抄録
Ferrite-rimmed spheroidal graphite cast iron composed of ferrite rich structure near the surface and pearlite-rich at the inner part of a cylindrical specimen was developed by a simple heat treatment. The structure formation process was investigated by interrupting the transformation during continuous cooling and isothermal heat treatment around the eutectoid temperature after austenitizing. The optimum heat treatment for the ferrite-rimmed structure consists of slow cooling at a rate of about 10K/min from austenitizing temperature and isothermal holding around 1013K, followed by air cooling. CCT and TTT curves obtained from a small specimen indicate that the optimum cooling rate and the holding temperature correspond to the closeness of the onset of the ferrite and pearlite formations. It was also found that the austenitizing condition affects the thickness of the ferrite-rim. The bending property of the newly developed ferrite-rimmed cast iron is superior to that of a homogeneous ferrite-pearlite cast iron with the same tensile strength.
