A graphene-coated steel sheet and a method for manufacturing the same are provided. The graphene-coated steel sheet includes a steel sheet and a graphene layer formed on the steel sheet. Therefore, the graphene-coated steel sheet can be useful in preventing corrosion of iron, such as oxidation of iron, and has remarkably excellent thermal conductivity and electrical conductivity, as well as excellent heat resistance resulting from thermal stability of graphene. Also, the method can be useful in manufacturing a high-quality graphene-coated steel sheet having a monocrystalline form and showing substantially no defects or impurities.

A surface treatment method for a metal material is provided which includes applying diluted sulfuric acid to a surface of the metal material that is composed primarily of iron, performing a heat treatment on the metal material in the presence of at least one of CO, CO.sub.2 and organic gas under nitriding conditions under which a nitrided layer is formed in a superficial layer of the metal material after the application of the diluted sulfuric acid to form a carbon film which includes at least one of carbon nanocoils, carbon nanotubes and carbon nanofilaments on a surface of the nitrided layer of the metal material.

A surface treatment method for a metal material is provided which includes applying diluted sulfuric acid to a surface of the metal material that is composed primarily of iron, performing a heat treatment on the metal material in the presence of at least one of CO, CO.sub.2 and organic gas under nitriding conditions under which a nitrided layer is formed in a superficial layer of the metal material after the application of the diluted sulfuric acid to form a carbon film which includes at least one of carbon nanocoils, carbon nanotubes and carbon nanofilaments on a surface of the nitrided layer of the metal material.

A method for manufacturing such steel sheet includes continuous annealing of a steel sheet which includes, in terms of mass %, C at 0.01 to 0.18%, Si at 0.4 to 2.0%, Mn at 1.0 to 3.0%, Al at 0.001 to 1.0%, P at 0.005 to 0.060% and S at 0.01%, the balance being represented by Fe and inevitable impurities, in such a manner that the dew point of the atmosphere is controlled to become not more than 45 C. during the course of soaking when the annealing furnace inside temperature is in the range of not less than 820 C. and not more than 1000 C. as well as that the dew point of the atmosphere is controlled to become not more than 45 C. during the course of cooling when the annealing furnace inside temperature is in the range of not less than 750 C.

A method for manufacturing such steel sheet includes continuous annealing of a steel sheet which includes, in terms of mass %, C at 0.01 to 0.18%, Si at 0.4 to 2.0%, Mn at 1.0 to 3.0%, Al at 0.001 to 1.0%, P at 0.005 to 0.060% and S at 0.01%, the balance being represented by Fe and inevitable impurities, in such a manner that the dew point of the atmosphere is controlled to become not more than 45 C. during the course of soaking when the annealing furnace inside temperature is in the range of not less than 820 C. and not more than 1000 C. as well as that the dew point of the atmosphere is controlled to become not more than 45 C. during the course of cooling when the annealing furnace inside temperature is in the range of not less than 750 C.

A method for producing a grain oriented electrical steel sheet includes a decarburization annealing process where an oxidation degree PH.sub.2O/PH.sub.2 is controlled, a final annealing process where hydrogen in mixed gas atmosphere is controlled to 50 volume % or more, an annealing separator removing process where water-washing is conducted using solution with inhibitor, a smoothing process where chemical-polished is conducted to control average roughness Ra, and an insulation coating forming process where insulation coating forming solution in which crystalline phosphide is included is applied.

A preparation method of glassless grain-oriented silicon steel includes the following operations. During a decarburization annealing, a thickness of an oxide film on a surface of strip is 1.5-2.5 m; an atomic weight ratio of Si element and Fe element in the oxide film satisfies: Si/(Si+Fe)0.76; during a high-temperature annealing, a cooling stage includes sequentially: cooling with an inner cover when a temperature drops from 1200 C. to 500 C.; wherein a protective gas is a mixed gas containing nitrogen and hydrogen, and a volume percentage of the hydrogen in the mixed gas is >3%; cooling with the inner cover when the temperature drops from 500 C. to 200 C.; wherein the protective gas is nitrogen; and cooling in air by removing the inner cover when the temperature is <200 C.

A preparation method of glassless grain-oriented silicon steel includes the following operations. During a decarburization annealing, a thickness of an oxide film on a surface of strip is 1.5-2.5 m; an atomic weight ratio of Si element and Fe element in the oxide film satisfies: Si/(Si+Fe)0.76; during a high-temperature annealing, a cooling stage includes sequentially: cooling with an inner cover when a temperature drops from 1200 C. to 500 C.; wherein a protective gas is a mixed gas containing nitrogen and hydrogen, and a volume percentage of the hydrogen in the mixed gas is >3%; cooling with the inner cover when the temperature drops from 500 C. to 200 C.; wherein the protective gas is nitrogen; and cooling in air by removing the inner cover when the temperature is <200 C.