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Re heat treating Japanese laminated chisels


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In 1982 a skilled woodworker friend traveled to Japan to acquire the best handmade chisels he could find. In 2018 he lost his timber framed shop, and all his tools,  to the now famous Camp Fire of northern California. I asked for the honor of saving these precious tools for him. My shop puts out about 2,000 precision woodcarving knives a year out of O1. The HT schedule I currently use is :

 

Austenize in salt bath @1485F with a 10 minute soak at target temp.

Each ring of 75 tools then goes  into a salt marquench at 420F for 10 minutes

At about 80F they go into low temp salt at 395F for an hour.

 

Hopefully the first pic below clearly shows the lamination line.

I presume these are a more shallow hardening carbon steel than O1, thus I have much less time to get past the nose of the curve to get them into the marquench bath.

Do any of you have knowledge of what steel would likely have been used?

The thickest section where there is lamination is 13mm.

Are salt baths even proper to use for a single lamination tool - would pre-heat be advised?

What would be a proper HT schedule?

 

Any knowledge that can be passed along is appreciated, these were made 38 years ago by a tool smith in Japan, and used since by a woodworker in the USA, both consummate craftsmen at their work, it must be done right.

Lyoroi 1.jpg

Lyoroi 3.jpg

Lyoroi 2.jpg

Lyoroi 1.jpg

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I would recommend getting in touch with one of the importers of high end Japanese wood tools. I think they would very likely have a big boner for your project and help to put you in touch with a smith in Japan or act in some other helpful way as intermediaries.

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I agree with Dan 100%.

 

However, if you insist on tackling it yourself, the steel is most likely to be either Hitachi white paper #3 or Hitachi blue paper #2.  The white paper steel is a very pure and clean very high carbon with almost zero alloying elements beyond carbon (think very clean W1), and is in the 1 - 1.3% carbon range.  Very shallow hardening stuff, and prone to chipping.  It's what they use on very high-end sashimi knives, the kind the chef will stab you with if you use it on hard vegetables.  If this is what they are, they need a few normalizing cycles to reset the grain which has no doubt grown considerably from the fire, then a very fast quench.  Salts are fine for austenitizing at around 1475 F, but white paper steel needs a very fast oil like Parks 50, assuming you don't use water (and I wouldn't!)   That chippiness of white paper steel (#1 is chippiest, #3 is toughest) makes me think that chisels may be blue #2.  If that's what they are, it's closer to O1 and your heat treatment setup may be fine.  Multiple normalizations will be required for it as well.  

 

Then I found this guy saying there is also a yellow paper steel (these names are from the color of paper they wrap it in at the mill) that is commonly used in woodworking tools: https://www.japaneseknifeimports.com/blogs/news/64514117-a-quick-summary-of-hitachi-carbon-steels-common-in-knives, but given the quality of these chisels I'd bet the smith used something better.  If he was going full-on traditional it would be white #2 or #3.  If he was going for best performance it would be blue #2 or super blue, which has been described as "O1 on steroids."  

 

So yes, I agree with Dan.  Unless you have access to an XRF gun to check for trace elements, it's going to be very hard to tell whether it's yellow, white, or blue paper.  For that matter, yellow and white are close enough it will be difficult to tell them apart with XRF, as it's not really sensitive enough to get the minute differences in P and S that make the two grades different, and it's really bad at checking carbon levels.  Blue has Chromium, tungsten, and vanadium, which an XRF unit will pick up.  

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