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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.
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.
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Conventional Casting
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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:
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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?
Knife Steel Nerds coffee mugs have been shipped to all current “Ultimate Steel Nerd” Patreon supporters.
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]:
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.
Thanks to Ben Wendel, William Brigham, Jeff Schafer, and Simon Moeskjær Balle for becoming Knife Steel Nerds Patreon supporters!
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.
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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:
