FRACTURE-MECHANICS BEHAVIOR OF AUSTENITIC COMPACTED GRAPHITE CAST-IRON

The fracture mechanics behaviour of high-nickel austenitic compacted g raphite cast iron was studied and the effects of graphite morphology, alloying elements and specimen thickness on the mechanical properties, plane stress fracture toughness, and fatigue crack growth rate were e valuated. It was found that the graphite morphology, i.e. the percenta ge of compacted graphite present, was the major determinant of all pro perties of the materials investigated. The irons with a greater amount of compacted graphite (the balance was nodular graphite in austenitic matrix) resulted in lower tensile strength, yield strength, elongatio n and K-C fracture toughness but higher crack-growth index values (poo rer crack-growth resistance). For 25 mm thick specimens, K-C values of the austenitic compacted graphite cast irons in this study were in th e range of 58-64 MPa m(1/2). This is higher than ferritic/pearlitic du ctile iron of 43-53 MPa m(1/2), and is compatible to Ni-resist austeni tic ductile iron of 64.1 MPa m(1/2). The addition of cobalt not only c ontributed to slightly higher values of mechanical properties, but als o higher plane stress fracture toughness and better crack growth resis tance. Optical microscopy, scanning electron microscopy and X-ray diff raction techniques were applied to correlate the microstructural featu res to the properties attained.