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Ed Caffrey's Workshop Talk to Ed Caffrey ... The Montana Bladesmith! Tips, tricks and more from an ABS Mastersmith.

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  #1  
Old 02-09-2008, 08:23 PM
Doug Lester Doug Lester is offline
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question on damascus

After reading Verhoeven's book on metallurgy and a couple of responces on the damascus forum it seems after a damascus billet is welded up, whether from standard bar or shim material, the carbon content should be pretty homogeous due to the carbon diffusing through the steel at welding and forging temperatures. That leads me to a couple of questions. What is the purpose of using a mild steel, such as 1010 or A203E, into a mix of 1070, 15N20, or 1095 when by the time I have it forged out to an adequate layer count that all I'm going to have is a billet of 1060/1070 with some bands of nickel running through it, which doesn't diffuse nearly as fast as carbon does? What gives the contrast between 10XX series steels if the carbon content is homogenous in the end product? Would it just be better to start out with steel of similar carbon content like 15N20,
L6, and 1070 where the carbon content starts out about the same and just have banding of chromium and nickel to resist the echant to cause the watering in the billet?

Doug Lester


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Old 02-10-2008, 12:06 AM
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Ed Caffrey Ed Caffrey is offline
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Your getting on the right track of thinking..... however, if I read your post correctly, you still missing a bit of it. Remember that not everything in print is the Gospel. I've read the same book, and although much of it makes good sense, there is also much of that book that just doesn't work the same in practice, as it does in theory (which it seems that much of the book's information is based on).
Always remember, use information, whether from a printed source, or a verbal source, as a very general guideline. I've had far too many experiences with so called "experts" in my Bladesmithing career, who have told me that something I was doing with steel is impossible, and that would not believe the proof in front of their faces. Again, many things that are theory, do not come out the same way in practice.

There are ways around the carbon diffusion, at least to the point of the steels retaining much of their identity. However, most of us who are serious about damascus have chosen to use all high carbon steels in our billets in order to avoid certain pitfalls, and in general make things as easy on ourselves as possible.

Nearly everything we do in Bladesmithing is a give and take scenario. You give up something, in order to acquire/achieve something, and with most of those situations there are ways around it, although more times than not those "ways around" are too costly in terms of time, effort, or materials.

Before you take ANYBODYS (especially someone who is not a practicing Bladesmith) word that something works the way it does, test the theory on your own. Had I believed everything that I had read or been told, I would have never been able to make a blade that would pass the ABS tests, never been able to produce many of the mosaic patterns I have successfully, nor even believed that differential heat treating was possible. At one time or another I have had "experts" tell me that all of those things were impossible. The fact is that an advanced level of education might give you a grand theoretical insight, but it does little where practical application is concerned. To temper that, I mean no disrespect to the book's author, all I'm trying to do is point out that until you prove or disprove it for yourself, it remains ONLY theory.
Sorry to be so long winded,


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Old 02-10-2008, 10:56 AM
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GHEzell GHEzell is offline
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Quote:
Originally Posted by Doug Lester
After reading Verhoeven's book on metallurgy and a couple of responces on the damascus forum it seems after a damascus billet is welded up, whether from standard bar or shim material, the carbon content should be pretty homogeous due to the carbon diffusing through the steel at welding and forging temperatures.
It depends on how many welding heats it takes. For a san-mai 3 layer that's welded in one heat, no, there is not enough time for the carbon to even out. It takes a few folds.
Quote:
Originally Posted by Doug Lester
That leads me to a couple of questions. What is the purpose of using a mild steel, such as 1010 or A203E, into a mix of 1070, 15N20, or 1095 when by the time I have it forged out to an adequate layer count that all I'm going to have is a billet of 1060/1070 with some bands of nickel running through it, which doesn't diffuse nearly as fast as carbon does?
Good question. The only time I use mild in a billet is when I want a low carbon billet (for fittings, or for the sides of sanmai), or when I want to purposely lower the overall carbon content of the billet.
Quote:
Originally Posted by Doug Lester
What gives the contrast between 10XX series steels if the carbon content is homogenous in the end product?
I've wondered that one myself, and I have a theory that it is the differences in manganese, silicon, and other trace elements that lends it the visible pattern. However, this still really doesn't quite explain why cable shows a pattern. I've stacked 12 pieces of 1095 together, welded, and had a subtle but definate pattern, even after 2 folds. I've had people tell me it is because of decarb forming on the surfaces before welding, but wouldn't carbon migration equal it right back out?
Quote:
Originally Posted by Doug Lester
Would it just be better to start out with steel of similar carbon content like 15N20,
L6, and 1070 where the carbon content starts out about the same and just have banding of chromium and nickel to resist the echant to cause the watering in the billet?

Doug Lester
The easiest to weld mix I've used was 1075 and 15N20, and I think it's because they're almost the same thing. Doing it this way not only makes for easier welds, but also less chance of bad things happening in the quench when steels of vastly different expansion and contraction rates might just come apart in a most unpleasant manner. To me it just makes sense that 2 different steels, that would make very good knives by themselves, would also make a superior patternweld mix, as long as they are not too unalike.

I'm with Ed, don't believe anything you read entirely without testing it yourself in your shop with your equipment and tools, patternwelding in particular. Most of what we bladesmiths do can be explained by science, but some of it is pure dark arts, and so far unexplored by the flashlight of science....
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Old 02-10-2008, 02:17 PM
Doug Lester Doug Lester is offline
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Thank you very much, gentlemen, that is what I was looking for, comments on the difference between theory and how it works at ground level. One of the charts in Verhoeven's books states that carbon CAN diffuse 500 microns in 8 minutes at 2100 degrees F. That doesn't say how much carbon or in what direction. Despite what someone else tried to say, I know that this happens randomly and in all available directions. The carbon is moving out of the 1010 into available spaces between the iron molecules in the austinite crystal latice of the 1095 at the same speed. The 1095 just has more carbon molecules on the move than the 1010 does, and initially, all the "voids" between the iron molecules in the latice are occupied whereas the 1010 has fewer molecules of carbon on the move and has many spaces avialble in the iron crystal matrix to absorb the carbon molecules. Verhoeven's book didn't touch on this randomness and I was wondering out how this effected things in the "real world".

Yes, it does sound like I have come up with some of my own answeres and I have spent about the last 24 hours rolling things around in my own head trying to make sense of things. Thank you again for your input.

Doug Lester


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Old 02-10-2008, 03:23 PM
cdent cdent is offline
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My understanding of it, is that the process is not really too random. It seems that if the conditions are right, the carbon will flow from high to low concentration areas.

I have a disc of a demo by Howard Clark, where he touches on many of the Verhoeven points. It's from 1993.

Take care. Interesting stuff to me as a beginer and I'm pretty sure many different ways to look at it, Craig
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Old 02-11-2008, 12:16 PM
Doug Lester Doug Lester is offline
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I've been ruminating over this question of carbon diffusion some more. I recall the program that Nova had on PBS about the Japanse sword. They showed the Tamahagane (sp) master making the steel. Even though he layered iron ore and charcoal in the furnace and cooked it for three days it still was not homogenous. It had clumps of various grades of steel and iron distributed throughout it's mass. Even the clumps of steel that the sword master bought from his was no homogenous because he had to fold and weld the billet many times to assure the even distribution of carbon and other element in the steel. There clearly has to me more to carbon diffusion than was mentioned in Verhoeven's book

Doug Lester


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