Ductile iron casting has a strict chemical composition when it is used. The carbon silicon content required for the original molten iron is higher than that of gray iron casting, and the content of manganese, phosphorus and sulfur in the ductile iron casting is reduced. The temperature of the molten iron is higher than that of the gray iron casting to compensate for the spheroidization and the loss of the temperature of the molten iron during the treatment.
In the ductile iron casting, only the spheroidizing agent needs to be added to the liquid. The inoculant is added for inoculation treatment. Ductile iron casting has poor fluidity and large shrinkage. Therefore, it requires high pouring temperature and large casting system size. Reasonable application of riser and cold iron adopts the principle of sequential solidification.
Heat treatment of ductile iron casting
1 annealing. A ferrite matrix is obtained to improve plasticity, toughness, stress relief, and improved cutting performance.
2 normalizing. A pearlite matrix is obtained to improve strength and wear resistance.
3 tempering. Obtain the matrix structure of the tempered sorbite and good comprehensive mechanical properties such as spindle, crankshaft, connecting rod and so on.
4 austempering. The parts with complex shape and high comprehensive performance are required to obtain the base structure of the lower bainite, and the comprehensive mechanical properties such as high strength, high hardness and high toughness, and avoid cracking during heat treatment, such as spindle, crankshaft and gear.