Nippon Steel Corporation

Hiroaki Morishige

Hironori Takano

Toshihiro Kosuge

Tomoaki Tanaka

Kensuke Shimomura

Hiroshi Iwasaki

Ryuji Nakao

Mayumi Okimori

Gaku Ogawa

Kenji Abe

Masaru Sadachika

Nobuyuki Makino

A vacuum/reduced pressure refining vessel (,) is connected, by an upstream duct (,) to a dry dust collector (,) that uses a filter (,). The dry dust collector (,) is connected to a reduced pressure evacuating apparatus (,) by a downstream duct (,), and a block valve (,) is provided in the upstream duct (,). At the start of a vacuum/reduced pressure refining treatment, a non-oxidizing gas is injected into the upstream duct at a position that is upstream of the block valve (,) to substantially replace the oxygen in the upstream duct and to hermetically close the upstream duct. After the hermetically closed state has been established in the upstream duct, the block valve (,) is opened and operation of the dry dust collector (,) is started. At the end of the vacuum/reduced pressure refining treatment, the block valve (,) is closed and only the non-oxidizing gas is injected into the upstream duct to return the pressure, and then the upstream duct is opened to atmospheric air, and preferably an open port on the side of the dry dust collector (,) is closed during a waiting period from the end of the vacuum/reduced pressure refining treatment until the start of the next vacuum/reduced pressure refining treatment.

Method for vacuum/reduced-pressure refining and facility for vacuum/reduced-pressure refining

The present invention provides a method for refining a molten chromium-containing steel by decarburization according to a combined-blown process, which contributes to an improvement in decarburization rate and realizes efficient decarburization while preventing [Cr] contained in the molten steel from being oxidized. The method is characterized in that, in a region where the [C] concentration of the molten chromium-containing steel is not less than 0.15%, oxygen or a gas mixture of oxygen with an inert gas is blown through a top-blown lance onto the surface of the molten steel under the following conditions:

Method for refining chromium-containing molten steel by decarburization

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Hikari, Japan

Hiroaki Morishige