Method for producing molten steel

Patent metadata

Field	Value
Publication number	US-12281365-B2
Application number	US-202017775502-A
Country	US
Kind code	B2
Filing date	Nov 11, 2020
Priority date	Nov 21, 2019
Publication date	Apr 22, 2025
Grant date	Apr 22, 2025

Abstract

A method includes, in a first furnace, melting 40% to 95% by mass of a solid-state direct reduced iron, and separating a molten pig iron having a carbon content of 2.0% to 5.0% by mass and a temperature of 1350 to 1550° C. and a slag having a basicity of 1.0 to 1.4. In a second furnace, a remainder of the solid-state direct reduced iron is melted together with the molten pig iron separated in the first furnace to form a molten material, and oxygen is blown onto the molten material to decarburize into a molten steel. The solid-state direct reduced iron includes 3.0% by mass or more of SiO 2 and Al 2 O 3 in total and 1.0% by mass or more of carbon. A ratio of a metallic iron to a total iron content contained in the solid-state direct reduced iron is 90% by mass or more.

First claim

The invention claimed is:

1. A method for producing a molten steel using a solid-state direct reduced iron as a raw material, the method comprising:
in a first furnace, melting 40% to 95% by mass of the solid-state direct reduced iron, and separating a molten pig iron having a carbon content of 2.0% to 5.0% by mass and a temperature of 1350 to 1550° C. and a slag having a basicity of 1.0 to 1.4; and
in a second furnace, melting a remainder of the solid-state direct reduced iron together with the molten pig iron separated in the first furnace to form a molten material, and blowing oxygen onto the molten material to decarburize into a molten steel,
wherein the solid-state direct reduced iron comprises 3.0% by mass or more of SiO 2 and Al 2 O 3 in total and 1.0% by mass or more of carbon based on a total mass of the solid-state direct reduced iron, a ratio of a metallic iron to a total iron content contained in the solid-state direct reduced iron is 90% by mass or more, and Cx specified by formula (1) is 0.2% by mass or more,
Cx=[C]—[FeO]×12÷(55.85+16)÷0.947  (1)

where Cx is an excess carbon content % by mass, [C] is a carbon content of solid-state direct reduced iron % by mass, and [FeO] is a FeO content of solid-state direct reduced iron % by mass.

2. The method according to claim 1 , wherein the solid-state direct reduced iron is melted by an arc in the first furnace, and the separating comprises continuously discharging the molten pig iron and the slag respectively from the first furnace.

3. The method according to claim 1 , wherein the remainder of the solid-state direct reduced iron is 5% to 60% by mass of the solid-state direct reduced iron.

4. The method according to claim 1 , wherein 40% to 90% by mass of the solid-state direct reduced iron is melted in the first furnace.

Assignees

• Kobe Steel Ltd

Inventors

• Tokuda Koji
• Mimura Tsuyoshi

Classifications

• C21C1/00

  Refining of pig-iron; Cast iron · CPC title

• C21C1/04

  Removing impurities other than carbon, phosphorus or sulfur · CPC title

• C21B11/10 Primary

  in electric furnaces · CPC title

• C21C5/54

  Processes yielding slags of special composition · CPC title

• Y02P10/20

  Recycling · CPC title