| 摘要 |
PURPOSE: A method is provided which not only maintains an equal level of fatigue life compared to a conventional method but also directly manufactures the molten steel into billets without passing through blooms by appropriately changing carburization and injection conditions of mole steel, thereby minimizing formation of scum in the billets. CONSTITUTION: In a billet manufacturing method by an open mold(2) comprising the processes of deoxidizing the molten steel(6) during tapping of molten steel for a pan spring from a ladle, and pouring the deoxidized molten steel into the mold in the atmosphere not using an immersion nozzle from a tundish(1), the method for manufacturing billets for plate spring steel is characterized in that the deoxidization is performed by injecting ferro silicon into the molten steel, and the pouring of the molten steel(6) is performed after maintaining a nitrogen atmosphere in a space between the tundish and the mold, wherein an amount of ferro silicon injected into the molten steel is selected in the range of 3.4 to 3.6 kg, and the nitrogen atmosphere in a space between the tundish and the mold(2) is made by supplying nitrogen into the inner space of the shielding material(4) through a nitrogen supply pipe(5) penetrating the heat resistant cloth(3) and shielding material after positioning a shielding material(4) with an inner space through which the molten steel passes between the lower part of the tundish(1) and the mold so that the molten steel discharged from the tundish is supplied into an injection hole of the mold, and covering the outer part of the shielding material with a heat resistant cloth(3).
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