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Jim Pierce

Blade tip snapped

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Finally forged a good blade, no fish lips, decent bevels and relatively straight. Normalized three times and then annealed in vermiculite. Ground and then heat treated, and tempered. Finish grind to 220 and no cracks or other issues. I decided to do a destructive test to see how it held up. Steel was 1/4" 1095 from Aldo, heated to around 1500 in the forge, and quenched in Parks 50. Two one hour tempers at 425. Tested Rockwell with a set of hardness testing files and it was between 60 and 65. Three hits on spine with a two pound hammer cut into brass rod without deforming edge, two hits into 1/2" mild steel same result. I was feeling pretty good then I stabbed into a 2x4 and tried to pry out a sliver and tip snapped off about 1/8". Looking at the grain through a jewelers loop it looked very fine. My question is where did I screw up? Tip was thin but not a needle and I thought a bend would happen before it snapped. I also bent the blade in a vice and it went to around 45 before a crack. Any advise would be appreciated. Thanks. 

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All I can offer is maybe the tip was a little thin?  That, and don't do the anneal anymore.  That undoes some of the good of normalizing.  If you slow-cool 1095 like that it forms laminar bands of carbides rather than the fully dissolved structure normalizing gives.  That may or may not contribute to a weak tip, since the carbides in 1095 go back into solution fast enough that the final heat before quench should have fixed it.

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It's the same with all steels.  The vermiculite anneal is just a bad idea left over from ignorant times.

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Don't pry with a knife! But as far as troubleshooting goes, I'm wondering if the blade was left too hard. What did you use to temper the knife? I think one hour temper cycles are too short unless you're using something like a salt pot. Next time try two cycles of two hours.

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Jim, 425 is a bit low of a temper for 1095 i'd say. Tips always suffer the most through out the whole process, decarb, overheating no matter how careful we are, and just plain fragile.

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Guest

In general, if you quench in the high above 60 you end up wanting to go higher on the temper as well, or multiple and longer tempering times depending on method? 

Also could be your blade's geometry, it plays a big part in how and where a tip(edit: or other stress point) will snap off, especially if it's not in line with the center of mass or spine (they can be different things but work the same way according to engineering text books anyways) if a part is isolated from the mass it will take stresses if it were a semi different part with a sheer point where it joins to a flowing mass, even if the material is flexible.

Other edit: a change in geometry is a change in mass flow and stress location.

I typically just heat my work parts evenly and then sit them ontop of the coals, turn the blower off and cover the forge and let it cool over night, then clean them up and move on to heat treat. 

Got any pictures of the breakage, profile and grains?

Edited by Guest

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