So who's gonna try them then?

I'm actually finding this a very interesting thread (I've gotta get out more) and am now genuinely intrigued as to how these Cryo'd discs would perform when given a right old beating.

 

They do - how else do you explain thermal shock?

Besides - the time honoured tradition of hardening is heating, then quenching.

The heat puts energy into the molecules and allowing them to align.

The cooling freezes them in position.

IIRC, the cooling of the nitrogen puts them, like peening, under a negative stress - hence the hardness.

 

as i said i have them, so far they have performed well. and i am beating on them. however not on the track at the moment

i have even had other parts of my car cryo'd

 

heating expands the molecules allowing them to "untangle" and align themselves better, quenching freezes them in that state leaving a large grain structure that cannot easily flow, this makes it hard but brittle
controlled quenching or tempering allows the metal to cool at a controlled rate and so controls the molecule size to give the desired strength and flexibillity
I think cryo is something similar just at the other end of the scale, its certainly not Snake oil its just another method to acheive better results, you wll probably see less results if it was done to a well cast disc over an average disc.
Dont get me wrong i am not advocating taking your old discs off and getting them done i think you would needto know exactly what they were made of and have it tested before allowing them anywere neaer a car, are they better than a good quallity set of discs? that i suppose depends on the quallity of the casting they started out with.

I might be wrong here but i thought thermal shock had more to do with the speed of the temp change rather than it being just too hot, a sudden very hard braking action on cold discs or running hot discs into cold water, resulting in uneven heating and expansion/contraction

 

It does

But it's still a change in composition

I know LN2 treatment isn't snake oil, but i'm just not sure of it's application with brakes due to how brakes work (eg pressure cobined with high temperatures)

 

You might want to a bit more research on this Ron.

You're somewhat off the mark on both how the heat treatment process works.

Its the effect off the heat on the grain structure of the metal that's all important and the distribution of the carbon in the iron (or steel if appropriate), not the alignment of the molecules that allows the heat treatment to give the metal its properties.

And cryo treatment is nothing like shot peening. Shot peening smooths the surface and locally hardens the metal. Cryo treatment actually changes the grain structure throughout the disc (or at least that's the theory).

 

I definitely know the effect of shot peening is to induce negative stress - it's something they were big on at Airbus.

It's just wierd that reducing the energy, at the molecular level, results in less movement/vibration of the molecules.

Can you see where i'm getting the conflict?

 

Shot peening plastically deforms the surface and compresses it creating a compressive stress in the surface and a subsequent tensile stress in the material below. This can improve its fatigue life and improve its corrosion resistance, hence the reason its used in aircraft parts. It would not be suitable for brake discs as it would deform the previously machine surface and give an irregular surface for the pads to run on as well as creating internal stresses which would make the disc more prone to warping when it got hot.

Cryo treatment allows the carbon in the material to continue to diffuse through the material which means more austentite converts to martinsite. Martinsite has a much smaller grain structure than austentite and therefore increases the hardness of the material, hence its wear resistance, and increases its strength. It also helps relieve any internal stresses which makes the material more stable under changing thermal conditions.

This process happens to some degree during the normal heat treatment of the disc during manufacturing. The debatable point is whether the cryotreatment actually provides any significant benefit to the disc.

I don't know where your comments about thermal shock come from. Thermal shock is sudden extreme cooling, something a brake disc doesn't really see unless you drive through a very large puddle when you've just completed a few track laps. When the material cools, it contracts very quickly which can cause cracking and also warping if one side of the disc were to cool more quickly than the other.

 

I decided to email Nitrac with a few questions that a few of us have been asking or wondering about; the main 2 questions being :-

1) When the rotors are heated up again under prolonged heavy use, such as would occur on a track day, does this re-alter the structure of the metal in a negative way? Or is the Cryo process a one way street regardless of how much heat is put back into the material.

2) How does the Cryo process affect the materials properties for heat transfer and dissipation?

I had a good long reply from them as follows
_____________________________________

Thank you for your interest in our discs.

The kind of scepticism and misinformation that revolves around cryo treatment is not unusual, somehow the concept that cooling a material can have similar effects to heating it isn

 

Thats some good work there olddogmeat, nice name too!

One question I have is how many grooves is better??

I'd of thought less grooves but if thats the case why do they offer more?

Rick