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For some reason I've been warping a lot of blades lately and I have no idea why. I don't take my blades to a high grit by any means before ht, but I make sure things are even and I ensure that my clay coats are even if I put that on. I do full quenches and don't swirl it around at all. Not sure if I'm getting a little bend during normalizing or what. It is almost like I'm in a ht "slump." :banghead:

 

I know this is more of a rant than a question, but anyone else go through a warping slump?

Edited by Burchtree
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Michael,

 

what sort of furnance/forge do you use for your HT?

are you sure that the heat is completly even?

 

might be a silly question, but I had once a forge where part of the refractory lining kind of was "limping" in front of the burners flare, preventing the Vortex and had a horrible hot spot... I didn't realy notice until closer examination....

 

How's your normalizing procedure?

 

Same steel? different batch?

 

 

how thin are the blades and the edge?

 

is there some warpage already befor the quench or does it happen during the quench?

 

same quenching medium? temperature?

 

 

dan

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I've found that if I don't leave enough meat on the blade, it's gonna wiggle. Of course, now I need to find out how much meat is enough! Tai Goo showed me a useful little trick: if after quench the blade has warped, you can bend it straight IF the metal is still hot. Just grab it in your gloved hands and heave! That's saved a few blades for me.

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Burch, as said above, blades are easily straighted right out of the quench, you have a good 5 minutes. Normalizing and lower heat at quench has helped me a lot but warping is part of the game. Also your mind may be warped :) Have you been hanging around Danbo lately ?

Edited by Don Hanson
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The mind is definitely warped! I tried to move one back after it cooled a bit, but snapped it right in half. The good thing is that it had great grain structure! :D I usually don't know about the warpage until it is too cool because I do the ht in complete darkness and usually do a few blades at a time. Probably need to step back and do one at a time and really figure out when the warpage is happening.

 

Dan -- normalize at low heat -- bring up to temp, allow to cool to black, repeat about 3 times. I quench in Parks 50 at about 120 degrees. The blades that do warp are usually around 3/16-thick at the spine and I usually leave around 1mm of edge for heat-treating.

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The mind is definitely warped!  I tried to move one back after it cooled a bit, but snapped it right in half.  The good thing is that it had great grain structure! :D  I usually don't know about the warpage until it is too cool because I do the ht in complete darkness and usually do a few blades at a time.  Probably need to step back and do one at a time and really figure out when the warpage is happening.

 

Dan -- normalize at low heat -- bring up to temp, allow to cool to black, repeat about 3 times.  I quench in Parks 50 at about 120 degrees.  The blades that do warp are usually around 3/16-thick at the spine and I usually leave around 1mm of edge for heat-treating.

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One thing I actually learned from randal (thanks !): if things break on you while straightening (don't use jigs, use the hammer), usually your normalizing cycle was not good enough...

 

I actually do mostly not straighten after the quench (too risky for my taste), I straighten after the first temper cycle... so it's: quench, and before it drops below 50°C (depending on the steel more or less) into the temperin oven... after about 30-50minutes -> straightening while still hot. then back to tempering...

 

hardened and tempered steel, if well normalized before the quench, SHOULD ALWAYS take a bend BEFORE it breaks.

 

This seems to work well for me, especially on long stuff...

I always almost freaked when it came to straightening swords or other long blades... until randal pointed me in the right direction...

it still can feel a bit "awkward" but it works and each time get better...

 

one thing I should mention above the procedure above... All my longer stuff get's differentially treated one way or the other... so this is a big difference I guess...

 

 

Describe your normalizing a bit more if you don't mind, and what steel?

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I concur with the general comments and questions asked here. I've found that successful normalizing pretty much eliminates warpage. Working to relieve the warp while the blade is still warm is a great idea. That may be the best place to review your processes.

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Thanks -- bending after the first temper cycle makes good sense. The one I broke was before tempering and was a smaller blade. I had a longer blade that I warped by hitting the bottom of the bucket with the point when quenching :banghead: and after the tempering cycles, it was not going to go straight -- it was set (damn W-2 :D).

 

I believe I'm normalizing properly, but I think I'll just have to keep an eye on that and see if maybe I'm not inadvertantly quenching the blade at an angle or something.

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I believe I'm normalizing properly, but I think I'll just have to keep an eye on that and see if maybe I'm not inadvertantly quenching the blade at an angle or something.

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believe is one thing, knowledge another :P:P

 

W2 is one of my favourites (and yes it can be tough to straighten.. .takes quite some pounding).

 

But how many normalizing cycles, at what temps and for how long each are there in your process....

 

I usually normalize two to four times, temps straight from the book, consequently getting lower, for each at least 10-20minutes...

so it's quite time consuming...

this is where I once did really skip things a bit, I mean I did one quick normalizing cycle followed by a slow cool down ... and especially for W2 this was NOT ENOUGH...

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I do three cycles -- slowly bring the blade up to austinization, hold for just a bit, then allow it to cool to black. No pyro on the forge so, I'm not sure of exact temp. Hopefully will be getting an oven soon to eliminate any inconsistencies (or a large chamber forge like Foggs with pyro). So many toys, so little money.

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I do three cycles -- slowly bring the blade up to austinization, hold for just a bit, then allow it to cool to black.  No pyro on the forge so, I'm not sure of exact temp.  Hopefully will be getting an oven soon to eliminate any inconsistencies (or a large chamber forge like Foggs with pyro).  So many toys, so little money.

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Oh, yeah, so many toys, so little money, strange I feel exactly the same, even after all the years ;)

 

consistent temps are a must for normalizing...

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Non-uniform heat transfer is another common cause of warping. If you get one side hotter than the other, you may get a slight delay in the hot side reaching the Ms temperature relative to the other. Since the formation of martensite is accompanied by a volumetric expansion, the side that transforms first will cause the blade to warp toward the other side. Now the hot side will eventually begin to transform and because it was somewhat hotter, it may expand slightly more than the colder side. It is really to complicated to predict but you get the idea. Stand the blade on its spine to heat and do not place it near a wall.

 

Bought a little Delta 1" belt grinder last week to do more of my carving knives. The blades are usually 1" - 1.25" long so it should work just fine. Now to actually get out and do some forging work.....

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  • 2 months later...

RKNichols is right - it is non-uniform heat transfer (center to surface or surface to surface) that causes warping from quenching. BUT, there are also a myraid number of other ways - non-uniform heating in the furnace; large gradients of residual stresses in the part before heat treatment; improper microstructure of the starting material; phase of the moon; design of the part; grinding stresses; decarb on the raw stock; banding in the material, etc. But it is always the heat treater or heat treatment that gets the blame.

 

What sort of quenchant are you using? What is the temperature of the quenchant, and how much agitation do you have? All of these things, plus thos above greatly affect the distortion.

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Scott you left out alignment with the, corrected declination for your lat/long, earth's magnetic field. Where in The Heat Treater's Guide is that chapter on phase of the moon anyway? :)

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You caught that one! Us metallurgists got to maintain some mystique!

 

BTW - actually magnetic field can manipulate quenching and annealing - producing some interesting microstructures, and create very fine grain. There was an interesting study on strong magnetic fields done at Oak Ridge National Labs....:

 

http://www.msm.cam.ac.uk/phase-trans/2004/magnet.html

 

Really amazing stuff - by turning on/off the magnetic field, grain size was manipulated. Further, increadibly fine pearlite can be created, yielding very hard vet ductile materials.....

 

But I digress - where was my astrolabe?

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I saw the magnet - it was impressive. It had another magnet on the outside, with opposite polarity to counteract the field so there was minimal leakage. It was about 4 feet in diameter, with a hole about 6 inches in diameter......

 

But it was really cool!

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Oh my. But OSHA does have a say in how they get to play with their toys. A bigger magnet to protect everybody makes sense. Don't want any lab rats falling over during an experiment. :lol:

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