Influence of Graphite Distribution on the Impact Properties of Spheroidal Graphite Cast Irons Produced via Permanent Mold Casting

Regarding the permanent mold casting (PM) method for spheroidal graphite irons castings, the attractive method has been developed to obtain a full graphite structure without forming Fe3C in the as-cast condition by controlling the free-nitrogen. When using this method, additional processes, such as heat treatment, are not necessary. However, heat treatment must be applied when using conventional methods owing to the formation of ledeburite (chills). In this study, sample castings were cast using conventional and developed PM casting methods, and the relationship between graphite distribution and impact properties investigated. Consequently, the graphite distribution of conventional samples was determined that order tendency was higher than developed samples. Furthermore, the impact absorbed energy of the samples with high ordinal tendency was lower than that of the samples with high random tendency graphite distribution. The total absorbed energy, crack initiation or propagation energy were strongly correlated with randomization or not in characteristic graphite distribution by both developed and conventional manufacturing methods. Therefore, the developed methods confer the benefits of not only less processing for casting but also better impact properties that enhance design safety.