Gray cast iron includes: ordinary gray iron, austenitic gray iron, chilled hard gray iron, wear-resistant gray iron, heat-resistant gray iron and corrosion -resistant gray iron. Performance and characteristics: The structure of gray cast iron consists of graphite and matrix. The matrix may be ferrite, pearlite or ferrite plus pearlite, equivalent to the structure of steel. Therefore, the microstructure of cast iron can be seen as graphite distributed on the steel substrate. The main factors affecting the structure and properties of gray cast iron are chemical composition and cooling rate. The carbon and silicon content in gray cast iron is generally controlled at 2.5% -4.0% of carbon and 1.0% -3.0% of silicon. Application: Gray cast iron is cheap and widely used. In the total output of various types of cast iron, gray cast iron accounted for 80%.
Ductile iron: Performance and characteristics: The mechanical properties of nodular cast iron are close to that of steel. It has good casting properties, low cost and easy production. It has been widely used in industry. Compared with gray cast iron, the carbon content of nodular cast iron is higher, and it usually varies in the range of 4.5% – 4.7%, which is favorable for graphite spheroidization. The tensile strength of ductile iron is much higher than that of gray iron, but comparable to steel. Therefore, for static loading of parts, the use of ductile iron than cast steel material saving, but also lighter weight, and has better fatigue strength. The results show that the torsional fatigue strength of ductile iron is even more than 45 # steel. Application: In practice, ductile iron is often used to replace steel to manufacture some important parts, such as crankshaft, connecting rod and camshaft, etc.
Vermicular graphite cast iron: Performance and characteristics: The strength of vermicular graphite cast iron is close to that of nodular graphite cast iron, and has certain toughness and high wear resistance. Vermicular graphite cast iron is made by treating molten iron with a certain amount of vermicular agent. Application: Vermicular cast iron is mainly used to produce cylinder head, cylinder liner, ingot mould and hydraulic valve.
Malleable iron: including black core malleable iron, white core malleable iron and pearlite malleable iron. Performance and characteristics: Malleable cast iron has high strength, plasticity and impact toughness, which can partly replace carbon steel. Black core malleable cast iron is obtained by graphitization annealing, and white core malleable cast iron is prepared by oxidation decarburization annealing. Compared with nodular cast iron, malleable cast iron has the advantages of low cost, stable quality and simple treatment process. Application: Malleable cast iron is often used to make parts with complex shapes, bearing impact and vibration loads, such as pipe joints and low-pressure valves.
Wear-resistant cast iron: Performance and characteristics: Obtained by adding certain alloying elements to cast iron. Wear-resistant cast iron is cast iron that works under abrasive wear condition and should have high and uniform hardness. White cast iron is one of these wear-resistant cast iron. But white cast iron is too brittle to bear impact load, so chilling method is often used to obtain wear-resistant cast iron.
Heat-resistant cast iron: Performance and characteristics: On the one hand, dense oxide film is formed on the surface of gray cast iron to prevent further oxidation, on the other hand, the critical temperature of cast iron is raised to make the matrix become monophase ferrite without graphitization. Application: Heat-resistant cast iron is the casting that works under high temperature, such as hearth plate, heat exchanger, transport chain in heat treatment furnace, etc.
Corrosion -resistant cast iron: Performance and characteristics: The corrosion resistance of cast iron can be improved by adding Si, Cr, Al, Mo, Cu and Ni to cast iron and forming protective film on the surface of casting. Common corrosion -resistant cast iron has high silicon, high silicon molybdenum, high aluminum and high chromium and other corrosion -resistant cast iron. Application: Corrosion resistant cast iron is mainly used for chemical components, such as valves, pipes, pumps, containers and so on.