Warped blade in 5160 - questions

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danrt2

Joined
Feb 7, 2013
Messages
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Hey guys. Been a lurker and infrequent poster for a few years now. Starting to get serious about knifemaking (finally), and I had a question about warped blades. I'm not a fulltimer, and I'm only producing a couple of blades a week at this point, so I have a little more time to dedicate to each blade. I'm using solely 5160 at this point. My question is this. If after quenching I have a warped blade, rather than trying to straighten immediately post-quench (around 500 deg F), why not just renormalize, then straighten under heat, then reanneal, starting the entire ht process over again? Sure, it's time consuming, but from a metalurgical and end product standpoint, is there anything functionally wrong with that approach?

So just to be clear, what I'm suggesting for input is the following:

Step 1: Renormalize
Step 2: Straighten in vise while still hot (is 500 deg F sufficient?)
Step 3: Start entire ht process over

Just to be clear, I tend to use a version of Ed Caffrey's ht recipe, if that helps.

Thanks in advance, guys. Any assistance would be much appreciated.
 
I am at a loss as to your steps you are suggesting. When a steel is normalized...it is brought up to around 1600f or better. If you did that...you would need to re-harden the blade. You can certainly do that in order to fix a bend (re-doing the heat treat completely). Yes....time consuming. Remember that after the quench, two gloved hands can easily correct a bend as the steel cools from 900F on down to 400f or whatever it is. But even if the re-heat treat fails, or if you can't get her straight after the quench while it is cooling, there is always the 3 point clamping method while tempering. Just remember to run one low temper cycle before setting the blade up in your jig. Then use 400F or higher temp. 500F will work...but for good edge retention that is too much heat.
 
If you redo your entire ht again there's a good chance that your blade will warp again, especially if it was ground too thin or was ground uneven. Either try and correct the warp right after hardening or during your second tempering cycle.
 
Hey guys, just wanted to give you an update. I finally got around to working on that knifeblade, and after re-normalizing and re-annealing it three times, it's pretty much dead nuts post-quench. I used the 3-point clamping process to straighten, and the vise to correct the slight twist. I will be posting pictures very soon. Thanks for the advice. Much appreciated.
 
In the future, perhaps you should think about doing a stress relief cycle before hardening assuming that you can get to 1200 or so handheld it for a good while. Once I started doing that, warping pretty much became a non issue.
 
Once the blade turns black in the quench you have a little time to get it straight until it is fully hardened. I use aluminum plates for the then chefs knives. Do a search on straightening jigs and there will be something you find and like and make work for you. as for the blade you already have that is hardened you can normalize again and reharden. Or clamp it a touch past straight in the temper cycles. Sometimes that takes out a slight bend.
 
It really depends on your HT method, too. You said Ed's way. He uses different methods, unless I am mistaken. Are you using a torch?
 
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