A spheroidal graphite cast iron comprising: C: 3.3 to 4.0 mass %, Si: 2.1 to 2.7 mass %, Mn: 0.20 to 0.50 mass %, S: 0.005 to 0.030 mass %, Cu: 0.20 to 0.50 mass %, Mg: 0.03 to 0.06 mass % and the balance: Fe and inevitable impurities, wherein a tensile strength is 550 MPa or more, and an elongation is 12% or more.

A spheroidal graphite cast iron comprising: C: 3.3 to 4.0 mass %, Si: 2.1 to 2.7 mass %, Mn: 0.20 to 0.50 mass %, S: 0.005 to 0.030 mass %, Cu: 0.20 to 0.50 mass %, Mg: 0.03 to 0.06 mass % and the balance: Fe and inevitable impurities, wherein a tensile strength is 550 MPa or more, and an elongation is 12% or more.

A nodular graphite cast iron for pistons according to an embodiment contains, in mass %, C: 2.7 to 4.3%, Si: 2.0 to 3.5%, Mn: 0.3 to 0.8%, Mg: 0.02 to 0.10%, Cu: 0.3 to 1.0%, Cr: 0.05 to 0.90%, and Mo: 0.05 to 1.00% with the balance being composed of Fe and inevitable impurities. Then, the C content and the Si content fall within a composition range defined by a line sequentially joining respective points of point A (2.7%, 3.5%), point B (3.2%, 2.0%), point C (4.3%, 2.0%), and point D (3.8%, 3.5%) indicated by (the C content and the Si content) in a graph illustrating the relation between the C content and the Si content.

A nodular graphite cast iron for pistons according to an embodiment contains, in mass %, C: 2.7 to 4.3%, Si: 2.0 to 3.5%, Mn: 0.3 to 0.8%, Mg: 0.02 to 0.10%, Cu: 0.3 to 1.0%, Cr: 0.05 to 0.90%, and Mo: 0.05 to 1.00% with the balance being composed of Fe and inevitable impurities. Then, the C content and the Si content fall within a composition range defined by a line sequentially joining respective points of point A (2.7%, 3.5%), point B (3.2%, 2.0%), point C (4.3%, 2.0%), and point D (3.8%, 3.5%) indicated by (the C content and the Si content) in a graph illustrating the relation between the C content and the Si content.

The present disclosure relates to a manufacturing method of high-strength flake graphite cast iron, the high-strength flake graphite cast iron manufactured by the method, and an engine body including the cast iron, and more particularly, to flake graphite cast iron and a manufacturing method thereof, wherein the flake graphite cast iron has a uniform graphite shape and low probability of forming chill and has high tensile strength of at least 350 MPa and excellent workability and fluidity by controlling the content of manganese (Mn) and a trace of strontium (Sr), which are included in the cast iron, within a specific ratio.

The present disclosure relates to a manufacturing method of high-strength flake graphite cast iron, the high-strength flake graphite cast iron manufactured by the method, and an engine body including the cast iron, and more particularly, to flake graphite cast iron and a manufacturing method thereof, wherein the flake graphite cast iron has a uniform graphite shape and low probability of forming chill and has high tensile strength of at least 350 MPa and excellent workability and fluidity by controlling the content of manganese (Mn) and a trace of strontium (Sr), which are included in the cast iron, within a specific ratio.

A centrifugally cast, hot-rolling composite roll comprising an outer layer formed by a centrifugal casting method, and an inner layer made of ductile cast iron and integrally fused to the outer layer; the outer layer having a chemical composition comprising by mass 1-3% of C, 0.4-3% of Si, 0.3-3% of Mn, 1-5% of Ni, 2-7% of Cr, 3-8% of Mo, 3-7% of V, and 0.01-0.12% of B, the balance being Fe and inevitable impurities, and meeting the relation expressed by Cr/(Mo+0.5W)<−2/3[C−0.2(V+1.19Nb)]+11/6, wherein W=0, and Nb=0, when W and Nb are not contained; and containing by area 1-15% of MC carbide, 0.5-20% of carboboride, and 0.5-20% of Mo-based carbide.

A centrifugally cast, hot-rolling composite roll comprising an outer layer formed by a centrifugal casting method, and an inner layer made of ductile cast iron and integrally fused to the outer layer; the outer layer having a chemical composition comprising by mass 1-3% of C, 0.4-3% of Si, 0.3-3% of Mn, 1-5% of Ni, 2-7% of Cr, 3-8% of Mo, 3-7% of V, and 0.01-0.12% of B, the balance being Fe and inevitable impurities, and meeting the relation expressed by Cr/(Mo+0.5W)<−2/3[C−0.2(V+1.19Nb)]+11/6, wherein W=0, and Nb=0, when W and Nb are not contained; and containing by area 1-15% of MC carbide, 0.5-20% of carboboride, and 0.5-20% of Mo-based carbide.

A centrifugally cast, hot-rolling composite roll comprising an outer layer formed by a centrifugal casting method, and an inner layer made of ductile cast iron and integrally fused to the outer layer; the outer layer having a chemical composition comprising by mass 1.6-3% of C, 0.3-2.5% of Si, 0.3-2.5% of Mn, 0.1-5% of Ni, 2.8-7% of Cr, 1.8-6% of Mo, 3.3-6.5% of V, and 0.02-0.12% of B (or 0.01-0.12% of B, and 0.05-02% of S), the balance being Fe and inevitable impurities, and meeting the relation expressed by Cr/(Mo+0.5W)≥−2/3[C−0.2(V+1.19Nb)]+11/6, wherein W=0, and Nb=0, when W and Nb are not contained, and containing by area 1-15% of MC carbide, 0.5-20% of carboboride, and 1-25% of Cr-based carbide.

A centrifugally cast, hot-rolling composite roll comprising an outer layer formed by a centrifugal casting method, and an inner layer made of ductile cast iron and integrally fused to the outer layer; the outer layer having a chemical composition comprising by mass 1.6-3% of C, 0.3-2.5% of Si, 0.3-2.5% of Mn, 0.1-5% of Ni, 2.8-7% of Cr, 1.8-6% of Mo, 3.3-6.5% of V, and 0.02-0.12% of B (or 0.01-0.12% of B, and 0.05-02% of S), the balance being Fe and inevitable impurities, and meeting the relation expressed by Cr/(Mo+0.5W)≥−2/3[C−0.2(V+1.19Nb)]+11/6, wherein W=0, and Nb=0, when W and Nb are not contained, and containing by area 1-15% of MC carbide, 0.5-20% of carboboride, and 1-25% of Cr-based carbide.