Nippon Kokan Kabushiki Kaisha

Masafumi Ikeda

Yoshimi Komatsu

Tsuneo Kondo

Hirohisa Nakashima

Molten steel is tapped from a converter into a refining ladle, and an ore such as Nb.sub.2 O.sub.3 ore is charged into the molten steel. Then, the interior of the refining ladle is held in an inert gas atmosphere. A reducing agent such as an Al reducing agent is charged into the molten steel. Electrodes are dipped in slag on the molten steel to form an arc therebetween so as to heat the molten steel with an arc. The ore is reduced by the reducing agent, so that a metallic component of the ore is added to the molten steel. On the other hand, carbon electrodes each having a gas supply port at its lower end can be used to inject an ore powder or particles from the injection ports to the arc between the electrodes and molten steel. The ore is reduced by electrode carbon with arc heat, so that a desired component is added to the molten steel.

Method of refining molten steel by arc process

The invention provides a process for obtaining low-nitrogen steel by tapping molten steel from a converter without deoxidizing and by then deoxidizing the molten steel in a ladle refining furnace from which slag has been removed, and a process for obtaining low phosphorus steel by tapping molten steel from a converter without deoxidation at a tapping temperature lower than conventional processes, and by performing deoxidation and composition adjustment of the molten steel in a ladle refining furnace from which slag has been removed.

Process for refining molten steel

The invention relates to a method of operating a ladle refining furnace for blowing Ar gas through bubbling lances submerged in molten steel in a ladle to stir the molten steel. The flow rate and the rate of change in the flow rate of the Ar gas blown through the bubbling lances are adjusted to prevent the iron lumps from attaching to the bubbling lances.

Method of operating ladle refining furnace

Molten steel is refined in a converter and is poured from the converter to a ladle. A ferro-alloy containing a component to be adjusted is added to the molten steel as needed. An amount of the alloy to be added to the molten steel in the ladle is calculated from a composition analysis value of the molten steel in the converter, and the amount of the alloy which is added when the molten steel is poured from the converter. The thus calculated amount of the alloy is added to the molten steel in the ladle. Electrodes are submerged in a slag layer on the molten steel so as to be arranged a predetermined distance from the molten steel. Power is supplied to the electrodes so as to generate electric arcs between the electrodes and the molten steel, thereby, arc-heating the molten steel. Simultaneously, a lance is submerged in the molten steel, and an Ar gas is injected in the molten steel therethrough, thus strirring the molten steel. Since deoxidation and composition adjustment of the molten steel can be simultaneously performed, processing time can be shortened.

Method for adjusting composition of molten steel in arc process

Nondeoxidized molten steel is removed from a steel converter and poured into a ladle. Carbon electrodes are submerged in a slag layer on the molten steel and are separated by a predetermined distance from the molten steel. The electrodes are energized to generate arcs with the molten steel. Argon gas is blown into the molten steel through a lance submerged in the molten steel to stir the molten steel with the gas. The molten steel is arc-heated and at the same time stirred. Carbon in the molten steel reacts with residual unstable oxygen in the steel to deoxidize the molten steel. The molten steel is also decarburized, thereby preventing an increase in carbon content of the molten steel in the arc process.

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Fukuyama, Japan

Masafumi Ikeda