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

Steel and Knife Properties, Toughness

How Chipping of Edges Happens at a Microscopic Level

Larrin

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: read more

History - Articles - Books, Steels

154CM – Development, Properties, Use in Knives, and Legacy

Larrin

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! read more