Evercut Knife?

[davidthomas8779]

Saw a link and ad for this knife http://www.aplusrstore.com/product.php?id=689 today.

Claims to last 25 years before sharpening (5x ceramic and 300x steel) and is made from titanium carbide fused onto steel. Have any of the resident knife geeks tried one out yet? For $225 if it never needs to be sharpened, it should sell very well.

[Shalmanese]

If significant advances in knife metallurgy happens, you will hear about it in a place that's not a shopping catalog.

[mrsadm]

What? No link to the study?

"Third-party testing by the UK-based CATRA (Cutlery+Allied Trades Research Association) assessed the international cutting standards of the Evercut against 450 knives "

[paulraphael]

You can categorically assume that any knife sold with the claim "never need sharpening" or "10X sharper than ________" or "stays sharp 10X longer than_________" —or anything similar—is going to be utter B.S.

Usually these claims are associated with cheap informercial knives, but in this case it's a $200+ rip off. Never mind that it's not even in a useful chef's knife / gyuto shape. For that money you can buy an excellent chef's knife, a decent set of sharpening stones, and some books or instructional videos to get you started.

In practice, becoming a competent sharpener is the only way you'll even have sharp knives (at least for more than a few days at a stretch).

[Dakki]

What Paul said.

Titanium carbide is a wonderful material; in my experience you can expect a 5 to 10 times improvement in the life of a wear surface, compared to D2 tool steel, not to mention the fact that it's virtually inert at normal operating temperatures. Plus, you can use it to coat a part made of inexpensive, easily machined steel and use that to replace parts made of expensive, hard to machine steels in many cases, so in many applications you can actually get those benefits -with a cheaper part-, and it can take an extremely fine finish relatively easily.

That's actually tungsten carbide but you get the idea.

(I love carbide coatings. They pay my mortgage.)

Unfortunately, none of that is going to help with a knife edge. It's going to need diamond stones to sharpen, which are dear and IMO not as consistent as a good waterstone. Every time you sharpen it, you're going to be removing carbide, so sooner or later you're going to end up with a knife made of steel that's probably not very hard. I can't tell what process they use to coat from the advert, but every coating process I'm aware of that can give you more than a couple of thousandths of an inch of coating requires the steel substrate be rather soft, so unless they're using something I don't know about, the carbide coating is going to be paper thin, or the steel is going to be soft, or both!

I also have to mention the ISO 9001 certification is pretty meaningless. Virtually everyone in my industry has it; all it means in practice is that you keep certain paperwork, basically so the buyer can cover his butt when the cheap crud he got from the lowest bidder inevitably fails. A bit off-topic but that's a pet peeve of mine.

[paulraphael]

The other issue is that carbides are there to provide extreme wear resistance ... but it's been shown that abrasive wear is not an important process in kitchen knives dulling. Wear resistance does make a knife hard to sharpen, as Dakki says.

For a knife to get sharp, do so easily, and stay sharp in spite of of an a thin / high performance edge geometry, it needs a steel with excellent edge stability. This requires, among other things, a relatively low carbide content. Carbides are big compared with iron molecules. A high volume of carbides gives you a very weak, brittle edge that can't be made very sharp. Putting a coating of carbides on the surface would gurantee from the get go that the blade isn't sharp by any serious knife standards.

[Dakki]

The other issue is that carbides are there to provide extreme wear resistance ... but it's been shown that abrasive wear is not an important process in kitchen knives dulling. Wear resistance does make a knife hard to sharpen, as Dakki says.

This is absolutely correct. As you said below, our most important factor in maintaining sharpness is edge stability, not wear resistance. Edge stability is going to be determined by hardness (to prevent the edge rolling or otherwise deforming) and (perhaps less importantly) by toughness, to prevent chipping. For practical use, I'd add corrosion resistance as well, in an environment where the edge is going to be exposed to humidity, acids, salt and so on. I've seen lemon juice utterly ruin a perfectly good edge on a simple carbon steel knife in minutes.

That said, titanium (or tungsten) carbide is just comically hard stuff, hard enough that you can't measure it on the RC scale. It's not all that tough compared to most steels, though.

For a knife to get sharp, do so easily, and stay sharp in spite of of an a thin / high performance edge geometry, it needs a steel with excellent edge stability. This requires, among other things, a relatively low carbide content. Carbides are big compared with iron molecules. A high volume of carbides gives you a very weak, brittle edge that can't be made very sharp. Putting a coating of carbides on the surface would gurantee from the get go that the blade isn't sharp by any serious knife standards.

Here's where things could get confusing. Precipitated carbides in the steel, which appear as part of the heat treating process (depending on the exact chemistry of the steel) will behave exactly as you said. A cemented carbide edge, made by applying carbide as a coating or by forming a solid carbide blade (with the usual cobalt or nickel binder) could probably be made sharp enough for kitchen use (I haven't actually tried this so I won't swear it's true). The problem is that the edge would be ridiculously brittle at the kind of edge geometries we're talking about, defeating the whole purpose of the exercise.

[vice]

My metallurgy's a bit rusty (oof, apologies for that): what is the distinction between hardness and toughness?

[Dakki]

Toughness is the ability of a material to resist fracture.

Hardness is the ability of a material to resist deformation.

To give an example, a ceramic plate is very hard but not very tough, meaning it won't bend very far but it will break very easily.