huh, you would think an electron micro-scope would show the difference

1987CR250R said:

There's no what?  Where do you come up with some of this stuff?  J.Y. Huang, et al, disagree with you.

http://en.wikipedia....genic_hardening

1987CR250R said:

That's news to me, they taught us about it in my crystal structures course in college when I got my engineering degree.

grayracer513 said:

You're quoting Wikipedia as a source?

My point is, cryogenic treatment isn't so fully understood as is heat treatment.  The engineering wolrd doesn't like things it doesn't fully understand.  If you burn through ASTM, ASME, SAE, or any other big standards organization, I don't think you'll find a single standard that specifies cryogenic treatment.

1987CR250R said:

It was quick, and the article was cited.  

What have you cited so far?  The concept that ASTM and others haven't established anything for it yet absolutely does not indicate there's no science behind it.

Didn't say no science, I said it's not well understood.

1987CR250R said:

Sorry, I thought you said...

1987CR250R said:

My bad.

"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,© 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."
Cryogenic Institute of New England

Edited by APBT, 02 October 2010 - 06:41 AM.

APBT said:

Carbon in iron and steel alloys doesn't for "diamond".  Carbon crystalizes with the iron to form austenite, martensite, cementite, etc...  In concentrations greater than can be absorbed into the iron it forms cells of graphite.  Graphite is the same stuff found in your pencil lead, hardly wear resistant.  I'm not saying carbon doesn't help the wear resistance, though.  To this day, gray cast iron (a high carbon alloy of iron which has graphite in its microstructure) is still one of the best materials to make cylinder liners out of.  The graphite holds oil well and acts as a lubricant for the cylinder.

We had some stainless steels parts at work that were over processed at heat treat, percipitating carbon out of the structure that came to the surface as Carbide nodes, a VERY hard particle that was causing us issues inside disc drives.  Our PhD metalurgist said that this was a common phenomena that was great for other applications, but bad for ours.  We would have loved it had it been a nice soft particle like graphite.  Carbide percipitating to the surface improves wear characteristics, as APBT stated.

Guys, I cant take credit for any of this info- its a copy/past from the Cryogenic Institute of New England as the last sentence in the post states.

I deal with carbide precipitation in stainless steel a lot.  It's an odd phenomena.  Basically within a certain temperature range, carbon in the steel combines with the chromium element to create chromium carbide.  I don't know this to effect the hardness of the material at all but chromium carbide can't oxidize to from the layer of chromium oxide on the surface of the steel that normally protects the steel from oxidation.  So, stainless steel subjecto to carbide precipitation, such as seen after welding, loses much of its corrosion resistance.  Pickling with acids, electropolishing, or normalizing through post weld heat treatment will restore the corrosion resistance.  Using low carbon modified stainless steels such as 304L or 316L all but prevent this.  Stabilized alloys like 321, 347, and 348 use titanium or other elements to prevent carbide precipitation.

I know that austenitic stainless alloys (anything in the 300 series) are generally not considered heat treatable.  They are, however, precipitation hardenable.  I'm not really sure what this process involves so I can't comment.

I know a V8 race engine builder that gave up on internal parts coatings in the mid 90's because the expense just added to the pain after a blowup and it all went in the bin.

Micropolished gears removes the surface condition that holds the oil film but it looks fast.

Tom68 said:

On the polished note.  Surface finish (especially towards the root of the tooth) has a significant effect on gear life.  AGMA (American Gear Manufacturer's Association) has some equations that relate characteristics of the gear to the stresses it can handle based on the material.  A hobbed gear (relatively rough finsih and the most likely finish seen on a dirt bike transmission) may see a stress multiplier 2-3x times higher than that seen on a precision ground gear depending on the speed the gear operates at.  Basically, at a given speed, a ground gear can tolerate 2-3x the load and still provide the same reliability and lifetime to failure as a shaped gear.

Edited by 1987CR250R, 04 October 2010 - 08:33 PM.

I did ceramic piston top on a round the world tour guys 640 in an effort to reduce combustion heat transfer to oil (bike is now on a boat as part of its last link, abt 20,000 miles with days of 8,000 RPM all day)
Also built a couple of Rally motors same deal

Tom68 said:

I could not disagree more with this final statement.

Superfinished gears have serious benifits from a reliability standpoint and is directly related to it's influence upon lubrication.

harrperf said:

This is especially true with respect to the reduction of stress risers, and especially at the base of the tooth.  

In theory, you could polish something so smooth that there would be no asperities in the surface for boundary lubricants to be impacted into, but boundary lubricants are only necessary in the absence of an oil film, and the oil film is not dependent on surface asperities.  In practice, surfaces can't really be polished quite that smoothly.

So how would a cryogenic treatment to a crank on say my crf250r increase reliability

Did some off-site reading where a guy racing RD350s had very good results with thermal barrier coating on the top of the piston. His theory was that keeping heat out of the piston helped it live longer, plus reduced the pre-heating of the charge in the crankcase, hence denser charge entering the cylinder. He needed a three-layer coating with a 0.020" buildup to get the results and maintain adhesion with thermal expansion of the piston. That was in the '80s, and I assume coatings have come a long way in 25 years.

Interesting comments here from HarrPerf. Can you elaborate on what kinds of coatings and where/how applied and tested?

Well I was trying to find a circle track article where they threw the swaintech book at a motor i found this

Coatings How much thermal coatings increase power depends on how well a motor is designed and built. "In all the testing we've done on our Pro Stock and Comp Eliminator engines, coating the piston crowns and combustion chambers has not proven to be worth lots of power, maybe 6-8 hp at most," Darin explains. "However, on an inefficient engine where thermal efficiency is lacking due to poor chamber design, cam selection, or poor inlet charge mixture motion, coatings can help quite a bit and give you 12-15 hp." In other words, a poorly designed motor--one with too much cam or too much port cross-sectional area--stands to benefit more from coatings than a properly built motor. There is a big difference between thermal coatings and lubricity coatings. "The Casidium coatings we use on our bearing and wrist pins have really saved us, and we put that stuff on everything. They let you get away with running half the oil that you ran before and allow tightening up the ring package as well.
http://www.chevyhipe...ps/viewall.html