San Mai close-up

Karl B. Andersen

Karl B. Andersen

Joined
Jul 27, 2003
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For those interested in such things.
I was sending a knife off and while cleaning things up noticed how nice it looked laying on the bench and catching the light just right.
Keep in mind these displays are really only a few thousandths of an inch in thickness, but we get to appreciate the view as we grind at a tangent to the layering.
A little etching and we can see the varying degrees of carbon/alloy concentration that happened while at welding temps.
The longer the blade is at high heat - if it's a larger blade - the more "stuff" happens.
Some folks use three pieces of steel that, together, are nearly the thickness of the blade they seek. So, they don't spend much time at welding heat.
Others, like myself use thicker steels which need to be drawn out. (I'm using 3/8" 1095 core and two layers of 1/4" 420) Staying at higher forging temps allows more time for migration to occur, and we get some cool displays of activity.
The shiny layer above the 1095 is where the carbon in the carbon rich tool steel "left" to equalize the carbon deficient 420 SS, which, now that it has some carbon, etches darker.
It sort of happens on stages over time. It's not a constant "flow" so there are varying degrees of activity.
(The undulations along the bottom edge are the results of my drawing dies as I draw out the billet)
Anyway, some eye candy to start the day.



 
There's a real beauty in that. If it was a painting I'd gladly have it hanging on my wall :)
And not to mention it's educational too ;)
Thank you for sharing.
 
I've also often enjoyed this activity as a good example of what is happening within our steel when using drawing dies.
If this was 300 layers of Damascus, we'd have the chatoyance that is so visually appealing.
 
I've done the same thing Karl. Stared at a damascus billet up close and taken pics just because. But I do love the carbon migration and the effect it reveals when etched in the stainless on carbon san mai. Simply beautiful. It's why I'm working so hard toward doing the same thing in my shop...

A macro of a 1095/15n20 damascus 'twist' billet I took lately after a quick etch. A little dirty as it was a quick 220 grind and etch... and a phone camera..
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And a cut-off end of a RR track section after I cut it with the torch. Looks like cooled lava to me just a bit.
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Nice pics Karl. I second the statement; I'd hang that on my wall too...

-Eric
 
What a great pic, Karl. The fact is that I'm having a hard time with your explanation of the layers. I would expect a more gradual diffusion if it was as simple as carbon moving toward "equilibrium" so-to-speak. My uneducated opinion would be that the shiny line is where carbon has almost completely burned away. I also can't help but feel that flux and other impurities are driving those distinct layers. It almost looks like grain growth... or at least a granular effect of some kind and the "shadow" is some sort of funky Hamon-type artifact cause by the close proximity of the weld area.

Like I said... my opinion is barely educated and purely instinctual... which is not always reliable with regard to metallurgy.
 
They really look fine ! I'd love to see these redone , carefully by hand and seen at higher magnification.
Diffusion [ not migration please ] is time and temperature controlled .It doesn't quickly happen .I'd like to see how much is diffusion and how much is differences in hardenability. Next time I see a really good Japanese blade I'll save it and post it to show all the different structures that can be seen.Had polishing will bring out the finest most delicate structure.
Keep up the good work -all of you !
 
Beautiful, thanks for the pictures!!
and i think i remember Karl stated that those structures could be seen in the unhardened blade too.
Very intriguing :)
 
I went over this in a bit of detail with Kevin Cashen this past weekend in Ohio.
Correct - it's diffusion.
And it doesn't happen in a gradual constant "wave" - it sort of happens in stages.
He referenced the question about why the carbon doesn't sort of "follow" itself and fill in the differences as time goes on. It's time dependent. It could happen over time, but before then, the knife is done.
Rick - there is no flux. This is a dry weld.
And you are correct - that is what I said in the first post - that shiny line is nearly pure iron where the carbon vacated.
And the darker line above it is basically where it went.
Kevin had some cool photo micro-graphs of San Mai like this and the carbon diffusion and gave a pretty cool explanation of the process.
 
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