[Diy_efi] cryogenic tempering?

[Jay Wallace]

At 10:53 AM 30-09-05, you wrote:
>http://www.kfor.com/Global/story.asp?s=3390503
>
>Any materials experts want to weigh in on this?  Maybe it increases
>durability but how could it affect mileage?


Methinks that I detect the strong odor of the dreaded 'technobabble' - and 
probably a lot of wishful (self serving) thinking / data. See technical 
info below if you are really interested or just plain bored. Bottom line: 
While cryogenic treatment has been shown to be worthwhile in some 
instances, particularly, where wear is involved and depending on the metal 
being treated, it is very difficult to believe that cryogenic treatment 
itself could reduce LUBRICATED friction in an engine enough to decrease 
fuel consumption by more than half. For me, I'll file this one along with 
the magnet that clamps over the fuel line and doubles the horsepower - and 
gives you shiny teeth and a brighter smile.

Jay

Technical stuff:

For my own information I looked up "cryogenic" in the ASM Metals handbook. 
Volume 1 (Iron and Steel) and Volume 2 (other metals) There was no mention 
of cryogenic other than mechanical behavior (yield stress, elongation, etc) 
of aluminum alloys tested at low temperatures. Volume 4 (Heat Treating) had 
several pages on cryogenic treatment of steels (not cast iron or aluminum). 
Several references and studies were quoted, but the final (skeptical) word 
was:

"Many other case studies with varying results appear in technical journals 
and engineering publications. The variability of the results listed in 
these articles does not disprove the effectiveness of cryogenic treatment; 
however, it does provide a cautionary note to anyone considering cryogenic 
treatment. The need for study of any potential application should be 
apparent, and a careful technical and cost-effectiveness analysis should be 
made before embarking on such a program."


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Further metallurgy - only for those seriously bored.

Metals are (usually) alloys and are (almost always) crystalline, but all 
metals do NOT react the same to heat treatment. Heat treatments (at 
elevated temperatures) are to increase atomic mobility to allow other 
phases to precipitate out / grow (the temper part of quenching and 
tempering treatment) or to allow strains to relieve themselves (stress 
relief anneal). There can also be "recrystallization" of cold worked metals 
that does result in grain refinement, but this also occurs by nucleation 
and growth of new grains at elevated temperatures. Cooling the material 
+decreases+ the diffusion rate and usually locks in the present structure, 
even if a phase boundary is crossed. The one important exception is in 
higher alloy steels that are quenched from high temperatures and contain a 
large amount of the high temperature phase (austenite) This phase can 
transform by a diffusionless (martensitic) phase transformation under the 
appropriate conditions on cooling, producing a hard (wear resistant), 
brittle phase, "martensite". This martensitic phase transformation does NOT 
occur in aluminum alloys and it is hard to believe that there is much 
retained austenite in typical cast iron or steel alloys.

If you are interested in basic materials science, a good place to start is 
a book by Van Vlack titled Elements of Materials Science and Engineering. 
There is a chapter "Multiphase Materials: Thermal Processing" that gives 
many of the basics. Be prepared to learn about phase equilibria, crystal 
structure, ttt diagrams, etc.