Characteristics of the fracture surface of gray magnesium cast irons after dynamic fracture

Abstract

Modification of gray test iron with as much as 0.08% Mg leads to globularization of graphite and greatly changes the average rate of fracture. The fracture of the pearlitic matrix is brittle in character. The fracture of the pearlitic matrix is brittle in character. Thus, the discrete pattern of crack propagation observed is due mainly to the presence of graphite inclusions, which are areas of scattering of the elastic energy of the crack — relaxation areas. Comparison of the electron fractographs of cast and heat-treated samples (alloy with 0.08% Mg) revealed new elements of brittle fracture in the latter. Crack propagation in the ferritic cast iron is a ccompanied by intensive twinning (Fig. 3g, positive replica). It should be noted that ferritizing annealing has a negligible effect on the average rate of crack propagation (∼350 m/sec).