Gray iron

Gray iron, or grey cast iron, is a type of cast iron that has a graphitic microstructure. It is named after the gray color of the fracture it forms, which is due to the presence of graphite. It is the most common cast iron and the most widely used cast material based on weight. It is used for housings where the stiffness of the component is more important than its tensile strength, such as internal combustion engine cylinder blocks, pump housings, valve bodies, electrical boxes, and decorative castings. Grey cast iron's high thermal conductivity and specific heat capacity are often exploited to make cast iron cookware and disc brake rotors. Its former widespread use on brakes in freight trains has been greatly reduced in the European Union over concerns regarding noise pollution. Deutsche Bahn for example had replaced grey iron brakes on 53,000 of its freight cars (85% of their fleet) with newer, quieter models by 2019—in part to comply with a law that came into force in December 2022.