Spheroidal graphite cast iron, cast article and automobile structure part made thereof, and method for producing spheroidal graphite cast iron article

A method for producing a cast article of spheroidal graphite cast iron meeting the following conditions:

• ti N(5-)≥250,
• N(5-20)/N(5-)≥0.6, and
• N(30-)/N(5-)≤0.2,
• wherein N(5-), N(5-20), and N(30-) are the number (/mm2) of graphite particles having equivalent-circle diameters of 5 μm or more, the number (/mm2) of graphite particles having equivalent-circle diameters of 5 μm or more and less than 20 μm, and the number (/mm2) of graphite particles having equivalent-circle diameters of 30 μm or more, respectively, among graphite particles observed in an arbitrary cross section of at least 1 mm2;
• comprising
• pressing a surface of a melt poured into a gas-permeable casting mold by a gas at pressure of 1-100 kPa, before said melt starts eutectic solidification;
• and
• solidifying said melt while supplying said gas into said casting mold.