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Gerhard Gerber

Quench noodle blues

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I got a digital kiln a few months ago, one of the first blades I HT'ed was a 40/45cm Bowie from unmolested bar stock 5160.

I got an evenness of temper colour never before achieved and I thought all was well.

The last three blades, my first attempts at chef's knives warped. :(

Nothing has changed in my process, I don't measure the temperature of my Canola but I do heat it till uncomfortable to the touch.......very scientific, I know.

I've broken 2 of the blades, the first trying to straighten between quench plates immediately after the quench, and yesterday 1" off a very pointy tip post temper.

My instincts tell me it's the oil but I also HT'ed a very skinny O1 blade for a friend and that came out nice & straight and the beautiful even straw colour after tempering......with my 2 warped blades.

Same piece of 5160, same me, just bad results.

I follow Mr Cashen's recipes..........

Any advice?

 

PS: Fair warning, I'm about to go buy a Rothco ammo can and align it with magnetic north for horizontal quenches :blink: :P :lol: 

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Gerhard,

Are you normalizing before heat treating ?    I go through a bit of leaf spring, which may or not be 5160 at times, and have gotten good results.  I usually normalize at least 3 times before I get to grinding.  I also sometimes normalize again right before the  quench.  Slightly uneven grinding on thin blades can lead to a warp.  Normalizing seems to help that.  Also, are you quenching vertically or horizontally ?   Do you get the same problem doing it either way ?  Your oil could be too hot also.   I usually go to about 120 - 140 degress.  Although that's not necessarily uncomfortably   hot for me.  Bit of rhino skin on my old paws.  A simple food thermometer if you can get one can help eliminate that possibility.

Are you getting even heats in the kiln, and are you convinced the temps are right ? Is this a new kiln or old ?  Do you get same results trying to heat from the forge instead ?

 Do you quench in the dark or in open light ?   Thin blades can be tricky.   Really need a consistent even heat, and the tip will always cool quickest.   You may want to set the kiln slightly hotter so that you have time for transfer to the quench as the tip will cool in open air.

Have you tried just doing an edge quench ?   A chef's knife does not really need to be full hard.  Just the edge.

I've heard that old oil can cause problems also.   How long has it been sitting there and how often has it been used ?

For very thin blades, I'm not sure that the quench plates do you any good.  When straightening right after the quench you want the blades to stay hot.  Putting them between plates would suck out all your heat I think.   I think when straitening you are shooting for the 400ish degree area, and you don't have much time.  I've had good success doing it on a hot anvil, so long as you are quick, you only have a few seconds.  How far you bend and how long you keep bending depends on your bravery.

How thick is the blade/edge when quenching ?   Forge thick and grind thin and all that, may be better to leave the blade slightly thicker during quench.  I believe really thin 5160 will air harden.  That might be causing a problem too.

That's all I can think of for now,  lots of possibilities to sort through.

Heck sometimes it could just be bad steel ?  Get it from a good source ?

Were the stars lined up to the left of North Easterly direction ? :P

 

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Hi Bruno

On this case we're talking about brand new factory fresh soft as butter 5160.

In the case of the last two blades I did normalize just to test.......

The kiln is a few months old, barely used and digitally controlled, no reason to doubt the accuracy as half of South Africa uses the same kiln.....

Vertical quench, the tank takes 6L+ and the oil is relatively new....no more than 15 blades quenched, maybe 4 months.

I was worried about decard on the tips so I heated the tang/ricasso  on each blade just before they went in, both blades were in for the few minutes it takes from about 750C to 830C and I soaked for about 5 minutes at 830C.

These were done in broad daylight and i trust the PID more than anybody's eye, especially my own.

No forging, stock removal only, and the Bowie I mentioned was if anything longer, thinner and pointier.....

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Posted (edited)

Edge quenching is the bees knees, for most stuff at least. Though, sometimes the blade will curve down.

Normalizing does seem to help with warps, ive had blades warp in the first cycle but not again or to a lesser extent after the next normalizings. 

I dont try to straighten hardened blades, ive done it a couple times, they have to be at least 400°F hot. Or if you really want to push your luck, you might be able to straighten after tempering by bending the blade until it takes a set, I wouldnt suggest anyone try that unless the blade is heat treated very well in a way that the blade will take a set before breaking. I would guess that would damage the blade some, so trying to straighten a blade after hardening is probably one of the more difficult and risky things you can do. Sometimes I can straighten a warp during edge quenching but you dont have much time for that, you can pull the blade from the oil before it gets below a certain temp and straighten then, its not easy to do if you quench in the dark though.

As mentioned before, just a little unevenness in a blade can cause a warp.

Are you moving the blade around in the quench? Sideways movement is asking for a warp.

Edited by steven smith

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Hi Steven

My quench tank is 120mmx120mm square tubing so sideways movement should be incidental, I do move Up&down during the quench.

 

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Do you have to go very far to get from the kiln to the quench tank?  Thin blades cool down quickly and unevenly.  If you have far to move, maybe the blade temperature isn't uniform anymore once it hits the oil.

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Gerhard,

I think the idea of getting an ammo can is a good idea.   I tend to do more of a horizontal quench, well it's more diagonal than anything.  Not saying it will solve your problem, but it's a good start.  At the very least, you might be able to see the warp happen in real time. It might lead to some clues.  Is it possible that you don't have enough oil for these longer blades ?  I do most of my quenches in one of the longer ammo cans, which holds a bit over 2.5 gallons of oil.    How thick is the blade going in ?    I would really try to do a quench or two when it is a bit darker in the sky.  At the very least you will be able to see more of the colors just to make sure everything looks right.

Also, I believe 5160 is one of those steels that can benefit from multiple quenches.  Not a huge amount, but some people do it.  I know that I've had blades come out warped/twisted before, so I would straighten them out in the forge and the quench sometimes 2 or 3 times, and it usually comes out straight eventually.  Just another thing to try...

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1 hour ago, Brian Dougherty said:

Do you have to go very far to get from the kiln to the quench tank?  Thin blades cool down quickly and unevenly.  If you have far to move, maybe the blade temperature isn't uniform anymore once it hits the oil.

Just far enough apart I'm sure there's no oil splatter on the kiln, about 1m.....one quick movement.

Quench tank, the kiln, the blades in question and the raw material.

The second blade from the top I straightened using the 3 pin method in the vice, bend was exactly in the middle of the blade.

IMG_20190722_173914[1].jpg

IMG_20190722_173720[1].jpg

IMG_20190722_173340[1].jpg

IMG_20190722_173253[1].jpg

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I can't give you a measurement, but on these as well as the Bowie that stayed straight I went thin enough that I basically just do the secondary bevel for sharpening, i.e. down to final thickness.

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Crazy face on the tipped blade, might be as well that one died ! :o

  • Haha 1

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9 hours ago, John N said:

Crazy face on the tipped blade, might be as well that one died ! :o

It lives! :D

Sorry, been bad about sharing recently.....

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