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David Kahn

Question about Carbon Migration

19 posts in this topic

I've been working on Japanese style kitchen knives lately, which start out as a piece of water hardening tool steel (for me, 1080, W-1 or W-2 usually) forge-welded to some wrought iron (old anchor chain). No folding; the steel stays on one side (the concave edge part), and the wrought iron forms the non-cutting side and the tang of the blade. Anyway, I recently read the article written some time back by Howard and Dr. Verhoeven -- "Carbon Diffusion Between the Layers in Modern Pattern-Welded Damascus Blades" -- and I got to wondering, when I forge-weld the steel and iron together and then forge to rough shape, at the end of the process, do I have steel laminated to a wrought iron backing, or do I have a single piece of steel with varying alloy content? (Assuming only the carbon migrates to any significant extent.) And if I start out with wrought iron and something with about 0.80 percent carbon, do I end up with an edge with about 0.40 percent carbon (assuming roughly equal amounts of steel and iron to begin with)? If so, maybe I should consider using steel with a higher carbon content. Any thoughts on this?

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All the san mai blades I have made seem to show a carbon diffusion zone between the wrought Iron and steel ,this is where the carbon has bled into the wrought iron a little. Given enough time at temp the piece would reach an equilibrium state .in reality it goes no where near that far with the single weld .

I would expect little or no discernable carbon drop at the edge

It is a question worth asking though .

Edited by owen bush

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Could have been fun to see how long you would have to soak a blade like that for the carbon to even out. Even at welding heat I think we're talking hours, the reason it often becomes an issue with pattern welded steel is because the layers are so thin.

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A study with micrographs showing migration of carbon was done on some of my wrought iron/52100 san mai blades by Byron Skillings three or so years ago.

I'll see if I can get him to post some of the info he found.

 

As I remember there was a high carbon center with decarbed edges along teh wled and the wrought carborized in a bit...so it had four zones going from the center to the outside...seven in total.

 

Ric

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Wouldn't mind reading that study. I think it could also be interesting to repeat the experiment with pure iron in stead of wrought to see if you get the same result with only homogeneous materials.

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Wouldn't mind reading that study. I think it could also be interesting to repeat the experiment with pure iron in stead of wrought to see if you get the same result with only homogeneous materials.

 

Leif,

That is an interesting suggestion. Below are two photos of folded steel. One is non homogeneous home made steel the other is a Nickolson file(s) folded. I am a little unsure about the welding details but one clearly shows the results of decarb and carbon migration while the other shocked me as I expected a different look (more homegeneous). This is not a substitute for the experiment you are describing but I am beginning to wonder. There are other iron makers who have welded and folded the home made material...a little etch would go a long way.

 

Jan

Home made steel folded about 8 times ...

Folded file (I do not recall the # of folds) Decarb. and migration visible

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Those are great pictures, Jan. Good pictures say more than a thousand words.

 

I think the way to go about such an experiment is to keep things as clean alloy wise as possible. Ideally iron and carbon only. So if one were to try it out in real life it would be to weld PI with W-1, and only known W-1, not something recycled unless it´s been metallurglically tested. Also time and temperature during the forgewelding would have to be logged.

 

Just an idea, though. I don´t have access to a metallurgy department that can analyze the material for me.

Edited by Leif S

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bm2345-1000x-1.jpg

A study with micrographs showing migration of carbon was done on some of my wrought iron/52100 san mai blades by Byron Skillings three or so years ago.

I'll see if I can get him to post some of the info he found.

 

As I remember there was a high carbon center with decarbed edges along teh wled and the wrought carborized in a bit...so it had four zones going from the center to the outside...seven in total.

 

Ric

 

Micro of the wrought iron, with stringers. Nothing exciting here.

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bm2345-1000x-1.jpg

 

Micro of the wrought iron, with stringers. Nothing exciting here.

 

However, Here is the interface between the wrought iron, and the 52100.

 

Pearlite is present in quantity, the boundary between the two alloys is clear, as is the buildup of carbon at the interface.

 

Micros at 1000X

bm2345-1000x-2.jpg

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However, Here is the interface between the wrought iron, and the 52100.

 

Pearlite is present in quantity, the boundary between the two alloys is clear, as is the buildup of carbon at the interface.

 

Micros at 1000X

 

Here is the last one, from a different region, rather more evenly distributed pearlite.

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Here is the last one, from a different region, rather more evenly distributed pearlite.

 

Well, here:

bm2345-1000x-3.jpg

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However, Here is the interface between the wrought iron, and the 52100.

 

Pearlite is present in quantity, the boundary between the two alloys is clear, as is the buildup of carbon at the interface.

 

Micros at 1000X

 

Byron,

 

Thanks for the photos, very interesting...would you elaborate on why the carbon buildup exists at the interface. Do you have any idea of the time lapsed since that weld and its time at welding heat(s).

 

Thanks

Jan

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Byron,

 

Thanks for the photos, very interesting...would you elaborate on why the carbon buildup exists at the interface. Do you have any idea of the time lapsed since that weld and its time at welding heat(s).

 

Thanks

Jan

 

Jan,

If I remember the bar was 1/8" 52100 and 1/4" wrought sides. Heated to welding in 4-5 minutes hand welded on the anvil, placed back in the forge for 2-3 minutes and run through the rolling mill twice to get to oversized 1/8" (0.130-0.160 thou). Normalized with two or three heat cycles after forging.

The time at temp was short over all.

Now I could do the same work in one welding heat and maybe limit the migration to a tiny fraction of the travel seen here, but that is just for the bar..if you forge the blade to shape all bets are off.

 

I would like to run a study with various simple combinations and time/temp to see migration....including nickel bearing steels and pure nickel and pure iron...and a whole series of stainless tests.

BUT..who has the time?

Most elements will migrate given time, but carbon moves fast...the large atoms can take 100 or 1,000 years to move any distance. I forget the calculation, but it is really fast.

 

Ric

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Jan,

If I remember the bar was 1/8" 52100 and 1/4" wrought sides. Heated to welding in 4-5 minutes hand welded on the anvil, placed back in the forge for 2-3 minutes and run through the rolling mill twice to get to oversized 1/8" (0.130-0.160 thou). Normalized with two or three heat cycles after forging.

The time at temp was short over all.

Now I could do the same work in one welding heat and maybe limit the migration to a tiny fraction of the travel seen here, but that is just for the bar..if you forge the blade to shape all bets are off.

 

I would like to run a study with various simple combinations and time/temp to see migration....including nickel bearing steels and pure nickel and pure iron...and a whole series of stainless tests.

BUT..who has the time?

Most elements will migrate given time, but carbon moves fast...the large atoms can take 100 or 1,000 years to move any distance. I forget the calculation, but it is really fast.

 

Ric

 

Ric

Thanks for the feedback..I have read that low nickel levels do not inhibit carbon migration much.... . . I agree the topic warrants some play with various materials.

This carbon build up at the interface....what causes it ...?

 

Jan

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Ric

Thanks for the feedback..I have read that low nickel levels do not inhibit carbon migration much.... . . I agree the topic warrants some play with various materials.

This carbon build up at the interface....what causes it ...?

 

Jan

 

I wish I knew Jan.

I must have something to do with the energy driving the migration of the carbon....

or

maybe the carbon in the lead tripped and the others needed to wait for him to get up? :blink::lol:

 

I seem to recall that de-carborized steel re-carborizes slower than steel which had not had its carbon lowered..so a steel of 1080 decarborized to 1050 and then packed in carbon would pickup less carbon than a steel which began at 1050 and was pack carborized....I have no idea why that would be.

I'm getting a microscope soon and will play with some things like that and other stuff which will never make money, but intrigues me.

 

I'll ask some folk and see if they know about the carbon buildup issue.

 

oh...maybe it has to do with absorbed oxygen from the weld zone and that O wanting to gather with the C?

Or some other contaminant at the interface?...borax/boron?

Maybe a decarbed layer slowing the carbon as I had heard above????

 

Ric

Edited by Richard Furrer

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Any updates guys? :)

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