Blade failure on 8mm thick Condor Heavy Duty Kukri!

Too much time and/or temperature during heat treatment causes excessive grain size growth, and corresponding brittleness. The grain size looks quite huge to me!
 
mete said:
All right !
The darkest part of the failure is probably an inclusion .That then started a crack around it. This crack then oxidized to cause that 1/4" + dark area. Then you whacked it and it was 'all she wrote ' !! The grain size might be a bit large.
For many years I was a fencer and picked up broken blades .They were poor quality 9260 with lots of large inclusions. Nicks on the edges from parrying, beating or failure at an inclusion were the two modes of failure .
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I agree. Looks like an inclusion-derived crack. I do also think that grain size looks large so it may have been exacerbated by an off-spec heat treatment. They'll definitely replace it--no question.
 
What a shame! I have never had such poor luck with any of my Condor blades. Keep us posted.
 
Two more pictures in good light.


Took it back this morning and its being returned to Condor for them to see what happened. I doubt we will hear what the problem was but i think it was a flawed blade/material. They were surprised it happened at all let alone where it did fail and offered me a replacement right away. I took it since i do like the blade so much. Going to use it as i did the first one and keep my fingers crossed. Cant happen twice......right? :eek:
 
David Lowry said:
This is the 3rd or 4th failure of something from Condor I've seen posted here in the last 2 years or so. I'm not thinking I'd want to buy one anytime soon.
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Condor makes a lot of different models and I am sure way more than 3 or 4 have had similar problems and even given that "fact" I would have no problem buying any of their knives or tools.

There will always be bad ones that get through and as long as Condor has a decent warranty threads like this make me feel confident about the Condor knives I own and future purchases.
 
T1nkerer said:
Two more pictures in good light.


Took it back this morning and its being returned to Condor for them to see what happened. I doubt we will hear what the problem was but i think it was a flawed blade/material. They were surprised it happened at all let alone where it did fail and offered me a replacement right away. I took it since i do like the blade so much. Going to use it as i did the first one and keep my fingers crossed. Cant happen twice......right? :eek:
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Yeah, like I said before the grain is blown, I noticed it from the 1st photos, looking at it on a 32" screen...... Easy to see...
 
As others have noted, the gain looks huge.

Something went massively wrong with the heat treat for a blade of this thickness to fail in the manner it did.
 
Every broken blade I've seen looks like the grain size is way too big, like the blade was made out of cast iron. But I don't think you can accurately tell what the grain size is without careful preparation of the metal and high magnification.

If grain size were the problem, I doubt the blade would have broken in what is basically the strongest part of the blade. It would have broken in a thinner place on the blade, probably near the handle where there would be leverage and stress risers to help.

The simplest explanation comes from the visible inclusion and the weathered area near the edge that are good signs of a pre-existing crack. That crack then became the stress riser. Grain size does affect blade toughness, but there is no reason to think this blade would have broken without that existing crack.
 
Twindog said:
Every broken blade I've seen looks like the grain size is way too big, like the blade was made out of cast iron. But I don't think you can accurately tell what the grain size is without careful preparation of the metal and high magnification.

If grain size were the problem, I doubt the blade would have broken in what is basically the strongest part of the blade. It would have broken in a thinner place on the blade, probably near the handle where there would be leverage and stress risers to help.

The simplest explanation comes from the visible inclusion and the weathered area near the edge that are good signs of a pre-existing crack. That crack then became the stress riser. Grain size does affect blade toughness, but there is no reason to think this blade would have broken without that existing crack.
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Pretty much my thoughts as well.
 
Heavier blades are not necessarily harder to break. On the contrary, given a similar quality of material, the larger blade will generate far more force, making it that much more likely that the blade material will yield at the point of impact. The idea is to work efficiently, to slow it up and allow the weight of the knife to do some of the work for you. It is about using the right tool for the job and using it in the right way to get the best results without breaking it.

n2s
 
Twindog said:
Every broken blade I've seen looks like the grain size is way too big, like the blade was made out of cast iron. But I don't think you can accurately tell what the grain size is without careful preparation of the metal and high magnification.

If grain size were the problem, I doubt the blade would have broken in what is basically the strongest part of the blade. It would have broken in a thinner place on the blade, probably near the handle where there would be leverage and stress risers to help.

The simplest explanation comes from the visible inclusion and the weathered area near the edge that are good signs of a pre-existing crack. That crack then became the stress riser. Grain size does affect blade toughness, but there is no reason to think this blade would have broken without that existing crack.
Click to expand...


If the HT was done properly in the first place the stress crack wouldn't have been there AND the blade wouldn't have snapped.....

Even if the stress crack wasn't there the blade would have still snapped or cracked due the blown grain....
 
Twindog said:
Every broken blade I've seen looks like the grain size is way too big, like the blade was made out of cast iron. But I don't think you can accurately tell what the grain size is without careful preparation of the metal and high magnification.

If grain size were the problem, I doubt the blade would have broken in what is basically the strongest part of the blade. It would have broken in a thinner place on the blade, probably near the handle where there would be leverage and stress risers to help.

The simplest explanation comes from the visible inclusion and the weathered area near the edge that are good signs of a pre-existing crack. That crack then became the stress riser. Grain size does affect blade toughness, but there is no reason to think this blade would have broken without that existing crack.
Click to expand...

I agree, I'm not a metallurgist but I pay them to tell me why stuff broke. They polish the metal and use a microscope to make that evaluation. It can't be done from a photo.

Something happened at that dark spot or near it. Could be a bad heat treat caused a weak spot, could be an overheating during sharpening, could be a lot of stuff. Then some stress caused a crack at the weak spot. Maybe a thermal stress as it came out of heat treat, maybe the blade was caught in a fixture and bent such that the weak spot was stressed, maybe something heavy fell on it or a grinding wheel broke during sharpening, whatever. A surprising amount of manufacturing damage comes when a fixture or drill or cutter or whatever breaks during machining. The immediate reaction is "machine down" and often no one notices the small booger on the part. But a crack started, that much is obvious. Then it grew, unnoticed, maybe a tiny bit with every chop. At some point the crack was large enough that the next chop caused it to go all the way.
 
In all reality, we don't know exactly how this blade was treated by the user, either. I've seen breaks like this happen to good tools when the user sinks the blade into the center of the round (as it looks like the OP was doing at the time)...... and then lifting the blade and block to slam them down to force the blade thru the wood.
Generally a large knife will handle this a number of times before failing, but at some point it will fail, especially if by manufacture or abuse it develops a crack.

To me the first couple of pics, due to lighting, look like large grain...but the last pic, in better lighting, doesn't.
The crack could've happened during manufacture, or it could've happened during usage.
I would be very hesitant to make any judgement based on the info so far in this thread and without clear explanation of usage and professional assessment of failure.
The good news is that the company replaced it regardless.
 
I've snapped greatly overheated metal with large grain like it was a dry stick, no stress raisers needed. REALLY overheated metal!:D

Overheated.jpg
 
Pondoro , I told you now where's my money ?

Mecha, While there is a decrease in toughness as you go higher in grain size there may be other things involved. That's why I didn't say more than I did. The common advice to anneal a file by heating then very slow cooling in ashes or in an oven turned off worries me . For 1% C or higher there is a distinct possibility to diffuse carbon to move carbide to the grain boundary sometimes even continuous carbide .That will make a really BRITTLE blade.
 
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