Generally speaking, the cooling rate of castings tends to be slower, the more favorable is the crystallization and transformation according to the Fe-G stable state diagram and the full graphitization; otherwise, it is beneficial to the crystallization and transformation according to the Fe-Fe3C metastable state diagram Finally get white iron. In particular, graphitization in the eutectoid stage, because the temperature is low, the cooling rate is increased, and atom diffusion is difficult, so in general, it is difficult to sufficiently perform graphitization in the eutectoid stage.

The cooling rate of cast iron is a comprehensive factor, which is related to factors such as pouring temperature, thermal conductivity of the transfer material and the wall thickness of the casting. And usually these factors have basically the same effect on the two stages.

Increasing the pouring temperature can delay the cooling rate of the casting, which not only promotes the first stage of graphitization, but also promotes the second stage of graphitization. Therefore, raising the pouring temperature can make the graphite powder to a certain extent, and can also increase the eutectoid transformation.