the first to use Hitachi's ATS-34 in US production. Spyderco was the first production company to use Crucible's CPM-440V in knives. Spyderco introduced ATS-55, a new steel developed by Hitachi and at the same time, we introduced VG-10.

In using new steels from foundries, there is little or no actual real world knowledge available. Only lab tests. VG-10 turned out to be more effective in real world testing than ATS-55, so ATS-55 was dropped and VG-10 became our "base" steel for Seki-City production.

When we first decided to make knives in China, most of the competitive knife-makers were already making knives in China. When we asked our Chinese vendors, "what is the best steel available in China?", We were told it was 440C. Looking at the knives coming in from China, most were marked 440. (We didn't know if that meant 440A, 440B or 440C). We told our makers that we would like to use 440C (which we assumed our competitors were also using). We went through a number of trading companies and quite a few factories before we came up with factories that seemed to be able to do the quality we wanted. (We did the same thing in Seki-City 20 years before). We tested the samples and the performance in edge retention was in the 440C range. We assumed it was 440C.

When the first production pieces came in, all of the knives were marked 440C as we had requested. We tested the steel in a lab for chemical content, something we'd been doing for years. We found from the chemical report that the chemistry was off for 440C. We informed our vendors that there was an issue with the mark. We asked them what the actual steel was that they were using? It performed well, but the mark was not accurate. They were surprised that we'd tested and told us the Chinese name for the steel was 8Cr13MoV and they supplied to us the foundry specs. The writing was in Chinese, but the elements and numbers were universal and they matched our own tests.

We told them that we had to put 8Cr13MoV on the blade. We felt that it was not proper of us to put one mark on the blade that was not the actual steel used. Since then we have marked our blades with the steel used which is 8Cr13MoV. We have a number of "byrd" models using this steel and a couple of Spyderco models. It is a good steel, especially at the price.

VG-10 is highly regarded and doesn't really belong with these steels. It's performance may be a testimony to the magic of Cobalt, but it has enough molybdenum to push it towards the next category. People say again and again that it is relatively easy to put an amazing edge on VG-10.

I am tossing Aogami "Super Blue" here also, despite having only a tiny amount of Chromium and not being stainless. Perhaps it may more properly be placed among the tool steels. This is another steel notable for taking a fine edge. Note that the magic element in this case is Tungsten.

Chrome-Moly Steels

I am putting steels with 2 percent Molybdenum (or more) in this group.

154CM (or CPM 154) is the flagship steel of this category. This is an excellent steel, especially for larger blades. For smaller blades, its main virtue is that it is inexpensive compared to other alternatives. This is not to say that it isn't a superb steel, which is kind of surprising given that it doesn't have a bunch of exotic metals in its formulation.

I find it interesting to compare 154CM with S30V (which really belongs in the next section on Vanadium steels) because these two steels are clearly the most widely used steels these days. Note that 154CM is an American made version (more or less) of ATS-34 steel that was made by Hitachi in Japan. CPM 154 is a powder metallurgy version of 154CM made by Crucible. As the stories go, 154CM is actually the original, made in ingot form, originally for jet turbines. Reportedly the "CM" denotes Climax Molybdenum. When Crucible dropped 154CM (perhaps back in the 1970's) Hitachi began making an equivalent as ATS-34. These days 154CM is back in production. Two of my Benchmade knives are labelled "154CM".

element 154CM S30V
Carbon 1.05 1.45
Chromium 14.0 14.0
Molybdenum 4.0 2.0
Vanadium 0.0 4.0

The following are some other steels in much the same class as 154CM

element 154CM ATS-34 RWL34 CTS B70P
Carbon 1.05 1.05 1.05 1.10
Chromium 14.0 14.0 14.0 14.0
Niobium -- -- -- 0.3
Manganese -- 0.4 0.5 0.5
Molybdenum 4.0 4.0 4.0 2.0
Silicon -- 0.35 0.50 0.30
Vanadium -- -- 0.20 1.0

The first three are simply versions of one another with minor tweaks.
CTS B70P somewhat distinguishes itself with the addition of a full percent of Vanadium along with 0.3 percent Niobium. Perhaps it could be a tough steel like 154CM with a little extra pizazz.

Vanadium steels

For me, CPM S30V is the knife steel by which all others are judged and to which all others are compared. If we want to talk about a new steel, we compare it to S30V.

CPM S30V is clearly a superior steel to 154CM for small folding knives. For big blades, 154CM is still used as it is tougher (it was originally developed for turbine blades in jet engines). The main difference in S30V is the addition of vanadium. Vanadium carbides are hard and make the edge last longer (as well as making the blade harder to sharpen).

Let's looks at some other steels in the CPM SxxV series.

element S30V S35V ELMAX S90 CTS 20CP S110V
Carbon 1.45 1.38 1.70 2.3 2.2 2.9
Chromium 14.0 14.0 18.0 14.0 13.0 15.25
Cobalt -- -- -- -- -- 2.5
Niobium -- 0.5 -- -- -- 3.0
Manganese -- -- 0.3 -- 0.5 0.4
Molybdenum 2.0 2.0 1.0 1.0 1.3 2.25
Silicon -- -- 0.8 -- 1.0 0.6
Tungsten -- -- -- -- -- 0.2
Vanadium 4.0 3.0 3.0 9.0 9.3 9.1

The main thing with S35V is the addition of Niobium. What I hear is that this doesn't particularly make the blade perform better, but it makes the material easier to work with for the manufacturer.

Elmax ought to perform about the same as S30V, but the word on the street is pretty lackluster:

I know it's not politically correct, but I'm just gonna say what everyone else is thinking here. Elmax is crap. Now hold on, don't hang me yet. It is crap for what you are paying, and for what you hear about it and expect from it.
This is just one comment, but it summarizes a lot of what you will read. Apparently Elmax has yielded highly variable (and sometimes disappointing) results. A steel in the M390 group is probably a better choice.

S90V has twice the Vanadium as S30V, which will definitely make a difference. CTS 20CP is Carpenter's version of S90V, not to be confused with CPM 20CV. Here is some fascinating information from a fellow at Carpenter:

In regards to the comments about naming, there is method to our madness. The CTS is intended to have a brand recognition. If it starts with a B, its origin is a bearing steel and if ends with a P means it is a powdered product. If it has a BD in the name, it was designed as a knife product (Blade Design). Example The mule out now from Spyderco is CTS B70P, its origin is a patented bearing steel CRB 7, so it is a bearing product which is powdered and the 70 is a mental note for the 7 in CRB-7. The only other letter we use is a Z which refers to a razor blade design (CTS BDZ1). Any other combination comes from a tool steel hence CTS 204P, comes from a stainless tool steel Micro Melt 20-4. From here you should be able to crack the code on CTS 20CP and its origin Micro Melt 420-CW.

S110V is another beast altogether, adding significant amounts of Cobalt and Niobium. People say though that in actual use S110V seems very similar to S90V.

CPM 20CV, M390 and CTS 204P

These are really just more steels in the "Vanadium group", but I have a special fondness for them, so here they are on their own.

These steels all have essentially the same composition, but are made by different makers. M390 is made by Bohler-Uddeholm (Europe). 20CV is made by Latrobe Duratech. CPM 20CV is made by Crucible and CTS-204P is made by Carpenter. Don't confuse 20CV with 20CP, which is entirely different. There are slight differences in composition, perhaps to avoid legal issues.

element S30V CPM 20CV CTS 204P M390
Carbon 1.45 1.9 1.9 1.9
Chromium 14.0 20.0 20.0 20.0
Manganese -- 0.30 0.30 0.30
Molybdenum 2.0 1.0 1.0 1.0
Silicon -- 0.3 0.6 0.7
Tungsten -- 0.6 0.65 0.6
Vanadium 4.0 4.0 4.0 4.0
Note the 20 percent Chromium. You aren't likely to have trouble with these steels rusting.

Tool Steels

These are steels with less than 13 percent Chromium. I used to avoid steels in this class, but now realize that rust can be managed with proper care and that there are some truly exciting steels in this group. Tool Steels are sometimes known to machinists as "high speed steels" (HSS) and are the steels used to make lathe tools and end mills and to cut other steels.

element S30V CPM M4 CPM 4V CTS 10V K390 Maxamet Cruwear
Carbon 1.45 1.4 1.35 2.45 2.47 2.15 1.10
Chromium 14.0 4.0 5.0 5.25 4.20 4.75 7.50
Cobalt -- -- -- -- 2.00 10.0 --
Manganese -- 0.30 0.40 0.50 0.40 0.30 --
Molybdenum 2.0 5.25 2.95 1.30 3.80 -- 1.60
Silicon -- 0.55 0.8 0.9 0.55 0.25 --
Tungsten -- 5.5 -- -- 1.0 13.0 1.15
Vanadium 4.0 4.0 3.85 9.75 9.0 6.0 2.4

M4 is sort of an odd bird. Many people are quite fond of it, including me at this point, though I was initially quite skeptical. In cutting performance it is similar to M390, so you have to ask what you are gaining by giving up corrosion resistance. It turns out what you are gaining is toughness, and you could argue that if you aren't using M4 in a big chopping blade there isn't much point. On the other hand, there is nothing wrong with toughness, and given that M4 has excellent edge retention, why not use it in a folder?

I hear amazing things about 4V. The MT21 Mule was in 4V.

CPM 10V and its brothers are in another league in terms of performance. Note that PMA11 and CPM 10V and K294 are all the same stuff, namely powder metallurgy versions of A11 tool steel. Oddly enough, CPM 10V looks a lot like CPM S90V with the Chromium reduced. CPM 10V has some of the most off the charts edge retention of any steel. It is as if by adding Chromium to gain corrosion resistance we soften the steel. I have no idea about comparing these two steels as far as toughness.

K390 looks like a very interesting steel. Spyderco used it in the MT17 Mule, and apparently a sprint run Military.

Tungsten (as well as Cobalt) are added to tool steels to get "red hardness". This may be important for use as machine tools used to cut other steels at high speeds, but I cannot see how it would be an important attribute for knife blades. But perhaps along with yielding red hardness these elements yield other virtues.

Further reading

You can spend days doing internet searchs on specific steels and how people on forums feel about them. This is a topic that attracts all kinds of attention, and naturally yields an abundance of opinions, information and misinformation. The following little gem from Sal at Spyderco is hidden away in the K294 discussion (which is a fascinating thread on its own merit):
I really enjoy Super Blue. Not the best edge retention, not much corrosion resistance, tough, but the real beauty of this steel is in its ability to take a very fine edge, like 52100.

Feedback? Questions? Drop me a line!

Tom's Knife Info / tom@mmto.org