Cast iron refers to an iron-carbon casting alloy with a carbon content of 2.11% or more. It is cast iron that uses cast iron as a raw material and is directly cast after remelting. There are many types of cast iron used in industry. According to the shape, organization and performance of graphite, it can be divided into gray cast iron, malleable cast iron, white cast iron, nodular cast iron and bushing casting sleeve vermicular cast iron. 1. Gray cast iron Cast iron plug valve gray cast iron usually refers to cast iron with flake graphite, in which carbon is mainly crystallized into free graphite, and the fracture is dark gray. The most common cast iron is gray cast iron, which has excellent fatigue resistance and shock absorption, so it is often used in automobile engine cylinders, gears, speed wheels, brake discs and drums, and large machine tool bases. 2. Malleable cast iron Malleable cast iron is made from a certain composition of white cast iron by graphitization annealing, in which most or all of the carbon exists in the form of briquette graphite. Because malleable cast iron has much higher plasticity and toughness than gray cast iron, it is customary Called malleable cast iron, it is commonly used to make some important small pieces.

At present, it has been widely used in various fields such as automobiles, railways, construction, electricity, textiles, home appliances, national defense, and machinery manufacturing. 3. White cast iron White cast iron, also referred to as white iron for short, is a cast iron that is completely crystallized according to the Fe-FeC3 phase diagram. It is caused by the local sharp cooling of gray iron or nodular cast iron in the mold, of which carbon All of the fractures in the form of carbonite are silver-white. Because white cast iron has a lot of hard and brittle FeC3.Therefore, white cast iron has high hardness, high brittleness, and is difficult to cut, so it is rarely used to directly manufacture machines, mainly used for steelmaking raw materials or for the manufacture of malleable cast iron blanks. 4. Ductile cast iron Ductile cast iron is formed by spheroidizing the molten iron before pouring, in which most or all of the carbon exists in the form of spherical graphite. Ductile iron has good machinability, fatigue and high modulus of elasticity; due to the small amount of magnesium it contains, its rigidity, strength and impact resistance are stronger than gray cast iron, but its vibration damping is worse than it.

Therefore, spheroidal graphite cast iron is mainly used for manufacturing various parts such as automobiles, tractor chassis and so on, as well as machine parts and valves, power line parts and so on. 5. Vermicular graphite iron Vermicular graphite iron is a kind of cast iron obtained by liquid molten iron after metamorphism treatment and inoculation treatment followed by cooling and solidification. Its graphite morphology is between flake and spheroidal graphite, which looks under an optical microscope. It looks like flakes, but unlike gray cast iron, its flakes are shorter and thicker, with a round head (like a worm), so it can be considered that worm-like graphite is a transitional graphite. Since the structure of vermicular graphite iron is an intermediate state between gray cast iron and nodular cast iron, the performance of vermicular graphite iron is also between the two, that is, its strength and toughness are higher than gray cast iron, but not as good as nodular cast iron. The wear resistance of vermicular graphite cast iron is better, so it is suitable for the manufacture of heavy machine bed, machine base, piston ring, hydraulic parts and so on.