Steel Properties that Knifemakers Care about and Users Don’t

Thanks to Markus Stark, Nils, and Brent Stubblefield for becoming Knife Steel Nerds Patreon supporters. And Kyle Daily for increasing his contribution amount.

Knifemakers vs Users and What they Care About in Steel

In some areas, users and knifemakers have significant crossover in what they desire. And when customers want a particular steel, knifemakers will try their best to provide. However, there are several properties that knifemakers and knife companies are looking for that make little difference to the end customer.

Forgeability

This is a big one in the divide of forging bladesmiths and stock removal knifemakers and companies. Forged knives are largely made from low alloy steels that are easy to forge. These include old standby grades like 1095, O1, 52100, L6, etc. Japanese grades like Blue Super, White #1, and V-Toku 1. And European grades like 1.2519, 1.2442, 1.2562, and 1.2842. It is not impossible to forge high alloy steel and stainless steels, only more difficult. And annealing them (making it soft for grinding and drilling) usually requires a controlled furnace. Low alloy steels usually have relatively low wear resistance, which can make them relatively easy to grind and sharpen. However, the low wear resistance means that slicing edge retention is limited compared to higher alloy steels. And stainless steels are infrequently used because of difficulty in forging, so corrosion resistance is also limited. Many fine knives can be made with low alloy steels, but selecting steels that are in the “easy to forge” group can limit the available range of properties. Historically, some knifemakers have claimed that stainless or high alloy steels do not “benefit” from forging, or even negatively affected by it, to justify their decision not to forge it. These claims are not true, but more care is required to forge high alloy steels. Read more about the differences between forging and stock removal in this article.

Hardenability

Hardenability is a measure of how fast steel needs to be quenched from high temperature to achieve full hardness. Read about hardenability in this article. Knife steels can be broadly categorized as “water hardening,” “oil hardening,” or “air hardening.” Water hardening steels require the fastest quench rate to harden and can sometimes be difficult to get to harden at all. Water is a very aggressive quench medium, and can lead to cracking of the knife during quenching. Because of this, knifemakers often use a “fast oil” to quench water hardening steels. This can make it more difficult to fully harden the knife but is considered to be preferred to a broken knife. On the plus side, knives with a “hamon” use the low hardenability of water hardening steels to make an interesting transition line between the edge of the knife that hardened and the spine that did not. Usually this is performed by using clay on the knife and partially grinding the knife, leaving a thin cross section at the edge and a thick spine. With the clay and the thick spine, the spine cools more slowly and does not achieve hard martensite, leading to a visible transition that can be brought out with etching. Common steels for a hamon include 1095, W2, White #1, and 26C3. The high carbon and low Mn and Cr give the steels low hardenability.

Oil hardening steels can be quenched more slowly. Oils come in different speeds, such as fast, medium, or normal oil and the slower the oil the less likely warping or cracking of the knife are. Oil hardening steels also come in different ranges of hardenability, so the type of oil can be tailored to the steel in question, up to some cross-section thickness where a faster oil would be necessary. Some steels I classify as “fast oil” steels such as 52100, 1080, and 80CrV2, and other steels work well with slower oils like O1 and 5160. Fast oils will not ruin a steel with higher hardenability, but those steels can use the slower oil to avoid issues.

Air hardening steels will fully harden even when left in still air after heating to high temperature (austenitizing). Most stainless steels and high alloy steels are air hardening. These include steels like CPM-3V, D2, M2, M4, 440C, 154CM, S30V, etc. Knifemakers often use a “plate quench” with air hardening steels, where the knife is clamped between two aluminum plates to accelerate cooling and to keep the knife flat. With this technique, in combination with the slower cooling rate compared to oil, air hardening steels can sometimes be easier to maintain flatness during heat treatment. Another important benefit to air hardening steels is they can be heat treated in large vacuum furnaces used by many commercial heat treaters. This allows large knife companies, or knifemakers that send out for heat treating, to use a wide range of heat treatment services and do not require heat treating companies that are set up for fast quench rates for oil hardening steels. And knife companies that do their own heat treatment with large furnaces can do large batches of knives and reduce heat treatment costs.

Availability

It may seem obvious, but a knifemaker can only use steel that they can buy. I am sometimes asked why I don’t do tests on certain common steels like AUS-8 or 8Cr13MoV, to compare “budget” steels to the higher end options I often test. While these steels are ubiquitous in relatively cheap knives, they are not readily available in small quantities to individual knifemakers. In part because the knifemakers are not interested in them, and in part because those steels are typically sold to large knife companies. The cost of selling individual bars to knifemakers is not very appealing. This is where knife steel supply companies come in. They buy larger batches of steel and sell small quantities to knifemakers.

Importing steel can also be costly and difficult. Hitachi steels like White #1 and Blue Super are relatively difficult to buy in the United States, and Hitachi has often restricted sales to Japanese knifemakers. Even steels like VG10 or SG2 can be somewhat difficult to purchase, though availability has improved over the last several years. European grades can often have high shipping costs, and even tariffs, that increase prices. And vice versa when purchasing steel within Europe.

And this is assuming that the products are being produced in convenient sizes for knifemakers at all. Some steels are primarily manufactured for industries that use round bar, and getting flat stock would require a special order to the steel company. Or strip steels like AEB-L and 13C26 can be difficult to obtain in thicker stock for larger knives. And those steels have especially good toughness which can make them a good choice in larger knives.  Sometimes steel companies can be difficult to convince to produce steel in a wider range of sizes because of the perceived lack of potential income for doing so (and often they are right). And some steel companies put a low priority on knife steel sales, leading to long lead times and inconsistent delivery.

Grindability and Finishability

On the surface, ease in grinding and finishing may seem like a property that both knife users and knifemakers can agree upon. After all, many knife buyers/users prefer steels that are easy to grind and finish to make sharpening easier. However, there are some differences.

When sharpening of knives with thin bevels, there is little material to grind away, so difficulty in sharpening largely ends up being a process of achieving a small edge width, and deburring, in those cases. And while end users will complain about high wear resistance steels that are “difficult to sharpen” there are cases where knife companies have been shown to be more sensitive to this property. For example, S35VN was developed in part to have better grindability than S30V. But the general perception of difficulty in sharpening does not appear to be vastly different between S30V and S35VN. To the knife companies, the rate at which abrasives are replaced is a significant cost both for replacing abrasives and the logistics of swapping them. And sometimes direct manufacturing issues can occur such as failing to get a sufficient “bite” in each grinding pass. There are differences between different steel types even at a similar level of wear resistance. For example, a smaller carbides size provides superior grindability.

Custom knives are often given a “hand rubbed finish,” but even a consistent “belt finish” can be difficult to produce with certain steels. Steels with vanadium carbides can be especially difficult to get a good finish on because those carbides are harder than the abrasives in most grinding belts and sandpaper (aluminum oxide and silicon carbide). This can be an issue even in steels with relatively low vanadium and wear resistance like CruForgeV that would not be considered particularly difficult to sharpen. The steel CPM-154 was produced by Crucible, in part, because of the complaints of many custom knifemakers that they did not like finishing vanadium-containing powder metallurgy stainless steels like S30V and S90V.

Heat Treatability

For knifemakers that heat treat with a forge rather than a controlled furnace, the length of time at the hardening temperature (austenitizing), and the sensitivity to different temperatures, are very important. Heat treating a high alloy or stainless steel is very difficult with a forge by eye because of the relatively long soak times required, and high temperatures. Very simple steels like 1080 can be austenitized by heating only a little higher than where the steel becomes nonmagnetic. And almost no soak is required. Even other low alloy steels like 52100 with its higher carbon and 1.5% Cr can be considerably more difficult to heat treat consistently. I don’t recommend heat treating with a forge with any grade, as results are always less consistent than with a controlled furnace, and toughness can be reduced with surprisingly small changes in temperature. But many knifemakers do not want to spend the money on a heat treating furnace or outside heat treating services, or they prefer to use “traditional” methods of knifemaking. If I had a dollar for every time a relatively new knifemaker asked for instructions on how to heat treat 1080/1084 in a forge, I would have a lot of dollars. Kevin Cashen has a DVD on heat treating 1080/1084, which I reviewed here.

Blankability

“Fine blanking” is a process performed to cut out the shape of the knife. It is a cheaper process for mass production than waterjet cutting, laser cutting, etc. Therefore it is used by knife companies for lower production costs and cheaper knives. This is especially important in the large retail store segment of knives, to keep costs low when compared with cheap imports. And many of the cheap imports are using fine blanking as well, of course. Good blankability is limited to steels with a fine carbide structure and very low annealed hardness. Otherwise the life of the blanking dies is short and there can even be failures to the steel or the dies. Making high alloy steels that are blankable is especially challenging, as stainless steels with 13%+ chromium want very much to form large chromium carbides. The limits of fine blanking are typically grades like AEB-L, 13C26, or 14C28N, which offer a combination of relatively high achievable hardness (60+ Rc), along with good corrosion resistance. Other common blanking grades include 420 and 420HC which are somewhat easier to blank than AEB-L because of lower carbon, and therefore they have less carbide and lower annealed hardness. Many common steels are not considered suitable for fine blanking such as 440C, 154CM, S30V, etc. I think there may be some opportunity for improved steels that can be fine blanked, such as through controlled additions of vanadium or niobium for enhanced edge retention. However, the knife company/companies would have to decide that the R&D costs and potential risks would be worth the investment in developing improved products.

Cost(ability)

I debated whether to add this category, but there are differences in how knife buyers perceive costs versus the knifemaker or knife company. Knifemakers can have a somewhat different view of steel cost because they are buying it in larger quantities. To a knife enthusiast, 5, 10, or even $100 more for a knife in an upgraded steel may sound worth it, but if that means several hundred or thousands more dollars for the sheet(s) of steel, the knifemaker may stick with lower cost options. The amount of steel in a knife, especially a folder, can be relatively small, but buying a whole sheet for many knives can still be daunting. For knife companies trying to make affordable knives where every penny counts, the cost calculations are in a different arena than for knifemakers and enthusiasts. There are also the costs of production such as many of those pointed out above; if a steel requires significantly more time in grinding and finishing, labor/time costs may be more significant than the steel itself.

Summary

As expected, many of the steel properties that concern knifemakers are those related to production of the knives themselves. These are mostly hidden from the customer apart from when this results in higher pricing. The knifemaker or knife company has to be able to purchase, cut out, forge (optionally), heat treat, grind, and finish the knives, which are all time-intensive and expensive steps for knife production. When knife companies announce a change in steel, or a custom maker asks that a knife be purchased in a different steel, the reasons are usually one or more of those given in this article.