Heat treating CPM 3V to 63 rc

cotdt

cotdt

Joined
Oct 2, 2006
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How would the following work to get 63 rc?

Austenize 2050F 20 minutes in electric oven
Air/plate quench to room temperature
Cryo in liquid nitrogen, soak until bedtime
Temper @ 400F before going to bed, knife should be ready when I wake up
Sharpen knife
Baton it through a concrete block to check for toughness
 
If you have the plates, just plate quench it and be done with it. There's no need to air quench unless you're worried about having to fix some warp in the blade. Your knife needs at leat one temper before and at least one temper after cryo. 63RC is the top end of the steel and it's noted that it may only reach 61 or 62RC with air quenching. Plates are the only way you're going to get it that high without oil.

I'm not sure what you want to keep the AQ hardness for. I would go with the recommended heat treating and temper at 1000-1050F. No reason you can't start at 1000F and work up to 1050 if you don't like the values you're getting. Note that the hardness drops off quickly between 1025 and 1050, so I would work up to it unless you know 100% that your oven is holding the temps within a few degrees. Note also that cryo will probably be far less beneficial in the high tempering range.

No matter what tempering range you use, you'll need to temper three times, not once for a very long time. I don't know anyone who would leave their oven running unattended overnight anyways...
 
for 3v you only need that snap temper is you feel like it
when i run it its quenched then into LN over night, temper in the morning at 400F

i have tested more then a few blades dont this way to make sure that the 1000F was not needed

now that said other then 400+or- i have no clue how it might act i have only treated blades at 1000 and 400
 
AcridSaint said:
Your knife needs at leat one temper before and at least one temper after cryo.
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Whats the reason for this? Everyone Ive spoken to about cryo says to do it after quenching then slowly ramp to ambient for beginning the tempering cycles. I realise this doesnt necessarily make it the best way so perhaps you could explain your ideas for doing it like you do.
 
Tempering before cryo is recommended to reduce the chance of cracking your blade. Going straight into cryo increases the likelyhood of a cracked or distorted part (in this case your knife). All recommended heat treating practices that I am aware of suggest immediate tempering as soon as the work is hand cool, this reduces the risk of the piece cracking or distorting at ambient temperature, introducing an extreme temperature drop only increases this risk. Additionally, since the steel must be tempered thrice, I see no reason to not temper before cryo.

For what it's worth, none of my data on 3V shows any cryo benefit, this is because the recommended heat treating practice is to use high heat tempering. Tempering in the ~1000F range greatly reduces retained austenite, possibly more than cryo treatment and low heat tempering. I don't have any micrographs or studies to back up my belief on this point, however, so please take it as merely speculation or a very slightly educated guess.

If one wanted to keep AQ hardness at a high heat temper, they could go to 950F, although I really don't see the point.
 
For the nervous types you can 'snap temper' at 300 F before cryo.
In general 1000 F temper will remove RA so no real need for cryo.
Jerry Hossom's experiments with 3V showed a benefit to a 950 F temper .He also uses cryo. This was done with Paul Bos.
 
Thanks everyone! So according to butcher_block and mete, I should try:

Austenize 2050F 20 minutes in electric oven
Plate quench to room temperature
Snap temper at 300F
Cryo in liquid nitrogen, soak arbitrary amount of time
Triple temper @ 950F, 2 hours each temper
Sharpen knife
Baton it through a concrete block to check for toughness

How does this work?
 
The Bos/Hossom receipe - 1975 F 15 min, Plate quench, snap 375, cryo, 950 F 2x2, 10 min FeCl [better corrosion resistance]
 
isnt heat treat fun
BTW every ones kiln will likely read a bit different temps and depending on how you have you blades in the kiln :)
i have figgered that my kiln temp is about 25 f cooler then the readout has it listed at so im guessing that im more like 2025F

this is one of those thinkgs you really get to play with so have fun testing what works best for you
 
cotdt you might also consider a stress relief cycle before quenching given the compression/tension stresses that occur in grinding. I dont know if this material will respond to efforts of refining grain size but that's worth exploring as well IMHO.
 
Mete what kind of hardness should you expect after quench using that receipe? We are having hard time getting it to just 60 and we are quenching it between two 2" thick aluminum plates. When tempered at 950 after the second time the hardness had dropped to 55.
 
what kind of toughness are you expecting at 63 Rc? Doesn't 3V go from 85 lbs to 40 when you increase hardness from 58 to 60?
 
hardheart said:
what kind of toughness are you expecting at 63 Rc? Doesn't 3V go from 85 lbs to 40 when you increase hardness from 58 to 60?
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Crucible lists 3V impact toughness as 40 ft-lb at 62 rc. For comparison, steels like D2/S30V/154CM are 20 ft-lb at 60 rc. So 3V is harder and tougher at the same time.

Actually in my experience with M2 and 1095, even if you harden it to 64-65 rc, and its "through the grain" impact toughness measures lower than the stainless steels, the edge itself is still significantly more chip resistant. It doesn't matter what the charts say, at the knife edge, carbon steels simply win in actual use. Can take thinner edges and still be more chip resistant.
 
ok, I just figured with that kind of drop, you might as well use M4 to get similar rockwell & charpy numbers
 
hardheart said:
ok, I just figured with that kind of drop, you might as well use M4 to get similar rockwell & charpy numbers
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Thanks, I do plan on using M4, but I want to get some 3V in before Crucible closes down. Mainly because I already have 3 knives in CPM M4, and want to try 3V.
 
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cotdt said:
Can you give us a link? Thanks. I am interested in this steel because it is a lot cheaper than CPM M4.
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Buy in bulk. It's cheaper no matter what steel you buy. The site is down but once it goes back up just look in the steel forum and there is a sticky on CPM3V which incudes a brief discusion on HT. Jerry HT's his fixed blades to 61 and swords to 58-59 IIRC....
 
Murdok72605 said:
Buy in bulk. It's cheaper no matter what steel you buy.
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We would need a group buy to buy in bulk. I don't think a hobby knifemaker like me would be able to use so much steel.

Well, CPM 3V is 40% cheaper than CPM M4 even if you do buy in bulk.
 
I really don't understand the hangup on HRC. It's only one value and most useful to tell you if you're heat treating the steel correctly. There have been many many knives made for many many years that would RC in the low 50's and were still thought to be "good". CPM3V in the low 50's would probably be "better" than many of those old knives. What are you getting with the extra 1-3 points of hardness?

You're approaching file hardness at 63. Why would one strive to get "better than average steel" results with a steel that can perform exceptionally just to get a couple rockwell points?

Maybe you're onto something, but the only real way to find out would be to do several at different hardnesses (and many blades in each hardness/heat treat) and put together a standardized testing method to see if full hard 3V performs better than the others in your application. If not, then you'll never really know if you got a better knife, or just a harder one.
 
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