When to Correct Warp?

ddavelarsen

ddavelarsen

Well-Known Member
First let me apologize for only stepping in here when I need something. It's been a long time since I posted here, mostly because I haven't been making lately. But that recently changed! Finally got some steel and ground out a couple of knives yesterday. Getting ready to HT and I have a concern.

I heat in an electric oven and quench in Houghton Quench G. The last couple of knives I've quenched came away warped, and this is really bothering me. I have a couple of questions about that.

First, should I be normalizing before quench? I'm a stock removal maker and haven't normalized since I've been using the oven. Maybe I should be. What's your opinion on that?

Second, at what point in the HT cycle should I try to correct a warped blade? Right after quench while the blade is still hot? Before tempering when the blade has cooled down some? After temper?

The last one I tried to correct broke; I attempted to remove the warp pretty much right after the quench. Wondering whether the steel is just too brittle then? But I don't think I'd have much luck after tempering either, once the blade is pretty much set in its final state.

I'm perplexed, and would really appreciate hearing from people who have successfully straightened a blade.

Thanks! And have a happy Sunday.
 
I'm curious what resonses you get. I didnt see where you mention what type of steel you use when it warps. I have had warpage on both carbon adnd stainless steel. On both I have used a torch on them after cooling, then go thru the process again. I am afraid that heating them hot enough to get the warp out ruins my heat treat, so I do it over starting with a fully annealed blade.
This has worked consistantly for me, but I am by no means an expert on this.
On the movie Red Tails one of the guys said "Experience is the exam, the lesson comes afterwards." (not verbatum)
True dat.
 
Dave,

Simple answer. IMHO the best time to straighten is directly out of the quench. I've never had success straightening out of the temper and believe this isn't really straightening the blade but merely bending it and inducing more stress into the steel. I've had better success torch heating the spine with the edge in water and clamping it up straight but I'm honestly not a fan of doing that either.

I've been using this method as insurance against warp and it works like a charm for me. See this thread post #13 for a description-
http://knifedogs.com/showthread.php?22806-Hometown-Hero-build-WIP

A stress relieving cycle before hardening IS a good idea even for stock removers. Cutting, grinding, drilling etc. all add induce stress into the steel that can contribute to warp.

More info could be helpful also-

What steel ?
Where did it come from ?
Whats your EXACT quenching procedure ?

Take care-

Josh
 
Thanks Josh and Eric. I should have mentioned the steel. I'm using precision ground O1 from Flatground.com. I've been using the same steel for many years, the brand is, I believe, Pesco.

My precise process is to heat to 600, apply Brownell's PBC non-scaling powder, ramp to 1455 and hold for five minutes and then quench at 140 degrees. I almost never had warping issues when I was HT in my propane forge, probably because I was only heating the edge to critical while today I'm heating the entire blade.

Josh's method of clamping flat is a good idea, though it won't work for me in most circumstances as I usually taper the tang - so I've got taper going in both directions from the ricasso. But your thought about straightening during martisite transformation is well taken, and that's when I'm going to try to straighten my blades if I need to. If they break, they break. :)

Any other ideas are well taken, since I won't be HT these blades until next weekend -- the honey-do list has been getting longer and longer as I type this... :D I'm out of the shop for today unless I can get enough done to get some free time. Sheesh, my wife talks all the time and often that talking is adding to the list of stuff I'm supposed to do. Makes me crazy! I need to be in the shop!

Thanks again.
 
How have you been Dave? I've been watching for you but, no show.

Stress relieve 01 if your doing stock removal 1250 for two hours after the grind. IMHO normalizing never hurts.

I straighten right out of the quench. I use this pattern makers vise set up with aluminum coated surfaces. It self adjust along the tapers and can be set to align with the bevels. I set it up for whatever blade is coming out of the quench; I use a quick count of 5 and move the blade to the vise and clamp it in place. and leave it there. I have no more issues with warped blades.

DSC01310.JPG
 
Hi Fred, nice to hear from you! I'll try to come up with a setup like that I can use with tapered tangs. I usually try to undo warp with a three point placement in my vice, just bend against the warp and hope for the best. I'll do this immediately after quench as you guys suggest. But who knows, I might get lucky and not have any warp! :) That never used to be a problem.

I'll stress relieve for two hrs as you suggest too, that sounds like a good idea. Normalizing is kind of a pain with an electric oven, but could be done. I'll try your method first and see what I get.

Thanks Fred!
 
I quench from 1475° with a vertical plunge immediately moving the blade fore and aft. After I think the blade is down to 400° I remove it from the quench. Any warp I get is very minor and can be hand straightened using a heavy rag for protection. With 01 you have about a 5 to 8 minute window to do this. If I don't get the warp out by hand, I go on with the temper. After temper I will lock it in my vise, locate the area of warp and heat the spine with a propane torch at this area, over flex the blade a bit and pour water on it. That will lock it in straight. You just have to control the heat to not reach the edge area enough to show color. A very old and simple smith trick. With 01, you may have to repeat a couple of times to get it as straight as you might want. I don't see how it would add enough stress to be concerned with.
 
Thanks, I'll give that a try. I set up a three point press in my vise when I'm HT, and use that to bend against the warp. I'll try the heat and water trick with that, might be the ticket. Something here is going to work! :)
 
Just be careful to keep the heat up near the spine, and go slow at it. Once color starts, it can quickly spread to where you might not want it to be.
 
LRB said:
I quench from 1475° with a vertical plunge immediately moving the blade fore and aft. After I think the blade is down to 400° I remove it from the quench. Any warp I get is very minor and can be hand straightened using a heavy rag for protection. With 01 you have about a 5 to 8 minute window to do this. If I don't get the warp out by hand, I go on with the temper. After temper I will lock it in my vise, locate the area of warp and heat the spine with a propane torch at this area, over flex the blade a bit and pour water on it. That will lock it in straight. You just have to control the heat to not reach the edge area enough to show color. A very old and simple smith trick. With 01, you may have to repeat a couple of times to get it as straight as you might want. I don't see how it would add enough stress to be concerned with.
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Quenched steel changes to martensite @ 400fh, wouldn't you want to straighten the blade while the steel was moving through the softer structures say 1000fh to 550fh? Once the steel crosses the 400fh threshold its much more brittle.
 
If you mean hand straightening out of the quench, 01 does not fully convert instantly at 400°. It takes at least five minutes of cooling beyond that, and more depending on thickness. I have continued tweaking after the temp has dropped low enough to hold the steel bare handed, but that is risky at that point. I don't even file check 01 before 15 minutes has passed. I have never snapped nor cracked an 01 blade. A-2 is much the same, but a tad faster. I did break a blade of it once, but it was more of a test blade anyway, and I knew it it was cool enough that it might break. I have been experimenting leaving 01 in the quench longer than I used to, in the vertcal position, and have been getting 2 out of three with no warp at all, and when one does warp, it is very minor and easily corrected by hand, but the window of opportunity is reduced to maybe just a couple of minutes before it gets risky. After doing the hand straightening a few times, you get a feel of how far you can take it by the resistance of it to respond. You soon learn to gauge the rigidity of the steel, and know when to stop trying. At that point alternative methods have to be used if you did not get it straight enough for your standards. You might be surprised at how much hand pressure can be applied to 01 when it has dropped even to maybe 200°. Give it five minutes more, you might break it with half that same pressure
 
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I am not a metallurgist and do not know how broad your knowledge is, so I am not trying to teach anything; this is just my understanding.
When steel is heated to its austentizing temp and then quenched, the steel can be safely removed from the oil once the steels temp. has passed the pearlite nose; its on its way to conversion to martensite which starts at around 400fh.
The steel is in its most ductile state when it is still at higher temps, as long as the steel has made the pearlite nose. It is far easier to straighten a blade @ 700 than it is @ 300 degrees; it is safer to do so as well; there's no chance of breaking the blade at these temps.
This is why I set up my mechanical straightener and stopped using my hands to straighten blades. Its damned hot work and iffy at best to do it by eye.

I've used the three point vise gadget to straighten blades and snapped a few before I gave it up.

As I get older, I'm pushing 70, I try to position myself to have the greatest chance of success. I do believe there is no single way to accomplish anything in knife making and that is how it should be. I compliment you on your success no matter what your approach.
Now lets see if Dave can turn out a straight blade or two.

Regards, Fred
 
Not all steels are viable candidates for hand straightening under 400°, but 01 and A-2 are, but one does not want to waste time getting at the job.
 
I'm using 3/16" steel, probably too thick for me to straighten by hand. I'm gonna stick with the three point bender until I get it right! All my tangs are tapered, so clamping flat probably would not work for my situation. Maybe if I rigged up some supports for the tang though. That's a thought.
 
Dave,

I've been just using the bench vise with angle iron laying over the jaws for clamping and this set-up will clamp up on a taper no problem. I REALLY like that vice Fred's got though !

To deal with the double taper- Clamp the angle iron on the blade side taper. The tang will be "floating" between the angle iron but very easy to eyeball and see that it's centered or not. If not just push a shim in to get it centered and leave it cool to room temp clamped up.

I typically dont get much warp if any but one big chopper that gave me fits got me looking for a solution. The clamp-up method works so well that I just always use it now as insurance against warping.

As far as temps are concerned my experience mimics LRB's post #11 To see this in action take a piece of scrap steel and quench in oil for 10 seconds just as you would a blade and file check it directly out of the quench and every 30 seconds thereafter. I believe you'll see first hand that the martinsite conversion is mostly a product of temp and as the steel cools it will resist the file more and more until it coverts enough to skate the file. The opposite would be too quench a piece until it comes out of the quench at room temp. In this case it'll skate a file immediately and be already converted to brittle untempered martinsite and any attempt to straighten would most certainly break the piece.

All I use to guage temp out of the quench is smoke and the flash point of the oil. If the blade's hot enough to smoke but doesn't burst into flames then I'm where I want to be for clamping the blade straight. I should mention that I'm quenching 1095 in Parks 50 which has a flashpoint of 275 degrees but I would think this simple temp guide would also hold true for other oils and steels.

I simply haven't had any issues with warp since going with the clamp up procedure but the though has occured to me to prove the theory by making a blade that's purposly warped pre HT and see if the clamp really straightens it out. Just haven't had the time for that experiment yet ;)

Let us know what you come up with !

-Josh
 
Thanks Josh, you might have convinced me to try clamping flat. We'll see how it goes. Hopefully all my blades will come out of quench straight as an arrow! :)
 
If you have the forward part of the blade clamped it should be much easier to hand straighten the tapered tang.

I am working on a more compact version of the pattern makers vise set up. It will swivel along both axis. My eyes are not sharp enough to visually align blades so the clamping set up is a must.
Best of luck to you Dave!

Good discussion LRB and Josh. Fred
 
Fred,

I've kinda held the opinion that keeping the spine straight will basically also keep the edge straight by default (for lack of a better term) so I'm curious if you've experienced edge warp on a clamped blade ?

I typically leave'em a bit thick for HT (.050 minimum) but I haven't experienced any issues at the edge even though my angle iron is only making contact at the spine.

Dave, FWIW most of the blades I've done like this have been hidden tang blades tapered in both directions.

I agree too Fred, another great, civil, thread among friends here on KD's :)

-Josh
 
I've had some luck straightening with a turning fork set up in my hardy hole. With the larger anvil being taken out of commission, I'll have to regrind the post on the one that I narrowed the gap on. There are multiple ways of doing it. Just find what works for you under what conditions.

Doug
 
Josh Dabney said:
Fred,

I've kinda held the opinion that keeping the spine straight will basically also keep the edge straight by default (for lack of a better term) so I'm curious if you've experienced edge warp on a clamped blade ?

I typically leave'em a bit thick for HT (.050 minimum) but I haven't experienced any issues at the edge even though my angle iron is only making contact at the spine.

Dave, FWIW most of the blades I've done like this have been hidden tang blades tapered in both directions.

I agree too Fred, another great, civil, thread among friends here on KD's :)

-Josh
Click to expand...
Josh, I take my blades to finished thickness in the edge, about .010 to no more than .015. I have never gotten edge warp without spine warp, and the edge straightens with the spine in my experience. I do use a double coat of ATP on the edge to prevent decarb.
 
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