Cryo treatment

[Seraphim]

I'm not a mettalurgist, nor a blade forger, but I did have an opportunity to use a cryo treatment for a investigation project here at work (I work at an R&D lab).

Some interesting articles you guys who may actually understand what is being discussed in these papers:

Cryogenic quenching of steel talks about austenite, martensite, etc.


Another one about wear resistance improvement.


Other papers are available on their site. They do $100 per batch for cryo treatment. I'm sure you can fit alot of razors in a batch!

I had thougt cryo was just for stainless (ala Friodurs, etc.) but it looks as if carbon steel would also greatly benefit from this process.

[Russel Baldridge]

I've heard of guys using Dry Ice and Acetone in a metal pan of some sort to simulate the Cryo process. Not sure exactly how cold that gets, but it's supposed to be cold enough to get the benefits.

And it may depend on the type of carbon steel. My understanding is that simple carbon steels do not benefit much form the process, but tool steels might, as they have more alloying agents that could respond positively.

But I haven't spent much time researching it so this is just regurgitation of what I've been told/read.

[Seraphim]

Well, I guess the article did mention that tool steel was used. Very interesting none the less...

Dry ice is -109 degrees F (according to a quick search...). One of the articles mentions cold quenching (about that temp) vs cryo quenching (liquid nitrogen -330 degrees F) having different results.


I'll just stick to making scales and handsanding....

[Mike Blue]

I'm not a mettalurgist, nor a blade forger, but I did have an opportunity to use a cryo treatment for a investigation project here at work (I work at an R&D lab).
...
I had thougt cryo was just for stainless (ala Friodurs, etc.) but it looks as if carbon steel would also greatly benefit from this process.

And a good question too.

To keep things simple, divide steels into two basic types. There are low alloy steels like the 10xx simple steels. There are high alloy steels which are more complex mixtures of basic steel plus alloying elements. Stainresistant steels fall into the high alloy category.

If a low alloy steel is heat treated correctly within it's specified parameters, there should be a minimum of retained austenite. If there is an excess of carbon (greater than 0.77%) even low alloy steels may have some retained austenite, but more likely from a poor heat treatment regimen. Essentially this means that all the possible martensite has been converted to the limit of the carbon carrying capacity of the material and what cannot be converted during the quench is leftover as retained austenite. This increases the brittleness of the material because the ideal would be to have only martensite and no retained austenite and then temper the martensite to improve toughness without losing hardness.

Practically all high alloy steels contain retained austenite to some percentage. There are graphs that will predict how much out there.

To convert retained austenite to martensite reducing the temperature will kick the RA over into martensite. This is best accomplished at the same time as the traditional quenching with the metal being in the metastable state during heat treatment. Then immediately tempered to convert the fresh martensite into tempered martensite according to the proper heat treatment regimen. Remember, this requires tempering after cryo, otherwise the untempered martensite is a weak point just waiting to crack.

If cryo is required to improve a low alloy steel, I have questions about the basic heat treatment regimen being used. It just isn't necessary for the most part.

Cryo will improve high alloy steels. It will reduce RA in most steels but I know of some alloys that just refuse to give up RA no matter what. Some of it you just have to live with.

Now, the biggest criticism, that I and a few others have, of this whole process is the not very well hidden conflict of interest. The PhD types who are writing these articles, are also heavily invested in the selling of the process.

And, I know of several folks well experienced in the tool and die industry who say that there is a statistical improvement in cutting ability, but, there may not be any practical recovery of the cost of the treatment in the sale of the product. It's expensive enough to make blades and sell them without adding several hundreds of dollars in equipment and then keeping a rapidly evaporating product contained long enough to be useful, then replacing it every month.

If you want to do it, go for it.

Just my simplified thoughts.

[Seraphim]

Thanks. Interesting stuff!

[JoshEarl]

Mike,

Great stuff. It was really helpful to realize that "stainless" is just another type of high-alloy steel. Demystifies things a bit for me.

What kind of hardness gains are we talking about with cryo treatments? I've heard one point Rockwell C thrown about. That doesn't seem to be worth the cost to me.

Josh

[Russel Baldridge]

Yes, very much appreciated info Mike!

I also remember hearing that the cryo treatment works primarily because of the chromium content in stain resistant steels and tool steels. Can you comment on whether that is accurate or not? Do other alloying elements affect the R.A.?

[Mike Blue]

... I also remember hearing that the cryo treatment works primarily because of the chromium content in stain resistant steels and tool steels. Can you comment on whether that is accurate or not? Do other alloying elements affect the R.A.?

There have been any number of "articles" published, even one in Blade that purported to show the gains made. I'm not going to try to recite all the factors since they are readily available on the net.

But, tungsten, cobalt, molybdenum and vanadium are the major players after chromium. Probably more of an effect is the hypereuctectoid steel referring to excess carbon, and that does not require alloying elements. If there is excess carbon you will get retained austenite. Martensite has a saturation point. Can't form carbides without carbon. The excess carbon become available to form T, C, M, W and Chromium carbides and all those individually and collectively have an impact.

Probably more than hardness, the concept of wear resistance is the one more influenced by cryo treatments.