"Cryo" Tempered Razor Blades for Longer Life?? 1

[wdornfeld]

I was web-shopping for cheap Gillette Mach3 razor blades, and ran across the site

http://greatrazors.zoovy.com/category/xx/

that advertises long lasting razor blades that are simply Gillette blades that have been cooled to -300°F for 24 hours (in the original box, no less! Read the site FAQ.)
Question is: Does this make any possible sense metallurgically? TNX

 

[Metalguy]

NickE,
"(all our steel tooling is cryo-treated as part of the heat-treating, likely retained austenite, but does also provide some dimensional stability, I'm still amazed that air-hardening steels will retain austenite thou.)"

Air-hardening steels are slow to transform to martensite, so *they* are the ones most likely to have RA. Anyway, if you have time and want to look up an interesting paper, I recall reading one a few years ago that talked about the *benefits* of having some RA for some cases. Can't remember any details now, but the cry-o-boys probably won't like it!

 

[Frederick]

There are several papers like that. The general theory is that the soft austenite provides a place to blunt cracks that go through the martensitic structure. It is similar to stop drilling a crack.

This is of no concern to cryogenic processors because all evidence shows that there is more than transformation of retained austenite going on. For instance, military spec heat treat on 9310 specifies a cold treatment. This cold treament will reduce the retained austenite to a minimum. Subsequent cryogenic treatment of the cold treated material gave essentially the same retained austenite levels with a substancial increase in the wear resistance. This data is taken form the US Army Aviation and Missile Command study.

If you just cold treat to -150F, you will transform virtually all of the RA that is going to transform. Both research and practical tests show that superior performance is obtained by going down to -300F. It is fair to say that the transformation of retained austenite is not responsible for this increase in performance.

 

[NickE]

Frederick- I apologise for the percieved insult. None was ment. I used the term snake oil incorrectly.

You must admit that the theroy of reduciton of micro cracks in grey irons (A type, class 35-45, mid size distribution) is not really applicable as the graphite flake acts the critical flaw. (I have seen some brake-rotor treating places state this.)

I used the term snake oil to describe a thing that works through an unknown mechanism. I agree that cryo-treatment works, ask my guitar player, the die shop we use, a buddy that races SCCA-club. My difficulty is that I've not seen a good metallurgical description of why. Retained austenite aside (and I'll have to read the references you give above), is there any known 1st principals or [s/p/p] reason for cryo-treatment to have the "incredible" effects that are generally credited?

nick

 

[Frederick]

NickE:
I appreciate your apology, and perhaps I came down a bit hard. It is very frustrating to those of us who are serious about this process to be lumped in with the "get rich quick" people. People who make wild, un-informed claims about "making metal denser", or "enhancing the molecular(!) structure of metals", or whatever have perhaps done irreparable harm to the field of cryogenic processing. Some companies are so paranoid about being scammed that they just will not use anything that has even the hint of taint to it. It is frustrating, because I see companies going broke because they are not competitive, and I have at least an answer to help them, AND THE ONLY WAY TO GET MORE RESEARCH DONE IS TO GET THE PROCESS MORE WIDELY USED SO IT ATTRACTS MORE RESEARCH.

I am not familiar with the theory of micro crack closure. Could you give me reference to go to on this? I would like to read it and also add it to my data base of cryo research.

Putting RA aside, especially since it does not explain why cryo works on copper, aluminum, some plastics, etc. cryogenic processing has been shown by NASA to reduce residual stresses in aluminum welds (Effects of Cryogenic Treatment on the Residual Stress and Mechanical Properies of an Aerospace Aluminum Alloy, Po Chen, Tina Malone, et al, Marshall Space Flight Center). There have been similar findings on steel, but I do not have their reference at hand. This in itself is interesting, though, because we treat a lot of valve springs that have been shot peened to induce compressive residual stresses to enhance fatigue life. We get about triple the life, so if I am reducing the compressive residual stresses, why does it last longer?

But I digress. Collins found the creation of very fine carbide particles. This may have some pinning affect to the crystal structure, but it is not valid for non-ferrous materials, of ferrous materials that lack carbide forming elements.

A common thread that is emerging from the studies that I have read is that something must be happening in the sub-micro structure. Any real theory would have to abandon the RA and eta carbide angle to work on other metals. I have put a theory forward to almost all the cryo researchers that I talk to. It comes out of looking at the metallic bond as if it were a chemical bond. I got this idea from reading some work by Dr. Mark Eberhard (Colorado School of Mines). His work states (as I understand it, as I'm a mechanical engineer, not a trained metallurgist) that for each atom in a crystal structure there is a preferred distance it wants to be from the other atoms in the structure. If it is not at that preferred distance, the structure contains more energy than the preferred state. My THEORY is that as we reduce the temperature of the crystal structure, we reduce the energy available to the atoms to be "out of place". By warming the part back up slowly, we do not put that energy back in, so the crystal structure is more perfect.

Please realize that this is stated in pretty simple, lay-man's terms. I have put this THEORY in front of a lot of metallurgists, and either they were being pretty polite and not laughing out loud, or they really did think that it should be investigated. I invite people to comment on this or other theories. This is the only way that we will be able to direct what few research dollars that are spent on cryo to the best possible experiments.

 

[Metalguy]

Question-what happens to cryo-treated materials if they are allowed to return to room temp. quickly?

 

[NickE]

Frederick- the micro crack reduction is grey irons is bunk. Grey irons gain their attractive properties because the graphite flakes are interconnected and relatively large on the microstructural scale (again A-Type mid sized clas 35-45 irons). These flakes have a severe disadvantage however in that they act as critical flaws in tension. Thus a grey iron piece loaded in tension fails w/ no elongation (to speak of) and catastrophically.

Hmmmm. I'm gonna be back at "my old school" next month, I'll ask a few of my old proffs what they think of the atomic spacing theroy.

FWIW: perfect crystals are amazing, IIRC the UTS of a ideal Fe-xtal is around 600ksi. These xtals dont exist in any but whisker forms. (too many dislocations exist above abs. zero due to thermo/kinetics laws {entropy})

Hmmm. had a thought, entropy is directly related to temperature only, so that cant be changed by a cycle to cryo temps and back since each degreee out (in cooling) has to go back in (during warming). What energy is not going back into the structure during the warmup? (i dont know, time to check the thermo books.)

nick

 

[bahas]

Thanks for all of the information. I am presently researching the profitability of Deep Cryogenics on tool steels for a particular tool and die industry.

Any and all help in resaerch would be appreciated.

Thanks.