ferritic nitrocarburized surface treatment of cast iron brake rotors providing oxidation resistance , good braking performance and absence of distortion . machined brake rotors are pre - heated , then immersed into a high temperature molten nitrocarburizing salt bath for a first predetermined dwell time . after removing the brake rotors from the nitrocarburizing salt bath , the brake rotors are directly immersed into an oxidizing salt bath at a lower temperature than the nitrocarburizing salt bath so that the brake rotors are thermally quenched . after a predetermined second dwell time in the oxidizing salt bath , the brake rotors are removed therefrom and further cooled to room temperature , either by water application thermal quenching or slow cooling in air . a fixture provides stable holding the brake rotors with a minimum of contact during placement in the salt baths .