If the steel used is a secondary hardening steel, it could be beneficial. If it isn't (and most steels used on brake rotors aren't) then it's not worth the added expense.

At least in my opinion. But I am not a metallurgist, just some guy that reads a lot....

What was the goal of cryo treating? Harder steel, longer life, more stopping power? Again, I'm not an expert, but it seems to me that a harder steel would resist the abrasion of the brake pads, and as a result, stopping power would be reduced. Consider that, in order to stop via abrasion, the coefficient of friction comes into play, and a harder steel would have a lower CF. Maybe. Again, I suppose that depends on the steel and what sort of microstructures are present through the depth of the rotor.

Hmm. Thinking about it, it seems to me that if you make the steel harder but more abrasive (by creating hard microstructures), you're going to go through brake pads a heck of a lot faster. So you have the tradeoff of having to buy those more often. That could actually be more expensive than just buying a set of rotors every few years.

Personally, I consider it a waste of money. Brake rotors are designed to be consumed slowly over their life, and the typical life of rotors (based on my experience alone) is about 100k miles. I suppose it could be useful on racecars in endurance races - like 24 Hours Of Le Mans to ensure that your rotors don't fail prematurely, but last I looked, those rotors weren't even made of steel - it's some sort of composite or high alloy (can't find the reference, too busy to look).

Anyway, I'm interested to see what the experts have to say.

Any cast or manufactured part has some built in internal stresses and brake rotors and pads are no exception. This is why rotors can warp just by sitting on the shelf.

The most effective way to completely eliminate these stresses is to do it in the controlled environment of a computerized deep cryogenic treatment system. CI’s controlled deep cryogenic treatment system and process is capable of treating a wide variety of materials, such as ferrous and non-ferrous metals, metallic alloys, carbides, plastics (including nylon and Teflon) and ceramics. The entire process takes between 36 to 74 hours, depending on the weight and type of material being treated. In the case of steel and its alloys, cryogenic treatment removes the built-in kinetic energy of atoms, which is the energy of motion. There is a normal attraction between atoms that makes them want to get together. But their energy of motion keeps them apart unless that energy is removed by low temperature cooling.

This special process is not a surface treatment; it affects the entire mass of the brake rotor, drum or pad being treated, making it stress free and stronger throughout. The hardness of the material treated is unaffected, while its strength is actually increased. This eliminates the danger of heat cracks, chipping and breaking. An additional benefit of the CI process is the elimination of vibrations caused by stresses in the rotor.

In steel, the CI treatment at temperatures of (-320°F) transforms soft austenite into hard martensite. This transformation improves rotor surface wear and heat resistance; more miles can be driven before costly changes are required. This reduces the changeover rate of the rotors, thus improving the over-all life, and saving on vehicle downtime and labor. In general, a forty percent reduction in heat is seen after brake rotors, pads, and calipers are deep cryogenically treated.