Decarburization of kitchen knife steel

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spoiledbroth

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I was wondering if anyone who's even nominally versed in metallurgy or smithing or whatever could answer this... What purpose would decarburization of a kitchen knife blade serve? If my caveman understanding of this process is correct, it would imply that carbon is actually being removed from the blade, which I would assume would make a poorer kitchen knife....

I ask because I was poking around the Fujitora website (Tojiro) and apparently DP stands for Decarburization Process which is something Tojiro supposedly has patented (the specific process relating to these knives, I'm aware decarburization itself was not invented by Tojiro).

Would it then be safe to assume that Tojiro knives, while being made from VG-10 do not actually contain 1% Carbon?

What benefit do you guys think this serves? If you wanted less carbon why not just start with something like AUS-8...?

:clown: Thanks for taking the time to read.
 
I was wondering if anyone who's even nominally versed in metallurgy or smithing or whatever could answer this... What purpose would decarburization of a kitchen knife blade serve? If my caveman understanding of this process is correct, it would imply that carbon is actually being removed from the blade, which I would assume would make a poorer kitchen knife....

I ask because I was poking around the Fujitora website (Tojiro) and apparently DP stands for Decarburization Process which is something Tojiro supposedly has patented (the specific process relating to these knives, I'm aware decarburization itself was not invented by Tojiro).

Would it then be safe to assume that Tojiro knives, while being made from VG-10 do not actually contain 1% Carbon?

What benefit do you guys think this serves? If you wanted less carbon why not just start with something like AUS-8...?

:clown: Thanks for taking the time to read.

This Tojiro page says DP means "Decarburization Prevention", not Decarburization Process.

http://www.tojiro-japan.com/products/227/ said:
When we make multi-layered materials by forge welding, decarburization used to be a big problem because it causes hardness reduction. However, we could finally solve this problem by DP(Decarburization Prevention) method...
 
well, this is embarrassing ... :eyebrow: guess all I needed was someone nominally versed in reading.

derp. :shocked3:
 
As a beginner bladesmith I'd love to explain what carburization/decarburization is to you guys in the hope that I can teach some of what I'm learning to you guys, or be told that what I'm learning isn't right! :laugh:

The whole topic of carburization and decarburization revolves around where the smith places the workpiece to heat it up. Lets take a look at the anatomy of a flame:

AnatomyFire.png


Starting at the bottom we introduce oxygen into the mix. In bladesmithing terms this is where you would have a blower (or bellows), pushing oxygen rich air into the base of the fire pit.
Moving up we introduce heat and fuel. Bladesmithing forges will always run on fuel that is high in carbon, which in turn reacts with the oxygen that is getting pumped in.
As you move higher up the flame you get less oxygen in the atmosphere as it mixes with the carbon to burn

If a bladesmith places a piece of carbon steel too close to the base of the flame, the oxygen rich air getting blown in will hit the steel and, combined with the heat, burn off some of the carbon contained inside it. This is known as decarburization.

Carburization is the reverse of this: If you hold the steel inside a flame which has is high in carbon instead of oxygen, the carbon will soak into the surface of the workpiece and create a higher carbon content in the steel. This happens near the top of the flame, between the terminal point and the dissipation of heat.

In between these two areas is the neutral zone and will not cause either carburization or decarburization.
A good bladesmith will use this knowledge together with a specific carbon steel to achieve a good balance of carbon in the end product. And if DP stands for decarburization prevention, it could be as simple as keeping the knife in or above the neutral zone.

This applies to coke, coal and charcoal forges. Unfortunately I have no idea about gas forges, but as I understand it there are virtually no Japanese bladesmiths that use a gas forge.
I hope this helps! :)
 
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