Straightening blade: post quench or post tempering..

nine9jack9

nine9jack9

Active Member
Have a shoe box full of blanks that aren't severely warped but aren't straight. I would like to be able to salvage them. I have heard that some people will grind them flat. That said, would like to be able to straighten any future blanks that aren't straight by bending them. Was wondering what the likelihood of snapping a blank if I attempt to straighten it post-quench and before tempering. Thinnest stock I use is 1/8 and I grind post heat treat to minimize warping. Any thoughts or suggestions?
 
If the blade were fully hardened, then the chances of them breaking are high. (blades cool enough to handle with bare hands). The chances are moreso if you try to straighten them pre-temper versus post temper.

I say it that way because one of the many reason I prefer differntially heat treated blades (edge quenched) is that even if hardened to 1/2 the width of the blade, they can still be straightened after cooling, without any serious fear of breakage.

You didn't mention the steel type, which makes a significant difference, nor if the blade were fully hardened or differentially heat treated......all thos factors impact the chances of successfully straightening a warped blade.
 
There are those who more or less straighten the blade during the quench by which I mean that they quench the blade for maybe about 6 seconds to get past the nose of the cooling curve and then take the blade out and let it air cool from the Ms to the Mf point. Between those points more and more martensite forms and the blade becomes harder and more brittle. If you work quickly before too much martensite forms you can work out any warping.

What I prefer is to do one tempering cycle and counter bend the blade against a piece of angle iron shimming with one or two pennies and holding with steel C-clamps and re-tempering the blade. I've tried counter bending the blade over three rods in a vice but it's nerve racking. Each time you give the screw a slight turn you expect to hear a tink and sometimes you do.

Doug
 
Steel is O1. I use 1/8 stock for smaller utility knives and such. Anything over 6-6.5" overall, I go up to 5/32 for larger hunting and camp knives. It was specifically because of warping issues along with other considerations that I went up to 5/32, never know when someone is going to use your knife for a pry bar. I have had to re-visit the issue because I am making an 8" kitchen knife. Another maker I know straightens them post quench, then again he uses A2 and I imagine that the air hardening gives him some time to play with it and get it straight. That is funny and yet not funny about the straightening in the vise; I have done just that only to hear "tink", you have to laugh otherwise you would cry...
 
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