CPM 3-V Heat Treat Process Help

[StevSimm]

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!

 

[DevinT]

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

 

[StevSimm]

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

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!

 

[Alex Topfer]

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/

 

[StevSimm]

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/

The item being treated is a 3/16"x3"x16" bowie knife.

 

[Alex Topfer]

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

 

[Lorien]

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 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.

 

[Alex Topfer]

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 )

 

[Seedy Lot]

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 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.

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?

 

[Signalprick]

My first couple blades in 3V I was doing the higher temper (900°) 3X's for a 61 rockwell. I switched to what Devin recommended above. I did 2000° for 25 min hold. Plate quench. 1 hour cryo. Temper at 400° 2 x 2hr cycles for a 62 rockwell.

 

[Stuart Davenport Knives]

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.

 

[Lorien]

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.