Carbon migration in a San Mai/single weld weld

Kentucky

Kentucky

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Dec 13, 2008
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Whats your take on carbon migration with only one weld? Like a san mai blade or the bit of an axe? Ive heard and read "4 welds to 50/50 in damascus,ect...What do you think?
 
How much migration happens with only one weld? A % if you will. Say you take a piece of 1018 for a axe body and then weld a piece of 5160 in it. How much carbon will migrate out of the 5160? Something like that..:)
 
There is not enough carbon migration in a single weld situation to worry about. If you use a high carbon steel for the bit or center of a .7 or higher it will be fine. Even a lower .5 will give you an adequate edge.
 
aye, I can only share info from experience.. but welding 2 bars of really good wrought to one bar of 1084.. even hardened I can bend the blade by hand..
 
I agree with Chuck, and especially Bill.....if you do things "correctly" one weld will not induce carbon migration. However, if the heat is too high, with too long a duration, you can literally wreck a billet. Now, that being said, once/if the carbon migration occurs, you cannot reverse it, but in relationship to the grain growth that can and does occur, that is reversible via other methods.
Personally, I would never recommend using 5160 in an application as you described....5160 simply does not play well with others (it does not work well or easy in a forge welding application).

In a forging situation, everything that occurs with the steel, good or bad, has to do with time AND temp.
 
There will always be some degree of carbon diffusion if the materials are friendly to it (e.g. not made of nickel, silicon etc...). The diffusion can be so little that it can be said not to count our it can be so great that it cannot be ignored, as pointed out this is all dependent on time and temperature. I have done a bit of studying of this and have a few images of both pattern welded and san mai weld zones, but am too wrapped up in the process of roofing my house right now to upload. With san mai, if you are quick and do not overheat the diffusion may only be around .005" deep, with more time and more heat, and particularly with folding the diffusion can be total.
 
I think that number of folds matters quite a bit. since carbon diffuses at a very slow rate (yes this is dependent on time and temp.) then if you have hundreds of layers each layer may be very thin, thus complete diffusion is possible
 
Uhhh, More folds = more time at high temp thus more diffusion. I don't remember for sure but IIRC the rate of carbon migration is .020 inches per hour at 1750 and increases as temperature rises so at welding temp it is moving rather quickly. How long does it take you to weld a billet and take i to 250 layers? For me in my shop I can do it in about an hour and use two welds.

Nebulae said:
I think that number of folds matters quite a bit. since carbon diffuses at a very slow rate (yes this is dependent on time and temp.) then if you have hundreds of layers each layer may be very thin, thus complete diffusion is possible
Click to expand...

Also I didn't say anything about wheather it was possible or not to get complete diffusion just that it was more dependent on time and temp than numder of layers.
 
Yes what you say is true, but it still seems to me that hugely increased surface area combined with the fact that the carbon need not diffuse so far would mean that # of layers is indeed a factor. That being said, the two are inseparable, and so with no actual data, or experience of my own, I'll take your word for it.
 
If we look at the OP, the carbon migration will take place in the transition zones only. So if you are putting a bite on an axe it is traditionally wedged into the blade and the edge is not actually welded, just the joint. If you are talking a full san mai then there might be (as Bill pointed out) .02 inches per hour at 1750F. The initial weld temp will be much higher so there will be a greater amount of migration. However even if it were to double say .04" per hour, the initial weld should only take 10-15 minutes so that would be 1/6th to 1/4 the amount. So that would range from .00666 inches to .01 inches per side. If it takes you another 20 minutes to forge it out there will be a little more but not worth the worry. If you are grinding into the core material, by the time you get to the center you should be working with close to "virgin" steel.

If we look at the layer count, it does have a play in this. A 250 layer billet forged to .25 inches each layer will be .001 thick. It does not take all that much time to cross a .001 boundary. It has to do with time temperature and thickness of material. Time and Temp are used as constants to see how far it will travel during carbonizing or case hardening steel. I had to do some case hardening and needed to know how long it would take to get to the .100 depth. It took roughly 7 hours, that was ramp up and soak. It took about 1.5 hours to ramp up so the .02/hour works out great.
 
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