The present disclosure provides a method for controlling an amount of silicon added to ductile cast iron, a method for casting ductile cast iron, and a cast product, which relate to the technical fields of metallurgical and cast iron alloys. The method for controlling an amount of silicon added to ductile cast iron includes smelting ductile cast iron using scrap steel as a raw material. After the scrap steel is melted into molten iron, a copper alloy is added so that the molten iron has a copper equivalent of 0.8% to 1.0%, wherein the copper equivalent is controlled by formula (II). Then, ferrosilicon is added so that the content of silicon added to the molten iron satisfies formula (I).

There is provided a centrifugally cast composite roll for rolling having excellent wear resistance and surface deterioration resistance at levels of a high-speed steel cast iron roll and having rolling incident resistance at a level of a high alloy grain cast iron roll. Its outer layer includes chemical components by mass ratio: C: 1.5 to 3.5%; Si: 0.3 to 3.0%; Mn: 0.1 to 3.0%; Ni: 1.0 to 6.0%; Cr: 1.5 to 6.0%; Mo: 0.1 to 2.5%; V: 2.0 to 6.0%; Nb: 0.1 to 3.0%; B: 0.001 to 0.2%; N: 0.005 to 0.070%; and the balance being Fe and inevitable impurities, wherein: a chemical composition of the outer layer satisfies Formula (1) and has 5 to 30% of M.sub.3C carbide by area ratio; an outer layer Shore hardness (A) of a roll surface satisfies Formula (2); and a residual stress (B) of the roll surface satisfies Formula (3),
2×Ni+0.5×Cr+Mo>10.0  (1)
Hs 75≤A≤Hs 85  (2)
100 MPa≤B≤350 MPa  (3).

There is provided a centrifugally cast composite roll for rolling having excellent wear resistance and surface deterioration resistance at levels of a high-speed steel cast iron roll and having rolling incident resistance at a level of a high alloy grain cast iron roll. Its outer layer includes chemical components by mass ratio: C: 1.5 to 3.5%; Si: 0.3 to 3.0%; Mn: 0.1 to 3.0%; Ni: 1.0 to 6.0%; Cr: 1.5 to 6.0%; Mo: 0.1 to 2.5%; V: 2.0 to 6.0%; Nb: 0.1 to 3.0%; B: 0.001 to 0.2%; N: 0.005 to 0.070%; and the balance being Fe and inevitable impurities, wherein: a chemical composition of the outer layer satisfies Formula (1) and has 5 to 30% of M.sub.3C carbide by area ratio; an outer layer Shore hardness (A) of a roll surface satisfies Formula (2); and a residual stress (B) of the roll surface satisfies Formula (3),
2×Ni+0.5×Cr+Mo>10.0  (1)
Hs 75≤A≤Hs 85  (2)
100 MPa≤B≤350 MPa  (3).

This ferritic spheroidal graphite cast iron contains 3.0% to 3.6% by mass of C, 4.0% to 5.0% by mass of Si, 0.020% to 0.10% by mass of Mg, 1.0% or less of Mn, 0.10% by mass or less of P, and 0.015% by mass or less of S, with the balance being Fe and inevitable impurities.

A spheroidal graphite cast iron having an excellent impact strength at low temperature and a method for producing the same are provided. The present disclosure relates to the spheroidal graphite cast iron comprising: C: 3.5 mass % to 4.2 mass %; Si: 2.0 mass % to 2.8 mass %; Mn: 0.2 mass % to 0.4 mass %; Cu: 0.1 mass % to 0.7 mass %; Mg: 0.02 mass % to 0.06 mass %; Cr: 0.01 mass % to 0.15 mass %; and the balance: Fe and inevitable impurities, wherein Mn+Cr+Cu is 0.431 mass % to 1.090 mass %, a graphite nodule count is 230/mm.sup.2 or less, and a pearlite fraction is 30% to 85%.

A spheroidal graphite cast iron having an excellent impact strength at low temperature and a method for producing the same are provided. The present disclosure relates to the spheroidal graphite cast iron comprising: C: 3.5 mass % to 4.2 mass %; Si: 2.0 mass % to 2.8 mass %; Mn: 0.2 mass % to 0.4 mass %; Cu: 0.1 mass % to 0.7 mass %; Mg: 0.02 mass % to 0.06 mass %; Cr: 0.01 mass % to 0.15 mass %; and the balance: Fe and inevitable impurities, wherein Mn+Cr+Cu is 0.431 mass % to 1.090 mass %, a graphite nodule count is 230/mm.sup.2 or less, and a pearlite fraction is 30% to 85%.

A nodular iron alloy and automotive components, such as a crankshaft, are provided. The nodular iron alloy may include iron, about 2.2-3.2 wt % carbon, about 1.7-2.3 wt % silicon, about 0.2-0.6 wt % manganese, a maximum of 0.03 wt % phosphorus, a maximum of 0.02 wt % sulfur, about 0.2-0.6 wt % copper, about 0.1-0.4 wt % chromium, about 0.4-0.8 wt % nickel, about 0.15-0.45 wt % molybdenum, about 0.2-1.0 wt % cobalt, about 0.02-0.06 wt % magnesium, and a maximum of 0.002 wt % rare earth element(s). The nodular iron alloy may have a Young's modulus in the range of 175-195 GPa and an as-cast ultimate tensile strength in the range of 750-950 MPa. This alloy possesses favorable strength, stiffness and noise/vibration/harshness qualities, making it suitable in crankshaft applications. A method of forming the nodular iron alloy includes feeding a magnesium-based material into a molten iron alloy through a continuous system at a constant amount.

A nodular iron alloy and automotive components, such as a crankshaft, are provided. The nodular iron alloy may include iron, about 2.2-3.2 wt % carbon, about 1.7-2.3 wt % silicon, about 0.2-0.6 wt % manganese, a maximum of 0.03 wt % phosphorus, a maximum of 0.02 wt % sulfur, about 0.2-0.6 wt % copper, about 0.1-0.4 wt % chromium, about 0.4-0.8 wt % nickel, about 0.15-0.45 wt % molybdenum, about 0.2-1.0 wt % cobalt, about 0.02-0.06 wt % magnesium, and a maximum of 0.002 wt % rare earth element(s). The nodular iron alloy may have a Young's modulus in the range of 175-195 GPa and an as-cast ultimate tensile strength in the range of 750-950 MPa. This alloy possesses favorable strength, stiffness and noise/vibration/harshness qualities, making it suitable in crankshaft applications. A method of forming the nodular iron alloy includes feeding a magnesium-based material into a molten iron alloy through a continuous system at a constant amount.

A high rigid spheroidal graphite cast iron, comprising: 2.0 mass % to less than 2.7 mass % or more than 3.0 mass % to less than 3.6 mass % of C, 1.5 to 3.0 mass % of Si, 1.0% or less of Mn, 1.0 mass % or less of Cu, 0.02 to 0.07 mass % of Mg and the residual Fe and inevitable impurities, wherein a carbon equivalent (a CE value) calculated by the mathematical expression (1): CE=C (mass %)+Si (mass %)/3 in terms of C and Si contents is 2.8 to 3.2% within a first range from 2.0 mass % to less than 2.7 mass % of C and is 3.6 to 4.2% within a second range from more than 3.0 mass % to less than 3.6 mass % of C, and the Young's modulus is 170 GPa or more.

A high rigid spheroidal graphite cast iron, comprising: 2.0 mass % to less than 2.7 mass % or more than 3.0 mass % to less than 3.6 mass % of C, 1.5 to 3.0 mass % of Si, 1.0% or less of Mn, 1.0 mass % or less of Cu, 0.02 to 0.07 mass % of Mg and the residual Fe and inevitable impurities, wherein a carbon equivalent (a CE value) calculated by the mathematical expression (1): CE=C (mass %)+Si (mass %)/3 in terms of C and Si contents is 2.8 to 3.2% within a first range from 2.0 mass % to less than 2.7 mass % of C and is 3.6 to 4.2% within a second range from more than 3.0 mass % to less than 3.6 mass % of C, and the Young's modulus is 170 GPa or more.