Fracture Toughness of Flake Graphite Cast Iron.

The fracture toughness of five gray irons was determined. The relation between fracture toughness and the structural components graphite and metallic matrix was analyzed. The effects of the volume fraction of graphite present, of graphite shape, size, orientation, and distribution, and of the toughness of the metallic matrix are discussed. It is concluded that the K//I//c value of different irons is attributable mainly to differences in flake size and the fraction of graphite volume. Fracture toughness, at almost constant tensile strength, can be increased (by slightly slower cooling in the pearlite interval), if the matrix is not completely pearlitic but rings of ferrite surround the graphite flakes. With a completely ferritic matrix, the fracture toughness is considerably higher.