Should you thermocycle before re-quenching a knife?

L

Leon Husock

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Jul 17, 2019
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I was heating the shoulders of a chef's knife to seat them in the handle a little bit and accidentally let the heat spread to the heel of the blade, bringing it all the way up to a blue color. Checked with my hardness files and it's somewhere between 52 and 55 Rc.

I think the only option is to re-quench. Do I need to re-thermocycle as well? The blade is 52100.
 
When you say "re-thermocycle", do you mean dry ice or LN after quench? My thinking would be if you do a full heat 'n quench cycle, you're back at the very start, and whatever you did then would be required now. Basically starting over from scratch.
 
I think you should be OK to austentize and quench and not need to thermocycle.

How thin is the blade? If it's thin, it may crinkle or "bacon" up on you. I did some blue #2 with around .030" at the edge and it bacon'd really bad on me, had to toss it.
 
Ken H> said:
When you say "re-thermocycle", do you mean dry ice or LN after quench? My thinking would be if you do a full heat 'n quench cycle, you're back at the very start, and whatever you did then would be required now. Basically starting over from scratch.
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No, no cryo cycle for me. I just mean normalize, grain reduction, and anneal before austenitize and quench as opposed to just austenitize and quench.

Taz said:
I think you should be OK to austentize and quench and not need to thermocycle.

How thin is the blade? If it's thin, it may crinkle or "bacon" up on you. I did some blue #2 with around .030" at the edge and it bacon'd really bad on me, had to toss it.
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Oh it's like .015-.02". Don't get me wrong, I'm probably fucked. I mean, follow-up question I suppose: is approximately 52-54 Rockwell too soft for the heel of a chef's knife? I favor a Japanese-style blade, thin and hard at the edge, but I know there are a lot of more German-style blades out there sitting at around 56 Rockwell. And if there's any part of a chef's knife to have be softer it makes sense to have it be the heel. Can I reasonably sell this rather than risking destroying it in a re-quench?
 
How far forward of the heel does it extend? Maybe trim the blade down from the heel and move the handle forward? Or add in a finger choil there?
 
Taz said:
How far forward of the heel does it extend? Maybe trim the blade down from the heel and move the handle forward? Or add in a finger choil there?
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It's probably at least an inch, maybe an inch and a half. Too far to re-grind unless I want to make it a petty knife, and I've already got the handle fitted so I'm not totally sure the new portion of tang I'd get from re-profiling would fit (though I suppose I could make a new handle, it's just curly maple).

I was thinking I could try a thin wash of satanite on the blade to prevent decarb, which I've heard about but never tried. Worst case it's an opportunity to experiment with quenching an almost finished blade.
 
Even without the decarb issue, you are in dangerous territory with a carbon blade with that thin of an edge and an oil quench. Even with satanite, I am guessing it will still warp/bacon at the edge?

If it was me, I'd make it into a petty and refit the handle to get some use out of it and keep it for myself or give it to my parents or something. 52100 is not that expensive so is may not be worth doing a lot to fix this blade. If you reground it to a longer Petty or utility shape, shorter height at the heel, you may be able to get away with reheat treating it since the edge will be thicker where it's groundless and be less likely to warp or bacon on you at the edge. How thick is it say a half inch up the blade?
 
weo said:
This all depends on how OK you are selling a product you know has a flaw.
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That's fair. I'm doing last minute production work for a craft fair next weekend, so I think probably what I'll do is finish it out as is and sell it with a disclaimer. As long as people know what they're getting I don't feel bad about it. Plus this is a low-end machine finished monosteel blade, nothing fancy.
 
Thescrawnylumberjack said:
That's fair. I'm doing last minute production work for a craft fair next weekend, so I think probably what I'll do is finish it out as is and sell it with a disclaimer. As long as people know what they're getting I don't feel bad about it. Plus this is a low-end machine finished monosteel blade, nothing fancy.
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This is a very bad principal. Selling a dinged washing machine at a discount because of a flaw is one thing .... Selling a handmade knife at a discount because it is of lesser quality is bad business.

Fix it or scrap it.
 
Stacy E. Apelt - Bladesmith said:
This is a very bad principal. Selling a dinged washing machine at a discount because of a flaw is one thing .... Selling a handmade knife at a discount because it is of lesser quality is bad business.

Fix it or scrap it.
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Ahh, I suppose you're right. I'll grind the edge back to avoid bacon-ing and maybe sell it as a sort of hybrid chef/slicer with closer to a 1.5" heel.
 
I have broken many a knife straightening a slight warp or other issue. I just reshape it into a smaller knife, I have made most of my favorite santoku and nikiri from a broken chef's blade.
 
Well I re-quenched it with a satanite wash. It's got a lengthwise warp that's being a little annoying to get out, but there's no warping at the edge. I haven't checked the hardness yet but I did the austenitization according to Dr. Larrin Thomas's recommendations (10 minutes at 1500-1525) so I have no reason to suspect it didn't harden properly. Thanks for the push, Stacy!
 
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