Category: Steel and Knife Properties
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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
Thanks to Matthew Hoffman, Tryggvi, and Ron Dillon for becoming Knife Steel Nerds Patreon supporters!
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.
What is Edge Stability?
Thanks to Keith Nix and Benaiah Brabant for becoming Knife Steel Nerds Patreon Supporters! The vote is still open on Patreon for what equipment will be purchased for future research.
Edge Stability
I got help directly from Roman Landes in writing this article (Thanks Roman!). The content below is based on Roman’s book, Messerklingen und Stahl: Technologische Betrachtung von Messerschneiden (Knives and Steel: Technological Examination of Knife Edges), as well as discussions with Roman. However, since the writing is mine the ideas are naturally filtered through me. Any mistakes are my own.
Tests of Knife Edge Toughness
Thanks to Jaethan Reichel for becoming a Knife Steel Nerds Patreon supporter!
In an earlier article I wrote about the microscopic mechanisms by which chipping and micro-chipping occurs in edges. However, that article did not cover specific tests of edge toughness. Correlating conventional toughness tests with edge toughness is difficult for many reasons:
Sharpness vs Cutting Ability
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CATRA, Sharpness, and Cutting Ability
I got several good comments on the article about CATRA edge retention testing regarding sharpness and cutting ability. The edges tested with more acute angles (20° edge is more acute than 50°) started out cutting better and remained that way through the standard 60 cuts. However, the measured width of the edge with the worn 20° edges was larger than with the 50°. So this leads to a question: which was sharper? And if the 50° was indeed sharper due to its narrower edge then why was it not cutting as well?
Steel History – The First Stainless Steel was for Knives
Update 7/23/2018: I added a small piece of new information on the development of 440C steel to the article.
Thanks to Greg Hanson for becoming a Knife Steel Nerds Patreon supporter!
The writing of this article was made much easier due to the existence of The History of Stainless Steel by Harold Cobb [1]. If you want more information on the history of stainless and the people who developed it, check out the book.
Review – Kevin Cashen’s Guide to 1080 & 1084
Thanks to Edward Braun, Mark Reich, and Alex Kaplan for becoming Knife Steel Nerds Patreon supporters!
Misc. updates: I added some toughness numbers that I had previously been unable to track down comparing 440C and 154CM to the 154CM article. I also added a summary of a very interesting new journal article about the effect of grain size on steel toughness to the Grain Refinement article.
Maximizing Edge Retention – What CATRA Reveals about the Optimum Edge
Thanks to Ed Schempp, Matus Kalisky, and Chin Lim for becoming Knife Steel Nerds Patreon supporters! Your support allows us to fund CATRA studies.
CATRA
Update 1/6/2020: I have since written more articles about CATRA looking at the effect of steel type: Part 1 and Part 2
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.