CPM 3-V Heat Treat Process Help

S

StevSimm

Joined
Jul 2, 2024
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Hi Everybody,

I'm new to the forum and had a question about the heat treat process for 3-V. I got my first kiln so I am new to this style of heat treating. The process that I've seen a lot is the Bos HT "1975 F for 30 min, rapid air quench, snap temper 400 F for 2 hours, cryo -280 for 10 hours,triple temper 975 F for 3 hours"

I do not understand what the "snap temper" means, and I also do not know at what point the knife has to enter the oven. I've seen people put the blade in at 1500 and rest there for 30 min, then ramp to to 1975, but I've also seen people put the blades in at room temp and ramp all the way to the final soak temp.

I have also seen variations in the tempering, some people go straight from plates to cryo, then 3 (2hr) cycles at 400f, but the Bos calls for a "snap" temper at 400, then cryo, then 3 cycles at 1000.

I'm looking for a 59-60 HRC and optimal wear/strength, Id like the blades to be heavy beating knives.

If somebody can just make more sense of this for me and maybe share a proven recipe that they use, dumbed down a little bit with the parts that I am confused about, I would greatly appreciate it!
 
Preheat your furnace to 1975’ for 30 minutes (at temperature).

Use heat treat foil, wrap blade and double fold the edges.

Place blade in furnace, after rebound, soak at temperature for 30 minutes.

Remove blade from furnace and plate quench or rapid air quench.

Cryo for one hour.

Temper at 400’ 2X for one hour each time.

No need for the upper temper. No need for a snap temper.

Hoss
 
DevinT said:
Preheat your furnace to 1975’ for 30 minutes (at temperature).

Use heat treat foil, wrap blade and double fold the edges.

Place blade in furnace, after rebound, soak at temperature for 30 minutes.

Remove blade from furnace and plate quench or rapid air quench.

Cryo for one hour.

Temper at 400’ 2X for one hour each time.

No need for the upper temper. No need for a snap temper.

Hoss
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So I'm placing the blade in the oven at 1975, then once it's back up to 1975 again start the timer at 30 min.

I stocked up on stainless foil and LN2 for the cryo, so I should be set. I also have a separate oven for the temper.

Thank you for simplifying this for me!
 
The long times in that heat treat protocol suggest it's for large, ~cubic parts. Given this steel was apparently a die steel that would fit, and would explain the high second temper as the focus is probably on toughness.

You want to go straight to the coldest temp after heat treatment (196c in LN2 in this case) to get the most benefit from it. The temper can stabilise the austentite. I'm guessing that for a large industrial die they're willing to sacrifice a little peak hardness to reduce risks of cracking and have the piece in a consistent thermal state before cryogenic treatment.
We're working with thin sections that have less work invested in them, and usually want the extra hardness, so it's better to go straight to the LN2

Dr Larrin Thomas has a write up on this if you want more details: https://knifesteelnerds.com/2025/04/15/cpm-3v-still-the-best-high-toughness-steel/
 
Alex Topfer said:
The long times in that heat treat protocol suggest it's for large, ~cubic parts. Given this steel was apparently a die steel that would fit, and would explain the high second temper as the focus is probably on toughness.

You want to go straight to the coldest temp after heat treatment (196c in LN2 in this case) to get the most benefit from it. The temper can stabilise the austentite. I'm guessing that for a large industrial die they're willing to sacrifice a little peak hardness to reduce risks of cracking and have the piece in a consistent thermal state before cryogenic treatment.
We're working with thin sections that have less work invested in them, and usually want the extra hardness, so it's better to go straight to the LN2

Dr Larrin Thomas has a write up on this if you want more details: https://knifesteelnerds.com/2025/04/15/cpm-3v-still-the-best-high-toughness-steel/
Click to expand...
The item being treated is a 3/16"x3"x16" bowie knife.
 
I meant the 'Bos HT' you were referring to in the first post. Sorry, should have been clearer about that.
Our stuff is a lot flatter, like your bowie. That affects how far the heat has to travel to get out of the part, the centre of yours being only 3/32 inch from a surface
 
say there was a guy who wanted to make himself a couple knives for shits and giggles, and as a result, heat treated them without a cryo quench because there was no LN2 on hand, he was impatient to clear his bench up, and besides one of his knives wouldn't fit in his tiny, stupid dewar. This guy is not too bright, but he does know that getting his knives cold after a plate quench is important and they end up in the freezer. He decides to temper them a couple times at around 400F.

Now, he still has the option of running high temperature temper before he goes and finishes up his knives...

so this theoretical guy might want to know what's going on with his steel on a granular level, option A vs. option B. He also might be thinking to himself that the low temperature temper he used might be leaving him with too much RA, but that the steel might be slightly more corrosion resistant. He might think that a higher temperature temper would minimize his RA and get him some corrosion

I bet he'd love to hear from someone like Larrin Larrin all about these two options. If he were to ask me, I'd send his lazy ass to www.knifesteelnerds.com so he could research it himself, although he might get caught off guard by all the syllables and numbers.

Obviously, this is purely hypothetical. I, personally, would 'probably' never make a knife using this class of steel without cryogenically quenching it.
 
Ah, so with these higher alloy steels the RA can get converted with higher tempering temperatures. So yeah, freezer followed by ~500c is probably better if you lack access to LN2. Might not be the perfect approach, but often you don't have the luxury of chasing perfection

(i don't work with any of these newfangled steels. too much chromium for my tastes :P )
 
Lorien said:
say there was a guy who wanted to make himself a couple knives for shits and giggles, and as a result, heat treated them without a cryo quench because there was no LN2 on hand, he was impatient to clear his bench up, and besides one of his knives wouldn't fit in his tiny, stupid dewar. This guy is not too bright, but he does know that getting his knives cold after a plate quench is important and they end up in the freezer. He decides to temper them a couple times at around 400F.

Now, he still has the option of running high temperature temper before he goes and finishes up his knives...

so this theoretical guy might want to know what's going on with his steel on a granular level, option A vs. option B. He also might be thinking to himself that the low temperature temper he used might be leaving him with too much RA, but that the steel might be slightly more corrosion resistant. He might think that a higher temperature temper would minimize his RA and get him some corrosion

I bet he'd love to hear from someone like Larrin Larrin all about these two options. If he were to ask me, I'd send his lazy ass to www.knifesteelnerds.com so he could research it himself, although he might get caught off guard by all the syllables and numbers.

Obviously, this is purely hypothetical. I, personally, would 'probably' never make a knife using this class of steel without cryogenically quenching it.
Click to expand...
Plenty of 3v knives out there that people love and they are high temper protocol. RA is minimized by secondary carbide formation versus cryo.

For fine edge stability with thin geometry I prefer low temper but plenty of people are happy with high temper and as long as they are happy are they wrong?
 
My understanding is that the upper tempers will give the blade a "little" bit more wear resistance over the lower tempers because of the carbide precipitation. However, the lower tempers will have better "apex stability", especially when lateral forces are applied, because the upper tempers rob a bit of carbon to form those carbides, so the apex suffers strength.
 
very curious to see how the high temper method holds up. Here's what I did;
aust at 1950 for 30 mins, plate quench to cold water to freezer for a couple hours. Two one hour tempers at 400...after some advice from a good friend...three one hour tempers at 975, between which brought to room temp fairly quick in the quench plates.
 
I don’t believe in the theory that high range tempering leads to lower edge strength due to more carbon dissolved from martensite forming secondary carbides.

60HRC steel is 60HRC. It’s the measurement of resistance to deformation no matter what’s the microstructure mechanical behinds that, 60HRC from pure martensite or from strengthening of precipitated carbides are the same.

However, higher range tempering does have more carbides in the microstructure. So the toughness will likely to be lower.

Edge stability is the combination of hardness and toughness so steel with higher toughness at the similar hardness will have better edge stability.
 
shqxk said:
I don’t believe in the theory that high range tempering leads to lower edge strength due to more carbon dissolved from martensite forming secondary carbides.

60HRC steel is 60HRC. It’s the measurement of resistance to deformation no matter what’s the microstructure mechanical behinds that, 60HRC from pure martensite or from strengthening of precipitated carbides are the same.

However, higher range tempering does have more carbides in the microstructure. So the toughness will likely to be lower.

Edge stability is the combination of hardness and toughness so steel with higher toughness at the similar hardness will have better edge stability.
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Have you tested your 60 Rc high temper vs low temper side by side?

Personally I have and I do see a difference in thin edge stability. If your edges are on the thicker side than you might never notice a difference.

Also low temper does provide better corrosion resistance which is also noticeable from my experience.
 
Regarding cryo/low temper vs high temper Cpm3v, in the words of the Master Roman Landes, a PhD metallurgist that even Cliff Stamp respected, "...Of course there is the question why not temper it at 540°C? 1st of all, if you don't have access to cryo than this is your way to go.
In my studies of edge stability a did extensive work to compare secondary hardening and low temper with cryo.
The results (reference is my graduate thesis 1999 Munich University of Applied Sciences) i found considerable higher edge stability with the samples that had low temper/cryo The material used at the time was ATS-34 all with the same charge and thus the same condition of austinization, but with different temper cycles.

RGDS Roman".
 
maybe the only bonus of high temperature tempering is not having to worry much about overheating during sharpening?
 
Lorien said:
maybe the only bonus of high temperature tempering is not having to worry much about overheating during sharpening?
Click to expand...
I still stand by that there are many perfectly fine knives made with a high temper protocol. I used it from 2007-2019. Never had a complaint.

But once I started using low temper cryo there was no other path for me.
 
it's always about doing things the best way that they can be, I definitely agree to that.
CPM 3V has a high quality, somewhat specialized recipe, and is made in the best way known.
although it's always good to shoot for the very best possible, there is a point when you're really splitting hairs.
I'm no expert, but my sense is that 3V ht'd to the data sheet spec is still going to outperform a lot of common options out there by a good margin, for an application where it is meant to excel.

I just finished two knives that I'm keeping for testing, which got 975 degree tempers and no cryo. I can already tell with certainty that corrosion resistance is noticeably worse than low temp/cryo. Seems to be holding up well after a small amount of cutting and chopping. Early days, though. We'll see how she goes.
 
here's a 3V knife with a fairly acute edge geometry and large radius hollow grind. It was tempered at 975 a couple times after going into the freezer apres quench
it's been used quite a lot on much smaller stems/vegetation, and I haven't touched up the edge or cleaned it up more than a couple times. I strop it against the welt of the sheath sometimes, mostly to get the gunk off the edge bevel. It goes straight into the sheath and stays there between uses, regardless of how much water is on the blade- these days it's pretty wet out there, so it definitely is seeing a lot of moisture.
 
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