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.

[bleasure]

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.).

Hi Karl,

Good news! As you'll see in my initial post, I define both terms, indicating some familiarty with the concepts I used, let alone the 'behavior of carbon in steel,' a highly unspecific topic relating to steel production in general and essentially unrelated to the question I was asking. I think you'll find reduced presumption and increased reading comprehension fruitful in future communications whether on or offline. The fact is, I *am* familiar with that very popular site! I did in fact take a peek there, and at several others, before coming to the forum to ask this question.

Happily I can further clarify things for you, not that you phrased anything in the form of a question: I was made aware of this specific species of "carbon migration" by the manufacturers of rust removal chemicals, who describe this as a phenomenon occuring when some non-stainless steels are treated with de-rusting chemicals that use chelation as their agent. As I'm sure you're well aware, engineering was not a relevant field of expertise regarding the question I was asking. I did not, however, consult with any chemists or physicists before coming to the forum, so perhaps I was lacking in due diligence; I'll email some colleagues in those departments at my university before posting in future, I'm sure they have nothing better to do.

Could be mistaken, but have a notion there may be one or two other ways to reduce the rates of corrosion on non-stainless steel. Glad you were here to correct and educate me on these points, will bear them in mind going forward!

[bleasure]

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.

Me too! I'm really curious about whether or not it would have any effect, and why/how it's different than a patina etc in efficiacy. I'm guessing that there's not nearly enough carbon that ends up on the surface to make a serious difference in rustability, vs. a patina which is pretty uniform across the surface if done correctly. But that's just a guess, would love to know more from someone who knows more.

[bleasure]

Here's an example of 'carbon migration' in the context of iron oxide chelation from a manufacturer's FAQs:


"I got a black film on some parts after using Evapo-Rust®. What is it, and how do I remove it?

The black film is carbon from the steel. Steel is composed of a combination of carbon and iron. In certain instances, steel will darken in color after rust has been removed from the surface of the metal. This is a natural phenomenon that chemists refer to as “carbon migration”. The carbon from the steel moves, or “migrates”, to the outer layer of the metal and settles into the pores.

The removal of the rust (iron oxide) reduces the proportion of iron to carbon, leaving a higher concentration of carbon on the outer surface. This heavier layer of carbon could cause a darkening of the metal due to the attributes of the carbon. The darkening does not have an adverse affect on the metal. It merely represents the movement of carbon from the interior of the metal to the exterior of the metal.

Since Evapo-Rust® is a highly effective rust remover, it stimulates the carbon migration process. Evapo-Rust®is not alone in creating the carbon migration effect. Other rust removal treatments will also result in carbon migration and a darkening of the metal. The primary difference between Evapo-Rust® and the acid based treatments is that Evapo-Rust® will not harm or weaken the metal. Unlike other treatments, Evapo-Rust® will not darken products made with low carbon steel.

With Evapo-Rust®, sometimes a wiping with a dry cloth or a more rigorous buffing can remove the dark coloring. A quick rinsing of the metal after Evapo-Rust® has been applied may also keep the carbon from settling into the pores of the metal.

There are several things that can be tried to minimize the effects of carbon migration. First, high carbon parts should not be soaked longer than necessary. Once the rust has been removed, the parts should be rinsed and dried. Second, a further dilution of the Evapo-Rust® formula may have a positive affect. The lower concentration of Evapo-Rust® will take longer to remove the rust, but may have less of an effect on causing the carbon migration."

[shunsui]

You got me more interested in rust removal than carbon migration.
Here's Evapo-Rust at the track meet. Lot of good information, including how to make your own Evapo-Rust clone.

[Wowbagger]

'patinas' . . . [ and ] progress [ of ] relatively stable oxide reactions

Speaking , or typing , about that . . . I have been , for quite a while today , soaking the sides of the M4 blade of my Tenacious with Golden Kiwi fruit skin hunks stuck on the sides of the blade to gain a highly prized ( by me ) darkish blue patina .
This rich blue color , I must confess , is hit or miss .
As often as not it goes from a vague light blue cast to black .
I have done this many many times with Case CV and CS as well as many M4 blades .
I have had good (and poor ) success stimulating the reaction with my heat gun set on the lowest setting = < 200 F .
anyway . . .
It is obvious I have nothing pertinent to add to this discussion .

Just wanted to say :
I'M WITH Y'A !
Threads such as this one are a prominent reason I haunt the knife chat room(s).
You made my day off !

THANK YOU ALL !
Give 'em H E L L ! ( or better yet Give 'em SCIENCE ! ! ! )
signed :
Enthusiastic fan .

[Wowbagger]

less of an effect on causing the carbon migration.

Being a British car enthusiast / mechanic (I know . . . I've been told I'm """special""" ) .
The rust removers that I have used have a Passivator one applies after ward . Does yours ?

[zhyla]

I’m struggling to conceive how carbon in steel can migrate at room temperature. It’s in a crystalline structure isn’t it?

The evaporust writeup might be referring to what it’s doing to the rust layers on the metal. I’m not really sure.