An austenitic cast iron including basic elements of C, Si, Cr, Ni, Mn and Cu; and the balance including Fe, inevitable impurities and/or a trace-amount modifier element, which is effective in improving a characteristic of the cast iron, in a trace amount; and structured by a base comprising an Fe alloy in which an austenite phase makes a major phase in ordinary-temperature region; wherein the basic elements fall within compositional ranges that satisfy the following conditions when the entirety of the cast iron is taken as 100% by mass: C: from 2.0 to 3.0%; Si: from 4.0 to 5.4%; Cr: from 0.8 to 2.0%; Mn: from 3.9 to 5.6%; Ni: from 17 to 22%; and Cu: from 0.9 to 1.6%.

A method for producing spheroidal graphite cast iron having a specific final composition includes: subjecting a molten iron to a spheroidization treatment using a spheroidizing agent of an FeSiMgCa-based alloy containing no rare earth element; conducting an inoculation treatment using a first FeSi-based inoculant; and conducting a pouring inoculation treatment with a given amount of a second FeSi-based inoculant containing 45-75% of Si, 1-3% of Ca, and 15 ppm or less of Ba.

A grade of ductile cast iron having a tensile strength (Rm) equal to or greater than 700 MPa, an elongation at break equal to or greater than 11%, a yield strength (Rp.sub.0.2) equal to or greater than 532 MPa, and a minimum ratio of yield strength (Rp.sub.0.2) to tensile strength (Rm) of 76% in a tensile test performed on a specimen taken from a tensile bar in accordance with standard EN 1563 and having a diameter of 25 mm and a length of 200 mm.

A method of repairing defect in cast iron workpiece, including: machining the workpiece in the area of the defect to remove the defective material and form a chamber opening at a surface of the workpiece; anchoring a receptacle to the workpiece above the chamber (2), the receptacle is provided with an orifice in communication with the chamber; adding molten iron (4) into the receptacle so that it at least part of it flows into the chamber; adding slagging agent (5) into the receptacle; heating the slagging agent and the molten iron with an electrode (6); adding nodulizing agent into the molten iron so as to segregate graphite; and allowing the molten iron and the workpiece to cool down slowly. The above-described technique also has applicability for connecting two cast iron workpieces (11,12) together.

Additive for the thermochemical treatment of molten iron in order to separate, distribute, agglomerate, precipitate, spheroidize and/or crystallize combined, solvated and/or colloidal carbon present in molten iron in the liquid state into graphite in its hexagonal diamond or Lonsdaleite form, in order to produce ductile, nodular, spheroidal, vermicular, coral, spheroidized or grey iron with superior mechanical properties, iron with high metal yield and zero contraction during casting; the additive comprises two or more elements in the metallic state selected from the S-block of periods 2 to 7 of the periodic table of elements; and two or more elements in the metallic state selected from F-block of periods 6 to 7 of the periodic table of elements. The additive makes it possible to produce cast iron parts with Type I and II spheroidal graphite in hexagonal diamond or Lonsdaleite form as per the ASTM-A247 standard.

Additive for the thermochemical treatment of molten iron in order to separate, distribute, agglomerate, precipitate, spheroidize and/or crystallize combined, solvated and/or colloidal carbon present in molten iron in the liquid state into graphite in its hexagonal diamond or Lonsdaleite form, in order to produce ductile, nodular, spheroidal, vermicular, coral, spheroidized or grey iron with superior mechanical properties, iron with high metal yield and zero contraction during casting; the additive comprises two or more elements in the metallic state selected from the S-block of periods 2 to 7 of the periodic table of elements; and two or more elements in the metallic state selected from F-block of periods 6 to 7 of the periodic table of elements. The additive makes it possible to produce cast iron parts with Type I and II spheroidal graphite in hexagonal diamond or Lonsdaleite form as per the ASTM-A247 standard.

Additive for the thermochemical treatment of molten iron in order to separate, distribute, agglomerate, precipitate, spheroidize and/or crystallize combined, solvated and/or colloidal carbon present in molten iron in the liquid state into graphite in its hexagonal diamond or Lonsdaleite form, in order to produce ductile, nodular, spheroidal, vermicular, coral, spheroidized or grey iron with superior mechanical properties, iron with high metal yield and zero contraction during casting; the additive comprises two or more elements in the metallic state selected from the S-block of periods 2 to 7 of the periodic table of elements; and two or more elements in the metallic state selected from F-block of periods 6 to 7 of the periodic table of elements. The additive makes it possible to produce cast iron parts with Type I and II spheroidal graphite in hexagonal diamond or Lonsdaleite form as per the ASTM-A247 standard.

Additive for the thermochemical treatment of molten iron in order to separate, distribute, agglomerate, precipitate, spheroidize and/or crystallize combined, solvated and/or colloidal carbon present in molten iron in the liquid state into graphite in its hexagonal diamond or Lonsdaleite form, in order to produce ductile, nodular, spheroidal, vermicular, coral, spheroidized or grey iron with superior mechanical properties, iron with high metal yield and zero contraction during casting; the additive comprises two or more elements in the metallic state selected from the S-block of periods 2 to 7 of the periodic table of elements; and two or more elements in the metallic state selected from F-block of periods 6 to 7 of the periodic table of elements. The additive makes it possible to produce cast iron parts with Type I and II spheroidal graphite in hexagonal diamond or Lonsdaleite form as per the ASTM-A247 standard.

A spheroidal graphite cast iron meeting N.sub.(5-)250, N.sub.(5-20)/N.sub.(5-)0.6, and N.sub.(30-)/N.sub.(5-)0.2, wherein N.sub.(5-) represents the number (/mm.sup.2) of graphite particles having equivalent-circle diameters of 5 m or more, N.sub.(5-20) represents the number (/mm.sup.2) of graphite particles having equivalent-circle diameters of 5 m or more and less than 20 m, and N.sub.(30-) represents the number (/mm.sup.2) of graphite particles having equivalent-circle diameters of 30 m or more, among graphite particles observed in an arbitrary cross section of at least 1 mm.sup.2.

A spheroidal graphite cast iron meeting N.sub.(5-)250, N.sub.(5-20)/N.sub.(5-)0.6, and N.sub.(30-)/N.sub.(5-)0.2, wherein N.sub.(5-) represents the number (/mm.sup.2) of graphite particles having equivalent-circle diameters of 5 m or more, N.sub.(5-20) represents the number (/mm.sup.2) of graphite particles having equivalent-circle diameters of 5 m or more and less than 20 m, and N.sub.(30-) represents the number (/mm.sup.2) of graphite particles having equivalent-circle diameters of 30 m or more, among graphite particles observed in an arbitrary cross section of at least 1 mm.sup.2.