Questions about 3v heat treat

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Steve_p

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Apr 9, 2019
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I’ve spent the past several hours reading older threads on this topic and it seems like there are two basic recommendations-

1. 1950f for 20-30 min, plate quench then into LN/dry ice, temper at 400f x3

2. 1950f for 20-30 min, plate quench, temper at 950-1050 x3

the general consensus I saw was use the lower temper with cryo and the higher without cryo. Is this still the standard recommendation?

The higher temper temp is what’s recommend in all the data that I’ve seen, but I’ve read that those numbers apply more to industrial tooling and dies than knife blades.

Being they cryo/sub-zero treatment is of limited benefit for 3v I’m wondering what kind of hardness numbers I would see using the lower temper numbers without cryo? I’d like to get 60-61 HRC if possible.

that I’ll as kind of long winded but I guess the main question is what hardness will I get with a 400f temper and no cryo/sub-zero?
 
1970F 30 min plate quench --> cryo --> temper 400F x 2 = 61HRC

Lower tempering yields better toughness, corrosion resistance, and higher edge stability. Higher tempering yield higher wear and temperature resistance. For knife I would rather stick with low tempering.
 
Nathan Carothers, who is VERY well known for his 3V blades, did some teting a few years back about how to get the most out of 3V, and it seems to apply to most of those type of tool steels. There are some tool steels that are so heavily alloyed that even cryo doesn't convert enough of the retained austenite, and you are left with the only option being to temper in the secondary hardening range (~1000°F). Think Rex "XX" or Maxamet, CPM T15, etc.

shqxk is right. Use the cryo and low temperature temps for better "apex stability". The higher temps in secondary hardeing rob the carbon from the surrounding matrix to form tempering carbudes. While this does increase overall wear resistance, it does so at the cost of toughness, corrosion resistance, and higher edge apex stability.
 
samuraistuart said:
Nathan Carothers, who is VERY well known for his 3V blades, did some teting a few years back about how to get the most out of 3V, and it seems to apply to most of those type of tool steels. There are some tool steels that are so heavily alloyed that even cryo doesn't convert enough of the retained austenite, and you are left with the only option being to temper in the secondary hardening range (~1000°F). Think Rex "XX" or Maxamet, CPM T15, etc.

shqxk is right. Use the cryo and low temperature temps for better "apex stability". The higher temps in secondary hardeing rob the carbon from the surrounding matrix to form tempering carbudes. While this does increase overall wear resistance, it does so at the cost of toughness, corrosion resistance, and higher edge apex stability.
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I have been trying to figure out where the cutoff in alloying is. So far, the only steel not to show an improvement in toughness with cryo/low temper was cast M2, and that was only one sample. (It was the same with either protocol, no better, no worse.) M4 does better with cryo/low temper. Larrin did A11 and k390, and got full conversion with cryo. I just did z-max and got Rc69/70 with cryo/low temper. Rex121 got Rc71 with cryo/low temper. I haven’t seen micrographs comparing them, but that will happen once samples get ground and tested for toughness.

This is the big question still unanswered fully in the testing.
 
Steve_p said:
I’ve spent the past several hours reading older threads on this topic and it seems like there are two basic recommendations-

1. 1950f for 20-30 min, plate quench then into LN/dry ice, temper at 400f x3

2. 1950f for 20-30 min, plate quench, temper at 950-1050 x3

the general consensus I saw was use the lower temper with cryo and the higher without cryo. Is this still the standard recommendation?

The higher temper temp is what’s recommend in all the data that I’ve seen, but I’ve read that those numbers apply more to industrial tooling and dies than knife blades.

Being they cryo/sub-zero treatment is of limited benefit for 3v I’m wondering what kind of hardness numbers I would see using the lower temper numbers without cryo? I’d like to get 60-61 HRC if possible.

that I’ll as kind of long winded but I guess the main question is what hardness will I get with a 400f temper and no cryo/sub-zero?
Click to expand...

If you don’t use cryo, you will get too much retained austenite. You have to use either cryo/low temper, or no cryo/high temper. 3V will be ok with sub zero instead if cryo, but z-wear needs full cryo. I think z-tuff/3v is the Max alloying that sub zero gets full or close to full results. After that, go with full cryo.
 
I was also reading about M4 and how carbide size increases as you get hotter and hotter on the temper.
 
There is no cutoff point based on steel. There's no such thing as steels that "don't need" cryo or steels that "don't benefit" from cryo. There are no steels that "need cryo" while others only need subzero or a freezer. Most of these steels because of their high carbon can be overaustenitized so that they have too much retained austenite. Even with cryo they can be overaustenitized for too much RA.
 
Thanks to everyone for the excellent answers. I was thinking that the low temper made more sense for our applications but wanted to confirm that with people who know more than me.

this forum is an amazing resource for guys like me, and I can’t thank you all enough for readily sharing your knowledge and expertise.
 
Larrin said:
There is no cutoff point based on steel. There's no such thing as steels that "don't need" cryo or steels that "don't benefit" from cryo. There are no steels that "need cryo" while others only need subzero or a freezer. Most of these steels because of their high carbon can be overaustenitized so that they have too much retained austenite. Even with cryo they can be overaustenitized for too much RA.
Click to expand...

this is interesting. So there is no volume of alloying that will prevent LN from getting a full conversion to martensite? I wonder how this myth got started? It’s not the alloying, but the amount of carbon in solution then?
 
Willie71 said:
this is interesting. So there is no volume of alloying that will prevent LN from getting a full conversion to martensite? I wonder how this myth got started? It’s not the alloying, but the amount of carbon in solution then?
Click to expand...
Alloy also contributes to Ms as you can see in the equations in my cryo articles.
 
Willie71 said:
I’ll reread them and see if my understanding is clearer. As long as we get to Mf, with cryo, the amount of alloying is not the main factor then?
Click to expand...
The complicated part is that even when “Mf” is reached there is still RA. The martensite transformation levels off at some temperature and going lower doesn’t transform anymore. The RA stabilizes. That’s why even with cryo you can still overaustenitize, putting too much carbon and alloy in solution.
 
Larrin said:
The complicated part is that even when “Mf” is reached there is still RA. The martensite transformation levels off at some temperature and going lower doesn’t transform anymore. The RA stabilizes. That’s why even with cryo you can still overaustenitize, putting too much carbon and alloy in solution.
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back to school for me. Time to reread.
 
Roman Landes Heat Treatment recomendation

:Now this is what I would recommend for heat treat cpm 3v:


1st preheat: 500-600°C, equalize

2nd preheat:800-900°C, equalize

Autenize: 1060-1070°C, equalize, soak 30-35min

Quench in Oil preheated 60-80°C

Cryo: immediately after cleaning, minimum -80°C or lower soak 30min

1st Temper: 150°C equalize, soak 2hrs, quench in water

Cryo: immediately after temper

2nd Temper: 180-200°C equalize, soak 2hrs

should give you 60+ and a fine durable grain.


RGDS Roman

This is why i would do it like this.


the "receipt" suitable is for a vacuum furnace (Quench with maximum pressure) or a regular cline, but surface protection has to be assured.


Salt bath will cut the soak time appx. by 1/3 and thus give better aus-grain.


The preheating steps will assure the the austenization steps can be done quick. Quicker speed >> smaller grain


Austenization temperature is dedicated to dissolve Chrome and Molybdenum >> fair hardness and some enhanced "Stainresistance" is to be expected.

The vanadium will remain in the steel bond as carbide, hence aus-grain cant really grow


The oil quench is suitable for any steel out of the air hardening classes. The thin cross sections get higher hardness after quench (greater volume fraction of martensite) and a less stabilized volume fraction retained austenite. (The volume fraction of RA can be expected (near guess) between 20 and 30% or even higher)


Warping of the blade shall not be an issue with these materials.

If you have done allot of hard mechanical work before hardening (milling, grinding,)than do a stress relief so warping gets less likely.


The cryo needs to be done as quick as possible below -80°C.

RA tends to stabilize rather quick after the quench (some reports speak of minutes)

The longer you wait, the less efficient the transformation to untempered martensite will be.

And a minimum of -70°C is necessary to get enough stress into the micro structure, so the transformation (RA>>Martensite) process can restart again.

Extensive soak time is not necessary since the process runs at hyper sonic speed.

But still there will be remains of RA that need to be addressed by the 2nd cryo.


The first temper is a low temper so the remaining RA is stabilized at the lowest level possible and at the same time there is enough stress relief in the martensite that has been build and furthermore the transformation from tetragonal to cubic matensite is started.

The water quench speeds the whole thing up and avoids precipitation of embrittleling phases.


Than the rest of the remaining RA will be attacked by the 2nd cryo (usually the RA will drop below 5% volume fraction) so burr formation is less likely.


2nd temper will now temper the untempered martensite build up by the cryo and bring the blade to a fully tempered matensitic structure with a low volume fraction of RA and a fair amount of carbides undissolved.


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

Over engineered is a "German" attitude and makes rockets fly...

Roman Landes
 
What would the second cryo after first temper do? Is there anything to be gained by the extra steps? If so when does it stop improving the blade? Larrin Larrin
 
Storm W said:
What would the second cryo after first temper do? Is there anything to be gained by the extra steps? If so when does it stop improving the blade? Larrin Larrin
Click to expand...
During tempering retained austenite can destabilize and transform to martensite during cooling, having a whole new martensite start and finish to the transformation. So a cryo at a colder temperature can mean more transformation of the destabilized austenite. In a high alloy steel like 3V it would need more temperature than 200C (400F) for the destabilization to occur, however. More like at least 900F. Therefore with low temperature tempering of high alloy steels I recommend a single cryo directly after quenching.
 
If you do not have cryo you should not be using the low-temperature process on 3V. Perhaps you should be using a different alloy.

to answer your question, your hardness values will be okay. But your edge stability will not.
 
Plenty of well know makers do not use cryo and follow the data sheet protocol for 3v and their customers are not complaining but raving. I understand that cryo and low temp tempering can provide a better edge but at a certain point besides the uber knife nerd category the average users will never notice a difference. It seems to be that the vast majority of the general public suck at sharpening knives, they will take a thin geometry knife and will never sharpen it or will sharpen it but with a more obtuse secondary bevel and thus eliminate some of the advantages that a tweaked heat treat can provide. At one point our forefathers used chipped rocks as their cutting tools and they seemed to survive.
 
Seedy Lot said:
Plenty of well know makers do not use cryo and follow the data sheet protocol for 3v and their customers are not complaining but raving. I understand that cryo and low temp tempering can provide a better edge but at a certain point besides the uber knife nerd category the average users will never notice a difference. It seems to be that the vast majority of the general public suck at sharpening knives, they will take a thin geometry knife and will never sharpen it or will sharpen it but with a more obtuse secondary bevel and thus eliminate some of the advantages that a tweaked heat treat can provide. At one point our forefathers used chipped rocks as their cutting tools and they seemed to survive.
Click to expand...
I mean, people buy and use the cheap chinese made dollar store knives all them time anyway, so why even heat treat in the first place? Just get some mild steel and put an edge on it.
People don't come onto forums usually to learn how to do something ok. They want to know how best to do it. The people on here saying low temp with cryo know what they are talking about.
 
Plenty of well-known people do lots of things wrong. Fortunately this creates some low-hanging fruit for folks who want to learn all they can about their craft and do it the best they can.

I think the average user who actually uses their knives would be able to tell the difference between high temp and low temp in normal use, it's pretty obvious. Those who use them to open envelopes and clean their fingernails might not notice.


the average knife that the average person buys at Walmart has so many compromises and areas that could benefit from a little bit more work that high-end custom makers making high-end pieces can truly make a piece that is legitimately better and differentiate their work from lower quality work. But a critical aspect of this is getting the heat treat right. If you're not going to get the heat right, why bother? Sure, you can make a functional knife, but a mediocre functional knife can be purchased at Walmart for 40 bucks.
 
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