Home /
T.O.C.
FAQs
 
Good
Books
Ref.
Libr.
Advertise
Here
Help
Wanted
Current
Q&A's
Search 🔍
the Site

World's #1 finishing resource since 1989
No login needed: Chime right in

topic 34078

Cryogenic metal treatment and surface wear?



2005

Considering cryogenic metal treatment,can someone explain to me why the RC hardness doesn't vary during/after treatment, yet the abrasion resistance increases threefold?

thanks.

Bill Cardoza
machinist - Elizabeth, New Jersey


2005

The best explanation I've heard is that after normal heat treating there is still some austenite left in the metal. Essentially, room temperature is not really the end of the heat treat cycle. If you extend the heat treat cycle to cryogenic temperatures, this retained austenite is converted to martensite, and wear resistance goes up, even if the overall hardness of the surface does not increase. One thing to keep in mind, however, is that increased hardness does not always translate into increased wear resistance. Wear resistance depends on other factors, such as frictional forces and the toughness of the surface. Very often making the surface harder reduces its toughness and increases its coefficient of friction, in which case wear resistance goes down.

jim treglio portrait
Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego, California


2005

There are three mechanisms related to cryogenic treatment of steels. The conversion of retained austenite (RA)to martensite is one. This mechanism is important and brings several benefits, including a contribution to increased wear resistance. Additionally, it provides for a more homogeneous grain structure, free of (grain) imperfections and voids, which contributes to enhanced thermal properties, (e.g. better heat dissipation). This is because the imperfections act as points of diffusion, effectively "blocking" or de-grading the thermal properties of the metal at those points.

A second mechanism, even more important to increased wear resistance, is the precipitation of eta-carbides in carbon steels. This has been documented by a team of Japanese researchers in a technical paper presented at ISIJ.

In order to understand its significance, I think that it is important to realize that the introduction of carbon to iron is what fundamentally makes steel. Carbon,(C) a non-metal, is chemically dissolved into iron (Fe). Chemically, the largest amount of carbon that can be dissolved into iron is somewhere around 7%. When people talk about "high carbon" steels -- those that are recognized for their high wear resistance properties -- they are often thinking about Tool Steels that may have somewhere between 0.7% and 1.2% Carbon content. So the point is that a little bit of carbon goes a long way in enhancing the wear resistance of steels.

Remember that Carbon -- AKA diamond --is the hardest element. By chemically blending it with iron (Fe), it effectively protects the iron molecules by providing a tough, highly wear resistant molecularly bonded partner.

On the down side, the more carbon that you add, the less ductile that the metal becomes. You could also say that it becomes more brittle or that it loses toughness (in a machine tool sense). So it is always a balancing act of having high carbon for high wear resistance versus not too much whereas the steel fails due its reduced ductility/ increased brittleness.

The whole point of this discussion is that CARBON is critical to wear resistance in steels. When carbon steels (and cast irons, etc.) undergo a cryogenic treatment, free carbon atoms are able to locate themselves within the chemical lattice of the iron / carbon (Fe-C) matrix in a place where they are more atomically attracted. This modification to the carbon microstructure (technically called "the precipitation of eta-carbides") can vastly improve wear resistance of carbon steels, cast irons, etc. In general terms, the more carbon, the better the effect.

Now, why does this occur? Again, it is all the result of TTT (Time Temperature Transformation)process. When steels are brought to a very low temperature (e.g. -300 F) for extended periods, heat is removed. As a result, molecular activity is reduced -- or molecular movement is minimized. (Remember at theoretical absolute zero, which is about -460 F, there is NO molecular movement.) So as heat comes back into the steel, e.g. as it gradually warms up, kinetic activity (molecular motion) increases and carbon atoms actually "tweak" themselves into a more ideal position within the chemical matrix. In a simply stated version, free carbon atoms are attracted to open spots within the iron matrix. This mechanism, ever so slight, can have big implications on increased wear resistance. It is the mechanism that the Japanese team documented and in my view is the one that is most critical to improving wear resistance in carbon steels.

As a final note, the third mechanism is residual stress relief. Einstein observed that matter is at its most relaxed state when it has the least amount of kinetic energy (or molecular activity). With a proper cryogenic treatment, any metal will be relaxed and residual stresses relieved. It is perhaps the least recognized benefit of cryogenic treatment. Parts that "walk" or "creep" during machining are the result of residual stresses in the metal that have been machined away that were keeping the part in a certain plane. So more and more people are cryogenically stress relieving metal parts to reduce the creep and walk factors that causes parts to go out of round or flat and fail critical tolerances. This is most successfully done after rough cut and before final machining. Again, this can benefit any metal and is unrelated to the other mechanisms cited above.

Robin Rhodes
Worcester, Massachusetts



2005

I would like to know if cryogenic treatments can be used on non-ferrous materials such as copper or noble metals?

Kelly Stinson-Bagby
research - Blacksburg, Virginia


2007

Are there notable benefits to aluminum during the cryogenic process?

Sean Trihey
racing - Phoenix, Arizona


February 7, 2011

yes, cryotreatment can be used on non ferrous metals, even plastics

Robert Wells
- el paso Texas usa



January 19, 2013

Q. I know about the Japanese study about cryogenic treatment on iron and steel but can you find anything about the process on bronze and brass alloys?

Steve Graves
Music Instruments - Cincinnati, Ohio, USA

none
finishing.com is made possible by ...
this text gets replaced with bannerText
spacer gets replaced with bannerImages

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

 
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g, Train'g
& Software


About/Contact    -    Privacy Policy    -    ©1995-2021 finishing.com, Pine Beach, New Jersey, USA