"Immortal Khukuri" is a name I just made up, so hopefully you guys like it. :jerk it: 
Anyway, there are a bunch of sorta-legends about ways of making khukuris that never need sharpening, one of which is the "magic rock" treatment, which at first glance is just polishing. How could being shiny have that kind of effect? Being super-shiny would make small flaws very easily visible, for better quality control, so maybe that's how the legend got started?
But, I've thought about it a lot, and I think the "magic rock" actually might cause a blade to be self-sharpening, to a degree, if done skillfully.
I spent way too much time trying to get the silhouettes and everything just right, so I hope you guys like the pic, too.
An attempt at a cross-section through the sweet spot, given what I know about how steel works. Darker areas are harder.
So you essentially start out with a blade that's already like a rat's tooth (which is harder on the front than the back, so they sharpen themselves as the rat gnaws), and then use intensive polishing to burn the temper out of only some of the steel, making the hardest area thinner, and surrounding it with softer steel. In use, the soft areas wear away faster, leaving the edge still sharp. It wouldn't self-sharpen enough to cut paper, or anything, steel being what it is, but such a blade could maintain a woodcutting edge for decades or longer, if made with an insane amount of skill.
And many, many users of HIs have noticed a thin layer of soft steel on the mirror-polished ones...
Edit: also, the internal stresses and things mean the asymmetrical hardness should actually improve strength. It's a bit like "tensegrity" engineering, preloading everything you possibly can. Intuitively, it seems like internal stresses are a bad thing, but in practice, things that are attempting to tear themselves apart from the inside out, actually end up incredibly strong.
Anyway, there are a bunch of sorta-legends about ways of making khukuris that never need sharpening, one of which is the "magic rock" treatment, which at first glance is just polishing. How could being shiny have that kind of effect? Being super-shiny would make small flaws very easily visible, for better quality control, so maybe that's how the legend got started?
But, I've thought about it a lot, and I think the "magic rock" actually might cause a blade to be self-sharpening, to a degree, if done skillfully.
I spent way too much time trying to get the silhouettes and everything just right, so I hope you guys like the pic, too.
An attempt at a cross-section through the sweet spot, given what I know about how steel works. Darker areas are harder.
So you essentially start out with a blade that's already like a rat's tooth (which is harder on the front than the back, so they sharpen themselves as the rat gnaws), and then use intensive polishing to burn the temper out of only some of the steel, making the hardest area thinner, and surrounding it with softer steel. In use, the soft areas wear away faster, leaving the edge still sharp. It wouldn't self-sharpen enough to cut paper, or anything, steel being what it is, but such a blade could maintain a woodcutting edge for decades or longer, if made with an insane amount of skill.
And many, many users of HIs have noticed a thin layer of soft steel on the mirror-polished ones...
Edit: also, the internal stresses and things mean the asymmetrical hardness should actually improve strength. It's a bit like "tensegrity" engineering, preloading everything you possibly can. Intuitively, it seems like internal stresses are a bad thing, but in practice, things that are attempting to tear themselves apart from the inside out, actually end up incredibly strong.
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