Month: March 2018

Steels

Is Blue Super Steel Actually Super? The Facts about Tungsten-alloyed Steels

Larrin

High carbon, tungsten-alloyed forging steels see consistent use in Japanese knives with steels like the Hitachi Blue series and Takefu V-Toku steels. These steels differentiate themselves from many other knife steels due to their use of tungsten alloying, but not for providing hot hardness like in high speed steels, but for wear resistance. Tungsten-alloyed steels are as old as tool steels themselves, as I covered in an earlier post: The First Tool Steel. However, simple tungsten-alloyed steels have been on their way out in the USA since at least the early 60’s [1]. The tungsten added to the steels leads to the formation of very hard tungsten carbides for steels that can be as wear resistant as air hardening steels like D2 or M2 but with the ability to normalize and anneal the steels without precise temperature control. read more

Annealing, Austenitizing, Forging, Heat Treating and Processing, Steel and Knife Properties, Steels, Tempering, Toughness

Cru Forge V – Toughness testing, Processing, and Background

Larrin

Cru Forge V was developed by Crucible for those who forge their steel for knives [1]. It was developed shortly before Crucible’s bankruptcy and is reported to have been tested with the help of knifemakers Howard Clark and Dan Farr and that the code name prior to its official name was 1086V [2]. The steel is not listed anywhere on Crucible’s website and does not appear to be in production any longer, but as of March 2018 is still available from some third party steel sellers [3][4][5]. The steel has the following composition [1]: read more

History - Articles - Books

The History of the First Tool Steel

Larrin

The steel largely recognized as being the “first tool steel” was developed by Robert Forester Mushet, a British metallurgist, in 1868 [1]. Mushet improved the Bessemer steelmaking process through the addition of a small amount of manganese [1]. Later Mushet was experimenting with various additions of elements and discovered that one of his bars of steel had become fully hard despite not being quenched. This was called a “self-hardening” and later “air-hardening” steel because it could be fully hardened in air rather than requiring a water or even oil quench. The reason for the ability to self-harden is due to the property of hardenability, which I have covered in a Bladeforums post [2]. Hardenability is essentially the property of how slowly a steel can be cooled from the hardening temperature while still achieving a hard martensitic microstructure rather than a soft ferrite-cementite microstructure. This steel was high in tungsten and manganese, and it is sometimes erroneously reported that it was the tungsten that gave it the high hardenability; however, it was primarily the manganese that gave it the ability to harden in air, as tungsten adds little to hardenability [3]. read more

Metallurgy Principles, Steel and Knife Properties, Toughness

How Does Grain Refinement Lead to Improved Properties?

Larrin

Update 6/21/2018: A new journal article has been released on the effect of grain size which is very interesting. I have added a brief summary of it at the bottom of this article.

In my posts on austenitizing I described parameters of heat treating to keep grain size as small as possible and therefore improve strength and toughness [1-3]. It is very difficult to improve both strength and toughness at the same time, usually increasing one decreases the other. By what mechanism does grain refinement improve both? read more

Austenitizing, Heat Treating and Processing

Austenitizing Part 3 – Multi-Step Austenitizing

Larrin

There are many modifications to a straight high temperature austenitize for a given hold time followed by quenching. I am covering a few of them in this article.

Preheating

Preheating is performed to minimize size change, distortion, and cracking during heat treatment. Often a single preheating is recommended, but for some grades two preheating temperatures are recommended. For example, the Vanadis 4 Extra datasheet recommends a first preheat temperature of 600-650°C and a second of 850-900°C, such as in the following schematic [1]: read more