Talk to me about Cryo Treating 1095...

[ARCustomKnives]

I'm fairly new when it comes to heat treating 1095, but I've been getting fairly good results just using my homemade HT oven and pre-warmed veg. oil. That being said, I've read in a handful of threads that 1095 can benefit quite a bit from a cryogenic heat treat.

So I'm curious about a number of things here... and I'm not really even sure where to start, or what questions to ask. I've tried to search various forums for info specific to 1095, but I haven't come up with much.

First, I guess I have some ?'s on cryo treatment in general.... I.E., what is the benefit of Liquid Nitrogen over Dry Ice? Where can I find either?

Is there a set method to cryo treating 1095, or like it's heat treating process, does it vary from maker to maker?

Does anyone know where I can find a tutorial on cryo treating in general? Or is this something that varies from blade steel to blade steel? Any info or resources you guys can share with me would be great...

[DaveL]

I have been looking for an outlet for dry ice, just may not know where to start. Nitrogen, there is an idea but just how

[Woodchuck Forge]

from my research 1095 or any simple carbon steel does not benefit from cryo treatment. It is more for the higher alloy tool steels. If you really want to give it a shot cry ice can be found at many welding shops, butcher shops that specialize in game animals and shipping and also ice cream shops.

[ARCustomKnives]

I guess another question I would have is how do you use the dry ice?
I know I have read about guys mixing it with acetone or alcohol. Is there a ratio I need to follow?
Also, do I simply stick the blade in the ice/aceton solution? Is there a set time it needs to be in there?

[son_of_bluegras]

Research has shown the hypereuctetoid plain carbons steel often have retained austenite when quenched to room temperature. Because of this any hypereuctetoid steel (plain carbon or alloy) and some other alloy steel can benefit from some form of cryo treatment to convert the retained austenite to martensite.
For something like 1095, if memory serves, -40˚ or -50˚ F should convert most of the retained austenite. So dry ice is sufficient for 1095. Some steel require much colder temperatures to get the full effect. Even household freezer temperatures convert some on the retained austenite to martensite and so is of some (though comparatively limited) benefit.

ron

[Woodchuck Forge]

I used dry ice and kerosene. It is not nearly as dangerous as the dry ice and acetone mix. Put 2lbs of dry ice with a small hole cut in the package in enough kerosene to cover your blades. The reason to cut a hole rather than unwrap the dry ice is it will last longer. It should get to about -70f. This should be put into a good Styrofoam cooler. A plastic sided cooler could crack at the extreme cold.

[ARCustomKnives]

Thanks for the input guys.

So let me get this straight...

I heat treat my blades as normal.... quench in my oil, then then when the blade has reached room temperature, I move it immediately to the dry ice mixture?

Then once the blade has had a chance to reach the temp of the dry ice mix, I let it warm back to room temperature and then temper as normal? Or am I missing some steps?

Does the blade have to soak in the dry ice for any length of time?

Thanks for any input guys...

[Ed Caffrey]

As Chuck mentioned, cryo on simple steels is somewhat of a waste. You consume a great deal of time, effort, and materials, and don't get a return on it.

Now, the whole point of cryo is an attempt to eliminate retained austinite in the steel, hopefully changing it to martensite. From the research and experimenting I have conducted, this does not BEGIN until right around -100F or less. If your using dry ice/acetone, your only going to make it around -70 MAX. This might sound coarse, but your wasting your time and materials.

OK, now that I've said that, on to your last post:

then then when the blade has reached room temperature,

I generally wait only until I can handle the blade(s) with my bare hands. THEN I perform a "snap" temper (at least 30mins at 350F). Many times you can "get away with" going straight from the quench to cyro, but with some steels it's risky...an example is 52100....it will often crack if you do not perform a snap temper prior to cryo.

Then once the blade has had a chance to reach the temp of the dry ice mix, I let it warm back to room temperature and then temper as normal?

Yes, BUT let it warm back to room temp slowly. For example, I generally place blades fresh out of cryo between to pieces of Kawool to prevent thermal shock. DO NOT lay freshly cyro blades on anything like a metal bench or other places where they will warm too quickly...and for heaven's sake, DO NOT put them in room temp or warm water! This will generally cause cracks.
Once the blade(s) are back to room temp, you will need to temper them as normal, with the exception that you will likely have to increase the tempering temp 25F higher than you would have done with non-cryo blades of the same material.

Does the blade have to soak in the dry ice for any length of time?

I cannot give you an exact time measurement, but my experience has shown that somewhere between 4-10 hours is necessary, depending on the material and it's dimensions. The individual that does my spectrographing tells me that in his opinion, 6 hours is a "safe" estimate.

[ARCustomKnives]

Thanks Ed... I may hold off on cryo treating until I get some steel that will "greatly" benefit from cryo. I'm just trying to figure out how to get the best possible performance out of my 1095 heat treating process. I at LEAST want to get my hands on some parks #50, rather than the veg. oil I've been using, but I'm having trouble sourcing any near by.

I know Kelly Cupples carries it, but shipping will be about $50, so I may have to wait before I can afford that, but I think it would be a worthwhile investment.

[son_of_bluegras]

I guess the question becomes, how much gain is worth how much time. From my research and the metallurgy texts I've read, 1095 can have up to 15 % retained austenite. It continues to convert as the temperature drops and the Ms finish is between -100 F and -150 F. You will get a bit at higher temperatures and from my reading, house hold freezer temperatures will get you up to 1 point Hrc and going to Ms finish temperatures can get you up to 2 points Hrc. So you have to decide if 1 or 2 points Hrc is worth the effort.
The other part is what happens if you don't do a cryo. In this case the austenite will slowly convert to ferrite and cementite. These structures tend to be weak and or brittle (although the cementite adds to wear resistance) and are generally considered bad in a knife.
A snap temper, from my understanding will start converting the austenite to ferrite and cementite so if you do any tempering between the quench and cryo you won't get as much out of it as if you go straight from quench to cryo. Of course you risk cracks in your blade if you go from quench to cryo.

If you can get a hold of a copy, Verhoeven's text or a good metallurgy text it will explain what happens and at what temperatures.

As to the quench oil, there is a study I read (and I don't remember where I found it) that shows vegetable oils to be faster and with a better cooling curve than petroleum oils. What you get from buying a "quench oil" is some expectation of consistency if you buy another batch of the same oil later and some additives to reduce the chance of flare ups when you quench and additives to prevent the oil from breaking down as fast.

ron

[cappaletti]

If ur looking for liquid nitrogen..it can be obtained from any welding supply house that sells oxygen, acetylene, helium, etc.

[ARCustomKnives]

Originally Posted by cappaletti

If ur looking for liquid nitrogen..it can be obtained from any welding supply house that sells oxygen, acetylene, helium, etc.

Thanks! I will definitely keep that in mind and check it out.

[levensailor.r]

last time I went to HEB they were carrying dry ice....

[Kevin R. Cashen]

Originally Posted by Woodchuck Forge

from my research 1095 or any simple carbon steel does not benefit from cryo treatment. It is more for the higher alloy tool steels. If you really want to give it a shot cry ice can be found at many welding shops, butcher shops that specialize in game animals and shipping and also ice cream shops.

Originally Posted by Ed Caffrey

As Chuck mentioned, cryo on simple steels is somewhat of a waste. You consume a great deal of time, effort, and materials, and don't get a return on it.

Now, the whole point of cryo is an attempt to eliminate retained austinite in the steel, hopefully changing it to martensite. From the research and experimenting I have conducted, this does not BEGIN until right around -100F or less. If your using dry ice/acetone, your only going to make it around -70 MAX. This might sound coarse, but your wasting your time and materials.

I concur with Chuck and Ed, but everybody here is correct, to an extent. Ed often cautions not to take the spec sheets too literally and this can be good advice since much of what is there, and in metallurgy texts, needs to be interpreted and seen in context of the base data used, and here is where the confusion can stem from.

An example that applies directly to this discussion is the differences in I-T curves you can see in many hypereutectoid steels. One curve for 52100 will put Ms at 450F while another will put it at 350F or even lower, leaving you scratching your head until you look for the austenitizing temperature for each chart, and then the light bulb turns on. One can heat simple hypereutectoid steels within a wide range and still not get other problems like grain growth etc..., but for every degree you heat beyond the eutectoid point, you can lower the Mf by saturating the austenite. With this super saturation also comes increases in retained austenite.

So steels like 52100, W1, W2, O-1 and 1095 can have problematic retained austenite, but do not have to have it, and the simplest solution without setting up for cold treatments is to accurately gauge your austenization temperature and keep it rigidly below 1480F.

[son_of_bluegras]

Originally Posted by Kevin R. Cashen

So steels like 52100, W1, W2, O-1 and 1095 can have problematic retained austenite, but do not have to have it, and the simplest solution without setting up for cold treatments is to accurately gauge your austenization temperature and keep it rigidly below 1480F.

That is great if you have the equipment to "keep it rigidly below 1480F". But not all of us have that equipment. I have a pretty primitive set-up and heat treat in a forge using either coal or charcoal with a manual blower for the blast. I doubt I can maintain that temperature with my equipment.

I seem to notice a small improvement by going from quench to household freezer overnight. It may all be in my head, I don't have the equipment to objectively test this either.
I think under these conditions that is not a bad thing.

I thoroughly enjoy these discussions as it keeps my mind open and I often learn something.

ron