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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.
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
Thanks to Devon Craun for becoming a Knife Steel Nerds Patreon supporter! Your support is funding knife steel research.
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]:
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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.
Thanks to Warren Krywko, Joseph Cannell, and Timothy Thomas for becoming Knife Steel Nerds Patreon supporters! Your contributions will help fund more research on knife steels.
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:
Update 6/19/18: I have added new toughness numbers from a 1962 publication comparing 440C and 154CM. Go to the bottom of the article to see them. Thanks to Russ Andrews for sending me the article.
Thanks to Sal Glesser, Brian Huegel, Mark Bellou, Timothy A. Johnson, Daemon Lindenmayer, and David Olkovetsky for becoming Knife Steel Nerds Patreon supporters! We reached our goal of funding an edge retention study!
Thanks to Phil Wilson for become a Knife Steel Nerds Patreon supporter. We have now reached our second goal of funding a toughness study! I will start putting together the plan and discussing it with the patrons. Next goal: funding an edge retention study.
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
Larrin,
Someone said austempered o1 would be as tough or tougher then martempered 80crv2. Could you help me wrap my head around that?
I have an affinity for fine grained simple steels, and o1 being precision ground and available in all different sizes is great, but if 80crv2 has a finer grains structure and is tougher I’d be sold. It’s for a run of belt hawks that will be used primarily for woods and hunting duties not destruction tools. But I’d also like to focus on one steel for a while and curious if for small to medium belt knives which you’d recommend? I’ve played with most of the high wear and too steels, but haven’t messed with too many of the high carbon steels as I hated 1095.
Thanks to Shawn Houston and Tyler Christian for becoming Knife Steel Nerds Patreon supporters. We have reached our first goal and therefore I will be interviewing Devin Thomas and posting it as an article to the website.
