Brake Rotor Metallurgy
There are two basic categories of cast gray iron used for brake rotors. First is the SAE J431 G3000 for general rotor castings, and the other is High Carbon (HC). G3000 gray iron is for car and light truck castings, which specifies the chemical composition, hardness, and tensile strength. This gray iron has a graphitic misconstruction and is composed of iron, graphite, silica, pearlite, and a small percentage of carbon for higher thermal conductivity and added strength while improving its sound damping qualities.
Other elements may be added by manufacturers to achieve a particular set of properties, including silicon, manganese, sulfur, and phosphorus. Final metallurgical qualities are also influenced by the casting temperature and cooling rates which affect microstructure.
High carbon rotors
High carbon materials for rotors provide benefits over standard gray iron for both the manufacturer and end vehicle owner. High carbon brake rotors have been used in racing since the 1970s. This form of gray iron exhibits superior casting and machining properties, a higher thermal conductivity for absorbing and dissipating heat, and good resistance to both distortion and thermal cracking for enhanced brake performance. These qualities further enhance the rotor’s ability to help prevent brake judder and reduce noise.
Even with a high carbon content, the hardness levels of these rotors are not much lower than those made from traditional low to medium carbon irons. As such, selecting the correct brake pad material will help ensure that rotor wear performance issues are minimized. Like low to medium carbon irons, final metallurgical qualities are also influenced by the casting temperature and cooling rates which affect microstructure.
Despite these advantages, HC rotors have only recently been gaining application for luxury and high-performance vehicles.