The effect of spheroidal graphite on fracture process initiation in cast iron

Abstract

Achieving a balance between strength, toughness and technological properties of cast iron requires knowledge of the relationships between local and macroscopic failure processes. High toughness is conditional upon the substantial dissipation of deformation energy during crack propagation and the initiation of ductile failure. In spheroidal graphite cast iron, toughness depends on the size distribution of these particles, their volume fraction, and the strength of the ferritic matrix/particle phase boundary. The proposed model of fracture surface formation shows how nucleation deformation depends on the local characteristics of the cast iron, graphite particle size, and the strength and energy of the phase boundary. Local fracture deformation during cavity coalescence is most strongly affected by the geometric characteristics of the structure, the spatial distribution of particles, their volume fraction in the matrix, and also the strengthening characteristics of the matrix. The model of fracture surface formation was successfully tested on commercially produced ferritic spheroidal graphite cast iron. The criterion of deformation energy equilibrium was used to predict nucleation deformation and deformation during cavity coalescence. The model can be applied in designing optimized graphite particle size distribution and developing optimized technological parameters for cast iron production.