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      04-15-2014, 06:28 AM   #12
Iron Man
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Quote:
Originally Posted by Dackelone View Post
Cool pics @MightyMouseTech I always enjoy reading your posts. I use to work at a VW Subbie store... its weird how the Japanese always want to "turn" the rotors while the German's just replace them. I think it also has to do with the type of steel(used) in the rotors. I think the German's use a higher quality of steel. Maybe thats why our rotors get surface rust so fast.

Btw... another reason why brake rotors warp or the brake pedal pulsates is due to the rotor not sitting flush on the hub. Most guys don't take the time to use a 3M "cookie" to clean off old rust on the hubs before mounting new rotors. Not doing so can make your pricey new rotors feel like worn out ones in no time.
Most OE rotors are made from Cast Iron, not steel. The entire rotor does warp due to phase changes in the microstructure of the cast iron rotor.

When rotors are initially cast, upon cooling they will have "retained austenite". Cryo cooled rotors will transform this structure, so the rotor is more uniform and this phase transformation does not take place. As you apply heat and stress to a rotor that has excessive retained austenite, it transforms to martensite, causing a change in volume, which results in a rotor warping to compensate.

Some rotor manufacturers may cryo cool or control cool their rotors after casting to minimize retained austenite, but it is an added expense, so I imagine few if any OE manufacturers have their rotors treated as such.

All cast iron rotors will rust and actually the quality of the cast iron has nothing to do with it. The only way to stop the rusting is to coat the rotor or use stainless steel or ceramics.
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