Anyone have an engine cryo tempered? what size? where? $$$$$
results?the whole engine? have to disassemble?

What does that mean exactly,when applied to our engines

Ed S

There is also a thread elsewhere on this.

It completes martensitic transformation after heat treatment quench but before temper of highly alloyed steels (crank shaft for example). Martensite is the iron-carbon phase that makes heat treated steel hard. Cryogenics (sub cooling in industrial circles) is most effective in very high alloy steel and completely ineffective in plain or mild steel. It also must be incorporated into the heat treatment process to work.

A properly engineered cryogenic process can enhance the fatigue life of a highly stressed component by a substantial factor. A "lets try it and see what happens" approach will most likely result in no change. The fact that it's popular with hobbyists is that they don't understand the cryogenic process, the mechanisms of metal fatigue, and it seems high-tech.

That's the short story.

I agree completly with ilikeplanes, he's right on. But I would like to add my two cents worth from a reactionary point of view.

Cryo tempering is just a bunch of hype for a model engine. In others words.. a fancy name... possibly to get some money out of you. In this case they are talking about subjecting the parts of an engine to several extreme temperature situations in order to stabilize it structurally. In other words, to normalize it.

High alloy steels are real touchy as far as internal stresses go. This would be a necessary step in the machining of some high allow steel piece with a large variance of sectional dimentions.

In the old days in a machine shop, they would rough machine a piece of metal and then they would nomalize it by throwing it out in the back yard for a few months and let it get wet, cold, hot in the sun, etc. Then they would bring it back in and finish machining it.

The car racing guys would rather have an old used motor block to remachine than a brand new one. If an old one is not available, then they will take a new one and have it normalized first. (possibly have it cryo tempered). If they had the time, they could just throw it out back for a year or two and the weather would do the same thing.

You can temper your new engine yourself by having several short runs that just gets it up to temperature and then let it cool down completely.

Then start all over again. Do this several times. Be sure you check the tightness of all the screws each time.

This is part of a break-in described in Model Airplane News a few months ago.

An old engine that has been run a lot is already tempered about as well as it is going to get. Cryo tempering would be a complete waste of time and money.

Watch yourself

Jim

YES !

Even some of the car people big on exotic processes are moving away from this treatment.

I did a search but didn't see the other thread(s) on this subject

Thanks for all the input though, I was thinking about having one done just as an experiment but I now think I'll take my money elsewhere. Thanks

Personally I see no benefit for model airplane engines. The only things I have seen that cryogenics actually improved is the tone of certain musical instruments (this is highly subjective of course) and the hardness of ferrous parts like crankshafts and brake discs. In auto racing it has been proven that PROPER cryogenic treatment of brake discs will make them last longer. This is very important in 24 hour endurance races. Also, properly treated crankshafts will have bearing journals that resist wear better. As far as actually strengthening or tempering metal the jury is out on that as opinions vary from person to person. The only hard facts that I have read in aviation and machining industry trade magazines point to what "ilikeplanes" said - it completes the martensitic transformation of ferrous metals. Meaning it completes the heat treating process which simply hardens the metal. Might be good for the crankshafts in bushing engines. Who knows?

I could not help giving another lesson:

Basic heat treatment of carbon and alloy steel goes like this:

1) Heat steel to transformation temperature. Usually 1250 degrees F or there abouts. This transforms the steel to what is called the martensite phase.
2) Quench the steel in water, oil, or a special solution at or slightly above room temperature. The fast cooling causes the martensite to be retained at room temperature. The steel at this point is called "as quenched" and will be very hard and brittle.
3) Heat the steel to the tempering temperature (300 to 800 degrees F). This transforms some of the martensite back to ferrite, pearlite, and austenite. The higher the tempering temperature, the less martensite is present and the steel becomes softer.
4) Cool the steel slowly until it reaches room temperature. You now have what is called heat treated, quench and tempered, or hardened steel. It can be up to eight times as strong as plain soft steel.

Here's some other stuff.

*The more carbon and alloy a steel has, the more martensite is transformed at the transformation temperature.
*In general, a hard steel is stronger but less tough than a soft steel. Many exception can be found however.
*Metal fatigue is a very complex science. Many factors play into the fatigue life of a component. Part geometry, material, heat treatment, and load history just to name a few.
*If a component is subjected to high temperatures in service, and that temperature is higher than the original tempering temperature, the service temperature re-tempers the component and causes it to soften. This is one of the reasons you never want to over heat an engine. Not even once.
*Cryogenic treatment occurs between step 2) and 3) above. It is intended to enhance the effects of step 2). The results from this process are VERY sensitive to steel chemistry.

Have fun.

When a ferrus steel is hardened the Martensite and austenite cooling transformation curved lines must cross each other or the metal will not harden. there is one carbon grade of steel that will not harden by heat treat and that is the 1035 grade. Yet 1035 takes kindly to case hardening. It will also work harden somewhat.

To get these curves to cross each other some steels are just air cooled after getting up to the high temperature. Some are quenched in oil, some water, and others are quenched in salt. If you quench an air hardened steel like A2 or D2 into water, it will explode.

After treating a steel to its maximum hardness, it has to be drawn back (they call it tempering) at a lower temperture like in the 300-800 degree range. Some steels like H13 have to be drawn back twice to consistantly be 40 Rockwell all they way through. Some tool steels like L-6 are oil quench types and are tougher than the air hard types. Air hard tool steels will machine very crisp and accurately. D2 will get up around 60 Rockwell when heat treated but must be tempered back down to 55 for punch dies.

After a steel is hardened and tempered it has to be finish ground especially if it is harder than 40 rockwell.

The only place any of this might be effective in a model 2 cycle engine would be the Crank. Yet, I have seen some that appear to be just a better grade of steel like 4140 that is only moderately hard like in the 30 rockwell range. Other cranks look like they were oil quenched, tempered, & finish ground..

In a 4 cycle engine, the tips of the pushrods must be hardened and the valves are often a special steel. At the camshaft the cam and lifters are often made of two different metals. One is generally a little softer than the other.

Enjoy,

Jim

Glad to see other MEs here.
Allow me to make one clarification about the heat treatment process described.

The three steps you described are more specifically termed:
1. solution treatment - in which the metal alloy is heated to above the solvus temperature, the effect of which you correctly described.
2. Quenching - as you decribed.
3. Age hardening - the metal alloy is heated to below the solvus temp and allowed to cool slowly. This process is repeated several times till the desired properties are reached. The end goal is typically for enough pearlite and other softer phases to be transformed into a matrix around pockets of hard martensite. This reduces the brittleness while retaining the strength of the quenched metal.

If all the martensite is allowed to be transform back to pearlite and such, the alloy is in effect annealed, not tempered.

Not all metal alloys are age hardenable. Many Al-Si alloys aren't. And solution treatment and quenching alone (cryogenic or not) may not produce the desired properties for engine components. One needs to know the exact metal alloy content in order to determine the eutectic and solvus temperatures and subsequently prescribe an appropriate heat treatment schedule. A blow torch and a bucket of ice does not tempered metal make.

Also, the cyclic heating and cooling of automobile engines do not get anywhere hot enough to enter the age hardening regime. Tempering engine blocks this way is a common misconception. At most what it will do is relieve some of the localized work hardening and residual stresses from the manufacturering processes.

One method of applying hardenability data is to make an experimental part from a steel for which the end cooled hardenabilty has been determined. A hardness traverse is made from the surface to the center of the part and the measrements obtained are compared to measurements obtained from the end cooled bar. It may be assumed that points of equal hardness will have the same cooling rate and the cooling rate can then be determined at the various points from the surface to the center of the part.

When dealing with IRON there is a chilling process in which carbon is retained in it's combined form in desired areas so that a mottled structure is obtained. To accomplish this cooling is accelerated to the extent normal graphitization does not occur in those areas.
This of course is not the cryogenic processs referred to.


The AGING process Ford employed has been mistermed as Normalizing or Stress relieving at times. The practice was to allow the iron to recover from the casting /quenching process. There is a marked change in physical properties over time ,even at room temperatures.The precipitated change in structure is often submicroscopic. The main benefit is improved structural stability.
The process may be accelerated by heating

I was primarily an EE but next year when I quit my current job I will be working as an ME/EE .

Good job fellas,

Glad to see some good stuff about heat treating here. There's a lot of miss information cast around. I'm glad you got it straightened out.

Jim

w8ye Good job fellas,

Fellas ? Did I say something wrong ?

Wow, good info all the way around. However, I feel the need to go to the Radios forum and spout some highly technical electrical knowlege out just to feel worthy!

My little sister is an ME, maybe I could get her to help spin some of the knowlege in here for her dumb old EE brother!

But seriously, good stuff.