A man at work was talking about aguy he knows who uses dry ice in his tempering process. I have never heard of this or seen it discussed on here. I did some reading on it last night,it's apparently very effective.
I guess you could call it cold treating.

normally heat is used to releive stress in tempering. cold is for hardening. please explain,

Well I was hoping someone else had more iinfo. what I got from the article last night was tools steel will have have an increase of 50% wearabilty. You keep the steel at subfreezing temps for up to 24 hours which does something to the grain structure, and then slowly bring back up to 300 f to aneal.
I'll try and find the link today it's pretty interesting.
I by no means know what I'm talking about.

Some steels (air hardening) can gain hardness from cryo treating. The super cool temps transform the remaining austentite into matensite. At least that's what I've read. Most heat treaters use liquid nitrogen, I did recently run across a book where a maker used dry ice in this process. One maker of L-6 recomended this process, I haven't tried it yet. It would be a good experiment though.

All of my stainless baldes are cryogenically treated. They are taken to -300f for a set time. You may wish to research the tepereature you can obtain from dry ice, and the length of time to hold it at temp. Also you may wish to find where in the heat treat cycle this needs to be done.

Dry ice sublimnates at -78C or -109F, liquid nitrogen is -196C or -321F. There is a considerable difference in cold here. Something else to consider is how cold do you need to achieve. There are specifications for cryogenic treatments, and if you do not take the material cold enough for its chemistry the desired results will not be achieved.

Phil

That is what I meant by the above post Phil!

Mf (the temperature at which all retained austenite is converted to martensite is about -100F for most (all?)
of the knife steels that need this treatment. Thus dry ice should be just barely cold enough for that.
However, liquid nitrogen is more economical for makers that do this frequently because you can keep
a dewar of it for a month or so.

There may be some added benefits to the lower temps of liquid nitrogen but that is more controversial.

Another effect of cryogenic treatment or so I heard is it breaks the crystal boundries in metals reducing it's susceptibility to stress and work hardening. If dry ice is cold enough it might be a lot better for the home shop as it's much safer.

Frosty the Lucky.

Another effect of cryogenic treatment or so I heard is it breaks the crystal boundries in metals reducing it's susceptibility to stress and work hardening. If dry ice is cold enough it might be a lot better for the home shop as it's much safer.

Frosty the Lucky.

Honestly, I think both products have similar safety requirements. I have used both for shrink fits, and lab work. They both are air/oxygen displacing materials as they evaporate, protection against extreme cold is required, in addition to regular PPE.

One is liquid, while the other is solid.

Phil

Honestly, I think both products have similar safety requirements. I have used both for shrink fits, and lab work. They both are air/oxygen displacing materials as they evaporate, protection against extreme cold is required, in addition to regular PPE.

One is liquid, while the other is solid.

Phil

It's the liquid and -300f that's the increased safety hazard. I've picked dry ice up with bare hands without ill effect, not for long. Dry ice doesn't boil either, it sublimes so there's no danger of it splashing or spattering. Air replacement is a hazard though a little less with ni.

Either or are well worth knowing what you're doing if you're going to handle it.

Frosty The Lucky.

since the question was about dry ice in tempering, . I use dry ice and acitone for cryo, to force the conversion of retained austinite, for some of my steels also. but thats not tempering. Hard to get correct answers if mis using tech terms. So I asked what he was talking about. He is honest tho, at least he knows he dont :D

since the question was about dry ice in tempering, . I use dry ice and acitone for cryo, to force the conversion of retained austinite, for some of my steels also. but thats not tempering. Hard to get correct answers if mis using tech terms. So I asked what he was talking about. He is honest tho, at least he knows he dont :D

Dry ice is what a co-workers friend used in "cold" treating his blades, which sparked my interest. I found this this website http://www.nitrofreeze.com/toolsteels.html
In the article it is described as a cryogenic tempering process.
Which terms being miss used? "tempering" I thought had to do with temperature, is it heat specific?

By the way Mr. Sells there was never a question. I had written a post about something new I had learned and hadn't seen discussed here before.

The link above to cryogenic heat treating, may or may not be correct. I don't know enough about it, but considering how poor Mister Lasky's interpretation of the history of iron and steel is I' d have a tendency to take much of what he says with a grain of salt. :ph34r:

After conversion of retained austenite to martensite you have untempered martensite present and you had better repeat your tempering process again!

Dry ice is what a co-workers friend used in "cold" treating his blades, which sparked my interest. I found this this website http://www.nitrofree...toolsteels.html
In the article it is described as a cryogenic tempering process.
Which terms being miss used? "tempering" I thought had to do with temperature, is it heat specific?

Tempering is a controlled softening of steel from it's full hard state. It lessens brittleness and increases toughness, flexibility, resilience, etc. Actually tempering refers to making a material more durable, flexible, etc. than hard as glass and ceramics can be tempered. Annealing softens steel or non-ferrous metals to it's softest state. Normalizing softens metals to near full soft but is used mostly to remove work hardening and stresses during forming.

Frosty The Lucky.

Dry ice is what a co-workers friend used in "cold" treating his blades, which sparked my interest. I found this this website http://www.nitrofree...toolsteels.html
In the article it is described as a cryogenic tempering process.
Which terms being miss used? "tempering" I thought had to do with temperature, is it heat specific?

You must temper the steel after your hardening process Before cryo treating, then temper again. The cryo treat in my experience does several things: it will relieve a little stress, raise the Rockwell hardness# by 1 or 2 points therefore requiring retempering, and refine the internal grain structure of the steel.
This process is not required though and I have heard some outlandish claims as to its effectiveness, but on most "stainless" and air hardening steels it helps a lot. Just my :2cents:

"Tempering" is a very very old word recently re-defined to a tighter meaning.

The original meaning was simply and vaguely "heat treating." About a century ago (give or take) the term "temper" was also used to refer to carbon content.

Nowadays "temper" means "a subcritical heat treatment to improve the toughness of martensitic microstructures by the formation of various distributions of iron and alloy carbides." (Definition paraphrased from George Krauss.)

seen cryo treatment, liquid nitrogen or helium, recommended by Carpenter and Crucible for their "HI TECH" steels, CPM S110V, CPM 3V ,ect...... not the sort of steel we would hand forge. they recommend doing cryo between the first and second temper. Has there been any kind of study as to what cryo treatment would do for more ordinary steel like 1084 or 1095?
scott

If you don't have much retained austentite you don't get much from it; though some folks do it for the "hype".

Experiments on plain carbon steels show no more than a point or so Rc improvement - less than the error range on your average Wilson tester. Still worth it for perfectionists or thrillseekers.

The higher alloy steels will see substantial improvement, as they have lower Mf temps and much more retained austenite.

"Tempering" is a very very old word recently re-defined to a tighter meaning.

The original meaning was simply and vaguely "heat treating." About a century ago (give or take) the term "temper" was also used to refer to carbon content.

Nowadays "temper" means "a subcritical heat treatment to improve the toughness of martensitic microstructures by the formation of various distributions of iron and alloy carbides." (Definition paraphrased from George Krauss.)

Temper has its origin in the old english word Temprian, with the meaning "to modify some excessive quality; to restrain within due limits" Temprian comes from the Latin word Temperare, which means "To mix correctly, moderate, regulate, blend"

Sorry. I've just got an arguing problem :P

Just hit it with a well tempered clavier and get on to forging!

Retained austenite will transform to martensite duriIng the tempering process. That is why many steels require double tempering. If you temper BEFORE you cryo treat, you do not get full effect. Lightly temper, cryo, final temper.