Category: Steel and Knife Properties
2 thoughts on “Steel and Knife Properties”
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What is Edge Stability?
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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
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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.
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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
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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
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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
How Much More Chromium Does D2 Need to be Stainless?
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Some materials like aluminum form a passive oxide layer that prevents further corrosion. Steel is not one of those materials. Instead, steel forms iron oxide, or rust, that doesn’t protect the underlying iron and flakes off leading to further corrosion. However, when sufficient chromium is added then a chromium oxide passive layer forms which protects the steel from corrosion in a similar way to a metal like aluminum with its own aluminum oxide layer. A simple schematic diagram shows the passive film vs rust [1]:
Toughness testing – Cru-Wear, Z-Wear, Upper vs Lower temper, Cryo vs No Cryo
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I recently completed some toughness tests on samples that were heat treated by knifemaker Warren Krywko. The steel was donated by Chuck Bybee of Alpha Knife Supply. The samples are subsize unnotched charpy specimens with dimensions as specified on the bottom of this page: http://knifesteelnerds.com/how-you-can-help/ If we can get more people to make toughness specimens we can have more comparisons between steels, hardness points, heat treatment parameters, etc. Patreon dollars are for the purpose of paying for machining, shipping, testing, etc. for tests like toughness and CATRA edge retention, so if you are able to contribute that way please visit the Knife Steel Nerds Patreon page.
How Chipping of Edges Happens at a Microscopic Level
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To discuss chipping we have to start with fracture mechanics of materials, and in this case steel. Chipping itself is just fracture, so by definition resistance to chipping is controlled by toughness. Unfortunately there are many definitions of toughness. I covered one definition of toughness in the article on spider silk, which is the area underneath the stress-strain curve:
Is Spider Silk Stronger than Steel?
This article was discussed on the very popular Skeptic’ s Guide to the Universe podcast: https://www.theskepticsguide.org/podcast/sgu/670
Nearly a year later they briefly discussed the article as being very impactful in correcting some common knowledge they had always believed: https://www.theskepticsguide.org/podcast/sgu/714
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.