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blade broke after quench

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i was hardening a bowie knife i made today. i made it from 5160 spring steel. i heated till it was nonmagnetic, then i quenched it in motor oil. i noticed it was a little warped and bent after the quench but i didnt see any cracks. i put it on the anvil to straighten it out a little and bam it broke in half. i didnt even hit it that hard. what did i do wrong?

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When it comes out of the quench and is cold it is as brittle as glass NEVER DO ANYTHING UNTIL AFTER TEMPERING!

I had a student who left a blade on his workbench after quenching as it was too late at night to temper---came back in the morning and it was in 3 pieces just due to the quenching stresses. TEMPER IMMEDIATELY!

If you do a differential temper You *might* be able to straighten a slight bend; but in general a bend requires reheating to straighten and then repeating the heat treatment---which is actually often a good thing metallurgically.

(there are situations with some alloys where you can straighten before it cools all the way down from a quench---but it's always a risk!)

The answer to the base question "what did I do wrong?" is: you didn't know what you were doing *before* you tried a tricky thing like blademaking. Why we suggest folks *learn* the basics before trying the graduate level skills. I mean you had practiced heat treating on similar shapes and alloys before doing the knife right?

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I'd skip the temper and put it right back in the forge in that case; but a temper never hurts! If your forge has a limited hot spot I might temper first to prevent more stress as only part of it gets heated at first.

BTW did you normalize several times before hardening?

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LOL! :lol: Reminds me of my first attempt. I made a machette out of a car spring, built a big fire and quenched it in a bucket of water. I wasn't happy with the shape so I started grinding on it and,,, :o it uncerimoniously broke in half. Learn the soft back draw/and or edge quench. If you get a little warp you can usually straiten the blade after its tempered.

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Only broken a couple that way, am mostly self taught apart from the club I am a part of. Been there since I was about 13 yrs old.
Broke one recently, it was one that I tried to make really thin. used spring steel. Had another file I used
the other day that was broken, drew it out and thinned it down a bit. If I hadn't it would only have a 1 1/2in or so blade.
Best I have hardened, First file I hardened.Kept on thinking it would break. Plenty left to break when I try other steels and blade styles later on. Bet we all do, even the experienced blokes. Can't seem to get the pictures right when you click on them though.

Edited by Aden Cassidy
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