球状黒鉛鋳鉄の生長に及ぼすふん囲気酸素濃度の影響

抄録

  The theory of irreversible diffusion was applied to dissolution and precipitation of graphite during the growth of cast iron. It was speculated that growth of spheroidal graphite cast iron of even the type not very susceptible to the effect of the heating atmosphere may be affected in some way by a small amount of gas molecules of the atmosphere penetrate into the iron. To test the validity of the speculation growth experiments were conducted on s.g. iron at austenited temperature range by changing oxygen concentration in the heating atmosphere. Amount of growth increased with increasing oxygen both in repeated heating and isothermal heating. Structural change by oxygen was recognized only on the iron surfaces and not inside. In deliberating the mechanism of the effect of oxygen attention was paid to the following observations.
  1) Increase in length as observed when self-carburization occurs was not observed after isothermal heating. 2) Slope of dilatation curves of both heating and cooling decreased with the progress of growth. 3) The difference between the slopes of the above two curves increased. 4) Number of fine graphite nodule precipitation increased roughly in proportion to the amount of growth. It was concluded that oxygen affected growth in such a way that the amount of graphite precipitation and redistribution in the austenite region increased with increasing oxygen concentration, because mobility, and hence, diffusion of carbon was reduced by a small quantity of oxygen penetrated into iron through the matrix and grain boundaries.