Most of the gray cast iron used in engineering belongs to hypoeutectic gray cast iron. During crystallization, this gray cast iron will first precipitate austenite. This austenite appears in the form of dendrite, which is called primary austenite dendrite, and then eutectic reaction will occur in molten iron to form eutectic group. It can be seen that, first, the primary austenite dendrite is a microstructure of gray cast iron applied in engineering. Second, because the primary austenite dendrite precipitates first in the molten iron, its quantity, morphology and distribution will have a certain impact on the subsequent eutectic reaction. Because the primary austenite dendrite region does not contain graphite, its strength will be higher than that of graphite region, many scholars at home and abroad begin to pay more and more attention to this structure. At the same time, many studies have been carried out on the relationship between the morphology of primary austenite and graphite structure and Mechanical properties of Hypoeutectic gray cast iron. G. Rivera et al. Believe that the primary austenite dendrite formed at the initial stage of solidification will have a certain effect on the formation and growth of graphite.
According to many data, the two main structural factors affecting the properties of gray cast iron are graphite and primary austenite. Sun Shaochun and others have shown that the main factors affecting the tensile strength are the primary dendrite spacing of primary austenite, the length of graphite sheet and the number of primary austenite. Therefore, improving the strength of gray cast iron should be analyzed from two aspects: primary austenite and graphite, including increasing the nucleation rate of primary austenite, increasing the number of primary austenite, improving the distribution of graphite, reducing the length of graphite sheet and so on. The cooling rate has an important effect on the primary austenitization of gray cast iron. At a fixed cooling rate, the secondary dendrite spacing is constant. The higher the cooling rate, the smaller the eutectic cluster size. Joel hemanth et al. Used different quenching methods to analyze austenitized quenched gray cast iron. The results show that the cooling rate has a significant effect on the dendrite arm spacing, the number of eutectic clusters and tensile strength. The tensile strength decreases with the increase of dendrite arm spacing, while the tensile strength increases with the increase of the number of eutectic clusters. However, with the increase of cooling rate, the number of eutectic clusters is inversely correlated with the dendrite arm spacing. The primary structure formed during solidification will affect the subsequent nucleation and eutectic growth, which means that the primary structure will affect the final properties of gray cast iron.