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No first hand experience, but here's my conclusions after much research: The only certainty is that they cost more. Cryo-treating done properly is an exacting and time-consuming process which does have benefits for toughness and wear, but I do not understand the metallurgy.
I think there are two areas where there is real benefit: Racing, which can be very hard on brakes, and overweight/underbraked vehicles in general e.g. cop cars and overloaded light trucks. (Seems crazy but a friend reported good results switching to cryo front rotors on his max-loaded van).
Good rotors of any sort are certainly better than cheap rotors of any sort, with or without cryo. I think the food chain is something like cheap rotors, Zimmerman, Porsche, good cryo (e.g. Frozen Rotors), then two-piece e.g. RB (which is what we have on our GT).
Porsche brakes are good (particularly 87+) and with good rotors and appropriate pads will take pretty much anything that you can throw at them with stock horsepower. With more horsepower you need more brakes but that's a different topic.
Makes sense Jim.
I only want our thick rotors (non drilled), but did hear of a cryo option for them. I was considering them for the increased length of life. I'm not especially hard or aggressive on them as a rule.
I guess being a metallurgist it's worth an explanation on how phase transformation in steel changes physical properties like resistance to abrasive wear. As always Wikipedia has a pretty good description.
As the Wikipedia article says, a quench to below room temperature reduces retained austenite (no relation!), and that's good for steels and things intended to be fully hardened, in certain situations.
Brake rotors are not such things, as far as I know. They are made from low-carbon steels, which are not heat treated, at least not in the way tool steel is. There are people who market cryogenic treatments for all sorts of things, such the detachable bells of French horns. It can have no effect on brass alloys - they do not undergo transformations - but there are certainly horn players who will swear that their money was well-spent.
As the Wikipedia article says, a quench to below room temperature reduces retained austenite (no relation!), and that's good for steels and things intended to be fully hardened, in certain situations.
Brake rotors are not such things, as far as I know. They are made from low-carbon steels, which are not heat treated, at least not in the way tool steel is. There are people who market cryogenic treatments for all sorts of things, such the detachable bells of French horns. It can have no effect on brass alloys - they do not undergo transformations - but there are certainly horn players who will swear that their money was well-spent.
In 2005 with 122K on the ODO, I bought a used big red setup to put on my '85 from a 993 racer, the rotors he said where cyro treated. ODO just turned 223K, on second set of brake pads, soon to put on third set, and there is hardly any wear on the rotors. No need to have them cut, they are thicker than min. thickness and they are wearing smooth and even. I have been using Hawk ceramic pads.
So in my mind at least, it does make a difference on the wear.
As the Wikipedia article says, a quench to below room temperature reduces retained austenite (no relation!), and that's good for steels and things intended to be fully hardened, in certain situations.
Brake rotors are not such things, as far as I know. They are made from low-carbon steels, which are not heat treated, at least not in the way tool steel is. There are people who market cryogenic treatments for all sorts of things, such the detachable bells of French horns. It can have no effect on brass alloys - they do not undergo transformations - but there are certainly horn players who will swear that their money was well-spent.
Originally Posted by Glen McCartney
In 2005 with 122K on the ODO, I bought a used big red setup to put on my '85 from a 993 racer, the rotors he said where cyro treated. ODO just turned 223K, on second set of brake pads, soon to put on third set, and there is hardly any wear on the rotors. No need to have them cut, they are thicker than min. thickness and they are wearing smooth and even. I have been using Hawk ceramic pads.
So in my mind at least, it does make a difference on the wear.
Yes, there are many types of materials used for brake rotors including cast iron, low alloy steel and a variety of stainless alloys. All apparently gain some wear benefit from deep cryogenic treatment including completion of austenite to martensite transformation, stress relief and formation of carbide phases.
Yes, there are many types of materials used for brake rotors including cast iron, low alloy steel and a variety of stainless alloys. All apparently gain some wear benefit from deep cryogenic treatment including completion of austenite to martensite transformation, stress relief and formation of carbide phases.
Had cryotempered rotors on both my 944 Turbo and my 90GT. Went to cryotempered and slotted rotors because my autocross and track driving style at the time was getting the rotors very hot causing them to warp. Cryotempered rotors solved that even when I got the brakes hot enough to boil the brake fluid. Color sensitive paint showed the rotors were getting to over 800°F.
Went from the 90 GT to a BoxsterS, the stock rotors were good enough on the BoxsterS to not have any problems. Later got a 928GTS with the bigger brakes. While not warping the rotors or boiling the fluid, they get a bluish hue AND I've melted the pad wear sensors in the front pads.
Had cryotempered rotors on both my 944 Turbo and my 90GT. Went to cryotempered and slotted rotors because my autocross and track driving style at the time was getting the rotors very hot causing them to warp. Cryotempered rotors solved that even when I got the brakes hot enough to boil the brake fluid. Color sensitive paint showed the rotors were getting to over 800°F.
Did you change pads (type/brand) when you went to the cryo rotors? Most warped rotors are actually uneven pad deposits from cooking a too-soft pad material. Cryo rotors shouldn't run any cooler, just last longer.
Originally Posted by RKD in OKC
Later got a 928GTS with the bigger brakes. While not warping the rotors or boiling the fluid, they get a bluish hue AND I've melted the pad wear sensors in the front pads.
Sounds like the pads should have melted, what were they?
Tried stock first, then went to hotter, then hotter pads.
When changed to cryotempered rotors went back down to just one level hotter than stock. Think they were EBC Yellow.
After a little research - still inadequate - I have to amend my remarks. Rotors are usually cast iron, with a choice of "regular" and "high carbon". As is common for terms used for marketing, I could not find a direct link to what these are. I'll guess that one refers to grey cast iron and the other to nodular cast iron, which typically has higher carbon.
Though steel is described as an alloy of iron and carbon, most forms of cast iron have much more carbon, plus silicon. The carbon forms bits of graphite during solidification; in steel, the carbon forms other stuff, later, which is manipulated by heat treatment. Anyway, the graphite can end up as flakes or as more rounded bits. Rounded bits leads to more ductility. The metal the graphite sits in is essentially steel, and can be heat treated like steel to produce greater strength. Coupled with the nodular graphite, ductility can still be adequate. Higher strength will give greater warp resistance. Thermal fatigue resistance has a complicated relationship with strength and ductility....
The quench and temper heat treatment of a "high carbon" rotor might indeed benefit from exposure to cold temperatures in order to fully complete the weird and wonderful martensitic transformation sought by quenching from above 1400F. If all this seems complicated, it is. Here is the iron-carbon phase diagram that provides some clue about what goes on (at equilibrium, which we rarely get or want in practice):
However, the intrusion of marketing means that someone switching to cryo-treated rotors may also be switching to a different cast iron, casting process and heat treatment, all at the same time. Where I practiced metallurgy, only the MAE (materials application engineer) assigned to a component would be acquainted with all the details, codified in a specification. I was not an MAE; they regarded me as woefully ignorant about real life. You should, too.
To the metallurgists, does the deep hard freezing have to take place during the alloy's fabrication whilst hot to get the benefit, or can it be done later on once the alloy and product have already been produced ?
05-13-2017, 10:04 AM
Cryo Treated Rotors
