DEFORMATION AND FRACTURE OF CAST-IRON WITH AN OPTIMIZED MICROSTRUCTURE

An optimized microstructure of cast iron has been developed. In situ s tudies with the use of scanning electron microscopy have been made of the microprocesses of deformation and fracture in tension. The surface microstructure and the corresponding fracture surface and matching fr acture were observed. The optimized nodular graphite-martensite interf ace, in combination with the high yield strength martensite shell, has been found to delay the initiation and propagation of interfacial cra cks. Subsequent propagation and the formation of cast iron cracks is h indered by the ferrite-plus-martensite matrix. During crack propagatio n, shear deformation, the fracture of ligaments between the crack tip and the microcracks ahead, crack deflection, and bridging take place. With the use of these observations, it is possible to explain why cast iron with this optimized microstructure has excellent strength and to ughness. (C) Elsevier Science Inc., 1997.