[Tomko]

For those of you wondering what the new for 2009 Ferritic Nitro-Carburizing (FNC) brake rotors are, here is the official explanation from GM:

"Beginning with the 2009 Cadillac DTS, GM is introducing a new brake rotor technology called Ferritic Nitro-Carburizing (FNC). In this additional step in the manufacturing process, the brake rotor is heat treated to create a hardened outer layer on the surface of the rotor. This layer reduces rotor rusting (corrosion) and allows the rotor to wear slower.

Also, because this new technology protects against excessive rotor corrosion, the rotor not only aesthetically looks better through open-spoke wheels, it helps reduce thickness variation which creates pulsation specifically due to “lot rot” corrosion."