Spheroidal graphite cast iron and method of producing spheroidal graphite cast iron, and vehicle undercarriage parts

A spheroidal graphite cast iron comprising:

• a chemical composition consisting of:
• C:
• 3.0% to 4.0%,
• Si:
• 2.0% to 2.4%,
• Cu:
• 0.20% to 0.50%,
• Mn:
• 0.15% to 0.35%,
• S:
• 0.005% to 0.030%,
• Mg:
• 0.03% to 0.06%, each by mass, and
• the balance being Fe and inevitable impurities,
• where Mn and Cu are contained at 0.45% to 0.75% in total;
• and
• a structure in which a spheroidal graphite and a ferrite layer which is situated around and forming a boundary with the spheroidal graphite are crystallized out in a matrix of pearlite,
• wherein in the structure,
• part of the pearlite penetrates from the matrix of pearlite into the ferrite layer and reaches a boundary of the ferrite layer and the spheroidal graphite at one or more areas,
• the ferrite layer has cluster of grains that are connected and joined to each other,
• wherein the cast iron has a tensile strength of 700 MPa or more and an elongation of 10% or more.