A centrifugally cast 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 being made of an Fe-based alloy comprising by mass 1.3-3.7% of C, 0.3-3% of Si, 0.1-3% of Mn, 1-7% of Cr, 1-8% of Mo, at least one of 2.5-7% of V, 0.1-3% of Nb and 0.1-5% of W (V is indispensable), and 0.01-0.2% of B and/or 0.05-0.3% of S, the balance being substantially Fe and inevitable impurities, the outer layer having a structure containing no graphite; the inner layer comprising a core portion fused to the outer layer, and a drive-side shaft portion and a free-side shaft portion integrally extending from both ends of the core portion; the total amount of Cr, Mo, V, Nb and W being 0.35-2% by mass in an end portion of the drive-side shaft portion and 0.15-1.8% by mass in an end portion of the free-side shaft portion, the former being larger than the latter by 0.2% or more by mass.

A centrifugally cast 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 being made of an Fe-based alloy comprising by mass 1.3-3.7% of C, 0.3-3% of Si, 0.1-3% of Mn, 1-7% of Cr, 1-8% of Mo, at least one of 2.5-7% of V, 0.1-3% of Nb and 0.1-5% of W (V is indispensable), and 0.01-0.2% of B and/or 0.05-0.3% of S, the balance being substantially Fe and inevitable impurities, the outer layer having a structure containing no graphite; the inner layer comprising a core portion fused to the outer layer, and a drive-side shaft portion and a free-side shaft portion integrally extending from both ends of the core portion; the total amount of Cr, Mo, V, Nb and W being 0.35-2% by mass in an end portion of the drive-side shaft portion and 0.15-1.8% by mass in an end portion of the free-side shaft portion, the former being larger than the latter by 0.2% or more by mass.

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.

A cast iron having high strength, hardness, and thermal conductivity for a cylinder liner of an internal combustion engine is provided. The cast iron includes 3.2 wt. % to 3.8 wt. % carbon, 2.2 wt. % to 3.2 wt. % silicon, 0.5 wt. % to 1.3 wt. % copper, and at least 75.0 wt. % iron, based on the total weight of the cast iron. The cast iron further includes 0.01 wt. % to 0.5 wt. % manganese, 0.01 wt. % to 0.2 wt. % chromium, up to 0.3 wt. % phosphorous, up to 0.05 wt. % sulfur, up to 0.2 wt. % tin, and up to 0.1 wt. % magnesium, based on the total weight of the cast iron. Preferably, the cast iron is free of molybdenum, nickel, and vanadium. The cast iron is also heat treated and solidifies to achieve fully spheroidal graphite.

A composite roll for rolling comprising an outer layer and an inner layer integrally fused to each other; the outer layer being made of an Fe-based alloy comprising by mass 1-3% of C, 0.3-3% of Si, 0.1-3% of Mn, 0.1-5% of Ni, 1-7% of Cr, 1-8% of Mo, 4-7% of V, 0.005-0.15% of N, and 0.05-0.2% of B; the inner layer being made of graphite cast iron comprising by mass 2.4-3.6% of C, 1.5-3.5% of Si, 0.1-2% of Mn, 0.1-2% of Ni, less than 0.7% of Cr, less than 0.7% of Mo, 0.05-1% of V, and 0.01-0.1% of Mg; the inner layer comprising a core portion fused to the outer layer, and shaft portions integrally extending from both ends of the core portion; at least one of the shaft portions containing 200/cm.sup.2 or more of hard MC carbides having circle-equivalent diameters of 5 μm or more.