Category: Toughness
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Ranking Toughness of Forging Knife Steels
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Low-Alloy Steel Testing
Over the past two years or so we have tested the toughness of many knife steels using a simple charpy impact test. You can read about the specifications of the test on this page. With the samples tested in this article I got a lot of help from Warren Krywko and Devin Thomas as well as donated steel from Alpha Knife Supply, Barmond Special Steels, and Achim Wirtz. This article focuses on the toughness testing performed on “low alloy” and carbon steels that are often used by forging bladesmiths. It is possible to forge high alloy steels, of course, though it does not appear to be very common even today.
Crucible S45VN Steel – Everything You Need to Know
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Thanks to Niagara Specialty Metals for getting me a bar of S45VN for the experiments necessary for this article.
Nitro-V – Its Properties and How to Heat Treat It
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Nitro-V Steel
Nitro-V is a stainless steel sold by New Jersey Steel Baron which was first released in 2017 [1]. The steel was designed and produced in collaboration with Buderus Steel as a version of Uddeholm AEB-L modified with nitrogen and vanadium. Another obvious comparison is with 14C28N which was designed as a version of 13C26 modified for improved corrosion resistance. 13C26 is nearly identical to AEB-L but produced by Sandvik. You can read more about the history of AEB-L, 13C26, and 14C28N in this article.
How to Heat Treat 26C3 Steel
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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:
How to Design Knives that Do Not Fail
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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.
New Micrographs of 42 Knife Steels
10/15/2020: I added M398, WFN, Nitrobe 77, and Vancron
2/24/2020: I added 420HC, CPM-T15, Rex 76, S125V, SPY27, and Z-Max/Rex 86
2/10/2020: I added 26C3, 1.2442, 1.2519, 1.2562, Blue Super, V-Toku 2, and A8 Mod.
How to Heat Treat 52100
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52100 Steel
I previously wrote about the history and properties of 52100 in this article. The steel has been around since 1905, has been known as 52100 since 1919, and has been used in knives since at least the 1940’s. It was developed for bearings and its common use in bearings meant it has been a ready source for knife steel for decades. It is known for its fine carbide size and good toughness. The chromium addition compared with the chromium-free 1095 means that it has somewhat higher hardenability so it is easier to harden in oil and obtain full hardness. The chromium also helps keep the carbide size small. The chromium also shifts up the temperatures required for hardening.
A2 Steel – History and Properties
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History
A2 steel is quite old, though determining the exact year it was released is a bit difficult. A2 steel was developed in the early 20th century during the explosion of tool steels that occurred after the discovery of high speed steel which was first presented in 1900. You can read about that history in this article: The History of the First Tool Steel. During the development of the first high speed steel included the switch from manganese to chromium as the primary hardenability element, and most high speed steels had about 4% Cr. That high chromium content was primarily for “hardenability” which is the degree of cooling required to achieve full hardness. A “water quenching” steel has low hardenability and must be quenched very rapidly from high temperature, and an “air hardening” steel can be left in air and it will fully harden. You can read more about hardenability in this article on quenching. The first high speed steel came to be known as T1, which had 4% Cr and 18% W (tungsten). The earliest record I have found of a precursor A2-type steel is in a summary of tool steels in 1925 [1], while summaries of tool steels from 1910 [2] and 1915 [3] do not have any similar steels. Therefore these types of steels probably arose sometime between 1915 and 1925.
How to Heat Treat 5160 – Optimizing Toughness
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5160
5160 is a low alloy steel known for its excellent toughness. It has been used by many forging bladesmiths due to its good properties and also wide availability, especially in the form of leaf springs. However, information on how to maximize the steel’s properties with heat treating is scant. So along with my father, Devin Thomas, we did a small study on the toughness of 5160.
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Just out of curiosity, did you ever test ztuff with a high temper. At one time I did some testing, and found it to be much tougher if tempered at around 1000 degrees. This was compared to tempering at 400 degrees!
I haven’t tested the high temper on Z-Tuff.
I think it would score quite a bit higher on you’re charts! Maybe in the future I could heat treat a few samples and send them to you. I’m interested personally!