Tang Strength

David Stifle

David Stifle

Joined
Nov 20, 2008
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I had a nice discussion in the KA-BAR forum with Paul Tsujimoto, Sr. Engineer, Product Development and Quality, KA-BAR Corp., Orleans, N.Y., in which he told me the original Military Specification (Milspec) for the tang of the Original U.S.M.C. KA-BAR was 35-45HRc at the blade/tang junction, and the rest of the tang was not to exceed 30 HRc. Now, the group over there swears they have done remarkable things with this knife, such as putting their full body weight on the handle, extensive prying, etc.

This got me thinking about how I approach heat treating in reference to the tang. I've always tried to keep the tang at a lower temp when heat treating, and I also try to not quench the tang. If I feel I did get it hardened, I've always drawn it back.

How do you guys ensure you have a tough as nails tang? How do you approach heat treating in regard to the tang? Curious minds want to know.
 
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I prefer to fully harden the tang and draw it back after tempering the blade. Tempered martensite is stronger than pearlite.
Same goes for non-hamon large blade spines.

On the subject of tang strength, welded tang extensions need to be 1" or more beyond the back of the guard.


(I fixed the typo in the header for you strenght/strength)
 
And don't forget that until you reach the modulus of elasticity/yield point of the steel, hardened and un-hardened steel of the same geometry will bend exactly the same.
Hardening it does not make it bend differently.
It just has a different failure point.
I've seen that demonstrated over and over.
And Stacy made a great point - tempered martensite is stronger than pearlilte.
The unhardened pearlite tang will bend/take-a-set and at the same deflection, the tempered martensitic tang will return to straight.
But the energy to get them both to that point will be exactly the same.
 
The design of the tang/blade junction is also very important. Sharp corners are not good for a knife or anything else!!
 
As for the USMC knife itself, the square shoulders make me nervous. Other than that, it kinda depends on whom you ask... you can quickly find a dozen guys who say it's nearly indestructable, and a dozen guys who'll say it's failed on them easily.

Stacy and Karl are both right.

But I think mete has really hit the nail on the head... it's my experience that geometry plays a bigger role than HT or even steel choice when it comes to breaking a tang or a blade.

Generally speaking, the area from right behind the edge down through the first couple inches of tang should be the thickest part of the knife, with no sharp inside corners. Most of my stuff these days is high-alloy steel hardened and tempered the same all the way through, and even with fully tapered tangs and blades, you have to try pretty dang hard to break 'em anywhere except the very tip.
 
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Thanks Karl, what do you do to get the lowest possible failure point? Mete, avoiding sharp corners is something I'm aware of, I leave significant curved areas on my tangs.

James, we had quite a discussion on the KA-BAR forum. The entire knife is surprisingly thin, around 5/32's, and the tang is narrow with 90 degreed square shoulders; although I was told there is a small radiused area. They admitted the tang has been know to break, but as you said, there were a lot of guys who swore up and down they had done all kinds of things and it withstood tons of abuse without breaking.

But, another thing that got me thinking about the strenght of my own tangs is the video Sam Wilson did on his hollow handle knife in the testing forum. He secured the knife in a clamp, and did chin ups using the handle. If Sam did that with a hollow handle knife, well, could it be done with a through tang?

I'm certainly going to ensure my tangs are radiused, thickest at the blade/tang junction, but, the heat treat going into the tang is important. That's the part I'm trying to get a "handle" on, haha! Gosh, I'm funny today.
 
David Stifle said:
I'm certainly going to ensure my tangs are radiused, thickest at the blade/tang junction, but, the heat treat going into the tang is important. That's the part I'm trying to get a "handle" on, haha! Gosh, I'm funny today.
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Use your favorite steel, make two or three with the geometry the same as possible, temper them differently, and start doing pull-ups and batonning them through hardwood. I think you may be surprised at how little difference there really is between them. I will take a wild guess and say that the main thing you'll see is whether they stay bent or come back true.

I've been wrong before, though :p
 
james terrio said:
Use your favorite steel, make two or three with the geometry the same as possible, temper them differently, and start doing pull-ups and batonning them through hardwood. I think you may be surprised at how little difference there really is between them. I will take a wild guess and say that the main thing you'll see is whether they stay bent or come back true.

I've been wrong before, though :p
Click to expand...

It actually sounds interesting. I'll give it a shot. As for being wrong, I can't remember one single time you've, ah, (cough, cough) been wrong.
 
Karl B. Andersen said:
Just pay as much attention to your tangs as you do the rest of the blade - metallurgically speaking..
Post-forging thermal cycles, grain reduction, etc.
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That's great advice, and I have to admit, I've never given the tang any special attention, but I'll give it serious attention now, just like the rest of the blade.
 
and for optimum strength all of your finish grind/sand marks should run longitudinally rather than transverse to the blade to minimize stress risers

-Page
 
I've always done that on my blades, of course, but I never really thought about doing it to the tang too. Good point, Page.
 
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