抄録
Although embrittlement of spheroidal graphite cast iron is caused by heating at about 450°C, it is the same as the temper embrittlement known in black-heart malleable cast iron. There have been many studies on this problem without any clear conclusion on the cause of this phenomenon. In this study, therefore, temper embrittlement in ferritic spheroidal graphite cast iron was re-examined from using new techniques such as instrumented Charpy impact test, scanning electron microscopy and ion microanalysis. It was found that temper embrittlement appeared mainly as the transition temperature rose, impact fracture loads at each position of the temperature transition curve decreased with the progress of embrittlement and intergranular type fracture occurred. No abnormality such as precipitation was observed on the surface by scanning electron microscope, but segregation of phosphorus and sulfur was observed clearly as a result of ion microanalysis. From this, it appeared that temper embrittlement was mainly due to normal segregation of phosphorus and sulfur at the grain boundary.
