1.Definition and development history
Ductile iron is a high-strength cast iron material developed in the 1950s. It obtains spheroidal graphite through spheroidization and inoculation treatment, which effectively improves the mechanical properties of cast iron, especially the plasticity and toughness, making its comprehensive performance close to that of steel.
2. Composition characteristics
The composition requirements of ductile iron are relatively strict. Compared with gray cast iron, its carbon content is higher, usually ranging from 4.5% to 4.7%, which is conducive to graphite spheroidization. In addition to carbon and silicon, its main components include manganese, sulfur, phosphorus, etc.
3. Mechanical properties
The tensile strength of ductile iron far exceeds that of gray cast iron, and is equivalent to that of steel. It has good fatigue strength. Experiments show that the torsional fatigue strength of ductile iron even exceeds that of 45# steel. Ductile iron with different matrices has very different properties. It also has the strength and toughness of ferritic ductile iron, which enables pipes made of this material to withstand high operating pressures.
4. Other properties
Ductile iron pipes are made of ductile iron, which has the characteristics of high strength, high corrosion resistance and high pressure resistance. Its interior is treated with molten magnesium to form a dense magnesium-iron alloy protective layer inside the pipe, which can effectively prevent internal corrosion of the pipe.
5. Production method and process
Ductile iron is made by adding a certain amount of spheroidizing agent to molten iron with a certain composition. The ductile iron pipes produced are usually made of molten iron above No. 18, after adding spheroidizing agent, and then cast by high-speed centrifugal casting in a centrifugal ductile iron casting machine. In addition, the manufacture of ductile iron pipes is inseparable from the annealing process. After annealing, the metallographic structure of the ductile iron pipe is ferrite plus a small amount of pearlite, and the mechanical properties are good.
