Carbon migration in stainless cladded knives

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Hi, everyone, I have a question again. Many of the hand laminated knives, especially stainless cladded carbon, seems to have very large areas of carbon migration, talking to one of my friend, he thinks it is very undesirable and indicts some problem in forging and heat treatment. While I do not own such knives, I do own knives from makers who makes such knives. I would love to hear your opinion and researches on how carbon migration impact knives, if they indicts a bigger problems in forging or just unfortunate fact in hand lamination.
Some examples here, I love my ShiHan, but some his stainless cladded knives seems to have large areas of carbon migration, his wrought iron and telegraph wire seems to be fine tho.

Some Takadas seems to also have it

Let me what you think!
 
It shouldn't be an issue. Carbon migration occurs through time and temperature, the hotter the steel, the less time it needs to be at that temperature to achieve the same level of carbon migration as it would at a lower temperature. Most of the carbon migration will occur when setting the initial forge weld, and less will occur throughout the forging of the blade itself. There are graphs somewhere that show the effects of time and temperature, but if memory serves it would take several hours worth of forging heat to produce the same amount of migration seen in just a few minutes at welding temperature.

I don't know that anyone's ever analyzed clad knife billets to see just how far the carbon migration has gone, but the general consensus is only a few thousandths of an inch. Makers concerned about carbon migration use a sheet of nickel between the cladding and core as the carbon will not migrate through it.
 
The amount of carbon migration is strongly influenced by the composition of the core and cladding steels. In most cases, it's not detrimental to the blade at all because it is only migrating from the outer edges of the core. The center of the core is relatively unchanged
he thinks it is very undesirable and indicts some problem in forging and heat treatment

Not only is it not undesirable. In most cases it's unavoidable. It is certainly possible to get excessive carbon migration but none of the examples above really show that. The effect is inherently quite dramatic an increase in carbon content in the jacket from the migration of 0.1% carbon can reduce the chromium in solution by around 1% which has a large impact on corrosion resistance.
 
So I heard the nickel layer (visible here) is added to prevent carbon migration from carbon core to stainless cladding. Is this a correct understanding?
It also seems like it does not block all migration, and my assumption is that without it, we would see much more migration.
 
So I heard the nickel layer (visible here) is added to prevent carbon migration from carbon core to stainless cladding. Is this a correct understanding?
It also seems like it does not block all migration, and my assumption is that without it, we would see much more migration.
I don't think any of the above knives had a nickel layer. Yes, nickel blocks the carbon migration because carbon has very low solubility in nickel.
 
I don't think any of the above knives had a nickel layer. Yes, nickel blocks the carbon migration because carbon has very low solubility in nickel.
Ok yeah what I thought was a nickel layer is probably just the weld line then looking more closely (I noticed that hand laminated steels tend to have more of this effect than pre-clad ones). The bottom one is carbon and iron so definitely not.
 
It shouldn't be an issue. Carbon migration occurs through time and temperature, the hotter the steel, the less time it needs to be at that temperature to achieve the same level of carbon migration as it would at a lower temperature. Most of the carbon migration will occur when setting the initial forge weld, and less will occur throughout the forging of the blade itself. There are graphs somewhere that show the effects of time and temperature, but if memory serves it would take several hours worth of forging heat to produce the same amount of migration seen in just a few minutes at welding temperature.

I don't know that anyone's ever analyzed clad knife billets to see just how far the carbon migration has gone, but the general consensus is only a few thousandths of an inch. Makers concerned about carbon migration use a sheet of nickel between the cladding and core as the carbon will not migrate through it.
The amount of carbon migration is strongly influenced by the composition of the core and cladding steels. In most cases, it's not detrimental to the blade at all because it is only migrating from the outer edges of the core. The center of the core is relatively unchanged


Not only is it not undesirable. In most cases it's unavoidable. It is certainly possible to get excessive carbon migration but none of the examples above really show that. The effect is inherently quite dramatic an increase in carbon content in the jacket from the migration of 0.1% carbon can reduce the chromium in solution by around 1% which has a large impact on corrosion resistance.
Thanks, it's great to hear from professionals, it seems more visible in hand laminated knife than prelaminated stocks, maybe the factory has better control over it.
 
Thanks, it's great to hear from professionals, it seems more visible in hand laminated knife than prelaminated stocks, maybe the factory has better control over it.
Yeah, the prelam stock has less carbon migration because they have the process really locked down and spend way less time at welding temps. Additionally, a lot of prelam stock doesn't get forged to final sharp so it isn't at forging temps for long periods of time.
 
Yeah, the prelam stock has less carbon migration because they have the process really locked down and spend way less time at welding temps. Additionally, a lot of prelam stock doesn't get forged to final sharp so it isn't at forging temps for long periods of time.
So what is the silver line actually in iron clad knives?
 
All I have for now is this blurry zoomed in pics. Will be a week before I have it in hand again
 

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I'm not really sure where that effect comes from. I think it's possible that the grains right at the boundary of the two materials corrode more easily leading to that line. It would be interesting to get that under a microscope to figure out what is going on.
I think you might be right on that count. I had a pretty neglected nakiri that was blue core stainless clad, and the line between cladding/core had actually turned black. With thinning that line was removed but I thought it was interesting that only that portion of the blade had turned black.
 

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Also worth noting it seems the thickness of core steel have some impact too, some of the really thin core steel cladded knives seem the have less visible migration lines.
 
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