Straightening a knife thats come back from heat treat?

oic0

oic0

Joined
Jun 16, 2012
Messages
368
Ok, I sent this knife off for heat treat and asked it to be 62-63 HRC if at all possible (its AEB-L). I have no idea what they would have tempered it at to achieve that since I don't know what kind of as quenched hardness they would have achieved. I also don't know what hardness they achieved period. It came back with just a packing list so I am assuming they either got it as hard as I asked, guesstimated it, or are hoping I don't have a tester- which I don't.

Anyhow, the only method for post heat treat straightening that I know is the one you guys told me last time I asked this same question. Get it hot in some clamps while slightly over bent, then quench it while still clamped. The problem being, assuming they did as I asked, the thing might have been tempered anywhere between 200*F and 350*F (according to the chart for it on AKS).

In other words, I want to get it straight. I don't want to lose any hardness. I don't know what the actual hardness is or what temperature it was tempered at. Is there some minimum temperature I can aim for when trying to straighten?

a2ewkk.jpg
 
Long story short, I tried the temper thing at 250. No effect. I flexed it on my knee a bit after the quench from that and got it almost arrow straight in about 2 seconds with very little deflection. :rolleyes: I never thought that would work since my last 1084 knife could bend like a friggen spring and snap back to how it wanted to be perfectly every time.
 
oic0 said:
In other words, I want to get it straight. I don't want to lose any hardness. I don't know what the actual hardness is or what temperature it was tempered at. Is there some minimum temperature I can aim for when trying to straighten?
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Ask your HT guy what temp he used and stay a little below that? Or maybe call Chuck at AKS and see what he thinks - he's worked with AEB-L quite a bit.

oic0 said:
I also don't know what hardness they achieved period. It came back with just a packing list so I am assuming they either got it as hard as I asked, guesstimated it, or are hoping I don't have a tester- which I don't.
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I'll say this much, I've never had a knife come back from my guy looking like that, nor without a work order detailing the final hardness.
 
I don't figure its at 62 if you straightened it across your knee. Especially the tip. Try a new file on it and see if it slides. At 62 its at file hardness.
 
I'm with Fred, I don't think its at 62 if you can straighten by hand. If it is indeed HRC 62 then it was tempered at or below 325. If you want to, send it to me and I'll test it for ya.
 
Well then its definitely not 62. A file will chew on it.
From what I've read I didn't think a heat treating service would babysit it enough to actually get it to 62 (it probably sat a long time between quench and cryo), but I was still hoping. Oh well. I think its harder than my torch treated 1084 knives that are tempered to 300*F, they didn't want to scratch it, but I'll play with that a little more when I get home from work. I've got some 1095 another knife maker treated, I'll see where it is compared to that. Although realistically, this knife needed to be hard hard. Its a gyuto. I think I could probably flex it a few degrees at the tip with my finger nail without my finger nail bending.

darrin sanders said:
I'm with Fred, I don't think its at 62 if you can straighten by hand. If it is indeed HRC 62 then it was tempered at or below 325. If you want to, send it to me and I'll test it for ya.
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Thank you for the offer, but I wouldn't spend the money on it to have it re treated anyhow :( The first time cost me $32 and its not a $100+ knife IMO. I'll either keep it or sell it for what it cost me to make it, sans labor, just to get more material.
 
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I read you temper your 1084 at 300* ..... why do you use that temperature?

Also

If you paid $32 for HT and you can bend it over your knee.....then chances are you did not get what you paid for.
 
AVigil said:
I read you temper your 1084 at 300* ..... why do you use that temperature?
Also
If you paid $32 for HT and you can bend it over your knee.....then chances are you did not get what you paid for.
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Not all of them, just some kitchen stuff I was experimenting with. That was the point where I didn't get any chips in light cutting duty. I'm using a torch and canola oil so my methods are far from perfect, a better controlled heat treat that gets a higher quenched hardness it would probably take higher temps.

I take it this knife, even being rather thin, should be a lot stiffer and not take a bend so easily?
 
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I would not attempt to straighten a hardened blade below 400* is something I learned from this forum.

But it is my experience if the bladed is harden throughout then trying to bend it over your knee, at room temperature, at the thickness you have there is unlikely to be successful.
 
First of all flex and hardness are two different animals.Flex has to do with geometry,take for example a razor blade.
Hardness will effect its ability to take a set.At 62 you should not be able to get it to take a set just by hand,heck even in the mid 50's should be the same.I don't think you blade was H/Ted correctly if at all.
I would contact your H/ter and get some answers.

Stan
 
The guys are right, a good hard blade that's nice and thin can flex pretty well, but it will come back straight, not stay bent. Think of a cheap fillet or boning knife - even with mediocre steel and low/mid-50's hardness they can keep a reasonable edge and spring back in line.

SBuzek said:
I don't think your blade was H/Ted correctly if at all.
I would contact your H/ter and get some answers.
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I agree with Stan and AVigil again, something's really screwy here. AEB-L is not a complicated alloy; I'm told it takes a little "babysitting" to really get the most out of it, but just to get it hard enough to at least resist a file shouldn't be that big of a deal. Not to mention keeping it straight.

Honestly, if I paid $32 to HT one blade and it came back in that condition, I'd be on the phone already, and probably not very friendly about it. Mistakes do happen of course, and if it's a reputable HT person/company, they should make it right (anneal, straighten and re-HT from scratch) at no charge. If not, I surely wouldn't do business with them again.
 
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Perhaps I am explaining the stuff wrong. Before I call em and fuss, here is a short video of what I'm describing its like in flex and vs files.

[video=youtube_share;UZIAfabOsHQ]http://youtu.be/UZIAfabOsHQ[/video]
 
OK, I understand better now. The flexing (and equally importantly, returning to plane) I'm seeing in your video seems fairly normal for a blade that thin. I really can't tell much from what you're doing with the files.

When we say "it takes a set", we mean that if you bend it, it stays that way. I'm still a bit concerned about the huge bend/warp in your first pic... that's not normal. At least, I've never had a blade come back from HT that way.

When we talk about "file-testing", dragging the butt over a file really doesn't tell us much of anything. I can do the same thing with annealed low-alloy steel and it has virtually no effect.

It would be more helpful if you use a new, sharp file like you would use a sharpening stone, and drag it over and past the edge. With moderate pressure, like when you're establishing an edge bevel. If the file bites in deep and leaves noticeable grooves, that's a bad sign.

There's other stuff you can do, like brass-rod testing that will kinda-sorta give you an idea what's going on... maybe. I don't place much stock in those tests.

Let's get down to the only test that really matters anyway... sharpen it up and start cutting stuff! (whatever it's meant to cut, in this case probably meat and veggies) Can you get it to shave hair and slice paper? AEB-L is very fine-grained; that should not be a big challenge at all. Slice up some 'maters and onions and steak.

If it takes a crisp edge and holds up OK on that, start cutting tougher materials like cardboard or natural-fiber rope. If it's not properly hardened, it will go dull very quickly on tough fibrous materials like that.
 
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james terrio said:
OK, I understand better now. The flexing (and equally importantly, returning to plane) I'm seeing in your video seems fairly normal for a blade that thin. I really can't tell much from what you're doing with the files.

When we say "it takes a set", we mean that if you bend it, it stays that way. I'm still a bit concerned about the huge bend/warp in your first pic... that's not normal. At least, I've never had a blade come back from HT that way.

When we talk about "file-testing", dragging the butt over a file really doesn't tell us much of anything. I can do the same thing with annealed low-alloy steel and it has virtually no effect.

It would be more helpful if you use a new, sharp file like you would use a sharpening stone, and drag it over and past the edge. With moderate pressure, like when you're establishing an edge bevel. If the file bites in deep and leaves noticeable grooves, that's a bad sign.

There's other stuff you can do, like brass-rod testing that will kinda-sorta give you an idea what's going on... maybe. I don't place much stock in those tests.

Let's get down to the only test that really matters anyway... sharpen it up and start cutting stuff! (whatever it's meant to cut, in this case probably meat and veggies) Can you get it to shave hair and slice paper? AEB-L is very fine-grained; that should not be a big challenge at all. Slice up some 'maters and onions and steak.

If it takes a crisp edge and holds up OK on that, start cutting tougher materials like cardboard or natural-fiber rope. If it's not properly hardened, it will go dull very quickly on tough fibrous materials like that.
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I feel dumb now. I figured air hardened steel would be uniform hardness so I've been filing at the handle to avoid making any marks I would have to clean up later. I did what you said and ran the file down the edge as if to set a bevel. Does not catch at all. It will eat up the handle, but not the edge.


I really did straighten it without much bending on my knee though lol. Voodoo magic I guess, or maybe there is some magic moment right after I got it hot in the oven and doused it with water (it was still warped when I took it out of the clamps and shims). Just as proof I'm not imagining things (hard to get the camera to focus on a small line in a big picture :/ )
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I can't tell for sure but it looks good now. If it is indeed HRC-62 it will make an excellent slicer with the right geometry.
 
All this talk of heat treating has got me wondering if there are some top people/company's that people recommend for sending out to for heat treat?
 
Widerstand said:
All this talk of heat treating has got me wondering if there are some top people/company's that people recommend for sending out to for heat treat?
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The names I always hear come up as the top choices had pricing structures that didn't favor doing just one knife at a time OR wouldn't touch aeb-l. There really aren't that many places though. Paul Bos and Peters are the ones I hear praised most often. I didn't use em for the above reasons. One the pricing structure sucked for one knife (but was great for bulk), the other didn't list my steel.
 
oic0 said:
One the pricing structure sucked for one knife (but was great for bulk), the other didn't list my steel.
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You're right about the pricing structure, but wrong about Peters' doing AEB-L. If they listed every steel they can do on the website, that page would be very, very long.

I think we get spoiled by seemingly having everything a click away... sometimes you still have to pick up a phone and talk to a real person ;)
 
I was under the assumption that post heat treat straightening was done with a brass hammer on a wood anvil or stump. To avoid shocking the steel or ruining the HT. At least that's how I've always seen it done.
 
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