An added data point in steel comparisions.

Carlos

Carlos

Joined
Jul 9, 2000
Messages
1,654

One thing that has always bothered me a bit about many arguments over the virtues and weaknesses of various steels used in knives is that the intent of the metallurgists that formulated these steels is generally omitted. One thing we tend to overlook is that most of these steels have been adapted for use in cutlery. Very few, if any, steels have been formulated expressly for the small (in industrial terms) knife industry.

So for my own edification I spent an evening digging around to see what I could find about the primary purspose of these steels which many of us are rather passionate about.
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I decided to share my findings with whomever may be interested:
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I've limited this to steels being used or expected to be used for production folding knives. Whenever possible, I've quoted manufacturer (or other expert) text. Any errors are my own.
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TOOL STEELS
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For the most part "tool steels" are those steels used for the tooling of industrial manufacturing processes. This includes both stainless and non-stainless alloys, and uses varying fom bearings, rollers, cutters/saws, dies, &c.


<u>High Carbon</u>

A-2: An air-hardened steel designed for "Gauges, forming rolls, thread rollers, bending dies, cold blanking dies, coining dies, cold trimming dies, punches, &c."

M-2: A "high-speed" steel that retains its temper in high volume, high temperature manufacturing operations. Designed for "drills, taps, punches, reamers, broaches, planer knives, lathe tools, forge dies, form cutters, milling cutters, end mills, gear cutters and many other cutting tool applications."

D-2: Considered by many to be "semi-stainless," is is designed to be used for: "Blanking, drawing, forming, coining, lamination, thread rolling and trimming dies, burnishing tools, gauges, lathe centers, punches."


<u>High-Carbon Stainless</u>

440C (and related Japanese AUS 10): "...Designed for a combination of high wear resistance and moderate corrosion resistance in mild environments." Appears to be primarily a ball-bearing steel: "This material is used extensively in bearing applications where precise tolerances and surface finishes are required." Actually all 400 grades seem to be ball-bearing steels, from 420 for low-grade bearings through 440C for high-grade bearings. I assume this is the same purpose of the equivalent AUS steels from Japan.


<u>High-Carbon Stainless Particle</u>

These new tool steels appear to have been produced by Crucible Metallurgy primarily for the plastics industry, which requires high corrosion-resistance as well as high wear-resistance for their tooling.

CPM-S60V (formerly 440V): "Corrosion resistance comparable to T440C stainless steel, with wear resistance many times greater than that of T440C, D2 and M2 tool steels."


CPM-S90V (formerly 420V): "The exceptional wear resistance and good corrosion resistance of CPM 420V make it an excellent candidate to replace 440C and other corrosion and wear resistant materials, particularly where increased wear resistance is a primary concern." Used for: "Injection and extrusion screw and barrel components; wear components for food, plastic, and chemical processing equipment; pelletizing knives; slitters, cutters, chipper knives; bearings, bushings, cams, gears, valves; rolls."

CPM-3V: "...Designed to provide maximum resistance to breakage and chipping in a high wear-resistance steel. It offers impact resistance greater than A2, D2, Cru-Wear, or CPM M4, approaching the levels provided by S7 and other shock resistant grades, while retaining the wear resistance, high hardness, and thermal stability for coating offered by high alloy wear resistant grades. CPM 3V is intended to be used at 58/60 HRC in applications where chronic breakage and chipping are encountered in other tool steels, but where the wear properties of a high alloy P/M steel are required." Used for: "Stamping or Forming Tools; Blanking Dies; Shear Blades; Scrap Choppers; Plastic Injection & Extrusion Feedscrews; Punches & Dies; Fineblanking Tools; Industrial Knives & Slitters; Rolls."
(Sounds almost ideal for knives, no?)


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AEROSPACE STEELS
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154-CM: Developed by Crucible for use in aircraft engine turbine blades, it is a "high speed" steel that can operate at high temperatures without losing temper. ATS-34 is Hitachi's clone of 154-CM, supposedly manufactured for the knife industry.

BG-42: A "high speed" VIM VAR* steel developed for use in bearings and rollers in turbine engines, as well as ball screws, aircraft gears, &c. (*Vacuum Induction Melt / Vacuum Arc Remelt.)


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CUTLERY STEELS
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Info on the origin of these Japanese cutlery steels is hard to come by, but here is what I've got:

ATS-55: A steel made by Hitachi, based on ATS-34 but modified specifically for use in cutlery.

VG-10: A limited production steel produced by a single small mill in Japan, it appears to have formulated specifically for use in cutlery. Hearsay links its creation either to the medical field for surgical knives, or to cutting implements used by horticulturalists.

>> Any thoughts, additions, or corrections?
 
I couldn't find any direct info on Japanese steels in English -- including AUS-6 and AUS-8. But since they seem to be generally considered equivalent to 440-A and 440-B respectively, I would speculate that they are probably ball-bearing steels.
 
ACK! AUS-8 is basically 440-B??? If I had known that, I wouldn't have ordered the micarta version of the Calypso Jr.!!! My only experience with it prior to this was my XL Voyager, which (surprise surprise) I didn't use enough to dull the blade. I would have gotten the lightweight Calypso Jr. or even the Native (whose steel has apparently been upgraded in my absense!). Grrr. Oh well. I'll figure something out.
 
Walt, thanks for the links. The last two would have made my life a lot easier. I will go through them and make additions and corrections.

Howie, my understanding is that the AUS steels are equivalent to the 440 steels the same way that 154-CM and ATS-34 are considered interchangeable.

AUS-6 = 440-A
AUS-8 = 440-B
AUS-10 = 440-C

You might want to check the Steel FAQ here at Bladeforums for more details.
 
Hello Folks,

Cutlery industry, as we speak about it, uses a minute piece of the steels produced in the mills. Only very large, or very popular productions of steel can be custom made for knives.
Second, the quality of a steel depends, in the end on the heat-treath. Böker claims there 440C cuts better then ATS-34. In reality, these steels are so similar, people cannot see the difference. If the same ATS-34 gets in the hands of Paul Bos or Benchmade, then it becomes better.
Spyderco treaths their AUS-8 much better then Coldsteel. It may have the same compositions, it will behave better.

A knife's performance is dictated by three keystones : Steel, heat-treath and blade geometry. We always nag about which steel is in a blade, but if you let me make a blade for such a folder, I'll use 52100 and heath-treath it myself and give it a few nitro-treaths, it will outcut any stainless steel. Most carbon steels will do this.
And most carbon steels are 1/10 of the price of stainless (carsprings..... files... ballbearings...)

I am not talking about CPM stuff. They can do marvellous things with steel, but you will pay the price for that.

I think a steel for a knife is chosen by these factors:
1. Corrosion resistance
2. Price (budget of customer)
3. Edgeholding
4. toughness - ductility
5. Easy to work
6. Availability

This is kind of a all-time all-stars topic, so insted of getting a riot over here you can also mail me... the icon above

greetz, Bart.

------------------
"If the world wouldn't SUCK, we'd all fall off !"

member of the BKS
http://www.expage.com/belgianknives
 
Bart raises a great point. The way a steel is Heat-treated (annealed, normalized, hardened, and tempered) plays a critical role in the performance of any steel. In fact, I think this is far more important than the elemental constition of blade steels. Any steel can be heated-treated in such a way that is will be too soft for use as a knife. Or to hard. There is always a compromise of conflicting properties.

Some steels allow a wider latitude than others in finding this optimal balance. When used as a blade, any of the the steels you mentioned will have very different physical properties compared to the way it is heat-treated for use in the tool and die industry, or as a bearing steel.

During heat treatment, there is a very complex and difficult to control rearragement of molecules into different kinds of crystal lattices and amorphous, glass like, structures. Finding the right way to optimally heat treat blade steels is a complex Art.

So I have no doubt that professional heat-treaters like Paul Bos will do a better job of making steels into better blades than some companies, or individual makers. I personally am fond of forged blades. I enjoy talking to makers about their philosophy of heat-treating steels. They do not all do it the same way. ATS34 from one place is not always the same as ATS34 from another. This is true for Any steel you can mention.

Some makers (like members of the American Bladesmith Society) do differential heat treatments to their blades. They start with good steel, and make it better for use as a blade by selectively controlling the hardness and flexibility of the edge, spine, and tang of a knife.

You are right about steels being adapted for use as knives. Some steels do make better knives than others. But it is much more complicated than just the ratio of elements in the steel.

Have a look at the articles on heat-treating at Don Fogg's and Ed Caffrey's web sites. This is an exceedingly complex issue. There is NO best steel for knives. There are only steels that are better compromises than others for specific applications.

Paracelsus
 
Sandvik 12C27 is another steel that I believe was developed for specifically for cutlery.

But what a steel was developed for has little bearing on how well it performs, steel is steel for the most part, iron and carbon. The largest differentiators in terms of characteristics are the amount of carbon and the amount of chrome added for stain resistance, and the effects of those elements are the same whether the steel was intended for knife blades or ball bearings.

ATS-34 is modified by removing most of the Molybdenum to make it ATS-55. This for the most part removes its ability to maintain hardness at high temps, around 900 degrees. It is easy to see how this would make ATS-55 a poorer bearing steel in high heat applications, but it is less easy to see how this makes it a better "cutlery" steel. The bottom line is that you get a steel that is very similar to ATS-34 for low heat applications, but costs less.
 
Good thread and thanks for the research, Carlos. Steve I think Sandvic 12C27 is also a bearing and tool steel used in tooling applications mostly compared with cutlery.

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Roger Blake
 
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