Breakup of eutectic carbide network of white cast irons at high temperatures

The fracture toughness of white cast irons is related to the morphology of eutectic carbides, being better when isolated than when network-like. In this paper observations on the breakup of eutectic cementite network during annealing treatment of white cast irons are reported using a high temperature microscope and scanning electron microscopy (SEM). Dissolution-induced breakup and capillarity-induced breakup are identified. The former occurs through growth of holes and pre-existing fissures as well as through fragmentation at narrow necks and narrow roots of branches. The latter is observed through growth of perturbations. Dissolution-induced breakup is closely associated with the morphology of the as-cast eutectic cementite. A combination of solidification processing and heat treatment thus produces a more positive breakup effect.