Water-quenching 5160 questions...

With Shop2 they've got far more "source steel control" than they had at Shop1 which they were only investors in. I'd be willing to bet any previous sightings of other steels were Shop1 related.

Let's keep the discussion to 5160 at this point.

Jim
 
Another thing: they're already used to pounding in the curves on khukuris, so getting the curve via tempering/heat-treat isn't what's being considered.

Jim
 
Hi all,

I am not bladesmith, just a collector of knives, Khukuris and katana. So I an not sure if I am qualified to chime in. But after reading all the posts, it is inresistable
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In quenching, the sudden cooling will form martensite and creat grain boundaries. The faster the quench, the more grain boundaries and the more internal stress, then the steel may just break into pieces.

Water is a very fast quenching medium, thus creat very much internal stress and also hardness for the steel.

Blades are in a special category in quenching as it is thin at the edge and thicker at the spine. The most unfavourable characteristic in knife blades is that we need a hard edge and soft(or springy) spine. Then the stress is greatest at the thinnest section so in most cases, slower quenching medium is much "safer".

Curvature created in clay coated quenching:

It is because martensite occupy more space. As the steel is heated up, the atoms vibrates and occupy more space and thus the steel swells up a bit. And in quenching, the cooling down makes it returns to it's original size but as the edge cools much faster and return to a state that occupy more space. Then it seems that the spine shrinks more in quenching than the edge and the blade curve backward.

So Jim, at the extreme difference of thickness of edge and spine in Khukuris, I think the edge is rather crack than the blade bends.

And in the making of Khukuris, the smiths pours water on the edge of blades. I think the process can better be described as spot hardening. The water touches a spot, martenste formation immediately, then the water evaporate real quick, heat from the spine (heat sink) bleed to the spot and temper it. I think the actual picture will be very complex. Depending on the individual smith, there will be alternating hard and soft little spots on the edge, even to different depth.So it is not surprising that the hardness is different on the two sides of the blade. But...... Khukuris are basically chopping tool, with the thick spine, it is pretty well suited to its role.

Japanese katana is basically a cutting tool(cutting flesh and bone). Japanese smiths creats ashi(little rat legs) of soft metal extending to the hard edge to resist chipping.

Realy don't know what a mess I've type in. Hope you all understand what I wanted to say.

Sorry for the poor english!

Joe Leung

 
Joe, it was quite clear and thank you.

One thing we know from people who have seriously polished their Khukuris and revealed the temper line is that the line is surprisingly uniform. They don't seem to be dribbling small amounts of water, they're doing a single continuous "pour" and being very precise about it.

Jim
 
no one has mentioned if the HI kukris are TEMPERED after hardening by the pouring water method. If they are not tempered, then I think we can conclude that the edge is not truely or FULLY hardened , but only half hard, or even almost normalized. A full hardening, whatever the method, would undoubtedly leav a dangerously brittle or flawed edge.
 
When I quench my first knife in water.....the steel I believe is W1(from a very old and big file). The experience is amazing. There was plenty of turbulance around the blade, plenty of hissing sound , then the blade shakes, then it just shattered! 2nd blade, same steel, slightly lesser soaking time in fire, 3 cracks on the edge, perpendicular to the edge, curved backwards.

Then I think, I asked (thanks again for the great advice from Darrel about annealing and normalising). The boiling point of water is just 100deg C. And the steel, when heated to its non-magnetic range is at least 1200deg C. There will be a layer of vapour jacket even it we quench it in a large bucket of water.

Jim, unless the Kamis use a hose to put the water on the edge
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. The hardening is not gonna even! etching show the difference in hardness, but it cannot say how hard and how deep is the hardness. Try etch less time and you'll see the hardened area with uneven color. But yet, it is not accurate as the concentration of the etchant and the etching time is slightly different from area to area.

Japanese smiths use clay coated method to heat treat a blade and they will intentionally leave soft metal extending from the spine right to the edge, perpendicular to the edge. They are called ashi, in order to prevent chipping.......or just to prevent large chipping.

Fox Creek,

The Khukuris are tempered! Do you know how the old timers used to make chisels? The heat up the whole steel, then quench just the tip in water or oil briefly. The part that is away from the tip is still very hot, take it out wait a while and the heat from the not-quenched side will heat up the tip and temper it. Then he will put the whole steel into the quenchant again. And the process is complete.Not accurate, but fast and simple. If the edge is not hard enough or too hard, simply do it again, quick and simple.

Joe Leung




[This message has been edited by JoeL (edited 19 November 1999).]
 
Joe, they *are* using "hoses", or at least the equivelent. They're pouring the water from a teakettle spout, which is close enough to "hose" as to make no difference. By pouring it that way they avoid the "boil next to the hot steel" problem, mostly.

Jim
 
There's really nothing mysterious going on here. The difference between a water quench and an oil quench is a water quench cools the steel faster. That is the only difference.

The kamis don't dunk the blade in water and cool it fast, though; they pour water on the edge and they pour it slowly. Evidently the way they do that cools the steel at the right rate.

That method of heat-treating cold chisels in one step isn't just an old-timer thing, by the way; it's routine to this day in America. The hardened tip of a cold chisel is only about a half-inch long (if it's a big cold chisel it's longer); once you've resharpened it enough times to get past that into the tempered zone you have to re-heat-treat it. (I suppose there are some people and some shops that throw them away instead.) That's the usual way it's done just because it's fast; you take a torch and a bucket of oil and a file and it only takes a minute. Some people prefer to wait till they have a bunch of chisels to do all at the same time; then you can do it as a mass-production job and harden them all first and then temper them all.

-Cougar Allen :{)
 
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