Sharpness

Sharpness vs Cutting Ability

Larrin

Thanks to Matthew Berry for becoming a Knife Steel Nerds Patreon supporter!

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? read more

Damascus, History - Articles - Books, Steels

Five Myths About Damascus Steel

Larrin

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]: read more

Corrosion Resistance, History - Articles - Books, Steels

Steel History – The First Stainless Steel was for Knives

Larrin

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. read more

Austempering, Heat Treating and Processing

Bainite vs Martensite – The Secret to Ultimate Toughness?

Larrin

Thanks to Thomas Busch for becoming a Knife Steel Nerds Patreon supporter!

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: read more

Heat Treating and Processing, History - Articles - Books, Metallurgy Principles, Reviews

Review – Kevin Cashen’s Guide to 1080 & 1084

Larrin

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.   read more

Corrosion Resistance, Metallurgy Principles, Steels

How Much More Chromium Does D2 Need to be Stainless?

Larrin

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]: read more

Heat Treating and Processing, Steels, Tempering, Toughness

Toughness testing – Cru-Wear, Z-Wear, Upper vs Lower temper, Cryo vs No Cryo

Larrin

Thanks to Paul Hart and James Covington for becoming Knife Steel Nerds Patreon supporters!

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.  read more