Question on a cracked blade

Gene Kimmi

KNIFE MAKER
I had a leftover piece of 1084 & 15n20 twist damascus that I made a small hidden tang blade out of. Last night I clamped it to my bench to sand and the clamp slipped off the tang and the blade hit the concrete. When I picked it up, I noticed the crack in it.
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Does it seem odd that this caused a crack, especially where it cracked. The blade was forged, triple normalized at 1600, 1550 and 1475. Then it was sanded to 220, heated to 1500 and quenched in quench oil I got from trugrit. No soak times on any of the heating. It was tempered twice at 375 for 2 hours each time.

I use this to check temperatures in both the forge and the toaster oven.
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That is an odd place to crack for sure....no matter what.

I have serious doubts that it happened from falling on the floor. Maybe it existed already and falling on the floor made it more noticeable? I'd break it and look at the fracture faces. Sometimes that can tell you some things.
 
The only part of your description that raised suspicion for me was the tempering temp.... if the blade achieved full hardening, 375F is rather low for tempering. At that tempering temp a blade of those materials/steels would be fairly brittle.

Just a thought....are you sure it's actually a crack? Is it visible on the other side? I've had/seen blades that have been dropped during hand finishing display similar things that looked like a crack, when in reality is was a scratch..... maybe not the case here, but since it means the difference between a usable blade and trash can fodder, it's worth asking the questions. :)
 
John,

It's a possibility that it was already there, but as much as I had looked it over up to this point, I sure didn't notice it.

Ed,

The tempering temperature was my first thought. I normally temper 1084 at 400. This knife was more for trying my hand at a hidden tang with a guard than anything, so I tempered it with a couple blades out of 52100 that I was testing at 375. The crack only shows on one side and part way through the spine, but when I sanded on it to see if it was a scratch, you could see the wd-40 work in and out of the crack.

I think I'll go ahead and break it as John suggested and see what's inside. If I can get good pictures, I'll post them.

Thank you both for your thoughts.
 
when I sanded on it to see if it was a scratch, you could see the wd-40 work in and out of the crack.

NUTS! I was hoping it might have been a scratch masquerading as a crack, and you could save the blade. As I often say..... Some days you eat the bear....and some days he eats you. :)
 
Well, I think John was right in that the crack was there before, I just didn't catch it.
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Thinking back, this blade was ground thinner than I normally do before quenching (chasing that perfect grind), and had a little warp to it. When I tempered it, I clamped it to a piece of 1" tubing with a thin shim to straighten it. I'm betting that was a bad idea and may have caused the crack.

Here's a couple pictures of the break using a 100x microscope.
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Thinking back, this blade was ground thinner than I normally do before quenching (chasing that perfect grind), and had a little warp to it. When I tempered it, I clamped it to a piece of 1" tubing with a thin shim to straighten it. I'm betting that was a bad idea and may have caused the crack.

That sounds reasonable..... I had the a similar experience when I "clamped" a warped blade before the 1st temper....it cracked. After that I learned to do any clamping AFTER at least one tempering cycle.
 
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