Straightening 5160 Post HT

Jonathans

Jonathans

Joined
Jan 9, 2008
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588
I recently forged out an 11" Gyuto at a class given by Bill Burke. I took the forged blade home to finish on my own.
It was normalized three times.
I ground it out and heat treated at 1540 full quenched in Parks AAA.
Tempered at 400 for one hour.
Hardness tested at 60rc
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The blade had a distinctive bend in it. I tried to straighten it in my vise with a wide three point straightening jig.
It just continued to spring back. I the went with a narrower three point straightening jig to work smaller sections at a time, and it still just sprung back.
So, I applied a little more pressure and the blade snapped.
image.jpg
The fine grain looked great!
So my 11" Gyuto is becoming a 6.5" Santoku.
image.jpg

Could I have approached the straightening process differently?
Could it be that the process I performed would have worked fine with let's say 1084, or W2, but not with a spring steel such as 5160.

Was the blade not tempered enough prior to attempting to straighten it (60rc)?

I'd rather not repeat this if possible.
Any comments or critique welcome.
 
What I do, is clamp it to a piece of 1/2" steel plate when it's on its second/third temper. This will pull most big sways out. Anything else I can grind out.
 
What viral said...
... basically a three-point bend during temper.

Here's a couple photos from old wips. (Note: these are both W2... but this should work similar for 5160)
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Erin
 
I never had a blade survive a cold 3 point jig. The way I was taught was to heat the blade to 400˚ for two hours in the oven then quickly get it to the 3 point jig and clamp with an over correction until it cools. I lost 5 blades before I tossed that method. The best way by far is the way viral and Erin do it. Do at least one temper cycle first with the bend. Starting with the second temper cycle, clamp the blade to something sturdy like these guys mentioned. Using some kind of spacer as a jack ( I use spare change) you are making a 3 point jig in essence but the heat is doing the work, not the clamp. Dial in an over correction about the same distance as the initial warp. When the blade gets up to temp the heat will relax the steel. It will spring back a bit which is why you over correct. It may take multiple tries but I have never lost a blade since I started using this method. I have had a few pretty wonky blades after quench. One blade took 15 two hour temper cycles to get all the warps out but it is straight as an arrow now. Using this method you can also work on multiple warps on a single blade at the same time.
 
Jim Crowell learned me a way of straightening blades 25-26 years ago when I got into knife making and forging that has served me well over the years and has absolutely no detrimental effect on teh blade or it's performance.

This can be done without a heat stop paste but if you have some handy, apply some along both sides along the edge and about a half inch up.
Use the 3 point jig like you have, clamp the knife in it just enough to hold it at the start. Using a hand held torch ( the kind plumbers use) start applying heat along the back on the area of the blade that is on the inside of the bend. Take your time and go slow so you don't overheat the blade, apply pressure (slowly) as you add heat. Best to alternate adding heat and pressure. Take it just past straight the other direction and stop. Leave it clamped until it cools to the touch, should be fine. The whole process minus the cooling off shouldn't take more than 10 minutes or so. Never try to straighten a blade without applying heat to it in some way, only adds stress.
 
If using a three point jig, you really need to be warming the spine with a torch. This is certainly the faster (albeit somewhat riskier) method. My preferred method is "over clamping" in a third or fourth tempering process.
 
viral said:
What I do, is clamp it to a piece of 1/2" steel plate when it's on its second/third temper. This will pull most big sways out. Anything else I can grind out.
Click to expand...
I usuallt straighten right out of the quench. Or ^this^ and what Erin showed. It works and is too easy to mess with anything else.
 
And 1 temper will not suffice. A blade will not survive extreme lateral stresses on one temper. And always make sure that your temper time is after the blade has reached your target temp. I always give my blade about 1/2 hour to get evenly warmed up to my target temp and then begin time count down.
In the first temper you might get new martensite from retained austenite, which will need an additional temper.

Under no circumstances do selective/isolated heat with a torch to straighten a blade.
After all the time to get it to this point don't be foolish.


You can 'over clamp' on your second temper, provided you got a full temper on the first cycle.

If you don't succeed on the over clamp on the second cycle, you can do a third cycle at 325 without effecting the hardness, yet still accomplish straightening.
 
Karl B. Andersen said:
And 1 temper will not suffice. A blade will not survive extreme lateral stresses on one temper. And always make sure that your temper time is after the blade has reached your target temp. I always give my blade about 1/2 hour to get evenly warmed up to my target temp and then begin time count down.
In the first temper you might get new martensite from retained austenite, which will need an additional temper.

Under no circumstances do selective/isolated heat with a torch to straighten a blade.
After all the time to get it to this point don't be foolish.


You can 'over clamp' on your second temper, provided you got a full temper on the first cycle.

If you don't succeed on the over clamp on the second cycle, you can do a third cycle at 325 without effecting the hardness, yet still accomplish straightening.
Click to expand...


Never had an issue of any kind with a blade made from 5160 from the things you say never do or the blade will not survive. But being new on this board I will digress to the established users here.
 
Jonathan, Sorry for you but it is a nice looking santoku. just bring the tip up a little bit and next time temper at least twice for two hours like we did in class.
 
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Take a look at the Time-Temperature -Transformation graph .As the blade has passed through the 'nose'of the curve you can check for straightness and bend it straight if necessary. As it becomes harder to straighten it's hit the Ms line so continue the quench from there. NEVER try to staighten a hardened piece of steel unless it heated to at least 400 F !!
@ hours is the standard time for each temper.
Never use a torch to attempt straightening.

Jonathans , It should never have gotten to that point . Review your proceedures - uniform heating straighten between normalizing if necessary.

Erin , working near a thing like a wedding gift is risking death !!!
 
Thanks everyone. I appreciate the detailed guidance. I never thought of clamping the blade out of a bend during the temper process. Now to get me some of those Sweet-Ass Shoes so I can do it right.
 
Karl B. Andersen said:
Look again at his second picture.
Click to expand...

I saw it the first time. Unless I misunderstood or misread he did not apply heat and tried to straighten the blade cold.

I have never personally had an issue straightening a blade using the method I described in my post. And I have never finished a blade past heat treat/tempering (and straightening if needed) without putting it through a performance test of cutting and chopping. Everyone has their favorite and trusted way of doing things and that is not a bad thing, just the opposite. I use and trust the way I learned from one of the best mastersmiths in the business and it has served me well and never failed over the years. And that includes single tempering in an oven @ 2-4 hours at 350.

Like I said, I'm the new guy here and ya'll don't know me and I don't know ya'll so it is what it is.

Just for clarification this method I use is done AFTER the tempering cycle, not before. My apology for not being clear with that.
 
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I've always been able to straighten by either one of the two methods already mentioned...no problems at all. Sometimes takes a re-do, or a re-re-do (singing classes anyone?).

Method one: You have a few minutes after quench before martensite formation makes the blade too stiff to move by hand. With gloved hands, straighten the blade in those few minutes. The blade will bend fairly easily until Ms temperature (around 400°F) is reached, then by Mf (around 150°F) it's a "stiffy".

Method two: AFTER one temper cycle has been done already, use the 3 point clamp system as Erin's cool pic shows. But the blade needs to have gone thru one temper cycle previously (to prevent it becoming two pieces), and the temperature to perform the bend MUST be 400°F or above. I've tried it at 375°F and even 390°F...no joy.
 
Also,
I dont like to rush straightening the blades during temper. I will do as many temper cycles as it takes. sometimes up to 5. It will work wonders if you give it the time to work.
 
So multiple tempers, even 5 or more doesn't decrease the blade hardness incrementally each time?
 
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