Gratitude
Thanks to cbw, Doug Siddens, Nick Dunham, and Robert Martin for becoming Knife Steel Nerds Patreon supporters!
I interviewed several knifemakers for this article. Thanks to Ed Schempp, Hank Knickmeyer, Steve Schwarzer, Rick Dunkerley, Jim Batson, Shane Taylor, Jeff Carlisle, Kelly Cupples, Daryl Meier, John Davis, Matt Diskin, Wade Colter, Barry Gallagher, Howard Clark, Bob Kramer, and Devin Thomas for talking to me.
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26C3 Steel
26C3 steel is produced by Uddeholmstrip (part of Voestalpine Precision Strip) as a razor and scalpel steel. This steel is also known as 1.2002 using the German designation. I don’t know much about the history of the steel but the marketing literature says, “voestalpine Precision Strip AB has long experience and were the pioneers of both the high carbon (UHB 26C3) and the martensitic stainless steel (UHB AEB-L) razor strip grades” [1]. In the 1927 patent for AEB-H [2], reference is made to “the purest Swedish carbon steel with ‘1.05% C and 0.4% Mn'” and in a 1970 patent for a razor blade steel there is a reference to UHB 26C (the 3 is not on the end) which has the same approximate composition as the current 26C3 [3]. So I think there was probably some evolution of the composition despite the claims of the marketing material. The composition of 26C3 is shown below:
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Failure Modes
A common engineering technique is to evaluate designs based on how they failed, or may fail. Failure modes are identified and the designs are modified to prevent those failures. These ideas are simple in concept but it is surprising how easy it can be to miss the forest for the trees. In terms of predicting failure modes in some cases it is easy and in some it is difficult. You would expect a large chopping knife to require heavier edge geometry to prevent chipping and rolling, or a seawater diving knife to require high rust resistance. Other times failure modes are identified through testing of the knife or by returns from customers. Whatever the source of the failure, there are usually relatively simple methods for fixing each one, though the trade-offs for doing so may not be desirable.
Thanks to John Bates, Kenny Lazarus, Robert Abel, and Matt Danielson for becoming Knife Steel Nerds Patreon supporters! I have some exclusive Patreon supporter content this week. Pete of the Cedric and Ada Youtube channel posted this past week a video summarizing his rope cut tests on 14 Spyderco Mule knives in different steels. This is a fun test because all of the knives are nearly identical and only the steel and heat treatment is different, so it is a better steel comparison than some of the others between different knives. I already have a previous article where I compared CATRA testing to rope cutting so this new test didn’t warrant a whole new article, but I offered an analysis of his test for Patreon.
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Forging by the Steel Company vs Bladesmith
When the steel company makes the steel they produce a large melt of the steel with the desired composition and pour it into a mold which solidifies and produces an ingot. A typical ingot size for tool steel or high speed steel might be 10″ thick either round or square depending on the production process and the desired final shape. Smaller ingots are better for limiting the segregation of alloying elements and keeping the cast structure fine. At that point the steel is in “cast” form. The ingot is then heated up to high temperature and forged either with a hammer or press to a form ready for hot rolling. In some cases the ingot is ready for rolling as-produced. Next the steel is hot rolled to the final desired thickness. Hot rolling in an industrial setting is typically done with relatively few reheats, typically single digits. That depends on how much reduction in necessary, how difficult the steel is to work, and the capability of the rolling mill.
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Cementite
The most basic carbide type in steel is an intermetallic compound formed between iron and carbon, commonly called cementite. Carbides are hard and brittle, similar to a ceramic material. Cementite has a relatively complex structure but in its simplest form it is 3 iron atoms for every carbon atom: Fe3C. However, other elements can partially replace the iron, so the carbide is sometimes given as M3C where M can mean Fe, Mn, Cr, etc. Cementite is typically present as either particles or in “pearlite.” I introduced what pearlite is in this article. However, cementite is the only carbide type that typically forms in pearlite, so to keep things simple for this article I will be focusing on carbide particles. Below I have a schematic representation of carbides (black circles) along with the grain boundaries (black lines).
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Legendary Heat Treatments
Last week I wrote about What a Good Heat Treatment Can and Cannot Do, and as part of that topic I wrote about how some knifemakers have a legendary or even mythical reputation for their heat treatments. In that article I argued that the big differences are between “bad” and “good” heat treatments, and that the differences between various good heat treatments are much smaller. And that edge geometry and knife design are more important to knife performance than the differences that are possible between different “good” heat treatments. So I think it makes sense to discuss a particular case of a knifemaker known for legendary, unmatched heat treatments, which brings me to…
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The Legend of Heat Treatment
There is some debate about knives that have steel with a “good heat treatment” vs those that have a bad or sub-par heat treatment. Some knifemakers have a near legendary reputation for their excellent heat treatments. What exactly is possible in terms of heat treating? How much better can steel be? How bad can it get?
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Austenitic Stainless Steels
At its most basic, H1 is an austenitic stainless steel. Austenitic stainless steels are about as old as stainless steel itself, being developed by German metallurgists in the approximate time period of 1909-1912. They worked on 18% Cr, 8% Ni steels which are quite similar to common austenitic stainless steels like 301, 302, and 304.
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I was interviewed by Shawn Houston on his Youtube channel about the micrographs article. See the video here.
Background
