Annealing Error, will it damage the blade??

galadduin

galadduin

Joined
Dec 25, 2004
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Hi all,
I am working on some blades ordered. 3 of them are ready for HT but the annealing operation I used to do for D2 steel was wrong after the stock removal. Info sheet says cool 20F/h rate from 1560 F to 1200 F then air cool. But I messed up with the temperature input to my kiln controller and actually I had 30F/h rate from 1830 F to 1000 F cooling. Will it hurt the heat treatment, do I need to do it again or is it safe to harden the blades? I'm worried of the grain growth... Also I have an option to stress relieve from 1200 F (hold 2 hours) then slowly to 930 F. Also I wonder this below critical operations will refine the grain size???
 
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That extra 300 F will have produced excessive grain growth ! Why did you anneal after stock removal ? A subcritical anneal [ 1200-1300 F] or normalize would have done what you needed. A subcritical anneal would not refine grain.
 
Thanks mete, that was what I feared most... So how would I refine the grain now, spheroidal anneal???

Bohler sheet was not recommending normalizing operation for D2, I used to anneal this steel for that reason. However Uddeholm sheet welcomes normalizing. In fact I was confused so to be sure I always annealed my blades before hardening.
 
I understand, slow cooling from austenisation temperatures encourages grain growth and to refine I need to get all the grains to a new structure, fine pearlite or martensite (cool not too slow). Then re apply all that process until I have the desired grain size... If I understood that, my problem is D2 needs long soaks and any air cooling operation causes it to harden and stress. I was thinking to austenise and soak then air cool to Ms then again austenise. Am I on the right track???
 
I'll have to do some research on this. My worry is that you now have grain boundary carbides which might be difficult to remove ! Grain size will be easy to change.
 
Emre, please don't let the grain growth paranoia that inflicts most of bladesmithing deprive you of too much sleep. As you can see mete gets it about the grain size fix. Grains grow, that is what they do, that is all they do, and they never shrink. But what they do before they grow is remake themselves in a whole new phase, come to a stable size and then grow by devouring one another. This happens again, and again to varying degrees with every heat past critical (ac1 to be precise). So fixing grains is the simplest of our operations and although a number of bladesmiths promote their skills on their ability to control grain size all they are doing is preying on the public’s ignorance of this topic. Reheat your steel without going to the higher temperatures and you grains will simply reform finer with every reasonable heat. That is the good news:) and now that I have you feeling better...

The bad news, the part that so many bladesmiths never seem to worry about because they are so focused on grain size, is the problem of carbide size and distribution:(. This is still not too tricky to fix with a steel as simple as say 1095 as the carbon will move around rather easily during many of the same heats that can refine grain size. However, when carbide forming elements are added to the mix the carbides become very stubborn and troublesome, it is actually this reason that most bladesmiths avoid steels that are stainless or borderline stainless.

Now for the really bad news:(, in D2 you have chosen about the most carbide rich stuff you can without going to stainless, about as far from 1095 as you can get without going over the top. This steel likes to form nasty course carbides that are a bear to break up. These carbides will be as much of a problem as any larger grain size.

Now for the better news. Follow proper industrial normalization concepts (even though there are none for D2) and you can fix the carbide issues :). Don't let bladesmiths talk you into low temperature cycling because of misguided ideas about grain refinement, low temp cycling will only make the carbide problem worse. Get it hot; recommended hardening temps are 980C to 1025C range, so this gives you and idea of how hot things have to be to begin putting carbide into solution. I would cycle it there a few times and then move on to grain refinement at a couple of lower temperature cycles.

The trick with this carbide stuff is how things cool more than how hot they got. Slow cooling with lots of dissolved carbide is a very dicey thing since it allows that extra carbide time to go where it wants to go, which almost never coincides where you want it to be. Your "anneal" wasn't bad because of the temperatures used alone; it was bad because of how slowly you cooled from that those temps.

For all the reason outlined above I just don't work with D2 so what I have outlined is mostly suggestions more than rules and I would pay attention to whatever mete comes up with on this as well. Also there are charts showing the marked grain reduction by going into your final quench from a less than annealed condition, no doubt by putting those carbides to good use.

P.S. Special considerations for decarb are often described for this steel, so you may have another nasty problem to be concerned with in all this heating and cooling.
 
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Thanks Mete I wait for your research on carbide issue. Also I would like to know what kind of problems I may face if it is not fixed but the grain size is refinied?

This helps a lot, thank you Kevin, you explain things in a very nice style. I was really afraid of the grain size issue, but after reading your reply I learned at least it is a fixable problem. I was thinking about some austenising and air cool cycles but as Mete points this maybe doesn't solve the boundary carbide problem.

A couple hours ago I run 2 980 C cycles. Now I wait for Mete's response on that issue, if it cures the steel I'll go for hardening... The hardening temprature I always choose is 1025 for most of my blades....

I accept the decarb problem will be a nasty issue but hopefully I left the blades unfinished, the shape can be altered, thickness can be reduced, no problem..
 
Normalizing - It's usually not recommended for D2 because the high chromium levels cause low heat conductivity.This will be more a factor in large sections. I would not expect the problem with a knife.
As for the carbides I have to do a WAG. Wrap the blade in foil. Heat to 1900 F, 25 min, air cool [ normalize]. Heat to 1800 F ,20 min,air cool. Heat to 1700 F 20 min , air cool . Hope that this breaks up the carbides.
Now harden from 1825 F ,20 min Plate quench if you have them.
The question remains about the structure - the size shape and location of the carbides. You might take a blade and break it [impact ] to see if it's brittle. Safer that way.
 
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Thank you Mete, I'll do that exactly how you say. I'll break a sample from the tiny part of the hidden tang of a blade see if it is coarse and after tempering if it is too brittle.
We'll see.. I'll post the results. Thanks Mete, Kevin, I think your efforts are keeping the Shop Talk area the most valuable scientific source on knifemaking on Internet....
 
Now this is what this whole forum is about! My hats off to Mete, Cashen and galadduin. Mete and Cashen for being so willing to take time out of their days to assist someone and to galadduin for being willing to listen with an open mind!

I am actually emotionally moved by this thread. Once again, my hats off to the three of you!!
 
Yeah, what Scott said!

Great thread all the way around.

Please keep us posted, Galadduin.


Thanks
 
Thank you all for kind words, I share the feeling for this thread and Mete's and Kevin's willingness to help...

Here is how it came out: I first broke a tiny part from the tang. It was so brittle that it was effortless to brake it with a thong. Then I cycled the blade exactly what Mete suggested. And then hardened as Mete said. Then again I tried to brake a part from the tang but it was not that brittle now and I had to smack it with a hammer...

As the image shows, the grain is apparently smaller at the left. The tiny part at the right is the part I took at the beginning. At the left you can see the tang tip after the normalizing cycle and hardening. I guess it did work out great. Thanks a million Mete and Kevin, your input really saved this weeks work....

Regards
 

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Maybe a little late but,…

Simple… take it up to forging temp., soak it a little, and air cool it from progressively lower temps… in logical/reasonable increments. (oldest trick in the book.) :)
 
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Tai Goo said:
Maybe a little late but,…

Simple… take it up to forging temp., soak it a little, and air cool it from progressively lower temps… in logical/reasonable increments. (oldest trick in the book.) :)
Click to expand...

The oldest trick applies for this steel too but the soak times and temperatures are high. Carbon steels and low alloys are easy to refine but it is D2 and it has tendency to produce big carbides, this was my main problem as Mete and Kevin told. Took about 5 hours to "normalize" 3 times this batch :rolleyes::eek:... The suggestion Mete came up was a modified normalization cycle for D2. But in fact it wasn't normalization as air cooling only hardens the steel. So we could say safely I triple quenched this D2 batch :p:D Sorry, I'm just kidding, couldn't resist :D
 
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... I can't believe Mete had to research this one... I'm find myself very disappointed. :(

... just multiple cycle the sucker down from progressively lower heats,... even into sub critical. It'll work! It'll come around! You can't miss! :D
 
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