multi-quenches

K

Ken H>

Joined
Dec 31, 2011
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Good morning all, and I do hope everybody is off to a GREAT start to the new year.

On FiF they're always talking about how damaging it is to do multi quenches, i.e. - warped blade or didn't harden first time. I've seen 2 and 3 quench attempts trying to get the blade hard. "IF" the blade is normalized to relieve any stresses, should this not put the blade back into a condition similar to before quench? Then a grain refinement to reduce any grain growth during normalization process - would the 2nd (or 3rd) quench be a problem?
 
normalizing/grain refinements are things that take Time to do. on FIF they barely get enough time to do things and they Rush
things like trying to harden a blade/throw any kind of handle on it...Not the Optimized realm of "Normal" knife making where you
don't fight a clock..
 
Half the time on FiF they have a hardened blade but file check right out of the quench vs waiting just a minute for it to cool down enough to finish hardening then decide to immediately go back in the forge, I think I’ve seen people say if you undershot the temp and it didn’t harden it’s safe to just go right back in and go a bit higher so say you brought a blade up to 1300 then tried to quench it wouldn’t harden but you’d be safe to try again and bring it up to the right temp but if you really overshoot the temp and brought the blade up to say 1800 you’d likely have coarse grain that would need refined assuming the blade doesn’t just crack which they have shown on the show when people have done 6-7 quenches and they get micro cracks through the entire piece from multiple quenches that were too hot or just too many attempts.
 
I've been away for a couple of days so haven't had a chance to check this thread.

Thank you all for the comments, but I think we all know FiF is NOT the place to learn knifemaking. While I do enjoy the show, it's prime focus is entertainment, not teaching. My question wasn't why FiF contestants don't do extra normalizations & grain refinement. My question was about multi-quenches itself - other than the usual concern about a crack during quench. I suspect more micro-cracks occur while forging rather than quench.
 
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The reason is time. Sometimes they have time to do them, but time is running out more often than not. The tempering is done at night by the technicians. The contestants have no control or input on the tempering parameters.
 
I was trying to harden my first forged knife. First quench, full cool down file was biting. I was not sure it it was just decarb, or needed to be rehardened. I was using a thermocouple in addition to my eyes and magnet. Found out the thermocouple was bad. It was fluctuating wildly. The eye and magnet were saying the temp was too high, thermo couple said way too cold.

I did a full normalization before re-harden.

Ended up refining shape and warp a bit after that.

So three quenches till I was totally satisfied. I was sure I saw cracks......

But once cleaned up, no cracks.

Likely would have been different result if I was using a less forgiving steel, but I think the normalization between attempts did not hurt much.
 
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