I recently used up my supply of purchased 1095 and 5160. So, I've been forging knives out of coil springs, of which I have a large supply of identical part numbers and have nailed the heat treat for through lots of trial and error and failure testing. However, I decided to use a worn out large bastard file for a change of pace. I treated it like 1095 throughout the entire process.
In addition, my belt grinder motor burned up a few weeks ago, so after forging all clean up was done with hand tools, which I prefer anyway. It was very easy to forge and cleaned up to make an attractive blade. So, I went on to the heat treat process.
The heat treat process was standard for 1095. Normalized twice, then I applied clay to the spine. I then brought it up to 1500F, soaked for about 2-3 minutes and quenched in hydraulic oil preheated to ~140F. There didn't appear to be any warping or cracks. I tempered it with two 120 minute cycles in a 450F oven.
When I tried clamping the blade to my knife board to clean up the decarb, I ran into a problem. I usually put a piece of thin suede under the blade, but this time the leather didn't run under the tang. The clamp was positioned in the middle of the tang and when I applied a moderate amount of torque on the clamp (a small 3" c-clamp), the tang snapped in half.
I thought to myself, after some colorful swearing, 'there should have been atleast a little springyness in the tang after two long temper cycles, what happened?'
Further inspection revealed a very small and uniform crystalline structure, as if the blade was merely quenched and not tempered. The crystalline structure appeared to be unaffected by the tempering cycles. (It should be noted that this is an assumption, since I didn't get to view the internal structure prior to tempering.) There was no evidence of any cracking that could have occured during the quench or initial forging - it was a clean break.
So, why did my blade break? It broke because I simply didn't know what I was working with. Obviously, I needed a higher temperature during the tempering process, perhaps as high as 550F or 600F. The only way to find out is to try again at a higher temperature.
Several hours of work are down the drain, because even if I HT it again, I won't be able to trust it.
Thus, instead, I will sharpen the knife and do an edge test and then see how far I can bend the blade until it breaks. I will post the results of the testing.
In the mean time, here is a picture of the broken tang. My camera can't take very good macro shots, so unfortunately, I can't post any photos of the crystaline structure.
Take Care,
BJ
In addition, my belt grinder motor burned up a few weeks ago, so after forging all clean up was done with hand tools, which I prefer anyway. It was very easy to forge and cleaned up to make an attractive blade. So, I went on to the heat treat process.
The heat treat process was standard for 1095. Normalized twice, then I applied clay to the spine. I then brought it up to 1500F, soaked for about 2-3 minutes and quenched in hydraulic oil preheated to ~140F. There didn't appear to be any warping or cracks. I tempered it with two 120 minute cycles in a 450F oven.
When I tried clamping the blade to my knife board to clean up the decarb, I ran into a problem. I usually put a piece of thin suede under the blade, but this time the leather didn't run under the tang. The clamp was positioned in the middle of the tang and when I applied a moderate amount of torque on the clamp (a small 3" c-clamp), the tang snapped in half.
I thought to myself, after some colorful swearing, 'there should have been atleast a little springyness in the tang after two long temper cycles, what happened?'
Further inspection revealed a very small and uniform crystalline structure, as if the blade was merely quenched and not tempered. The crystalline structure appeared to be unaffected by the tempering cycles. (It should be noted that this is an assumption, since I didn't get to view the internal structure prior to tempering.) There was no evidence of any cracking that could have occured during the quench or initial forging - it was a clean break.
So, why did my blade break? It broke because I simply didn't know what I was working with. Obviously, I needed a higher temperature during the tempering process, perhaps as high as 550F or 600F. The only way to find out is to try again at a higher temperature.
Several hours of work are down the drain, because even if I HT it again, I won't be able to trust it.
Thus, instead, I will sharpen the knife and do an edge test and then see how far I can bend the blade until it breaks. I will post the results of the testing.
In the mean time, here is a picture of the broken tang. My camera can't take very good macro shots, so unfortunately, I can't post any photos of the crystaline structure.
Take Care,
BJ
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