First, an extra special thank-you to Bill for his extremely generous offer. That, if I may say so, is what makes doing business with HI so special. But it was entirely my fault that the blade got broken, so it wouldn't be right to take advantage of your kind offer.
Now that I've had some time to inspect the fracture and think about it, I'm mostly convinced it was an unlucky million-to-one fluke. The fracture lies clean across the khuk's centre of percussion, and the exposed grain is distinctly crystalline, which suggests a hard spot, where the blade for some reason remained fully hard (and brittle)
Since the break lies across the center of percussion, which is where the maximum stress falls when I take a cut, this hard spot must be very small indeed, or the khuk would've failed a long time ago. Now I've cut down big trees with this khuk; chopped through nails, split logs, chopped up steel oil drums &c; the sort of abuse a lightweight blade of this kind was never intended to cope with; and it always took it in its stride, no worries. I think we're talking about a flaw that was maybe only a hair's breadth wide, which I just happened to catch with an unlucky blow that just happened to connect with a buried stone. That's what I mean by a million-to-one fluke.
Interestingly, I was just reading the other day on the Bladesmiths' Cafe board on SwordForums about similar experiences other people have had with 5160 steel. Apparently, because 5160 (which is almost identical to what the kamis use) is so responsive to heat treatment, it's possible for heat to bleed back into the edge of a differentially-quenched blade from the spine to such an extent that it brings the already-quenched steel back to the temperature at which the material's crystalline structure changes - in other words, under certain conditions it can actually reharden itself after quenching. Some of the best smiths in the USA have had this happen to their blades, so once again I should stress that this isn't intended to suggest that Kumar was in any way negligent when he made the khukuri. It's simply a fluke that sometimes happens, and there's no way of telling until the blade breaks.
Another possibility, which old-time smiths have told me about, is a drop of sweat falling off the smith's forehead onto the cherry-red-hot steel and forming a 'chilled spot', at which point the blade is vulnerable. Again, this could happen to anybody, from the village kami to the finest swordsmith in the States or Japan.
Anyhow; I've talked it over with my bladesmith buddy here in Somerset, and we're going to try drastic measures to get the old warhorse back together; strip off the woodwork, put the two bits into the fire and try a forge-weld. Ordinary stick or mig welding simply wouldn't be enough, because of the break being right on the point of maximum stress; but a full-fusion forge-weld might just do it, and save the blade. In essence, we'll be heating the broken ends to just short of melting point, at which stage it should be possible to achieve a joint that'll be as strong as the unbroken blade itself - assuming we don't screw it up and burn the steel, or get a cold shut or a slag inclusion...
Of course, we'll have to do the heat-treat right over from scratch, and if we get that far we'll do it Japanese style, caking the blade with clay to achieve the differential quench - we won't risk the Nepalese method, since we haven't got the lifetime's experience in judging the heat that the kamis have!
If anybody's been to see Lord Of The Rings and remembers the bit about the Sword That Was Broken - well, it's gonna take a little touch of magic to pull this off. But I've got to try. I owe it to my best and most trusted friend...
Thanks again, Bill.
Tom
