Need Some Help on This One

Laredo7mm

Laredo7mm

Joined
Jul 8, 2002
Messages
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Hey all, I need some advice on this post over in the Knife Review area:

Thread Link

It is from my pass around knife where it got stuck into a tree, slightly twisted and broke the tip. Take a look and let me know what might be the root cause of the failure.

Thanks In Advance-

Sean
 
It's a fine edge so that may be part of it. If you did this in a forge I would suspect overheating the tip , getting large grain which is brittle .It's very easy to overheat a tip.
 
I got the answer for ya, Sean: fine tip knives aren't meant to be jammed into wood and then wiggled out. Steel has limitations. What the heck is with people? :(
 
Amen Fitzo is my hero!!!!!



He said what I was thinking I am getting a little tired of people putting every knife that comes into their hands through a demolition test use it for what it was ment to do.

That is a fine looking knife with a fine edge looks like it would clean out an animal well. Never really had call to gut a tree.

Breaking lknives especiallly stock reduction knives doesn't prove much practically nothing at all forging gives you some info but the number of knives you would have to break to get a conclusive answer on any thing well lets say you wouldn't be selling any for quiet a while.

Abe
 
Thanks guys, I did not expect it to be put into a tree, but I am very interested in getting the knife back to take a look at the grain structure. When I HT in the forge I will use my pyrometer to set the temp at about 1575 (about as low as I gan go) but that will still allow the tip to be able to held at above critical for some time.

It will also be interesting to see what the reground profile will look like. :rolleyes:
 
It might well have large grain at the tip, Sean, which will mean you have to change methodology a bit. When you get the blade back, look carefully to see whether it snapped or tore. If it's perfectly flat and it's obvious it's a steel failure, that's one thing. Most all of us knife nuts learn, though, early on, that jamming a knife in a tree is a good way to lose a tip. Live trees seem to have a helluva grip. That blade was not meant to jam into trees.

Heck, I know this one big ugly mofo who broke the tip on a military KBAR jamming it into a tree as a kid. ;) He learned while still a whippersnapper.

There are those whose continued reportage of ridiculous abuse of cutting instruments has fostered this fallacious school of thought that every quality knife should tolerate that type of treatment. That's PURE BS! :mad:
 
I'd say thats what happens when you stab knives into trees. A super thin tip like that might even be fairly flexible but it will still break on you. For one thing, the grain in the wood isn't a consistent material and it grows in rings around the tree. The tip could very well get curled to the side as you push it in. Then when you try to pull it out, you wiggle a little bit and its flexed twice as far as you think you did.
Now I'm not saying I've never stuck my knife in a board or stump while I was working on something, but some knives you just don't do that with. Skinners with a tiny little scalpel like point like that being one of them IMHO :)
 
The 1095 in our area has had problems with alloy banding. A local knifemaker named Lyle Brunkhorst has been working with a metallurgist to provide a solution for knifemakers. He said he got best results from 1095 after soaking below critical for about 20 minutes, then heat treating. He uses salt pots for soaking & heat treating.

He also said after having lots of 1095 analyzed, it is notorious for having different composition from one batch to another.
 
I have been noticing a range of difference in the 1095 I have ben using. Sometime when drilling for a handle I cut through like ba hot knife through butter. And other times its like hitting a wall. i have even experienced it while drilling the same handle from one hole to the next.

Abe
 
Leave the testing to the PROFESSIONALS or knifemakers. The steel should be fine. I can break any knife but the question would be why. How did your knife hold up otherwise. can it still chop thru a concrete block????
Use the pass around to get feedback on feel and fit. never take a knife to breakage point unless the maker tells you to. Waste of a good knife!!!! :mad: :mad: :mad: :mad: :mad: :mad:
 
First off, it shouldn't have been poked into a tree -- you made a nice gentleman's knife there, not a survival blade.

But, I'm with Mete on this one. You said you did it in the forge and you probably overheated the tip on accident.

BTW -- good work as usual. :)
 
If you send a knife to Kim, be aware that one of his tests is to throw the knife out the window (Hey, Kim, some day I'll be done with your knife! Just don't hold your breath, I guess!). :cool: I'll bet this is more operatoor error than knife error. That said, I'm goiing to go out today with your Damascus knife you made me for the KITH and see if I can break it in half. Wish me luck! :D
 
Laredo7mm said:
What do you guys mean by over heated?
Click to expand...

The reason I ask that is because if I have my forge at 1575° how could it get over heated? When I heat treat in the forge (which isn't very often) I don't grind the bevels just profile the blade.

Anyway here are some pics. What does that 45° fracture angle mean?

I think I know what happened (looks knida grainy to me), looks like the tip was held above critical too long.

In the back ground is a millimeter scale for some sort of reference. There is also some sort of "crud" on the broken surface that won't come off even when i scrubbed it with a dry tooth brush. I don't know what that is. Could it be that the tip broke going into the tree and that is embedded wood?

Let know what you all think. Thanks again for the help. All the more reason to HT with molten salts. :rolleyes:


tip1.jpg


tip2.jpg


tip3.jpg
 
Sean, in those fotos it does look grainy, yes. 1095 can get grain so fine you can't hardly see it with the naked eye. The discoloration is interesting, too. If it is from "tree", then it should wash off with some turpentine. If it is oxide (rust) then one must wonder if there wasn't a microcrack there prior to the "snap".

I still don't agree with sticking fine-tipped knives into trees, but that may not be the cause of the failure, just the precipitating action in this case.

Rather than trying to reprofile the edge, I would consider simply grinding it smooth to the break angle. I have a couple production folders that came with that type of tip and they work out pretty nice.

The problem is going to be you can't know for sure if the rest of the blade doesn't have large grain without destroying it. :( This is one of those days where knifemaking is a PITA, but you'll learn stuff from the experience. :)

'Luck with it.
 
In real life it does not look that grainy. The pictures are magnified by about 20X. The widest part of the fracture is less than 1mm. But what you can see by eye still does not look like the nicely refined grain structure, I am used to seeing coming out of my salt pots.

So, what does this mean? I am going to sacrifice this knife and see what the rest of the grain structure looks like. And also save the forge heat treatment for my prototypes like I normally do. :D
 
I hope you'll report back as to the comparison of grain size in the rest of the knife, Sean. While it will be good info, I am sad to know you have to sacrifice a very nice looking finished piece.

I have asked the question before regarding whether grain growth is a rate-based phenomenon or solely a temp phenomenon. I have been told everything from time has nothing to do with it, only temp, to an explanation that there is somewhat of a threshhold temp beyond AC3 where it will occur. The implication in that statement was that normal austenitizing temps wouldn't provoke grain growth. It was suggested that, at a given temp, grain growth will initiate and grow to a certain point and stop. I still don't have a good answer and my reading hasn't provided one.

It would be real nice if, once Kevin has some time, he might revisit this thread and make a couple comments. Perhaps Robert may have some insight, also. I would enjoy expanding my understanding.

I vastly prefer my furnaces to HT with a forge or torch, and the only thing I would like better is a set of salt pots. The drawback, of course, is that it is a lot of work for one blade, which I feel is what most likely led you to using the forge on this one. Two possibilities that occur to me are that 1) your probe has lost its accuracy (that's happened to me), or, 2) in the chaotic environment of a forge, where you measured the temp versus where the blade got hot may be two different temps. That's two possibilites; I'm sure you've considered more. Good luck with your troubleshooting. I'm sure you're as obsessive as me wanting to know an answer.... ;)
 
I think part of the problem also is that since i can't get my forge to go much below 1575° it is difficult to get good normalizing cycles on the blade as compared to when i use my salts. The grain structure on this knife looks better than my prototypes that I just normalize once in the forge before HT.

This blade was differentially heat treated so that will be cool to see how that turned out as I start breaking the blade back further. Hopefully it will start to just crack the edge and bend the spine.
 
Here are some more pictures. I decided to destroy the blade and not just fix her up.

Nicer looking grain and some ductile failure a bit further back from the initial break:

destruct1a.jpg



Ductile Falure of the non hardened spine:

destruct2.jpg



Bits and Pieces:

destruct3.jpg



Busted up Amboyna :grumpy:

destruct4.jpg
 
Sean,
After doing some testing and some photos, I see what you mean about the magnification making the grain look more coarse than it does to the naked eye, but even with this in mind, in all the shots you made, the grain just looks too large to me.

Here are a couple of shots I did today on a test blade. I did not use all the thermal treatments that I normally use, so the grain is probably not as fine as usual. But it will at least give you an idea of why I feel the grain is too large in all the shots you made.

tip.jpg

This is a cross section shot of the tip of the blade. I snapped off a half inch or so in the vise.

side_shot3.jpg

This is a cross section farther up the blade. The quench line is marked in the shot. The grain remains fairly small on up to the spine.

As you stated, the magnification does make it look more coarse. To the naked eye, these pieces both were a silky smooth matte gray.
 
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