Nippon Steel Corporation

Nittetsu Plant Designing Corporation

Koichiro Yoshino

Tomoaki Tanaka

Ryuji Nakao

Masao Igarashi

Kosuke Yamashita

Makoto Sumi

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

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Hikari, Japan

Koichiro Yoshino