Qualitative and quantitative studies of fracture surfaces in ductile and grey cast irons

Abstract

This work shows the results of qualitative and quantitative studies about the micromechanisms of fracture found on tensile, fracture toughness, impact and fatigue precracking test specimens of ductile and grey cast irons having four different matrix microstructures (ferritic, pearlitic, ausferritic and bainitic) and three different piece sizes.It was found that in the case of ductile cast iron the fracture process takes place mainly across the matrix, with the participation of different percentages of ductile and brittle fracture mechanisms, depending on the mechanical test and matrix microstructure. However, in all the grey cast irons tested, the fracture took place mainly by decohesion of graphite flakes from the matrix. Moreover, the fracture mechanisms found in both tensile and fracture toughness specimens were similar for ductile and grey cast irons. The impact tests were associated with a reduction in the amount of ductile fracture in all cases. Under fatigue conditions the fracture process takes place by striation and quasicleavage mechanisms. Piece size has a minor effect on the fracture mechanisms. The results are in agreement with the literature.