The invention relates to a plant complex for steel production comprising a blast furnace for producing pig iron, a converter steel mill for producing crude steel, a gas-conducting system for gases that occur in the production of pig iron and/or in the production of crude steel, and a power-generating plant for electricity generation. The power-generating plant is operated with a gas that comprises at least a partial amount of the blast-furnace top gas that occurs in the production of pig iron and/or a partial amount of the converter gas. According to the invention, a chemical or biotechnological plant is provided and connected to the gas-conducting system and arranged in parallel with the power-generating plant with respect to the gas supply. Externally obtained electricity and power-generating plant electricity are used to cover the electricity demand of the plant complex.

The invention relates to a plant complex for steel production comprising a blast furnace for producing pig iron, a converter steel mill for producing crude steel and a gas-conducting system for gases that occur in the production of pig iron and/or in the production of crude steel. According to the invention, the plant complex additionally has a chemical or biotechnological plant connected to the gas-conducting system and a plant for producing hydrogen. The plant for producing hydrogen is connected to the gas-conducting system by a hydrogen-carrying line. Also the subject of the invention is a method for operating the plant complex.

The present invention provides an electric furnace including: a furnace body that includes an electrode; and a slag holding furnace that is configured to hold molten slag in a molten state and is capable of pouring the molten slag into the furnace body when tilted, in which the furnace body includes a cylindrical furnace wall, a furnace cover that is provided at an upper end of the furnace wall, a furnace bottom that is provided at a lower end of the furnace wall and includes a deep bottom portion and a shallow bottom portion as a region having a height of 150 mm to 500 mm from a deepest point of the deep bottom portion, and a slag pouring port that is provided at the furnace cover and through which the molten slag is poured from the slag holding furnace, the slag pouring port overlaps the shallow bottom portion in a plan view, and the area ratio of the shallow bottom portion to the furnace bottom in a plan view is 5% to 40%.

A converter steelmaking method has molten pig iron subjected to dephosphorization process for dephosphorized molten iron, dephosphorized molten iron is subjected to decarburization process for molten steel. For dephosphorization process, a first cold iron source in amount meeting Formula (1) is charged into first converter-type vessel, then undephosphorized molten pig iron is charged and subjected to dephosphorization process. Dephosphorized molten iron is discharged and held in molten metal receiving vessel. After second cold iron source is charged into first converter-type vessel in which dephosphorization process has been performed, the dephosphorized molten iron held in molten metal receiving vessel is charged and subjected to decarburization process. % W.sub.s00.1186T134 (% W.sub.s00) . . . (1), where % W.sub.s0: a ratio (%) of first cold iron source to sum of first cold iron source and charge amount of undephosphorized molten pig iron, and T: a temperature ( C.) of undephosphorized molten pig iron.

A converter steelmaking method has molten pig iron subjected to dephosphorization process for dephosphorized molten iron, dephosphorized molten iron is subjected to decarburization process for molten steel. For dephosphorization process, a first cold iron source in amount meeting Formula (1) is charged into first converter-type vessel, then undephosphorized molten pig iron is charged and subjected to dephosphorization process. Dephosphorized molten iron is discharged and held in molten metal receiving vessel. After second cold iron source is charged into first converter-type vessel in which dephosphorization process has been performed, the dephosphorized molten iron held in molten metal receiving vessel is charged and subjected to decarburization process. % W.sub.s00.1186T134 (% W.sub.s00) . . . (1), where % W.sub.s0: a ratio (%) of first cold iron source to sum of first cold iron source and charge amount of undephosphorized molten pig iron, and T: a temperature ( C.) of undephosphorized molten pig iron.

A process for steel production that includes: production of sponge iron from iron oxide-containing starting material by direct reduction with reduction gas, wherein the reduction gas has at least 20% by volume of hydrogen H.sub.2, and production of an iron melt having a carbon content of 1-5% by mass from the sponge iron.

Sponge iron is subjected to a treatment that includes: energy input and addition of additives to produce a melt and a slag, wherein the energy input is effected substantially from electricity and wherein the slag has a basicity B2 of less than 1.3, preferably less than 1.25, particularly preferably less than 1.2, adjustment of the carbon content in the melt, reduction of at least a sub-amount of the iron oxides present in the sponge iron

The slag is separated during and/or after the treatment.

The present invention provides an electric furnace including: a furnace body that includes an electrode; and a slag holding furnace that is configured to hold molten slag in a molten state and is capable of pouring the molten slag into the furnace body when tilted, in which the furnace body includes a cylindrical furnace wall, a furnace cover that is provided at an upper end of the furnace wall, a furnace bottom that is provided at a lower end of the furnace wall and includes a deep bottom portion and a shallow bottom portion as a region having a height of 150 mm to 500 mm from a deepest point of the deep bottom portion, and a slag pouring port that is provided at the furnace cover and through which the molten slag is poured from the slag holding furnace, the slag pouring port overlaps the shallow bottom portion in a plan view, and the area ratio of the shallow bottom portion to the furnace bottom in a plan view is 5% to 40%.

An immersion device for collecting a slag sample and measuring a molten metal parameter is provided. The immersion device includes an inflow conduit for directing the molten slag to a slag sample chamber and a measuring element for measuring the parameter of the molten metal. The inflow conduit and the measuring element are arranged in the top area of an immersion end of the immersion device and/or are facing towards an immersion direction. During immersion in the immersion direction into the molten slag and then the molten metal, the molten slag enters an external portion of the inflow conduit and is directed through an inner portion of the inflow conduit to the slag sample chamber. Reliable slag collection and molten metal measurement also in a converter can thereby be achieved. A method of collecting a slag sample and measuring a molten metal parameter is also provided.

The present disclosure relates to a spheroidizing-annealed steel for the ball screw having high strength and resistance to low temperatures, wherein the chemical composition of the steel in mass percentage is: C: 0.40-0.70%, Si: 1.20-1.80%, Mn: 1.00-1.60%, Cr: 0.80-1.20%, S: ?0.025%, P?0.025%, Ni: 0.10-0.60%, Cu: 0.30-0.80%, Mo: 0.10-0.40%, Al?0.05%, Ca?0.0010%, Ti?0.003%, O?0.0010%, As?0.04%, Sn?0.03%, Sb?0.005%, Pb?0.002%, the balance is Fe and unavoidable impurities. In microstructure of the steel, cementite exists in a spheroidized state with a diameter of 0.1-0.5 ?m, preferably 0.3-0.5 ?m, a spheroidizing rate is 95% or more, and the rest is ferrite.

The present disclosure relates to a spheroidizing-annealed steel for the ball screw having high strength and resistance to low temperatures, wherein the chemical composition of the steel in mass percentage is: C: 0.40-0.70%, Si: 1.20-1.80%, Mn: 1.00-1.60%, Cr: 0.80-1.20%, S: ?0.025%, P?0.025%, Ni: 0.10-0.60%, Cu: 0.30-0.80%, Mo: 0.10-0.40%, Al?0.05%, Ca?0.0010%, Ti?0.003%, O?0.0010%, As?0.04%, Sn?0.03%, Sb?0.005%, Pb?0.002%, the balance is Fe and unavoidable impurities. In microstructure of the steel, cementite exists in a spheroidized state with a diameter of 0.1-0.5 ?m, preferably 0.3-0.5 ?m, a spheroidizing rate is 95% or more, and the rest is ferrite.