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Conventional Casting
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?
Five Myths About Damascus Steel
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What is Damascus Steel?
There are two major steel types that are called Damascus:
1. Crucible, or Wootz, steel was first produced in India and Central Asia and produced into swords anciently from at least the 3rd century AD [1]. It is made by producing small ingots of high carbon steel that are then forged and thermal cycled in a specific manner to lead to carbide bands that produce the final pattern when the steel is etched [2][3]:
Book Recommendations for the Knife Steel Nerd
Update 10/29/2020: Since writing this article I published my own book called Knife Engineering: Steel, Heat Treating, and Geometry. Of course I still recommend the other books on the list below.
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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.
Bainite vs Martensite – The Secret to Ultimate Toughness?
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Misc. update: I have added a set of supporting micrographs to the introduction to Austenitizing steel.
Tempered Martensite
To begin describing what bainite is it makes sense to start with martensite first. To form martensite we heat up the steel to high temperature to transform to a phase called austenite where we dissolve carbon in between the iron atoms (see Austenitizing Part 1), then quench the steel to lock in the carbon and form a hard phase called martensite (see What Makes Quenched Steel so Hard?). Following that we temper the martensite to allow some of the carbon out and increase the ductility of the martensite; the carbon comes out as very small carbides, a compound of iron and carbon (see What Happens During Tempering?). In the article on martensite formation I shared the following YouTube video to see the formation of the martensite laths:
Interview with Knifemaker Phil Wilson about Performance Blades and His Journey with Knives
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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