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 Post subject: Bending Metal
PostPosted: Fri Dec 14, 2012 2:51 pm 

Joined: Tue Jul 24, 2012 1:28 pm
Posts: 459
I was given an 8inch Shun Chef knife with a very pronounced bent tip. The owner dropped it and the resulting damage left the tip about 7mm of steel shifted about 40 degrees to the right, so definitely enough to hinder both cutting and sharpening.

I've been waiting for an opportunity to try and fix a tip that is just bent and not broken. I only know two ways to do it:
1. Bend it back in place
2. Remove the bent portion and create a new tip.

My plan (in my head) was to use heat to get the knife red hot and bend it back in place with pliers. By the time I had the knife in my hand to the time I got downstairs to perform the operation I changed my mind. I was worried that the metal
(VG-10) was already weakened by the initial plunge on the cement floor, me heating it and then bending it back in place would further weaken the steel at a molecular level. What if I bent it a little too far back and now I am bending it back and forth.
The other problem I had was that heating the metal would discolour the blade, it would leave blue heat stress marks on an otherwise flawless blade.

So I decided to simply try bending it back in place very gently with pliers, knowing that this was not likely to work at all and the tip snapped off exactly where I would have wanted it to break, I could feel it starting to bend, got excited and then went too far.

So I went to Plan B and just created a new tip, the result was fine, no problems and the damaged portion, the bent metal was gone.

So I never did get to try heating the metal to see if I could simply bend it back in place. I do know if that would have been better but I think not?

When I showed the knife to the owner, (we had discussed the two options, bending or grinding a new tip), he could not tell which method I used so at the end of the day he was happy with the knife.

I still wonder if I can bend metal by heating it without discolouring the blade and not altering the temper.


All good fun though.


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 Post subject: Re: Bending Metal
PostPosted: Fri Dec 14, 2012 3:10 pm 

Joined: Tue May 01, 2012 9:37 pm
Posts: 324
Location: Pensacola, FL, USA
Sailor wrote:...

I still wonder if I can bend metal by heating it without discolouring the blade and not altering the temper.

...


In a word, no.

You might have considered trying to straighten it with a plastic tipped mallet, or by clamping the tip in a vise and trying to bend it back.


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 Post subject: Re: Bending Metal
PostPosted: Fri Dec 14, 2012 3:16 pm 

Joined: Fri Aug 03, 2012 10:01 pm
Posts: 203
Valid question Sailor, I've wondered the very same thing. Since tempering is carried out at much lower temperatures than annealing or quenching, so it would stand to reason that a blowtorch, or other heat source, could easily drive the steel above normal tempering ranges, so one might wonder if it could compromise the established the temper of a blade. For anyone who hasn't check it out already, Murray Carters Bladesmithing book he published a couple years ago is a fascinating read.


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 Post subject: Re: Bending Metal
PostPosted: Fri Dec 14, 2012 3:19 pm 
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Joined: Thu Apr 26, 2012 5:13 pm
Posts: 2646
Location: CT
What Rick said. Heating steel enough to discolor it is bad for any steel. "Red Hot" usually means that the steel is getting ready to be quenched. In carbon steels, I usually heat until it is non magnetic (cherry red) and then quench it. If you heat to the Cherry Red and then slow cool in vermiculite, it will generally anneal a simple carbon steel. Stainless is a little different and higher temps, but is somewhat close. Some Stainless steels are tempered at a higher tempering cycle, like 900 degrees, but I still wouldn't have to heat a blade to 900! Also, is the Shun a clad blade?? I'm guessing that heating may delaminate the cladding, especially if done in a small area and high temps.

So what Rick said; rubber mallet, vise, etc, go slow and careful (and the steel may be too stressed and break anyway) or break/file/sand it off and redo the whole tip.


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 Post subject: Re: Bending Metal
PostPosted: Fri Dec 14, 2012 3:26 pm 

Joined: Tue Jul 24, 2012 1:28 pm
Posts: 459
Thank you folks and yes Rick, the plastic tipped mallet and a vise did pop into my head actually, I just don't own either so I took the easy route and now chalk it up to another lesson learned. I got off lucky this time.

I'm glad I didnt use the torch though.


As always, I appreciate your replies.

Peter


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