Features, causes and prevention of the uneven hardness and coarse graphite defects of the castings


Coarse graphite: the size of graphite in the metallographic structure is very large, or there is massive graphite, and many small pits are distributed on the processing surface of the casting. Affect the finish and other properties of castings.

Uneven hardness: the hardness deviation in different positions of the same casting (such as the west end of flange of Grundfos pump case series) is too large, exceeding the hardness range required by the customer.


The coarseness of graphite is the result of excessive growth of graphite, which is related to high CE value or slow cooling rate.

The uneven hardness is the result of different wall thickness, different structure, different solidification temperature and speed.

Plan improvement measures:

A. Generally speaking, the hardness of castings with the same wall thickness is lower than that of other locations. Therefore, changing the position of water entry or increasing the high hardness position of the riser will equalize the hardness.

B. Considering the improvement of the heat distribution of the whole panel again, we should strive for the reasonable heat distribution, moderate solidification speed and correct sequence, so as to obtain the castings with dense and uniform structure and satisfactory properties.

C. If the graphite in the water is thick. Change the water inlet position. Keep the water inlet away from the area with large graphite.

D. It is suggested to reduce CE value, enhance inoculation effect and improve graphite size.