SPHEROIDAL GRAPHITE CAST IRON MEMBER AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide a spheroidal graphite cast iron member formed into a double structure of that essentially consisting of ferrite low in notch sensitivity and large in the number of graphite grains on the surface layer and that high in strength on the inside and to provide its production method. SOLUTION: This method for producing a spheroidal graphite cast iron member includes a step in which at least one or more kinds of pearlite transforming elements selected from the groups consisting of, by weight, 0.1 to 1.0% Cu, 0.1 to 0.5% Mn and 0.02 to 0.1% Cr and 2.0 to 2.8% silicon are added to molten metal and a step in which the molten metal is cooled to the eutectic point of the molten metal in such a manner that the rate in the surface part 13 is controlled to 140 to 400 deg.C/min which is also higher than that in the inside 17 of the molten metal by >=10% and a step in which the molten metal is cooled to the eutectic point of the molten metal at 15 to 50 deg.C/min and also in such a manner that the cooling rate in the surface part 13 is made higher than that in the inside 17.