As we all know, there are several typical types of cast iron like grey cast iron, white cast iron, and ductile cast iron according to the composition of carbon and silicon. Most or all carbon in cast iron exists as flake graphite in free state. Gray cast iron is the most common and widely used cast iron. Its graphite is distributed in flake and the fracture is dark gray. The carbon content of gray cast iron is more than 4.3%. According to the position of chemical composition on Fe-C phase diagram, gray cast iron can be divided into subeutectic, eutectic and hypereutectic. The solidification structure of gray cast iron includes primary austenite, primary graphite, eutectic (eutectic austenite) and eutectic grain boundary growth.
Gray cast iron is formed by slow cooling during the smelting process. The presence of a large amount of silicon can promote graphitization. Gray cast iron is a high strength inoculated cast iron (also known as metamorphic cast iron), which is obtained by inoculation. It has excellent casting, cutting, wear resistance and shock absorption. The compressive strength and hardness are close to that of carbon steel, but the tensile strength and plasticity are lower and the brittleness is higher. It’s the most widely used one of the cast iron due to its simple production process and low price, mainly used in mechanical engineering for the manufacture of machine tool bed, cylinder, box and other structural parts.
White cast, sometimes known as malleable cast iron is a carbon to permeate (Fe3c) of the carbide form does not contain graphite, fracture, microstructure of white cast iron. Its carbon content in about 2.5% and silicon content is below 1%. To require a higher surface hardness and wear resistance, chilling method are available in the casting surface white iron and retain the core of gray iron, so it is also called "chill cast iron". White cast iron can be divided into: subeutectic white cast iron (CE<4.3%, Sc<1), eutectic white cast iron (CE=4.3%, Sc=1) and supereutectic white cast iron (CE>4.3%, Sc>1). Eutectic degree (Sc) refers to the ratio of carbon content of cast iron to the actual carbon content of eutectic point.
White cast iron is hard and brittle, not easily machined, rarely used directly in casting parts, has been typical used in some hard and wear resistance parts such as rollers in rolling mills, railroads wheel, farm tools, grinding balls, blades, pumps, rollers, ect.
P.s: Equivalent materials from different counties: