球状黒鉛鋳鉄の機械的性質と耐酸化性に及ぼすけい素の影響

抄録

  In order to develop spheroidal graphite cast iron with a good heat resistance for automotive parts, the influence of silicon content on mechanical and anti-oxidation properties of the iron was investigated. The specimens containing from 2.4%—5.0%Si were heated at 700°C and 850°C for 100hrs, then the amount of oxides eliminated by means of shot blast treatment were measured. On the other hand, tensile strength, elongation and hardness from room temperature to 700°C and impact value from −70°C to 200°C were measured. The reasons why adding Si contributes to improvement of anti-oxidation are considered to be that Fe₂SiO₄ content increases in the oxide layer, and that decarburization reaction is accelerated as the upper point of eutectoid transformation temperature rises. The higher the temperature, the smaller the effect of Si content on the tensile strength is. Adding Si is not effective in improving the strength over 500°C. As the elongation at 500°C abruptly declines at 4.7%Si in the annealing specimens and at 4.4%Si in the as-cast specimens, improved elongation is detained by annealing. The relation between strength and hardness is drawn by a straight line from room temperature to 300°C.