As we all know, the formation of shrinkage cavity and porosity ofis determined by its solidification characteristics, solidification process and production process. The solidification and shrinkage porosity characteristics of ductile iron are very complex, and there are many influencing factors. Therefore, the formation mechanism of shrinkage porosity of ductile iron has not formed a unified and comprehensive understanding. Generally speaking, product structure and (gating system, mold, gas generation and exhaust), composition of molten iron, metallurgical factors and dynamic factors of pouring process are the main aspects related to shrinkage cavity and porosity of ductile iron. In this paper, the melting control of molten iron and the influence of metallurgical factors on shrinkage cavity and porosity of ductile iron are discussed.
(1) The metallurgical quality is affected by many factors. The undercooling degree is an important quantitative index to judge the metallurgical quality of molten iron. The undercooling degree directly reflects the metallurgical quality of molten iron.
(2) With the improvement of molten iron purity and metallurgical quality, the consensus that the eutectic point of ductile iron moves to the right needs to be further studied. Reducing the carbon equivalent of some ductile iron castings is conducive to reducing the shrinkage cavity and porosity of ductile iron castings.
(3) According to the structure and wall thickness of different castings, the appropriate proportion of the amount of the return charge can improve the metallurgical quality of the original liquid iron and reduce the shrinkage cavity and porosity of ductile iron castings.
(4) Using customized ultra-high purity pig iron, high purity pig iron and recycled materials can not only produce high quality nodular iron castings stably, but also reduce the scrap rate and improve the processing performance, so as to reduce the production cost and improve the economic benefits.