Effects of contents of carbon and silicon, and spheroidizing conditions such as amounts and kinds of additives and their treating temperatures on chilling tendency of spheroidal graphite irons cast in a metal mold 30mm in diameter were studied. When additives of 9.30%Mg-4.02%Ca- 2.72%RE-44.7%Si-Fe are used, eutectic carbides disappear at Si 2.6 to 2.7% (3.4 to 3.6%C) by reducing the amount of additives down to 0.4% and lowering the treating temperature down to 1,350°C. When treated at 1,400°C, low Mg additives of 3.14%Mg-1.13%Ca-1.6%RE-44.5%Si-Fe show lighter chilling tendency than the others at the same retained Mg. At carbon saturation values 1.07 to 1.09, low carbon irons of 3.1 to 3.3%C are free from eutectic carbides, but irons of about 3.6% have fine Ledeburites in spite of graphite nodules up to 1,750/mm
2. The chilling tendency of spheroidal graphite irons cast in metal molds depends not on the number of graphite nodules but on mainly spheroidizing temperatures and is moderated by suppressing the explosive reaction in treating.
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