Rotors are usually made of gravy iron due to its superior heat handling and damping (vibration absorption) character. The quality depends on a combination of Physical properties, Chemical composition and Inferior microstructure.
Physical properties
Specified by SAE J431 G3000 standard for the automotive brake rotor and drum includes:
Hardness by Brinell: 187-241,
Minimum tensile strength of 30,000 psi
Chemical composition G3000 grey iron:
Carbon 3.10%-3.40%,
Silicon 1.90%-2.30%,
Manganese 0.60%-0.90%,
Sulfur Max 0.15%,
Phosphorus Max 0.15%,
Total Carbon equivalent of 3.9%-4.15
Inferior microstructure
Pearlitic microstructure = the graphite distribution and matrix structure of the cast iron.
This matrix should be predominantly pearlite, with not more than 5% ferrite and less than 1% cementite.
This matrix should be predominantly pearlite, with not more than 5% ferrite and less than 1% cementite.
