Can I reheat treat D2 (Answered)

[EntrancedVermin]

I recently HT'd three knives in D2 and one of them I messed up my surfaces grinding on, I decided to heat-treated any ways to test it. So I ended up beating the hell out of it and then snaping it in half. It held up very well to my test but the grains we're not as dissolved as I would have liked. So I figured out what I did wrong and now I'd like to know if I could re HT the other two knives I did. I know i can do it better since I did a test piece that had very fine grain.

And yes I was using foil in a temperature controled kiln. Plate quenched, tempered at 400 for two hour, liquid nitrogen cyro for and hour, second temper cycle at 400.. next time I want to do the second one at 375 or maybe try the 1000 temper.

The knife i tested

The test piece i did

 

[JTknives]

I always do liquid nitrogen before the first temper and it’s 24hrs minimum. What was you soak time and temp?

 

[EntrancedVermin]

I always do liquid nitrogen before the first temper and it’s 24hrs minimum. What was you soak time and temp?

I read that the you should do a temper cycle and then cryo, and that anything over an hour of cyro is not necessary on D2 (i could be wrong thats just what i read on here). My soak time on both was a little over 30 minutes. the knife was @1900 ( which is were i believe i mess up) and then the test piece was @1850 ( which i read is the best temp but 1875 is the max).



My real question is if i can reheat treat it?

Edit: since i have you here Jarod do you think D2 i a good steel to plasma cut

 

[samuraistuart]

In the past a “snap” temper was recommended after quench, but prior to the cryo treatment. This was to help with distortion issues, and is not the best practice. The whole idea of using cryo is to eliminate retained austenite, and tempering stabilizes austenite, exactly what you don’t want to happen. The best practice is to go directly from quench, down to ambient temperature, into the cryo bath, and the finally tempering. No tempering should be done prior to cryo bath. It should be a continuous quench (drop in temp from austenitizing down to -300f).

As for doing a 2nd HT on D2.....
D2 really should be re-annealed after a botched heat treatment. Maybe Larrin or someone can give exact procedure on doing that, but it requires a hold at “x” temp for “y” time, and then drop down to “z” temp at a rate not to exceed “xy” degrees per hour. Then there is the more simple “bladesmith anneal”. Once a blade has been quenched to form martensite, “temper” at 1200f for 2 hours. This is another method of spheroidizing steel, setting it up for a 2nd attempt.

Simple low alloy steels can be re hardened after a bad HT without the anneal. Higher alloy steels like A2 and D2 should be re-annealed prior to attempting a 2nd HT.

 

[JTknives]

Not sure where you read your information but my understanding is you use liquid nitrogen to complete the quench and reduce the amount of retained austenite. The long soak is used to precipitate EDT carbides. An alloy like AEBL does not need the long soak as all your wanting to do is reduce retained austenite from the quench. In my experience D2 is fantastic with a long cryo and 2 tempers.

I don’t think 50° in austenite temp will cause a noticeable difference to grain size that would be apparent with your eyes. And in fact your oven could be 50° off from actual temp this is why testing is so important with the ovens we use. The Vanadium in D2 is used for a few things. It refines the grain and makes it less sensitive to overheating and grain growth. It also increases hardenability but does not require very much for that. Any extra is used to create carbides and adds that secondary hardness bump you see in the 900° range.

As for reheat treating I have done it but usually it fallows a full anneal cycle. But nothing to me stands out saying you can’t re heat treat a heat treated blade. I know Abel does not like it but not sure on D2. As for plasma cutting there is no problem. The plasma does not care what the alloy is and I have not found anything it won’t cut. And in fact I cut out a glass platten with it years ago. I just laid a thin strip of steel over the top and started cutting. Still using that platten today.

 

[Nathan the Machinist]

the book says that you must do a full anneal on D2 before you can reheat treat. However practice has shown that is not always the case it depends on your original austenitizing temperature and your batch of D2.

The problem you run into with D2 and other complex steels like it is the carbides that pin the grain boundaries can dissolve completely on the second heat before the carbon reaches equalization and your grain size can explode. You're supposed to reset it. Considering that you went a little hot on your first heat, that's what I would recommend.


Edit to add, a "bladesmith anneal" probably isn't going to do the trick.

 

[EntrancedVermin]

In the past a “snap” temper was recommended after quench, but prior to the cryo treatment. This was to help with distortion issues, and is not the best practice. The whole idea of using cryo is to eliminate retained austenite, and tempering stabilizes austenite, exactly what you don’t want to happen. The best practice is to go directly from quench, down to ambient temperature, into the cryo bath, and the finally tempering. No tempering should be done prior to cryo bath. It should be a continuous quench (drop in temp from austenitizing down to -300f).

As for doing a 2nd HT on D2.....
D2 really should be re-annealed after a botched heat treatment. Maybe Larrin or someone can give exact procedure on doing that, but it requires a hold at “x” temp for “y” time, and then drop down to “z” temp at a rate not to exceed “xy” degrees per hour. Then there is the more simple “bladesmith anneal”. Once a blade has been quenched to form martensite, “temper” at 1200f for 2 hours. This is another method of spheroidizing steel, setting it up for a 2nd attempt.

Simple low alloy steels can be re hardened after a bad HT without the anneal. Higher alloy steels like A2 and D2 should be re-annealed prior to attempting a 2nd HT.

I read the temper cycle then cryo thing on AKS and i was wondering about it too. Ive always heard the quench and cryo thing and it made more sense then the method i did. I actually did read about the annealing process and i will try it out this weekend.

Thank you

 

[Nathan the Machinist]

You should not snap temper D2 before cryo when making a knife. This is one of the primary causes of poor edge stability in D2.

 

[EntrancedVermin]

Not sure where you read your information but my understanding is you use liquid nitrogen to complete the quench and reduce the amount of retained austenite. The long soak is used to precipitate EDT carbides. An alloy like AEBL does not need the long soak as all your wanting to do is reduce retained austenite from the quench. In my experience D2 is fantastic with a long cryo and 2 tempers.

I don’t think 50° in austenite temp will cause a noticeable difference to grain size that would be apparent with your eyes. And in fact your oven could be 50° off from actual temp this is why testing is so important with the ovens we use. The Vanadium in D2 is used for a few things. It refines the grain and makes it less sensitive to overheating and grain growth. It also increases hardenability but does not require very much for that. Any extra is used to create carbides and adds that secondary hardness bump you see in the 900° range.

As for reheat treating I have done it but usually it fallows a full anneal cycle. But nothing to me stands out saying you can’t re heat treat a heat treated blade. I know Abel does not like it but not sure on D2. As for plasma cutting there is no problem. The plasma does not care what the alloy is and I have not found anything it won’t cut. And in fact I cut out a glass platten with it years ago. I just laid a thin strip of steel over the top and started cutting. Still using that platten today.

Honestly i cant remember but i think i saw it on here about the hour cryo. I actually built my own furnace and i know its pretty damn close to temp. I will try re-HTing this weekend and let you know.



When i asked about the plasma cutting i meant how does it effect the D2? I have a local guy that does it full time and was wanting to go through him since i wouldn't mess with shipping.

 

[EntrancedVermin]

So if all the information i gathered is correct D2 needs to be Full annealed according to spec and then i can re-HT, cryo, then temper.

Edit: i appreciate all the help and glad i learned a few things

Thank you!

 

[JTknives]

When i asked about the plasma cutting i meant how does it effect the D2? I have a local guy that does it full time and was wanting to go through him since i wouldn't mess with shipping.

Then why not ask him?
I’m in the business of plasma cutting, heat treating and surface grinding. I am more then willing to Help anyone I can here on the forum with just about anything. But that being said I seem to be less motivated to drive business into the arms of another company. I’m not trying to offend anyone or sound angry. But in all honesty if your going to have someone else plasma cut your blades then I would talk to him. It’s quite a bit different then cutting mild steel sign art.

 

[EntrancedVermin]

Then why not ask him?
I’m in the business of plasma cutting, heat treating and surface grinding. I am more then willing to Help anyone I can here on the forum with just about anything. But that being said I seem to be less motivated to drive business into the arms of another company. I’m not trying to offend anyone or sound angry. But in all honesty if your going to have someone else plasma cut your blades then I would talk to him. It’s quite a bit different then cutting mild steel sign art.

I understand, and I'm not going to get mad at you for it. I did ask him he has never worked with D2. I didn't mean to be rude about it I was just curious if it hardened the area that was cut and if I'd have to grind it off.

Anyway I appreciate all your help and advice.

Edit: I like supporting small local business when I can and if you were local I'd do the same.