# Copper bonding layer in laminated steel blades?



## Bert2368 (Feb 19, 2019)

I had previously seen a number of knives by a (now deceased) Japanese smith which used a layer of Copper between core and outer layers of steel, will try and run down the pics.

(Edit)

Here is where I found the Japanese knives (Jin from Japanese Knife Imports), and a sample picture showing the Copper layer-

https://www.japaneseknifeimports.com/search?type=product&q=Jin










And I have just run across a Kershaw Leek variant which looks like it has the same lamination between core and outer steel!

The Japanese smith was said to favor "tool steel" for the cutting edge. The Kershaw knife claims to use "D2", which is a tool steel, albeit used more for punches and dies than cutting tools in industrial settings.

https://www.amazon.com/dp/B0017KN4MS/?tag=skimlinks_replacement-20

See this screen grab:






Could any experienced smiths speak as to the utility and/or desirability of this Copper/Copper alloy bonding method?

Is the technique essentially what I was taught to call "brazing" back in an engineering materials & machining techniques course about 40 years ago, rather than the (more common) "forge welding" I assume is used for most steel blade lamination?


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## keithboyle13 (Feb 19, 2019)

This process would be done the same as making Mokume Gane. The clean flat surfaces pressed together and heated to withing approx 50-100 degrees short of melting the copper. The materials are held at this temperature for a period of time to allow diffusion bonding to occur. This is not unlike brazing. 

there would need to be a fair bit of experimentation to make this work with normal alloys. D2 being and air hardening steel would work with this process and is pretty stable dimensionally during heat treatment. 

Visually it is quite pretty and will work like a laminated blade. It's a bit of a hype thing that really offers nothing special over compared to a normal laminated blade.


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## milkbaby (Feb 19, 2019)

OhMai Billet making | Facebookhttps://www.facebook.com/media/set/?set=a.857914304299091.1073741880...1...

https://suwanneeriverknife.com/oh-mai/


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## Bert2368 (Feb 19, 2019)

Whoa. That's an interesting effect- I looked through the process pictures and am amazed that works without flux or a vacuum chamber.

If it is difficult to bond stainless to Carbon steel by ordinary forging under atmospheric conditions, would this technique be of any use for bonding such dissimilar steels?


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## Nikabrik (Feb 20, 2019)

Kai also makes a composite brazed kitchen knife series, the Seki Magoroku 10000ST. Like the Kershaw, there's an edge/bit bonded to a blade body.

There are some very high strength brazing alloys, and bond strength can be incredible when the gaps are small, but I have to wonder what the feel in the hands is like - is it dampened at all?

One question for smaller makers is the brazing temp vs HT. I believe some brazing alloys are designed to be applied at the same time as austenitizing - so perhaps you'd cut out your blank, braze & HT, then grind. On the other hand, running it through a roller mill would be cool...


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## keithboyle13 (Feb 20, 2019)

Hi Bert,

Welding Stainless to carbon is a forge environment is a pretty difficult thing to do. It can be done though. Copper in the laminate presents almost identical challenges with chromium oxide on the stainless steel. These can be dealt with using fluorite fluxes, but these are very nasty and turn to Hydrofluoric acid at the temperatures for it to work. 

Other methods such as tig welding the entire way around a billet of clean material offer a healthier way to go about this process.

Nikabrik does raise an important consideration for this method as the copper/filler layer needs to be able to withstand the temperatures required to heat treat the steel, and still survive the quench. Its a cool process, but it would be a binge of frustration trying to get materials to play well together through the heat treatment process.


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## Bert2368 (Feb 22, 2019)

Wish that old Japanese Smith were able to answer questions on his process- If this WAS a traditional process which has gone out of practice, does anyone making blades in Japan yet remember how- and possibly more important, WHY the technique would be chosen?

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I spent a good bit of time looking at the mokume gane process. Thanks, it's a new process to me.


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