Correcting post quench warp during temper

[Eddie Mullins]

Just thought I'd share my method for correcting warp post quench. I have done this before and am currently doing so on my longest knife to date, a forged 5160, 1/4" thick, 1 1/2" wide, 15 1/2" blade. After the first 2 hour temper cycle I start applying 3 point pressure to correct through additional temper cycles. I do this using a piece of angle iron, a small c clamp and a couple of shims and putting the clamped blade back in the oven. I may be being too conservative but I do not try to correct all at once. After additional cycles I release the pressure , check for straightness and then adjust and repeat, using shims you can over bend if needed, but I do so gradually. I know there are other methods but this has worked for me and thought it might help some one else.

 

[GHEzell]

This method has saved me many broken blades....

 

[samuraistuart]

This method has saved me many broken blades....

Me too! A few points...
1. Temps below 400F don't seem to do anything for me. Temp must be at least 400F. Which, if making hard kitchen slicers at higher Rockwell hardness levels, this method is a NO GO.
2. Blade must be bent in an "overcorrected" method. Bending it dead straight will not correct the warp.
3. Be careful as to what you use as a fulcrum point. I used to use a small nail....and of course this would scratch the blade...and if you're basically at finish polish/dimensions pre heat treat...what a nightmare. Started using a brass pin...much better!
4. As mentioned, this may require a few attempts. Don't worry about ruining temper. Losing hardness during tempering is WAY more temp dependent than time dependent.
5. Warps can also be corrected immediately following the quench. There is a period of time before martensite starts to form when the steel is still very "bendable" by hand (gloved of course).
6. I've had a few warps not manifest until after temper cycle 1. In that case, the 3 point clamp method is going to have to work, or re-heat treat and try again.

 

[stezann]

Stuart, it is true that you get the most in the range of 400 °F, but if you want to save your super hard edge, please consider the following procedure i use (3 brass pins in the leg vise)
- oven: bring to your desired tempering temp. (<<400°F)
- put it in the vise and use an heat gun to keep the temps in the edge and rise it aiming at the spine.... Take advantage of the taper, the thin edge will bend cooler with no harm, while the thick, massive spine will get benefit from the higher temps and will bend without breaking in the correct temp range, and will hold the new set...quench, check and repeat....little steps go for a long way.

I mentioned the leg vise; i prefer it for the increased feedback it has vs. machinist vises, but this method also works with thinner blades simply with a wooden notch and a thong by hands

 

[samuraistuart]

Stuart, it is true that you get the most in the range of 400 °F, but if you want to save your super hard edge, please consider the following procedure i use (3 brass pins in the leg vise)
- oven: bring to your desired tempering temp. (<<400°F)
- put it in the vise and use an heat gun to keep the temps in the edge and rise it aiming at the spine.... Take advantage of the taper, the thin edge will bend cooler with no harm, while the thick, massive spine will get benefit from the higher temps and will bend without breaking in the correct temp range, and will hold the new set...quench, check and repeat....little steps go for a long way.

I mentioned the leg vise; i prefer it for the increased feedback it has vs. machinist vises, but this method also works with thinner blades simply with a wooden notch and a thong by hands

Heat gun....NICE Stefano!

 

[stezann]

eh eh...i switched to the heat gun once i went a bit overboard using a torch.
I also have an infrared thermometer at hand (paint black the blade with a sharpie for better readings), but most of the times i just sizzle the blade with water to get a feel for the tempteratures at play...but since you are operating mostly on the spine with a moderate heat source, the risks are at bay during the procedure.

Where i am a real goofy is straightening directly above MS at the quench, unless it were for just correcting gross bending i find fine tuning is better after the tempering.

 

[samuraistuart]

Stefano, that last statement about correcting during Ms, you again are most right. If you have a bow in the blade, then you can get it pretty darn straight that way, and fine tuning may be needed during tempering! I've been getting lucky lately.....blades coming out straight, and only the most MINOR amount of ripples (stuff you cant see unless you sight down the blade in light), due to my habit of taking edges to almost finish dimensions pre heat treat. The rippling I do get occasionally is so minor, it comes right out when I form my thin cutting edges and post heat treat polish. How thin do you go pre heat treat? Well, I'm glad you asked!!! ha ha I've been getting away with .013" - .015" on stock that's .070" thru .125". P50 and canola. From paring knives to 8" chefs. Shallow and deep hardening steels. NOT recommended to go that low! Stay above .020".

 

[stezann]

I had to do conversion into metric
Yes .020 seems safer, and i believe i ht in that range, sometimes more, yet i don't actually measure my edge thickness. Surely is a pita getting rid of the extra meat after the ht!!! And my wet grinding setup is very primitive and messy
Against ripples my opinion is that entering the quenchant more on the spine side will help, since the volume increase should more synch. between edge and spine.

 

[samuraistuart]

I had to do conversion into metric
Yes .020 seems safer, and i believe i ht in that range, sometimes more, yet i don't actually measure my edge thickness. Surely is a pita getting rid of the extra meat after the ht!!! And my wet grinding setup is very primitive and messy
Against ripples my opinion is that entering the quenchant more on the spine side will help, since the volume increase should more synch. between edge and spine.

I've read that, go spine first. Or tip first, if your tank is set that way. You know, I am a creature of habit, hard to break things. I need to try spine first sometime, just to say I did!