Super duper CPM-s3v heat treatment recipe?

www.pdhonline.com/courses/m461/m461content.pdf
Add this one also.
Finally we're getting good scientific info about this mysterious 'cryogenic ' stuff!!! I spent many many hours searching and now we can better understand [at least we metallurgists can].. Much of the cryo papers involve wear .Note the change in wear resistance for CPM-10V !! Some of you are using that . Understand that the tempering is not the same as typical tempering. Note also that the -300 F does not do anything for the extra wear resistance for more martensite , only the eta carbides do !! Don't look for them unless you have a 20,000 X microscope ! Good things come in small packages .
Ask your questions !
 
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Mete: are you saying 0.12 hrs as in 7.2 minutes at -300ºF?..... or perhaps 12 hrs? When cryo'ing is there any problem with too long?
 
Willie71 said:
The temp in the chamber is all below the conversion end point (Mf). With the majority of the blade in the LN, you are fine. As long as you still have LN in the tank, you will reach Mf, even if the blade isn't in the liquid.
Click to expand...

A couple of questions here for clarification please.

1. Are you saying the vapor area above the liquid nitrogen is below -300ºF? LN is -321ºF.

2. Are you saying with only the majority of blade (cutting part of blade, not including tang) in LN it's just fine? I would have thought total blade with perhaps at least an inch of tang would need to be submerged in LN. Not part of blade in LN, and part of blade in LN vapor.

Thanks to all for any clarification.

Ken H>
 
for me the 12 hours is more due to the time of HT i do it in the afternoon/evening then till the kiln cools its really just easier to put the blades in over night let the kiln cool slowly and wake up in the morning and start tempering
as for temps in the LNtank i dont know for sure but with the Ln at -300 the inside of the chamber only needs to be colderr then -100 for MF
 
Yes, you're right, for Mf -100ºF is all that's required which I get with Dry Ice. It was the eta carbides that I was thinking when reading Willie's post. Not sure if he was thinking Mf, or ETA.
 
Do you really believe a 400% increase in wear resistance with 52100 simply because of eta carbide formation? I take that to mean that it would take 4 times the effort to sand that steel simply because it was cryoed. I have a hard time believing that. Not challenging anyone, least of all, you, Mete! Your input is always appreciated. I've seen that same chart, or similar anyway, about the increase in wear resistance due to cryo treatment, and the cause of that being eta carbide precip. I do indeed have a hard time believing that eta carbides will give a 400% increase in actual wear resistance, under the impression that the wear resistance of a steel is directed by primary carbides. (understood we're not talking edge retention, but rather actual wear resistance). Am I wrong in my thinking? I'd gladly admit it! Well, maybe not "gladly"! ...that cryoed 52100 would need 4x the effort to abrade it over non cryoed 52100?
 
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"Under the impression ", we've all been there LOL. Apparently the best part of cryo is with wear resistance . Many tests show similar results .They are done with specific test criteria. It may a bit different when we look for over all knife performance. Misinformation and just plain BS have been common with cryo but now we are seeing science arriving !
 
This is why I've wanted to carefully define things Sub-zero for - 100 F , and Cryogenic cooling -300 F. My posted paper clearly states that dropping to -300F for less RA Does little to add more wear resistance .The wear resistance is there due to the eta carbides !
 
A few years ago, the brother-in-law forged, ground, and hardened an integral from O-1 at my shop.

It was late in the afternoon and he had plans to go out for dinner that Saturday night. He told me he would do a snap temper at 375 in Mama's oven when he got home (half a mile from my shop).

When he got home, his son was there and he just plain forgot about putting that blade in the oven.

Next day after church, he remembered.......... When he looked at the blade, it resembled a road map of Georgia dirt roads. It had self destructed because of stress. He learned a valuable lesson that day.
 
I'm not sure how cold it is in the chamber above the LN, but it's cold enough for full conversion. Whether it's cold enough for the eta carbides would require the proper thermocouple to measure the temp. I'll look into this.
 
I read the paper, very informative. Are eta carbides only formed in the more complex steels or do they form in things like 1095? I can't seem to find any thing as to which alloys or all alloys, etc.

The ultimate question being which alloys see no benefit from cryo because their Mf temperature is above room temp and they don't form eta carbides.
 
Not sure on this but a friend who works with LN every day told me that the vapor above the surface of the liquid is ~-160 F. How about it Andy, you following this thread?
 
That I don't know. But the 'normal' carbide formation is different from the eta situation. Some day soon we'll have the whole story.
 
The only alloy I can recall that benefits more from DI treatment is AEB-L since it does not form eta carbides with an extended cryo soak.
 
Since RA is complete at -100ºF, DI is all that's required for any alloy that does not form ETA carbides. Cyro (-300ºF) does not "hurt", but gives no added benefit... That's my understanding anyway. Only alloy that will form ETA carbides will benefit from Cyro (-300ºF).

Mete - please correct if the above info is not correct.

Ken H>
 
Ken , yes and some of the papers clearly say that the benefit for wear is not less RA but only but is due to ETA.
The CTP website is very interesting as it gives applications , history etc. Cryo is a whole new field.
 
Mete: Thanks for confirming. Now, is there a list of alloys that do form ETA carbides with Cyro? What about AEB-L? In an earlier post it was stated AEB-L didn't form ETA carbides - if not, Cyro is the same benefit as Dry Ice treatment.
 
This is indeed confusing to me, and apparently I'm not the only one. I thought (under the impression again!) that if a steel has alloying (most do, but 1084/1095/White not so much), it will form eta carbides with an LN2 soak/temper. It may the case that some data on AEB-L says LN2 is not needed with AEB-L, but I would expect that statement based solely upon Mf completion, which AEB-L has most of it's RA taken care of with sub zero ~ -100F, and not have anything to do with eta carbide precip/wear increase.
 
Well, I'm looking for advice from anyone who can give it. What type of sensor is needed to measure temps that cold? I looked through auberins and did some google searching, but came up blank.
 
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