To prevent steel scraps from adhering to each other through oxidation by preheating the scrap at a specified temperature while controlling the limit oxygen concentration representative of the oxygen concentration in a heated atmosphere to a level shown by a specified formula.
In a vertical filling furnace, steel scraps 5 are preheated at 900-1200° by high temperature atmospheric gas 6 and molten iron 19, and the like, are discharged from furnace bed. At the time of preheating the steel scraps 5, the limit oxygen concentration (%) representative of the oxygen concentration in a heated atmosphere is controlled to a value of -37.4×(T/1000)3+53.58×(T/1000)2-29.59×(T/1000)+25.89 or below. Since the steel scraps can be prevented from adhering to each other through oxidation, they can be preheated up to a high temperature resulting in the reduction of melting energy cost in steel making or steel pigging process.
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