Nippon Steel Corporation

Nittetsu Plant Designing Corporation

Ryuji Nakao

Tomoaki Tanaka

Koichiro Yoshino

Masao Igarashi

Toshihiro Kosuge

Makoto Sumi

Hironori Takano

Kosuke Yamashita

Hiroaki Morishige

A refining method and apparatus for decarburization refining of chromium containing molten steel in a vessel having a first step of blowing oxygen while the inside of the vessel is at a pressure of between 400 Torr and atmospheric pressure, a second step of blowing oxygen while evacuation the inside of the vessel to 250 to 400 Torr and a third step of blowing gas while evacuating the vessel to not more than 250 Torr. Further, a refining method and apparatus for ultra-low carbon chrome melt by performing a first vacuum refining until the third step, then restoring the pressure in the vessel to at least 400 Torr, then performing second vacuum refining while making the bottom blowing gas blow rate at least 0.4 Nmper to steel.

Refining method and refining apparatus for chromium-contained molten steel

The present invention: solves the problems of hitherto disclosed technologies, such as insufficient suppression of the oxidation loss of &lsqb;Cr&rsqb; and the excessive erosion of refractories, in the decarburization-refining of chromium-contained molten steel under a normal or reduced pressure; and is characterized by: determining, in sequence; a molten steel temperature during the refining through actual measurement or computation from a molten steel temperature before the refining and refining conditions; &lsqb;C&rsqb; and &lsqb;Cr&rsqb; concentrations during the refining through actual measurement or computation from molten steel components before the refining and refining conditions; a CO partial pressure P in an atmosphere during the refining from the total pressure P of the atmosphere, an oxygen gas supply rate and an inert gas supply rate, a Hilty's equilibrium temperature T from said &lsqb;C&rsqb; and &lsqb;Cr&rsqb; concentrations and P ; the difference &Dgr;T between said molten steel temperature during the refining and said Hilty's equilibrium temperature T : and controlling the refining conditions so that said &Dgr;T is equal to a prescribed value or higher.

Method for decarbonization refining of chromium-containing molten steel

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

Ryuji Nakao