抄録
The object of the present work was to produce ferrite matrix spheroidal graphite cast irons by metal mold casting with great toughness, especially high elongation, in the as-cast state by systematically changing the Si and Mn contents. Specimens were made from high purity pig iron and poured at 1,340 degree C into metal mold (30φ×170mm) by horizontal casting method. Si and Mn contents were varied from 2.5∼4.8% and 0.009∼0.25%, respectively. Other chemical composition was about 3.4% for C, 0.025% for P, 0.01% for S and 0.035% for Mg. Except for the 2.7% Si-0.25% Mn specimen, eutectic cementite was not observed. As the Si content was increased from 2.7 to 3.0%, the amount of eutectoid cementite was drastically reduced and an almost complete ferritic matrix was obtained with 4.7% Si even in the series of 0.25% Mn. Elongation over 15% was obtained in all the Mn series with the Si content range from 3.0 to 4.5%; especially notable was that in low Mn content series of 0.009% Mn, elongation over 20% was obtained. But beyond 4.5% Si, elongation value decreased due to the appearance of exploded graphite. The proof stress and tensile strength were higher than 40kg/mm2 and 54kg/mm2, respectively. Impact value at room temperature higher than 1.2kgm/cm2 was obtained up to 3.5% Si. It is concluded that it is commercially possible to produce an as-cast ferritic high elongation spheroidal graphite cast iron by metal mold casting, if hyper-eutectic melts of high Si and low Mn content are used.
