Spyderco byte January 2023 - EDGE-U-CATION® CPM MAGNACUT

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Spyderco byte January 2023 - EDGE-U-CATION® CPM MAGNACUT​


Few developments have caused as much excitement in the knife industry as the development of MagnaCut steel. A uniquely different approach to stainless steel metallurgy, it offers an unparalleled synergy of toughness, edge retention, and corrosion resistance. To fully understand the brilliance of this remarkable blade material, it helps to understand the man behind it: Dr. Larrin Thomas.


Larrin Thomas is the son of Devin Thomas, a renowned custom bladesmith and one of the pioneers of making stainless Damascus steel. After attending the Las Vegas Custom Knife show with his father at age 16, Larrin became fascinated with the performance aspects of various blade steels and how they are affected by their alloy composition and heat treatment protocols. That fascination ultimately led him to earn a Doctorate of Philosophy (PhD) in Metallurgical and Materials Engineering from the prestigious Colorado School of Mines.

Although he works full time as a metallurgist in the automotive industry, Larrin’s deep passion for knife steels made him an active participant in various Internet knife forums. That later inspired him to create KnifeSteelNerds.com, a website dedicated to providing in-depth, science-based information on all aspects of blade steel performance, testing, and history. He is also the author of Knife Engineering: Steel, Heat Treating, and Geometry, a definitive book on all aspects of knife performance.


The Logic of MagnaCut:

Larrin’s inspiration for MagnaCut began with a fascination with Crucible® Industries’ CPM S30V, a powder metallurgy stainless steel developed specifically for use as a knife steel. Early powder metallurgy steels like CPM S60V®, Elmax, and M390 combined vanadium with a high chromium content (17-20%), resulting in steels that offered good wear resistance and corrosion resistance, but relatively low toughness. The high chromium content of these steels promoted the formation of chromium carbides, which produced a coarse microstructure that was detrimental to their toughness.

In contrast, non-stainless powder metallurgy steels have small vanadium carbides that provide excellent wear resistance and a finer microstructure. These steels, like CPM 3V, CPM 4V, and Vanadis 8, offer a much better balance of wear resistance and toughness, but at the expense of corrosion resistance.

In developing, CPM S30V, Crucible reduced the amount of chromium in the steel to limit the formation of large chromium carbides. While it would seem this would compromise the steel’s corrosion resistance, it actually allowed the other alloys in the steel matrix to form carbides and left more chromium “in solution.” Chromium in solution is the key to a stainless steel’s corrosion resistance properties, as it is what enables the steel to form a microscopic layer of chromium oxide on its external surface, protecting it from rust.

Based on this principle, Larrin’s idea was to reduce a steel’s chromium content even further while promoting the formation of smaller, harder, wear-resistant carbides. Those would maximize the toughness and edge retention of the steel while leaving practically all its chromium in solution to provide corrosion resistance.

Larrin’s first efforts to pursue this idea involved modeling it in metallurgical software called Thermo-Calc. Initially, the results were not encouraging. According to the software, reducing the chromium content of a steel like S30V would actually decrease the amount of chromium in solution, lowering the steel’s corrosion resistance without reducing its volume of chromium carbide. Achieving that would require reducing the carbon content, but at the risk of compromising the steel’s hardness. After much trial and error, Larrin found a narrow range of carbon and chromium content that would provide hardness and adequate chromium in solution for corrosion resistance while promoting the formation of vanadium and niobium carbides for wear resistance and toughness. To optimize the balance of those properties, he decided to focus somewhat more on toughness than edge retention, since there were already a number of other particle metallurgy steels that emphasized wear resistance. His goal was to equal or surpass the performance of CPM 4V and CPM CRU-WEAR®, but in a stainless steel.




From Theory to Reality
Making the leap from a theoretical material conceived in software to an actual steel proved to be a significant challenge. Small-scale powder metallurgy production is a very expensive proposition, so Larrin decided to contact one of the major steel manufacturers and try to get them to embrace his logic. Since he began his journey with a fascination for CPM S30V, he approached Crucible Industries first. In addition to being a leader in the development and production of steels geared toward the cutlery industry, they had a close partnership with Niagara Specialty Metals to do the hot rolling.

Larrin prepared a detailed PowerPoint presentation on his idea and actually pitched it to Niagara first. They were intrigued by the concept and agreed to help present it to Crucible’s experts. After fielding countless questions from the Crucible staff to prove his credibility, Larrin succeeded in convincing them to produce a heat of the steel. He then sent samples of it to a select group of custom knifemakers who specialize in the use of high-alloy steels and the performance testing of their knives. They confirmed that the theory of his creation held up in practice. Larrin had indeed created a very special blade steel.


MagnaCut Composition and Properties:

The chemical composition of CPM MagnaCut includes 1.15% Carbon, 10.7% Chromium, 2.0% Molybdenum, 4.0% Vanadium, 2.0% Niobium, and 0.2% Nitrogen. When heat treated, this careful balance of elements produces a carbide structure that is significantly finer than typical powder metallurgy stainless steels like CPM 154, M390, Elmax, and CPM S35VN. Although the total carbide volume of the steel is comparable to CPM 4V, the finer niobium carbides reduce the overall carbide size within the steel to yield a superior carbide structure.

MagnaCut is capable of achieving relatively high hardness—over 63 on the Rockwell “C” scale (RC) without cold treatment after quenching and 64-65 RC with the benefit of cryogenic treatment. In terms of toughness, it is very comparable to CPM 4V and Vanadis 4 Extra and surpasses even non-stainless steels renowned for their toughness, like CPM M4 and A2. Even at its maximum hardness of approximately 65 RC, its toughness rivals the best powder metallurgy stainless steels when they are tempered to typical knife blade hardnesses of 60-61 RC.

The edge retention of MagnaCut is on par with blade materials like CPM S35VN, CPM 4V, and CPM CRU-WEAR—all well-respected steels in terms of edge holding. However, perhaps its most surprising quality is its outstanding corrosion resistance, which approaches that of Vanax and LC200N. Interestingly, those steels can only achieve a hardness of about 60-61 RC, even with cryogenic treatments. MagnaCut is clearly capable of achieving higher hardnesses, while still offering excellent corrosion resistance and outstanding toughness.

By challenging the conventional wisdom of steel design, Larrin Thomas has created a remarkable blade material that is sure to have profound impact on the knife industry. While the number of MagnaCut knives in the field is still limited, real-world feedback from end users and custom knifemakers has so far been extremely positive. Spyderco is grateful to Larrin Thomas for raising the bar of steel performance and excited to feature MagnaCut in more of our products very soon.

To read more about Dr. Larrin Thomas and the development of MagnaCut, we encourage you to visit and support KnifeSteelNerds.com.


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