The effect of microstructure on the toughness of ferritic nodular cast iron

Abstract

The ductile-brittle transition behaviour in ferritic nodular cast iron appears to depend not only on chemical compositions but also on many microstructural variables. The ferrite grain diameter and the mean free path between graphite nodules are studied here as the main microstructural variables, and the effects of these on toughness are investigated mainly by the instrumented Charpy impact test. The results show that the transition temperature is lowered when the ferrite grain size or the mean free path is decreased. On the other hand, increase in the ferrite grain size or the mean free path leads to a rise in the upper shelf energy in the ductile fracture range. Equations to predict the dynamic lower yield load (P _y) and the maximum load transition temperature (T _rpm) are derived from the relation for steel dispersed with spheriodal carbides.