Neep help with big heat-treating project

Chiro75

Chiro75

Joined
Feb 4, 1999
Messages
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I am considering a rather large heat-treating project and need all the help I can get. I have a 15" OAL (7/16" thick!) Himalayan Imports khukuri that has lost its temper die to some overheating while an imperfection was being ground out. The kamis (Nepalese kkhukuri and tool makers) differentially heat these knives by pouring water from a ketlle on the edge. It takes a lot of skill, and these knives MUST be differentially heat treated so that the edge is hard (55-58 Rc) and the spine and tang are soft.
The knife is large, as you can see, and I have never done anything like this before. I was hoping to do a japanese clay temper to give the khukuri a totally unique appearance, but I would assume this adds a lot of work, especially for a first-timer! The khukuri is hand forged from car leaf springs, so it is probably 5160, although it could be anything. Any tips?

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My Custom Kydex Sheath pagehttp://www.geocities.com/CollegePark/Lab/1298/knifehome.html
Palmer College of Chiropractic
On Two Wheels
 
I`m no expert and I don`t even play one on TV but I have been doing quite a bit with 5160 (leafspring stock) lately and having good luck with it. I use an oxy/acetelene torch to supply the heat. I heat an area 1/2 to 2/3 the width of the blade ,as uniformly as possible to critical temp. (non magnetic). I check it with a strong magnet as I go and also look to make sure the color is even. Once it`s to temp I edge quench it to the desired depth in oil. I`ve been using motor oil but I have it on good authority that a lighter oil such as ATF or even vegtable oil would be better. He also said that ideally triple heat and quenches, allowing it to cool thoroughly in between, will make for better grain structure. I haven`t tried it yet but considering the edge holding I`ve been getting from a single quench it should be really impressive. After this I clean the scale off and temper it in my home oven. I`ve been using 3 cycles of 45mins. at 400 degrees but again I`ve been told I`d be better off doing one long (2 hours+) at 350 degrees. This process isn`t fancy but I recently had one of my monster camp knives come back from a 4 week long wilderness adventure where it chopped and split all the wood, cleared all the camp sites etc. for 4 guys,without being sharpened and it was still fairly sharp! This just goes to say that 5160(and probably it`s close relatives) must be just about idiot proof where heat treating is concerned.
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Hope this helps. Marcus
 
I do just about the same thing except I use oxy/propane. I think it's alittle cleaner burning. When you start, warm the whole blade with your flame to help avoid warping. I start at the spine and work down to the edge and then work he edge up to non magnetic. I use ATF to quench. It's cheap and has a high flash point. I usually temper at about four hundred for an our or more, depending on the size and thickness, then turn the oven off and let the blade cool down in the oven.I've been told that this will RC 5160 at about 58-60, but I don't know for sure. It is hard though.
 
Thanks for th input so far, guys, and please keep it coming! The problem with edge quenching a khukuri is that due to the big recurve you can't get the entire edge in the quench at once without hardening a lot of the rest of the blade. I believe this is probably the primary reason the kamis in Nepal pour water from a kettle onto the edge. Any ideas?!

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My Custom Kydex Sheath pagehttp://www.geocities.com/CollegePark/Lab/1298/knifehome.html
Palmer College of Chiropractic
On Two Wheels
 
Hi Chiro,

5160 and a few other carbon steels can be heat treated several times in order to fix a problem like the one you described or if the first effort went wrong somewhere, but first you will absoloutly need to anneal the blade bringing it back to the full soft condition. To do this you'll have to remove the handle material, bolsters if any and anything else on the blade that will burn, melt warp or be damaged by exposure to temps of around 1,200 F or so. Then find a way to bring the entire blad (tang and all) to a dull cherry red and place the blade in a fire proof box filled with vermiculite. (wood ash will do almost as well) and let it cool ever so slowly for 12 to 18 hrs.

Having done this bring the entire blade (not necessarily the tang) up to critical temp, non-magnetic, which will be about 1500 F and quench the entire blade in oil point down. Do NOT move the blade from side to side during the quench or it will warp badly. Clean the blade off thoroughly and temper immediately for two hours 425F, let air cool to room temp then temper again at 400F. Now the entire blade should be at a RC58 or so.
Due to the re-curve you wont be able to put the entire edge in water so get some heat absorbibg paste at a local welding supply and apply thickly to the edge whe you want it to remain hard. Now heat the rest of the blade with a torch until you get the oxidizing colors started. Do this as evenly as possible. The colors will start at a pale gold or straw color and progress to brown then purble then blue. When the color is royal blue to sky blue you will have acheived a very close approximation of a fuul spring temper.As soon as it turns blue quench it in warm water to stop the heat progression. The heat absorbing paste should have kept the heat away from the edge leaving it good and hard.

This is getting real long, but I would not recommend using a torch for the annealing process OR the hardening process. The blade is just to big for that. See if there is a bladesmith in your area that can use a coal or gas forge for these steps.

Hope this helps...Gary B
 
One other thing I forgot. Sorry for being so long winded. The 5160 wont show a very good temper line through conventional polishing like a 1095 steel would but it will show nicely if you give it a quick etch in Ferric Chloride.

GARY B
 
I'm not sure of all the facts. Did you get
most of the blade too hot or just a small
portion?
You can harden part of the blade on just the
edge without reannealling the whole blade if
that part of the blade has been softened.
what exactly occured?
Conoco pale parifin quenching oil is the 2nd best for quenching behind Texaco type A quenching oil. I have found that a single
temper after hardening 5160 at 350 degrees
for 2 hrs works the best above that it softens the edge too much and takes several
sharpenings to get it to hold a decent edge.
By heating up the thin edge you will most likly burn off some carbon and loose some
edge. If you use color to temper you will
find that deep blue is 500 degrees plus
light straw is 350 dark straw is 380 blue-
green is 400 + and blue is 480+.. Temp sticks
will sometimes give you an aid. but usually too broad.
Again can you elaborate on what happened


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