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Carbon migration question


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Since the failure of my Naginata project (broken in the quench :angry: ), I have been looking at my stock pile and trying to decide which steel would be best for the next try at a Naginata. I would like to do a water quench, though I could be talked out of it. I was thinking that something like 1060 is the steel I would like to use. However, I don't have any 1060, which got me thinking (always a dangerous thing). In a thread with JPH he talked about adding shims of stock to tweak the carbon and steel content (someone please chime in here if I have mis-remembered).

 

My questions then are as follows.

 

1) Does carbon migration happen?

2) How quickly (number of heats)?

 

My understanding is that, in simple steels, like 10xx, carbon content flows from high to low when the pieces of stock are forge welded together. So that, if I had welded a piece of 1084 to an equal amount of 1018, quite quickly I'd have something like 1050. Is this correct, or am I completely off base? At a knife show last weekend I talked about this idea with a couple of other local makers, and there were about as many opinions on carbon migration as people. There were two camps, those who thought carbon migration happened, though to varying degrees, and those who didn't, but were not sure.

 

Thinking about the topic has lead me into heresy, I think. If carbon migrates in hot steel from high content areas to low content areas, then what is the point of building a sword with a low carbon core and a high carbon edge. If carbon is migrating from high to low, by the time you welded your high carbon edge to the core and drawn the blank out, the carbon content would be spread throughout the billet.

 

If I have fallen in error, I would like to hear that. If not, then I would like to hear the discussion that should follow.

 

Thanks folks,

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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carbon diffusion happens but only to a degree and over time so the hard shell soft core sword should be just that hours of folding thin steel should end up purty darn even in content

 

 

think san mi then think shear steel

Brandon Sawisch bladesmith

 

eagles may soar but weasels don't get sucked in to jet engines

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I'll reply by means of my own experience by watching what happens when forge welding layers of 1050 and 1095 together and etching after each weld. Just by looking at the color of the etched material (I don't have any means to measure pinpoint carbon content) I will asure you that carbon moves. It will move to create an even layer by the 3rd or 4th weld. I would say that it moves based on the amount of time that the steel is exposed to a given temperature and therefore how far away it moves will depend on the thickness of the layer being welded. Everything in nature tends to want to be at an equilibrium given the proper conditions. But bear with me a little longer, if you put a layer of 15N20 between the 1050 and the 1095 the story changes. You see, all those carbon atoms are tiny and move relatively freely in the hot iron matrix. Nickel atoms are bigger and will interfere with the diffusion of carbon atoms. Now you can draw your own conclusions as to what happens to a higher carbon steel jacket with a lower carbon core sword. Think time, heat, number of welds...

Enjoy life!

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I'll reply by means of my own experience by watching what happens when forge welding layers of 1050 and 1095 together and etching after each weld. Just by looking at the color of the etched material (I don't have any means to measure pinpoint carbon content) I will asure you that carbon moves. It will move to create an even layer by the 3rd or 4th weld. I would say that it moves based on the amount of time that the steel is exposed to a given temperature and therefore how far away it moves will depend on the thickness of the layer being welded. Everything in nature tends to want to be at an equilibrium given the proper conditions. But bear with me a little longer, if you put a layer of 15N20 between the 1050 and the 1095 the story changes. You see, all those carbon atoms are tiny and move relatively freely in the hot iron matrix. Nickel atoms are bigger and will interfere with the diffusion of carbon atoms. Now you can draw your own conclusions as to what happens to a higher carbon steel jacket with a lower carbon core sword. Think time, heat, number of welds...

 

 

well put !!

infinite edge cutlery

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It's a matter of time and distance and temperature. Whether you start out with thin strips of shim or do multiple folds to creat 200-400 layers of steel the carbon doesn't have all that far to travel in pattern welded steel. If you weld a half inch piece of high carbon steel to a low carbon steel core the carbon has to travel a lot farther to move from the outer edge of the high carbon steel and into the core of the blade. Also you don't expose the steel to welding temperatures for as long. Temperature is also a factor in the rate of carbon migration; the rate of migration increases with temperature. Once the weld has been established, the blade is then forged at lower temperatures. Overall carbon migration will be mitigated by not heating the blade hotter than is necessary to forge and only heating the section of steel that can be worked in one heat.

 

Doug Lester

HELP...I'm a twenty year old trapped in the body of an old man!!!

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There is an article on this topic by John D. Verhoeven and our very own Howard Clark: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TXJ-3VNGMVW-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1128097491&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=186f6d30f341b400854e97214499eabe

 

It's my understanding that because of the way carbon atoms are situated within iron, such migration occurs very rapidly, even when dealing with relatively thick layers.

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I don't have anything technical to add, but if you are trying to add carbon to a blade you could try a case hardening process. Ariel has a good tutorial on his website where he case hardens a couple hammers by sealing them into a square tube packed with a charcoal fines/salt mixture: http://www.aescustomknives.com/docs/tutorial15.htm

Edited by Cylvre
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