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Another PSA: Cryogenics and Cold Treatment

Posted by me2 
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me2
Another PSA: Cryogenics and Cold Treatment
November 10, 2012 01:17PM
There's a lot of bs floating around about this and I figured it warranted another PSA.

First, cryogenics and cold treatment are not the same thing. Cold treatment goes down to about -100 F generally, while cryo goes to liquid nitrogen temperatures or lower, -300 F and down. Cold treatment can be done with dry ice and some solvent or anti-freeze. Cryo is trickier to do at home.

Second, just because someone does a cold treatment or cryo, they are not propping up a bad heat treatment. I see this put forth in some circles and I can't see why anyone would think it's always true, though it can be true. By the same token, a cold/cryo treated blade isn't guaranteed to be a good one.

Some makers find it useful, some don't. High alloy steels benefit more than low alloy or plain carbon steels.

That is all, for now.
Re: Another PSA: Cryogenics and Cold Treatment
November 10, 2012 03:27PM
I have heard the "fixing" argument a few times and it is very curious, all either does is extend the quench as many steels have a Mf point below room temperature. At liquid nitrogen temperatures there are also a different type of precipitate carbide formed which has support for greater wear resistance. However the most beneficial part of any extended quench is just, well, extending the quench and thus increasing martensite formation and reducing retained austenite.
me2
Re: Another PSA: Cryogenics and Cold Treatment
November 10, 2012 04:35PM
Right. However, it gets claims for all sorts of weird things. Increased toughness, higher corrosion resistance, and some other odd ones I can't remember. There is a paper floating around that addresses these widely varying claims and argues that each could be possible, but not all at the same time. It was published from Dublin, Ireland, but I can't remember where I found it. I have a paper copy.
Re: Another PSA: Cryogenics and Cold Treatment
November 10, 2012 09:35PM
My take on CYRO treatments is it's a necessary part of the process to get the very best out of the High Alloy steels, yes it adds two steps to the whole process and expense.

To get the very best blade that is possible the whole process CYRO included needs to be done and done correctly, that's if they want to get the highest performing blade at optimal hardness with min possible issues.
Re: Another PSA: Cryogenics and Cold Treatment
November 11, 2012 02:26AM
Quote
me2
Right. However, it gets claims for all sorts of weird things. Increased toughness, higher corrosion resistance, and some other odd ones I can't remember. There is a paper floating around that addresses these widely varying claims and argues that each could be possible, but not all at the same time.

The problem is that how these are true/false even depends on what they mean as metallurgically they can be measured different ways. For example toughness can mean almost anything depend on who says it, and corrosion resistance to what exactly - salts or acids? At a basic level for example using cold to extend the quench will decrease retained austenite which will lower impact toughness on a gross level (charpy/izod) but it will increase toughness in regards to edge chipping because chunks of retained austenite will vastly reduce edge stability. So does it make the steel tougher or not? And what happens if you decrease the temper draw to equalize the martensite hardness, this is obviously going to increase the toughess - or further still what about if you decrease the soak temp because you know the cold will gain you 1-2 HRC points that you don't need as you are only aiming for 58 HRC anyway?

This is Dozier :

Quote
Dozier
We do not cryogenic treat our blades in this shop and have had maybe, three blades broken in the last ten yrs. At least one was badly abused and would have broken anyway. Some of you guys would break a round iron ball with a rubber hammer.
I had some milling cutters treated about 10 or 12 yrs's ago and could not see any difference in them and have not tried it since.
Cryogenic treating was developed for dimensional stability and nothing else. It completes the martensite tranformation and nothing else. If the heat treat is done proper, there is no use for it. Gun barrels are treated so they will not move later and effect the way they shoot. Austenite becomes stable after a time and will not transform, meaning that it should be done soon after heat treatment and not a yr. later. So there is a large amount of smoke over cryogenics. You do gain a point of hardness with some steels, but this has nothing to do with the final product after tempering, as a proper draw will transform most of the austenite and what is left to change will not make much difference. I understand there are some steels that are improved by this but again most steels if heat treated properly and given the proper draw, do not need this.

If any one feels the need to chalenge this, do so and I will follow up.
Maybe if I cold treated my blades, they would never need sharpening.



You know this can start a riot.

Bob D.

[www.dozierknives.com]


Quote
Ankerson
My take on CYRO treatments is it's a necessary part of the process to get the very best out of the High Alloy steels, yes it adds two steps to the whole process and expense.

Depends on the steel, if they are HSS, then cold treatments will have very little effect as they can not complete martensite transformation due to the extreme stability of austenite with the extreme levels of dissolved alloy, even the simplest of HSS like M2 have to have repeated high tempers instead because of this - it is why they in general make poor knives (relatively speaking) compared to the cold work versions.
Re: Another PSA: Cryogenics and Cold Treatment
November 11, 2012 04:00AM
Quote
CliffStamp


Depends on the steel, if they are HSS, then cold treatments will have very little effect as they can not complete martensite transformation due to the extreme stability of austenite with the extreme levels of dissolved alloy, even the simplest of HSS like M2 have to have repeated high tempers instead because of this - it is why they in general make poor knives (relatively speaking) compared to the cold work versions.


Yeah I know, when I talk about those kinds of steels I am talking about steels like S30V, S90V, S110V, 10V, M390, ELMAX etc.
Re: Another PSA: Cryogenics and Cold Treatment
November 11, 2012 04:08AM
I would bet some of them are being hardened in the secondary cycle as it will maximize wear resistance and it greatly enhances ease of finishing/grinding, especially if they are being ground after HT. All of the ultra-high Vanadium ones are, 10V, etc., I doubt anyone is running low tempers on them for the same reasons. I believe Crucible even directly warns not to temper below 1000F for them.
cKc
Re: Another PSA: Cryogenics and Cold Treatment
November 11, 2012 07:55AM
If anything. A Cryo will probably make a bad HT worse as it could induce even more stress in the steel of you'd buggered it before throwing it down to -85c

I use Cryo on steels where its reccomended. I also use it in some steels where its not reccomended because my personal experience shows a benefit. Can I proove the benefit scientifically? probably not..

O1 is a good example of this.. but the problem is.. It could be the cryo, or it could be the temper.. it could be the combination.. So I cannot definitivaly isolate one..

I do know that when I used to do O1 to 60RC with quench and double temper it seemed fine.. However when moving to 3 Tempers and Cryo, it is most definately easier to grind (even at 62RC) and is more likely to roll rather than snap than when I was just doing 2 tempers.

I cannot say if it is the Cryo, or just the 3rd temper.. And I doubt anyone else can either without studying the steel.. What I do know is that the combination is aboslutely better in the end knife, and the machining, so I just pay double the cost and be done with it. smiling smiley

I know that Bohler claims any steel of 1%C or more becomes a lot finer grained in doing 3 tempers over 2.. so that could be what made it work so well. All my large 60-62RC O1 blades do seem to work well.

Calmax however is pretty simple steel and I just do the 2 tempers with that it it works great.

At the end of the day.. I think testing is most important. I dont care what a maker says they did to a knife, I want to see what the end result knife can do.. thats the real important thing.

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
me2
Re: Another PSA: Cryogenics and Cold Treatment
November 11, 2012 01:24PM
Does Bohler give the mechanism for grain reduction during tempering? AFAIK just tempering will not reduce grain size. Do you mean 3 quenches?
Re: Another PSA: Cryogenics and Cold Treatment
November 11, 2012 06:52PM
The first thing I would ask is what exactly are they referring to when they say the grain of the steel, it can not be for example the austenite grain boundries as they are set in the soak and can not be effected unless that entire cycle is repeated. However during tempering above 200 C then the carbon will come out of solution and form a transition carbide and then further transform to cementite and the austenite will decompose as well, and the martensite itself loses its tetragonality . Depending on what you call grain size these would decrease it.
me2
Re: Another PSA: Cryogenics and Cold Treatment
November 12, 2012 12:12AM
You're starting to sound a little like Tai Goo, just so you know.
Re: Another PSA: Cryogenics and Cold Treatment
November 12, 2012 01:01AM
I channel lots of people, we are anonymous.

Grain size and toughness are two of the most commonly misused terms in discussing knives, they have very clear definitions in metallurgy but for some reason while strength, wear resistance, corrosion resistance, ductility etc. are very well known, those first two can and are used to mean anything under the sun. I have even seen makers claim a steel was "insanely tough" and then after a few exchanges determine that they used a lot of belts to grind it because it was so hard to work. Grain size is usually smeared out over the austenite grain size, the primary carbide size, the primary carbide aggregate, and the martensite size (which is a bit fuzzy in and of itself) - it gets even worse when you are talking about blades with pearlite as what is the grain size of that describing (bainite as well).

In general some people want to be vague as it allows the semblance of science without the liability, a stark contrast to this is a maker like Cashen who will literally drown you in the details if you ask him to define what he means when he says something.
me2
Re: Another PSA: Cryogenics and Cold Treatment
November 12, 2012 03:47AM
Now you sound like me. Scary.
cKc
Re: Another PSA: Cryogenics and Cold Treatment
November 12, 2012 10:46AM
Quote
me2
Does Bohler give the mechanism for grain reduction during tempering? AFAIK just tempering will not reduce grain size. Do you mean 3 quenches?

3 Quenches? no.. 3 tempers.. Of course.. it could be a case that my laymens terms are indicating the wrong way of describing what I mean..

www.uddeholm.com/files/heattreatment-english.pdf

read the sections on tempering and 3rd temper results in the graph.

there was another document, but I'm having trouble finding it. it had photos of the microstructure in 2 or 3 tempers.

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen