Ceramic knife . . . fail

The one certain thing about any knife on earth is that it will eventually become dull with use. Since steel was first created by the accidental introduction of carbon into iron, knife makers have strived to balance several conflicting requirements, among them the ability to hold an edge and the ability to be sharpened easily. Obviously it’s essentially impossible to have both properties in the same blade (the Italics are there because it’s not quite a black and white choice). Serious knife users tend to fall into two categories: those who prefer a long-lasting edge and are willing to put up with the extra work necessary to sharpen it when it finally dulls, and those who want to be able to sharpen the knife quickly and are willing to do it more often. Count me in the former category: I don’t mind spending half an hour sharpening one knife at home if it will last through, say, skinning and butchering an elk in the field without needing touching up.

The basic gauge of steel hardness is the Rockwell Scale, named for Hugh and Stanley Rockwell, who developed a machine to quantify it. The Rockwell test for knife steels employs a 300-pound-plus weight that presses a sharp diamond cone into the material. The depth to which the cone penetrates the surface reveals the hardness of the material (on older Puma knives every product was subjected to this test, and the resulting tiny crater in the steel proudly indicated with a sticker).

So far, so good. Obviously, the harder the steel the stronger, and the better it will hold an edge, right? Simply buy a knife made from the hardest steel you can find. Done.

Not so fast. As steel becomes harder, it also frequently becomes more brittle, and this can make a fine edge—indeed the entire blade—susceptible to bending or impact forces.

A proper knife blade must thus balance several qualities. As described by knife makers:

Wear resistance indicates the resistance of the knife to abrasion. This is largely determined by the density and distribution of carbides (compounds of carbon and other metalic elements) within the finished blade.

Toughness describes the ability of the knife to survive impacts or bending without breaking. On the edge this translates to resistance to chipping.

Strength is the ability of the knife to resist bending in the first place. This is directly related to the Rockwell hardness. Strength helps prevent microscopic folding of the edge during use, which is perceived by the user as dulling.

Edge holding: Not the same thing as wear resistance, edge holding ability varies with all of the above properties.

Stain resistance is the least important quality of the steel, unless you really like shiny knives. Many stainless blades (which are only stain-resistant) lack the toughness and edge-holding of some non-stainless blades.

The science of making knife steel revolves around the blending of various alloys to achieve the best possible compromise. It’s easy and cheap to make a steel that holds an edge well or can withstand bending or is easy to sharpen; it’s extremely difficult to make one that displays all those qualities. But modern alloys are resulting in knife blades that are both tougher and stronger than those of just a decade ago. Manufacturers have found new ways of making steel, such as the particle metallurgy pioneered by Crucible Industries, which results in extremely fine microstructures in the finished alloy, enhancing virtually every desirable characteristic.

Once the steel is in the hands of the knifemaker, the art begins, because how the maker heat treats the blade determines how the particular alloy being used will perform in the end product. Heat treating involves successive heating and cooling of the blade, at different temperatures and speeds, sometimes on specific areas of the blade, sometimes immersed in different mediums to control certain aspects of the process. The result is that two knives made from an identical steel alloy can display significantly different performance. In fact, good steel can ruined with improper heat treating, and the lowliest carbon-steel knife can display awesome performance given careful differential heat treatment.

There are two other ways to alter or augment the properties of knife steel: laminating and pattern-welding. Laminated blades combine a center of very hard steel with outer layers of softer steel, to give the knife both superior edge-holding and toughness. Pattern-welded steel produces the lovely swirled effect you see on many high-grade knife blades. Commonly, but incorrectly, called Damascus (which is entirely different), pattern-welded steel comprises layers of different types of steel, repeatedly heated and folded over to gain a blade that can have hundreds of layers. The original intent of pattern-welded steel was to combine soft iron and brittle carbon steel to combine edge-holding and toughness. With today’s steels this is not necessary; most modern pattern-welded blades are done strictly for effect.

An extreme example of this can be found in ceramic knives—not steel at all of course, but sintered zirconium oxide or zirconium carbide. Ceramic knives, which display a Rockwell hardness of around 75 (compared to the R58 to R60 of an average knife), hold their edges fabulously well, but are relatively fragile: they can chip if torqued when cutting, and can actually break if dropped on a hard floor.

You can spot three obvious chips in this short section of the Tachi's blade.

Several years ago I decided to give ceramic blades a try. I chose a small Tachi kitchen knife, thinking that if it worked out it would be a good size for the camper. 

Right off the bat, I was disappointed in the edge as it came from the factory. Given the hype, I expected scalpel-like cutting; instead, we found that any one of our steel Henckels knives easily exceeded it at such tests as cleanly slicing tomatoes. Okay, so we’d have a sort-of-sharp blade that would last a long time, right? Nope. Even with firm parameters as to how we used the Tachi—essentially as a vegetable knife, period—we soon noticed micro-chips in the edge, followed by several not-so-micro-sized chips. We wondered simultaneously: Where are those little missing chips going? An alarming thought. Since a ceramic knife can only be sharpened with specialized equipment, we were stuck either living with it or sending it back in for the $10 service. Instead, we simply found ourselves using it less and less. Finally, Roseann managed to drop the thing (subconsciously on purpose?), and snap. The partial-tang blade parted ways with its handle.

The technology might improve—one imagines some sort of steel/ceramic hybrid—but for now, I’ll stick with steel knives.