In order to make a good working knife, one needs 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.
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. One can buy fancier D2 knives or one can buy less-expensive D2 knives. But when you want a knife that can cut as good as any made with D2 alloy, Dozier Knives continues to be the comparison standard.
Butch Winter sagely stated there were 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 (being in the top 50 percent) to phenomenal (being in the top 1 percent).
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.
The chemical content for D2 tool steel is 1.4 to 1.6 percent carbon, 0.60 manganese, 11.00 to 13.00 chromium, 0.30 nickel, 1.10 vanadium, and 0.70 to 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 production 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 plus or minus fluctuations in the component contents. This means that it is possible for the variables to stack in a way that may either result in an ordinarily serviceable knife or in an extraordinarily good knife. 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 Bob expects from his proprietary heat-treatment procedures.
Not all knifemakers are as conscientious or demanding about quality control in their heat-treating as Bob Dozier. Every time we talk, he stresses it is consistency and uniformity of heat treatment that is the primary factor in his knives performing in a superior way, knife after knife. Bob confirms that in order to make a good working knife, one needs a good piece of steel.
You can’t tell how a knife will cut 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 cut with knives in side-by-side cutting comparisons while doing daily cutting chores to distinguish which knives cut with the fewest limitations. For example, 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 have tested and compare them by cutting the neck off a plastic beverage bottle. One can accomplish this cut with a single slice. The other requires 15 slices. In this case, the different heat-treatments achieve different carbide grain sizes and the larger carbide grain apparently cuts plastic better than the nano-grain carbide, which is 10 times smaller.
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 proof-test it with repeatable cutting tests. It’s like accuracy testing a firearm. Experience may indicate a certain type of gun usually performs well. However, how well it performs can depend on the ammo used, and preferences will vary from individual gun to individual gun.
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 coincident. The only way to find out is to cut with your knife and proof-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 will ultimately need more than one knife to accomplish all your cutting chores with the least applied effort. But you won’t be able to 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. Proof-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 get harder when they are heated above a certain temperature (usually 1,600 degrees 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 degrees 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 proof-testing the knives, you’ll never know what they might be able to do and whether you want it done that way.
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 knifemakers 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 knifemakers who question whether the structural integrity of the steel is consistent. The powdered process CPM D2-bladed knives I have tested from commercial and custom sources have proven to be a delight to use for every day cutting purposes.
The resistance a D2 knife blade can exhibit to breakage can depend 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-degree 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 its cutting endurance was still on the high end of good, therefore exceeding what half of all knives deliver in comparable testing.
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 to 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 degrees 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.
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 predicable 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 such as plastic and seasoned wood. Since the first four knives produced by Diamond Blade were primarily hunting knives for processing harvested game rather than bush craft, this will probably not be 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.
For bush craft 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. Properties of more consistent carbide structure at the blade edge and longer cutting endurance are claimed. Of course edging, alloy content and final heat treatment will 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 that is used for forged knifes with any frequency. The steel is difficult to move with a hammer and prone to decarburizing when heated high enough to make 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 benefit from cryo treatment?
Cryo treatment is subjecting semi-finished blades to temperatures as low as 300-degree F below zero for a specified time. Bob Dozier doesn’t use cryo treatment for his knives. Other makers swear by it. I have seen evidence that some steels that have been 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 to 68 to be any more difficult to sharpen than his Knives of Alaska blades that Rockwell at 58 to 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 what kind of knife can D2 steel 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 is 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.
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.
By Michael S. Black