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I have a O1 blade that warped after heat treatment in oven.  It was straight out of the quench. I just lay them on the rack. Do you put a plate steel in to put them on? Can it be straightened? Will I have to reheat treat? 

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That looks to be a pretty straightforward bend.  You should be able to straighten that out by counterbending it and running another temper cycle.

I typically usea piece of angle iron, shim behind the apex of the arc,  and then draw the end down tight with small c-clamps.  I usually try to counterbend it about the same amount as the existing warp, maybe a touch more.   Run another temper cycle and then check it.  You may have to repeat a few times until you get the hang of exactly how much to counterbend.

One note.  Run at least one temper cycle before doing this.  Trying to counterbend an untempered blade can easily leave you with two significantly shorter blades!:D

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Thank you Alex. 

I did try that but only one cycle.  Let it cool to room temp while in the clamps. When I took them off still had a slight bow. Figured I'd pull it a little bit more by hand and in vise. Epic failure. 

Looking at the grain can you tell anything about the heat treatment?

 

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Edited by David Pessall
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That grain indicates overheating, or holding at heat for way too long.  O1 is pretty forgiving of minor overheating, but it gets ornery if you go over around 2100 degrees.  What was your heat treat process, including forging times and temps?

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I use a brick forge with propane.  I heat the blade to non magnetic. Not more than 10 minutes and quench in oil. Then in oven at 400 degrees for an hour.  Cool to room temp and another hour in oven at 400 degrees. 

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I don't take it to room temperature.  It's out of quench just long enough to quickly scrape off anti scale and run a file across it. Then into preheated oven.

 

Edit...I do heat the oil to 175 degrees before blade go in.

Edited by David Pessall
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Not what I meant.  Normalizing is the process of thermal cycling the blade after forging, but before hardening (quenching).  If you do a forum search you can find many threads that describe it in great detail.  I'm not extremely familiar with O1, but it does wonders on 1084 and 5160.

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Well, I got nothing then.  If you were starting from new stock, I wouldn't think that the grain would be that large.  Unless you accidentally overheated it, I dont know what would cause it.  Hopefully someone else can shed some light.

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always normalize, normalize, normalize. at least three times. and dont harden your tang if you can avoid it unless the tang needs to resist bending like in a thin dagger

 

are you sure youre holding the blade at the right temperature, do you have a thermocouple? 

 

nonmagnetic is below critical and holding a blade at that temperature wont do much, the fact that so many people manage to harden blades from "nonmagnetic" just goes to show that their judgement of temperature is off quite a bit. i quench by eye and the only reliable way* is to watch for descalescence, the steel appears to cool slightly as it reaches critical temperature so you can see right when and where its happening although its hard to see. 

 

if you dont have a temperature controlled furnace then skip the 10 minute hold at critical, o1 should still preform pretty well. 

 

you should break the blade to check the grain there, its possible that the tang was all thats overheated because it doesnt look like the blade warped, overheating can cause warpage, a cooler blade being quenched will go through less stress.

 

the surface of the steel doesnt look terribly overheated, it actually looks fine at the blade end. your stock could have slightly large grain.

 

*you could hook up an incandescent light bulb to a dimmer switch and adjust the light so the hot wire in the bulb is the same color as the temperature steel you want  

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I think a few normalizing cycles would help.  That may just be large grain as-supplied.  It's not huge, just bigger than desired. 

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There are a couple of things going on here.

Normalizing is required, even for stock removal blades. O1 is best normalized below critical temp, so around 1200-1250*F is optimal.

 

8 hours ago, steven smith said:

dont harden your tang if you can avoid it

This is debatable. I am in the other camp, which through hardens everything to avoid a phase transition, and then drawing back the tang area to a dark blue well into the ricasso area. (yes, full tang knives get the same treatment)

 

Tang drawback V2.jpg

 

Never try to straighten in a vice while the steel is cold. You now know why.

I am confused by the apparent contradiction in these two statements:

 

20 hours ago, David Pessall said:

It was straight out of the quench. I just lay them on the rack.

 

15 hours ago, David Pessall said:

It's out of quench just long enough to quickly scrape off anti scale and run a file across it. Then into preheated oven.

 

Do not preheat the tempering oven. Set the blades in the oven at room temp and allow the blade and oven to come up to heat together.

I never cool my blades out of a quench on a rack. That will lead to warping. Hanging dead vertical is better for avoiding the dreaded quench warp.

You have a vice, so I would suggest you try my method of quenching. It has proven to be successful at avoiding warping in the quench.

https://youtu.be/iWWtIAsIKGo

 

 

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9 hours ago, steven smith said:

always normalize, normalize, normalize. at least three times.

I'll suggest editing this to "no more than 3 times".  It is possible to refine the grain so much that it won't harden.

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28 minutes ago, Joshua States said:

Do not preheat the tempering oven.

Why not, Joshua?  This is the first time I've heard that suggestion.  I've always heard to get the tempering oven up to temp first to avoid overshooting your target temp of the blade during pre-heating.

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I'm trying these suggestions this morning.  I normalized it twice. Heated to orange color, checked as nonmagnetic, quenched in hotter oil this time (220 degrees), wire hand brushed off anti scale,  checked hardness with a file, placed on oven rack at 400 (oven was pre-heated) degrees.  The blade was straight going into oven. Now I wait.  

Thanks for your help!!!

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After the 1st temper it's straight.  

 

Broke the other one at handle blade area. Grain looks a little smaller. 

 

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That grain does look a bit better.  That helps suggest that it's the steel condition when you got it rather than overheating on your end.  

 

Other things:  I like a preheated oven myself.

 

Your oil doesn't need to be that hot.  130 degrees is plenty.  

 

Nonmagnetic is 1425 degrees F, unless you soak for more than 10 minutes, at which point it starts drifting lower.  It can get as low as 1375 during a long soak.  

The phase change in O1 happens between 1550-1575 degrees.  Thus, a magnet doesn't tell you much, other than that you're in the vicinity.  That's where the decalescence Stephen mentioned above comes into play.  When the steel goes through the phase change that makes it hardenable you'll see it dim a little.  Looks like shadows, starting at the thin edge and moving towards the thicker parts.  It is a trick to see it in bright light, so if your forge is big enough to hold one, use a bit of tubing (with one end sealed, that's very important) big enough to hold the blade as a muffle tube in the forge.  With that you can easily spot decalescence, even through a thin layer of anti-scale compound. 

 

The reason to look for decalescence rather than color is that we all see color a little differently, and what we perceive as incandescent color depends greatly on ambient light.  1500 degrees F in total darkness is a bright orange, in full sun it's black.  In my usual shop lighting it's a little lighter than cherry (Maraschino, not bing!), red.  Once you get used to looking for the shadows to disappear on the way up, you can successfully harden any non-stainless high carbon steel.  It's easy because you're seeing the actual phase change take place, not just guessing by color whether your 1095 is at 1425 or if your 5160 is at 1600.  

 

And, if you use a muffle tube, you can push a bit of charcoal into the far end and you won't need the antiscale.  The charcoal will scavenge all the oxygen from the tube.  That's one of two reasons having one end sealed is important.  The other reason is for even heat distribution. An open-ended tube will act as a chimney and be cooler towards both ends, which limits the length you can easily harden as well as allowing oxygen to flow through.

 

So:  I think you see where we're steering you now.  Normalize (take to critical and air cool to black) two or three times after grinding to de-stress the steel and, more importantly, to refine the grain, and in the case of O1 in particular, to ensure the carbides are properly in solution before hardening.  After hardening, allow the steel to come to room temperature.  If your martensite isn't finished forming before you stick it in the oven, you'll get stuff like Bainite instead of tempered martensite.  That's not that bad a thing, bainite is far tougher, but it won't hold an edge as long.  I don't remember the Ms finish point for O1 right off hand, but I think it's around 400-450 degrees F.  It's always a good idea to let it get cooler than that to ensure full conversion with as little retained austenite as possible.  

 

Confused yet? :lol:  I tend to geek out with this stuff, if I'm going too far out in the aether here tell me and I'll try to dial it back a bit. 

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3 minutes ago, Alan Longmire said:

I tend to geek out with this stuff,

Oooohhhh....I can't wait 'till I can disclose...:ph34r:

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11 hours ago, billyO said:

Why not, Joshua?  This is the first time I've heard that suggestion.  I've always heard to get the tempering oven up to temp first to avoid overshooting your target temp of the blade during pre-heating.

I have always been told otherwise. There is nothing to gain from putting a cold piece of steel into a hot oven, except a sudden drop in oven temp as the blade picks up the heat.  If you bring both up to heat simultaneously, you get a much smoother heating of the blade and you know when the blade has reached the desired temp. I use a programmable Paragon, and it's really pretty good at bringing the oven up without overshooting the target by more than a couple of degrees. Most of your electric kitchen ovens are the same. I also do not see how putting a cold heat sink into a warm oven will avoid overshoot. When the oven temp drops, the logic will kick it back on. This is almost certainly going to cause the oven to push out more heat, and do it suddenly. I think that is far riskier than bringing both up to heat together.

Edited by Joshua States
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There's some great replies in this thread for me and anyone else using O1. I really appreciate you helping me out! In the future I will most certainly be  normalizing prior to hardening. Also,  cooling down before going into oven for temper.  This blade came out very straight. 

 

Again thank you all for taking your time with me! I'm still new and learning all the time and excited about it!

 

 

 

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On 11/22/2020 at 7:02 AM, Joshua States said:

Normalizing is required, even for stock removal blades. O1 is best normalized below critical temp, so around 1200-1250*F is optimal.

This is not normalizing.  Normalizing requires a phase change.  Keeping it below critical will help with stress relief, but won't do much for grain size reduction.  

 

On 11/22/2020 at 7:02 AM, Joshua States said:

This is debatable. I am in the other camp, which through hardens everything to avoid a phase transition, and then drawing back the tang area to a dark blue well into the ricasso area.

This gets you a little bit of blue brittle martensite, which is bad.  If you don't harden it you get a phase change gradient, which isn't too bad at all.  Metallurgically speaking, your way is worse.  Practically speaking though, I would doubt that it is significantly, or even measurably different.  Unless of course you need a harder tang, then you have to do what you have to do.  

 

On 11/22/2020 at 7:02 AM, Joshua States said:

Never try to straighten in a vice while the steel is cold. You now know why.

This is very important and was the first thing I was going to suggest when I didn't see it in the original straightening post by Alex.  

 

22 hours ago, Alan Longmire said:

I don't remember the Ms finish point for O1 right off hand, but I think it's around 400-450 degrees F.

The book says for O1 95% martensite doesn't occur until 210F.  So make sure you get it all the way down to room temp before tempering.  Or at least to where you can comfortably handle the blade bare handed.  Ms is 445F.  O2's Ms is about 300-355F, without a Mf listed.  My other book at home may have more details.  

 

As to a pre-heated tempering oven or not:  Doesn't matter too much.  I prefer to have things pre-heated, including a tray/pan of sand.  Bury the blade in the hot sand to quickly and evenly heat the blade, then back in the oven to maintain the hot temp.  I prefer this over the slower heating because I don't like un-tempered martensite hanging around.  Since we are tempering for an hour each temper cycle, it isn't really that critical how long it soaks.  There won't be a significant difference between 55 minutes and 90 minutes.  I always suggest going on the longer side (but not crazy like 5+ hours).  The important part is to ensure that the heating is as even as possible.  

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18 minutes ago, Jerrod Miller said:

The book says for O1 95% martensite doesn't occur until 210F. 

If I'm reading right, according to Larrin Thomas's book, Mf (99%) is right above the zero line on the y-axis. (Fig 24.16 on p309)

 

Seeing as how I've got the book out, I've got a question for you, @Jerrod Miller :  on p283, (Fig 22.16) there's a diagram of 1080 tempering scale showing the time/temp dependence.  On my blades, I shoot for about 62 HRC, so in theory... could one temper at 600F (~315C) for  ~10 seconds and get similar results as 400F for 60 min?

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The book I was referencing it the ASM Heat Treater's Guide.  I do not have Larrin Thomas' book.  

 

And yes...In theory shorter times at hotter temps can yield the same hardness as longer times at lower temps.  This is a fairly dangerous game to play (but to be fair, this is done a lot in industry).  Especially with steep curves it is best to avoid that practice.  But when you are looking much later in the curve (note that the one you pictured is a log scale on the time axis) then you don't get nearly as much hardness loss for the same amount of hold time.  (e.g. The first minute of tempering softens much more aggressively than the 60th.)

 

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37 minutes ago, Jerrod Miller said:

note that the one you pictured is a log scale on the time axis) then you don't get nearly as much hardness loss for the same amount of hold time.  (e.g. The first minute of tempering softens much more aggressively than the 60th.)

I did notice the logarithmic scale, and your last sentence makes me wonder about what I've heard in the past about the above question on putting the blade into a cold oven or pre-heated oven for tempering.  I was taught that because tempering is both time AND temp dependent, not to worry about the temp swings that happen.  But what I got from that discussion was that the higher temps during the swings don't last very long, so it's not something to worry about.  But if the element (and oven temp) gets up to, say, 800F while pre-heating, then we get to 60 HRC or lower just after a few seconds.    I realize part of the answer will depend on how extreme the temp swings are in the oven when going from room temp to , say, our target temp of 400F.   

So in my way of thinking, the above is a reason to have some thermal mass surrounding the blade to help prevent the blade from overshooting one's target temp.

 

Edited by billyO
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