[Tom McQueen]

Looks like I will build up the new engine early next year. I would like to get my IA block seasoned (multiple thermal cycles). I figure if I heat it to 250 degrees for an hour and then allow it to cool to ambient a couple dozen times, that should do it. If anyone has any specific knowledge/experience with this process, Id appreciate your insight.

[Tom McQueen]

Looks like I will build up the new engine early next year. I would like to get my IA block seasoned (multiple thermal cycles). I figure if I heat it to 250 degrees for an hour and then allow it to cool to ambient a couple dozen times, that should do it. If anyone has any specific knowledge/experience with this process, Id appreciate your insight.

[Vascar]

Cryo the block and then go to town on it. When you cryo it the block will be as good as any seasoned block. Good luck

[KEV]

Hey Tom! Why do you feel it is necessary to season the block? What do you gain by doing this? I have never heard of this before, just curious what this does.

Thanks,

[Tom McQueen]

Kev.... Im no expert in metals, but after a certain number of thermal cycles (heating and cooling) the newly formed cast iron relaxes into its final shape. The movement we are talking about is not much, but its enough to be concerned about.

Vascar....I have no experience with the cryogenic process. No idea if theres even a local company doing it. Ill check it out.

[Vascar]

You will have a fully stress relieved block as well.. Cryoing is the best thing you can do to it.

[Scott Misus]

What about heat treating, and a process called "Metallaxing?" Anybody know anything about this?

[LarryF]

Tom, the first thing you should do is talk to Indian Adventures to see what they recommend.

When you "season" the block, all you are doing is stress relieving it. Like all metallurgical processes, the time depends on temperature. Higher temperature will work more quickly, but there is a limit so you don't cause any damage or drastically change the microstructure. 250 F is too low - it would literally take months or even years at that temperature to have any effect.

To properly stress relieve gray iron (and do it in a practical amount of time), the temperature needs to be somewhere in the neighborhood of 1000 degrees F, depending on exactly which alloy it is. Needless to say, this can't be accomplished in your kitchen oven. After this, the block will have to be completely remachined.

Depending on how they process the raw casting, it may not need to be stress relieved. If it is cooled in the mold, it will probably already be just about free of stresses.

Cryo treating has it's place, but it seems to be advertised as a one-size-fits-all process. It has been used for years to complete the hardening cycle on heat treated alloy steels, but I have yet to see any evidence or explanation of what it is supposed to do to non-martensitic (hardened steel) metals. Several metals, such as 304 stainless steel, aluminum and copper are commonly used at cryogenic temperatures because there is no change in microstructure at these temperatures. This contradicts what some of the cryo treating companies claim, since something has to change to reduce stress or change properties.



------------------
Larry

'63 421SD LeMans...
in pieces in my garage
and basement

[Steve C.]

300 Below Cryogenic Tempering Service Inc.
www.300below.com or 217-423-3070

[Floyd Hand]

See March 2001 issue of CAR CRAFT, page 50. Stress-Relieving: Pro Engine Builders" Best Kept Secret

[LarryF]

From 300 Below's own website: "Cryogenic Processing is not a substitute for heat treatment, it is rather, an extension of the heating/quenching/tempering cycle and continues the transformation whereby greater amounts of retained austenite are decomposed, martensite is increased and material attains more uniform hardness".

You aren't going to find any retained austenite in a gray iron engine block. Like they say in the website, the primary use of cryo treatment is for tool steels and other highly alloyed steels, which can have a significant amount of retained austenite after the hardening heat treatment. The extremely low temperature of the cryo treatment increases the driving force for austenite to transform to martensite, which is the hard/high strength microstructure of steel (austenite is soft). The last step is tempering, which restores some ductitily and toughness to the otherwise brittle martensitic structure.

Also note that there is probably a big difference in processing between a low volume IA block casting and a high production casting where they need to make as many in a given time as possible. The production blocks would probably be removed from the mold as soon as they were solidifed, so they would cool more quickly leaving residual stress in the casting.



------------------
Larry

'63 421SD LeMans...
in pieces in my garage
and basement

[Wade Congdon]

Not that Larry needs anyone to add credibility to his statements, but he is absolutely correct. Metallurgical phase diagrams are an excellent visual aid to analyze this process. (Stared at way too many in college) Many people think that cryo treatment allows the molecules to pack closer together increasing strength and hardness, this is not the case. As Larry stated it allows more martensite to form by allowing the quenching process to continue beyond normal methods. Thanks for your time and input Larry, very informative.

------------------
Wade Congdon - BOP Engineering
www.bopengineering.com
"If you can turn left you're going too slow"

[Brian Baker]

Now there's a mind blower. To think that the quench process can continue long after a piece was cast in a mold and allowed to resort back to room temperature.

[Bigred455]

Juats an FYI, but there is also an article on cryogenics in this month's Pop Hot Rodding.

[Wade Congdon]

Brian,

Actually certain types of metals continue to harden over time. This occurs when molecules move or precipitate from one from one part of the structure to another. This is commonly called precipitation or age hardening.

------------------
Wade Congdon - BOP Engineering
www.bopengineering.com
"If you can turn left you're going too slow"

[SLOW 77]

Learned something new today.

[LarryF]

Brian, a good example of what I am talking about is 304 stainless steel. If you have ever tried working with 304 it is very tough to machine, yet it is also soft. The reason is that 304 is a metastable austenitic steel, even at cryogenic temperatures. The austenite is metastable, meaning that given enough outside influence, it will become unstable and then transform to martensite (its like someone balancing a ball on their nose - a little outside force will knock the ball off). 304 will remain austenitic indefinitely (at least at room temperature), but if you mechanically work it (forming or machining) it will transform to martensite.

The same thing happens (to a lesser extent) with alloy steels and tool steels that are hardened. After hardening, some metastable austenite remains (retained austenite), but when the part is stressed some of the retained austenite will transform to martensite. Hardened steels are almost without exception tempered after being hardened, because untempered martensite is too brittle and contains too much residual stress (so much that parts can spontaneously fracture while sitting on a shelf).

Cryo treating the hardened steel raises the driving force high enough that all (or nearly all) of the retained austenite will transform to martensite. The part can then be tempered normally by heating to an intermediate temperature and there won't be any untempered martensite that transformed later during use.

Also keep in mind that retained austenite is not a problem with most steels. Low alloy steels, like 4340, can be heat treated normally without a problem. It is in highly alloyed steels, like tool steels, that retained austenite is a problem, so don't rush out and have all of your steel parts cryo treated. There might be a slight improvement with the types of steel used for rods, etc., but it wouldn't be very dramatic. With gray cast iron and mild steel, there won't be any austenite or martensite, so I doubt if cryo treating would do anything except make your wallet lighter.

------------------
Larry

'63 421SD LeMans...
in pieces in my garage
and basement

[455T/A]

Try a little garlic some olive oil and cook very slow...LOL