patina vs. carbon migration: advantages?

[bleasure]

was cleaning some different old folders' springs using evaporust and, like many before me, accidentally discovered the phenomenon of carbon migration. i thought the darkening effect it produced was very attractive, and judging from the amount of elbow grease and flitz it took to remove it from the exterior, reasonably durable.

as i understand it, the difference between patina and carbon migration is that most 'patinas' are relatively stable oxide reactions that don't quickly progress into rust, offering some degree of surface chemical stabilization and rust protection, where carbon migration is a consequence of the chelation process that results in higher proportions of carbon on the exterior of a treated steel.

my question: is it established whether carbon migration has any usefulness, i.e. *meaningful* protectant effects on non-stainless steels? or is it essentially cosmetic, and a true patina is necessary for that purpose? this is spyderco-relevant insofar as it was prompted by thinking about eventually getting a k390 dragonfly and how i'd like to go about treating its surface

[Danke]

I force a patina on all my tool steel knives. After that I don't see rust. Pics coming.

[Danke]

[Doc Dan]

Isn't carbon migration where, when making damascus steel the carbon from one steel migrates to the steel with less carbon? So, in your case, it is simply patina and you can see where the different carbides are clumped. Now, I am just guessing.

[ChrisinHove]

As far as I understand the rust resistant effect of most carbon based coatings is secondary to other effects such as surface wear resistance and colour, and mostly relies upon the trapping other more effective rust inhibitors / oils.

I don’t see why a carbon coating created by migration methods would be any different, but I’m more than happy to be educated.

[Mat_ski]

I am not sure what is carbon migration. I tried searching online and found ASM handbook chapter on atom diffusion, but I don’t have access to it.

https://dl.asminternational.org/handboo ... m=fulltext


Can someone please provide some short(ish) definition?

[Pokey]

I wondered what carbon migration is too. I did an online search and didn’t come up with anything. Google suggested, “Caribou Migration,” but I’m thinking that’s not what bleasure meant in his original post.

Here’s a link to a company that describes different kinds of rust, including black rust, or patina.

https://www.armorvci.com/corrosion/types-of-rust/

[Doc Dan]

The only use of that term I've ever heard is when laminating or making damascus and the carbon from a higher carbon steel migrates to the lower carbon layer. But, I might be remembering it wrongly. As I said above, I think those dark spots are just the carbides or something clumping in a certain area of the steel and when he patinates it they show up.

[ChrisinHove]

What popped up on google for me was carbon migration laser etching. The high surface temperature of the laser causes carbon to migrate to the surface of the steel, darkening it.

[wrdwrght]

From my iPhone’s Perplexity app:

https://www.perplexity.ai/search/what-i ... ADOKOgLTbA

[Karl_H]

I think you should educate yourself by going to knifesteelnerds.com.

I have no idea where you might have heard about “carbon migration”, but it certainly isn’t an accepted engineering term that is used in the way that you are using it. I would suggest starting with the following articles, if you want to know what happens to carbon in steel.

- https://knifesteelnerds.com/2021/08/28/ ... ife-steel/
- https://knifesteelnerds.com/2019/07/15/ ... fe-steels/

The only ways to effectively reduce the rate of corrosion are a stable oxide layer (I.e., black iron oxide patina or a chromium oxide), or corrosion inhibitor (blade oil, desiccant, coating, etc.).

[RustyIron]

Carbon migration refers to the movement of carbon atoms within a material or between different materials. This phenomenon primarily occurs in:

1. Metallurgy:

Laser marking: When a metal is heated with a laser, carbon atoms present in the metal or the environment can migrate to the surface, creating a dark mark. This is often used for permanent marking.

Welding: During welding, carbon can migrate from one part of the metal to another, influencing the properties of the weld. This can be both beneficial and detrimental depending on the desired outcome.

Forge welding: When different types of steel are welded together, carbon can migrate between them, resulting in a material with a blended carbon content. This is a key process in blacksmithing and Damascus steel production.

2. Geology:

Carbon cycle: This refers to the long-term movement of carbon between the atmosphere, biosphere, geosphere, and hydrosphere. It involves processes like photosynthesis, respiration, decomposition, and the formation of fossil fuels.

3. Environmental Science:

Carbon sequestration: This involves capturing and storing carbon dioxide to mitigate climate change. This process can involve carbon migration within geological formations.

[Pokey]

Carbon migration refers to the movement of carbon atoms within a material or between different materials. This phenomenon primarily occurs in:

1. Metallurgy:

Laser marking: When a metal is heated with a laser, carbon atoms present in the metal or the environment can migrate to the surface, creating a dark mark. This is often used for permanent marking.

This is why the bug on Spyderco blades will rust.