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  #1  
Old 11-28-2017, 04:46 PM
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Grayshadow95 Grayshadow95 is offline
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new problem with D2 heat treat


OK guys, need info please.
Did the heat treat on my next two D2 blades today.

One turned out great, perfectly flat, nice and hard. Still have to temper it.

The second one is the problem. I don't know if I didn't press down hard enough during the plate quench or if there was an obstruction somewhere I didn't see, or what ever, but it has a very slight warp, just enough that I can see daylight between the middle of the blade and my table saw top. I have to look closely to see the warp when holding it up to a reference line, but it's there. Obviously this will cause significant issues with sharpening. People with better eyes might be able to see it more easily than I can.

So can I re-heat treat it to take out the warp being more careful during the plate quench, or do I have to start over??????
Yes. it was straight before the heat treat process.
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Old 11-28-2017, 06:32 PM
epicfail48 epicfail48 is offline
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Assuming the warp is enough so you cant get rid of it when finish grinding, yes? If that's the case, I'd want to anneal and normalize the blade before attempting the heat treatment a second time. For carbon steel blades I've gone straight to re-heating, but an alloy like d2 I'd want to keep everything as by-the-book as possible
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Old 11-28-2017, 07:03 PM
argel55 argel55 is offline
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temper at 400 and counter bend opposite way it has bend now. I put it in my vice with three brass rods to over bend it, let it cool down. Your bend should be corrected.
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Old 11-28-2017, 07:21 PM
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Grayshadow95 Grayshadow95 is offline
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Epiccfail48,
Well, I finish grind before heat treating, unless you consider hand sanding with 220, 400 & 600 grit paper finish grind . . . . .

The warp at the center is less than 1/32 from the saw top, didn't have a real accurate measure handy. But grinding even that much out would make the blade much thinner than what I was wanting it to be, plus I don't have any practice doing that kind of grinding.
It started from NJSB 0.159 bar stock which I make sure is flat before I start grinding.

Argel55,
Hmmm, I've seen them try to do that on Forged in Fire . . . . some times it works, sometimes not.
I have several ends of brazing rod that might be useful for trying something like that.
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Old 11-29-2017, 12:33 AM
epicfail48 epicfail48 is offline
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Quote:
Originally Posted by Grayshadow95 View Post
Epiccfail48,
Well, I finish grind before heat treating, unless you consider hand sanding with 220, 400 & 600 grit paper finish grind . . . . .

The warp at the center is less than 1/32 from the saw top, didn't have a real accurate measure handy. But grinding even that much out would make the blade much thinner than what I was wanting it to be, plus I don't have any practice doing that kind of grinding.
It started from NJSB 0.159 bar stock which I make sure is flat before I start grinding.
.
Yeah, thats not much finish grinding. I tend to leave my edge thickness about double where i want it to end up on the finish blade before heat treatment, that way if i see any warp during heat treatment i can correct it afterwards. Not really an option in this case though.

In your case id go the anneal -> normalize route. Most of the time warp gets caused by internal stresses in the steel, and the rest of the time its cause by asymmetric cooling causing internal stresses. Trying to force the warp out almost never works, it might be straight for a bit but half the time the warp comes back, and thats assuming the blade doesnt just snap while youre trying to bend it back. It takes longer, but the reheat route is safer and will likely result in a better end result

EDIT: Realized after posting this that D2 doesnt have a recommended normalization process, which makes sense being that D2 is air hardening. Annealing followed by stress reliving is what i shouldve said.

Last edited by epicfail48; 11-29-2017 at 12:36 AM.
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  #6  
Old 11-29-2017, 11:21 AM
dtec1 dtec1 is offline
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Ok first....did you temper the other blade? in your first post you had said you hadn't tempered it...That's not good UNLESS your putting it into liquid nitrogen it should be tempered as soon as possible it can cause some micro stress fractures in the blade ad then it can crack when used...I even heard of a knife cracking it self while sitting on the counter and I think that was d2 (ray correct me if I am wrong about the steel type) either way

see I ONLY profile my blades before heat treating less chance of a warp and easier to grind out... I would anneal and fix it and then go back and heat treat after you get it straight deffinitly don't try to bend it as is you have a good chance of snaping it in half.
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Old 11-29-2017, 11:37 AM
jimmontg jimmontg is offline
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Al, you can bend it after temper.

I did it all the time with paper cutting D2 blades 18" to 48" and they always warped, no exceptions. That said we tempered at 425, not 400. Most of my D2 knives had a little bit of warp. 1/32 isn't bad at all. Here's the catch, I used a hydraulic press which pushes down between two blocks and I also used my TIG torch which can lay down a very precise area of heat away from the edge and it curls up on the heated area side. I recently had a blade that was slightly warped and I straightened it with a vise and it worked. Depending how big the blade is depends on if the 1/32 is a lot. A 7" blade it isn't much, a 4" blade it is.

When it comes to applying heat to the blade Peters HT does it all the time. When I welded a bolt to a hidden tang I kept the blade area under an ice cold wet rag and stopped if I heard sizzling to add water. With a blade I heated the spine a tiny bit and immediately put a wet rag on it. Again I used the Cadillac of welding, the TIG, but a small oxy/acetylene tip will work too. Just a tiny bit and cool with rag. You'll be surprised at how much it curls back up with that small amount.

To bend it straight take little bites, bends, start at the very center of the warp and bend in opposite direction and move the blade a little at a time, turn it around and start in the other direction from the center. That should get rid of most the warp, remember I had a tolerance of +- 0.008 or .2 mm flat. Take a feeler gauge and see exactly how much warp there is. Don't expect to get perfectly flat with this method.

To anneal an air cool steel takes all day (and then some). You have to use your oven and drop it down so many degrees per hour, I don't have the chart right now and there is still a chance it warps again.


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  #8  
Old 11-29-2017, 12:19 PM
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Grayshadow95 Grayshadow95 is offline
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Dave,
I tempered the blade that was straight the same day, but not the one that is warped.

The process I've found for annealing D2 is:

"Heat slowly to 1550?-1600?F, hold until entire mass is heated through, and cool slowly in the furnace (40?F per hour) to about 1000?F, after which cooling rate may be increased. Suitable precautions must be taken to prevent excessive carburization or decarburization."

Does this look correct?
Since I use an electric kiln for heating, heating slowly isn't an issue, that's the only way it works!
Cooling at 40 degrees per hour would be more difficult. My kiln doesn't have precise temperature controls, just a rheostat with settings from OFF to HIGH in 7 segments, but it does have a good temperature readout. Would simply shutting off the kiln and letting it cool down over night with the door closed be an appropriate course of action? I never thought to time how quickly the kiln cools down.

So, once it is annealed, I can then attempt to straighten it? About the only way I could bend it now would be to clamp it in my big bench vise with 3 rods and a lot of force! These blades are very tough.

Jim,
Interesting process. I do have a 20 ton hydraulic press, but I'm out of acetylene for my torch. Have been meaning to get more, but I don't use it all that much.
The blade is 6.5 inches long, and the tang is a little over 4 inches. The warp is in the blade only, and is basically a continuous curve starting at the tang and going to the tip.

Thanks for the info guys, I'll have to give this a bit of thought.
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Old 11-29-2017, 12:30 PM
samuraistuart samuraistuart is offline
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Dealing with warps post HT is something every knife maker needs to master. Its very easy. If a blade is already hard (tempered or not), and develops a warp, use the 3 point clamp method. It works....every time. You may need to do it a 2nd time if the warp didn't straighten, or if it was over-corrected, but eventually you will get it straight, and doing it multiple times is not going to drop your HRC.

Find something like a piece of scrap steel, about the length of your blade.
Find a fulcrum point....I like to use a brass pin...nails can scratch your finish...brass not so much
Find 2 clamps that can be put into the oven.

It's pretty self explanatory, but clamp the scrap steel on your blade near the back of the handle, on the side of the bend that is convex. Place the brass pin (fulcrum point) in the middle of the bent area between the blade and scrap steel. Use your 2nd clamp near the tip, and crank down until the bend has been over-corrected by the same amount in the opposite direction. Place into oven 400F for one hour. After the hour, I take it out and set it in the sink and spray with water (steam!). Not necessary to spray with water, but it makes the cool down (did it work?) faster...and may be of some benefit. Usually it takes me just once. But I did have a 52100 chef give me fits recently....had to run it 3 times.

I've heard some say they clamp the piece dead straight and put it into the oven. I don't see how that can possibly work. The result would be a bend that is half way between dead straight and what it was when you started. (If it was bent 5?, the result would be a bend in the same direction 2.5?...roughly). I have ALWAYS had to over-correct a warp to make it straight (once the blade is hardened and/or tempered as well).

Yeah...Peter's does use a torch to straighten. While it works, I don't like the idea of a soft spot on the spine of my knives. AT ALL. Not really a huge deal...but not the best way. But they have to figure a way to make it economical for them.
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Old 11-29-2017, 09:15 PM
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Grayshadow95 Grayshadow95 is offline
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Well Stuart, decided your method would be the best one to try first because I already have everything I needed to do it!

Have a heavy duty piece of 1 inch angle iron, two small c-clamps and a short piece of brazing rod. Figured out how to get it all put together, and gingerly tightened the clamp. Cooked the whole mess at ~400 degrees for an hour, then set it on my table saw top to cool.
When I removed the blade from the clamps, you were correct, about half the warp was gone. So, I put it all back together and did it again.
Glory be! when I took the blade out the second time it is perfectly straight!!!!!
It did develop a slight warp in the tang, may be because the angle iron was only about half an inch longer than the blade. But when I put all of the pieces for the handle on the tang I couldn't see the warp at all, AND all of the pre-drilled holes lined up!

Ran a file across the edge and it didn't bite in at all.

I am now doing the temper on this blade. Hopefully it will still be straight when that's done!

I will also do some rigorous testing when it's done.

Thanks a very much!

AL
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Old 11-30-2017, 01:55 AM
epicfail48 epicfail48 is offline
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Quote:
Originally Posted by Grayshadow95 View Post
Well Stuart, decided your method would be the best one to try first because I already have everything I needed to do it!

Have a heavy duty piece of 1 inch angle iron, two small c-clamps and a short piece of brazing rod. Figured out how to get it all put together, and gingerly tightened the clamp. Cooked the whole mess at ~400 degrees for an hour, then set it on my table saw top to cool.
When I removed the blade from the clamps, you were correct, about half the warp was gone. So, I put it all back together and did it again.
Glory be! when I took the blade out the second time it is perfectly straight!!!!!
It did develop a slight warp in the tang, may be because the angle iron was only about half an inch longer than the blade. But when I put all of the pieces for the handle on the tang I couldn't see the warp at all, AND all of the pre-drilled holes lined up!

Ran a file across the edge and it didn't bite in at all.

I am now doing the temper on this blade. Hopefully it will still be straight when that's done!

I will also do some rigorous testing when it's done.

Thanks a very much!

AL
Hold off a bit before finishing that blade, theres even odds that the warp works its way back. If you can, let it sit for a week before you go putting a handle on it, last thing you want it to spend a ton of time finishing a blade only to end up with a handle on a potato chip

Wanna know how i know that?
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Old 11-30-2017, 02:07 AM
jimmontg jimmontg is offline
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Al, I might want to add that a near stainless steel will warp with very little heat

If you ever welded a lot of stainless like I have done (including high carbon) you would know to keep a wet rag handy and when the welded joint was almost to the angle, or flatness you want, you then use the wet rag on it and freeze it in place. You do have to take into account how much the rag will warp it too. Practice on a scrap piece in the future and you won't have to worry about possible breaking from cold bending.

By the way Stuart, it will not change the HT much if at all, even on the spine as long as you do it properly. I have a D2 knife I made and heated to remove the warp and took all of one-two minutes and the HT didn't change at all. See as an air cool steel it gets soft, then it gets hard. That process causes the counter-warp so to speak. I know it's counter-intuitive, but so is check and straightening O1 immediately after quench which you taught me and it bloody well works! If I am a master at anything it is moving metal with heat. Even if it's brass or aluminum. The O1 acts like aluminum/brass at T6 hard, but a 450 degree heat will make them soft for up to 3 hours.

I have over 30+ years doing it, mistakes and all. Once you know stainless it's actually quite easy. For a big curve you use less heat, about 400-500 degrees on three or four spots. Wished I lived near you to show you Al. It really is easy.


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Old 11-30-2017, 08:29 AM
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Grayshadow95 Grayshadow95 is offline
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Wow, you guys second shifters?? Posting at 2 o'clock in the morning?
(My son works second shift.)

Got the heat treat done last night. (my wife didn't appreciate my tying up her oven that long!)

the blade has now set out for over 10 hours and is still straight (So far).

No problem letting it set for a few days, still finishing my first D2 knife handle, and have to make the sheath. Plus have to attach and finish the handle for the second one, that will take over a week anyway. This third one can set all that time.

One curious note, the first blade had real nice color hardening, lots of different colors. The second one had less color hardening, but still several colors. This third one turned out solid what I would call gun metal blue, no variation in color. The second and third blades came out of the same bar!
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Old 11-30-2017, 12:16 PM
samuraistuart samuraistuart is offline
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Glad that the 3 point clamp worked for you! It works for me 100% of the time. You sometimes have to do it a couple/three times to get it straight....but it's a good method.
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Old 11-30-2017, 02:45 PM
dtec1 dtec1 is offline
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glad it worked! you may run into problems if it was hardened but not tempered for so long not gaurentee and I don't use d2 so cant promiss anything but I have heard that other have had problems with that in that steel....
how are you grinding the bevels and all that. IF you have a grinder just profile the blade NO bevels and HT it like that then grind the bevels after I do this on ALL of my blades and they don't warp at all maybe if you stirred it in the oil but I have never had a problem when I did it like that...
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