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"Ultimate" san mai - speculative fun
- Thread starter RX-79G
- Start date
- Joined
- Nov 27, 2002
- Messages
- 2,088
Carbon dosen't Diffuse as much or as quickly as one might suspect...
I did an experiment with a core of .5% carbon steel, and outer layers of 1%
carbon steel.....each @ about .2 thickness.....welded them up...took my time
drawing them out to about .3 thk...then ground the surface layer off. The piece was checked with FC
to be sure that the 1% material was removed from 1 side.....then the piece was numbered
and sent out, along with a piece of the .5 carbon steel, for analysis.
There was NO difference in the carbon content between the laminated and non laminated
pieces.
I did an experiment with a core of .5% carbon steel, and outer layers of 1%
carbon steel.....each @ about .2 thickness.....welded them up...took my time
drawing them out to about .3 thk...then ground the surface layer off. The piece was checked with FC
to be sure that the 1% material was removed from 1 side.....then the piece was numbered
and sent out, along with a piece of the .5 carbon steel, for analysis.
There was NO difference in the carbon content between the laminated and non laminated
pieces.
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That's a neat experiment and results.
The only thing that could have made the results funny is if there was a fair amount of decarb in the whole process. But that would mean that the .5% came up as it pulled carbon out of the 1%, then they both dropped down until the .5% piece was back where it started. The coincidence is probably too great.
Willie71
Warren J. Krywko
- Joined
- Feb 23, 2013
- Messages
- 12,214
I looked this up in Verhoeven a few months ago when I started playing with San Mai. At welding heat, the steel would be equal in 1-2hours, (carbon moving 1mm in about 20 minutes) of course, San Mai fan be welded in one or two heats, not staying at those temps for more than a few minutes. At forging temps, it would take multiple hours. http://www.hybridburners.com/documents/verhoeven.pdf Page 60.
Great reference! I've been looking for something like this for years.
If I'm reading everything right, it appears that the secret of keeping your carbon levels discrete for san mai is to do your welding with fairly thick stock, then thin the sandwich at forging temps. This keeps the center of the core furthest from areas of high diffusion at the highest diffusion temperatures. Once welded, forging temps are so much slower that squishing it down to blade thinness should cause very little diffusion.
1/4" stock? 1/2"? I can see the argument either way.
Am I understanding this correctly?
The company demonstrating the ultrasonic welding was "Fabrisonic LLC" Of course the implications to knife blades didn't hit me until I was driving home, so I didn't spend nearly as much time talking to them as I should have. Looking at their website and a video interview with the CEO, it seems their process is low temperature and preserves the properties of the materials before welding. Also they work with foils, so the center layer of the san mai could be really thin. Bring on the bling san mai of gold and S110V. On a more serious note, this process solves the issues brought up in early posts about welding stainless to a carbon steel core
Carbon diffusion in san mai it is not that different than decarburation in the furnace. It happens, not the end of the world, but to be taken into account with the thicknesses and by keeping the steel at very high temperatures only for the strict necessary to complete the task.
It is also truth that SS needs quite Cr in solution to be actually stainless, but even when underaustenitized it exibits still uncomparable stain resistance Vs carbon steels.
It is also truth that SS needs quite Cr in solution to be actually stainless, but even when underaustenitized it exibits still uncomparable stain resistance Vs carbon steels.