Method of producing a spheroidal graphite cast iron

Claim 1

A method of producing spheroidal graphite cast iron, comprising the steps of: providing a molten metal for a casting which contains 2.5-4.1 wt. % of carbon, 1.5-3.5 wt. % of silicon, 0.3-1.0 wt. % of manganese, not more than 0.15 wt. % of phosphorus, not more than 0.03 wt. % of sulfur, 0.005-0.08 wt. % of magnesium, at least one of 0.3-1.5 wt. % of copper, 0.27-0.5 wt. % of molybdenum and 0.1-3.5 wt. % of nickel, and a remainder of iron; forming a casting of spheroidal graphite cast iron containing not less than 250 graphite grains/mm 2 from the molten metal while adding an inoculant to the molten metal by a pouring inoculation method or an in-mold inoculation method at the time of forming the casting; annealing the casting by heating and holding the casting at a temperature of not more than the A 1 transformation point for 0.5 to 8 h. so as to change its matrix to ferrite; machining the casting; and austempering the casting so as to subject the casting to austenitizing and isothermal transformation.

Claim 2

A method of producing spheroidal graphite cast iron, comprising the steps of: providing a molten metal for a casting which contains 2.5-4.1 wt. % of carbon, 1.5-3.5 wt. % of silicon, 0.3-1.0 wt. % of manganese, not more than 0.15 wt. % of phosphorus, not more than 0.03 wt. % of sulfur, 0.005-0.08 wt. % of magnesium, at least one of 0.3-1.5 wt. % of copper, 0.27-0.5 wt. % of molybdenum and 0.1-3.5 wt. % of nickel, and a remainder of iron; forming a casting of spheroidal graphite cast iron containing not less than 250 graphite grains/mm 2 from the molten metal while adding an inoculant to the molten metal by a pouring inoculation method or an in-mold inoculation method at the time of forming the casting; annealing the casting by heating and holding the casting at a temperature of not more than the A 1 transformation point for 0.5 to 8 h. so as to change its matrix to ferrite; machining the casting; and austempering the casting so as to subject the casting to austenitizing and isothermal transformation.

Claim 6

A method of producing spheroidal graphite cast iron, comprising the steps of: providing a molten metal for a casting which contains 2.5-4.1 wt. % of carbon, 1.5-3.5 wt. % of silicon, 0.3-1.0 wt. % of manganese, not more than 0.15 wt. % of phosphorus, not more than 0.03 wt. % of sulfur, 0.005-0.08 wt. % of magnesium, at least one of 0.3-1.5 wt. % of copper, 0.27-0.5 wt. % of molybdenum and 0.1-3.5 wt. % of nickel, and a remainder of iron; forming a casting of spheroidal graphite cast iron containing not less than 250 graphite grains/mm 2 from the molten metal while adding an inoculant to the molten metal by pouring inoculation method or an in-mold inoculation method at the time of forming the casting; annealing the casting by heating and holding the casting at a temperature of from 700° to 750° C. for 0.5 to 8 h. so as to change its matrix to ferrite; machining the casting; and austempering the casting so as to subject the casting to austenitizing and isothermal transformation.

Claim 7

A method of producing spheroidal graphite cast iron, comprising the steps of: providing a molten metal for a casting which contains 2.5-4.1 wt. % of carbon, 1.5-3.5 wt. % of silicon, 0.3-1.0 wt. % of manganese, not more than 0.15 wt. % of phosphorus, not more than 0.03 wt. % of sulfur, 0.005-0.08 wt. % of magnesium, at least one of 0.3-1.5 wt. % of copper, 0.27-0.5 wt. % of molybdenum and 0.1-3.5 wt. % of nickel, and a remainder of iron; forming a casting of spheroidal graphite cast iron containing not less than 250 graphite grains/mm 2 from the molten metal while adding an inoculant to the molten metal by pouring inoculation method or an in-mold inoculation method at the time of forming the casting; annealing the casting by heating and holding the casting at a temperature of from 700° to 750° C. for 0.5 to 8 h. so as to change its matrix to ferrite; machining the casting; and austempering the casting so as to subject the casting to austenitizing and isothermal transformation.

Claim 8

A method of producing spheroidal graphite cast iron, comprising the steps of: providing a molten metal for casting which contains 2.5-4.1 wt. % of carbon, 1.5-3.5 wt. % of silicon, 0.3-1.0 wt. % of manganese, not more than 0.15 wt. % of phosphorus, not more than 0.03 wt. % of sulfur, 0.005-0.08 wt. % of magnesium, at least one of 0.3-1.5 wt. % of copper, 0.27-0.5 wt. % of molybdenum and 0.1-3.5 wt. % of nickel, and a remainder of iron; forming a casting of spheroidal graphite cast iron containing not less than 250 graphite grains/mm 2 , in which precipitation of chill is restricted, by adding an inoculant to the molten metal by a pouring inoculation method or an in-mold inoculation method; machining the casting; subjecting the casting to austenitizing by heating the casting; rapidly cooling the casting; subjecting the casting to isothermal transformation; and machining the casting.

Claim 9

A method of producing spheroidal graphite cast iron, comprising the steps of: providing a molten metal for casting which contains 2.5-4.1 wt. % of carbon, 1.5-3.5 wt. % of silicon, 0.3-1.0 wt. % of manganese, not more than 0.15 wt. % of phosphorus, not more than 0.03 wt. % of sulfur, 0.005-0.08 wt. % of magnesium, at least one of 0.3-1.5 wt. % of copper, 0.27-0.5 wt. % of molybdenum and 0.1-3.5 wt. % of nickel, and a remainder of iron; forming a casting of spheroidal graphite cast iron containing not less than 250 graphite grains/mm 2 , in which precipitation of chill is restricted, by adding an inoculant to the molten metal by a pouring inoculation method or an in-mold inoculation method; machining the casting; subjecting the casting to austenitizing by heating the casting; rapidly cooling the casting; subjecting the casting to isothermal transformation; and machining the casting.