Theres an old post about this but not much information. Does anyone know some good information about it?

If I have a cast crank done is it gonna be stronger then a forged crank?

 

Maybe more resistant to wear on the journals, but not stronger.

 

Wanna explain a little more? I am like retarded to the process.

 

The following are generalizations, forgive me if I mix up the terminology a bit...

Heat treating parts is where you heat the part up to a specified temp, then cool it at a set rate, until room temp. Quick cooling is like martenizing it, makes it hard and brittle. Very slow cooling is more like annealing, or normalizing, makes it more ductile.

Now, it's the cooling at a certain rate that changes the properties of the metal, so, instead of heating it up a lot, then cooling to room temp, just keep cooling it. Hence cryogenic cooling.

So what you would do with heat treating, you can do with cryo cooling, except now you have more of a heat range to work with (ie, heat it up, then cryo cool it).

so when you heat treat something to "case harden" it, you just make the "case" (outer few thou or so) hard. Harder makes it wear less then a softer case.
If you heat treated it for longer, you could fully harden it, which would make the entire part harder, so it's more wear resistant all the way through... (but why?)

however the part is still a cast part, so the grain structure doesn't change, so the part isn't "stronger". That's basically the gist of it.


I think I confused myself, as I do remember heat treating changing the grain structure (martensitic, pearlitic, etc), as does cold working, ie forging, so.....? Forgive me, I did terrible in that class...

 

The grain does change, austenitic steel has coarser, more irregular grains than martensitic. Martensite is stronger but more brittle than austenite. The idea as I understand it is that cryogenically tempering converts more of the steel to martensite than conventional tempering and quenching does.

 

hmm, ok, heat treating does change grain structure....
Then forging, cold working, etc, does that just 'compress' the grain structure, without changing the particle size/type?

 

Something like that anyway, I'm no metallurgist. Forging works the metal before the grain structure has fully formed.

 

How can something be stronger, but more brittle? Is it something like it is hard to bend, but if it bends then it is more prone to break? Kind of like concrete, no shear strenght?

 

you're confused.

brittle = harder. wears less. It can take force, but when near it's breaking strength, it shatters, rather then bending much. think concrete, cast iron, etc.

ductile is less hard. wears easily. think aluminum. When approaching breaking strength, it has more elastic bending, then plastic bending, before it ultimately fails.

yet these two materials can have the same "strength". strength is really hard to define in metallurgical terms. "Toughness" is pretty close.
remember, there's tensile (pull), compression (push), shear (sliding a deck of cards), bending (duh, technically tensile and compression), twisting (forget the official name there), etc etc.
concrete is great in compression, but poor in tensile.

I sholud read through my materials book, it is pretty interesting.

 

All technical aspects aside, let's boil it down to practical concerns.

I think you'll find, that it costs more to do all that to some crap cast crank, than to buy a forged one in the first place; which will be better for less money than a cast one no matter how it's treated.

Spend more, do more work, get less results. Hmmm.......

Which is probably why you don't see a whole lot of people doing it.

 

I get it. Thanks for straightening that out.

 

A forging will always be stronger then a casting when used for the SAME application.

 

Hardness: Resistence to penetration.
Strength: Force per unit area the material can support (a rod with one inch of cross sectional area that can hold up 50,000 pounds has a strength of 50,000 psi). Strength and hardness typically follow each other.
Ductility: The amount of deformation a material will exhibit before breaking. If the amount of deformation is greater, it's ductile; if lesser, it's brittle. Typically defined as a reduction in area of the cross-section, or elongation. A brittle casting, for instance, can break before exhibiting any significant deformation or reduction in area - but, it may be stronger than a more ductile material. Brittle materials are typically more susceptible to impact fracture.
Heat treatment: Heating and cooling a metal or alloy to obtain desired properties or conditions. What you do and what you get depends upon the alloy and how it was formed.
Martensite: In carbon steel, a hard, supersatuated solid solution of carbon in a body-centered tetragonal lattice of iron. Typically very hard and brittle. Formed by heating the metal above the eutectoid temperature and quinching it rapidly.
Austenite: Gamma iron with carbon in solution. Typically soft and ductile. Formed by heating the metal above the eutectoid temperature and letting it cool slowly.
Temper: To soften hardened steel or cast iron by reheating to some temperature below the eutectoid temperature. For instance, tempered martensite is stronger and harder than austenitic, but more ductile than martensitic.
Cryogenic treatment: a) Done to ensure there is no retained austenite in the martensite. Retained austenite degrades the properties of the marensitic material, whether final tempered or not. Only effective with high carbon steels & alloys, because medium and low carbon steels do not have retained austenite when quenched to room temperature. b) Stress relieving process for castings and machined parts. Improved fatigue resistance.

To answer the original question: If you have a cast crank cyrogenically treated it won't be stronger, but it would be more resistent to cracking over time (fatigue) due to the stress relieving properties of the treatment.

 

now that was well said!
thanks for clearing that up.

 

Buddy of mine had a 400SBC cast crank "ICED".

Ran it in his pro street race nova (8sec) 1000HP + 18 deg 406SBC with NOS
for years. COuple rebuilds, couple smashed pistons, tons of runs. The bearing journals always looked like new on teardown. Crank never broke.

It works.. beauti for lifters and cams too.

 

I could really see the benefits of this. Since the major drawback of cast cranks is they are more prone to wear than a steel crank. I recently was reading how cast cranks benefit one factor above a steel crank. The fact they are more ductile means they can absord shock a little better than a very hard steel crank that could shatter under the right condition. Not trying to start an argument or say one is stronger than the other but just passing along an article I read on metallurgy.

 

If the cost of cryo treatment greatly exceeds the cost of a cast crank I wouldn't call it much of a benefit.

 

Ok well while we are on the topic since I really know nothing of this other than what im reading here. Exactly what would be done to accomplish this and what would be the cost? It would be interesting to discuss it even if its all just theory and conjecture.

 

But it does not . It cost less and the crank stood up
Could not believe how nice the journals looked after all the punishment this thing saw. Just like new. Well worth it.

 

anyone care to toss out a # on how much this does cost?

f-bird?

Is it based on, "well, we can cryo treat anything you can fit in this box here for x dollars, or this bigger box for X dollars.."
or is it per part in the "tank" or whatever?

 

it was under $200 to do the crank here in Niagara.
Was done at local industrial oriented Cryo Co. If you walk in to your typical speed shop/race engine builder and say "how much?"
You'll like pay a premium. But the No Bull cost is not that much considering the life extention of these critical parts in a hi output motor.
.
A lot less total preparation cost than a Scat or Lunati forged crank either way you look at it and did the job. hard to $knock$ cryo treatment.

 

Found a place to do the entire rotating assembly for 620$ (Pistons, Rods, and Crank)

 

http://www.diversifiedcryogenics.com/whatiscryo.htm

There's some good info there explaining the process, sounds like it changes the properties by making the grain structure more uniform. Less weak spots.

"Deep cryogenic processing permanently refines the grain structure of metals at the atomic level. Carbon particles precipitate as carbides into a lattice structure and fill in the microscopic voids."

 

a complete engine costs about $400.four the fourbanger.


http://www.cryopro.com/engine.htm


and you get 10% better milage AND hp.and NO ONE has blown a motor that has been cryoed by this company.

its DEFINITLY worth the money.especialy with the gains you get and the durability.

 

There is a place around me (Decatur Illinois) called 30*below(not sure if that is *C or *F). They will actually warrant their work to a small amount, they also have many ametuer circle track and drag stripers that have attested to the process as helping them. I remember one of the guys claimed he went from 5-7 1/4 mile passes on the "regular" axles to 14-16 passes on the "treated" axles. I will have to call for a price again.