Creep behavior accompanying oxidation of compacted graphite cast iron

The creep behavior accompanying oxidation of a compacted graphite cast iron (CGI) containing Cu, Mo and Sn elements was studied at temperatures ranging from 350 °C to 550 °C and creep loads ranging from 40 MPa to 150 MPa. The creep damage was observed using both optical and scanning electron microscopy (SEM). The results showed that obvious creep deformation occurred when T/Tm＞0.5 (T is testing temperature, Tm is melting temperature of the CGI) and the load is higher than 150 MPa. The creep deformation in specimen was accounted from three parts: (I) deformation of matrix, (II) initiation and propagation of creep cavities and (III) debonding between graphite and matrix. In addition, two models of crack were observed during creep deformation: (I) cracks propagated preferentially in ferrite phase and combined with debonding between graphite and matrix and (II) creep microcracks caused by creep cavities in the grain boundary. These two types of crack are usually accompanied with oxidation and the former one is more harmful than the latter one because of high crack propagation rate accelerated by interfacial debonding indirectly. Finally, the mechanism of creep deformation and fracture was discussed.