| Nodular graphite cast irons which are consisting of three kinds of matrix, i.e. pearlite, mixture of pearlite and ferrite, and ferrite, have been prepared, then the plastic deformations and fracture behaviors have been studied by the methods of observing the stress-strain curves in tension test and load-time curves in impact test respectively. The results obtained are summarized as follows: (1) The stress-strain curves for the nodular graphite cast iron of ferrite matrix have shown discontinuous yielding behaviors as observed in those of mild steel. (2) The tensile and yield strength for the three kinds of nodular graphite cast iron are almost independent of the strain rate between 1.5×10^(-5) and 1.5×10^(-3)sec^(-1). (3) The equation σ_t=Kε^n_t seems to be correct in the plastic regions of the stress-strain curves for all kinds of nodular graphite cast irons we prepared. (4) The nodular graphite cast iron of ferrite matrix shows better performance is combination of strength and ductility compared with other two cast irons. (5) The nodular graphite cast irons of two types of matrix, ferrite, and mixture of pearlite and ferrite, show the quite similar fracture behaviors in impact tests. (6) It is concluded that the impact energies of the nodular graphite cast irons of three types of matrix are not more than the crack initiation energies. |
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