Stainless steel Damascus: elemental migration as measured on scanning electron micros

[tapforge]

So here's the story, my friend William Brigham, makes this awesome stainless steel Damascus out of aeb-l and 304 stainless steel. I'm a machine shop manager and instructor for university of California Irvine engineering school as such I have access to a some really cool research equipment, and I have made friends with multiple materials science graduate students. Awesome combo for a bladesmith, knifemaker!
So here is more info than u bargained for:
Material AEB-L and 304 stainless steels forge welded together in a purged argon container at 2350*F for multiple hours forged under a 30 ton press (thanks William!) here are some sem scans and some hardness testing (can't see carbon on sem) so we can ascertain carbon migration via hardness testing comparisons.

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[tapforge]

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[tapforge]

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[KenH]

That is all fascinating, but give us some explanation of each photo, such as what is the big white spots?

What about the last graph - what is it showing us other than the elements in sample? Why does the Ni go from high on graph to low on graph? The scale on bottom of graph that goes from 0 ti 200, what units is that?

Ken H>

 

[tapforge]

That is all fascinating, but give us some explanation of each photo, such as what is the big white spots?

What about the last graph - what is it showing us other than the elements in sample? Why does the Ni go from high on graph to low on graph? The scale on bottom of graph that goes from 0 ti 200, what units is that?

Ken H>

Hi Ken,
The white spot are microscopic dust! Measuring about a couple microns. The first few pics show us the crystalline structure and the weld zone. The chart shows us that it's bonded on the atomic level, we are looking at a span of 200 microns (the numbers on the bottom) and we see a smooth transition of elemental migration between the two metals. Further testing is needed to tease out more details.


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[Darrin Sanders]

No big surprise here. Any time you forge weld two different materials together you're going to have carbon migration. Were these tests performed on as forged material?

 

[tapforge]

No big surprise here. Any time you forge weld two different materials together you're going to have carbon migration. Were these tests performed on as forged material?

Yes all forged for long time and the tests actually showed very little carbon migration


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[me2]

Good stuff there. So in several hours near melting, the nickel depleted from the 304, and migrated to the AEB-L, but only over a distance of about 0.003" or from about 75 to 160 microns on the scale in the picture? Also, it appears Mn and Cr move either at very similar rates or move together, ie the changes wouldn't be the same if one or the other weren't present. Also, just from the graph, it appears iron moves from the AEB-L (going right to left) into the 304, but I'd guess this is just because the graphs are based on relative amounts and AEB-L is a less alloyed steel than 304, so the relative amount of iron is higher there.

Other than hardness, have you tested for carbon with other methods? It would be very interesting to see how 304 reacts to having some carbon introduced while the nickel is reduced and then quench the whole thing in oil, as is sometimes done for AEB-L.

It's certainly a good weld. Did you look at other areas to see overall how good the welding was?

 

[me2]

Can't believe this thread hadn't had more traffic. Excellent information regarding welding of Damascus and element migration. Note how slowly the elements move. This spent hours only a couple hundred degrees below melting and the concentrations changed over only a couple thousandths of an inch.