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I am making a knife as part of a Christmas present for my brother and sister-in-law. It's a simple kitchen utility knife and it fit perfectly on a piece of 80CrV2 I had, so I figured I'd just do stock removal. No sense in making things more difficult than they need to be. Ha!

 

The steel started nice and flat. Glued my pattern down to it and cut off some of the major chunks before taking it to the grinder and roughing it out. When I got done roughing it out, I noticed that the steel now had a noticeable bend to it like a leaf spring - probably 1/8 of an inch off of flat. Have no idea how it happened as I was roughing it on my work rest. Since it was (supposedly) fully annealed from the supplier, i just bent it back into straight. Then I started in on the bevels. As I'm grinding the bevels, I can see it start to warp again in the exact same place as before. I went and straightened it again and continued with the bevels. Dang it wouldn't you guess that it starts warping again. Now I'm getting a bit upset. I'm spending more time straightening the blade than grinding the blade. It reminds me of what would happen with a leaf spring if it wasn't heat treated correctly and keeps going back to its original shape. 

 

Any ideas why this may be happening and how to fix it? I'm worried about heat treating it and really getting a bad warp.

 

A few other bit of information: 

Steel is 1.5"wide  x 7/64" thick 80CrV2 from AKS.

I grind bare handed so the steel never gets real hot before I'm dunking it in water.

I have NEVER had this issue with any blades that I have forged. Making me want to never do a stock removal again.

 

Thanks for any suggestions.

 

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Have you tried normalizing it?  The piece may well have stresses in it that you are causing to be imbalanced as you remove material.  Normalize to remove stresses and see how it goes.  

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30 minutes ago, Jerrod Miller said:

Have you tried normalizing it?  The piece may well have stresses in it that you are causing to be imbalanced as you remove material.  Normalize to remove stresses and see how it goes.  

Thanks for the suggestion. Will give it a try tomorrow. Seems odd though to be thinking about normalizing an annealed piece of steel. I assume even annealed steel can still have stresses?

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4 hours ago, Brian Dougherty said:

I'm not sure how big mills do it, but it may have been annealed in a coil before your piece was cut from it.

Or something when wrong at some point after annealing and the bar got bent and re-straightened. At any rate, the bar should have been stress free after annealing, but something could have happened to introduce new stresses.  

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From what I remember from reading about that alloy on other knifemaking forums, is that 80CrV2 is known for warping at almost every step it seems.  

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I've had cold rolled stock removal 26c3 blades warp several times even though the blades were quenched at full thickness and the bevels were unground. They were heat treated in my kiln and I believe the temp was equalized due to the 10 minutes soak, so it's was not an uneven temp issue. 

 

I believe it's because the steel was cold rolled and there was stress left in the steel, as Jerrod mentioned. 

 

AKS mentions if their steel is either C/R or H/R. What about yours?

Edited by Joël Mercier
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44 minutes ago, Joël Mercier said:

so it's was not an uneven temp issue

Could be uneven cooling, too.  The heating up to austenitic should have relieved all the stresses.  Then again, if the grains weren't completely even (say from excessive growth in a single direction due to rolling), that could cause warping with even heating and cooling.  So many variables!  Isn't this fun?

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On 11/11/2020 at 1:57 AM, Jerrod Miller said:

Have you tried normalizing it?  The piece may well have stresses in it that you are causing to be imbalanced as you remove material.  Normalize to remove stresses and see how it goes.  

 

 this is one of the things i see written time and time again ....It does not reflect my experience. nothing wrong with normalising its a v important step  (steps) in the process but I have found it has no effect on preventing warpage.....straightening is probably the most important repeated step in the knife making process. I often have to straighten a blade many times . and then re straighten in the temper before final grinding.

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20 hours ago, Joël Mercier said:

AKS mentions if their steel is either C/R or H/R. What about yours?

AKS claims it is hot rolled pickled annealed

 

19 hours ago, Jerrod Miller said:

 So many variables!  Isn't this fun?

Oh yeah...

12 hours ago, owen bush said:

 

 this is one of the things i see written time and time again ....It does not reflect my experience. nothing wrong with normalising its a v important step  (steps) in the process but I have found it has no effect on preventing warpage.....straightening is probably the most important repeated step in the knife making process. I often have to straighten a blade many times . and then re straighten in the temper before final grinding.

I don't feel so bad now Owen if you are always having to straighten many times.

 

It was raining last night here so I couldn't get the forge out to try a real normalizing. I tried it with a MAPP torch but I don't think I got it hot enough. Straightened the blade out before heating it up (dull red in a completely dark room), then let it cool in still air. Was straight when I went to bed. Checked it this morning before starting work and it had a bend to it. Not as bad as before, but still noticeable. Clear cool night tonight so I'm breaking out the forge and thermocouple and doing it right.

 

Thanks again for all the help.

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