Is tungsten carbide ferrous?



The you would certainly be wrong, Don. WC is a ceramic. Tungsten-carbide tools are made of a powder-metallurgy composite of WC ceramic and metal powders.
Ed Huntress
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On Sat, 07 Feb 2004 17:58:50 GMT, "Ed Huntress"

Well I disagree WC is not a ceramic.
Take a look at a dictionary definition.
We called them cermets and we probably made more of them than any other manufacturer.
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'alien
that.:-)
Tungsten-carbide
HOkay, sometimes I lose track of the confusion that's propagated about this material, and the common uses of the term "ceramic," as well as the vague terms used in metallurgy to describe WC and TaC, which are interstitial carbides. On top of it all, the metalworking- and other industrial fields have added their own jargon. This is going to be one of my lengthy dissertations, so I'll apologize in advance and warn off anyone who doesn't really give a damn. On the other hand, they may find this interesting, because it's the result of research I did on the history of carbide tools in 1977, plus years of exposure as Materials Editor of American Machinist, and more recently as Tooling Editor of Machining magazine. You won't see it put together quite this way anywhere else, I believe.
The term "ceramic" is old and vague as hell. It can include any non-metallic material, or compound of a metal and a non-metallic material, that's hard and brittle. You will sometimes see plain sand- and lime-putty mortar, which has a compression strength of only 75 - 350 psi, described as a "ceramic" in the building-restoration literature. This is not as ridiculous as it sounds; when lime putty (hydrated lime, Ca(OH2)) picks up CO2 from the atmosphere, it becomes CaCO3 -- limestone. That fills the bill: non-metallic and somewhat hard, somewhat brittle. As reconstituted limestone goes, lime mortar pretty lousy, but it's still within the definition. The definition of "ceramic" actually is that broad. Fine-clay dishware is generally described as "ceramic," as another example.
There is no absolute technical definition, although engineers of advanced ceramics from around the world got together in 1993 and wrote one for their own use. It doesn't apply to anything we're interested in. It applies only to the newest, most advanced engineering ceramics. In Europe, engineers define plain glass as a ceramic. We're not interested in that definition, either.
What we're interested in is something that will help us sort out the often contradictory uses of the term in industry. Here's a good one from Encyclopedia Britannica:
"Industrial ceramics are commonly understood to be all industrially used materials that are inorganic, nonmetallic solids. Usually they are metal oxides (that is, compounds of metallic elements and oxygen), but many ceramics (especially advanced ceramics) are compounds of metallic elements and carbon, nitrogen, or sulfur."
There's tungsten carbide for you: a metal (tungsten) compounded with carbon. It's hard, it's brittle, it's refractory, and it doesn't even melt like a metal. That's a ceramic. The bonding of W and C fit well within the more technical chemical definitions, which allow for both ionic and covalent bonds, plus various combinations thereof.
WC is a particular type of ceramic: an interstitial carbide. Here's Britannica again:
"Interstitial carbides are derived primarily from relatively large transition metals acting as a host lattice and the small carbon atoms occupying interstices of the close-packed metal atoms...Several have industrial importance, including tungsten carbide (WC) and tantalum carbide (TaC), which are used as high-speed cutting tools because of their extreme hardness and chemical inertness."
Now for some background on the confusing, often contradictory uses of the terms.
Back in the 1920s, some Germans came up with a way to make tools out of this hard stuff by mixing some WC powder and some cobalt powder, and then pressing and sintering them together into a composite material. It was NOT a compound. The carbide particles remained distinct in the composite. It was something like concrete in that regard.
At about the same time, Philip McKenna (Kennametal) was experimenting with WC for cutting tools, too, trying to make them out of solid WC. You do this by taking straight WC powder and pressing it, and then sintering it at extremely high temperatures. I think WC sinters at around 4700 deg. F. Very difficult, and quite expensive (what do you make the pressing tools out of, for example?). He made the WC into billets and then sliced them into cutting tools with diamond saws.
McKenna had some success but the result was too brittle and too expensive. It *was* capable of handling higher temperatures than the German stuff, and it was harder. But it was a no-go commercially. (Aside: the US Army is making big pieces of solid tungsten carbide again, much like McKenna's billets he made in the 1920s. Only the Army is using it for artillery shells.)
So McKenna reverted to the German method, and these carbide/cobalt (and sometimes nickel) composites became available around the world, and were commonly called "cemented carbides." The cement, also known as the matrix, is the cobalt.
First terminology problem: People got sloppy and started dropping the "cemented" part of "cemented carbide." It was just "carbide," or "tungsten carbide." Only it wasn't, really. It was some tungsten carbide mixed with some metal and sintered into a composite material.
Second terminology problem: Metallurgists are more contrary than chemists, and they sometimes call tungsten carbide "metallike," or even a "metal." Chemists object. Metallurgists don't care. Machinists wind up confused. It's metallike, only it allows almost no slippage of crystals along slip planes: it has virtually no ductility, in other words. It behaves like a ceramic. It fits the definitions of ceramics that chemists and other scientists use. Metallurgists still don't care. They have their own little world.
Third terminology problem: As newer ceramics came into play in the emerging world of "hard materials," they, too, got mixed with metal binders or matrices to form composites, and were given the name "cermets." Snappy, descriptive, and neat. However, somebody forgot about tungsten-carbide/cobalt composites. They're cermets, too. Marketing people in the cutting tool business didn't care. They had a snappy new name to apply to their new products, and they weren't going to let lowly old tungsten carbide horn in on the action. Machinists wind up confused. Tool companies don't care.
So, does that help? There are no WC tools on the market that I know of. They're all cemented, metal-matrix composites made of ceramic WC, refractory metals, and sometimes odds and ends of other metals and ceramic compounds. A pure mass of WC is a pretty rare thing, and is not used for cutting tools today. It never was, except for some experiments.
'Sorry for the length. I didn't have time to write it shorter. <g>
Ed Huntress
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Excellent dissertation and very helpful. Thank you.
Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though.
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I knew there was a real reason for spending so much time reading this NG.
Nice post, Ed!
Mike Eberlein
Ed Huntress wrote:

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Thanks, Mike. I used to get paid for that kind of stuff. Now it's just a bad habit. <g>
Ed Huntress
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On Sun, 08 Feb 2004 07:49:38 GMT, "Ed Huntress"

I am going to delete some of your material here in the interest of length. Your discussion covers most of the vagueness of the term "ceramic" and I doubt if we would have any disagreement if we had the opportunity to spend a couple hours in a face to face discussion of the topic.
I am a research chemist and spent the first 15 years of my career in the metallurgy research laboratory of a large corporation. What the hell it was the General Electric Research Laboratory. The second 18 years I was at the same facility and although still dealing with the metallurgists and ceramists I also had to contend with a bunch of organic chemists. Ceramics was my second major in a PH.D. program at the University of Illinois.
We probably made more cemented carbides than any other company and at the time I started we were in the midst of developing the production of synthetic diamonds. None of cemented carbide research or the synthetic diamond research was done in our Ceramics Laboratory.
Yes the term is vague, widely used and widely miss-used. The following information on ceramics is blatantly copied in part from the "Encyclopedia of Chemistry" edited by G.L.Clark a well-known chemist and one of my U of I professors. Parts of the stuff below was authored by A.I. Andrews head of the Ceramics Department at the U of I and one of my committee members.
**An all-embracing definition is rather difficult because it includes what appears by a cursory examination to cover widely diverse areas. A recent committee of the American Ceramic Society defined ceramics to include those industries which manufacture products by the action of heat on raw materials, most of which are of an earthy nature, in which the chemical element silicon together with its oxide and complex compounds known as silicates occupy a predominant position.
They go on to say "It is much easier to understand the scope of the ceramic industry by a consideration of specific products. It may be divided into seven major areas:"
For brevity's sake the areas are listed here by title only without expansion...Structural clay products, Whitewares, All varieties of glass products, Porcelain enamel products, Refractories, Cemented materials such as Portland cement, & Abrasive materials such as alumina, silicon carbide. ***
Now I can see a quick Ah Hah from Ed but would hasten to point out that although cemented WC certainly fits in some of those categories it is not specifically mentioned in the definitions. In addition Cermets, Refractorys, & Abrasives are covered separately in the Encyclopedia.
My problem with calling WC a ceramic probably comes from the viewpoint of a chemist tainted by a long association with a bevy of ceramists and metallurgists. Here is my reservation in a nutshell...Would one call the following compounds ceramics: iron carbide, aluminum carbide, iron oxide, calcium oxide, calcium carbide, silicon dioxide, molybdenum sulfide, etc. If it is a single compound I would be very hesitant to call it a ceramic. So by my definition one needs two or more compounds along with some interaction so as to not have a simple mixture to get a ceramic. WC (to me) is a chemical compound (it is a carbide) as is e.g. SiO2 an oxide and not a ceramic. Quartz might give me some hemming and hawing as one could consider it a glass which sort of puts it in the ceramic category.
Cemented carbides fall very nicely into the category of "Cermets" which is from my point of view a better and more descriptive and well recognized category.
If the question had been "cemented WC" I probably wouldn't have made the same comment but when the topic was WC it created all sorts of misgivings to let that go by as a ceramic. Actually I am crotchety enough in my old age so I still consider cemented carbides as cermets not ceramics but how one classifies them probably depends a great deal on one's background.
To repeat... Ed's excellent dissertation is deleted for brevity. It certainly exhibits why there are differences of opinions even by those actively working in the field which I haven't done for almost 18 years now.

No need to apologize. Your points are well taken,interesting, & instructive.
Don
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Both great dissertations. Thanks for another interesting discussion.
Tim (TOP-posting for brevity)
-- "That's for the courts to decide." - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms

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    I agree with this.

    However -- *why* did you quote the whole thing yet again? You did not need to quote it all -- it was all out there in the newsgroup still, and any *reasonable* newsreader could have followed a link back from your article.
    Instead, you quoted 143 lines, with no need at all. That does not qualify as "brevity" in my book.
    *This* is why people object to top posting. Once someone does that, they seem to feel no need to trim excess quoted material.
    If you *must* top-post -- *please* trim most of the quoted material.
    Enjoy,         DoN.
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If it weren't quoted some people might be confused as to what I'm replying to.

Far better than putting my one-liner at the very bottom.

I usually do...just lazy this time.
Tim
-- "That's for the courts to decide." - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms
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You'll note, however, that handbook descriptions of ceramics sometimes note that diamond technically falls within their definitions of "ceramics." It's not included in the common explanations because of convention, not because of some technical exclusion.
In the US, it's conventional to include only compounds among the ceramics. In Europe, that's not necessarily so. Again, it's more a matter of technical conventions.

However, that's just industry convention and internal definitions. For example, WC is listed as a ceramic in the NIST ceramics database.

Again, conventions, not technical exclusions. For example, your "single compound" [I assume you mean "two-component" compound] definition runs into a big problem with the fact that the overwhelming volume of engineering ceramics (sometimes called "technical ceramics," especially in Europe) is two-component compounds: silicon nitride; silicon carbide; aluminum oxide; and zirconium oxide. Together, that group is the one usually called the conventional "engineering ceramics" in engineering.
The definitional problem you're raising is similar to the one that those engineers who got together in 1993, as I mentioned, were facing. The newest, highest-performing engineering ceramics are mostly complex compounds. They're used primarily in electronics and in aerospace. However, two-component ceramics are the dominant ones in industry, and no one that I know of would reject, say, silicon nitride or zirconium oxide as major industrial ceramics.
As for iron carbide, iron oxide, etc.: iron carbide most definitely is considered a ceramic carbide in engineering. Iron carbide, along with chromium carbide and vanadium carbide (the dominant one in terms of performance) are the ceramic carbides that make up a percentage of the better high-speed steels. In the very high-performance HSS, such as CPM Rex 121, they make up over 30% of the total mix, and they're very important to the materials' properties.
Iron oxide is one that tests the definitions. Red rust (Fe2O3) meets some peoples' definitions but not others'. It would be interesting to see what its properties were if it were compacted and sintered. Black rust, on the other hand (Fe3O4), the tenacious stuff that often tends to hang on when we strip red rust off of steel with phosphoric acid, is sometimes called the "ceramic form" of iron oxide. Now, since you're a chemist, I should say that I'm aware there are two different forms of Fe3O4, and that only one of them meets this definition (magnetite). But the point is that some iron oxides exhibit ceramic properties, and are justly called "ceramic" by the common definitions.

Cemented carbides, definitely. But "cermet" is a marketing term, not a technical term.

You're right, they definitely are cermets, or metal-matrix ceramic/metal composites, if you want to get precise. They most definitely are NOT ceramics! They CONTAIN ceramics, in a mechanical mixture of metal and ceramic powders that is sintered into a solid mass. Their properties fall somewhere between the properties of ceramics and metals. But that's due to the mechanical mixture, and their properties adhere to the law of mixtures, as it's known in materials science.
But "carbide" tools, or "WC" tools, are neither carbides, nor tungsten carbide, nor ceramics.
Let's make sure we're clear on this: WC is a ceramic. Tools are not made of pure WC, any more than a "fiberglass" Corvette body is made of pure glass. Cemented carbides are metal-matrix composites that *contain* WC. I hope we have agreement at least on the point that "carbide" tools are not ceramics. They're mixtures of ceramics and metal(s).

I'm sure your definitions are considered the more useful ones in the technical end of your former business, Don. That's perhaps a good chemist's definition. But it is a minority position within industry. The mainstream definition *within engineering* doesn't think much of including hardened lime putty among ceramics, but the people who make decorative ceramics, and who call themselves ceramicists, probably would disagree. The word "ceramics" comes from the Greek word for "potter's clay." A lot of different people, in diverse arts and industries, believe their definition is the correct one. <g>
But within mechanical engineering and the closely related arms of materials science, tungsten carbide, silicon carbide, tantalum carbide, vanadium carbide, aluminum oxide, etc. are all mainstream engineering ceramics.
It *is* a matter of definition. But consider the relevant issues in mechanical engineering, or most other aspects of engineering: these materials are all hard as hell; they non-ductile; they're highly refractory; they're compounds of metals (iron, aluminum tungsten) or metalloids (boron, silicon) and non-metals (oxygen, carbon, nitrogen, etc.); and they're generally quite inert. Those are the properties that are relevant, and they're the ones that fit the mainstream, engineering definition of ceramics -- including tungsten carbide. The fact that some include these materials in their definitions of ceramics and others do not is a matter of convention and tradition more than of some chemical definition. And that's true because there is no precise chemical definition of a ceramic.
--
Ed Huntress
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says...

This portion of your excellent discussion is what does it for me, the fact that cemented carbides are composed to some large degree of cobalt metal means that I would tend to shy away from the 'ceramic' label. Though I have to agree that the issue is a confusing one - here the thing's name really depends on who is doing the describing: physicist, ceramist, chemist, machinist, etc.
Jim
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Ed Huntress

elements
So would I. Cemented carbide cutting tools are NOT ceramics. They *contain* ceramics, especially WC and TaC.
That was my main point. <g>

Another good point. Note Don's hesitations, based on the definitions he accepts as a chemist.
The problem is, chemists don't have a hold on the definitions. They have never bothered to make a precise, technical definition of ceramics, because it's not really a technical term.
Engineers of advanced ceramics have created a definition for their own use, back in 1993, as I mentioned. But they freely acknowledge that the definition is only for their purposes, to help avoid confusion within their own field. They're not trying to convince the world that they have the "correct" definition.
Ed Huntress
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wrote:

Actually the cobalt content of cemented tungsten carbide is small compared to the WC and other carbides. The reason cobalt is used is that it wets the surface of WC and doesn't run wild dissolving the carbide. Nickel or iron or a lot of other elements would be cheaper.
How you label these materials certainly will depend on your background. I thought Ed and I might agree but it ain't gonna happen. That makes no difference because we are both correct in the environment in which we work.
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Ed Huntress

used
metal
elements
Oh, I don't think we disagree, Don. I'm just being contrary. <g>
In trying to clarify something like this it's often more important to identify the points of disagreement than those of agreement. I don't write to explain things to people like you, who know more about the chemistry of it than I'll ever know. I write to make as clear as I can the things that are relevant and distinctive to the machinists and people with an applications-engineering interest in materials.
So don't think we really disagree. My point there was that your understanding of ceramics is based on a chemist's needs and understanding, which is at the opposite pole from a ceramicist's needs and understanding. People who do metalworking with these materials are somewhere in the middle of those two extremes.
Tungsten carbide is a misunderstood material, lost in jargon and convention within the metalworking trades. I've tried to deal with that and explain it to a magazine audience for roughly 30 years, although not quite in the terms we've been using here. Having your POV on it is extremely helpful -- for the contrasts more than the similarities, actually. One could make a case that it's a lack of confrontation between the different views on this subject that have helped to muddy the waters over the last 80 years.
Now, if we had a potter here on the NG, we'd really be able to put some perspective on it. <g>
Ed Huntress
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wrote:

Or maybe the guy we heard about who was supposedly caught stealing ceramic tool bits back when they were still quite a new thing. Supposedly when they checked his house, they found that he'd tiled his bathroom floor with them. Probably an urban myth, but quite a story, especially when they used to cost about 10X what they do today.
Karl Pearson
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Ouch! I hope they were negative-rake.
Ed Huntress
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On 6 Feb 2004 17:29:55 -0800, snipped-for-privacy@hotmail.com (benwoodward.com) wrote:

Just put it in the "FM" category.
Gunner
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