Category: Steel and Knife Properties
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Which Steel Has the Best Edge Retention? Part 2
Thanks to Chad Kelly, Isaiah Schroeder, and mflgrmp for becoming Knife Steel Nerds Patreon supporters!
Background Information and CATRA Curves
Make sure you read Part 1 first so that you understand all of the background information for this article.
Which Steel Has the Best Edge Retention? Part 1
Thanks to Mark McKinley and Alfredo Faccipieri for becoming Knife Steel Nerds Patreon supporters!
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:
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.
All About D2 Steel – Development, Use in Knives, and Properties
Thanks to Robert Erickson, knifeandgear_swiss, Dale Bushness, and Paul Hart for becoming Knife Steel Nerds Patreon supporters!
Update 10/22/2020: I now have an article with how to heat treat D2, PSF27, and CPM-D2 and it also includes toughness testing of each steel and edge retention testing of D2. https://knifesteelnerds.com/2020/08/31/how-to-heat-treat-d2-psf27-and-cpm-d2/
The Sharpest Youtube Channel in the World
Thanks to Rusty Craig, Dylan Curtis-Reeve, Brendan Porter, and Ian Cox for becoming Knife Steel Nerds Patreon supporters!
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.
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:
What is Edge Stability? Part 2 – The Experiments
Thanks to Gary Creely and Sans Jeux for becoming Knife Steel Nerds Patreon supporters!
Background
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.
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.
Carbon vs Stainless Steel in Knives
Thanks to Matt Davidson and Barton Smith for becoming Knife Steel Nerds Patreon supporters! I put in the order for the small impact tester for knife edges. The purchase of the impact tester was decided by Patreon voting members and purchased with money from Patreon supporters.
Ranking the Steel Ranking Articles
Note: I now have a steel ratings article of my own, read it here: Knife Steels Rated by a Metallurgist
Intro
Thanks to Stacy Apelt for becoming a Knife Steel Nerds Patreon supporter! Based on a poll of Knife Steel Nerds Patreon voting members, we have decided to purchase a small impact tester for knife edges. This will allow us to study the effects of steel, heat treatment, edge geometry, sharpness, etc. on chipping and rolling of edges.
Those photos and drawings will help people understand ! Orientation – I was curious about what Crucible does with that .Their CPM goes to Niagra Metals for rolling and they cross roll the steel. Cut into squares and rolled alternating direction to minimize directional properties. I think Matt Gregory found that in his visit.
It would be interesting to test the transverse toughness of those steels for sure.