The microstructure and hardness of casting a solid brake disc after late graphitizing modification

Abstract

The features of graphite formation in hypoeutectic and hypereutectic gray cast iron are considered. It is shown that this process in hypoeutectic gray cast irons is easier to control than in hypereutectic, because the formation of a predominantly rectilinear uniformly distributed graphite with a smaller size range and the presence of other distributions is achieved by an one-stage operation of ladle graphitization. The structure of graphite in hypereutectic gray cast irons is characterized by a large variety of its shapes, sizes and distributions, and it is also less technologically stable and controllable. Its characteristics can be approximated to the structure of hypoeutectic gray cast iron due to the obligatory second stage of graphitization. The microstructure and hardness of casting a solid brake disc after late graphitizing modification in a mold are investigated. The content of interdendritic distributions of graphite PGr8, PGr9 and short inclusions of graphite PGd45-90 (GOST 3443-87) was minimized due to the operation of the secondary (late) graphitizing modification. And Brinell hardness of the solid brake disc meets production requirements.