球状黒鉛鋳鉄の凝固時間，過冷却及び黒鉛粒数の関係

抄録

  Solidification of spheroidal graphite iron of Fe-C and Fe-Si-C eutectic alloy systems was analytically investigated by means of quantitative metallography. Small specimens, some of which were inoculated, were cooled and solidified at varied rates and quenched at about 1,000°C. The volume fraction of graphite V_G and the number of graphite nodules in a unit area N_A were measured in a longitudinal section of each specimen. Growth rate constants of austenite spheres in liquid K were computed by
    V^-1/3N_AKt_S=0.33,
where t_S denoted the conventional time for complete solidification at an average temperature. The values of K thus determined were all in good accordance with those Fe-C and Fe-Ni-C eutectic alloys reported previously. The above equation and the temperature dependent values of K explained the small undercooling in Fe-Si-C and inoculated alloys with increased nodule numbers. A chart for computation of N_A, which is one of the important matrix controlling factors, from temperature and time of solidification was also shown.
  As the maximum value of K determined was approximately 4×10^-7cm₂/sec, V_G^-1/3N_At_S should be larger than 8.25×10⁵ sec/cm² in order for solidification to be completed by diffusion controlled gowth of austenite spheres under consideration. Otherwise, a different mechanism must be considered in the solidification process of ledebulite formation among austenite spheres, which occured in the later stages of solidification when Fe-C alloy was cooled relatively fast.