Edge Retention

Which Steel Has the Best Edge Retention? Part 1

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CATRA Testing

I previously wrote an article on what CATRA testing is and what it is revealing from a set of tests on 154CM: Maximizing Edge Retention. The CATRA edge retention test uses the slicing of 5% silica-impregnated cardstock and therefore tests slicing edge retention. A standard test uses 60 cuts with a fixed load and slicing length and the amount of cardstock cut per slice is recorded. The edge retention is then often reported as the total cardstock cut with all 60 cuts, and given as TCC (total cardstock cut) in mm. I shared this same CATRA test video in the earlier CATRA article to see the test in action: read more

Hardness, Metallurgy Principles, Steel and Knife Properties

Rockwell Hardness is the Megapixels of Knife Steel Specs

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Hardness and Megapixels

In the early-to-mid 2000’s with digital cameras and somewhat more recently with smartphone cameras we had the battle of megapixels. The number of megapixels is simply the number of pixels that are captured by a digital camera. When we had 0.3 megapixel cameras the pictures were quite blurry and jumping up to 2 or 3 megapixels made a big difference. However, when comparing 5 to 7 megapixels the quality of the image was much more likely to be controlled by the quality of the lens and sensor than simply the number of megapixels. Despite that, megapixels became an easy marketing point because it is a simple number to present to the public. We haven’t seen rockwell hardness climbing for no reason other than marketing, but it is one of the few simple numbers that are used to advertise for a knife. Therefore it is often misunderstood by knife buyers, and yes, even some knife makers. In this article I cover some simple reasons why hardness is not as important as other factors for predicting most steel properties. And then we get into the nitty gritty with why hardness is not always the same as strength and how heat treatment can affect strength independent of hardness. read more

History - Articles - Books, Powder Metallurgy, Steel and Knife Properties

All About D2 Steel – Development, Use in Knives, and Properties

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D2 Steel

D2 is a common tool steel and knife steel. It is also known by other names such as the Japanese designation SKD11, German designation 1.2379, Hitachi SLD, Uddeholm Sverker 21, and many others. How long has it been around? Where did it come from? Who started using it in knives? How do its properties compare to other steels? Find your answers here! read more

Sharpness, Steel Alternatives, Toughness

The Sharpest Youtube Channel in the World

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Kiwami Japan

A popular Youtube channel called “kiwami japan” includes several videos of making knives out of unusual materials such as jello, pasta, chocolate, etc. The video on making a knife out of cardboard has over 20 million views which means that these videos have reached a broader audience than just knife makers or enthusiasts. As a materials engineer I find the videos interesting from a materials perspective, but they are entertaining in other ways as well. The videos are a bit quirky so I decided to take a dive into these videos and try to figure out what is going on. I also e-mailed the person who makes the videos and he answered a few of my questions. I will refer to him as “Kiwami” for the rest of this article though I know that is not his name. Kiwami means extreme in Japanese.  read more

Silicon-Alloyed, Tempering

Silicon Additions for Improving Steel Toughness

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High Toughness Steels

There are a series of shock resisting steel designed for high toughness (see this article to learn about toughness). A popular one is S7, an air hardening steel that can reach relatively high hardness. Another steel in the “S” series, S5, is reported to be even tougher [1][2][3][4]: read more

Damascus, Nitrogen-alloyed, Steels

New Steel Analysis – Damasteel N11X and Damacore DC18N

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N11X and Damacore DC18N

Last month I released an article about nitrogen-alloyed knife steels. After I posted the article I was informed about a new Damasteel product that includes a nitrogen-alloyed stainless steel as the core in a san-mai damascus steel product. At the time there was no information on the core steel other than its name: Damacore DC18N refers to a product with a core of “N11X” nitrogen steel and has san-mai damascus sides of RWL34 and PMC27 (their standard damascus mix without a core steel). Damasteel has recently released a datasheet for the new product which has provided more information: http://damasteel.se/wp-content/uploads/2018/06/Data-Sheet-Martensitic-Damacore-Final-Version.pdf read more

History - Articles - Books

How I Became a Knife Steel Metallurgist

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When I was 16 I went with my father to the Las Vegas Custom Knife show. My interest in custom knives up to that point had been pretty limited. My father, Devin, has run a Damascus steel business for as far back as my memory goes. I remember looking at the A.G. Russell catalog and seeing some of the cool knives. I remember wanting a pocket knife, but I don’t remember being any more interested in knives than I was in, say, Vans shoes. At the knife show, however, my perspective changed. There was table after table of custom knives and custom knifemakers all with different styles and stories to sell their knives. Knifemakers come in all different types from the aw-shucks cowboy to the intense self-defense salesmen. I was most interested in the knifemakers that were making claims about the superior performance of their knives. From the lockup, to edge geometry, to steel, etc. there were barkers promoting it all. I spoke to a man who claimed that he had a proprietary steel for his fillet knives that was better than any other available. He flexed the knives 90° to demonstrate the superiority of the steel. Another knifemaker boasted about his extensive heat treatment protocol that would lead to the best performing hunting knives available. read more

Edge Retention, History - Articles - Books, Steel and Knife Properties, Steels, Super Steels, Toughness

Super Steels vs Regular Knife Steels

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Super Steel

I see frequent references to “super steel” online, and I was curious about how long that terminology has been around. I did searches on bladeforums as it is one of the oldest knife forums. The number of references to “super steel” has increased over time, but so have the number of posts on bladeforums. I saw how many references to “super steel” there were in each year, and then as a proxy to how many posts there were on bladeforums I did a search for “154” and saw how many references there were each year. Google tops out at 200 results but at that point the dataset was big enough to get an idea: read more

Edge Stability

What is Edge Stability? Part 2 – The Experiments

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Read Part 1 before this article as it covers the ideas behind the Edge Stability theory and how things like hardness of steel, carbide volume, and carbide size are thought to affect knife edges. Then you will have an understanding of what we are looking for in the experiments described below. read more

Corrosion Resistance, Nitrogen-alloyed, Steels

Nitrogen-Alloyed Knife Steels

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In previous posts I have written about the process by which steel is hardened. The steel is heated to a high temperature phase called austenite, where carbides are dissolved and carbon goes into solution in the austenite. During rapid quenching the carbon is trapped between the iron atoms and a phase called martensite is formed. Martensite gains its high hardness from the distortions to the atomic structure that come from carbon in between the atoms.  read more