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In the production and casting process of ductile iron castings, in addition to the general casting defects, there will be some special defects, such as shrinkage, slag inclusion, subcutaneous pores, poor spheroidization and recession. These defects affect the performance of castings and increase the scrap rate of castings.

In order to prevent the occurrence of these defects in ductile iron castings, it is necessary to analyze them, summarize the various influencing factors, and propose preventive measures in order to effectively reduce the occurrence of defects and improve the mechanical properties and production efficiency of castings.

Before putting forward effective preventive measures, we should first understand the causes of shrinkage porosity in ductile iron castings. First of all, of course, related to the carbon content, increase the amount of carbon, increase the graphite expansion, can reduce the shrinkage porosity. In addition, increasing the carbon content can also improve the fluidity of ductile iron, which is conducive to feeding.

When producing ductile iron castings, if the phosphorus content in the molten iron is high, the solidification range will be expanded. At the same time, the low melting point phosphorus eutectic cannot be replenished during post-solidification, and the casting shell will be weakened, thus increasing shrinkage cavity and shrinkage porosity. Therefore, the phosphorus content in the molten iron should be strictly controlled to make it less than 0.08%.

Excessive rare earth residue will deteriorate the shape of graphite and reduce the spheroidization rate, so the rare earth content should not be too high. And magnesium is a strong stable carbide element, hinder graphitization. It can be seen that the amount of residual magnesium and the amount of residual rare earth will increase the white mouth tendency of ductile iron and reduce the expansion of graphite, so when their content is higher, it will increase the shrinkage cavity and shrinkage tendency of ductile iron castings.

When the surface of ductile iron castings form a hard shell, the higher the temperature of the internal metal liquid, the greater the liquid shrinkage, the shrinkage cavity, the volume of shrinkage not only increases, the relative value also increases. In addition, if the wall thickness changes too suddenly, the isolated thick section can not be replenished, so that the tendency to produce shrinkage porosity increases. In addition, it is also related to the pouring temperature, the compactness of the sand mold, the gate riser and the cold iron, which need to be adjusted from here.