By Michael S. Black

To make a good working knife, you need a good piece of steel.

Besides being a talented writer, the late Butch Winter was also an enthusiastic hunter, with what was once the largest privately owned collection of custom knives in America. When Butch wrote a published article stating he didn’t care much for D2 tool steel because knives made with it tended to either be too hard or too soft, it made an impression.

D2 steel blade

Integral drop-point hunter with cast D2 steel blade and cocobolo handles by Robert Fisher. Knife style is scapel-inspired.

In the years preceding his death, Butch found knives like Bob Dozier’s, which were made with D2 steel, to be to his liking. Dozier’s D2-bladed knives have set a performance standard for years. You can buy fancier D2 knives or less-expensive D2 knives. But, when you want a knife that can cut as well as any made with D2 alloy, Dozier Knives continues to be the comparison standard.

Butch Winter sagely stated there are no bad cutlery steels, although some might be better-suited for certain applications than others. My personal experience with knives made with D2-steel blades has been that the steel is capable of providing a performance range that stretches from good (in the top 50%) to phenomenal (in the top 1%).

How does a buyer determine where the knife is on that scale? It’s a valid question, but one for which I don’t have the definitive answer. I do have a better-than-average comprehensive explanation for why that definitive answer is elusive.

D2 Steel Makeup

The chemical content for D2 tool steel is 1.4-1.6% carbon, 0.60% manganese, 11.00-13.00% chromium, 0.30% nickel, 1.10% vanadium, and 0.70-1.20% molybdenum. The primary use of this steel is for making stamping dies that cut steel pieces out of other, softer steels. The actual percentage of D2 tool steel produced by steel makers that winds up in use as knife blades is quite small.

While I have no evidence that distribution of available product might prejudice how steel makers provide the D2 steel they make, as a chemist, I can tell you that all D2 steel is not identical. Every production lot has allowable fluctuations in the component contents. This means that it’s possible for the variables to stack in a way that may either result in an ordinary serviceable knife or in an extraordinarily good knife. And the result may not be evident until after a knife is finished.

Bob Dozier told me during a telephone conversation that, once in a blue moon, he has to send a shipment of D2 steel back to the steel supplier after heat treatment of the first blades when, after testing, they did not give the results he expects from his proprietary heat-treatment procedures.

Not all knife makers are as conscientious or demanding about quality control in their heat-treating as Bob Dozier. Every time we talk, he stresses that it’s consistency and uniformity of heat treatment that’s the primary factor in his knives performing in a superior way, knife after knife. Bob confirms that to make a good working knife, you need a good piece of steel.

Don’t Judge D2 Steel by its Looks

You can’t tell how a knife cuts just by looking at it — you have to cut something with it. I perform cutting tests in materials that have proven to be hard to cut for all but the very best knives. I also do side-by-side cutting comparisons while doing daily cutting chores to distinguish which knives cut with the fewest limitations.

For instance, the D2 knives that made the fewest cuts on rope using only 1-inch of blade, and comparable edge geometry, still accomplished enough slices to be on the high end of “good” by my evaluation criterion. The longest-cutting knives will cut 10 times longer between sharpening, than the knives with the least cutting endurance.

I can take the two very best D2-bladed rope cutters I’ve tested and compare them by cutting the neck off a plastic bottle. One blade can accomplish this with a single slice; the other blade requires 15 slices. In this case, the different heat-treatments achieve different carbide grain sizes, and the larger carbide grain apparently cuts this plastic better than the nano-grain carbide, which is 10 times smaller.

So, what kind of knife does D2 steel make?

It varies from good to extraordinary, depending on the production lot of steel, the way the steel is heat-treated, and the way the blade edge is beveled and finished. The knife owner can control the last two variables, but the others are established invisibly before the knife is purchased.

The only way to know how good your knife is, is to test it with repeatable cutting tests. It’s like accuracy-testing a firearm. Experience may indicate that a certain type of gun usually performs well. However, the way it performs can depend on the ammo used, and preferences will vary from individual gun to individual gun.

D2 steel folders

Out-of-production models, such as the Camillus-produced EDC designed by Daryl Ralph, and Ka-Bar’s D2 Extreme folders, can still be found.

The D2 knives that cut the longest in rope may not always cut the best in other materials. Quantity of cut and quality of cut are usually, but not always, coincidental. The only way to find out is to cut with your knife and test its capabilities. You can at least then be either satisfied or disappointed enough to stay with what you’ve got, or try something different.

Chances are good you’ll ultimately need more than one knife to accomplish all your cutting chores with the least applied effort. But you can’t tell  — without comparison-cutting with different knives on the same tasks  — which knife is the easiest to use for that task.

Every knife has the potential to be a unique performer in your hands, no matter what any authority tells you to expect on the basis of their experience. Test your own knife, and you become the definitive authority on the knife in your hand. The same conditions apply to every knife with any martensitic steel alloy used for knives.

Martensitic Steels

Martensitic steels get harder when they are heated above a certain temperature (usually 1,600°F or higher) and then rapidly cooled or quenched. The exact temperature the steel is heated to, how long it is held at that temperature and how rapidly it is quenched is called heat-treating. Tempering occurs by heating the steel to lower temperatures (like 400 to 600°F) to gradually soften the steel so it will be less brittle.

The actual range of cutting performance exhibited by different D2-bladed knives is wide enough to make one doubt that the same steel is in use. Without actually testing the knives, you’ll never know what they can do and whether you want it done that way.

What About Powdered Process Steel?

Powdered process steel is a more costly method of steel production. First, melted steel alloy is sprayed through an atomizer nozzle to form tiny droplets of fine steel powder. The steel powder is loaded into a molding chamber where tons of pressure (and sometimes heat) is applied to fuse the powdered particles back into a solid steel billet (or in some cases, into a molded shape as a steel part). The theoretical advantage powdered process steel has for knife blades is the resulting steel billet is finer-grained with a more even carbide distribution than a poured and rolled steel plate may provide. Knife blades made from powdered process steel are often touted as being more chip- and break-resistant as a result.

There has been, and continues to be, debate about how clean the steel produced by powdered process is expected to be. Some prominent knife makers candidly told me that many lots of powdered production steel couldn’t be mirror-polished without revealing inclusions that look like scratches or blemishes in the steel. Production of blades with bead-blasted finishes or finishing coatings makes this issue of less relevance to the consumer, but it remains a concern to some knife makers who question whether the structural integrity of the steel is consistent. The powdered process CPM D2-bladed knives I’ve tested from commercial and custom sources have proven to be a delight to use for every day cutting purposes.

Break Testing

D2 knife blade breakage-resistance depends largely on blade thickness and heat treatment, according to the doctor of D2, Bob Dozier. Thicker blades with higher Rockwell hardness ratings will have less elastic stretch.

When deliberately break-testing the blade of a Queen Razor Blade Trapper model with D2 steel blades, I was once able to bow the 0.095-inch-thick RC57 Razor Blade more than a full 90° bend, before forcing it to snap. I was startled by the ability of this knife’s D2 blade to be able to endure so much lateral stress. Most normal users wouldn’t have continued to push the blade past its failure point, since it exhibited so much spring-like flex. This blade predictably performed as a rope cutter on the low end of D2 range, but it was very easy to sharpen.

Readers need to keep in perspective that its cutting endurance was still on the high end of “good,” therefore exceeding what half of all knives deliver in comparable testing.

D2-bladed folding knives

Queen Cutlery makes traditional-style folders with D2 blades in a variety of patterns.

When it comes to producing D2-bladed knives with more potential resistance to breakage in thicker blade stocks, the new Friction Forged D2 Diamond Blade Knives might have a theoretical advantage. Friction Forging results in a blade with a zone-hardened edge (Rockwell hardness 66-68) for extraordinary cutting endurance supported by a much softer steel back. The soft, spring-like steel back can (in some cases) be flexed to over 90° without breakage. The friction-forged edge has a nano-grain carbide structure so fine that it may not be as prone to cracking and tearing as it is flexed.

Other Features

Sometimes features added to a blade for user convenience, like friction grooves on the blade spine, can create stress risers that negate the resistance to blade breakage of zone-edge hardening. Sometimes different production lots of steel exhibit different reactions to zone hardening due to allowable fluctuations in chemical composition. User discretion is the single most predictable way to avoid blade failure from lateral flexing. D2 is probably not the best choice of steel to make sharpened pry bars from, even with zone-edge hardening.

The downside to the nano-grain of the friction-forged edge is it exhibits less “tooth” for reduced cutting efficiency while carving materials like plastic and seasoned wood. Since the first four knives produced by Diamond Blade were primarily hunting knives for processing harvested game, rather than bushcraft, this is probably not a significant issue to Diamond Blade knife users. The knives can cut more meat and hide between sharpening, as only the “best of the best” can.

Bushcraft and Utility Knives

For bushcraft and utility applications, I would choose a D2-bladed Knives of Alaska model from this sister company which is also run by Diamond Blade’s managing partner Charlie Allen. The KOA D2 blades are conventionally heat treated, double-draw tempered and cryo-treated for remarkable performance in their own right. They just don’t match the Diamond Blade for overall cutting endurance between sharpening.

Yet another way to produce knife blades out of D2 steel alloy is by casting the blade blank out of molten D2 steel. The blank is then finish-ground and heat treated to individual specifications. Selected handle materials help to create each cast blade into a distinctively individualized knife.

Cast D2 is sometimes called Dendritic D2. The proponents of this production method believe the steel grain of the blade has more predictable properties from casting, then what can be attained with other methods. They claims to have more consistent carbide structure at the blade edge and longer cutting endurance. Of course edging, alloy content and final heat treatment still play a dominant role in determining the performance of each finished knife, regardless of steel production or blade-creation methodologies.

D2 is not an alloy used for forged knives with any frequency. The steel is difficult to move with a hammer and prone to decarburizing when it’s heated high enough for easier metal movement. D2 is occasionally incorporated into Damascus blades, but there have been problems with some D2 Damascus experiencing de-lamination of the layers under lateral stress.

Does D2 Steel Benefit from Cryo Treatment?

Cryo treatment is subjecting semi-finished blades to temperatures as low as -300°F for a specified time. Bob Dozier doesn’t use cryo treatment for his knives, while other makers swear by it. I have seen evidence that some steels subjected to specific heat treatment procedures benefit markedly from cryo treatment. But the benefits are not uniform for all steels, and cryo treatment temperatures and soak times do vary. As with all other aspects of knife making, cryo treatment results vary with different application methodologies.

Is D2 Difficult to Sharpen?

There is no definitive yes or no for this question. I don’t find Charles Allen’s Diamond Blade knives, which Rockwell test at 66-68, any more difficult to sharpen than his Knives of Alaska blades that Rockwell at 58-60. I have found D2 knives that were much more resistant to abrasion from even diamond hones. But I have found D2-bladed knives from the same manufacturer that produced the most difficult to sharpen examples. Individual results vary even within the same brand.

So, Then, What Kind of Knife can D2 Steel Really Make?

There is something for everyone, and I am going to let each knife enthusiast discover what suits him or her best. For me, that’s the fun part. I will tell you that, for my knife applications, I usually carry more than one knife, and as often as not, one of those knives has a D2 blade, while the second doesn’t.

Which D2-bladed knife I carry depends on the circumstances. If there is one knife that does all things equally well for all applications, I haven’t found it — but I will keep looking. If nothing else, it provides my loved ones with the certain knowledge of one thing — I will always appreciate getting more knives on special occasions.

D2-bladed knives

What kind of knife can you get with D2 steel? Just about any type ranging from Dawayne Batten’s handmade spring-back gentleman’s folders (top and bottom) to Microtech’s hard-use tactical fixed-blade Currahee model (center). Enjoy making your choice.

I conclude by paraphrasing the late Butch Winter. There are no bad D2 knives, although some may suit certain applications better than others. You decide for yourself which D2 knife suits your needs best. I should warn you that I have been unable to stop with just one.


This article was originally published on March 22, 2016