What do you think I done wrong?

Yvsa · Jul 25, 1999

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I found that I had room in a H.I. Kuhkuri sheath for a little bigger karda. Going along wth the American thng that bigger is better I made a new karda.
I made it from an old bayonet blade I had and when the blade was like I wanted it I brought the edge to critical temp and dipped the edge in water from the tap.

Everything was fine. It hardened to where a file wouldn't quite cut it. Just exactly how I wanted the blade to be.I could still file it across the back. I had taken all the carbon off of it and was putting the final edge on.I layed one thing down and was looking on my workbench to find what I was looking for,I heard a "tink" and thought "Oh No!!" Yep,I looked down and a 1/4" from where I had started the edge it had cracked. It was straight up toward the back of the blade and 1/2 way through.

I am thinking I should have thrown it in the oven at 400* for an hour right after I had tested the edge for hardness. I think that may have prevented the thing from cracking. What do y'all think?

I am probably going to start another one tomorrow from an old pair of pruning shears.I am wanting to learn the hardening process with water and will do this one the same way. I am also thinking about heating the water to about boiling to see if that would be less of a shock. I don't know though. I would have thought that if the tap water was gong to crack it that it would have done it when I first dunked it. I just don't know,but I am going to learn how to harden wth the water.

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>>>>---¥vsa---->®
The civilized man sleeps behind locked doors in the city while the naked savage sleeps (with a knife) in a open hut in the jungle.

Spencer Stewart · Jul 25, 1999

It may help to know the composition of the steel. If you would like to use water for the quenching meium, I would suggest a chuck of W1 or 1095 steel. both are pretty cheap to buy.

Spencer

Edward R Schott · Jul 25, 1999

Hardened steel must be tempered immediately after it cools from the quench(120-150F).
If not stress will cause it to crack and in some steels it will start to fly apart. At the rolling mill plant I saw a roll that had come back from the heat treater that had not bin tempered and it was throwing pieces all over the place like big potato chips, snap, crackle and pop.

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Edward Randall Schott
Knifemaker
www.angelfire.com/ct/schottknives/index.html
edschott@javanet.com

Marcus · Jul 25, 1999

I am NO EXPERT but maybe you should try warm oil for the quench instead of water. It`s my understanding that it`s not as likely to cause cracking as water. I imagine this also has a lot to do with what type of steel it is. I`ve had good results with it using 5160 and O1. Marcus

Ed Caffrey · Jul 26, 1999

Even water hardening steels should be quenched in oil to avoid warpage and possible cracks. I have seen W-1/W-2 that was water quenched "spider web" crack on a very small scale, that was only visible as tiny black lines, and then only when a 400 grit finsh was reached. Use a magnet to determine critical temp, and quench in a low viscosity, warm oil such as ATF, mineral oil, or even vegtable oil. Doing so will eliminate the cracking problems, and the piece will be much less likely to warp. When tempering, ensure your oven is pre-heated, and temper for at least two hours.

www.mtn-webtech.com/~caffrey

BOB26 · Jul 28, 1999

Use brine not water. Brine is water that has salt, A LOT of salt added to it, like enough to make an egg flote. It needs to be (I belive) at about 120 degrees F. I agree with the above though use oil.

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The spirit grows, strength is restored by wounding

Osbourn · Jul 28, 1999

It sounds like you're trying to do a differential heat treat. In that case, have you considered a refractory clay? That would allow for better heat control. I'd also have to agree with you on annealing it before the heat treat. There's no telling what kinds of stresses it was going through before you hardened. One other idea is to harden the entire blade, then draw down the spine with a torch, keeping the edge cool with a tray of water. I learned these ideas from the Blades N Stuff catalog by Bob Egnath. He wrote some very useful info on the subject.

Yvsa · Jul 29, 1999

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Thanks guys.
I had some partial success with the pruning shears.I managed to save the blade.It cracked but only had about 1/16" or so straight up towards the spine again. I put it in the oven at close to 400* and was able to grind the crack out. It hasn't cracked any further and has a nice temper line if I want to bring it out. You can visibly see the difference between the hard and soft steel. It isn't quite what I wanted,but it will outlast me I am sure.

I have used the oils and other things in the past,but wanted to do just a straight water quench like the Kamis in Nepal do the Kuhkuris' and the karda and chakma. I guess it is one of those things I just want to learn to do. They use straight cold water and just pour it on the Kuhkuri in a special slow way and get the differential temper without drawing or anything. I find it amazing that it can be done at all !! The material is old used car springs from a Mercedes Benz,prefered. Probably a 5160 steel.
I imagine the pruning shears are 1095 or the like. It is a pretty cheap although very good steel.IMO.

I figure if these people can do it under thier very primitive conditions then I should be able to learn how to. My conditions aren't quite as primitive as thiers,but I think thier forge gives a better source of heat than the gas burner on the stove and my propane torch with the Mapp gas.
I am going to do another knife and harden the whole blade and then draw it in the oven again. That seems to work quite nicely.

I may do as was suggested and draw the spine with the torch. It would be acceptable to leave it very hard and use it as the chakma as well as a blade. I tried the other blade I messed up on and it strikes sparks with flint very well.

I am shooting for a system that I can use in place of other knives and such. With this new karda a long as it is and another almost as long it will handle most any task with ease. It is going to take some getting used to use the Kuhkuri in place of my CS Trailmaster though. I will start another one in a day or two.
Thanks for all the suggestions. I should have explained better at the beginning.

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>>>>---¥vsa---->®
The civilized man sleeps behind locked doors in the city while the naked savage sleeps (with a knife) in a open hut in the jungle.

[This message has been edited by Yvsa (edited 29 July 1999).]