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M398 Steel
Edit 11/19/2020: Since the release of this article I have experimentally evaluated M398, which you can read about here.
Which Steels are Easiest (and Most Difficult) to Forge?
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Forging Steel
Typically forging bladesmiths have restricted their steel selection to low alloy steels like 1095, 1084, 5160, 52100, O1, etc. There are a variety of reasons given for why the bladesmiths usually use these relatively simple steels. Often “ease in heat treatment” is a common one. However, this article will focus on which steels are physically more difficult to deform with the hammer and which crack most readily. What controls “forgeability” or steel?
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 Stress Risers Lead to Broken Blades
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Stress Risers/Concentrations
In an ideal world when a force is applied to a knife, that stress is distributed evenly across the piece. There can be certain features to a design, however, that leads to a stress “concentration” where the stress is locally higher than the rest of the piece. Stress is load divided by cross section, so a very simple way stress is concentrated is by having a locally smaller area of a part.
Does Sharpening with a Grinder Ruin Your Edge?
Update: Michael Drinkwine sent me another report from Global where they reported factory sharpened and waterstone sharpened knives. I added it to the “CATRA Testing” section of the article.
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.
Heat Treating Vanax – How Hard Does it Get?
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Vanax
Vanax is an interesting steel because of its good combination of toughness, wear resistance, and corrosion resistance. I wrote about Vanax along with other nitrogen-alloyed steels in this article, to describe how the steel is designed. While the datasheet shows it being capable of 59-61 Rc, I was curious about how hard the steel can go. The steel may be good for kitchen knives, for example, where very thin edges and high hardness is common. And kitchen knife users may appreciate the excellent corrosion resistance of Vanax in the presence of water, salt, and acidic foods.
Can You Trust Your Magnet During Heat Treating?
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How a Magnet Helps in Heat Treating
It is somewhat common for knifemakers to heat treat low alloy steels in a forge or with a torch, two methods where tight temperature control is not possible, and the temperature is frequently not even known. A magnet is often used to check the temperature of the steel because the point at which the steel becomes nonmagnetic is near the temperature at which the steel should be quenched to achieve high hardness. How does steel magnetism work? How reliable is checking the steel with a magnet?
Cold Forging of Steel
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Cold Forging
Cold forging is a lot like hot forging except it is at or near room temperature. The lower temperature means that the steel is much stronger and it is much more difficult to forge. That also means the steel is more brittle and therefore more likely to crack during forging or rolling. The shape of the grains in the steel are changed through forging. You can read about what grains are in this article. Steel is made up of planes of iron atoms, and if the steel was made up of only one grain these planes of atoms would all be parallel to each other:
All About AEB-L
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History of AEB-L and 13C26
Tracking down the history of AEB-L was surprisingly difficult. The Uddeholm website claims that AEB-L was patented in 1928 [1]; however, that is not entirely truthful. Uddeholm did patent a stainless steel in 1928 [2], which was named AEB, and later AEB-H to differentiate it from AEB-L. This was a very early stainless steel, so its development and patent needs to be viewed in that historical context. You can read about the development of stainless steels in this article. The AEB patent was for 0.7-1.1% carbon, 10-16% chromium, and 0.75-2.0% manganese. The original Brearley and Haynes stainless steel patents were still in effect; they got around them by using a higher carbon content than the Brearley patent (had a 0.7% max), and by claiming that high Mn led to improved corrosion resistance (it actually doesn’t). The nominal composition of AEB became 1% carbon and 13.5% chromium, which gave it a relatively large carbide structure compared to AEB-L, but it did see some use as a razor blade steel.