Japanese Kitchen Knives

Joined
Feb 1, 2004
Messages
360
Hello all, I've been looking at some Japanese kitchen knives online lately and it appears that the expensive professional models are made of either blue or white steel.

First off what are these steels? What are they closest to and what composition are they, does anyone know?

And secondly how on earth do they get the edge at 63-65?

From all I have heard on the errornet any knife above 58 RC will instantly shatter because it is too brittle and stressed. I understand traditionally katanas were not tempered after being hardened, I'm not sure if this is correct but is this whats going on here, they simply harden it but do not temper to relieve stress and brittleness?

http://watanabeblade.com/english/pro/iwahusa.JPG

Clearly this knife would cut like crazy just from looking at that edge. :eek:

Thanks everyone, in advance.
 

Daniel Koster

www.kosterknives.com
Knifemaker / Craftsman / Service Provider
Joined
Oct 18, 2001
Messages
20,978
sounds like you've been getting all your info from the errornet...


wait...you already said that. ;)


A few thoughts I've gathered from books I've read, or folks I've talked with, or just my-humble-experience:


60 HR is usually as far as most folks would like to take their knives. 57-58 if usually favored for toughness and sharpenability. Kitchen knives can go higher because typically they don't get abused and edge-holding is important.

Different steels at the same hardness will behave differently. Some steels are difficult to even harden up that high.

Blue/white are the "flavors" of the Hitachi brand of stainless steels (IIRC).

A higher Rockwell hardness does not necessarily mean it will be brittle. Just means harder. On some steels, hardening over 60 makes them very hard to sharpen.


The 1095 I use for my kitchen knives gets very hard after quenching...probably 62-64, and I temper it back down to 59-60 (375-400F). If I was to harden it at 350F, it might stay as high as 61.
 
Joined
Oct 3, 2002
Messages
12,297
Don't think these steels are stainless Daniel. White steel is very similar to W1 and blue steel is very close to 01. Here's what I found on the steels:

The Steel Used In Japanese Knives
When people talk about traditional Japanese knives, you may hear them say that the knives were made from "white (Shiro in Japanese)" steel or "blue (Ao)" steel. Alternatively, they might say "white paper (Shiro Kami)" steel or "blue paper (Ao Kami)" steel. These are not technical standards but refer to the color of the labels that Hitachi uses for some of their commercial grade steels. Among Japanese manufacturers, these become "Blue Label #1," "White Label #2," and so on. Both types are high-carbon steels in the 1.0% to 1.2% carbon range alloyed with silica (0.1% to 0.2%) and manganese (0.2% to 0.3%). The "blue paper" steels also have chromium (0.2% to 0.5%) and Tungsten (1.0% to 1.5%) added for toughness. Japanese manufacturers routinely produce knives from these steels in the Rc62 to Rc65 range, substantially harder than any Western-style blades.


For the soft-steel back, they use a very low carbon steel (0.06%) with a bit of silica and manganese (both at 0.2%). The highest-quality tools still use wrought iron from old anchors or anchor chain as the backing material.

Edit to add: I also wanted to say that I have one of these traditional Japanese kitchen knives and the edge is super thin and hard. It is a high carbon steel with soft iron clad on either side, then forged thin and when sharpened, about 1/8'' of the hard steel is exposed at the edge, it's only around 1/16'' thick at the spine and tappers down to a 0 edge, no secondary bevel.By far the sharpest knife I've ever handled, made for cutting vegtables and meat, NOT chopping. The edge will chip if not careful but it'll cut all day and is a pleasure to use.
 
Joined
Feb 1, 2004
Messages
360
Thank you both, sunfishman thats exactly the answer I was looking for. I bet your kitchen knife is sharp as hell!
 
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