Tempering cpm 3v

[William2112]

The other night I heat treated 4 blades Im working on. The material is cpm 3v . The procedure I used was I brought them up to 1500F and let equalize for 15 minutes. Fast ramped up to 1975F for 35 minutes. Plate quenched between two 1 inch thick aluminum plates until I was able to touch them. I then snap tempered them at 300F for an hour. Let them cool to room temp and cryo treated them in dry ice and kerosene over night. The tempering temps that Ive been seeing on here for cpm 3v range anywhere from 400F to over 1000F. That seems like a huge range to me. Can anyone please clarify or help explain why there is such a variation in tempering temps. Any insight would be greatly appreciated.

 

[PEU]

I recently did exactly as Crucible recommends:

Recommended Heat Treatment:
For the best combination of toughness and wear resistance, austenitize at 1950°F (1065°C), hold 30-45 minutes, and quench.
Temper 3 times at 1000°F (540°C).
Aim hardness: HRC 58-60

And got 58-59RC on my hardness tester testing about 10 times on the tang.


Pablo

 

[jdm61]

I would try to find some cryo information for 3V. According to all that I have been told, the low temperature temper on those high alloy steels works effectively ONLY if you got the blade cold enough to convert most of the RA. Some steels, like Elmax require liquid nitrogen as dry ice and acetone or kerosene don't get cold enough.

 

[aarongough]

So in terms of terminology it's important to restate that:

Cryo = Liquid Nitrogren
Sub zero quench = Dry ice

Lower temperature tempers (ie: 400ºF) should only be use on 3V when cryo or sub zero treatment has been used. I don't like 3V personally when it's tempered at 1000ºF because I find that the edge tends to deform more easily than it should. I've heard from sources that I trust that sub-zero/cryo in combination with a 400ºF temper vastly improves the edge stability of 3V though I haven't tried it personally. I would test with a test blade first though of course.

Do not snap temper your blades before cryo/sub-zero. Doing so will stabilize a bunch of the retained austenite.

Also soak time is not needed when doing a sub-zero quench. The blade just has to come down to the temperature and it's done. 30-60 minutes should be more than enough to ensure the blade reaches the temperature of the bath.

Long soaks can be used with Cryo but doing so has a different goal. A short cryo/sub-zero quench right after the main quench helps to convert retained austenite to untempered martensite. Long soak times of 12+ hours in liquid nitrogen can also produce secondary carbides called ETA carbides. This does not occur with dru ice regardless of time! Whether you want to do this or not when using liquid nitrogen is likely a judgement call (and would require testing) as usually increasing carbide volume will decrease toughness.

My recommendations for a test heat-treat:
Austenitize 1975ºF for 35 minutes
Plate quench
Straight into cryo or sub-zero quench for 60 minutes
Temper 400ºF for 2 hours, 2-3 times.

Also I would strongly recommend making sure that you know exactly what you're planning to do before you do your heat-treat. Letting the blades sit around between the quench and the temper will allow retained austenite to stabilize. Allowing a completely untempered blade to sit around can see the blade spontaneously crack (though this is less likely with a deep hardening steel like 3V).

It's best overall to keep the heat-treat process flowing immediately from one step to the other as most of these processes are time sensitive.

Hope that's helpful!

 

[Nathan the Machinist]

To reiterate, the 400 degree temper is a tweak for better edge stability for cutlery applications, but it needs cryo as a part of the quench or it doesn't work.

 

[aarongough]

To reiterate, the 400 degree temper is a tweak for better edge stability for cutlery applications, but it needs cryo as a part of the quench or it doesn't work.

Nathan do you use LN for your low temperature treatments? Have you tried a 400ºF temper with dry ice instead of LN?

 

[Nathan the Machinist]

Nathan do you use LN for your low temperature treatments? Have you tried a 400ºF temper with dry ice instead of LN?

No

Yes

I use dry ice here for heat treat in my shop, but when I have it done at Peter's they use LN.

They do not dunk directly into LN. I don't know if that would be a good idea with an untempered blade.

Peter's runs my protocols and I've run experiments with their setup.

I might get a little better heat treat response here because I plate quench, which is faster than an atmosphere quench, even though they can do that with several bar of pressure. When I first started having them run stuff for me I had them add sub zero as a part of the quench but the results were not as good as I was getting here with dry ice. I started with them going to -100, then -150, but having them do full cryo as a part of the quench addressed that issue and is probably better than a plate quench with dry ice. Perhaps the quench rate effects temperature you need to quench to. I'm certain it does, a faster quench increase strain energy would effect both % conversion and Mf. But with that said, in the alloys I'm working with, I don't see much difference between the two approaches. The primary benefit to me, using Peter's and their LN setup is less to do with the quality of the HT and more to do with the cleanliness and consistency of their work.

I don't see any difference between the second (full) cryo and without. I know the long duration cryo creates eta carbides that can be demonstrated in a lab to improve abrasion resistance, but I can't see a difference in my testing. I have them include it my HT because it is "scientifically proven" to be beneficial and people want it, and I don't think it hurts anything, but I have looked for and can not see the difference. Apparently it's pretty significant when applied to brake drums.... *shrug*

I think the timing of the steps is more important than -300 vs -100. If Mf is -100, going colder isn't going to do a lot. But any delay in getting there will allow RA to stabilize. At that point, a deep cryo might convert RA, but into what? Martensite? Not necessarily. It's my understanding that converting stabilized RA will include structures like Bainite and regular ferrite/cementite/graphite

 

[aarongough]

No

Yes

I use dry ice here for heat treat in my shop, but when I have it done at Peter's they use LN.

They do not dunk directly into LN. I don't know if that would be a good idea with an untempered blade.

Peter's runs my protocols and I've run experiments with their setup.

I might get a little better heat treat response here because I plate quench, which is faster than an atmosphere quench, even though they can do that with several bar of pressure. When I first started having them run stuff for me I had them add sub zero as a part of the quench but the results were not as good as I was getting here with dry ice. I started with them going to -100, then -150, but having them do full cryo as a part of the quench addressed that issue and is probably better than a plate quench with dry ice. Perhaps the quench rate effects temperature you need to quench to. I'm certain it does, a faster quench increase strain energy would effect both % conversion and Mf. But with that said, in the alloys I'm working with, I don't see much difference between the two approaches. The primary benefit to me, using Peter's and their LN setup is less to do with the quality of the HT and more to do with the cleanliness and consistency of their work.

I don't see any difference between the second (full) cryo and without. I know the long duration cryo creates eta carbides that can be demonstrated in a lab to improve abrasion resistance, but I can't see a difference in my testing. I have them include it my HT because it is "scientifically proven" to be beneficial and people want it, and I don't think it hurts anything, but I have looked for and can not see the difference. Apparently it's pretty significant when applied to brake drums.... *shrug*

I think the timing of the steps is more important than -300 vs -100. If Mf is -100, going colder isn't going to do a lot. But any delay in getting there will allow RA to stabilize. At that point, a deep cryo might convert RA, but into what? Martensite? Not necessarily. It's my understanding that converting stabilized RA will include structures like Bainite and regular ferrite/cementite/graphite

Excellent! Thanks for the detailed response Nathan.

I will be using Dry Ice to do the sub-zero treatments on CPM3V when I do my next round of steel testing, so it's good to know that I should get the right results!

 

[Nathan the Machinist]

Excellent! Thanks for the detailed response Nathan.

I will be using Dry Ice to do the sub-zero treatments on CPM3V when I do my next round of steel testing, so it's good to know that I should get the right results!

I think you will, but I'm not an expert. Test it.

 

[William2112]

Thank you all for your responses! I was a little unclear when i said i heat treated theses blades the "other night". It made it sound like there was a large gap of time between steps. I made sure that the blades did not sit around in between the different steps I used. It was literally no more than a matter of a few minutes from the time I could hold them in my hand until they went into the next step. Im always humbled and amazed by the wealth of information that I find on here. Gough, Im a huge fan of your YouTube videos and i look forward to seeing whatever you post next!

 

[mete]

Let me go back to the beginning !!
Sub-zero , converts RA to martensite.must be then tempered.
Cryo , converts RA to martensite more than sub-zero does
Cryo ALSO changes the lattice making possible the formation of small "eta " carbides upon tempering !! The formation of the eta carbides gives 1-2 HRc points harder and a more wear resistant edge .
A 1000 F temper was developed for dies for the best , most stable dimensionally, HT . For knives best performance is cryo ! I'd like to see tests but I don't think a second or third temper when doing Cryo is going to do anything for you !
So for knives , harden, plate quench, cryo ,temper 400 F. The RA transformation during cryo or sub-zero is a martensitic transformation , that is, fast. In cryo the accompaning tweek of the lattice is slower .It seems that about 6 hours is often used.
Metallurgy is your friend !

 

[PEU]

But for the eta carbides to develop, I read some of the papers you suggested in the other forum, and they said that several hours in LN are needed...


Pablo

 

[mete]

Yes , as I said . However I haven't seen as far as I remember any details of how long to tweek the lattice and how long it takes to form the carbides ! The most common time I've seen is 6 hours total.

Retired I'm "out of the loop " but I still spent many , many hours reading through technical papers to find what I did. If anyone finds details of the process please post them. If you care to experiment please keep carefull records. But the basics are short time for martensite transformation and long time for lattrice change and carbide formation.

 

[aarongough]

Thank you all for your responses! I was a little unclear when i said i heat treated theses blades the "other night". It made it sound like there was a large gap of time between steps. I made sure that the blades did not sit around in between the different steps I used. It was literally no more than a matter of a few minutes from the time I could hold them in my hand until they went into the next step. Im always humbled and amazed by the wealth of information that I find on here. Gough, Im a huge fan of your YouTube videos and i look forward to seeing whatever you post next!

Thanks for watching the videos mate! Glad you like them!

I hope your CPM3V goes well! I'll be doing more testing with 3V and 4V next year, should be fun!

 

[jdm61]

Whereas i have read that to convert RA, you merely need to get to the target temperature and the transformation happens very rapidly.

But for the eta carbides to develop, I read some of the papers you suggested in the other forum, and they said that several hours in LN are needed...


Pablo

 

[aarongough]

Whereas i have read that to convert RA, you merely need to get to the target temperature and the transformation happens very rapidly.

That's correct as I understand it. Soak time is only needed for the formation of ETA carbides which is a slower diffusion process.

To convert RA you're literally 'quenching' at a lower temperature, once you reach that temp the job is done. Same as we don't leave the blade sitting in oil for 24 hrs when we quench

 

[mete]

This seems to be very confusing ! Let me try again !
Martensitic transformations are FAST . Changes in lattice structure are slower as are precipitaion of carbides.
With Cryo when the temperature reaches the Mf the RA is quickly transformed to martensite . Following that , the lattice is tweeked [ don't know how long ].Then when tempering ,the eta carbides precipitate in the spaces produced by the cryo.
If you're still confused please ask questions ! If I could find the tech papers I would surely read them .

 

[Nathan the Machinist]

^ With Cryo when the temperature reaches the Mf the RA is quickly transformed to various structures, including martensite ...

I wanted to clarify this. If Mf is reached as a part of a continuous quench you'll get martensite. However, if cryo is being used to convert old stabilized RA you'll get a mix of stuff, only some of which will be martensite. One important reason to not snap temper in applications where it matters such as knife edges.

 

[jdm61]

The most common target number that I have seen is no more than 5% RA and the common LN2 methods can get you there with any steel that we would ever use. The question becomes which steels can get there using CO2? The guy from B-U who was manning the booth at Blade in 2012 or 2103 said that the typical dry ice and either acetone or kerosene bath comes up up short or high if you will, of the mark for Elmax. It gets down to around -80 F or -62C and Elmax requires- 80C or -112F for maximum transformation. I am not sure about the less finicky PM steels like CST-XHP or lower carbon high alloy stuff like the aforementioned 3V. B-U has been the only company that had a big chart laying out all of those requirements in one place that I have seen. What I have read and been told says that the old school simple stainless stuff like AEB-L is probably going to do just fine with dry ice and I do recall seeing some other more complex stuff that looked like it would be okay at -80C. Then again, I know some people that don't bother to cry0 or even dry ice cold treat crazy high alloy stuff like S110V or M390, but I shan't be doing that anytime soon!!!!

 

[mete]

If you want max performance with these super steels you have to do it right ! Otherwise you're wasting your money.The eta carbide is small and it's benefit is cohesion [straining the matrix around the precipitate particle ] /.