A continuous casting process of a steel semi-product is provided. The process includes a step of casting using a hollow jet nozzle located between a tundish and a continuous casting mould. The nozzle includes, in its upper part, a dome for deflecting the liquid metal arriving at the inlet of the nozzle towards the internal wall of the nozzle, defining an internal volume with no liquid metal. A simultaneous step of injecting powder through a hole of the dome occurs. The powder has a particle size of 200 ?m or less. The dome includes a first device to inject the powder without any contact with the dome and a second device to avoid sticking or sintering of the powder onto the first device.

A continuous casting process of a steel semi-product is provided. The process includes a step of casting using a hollow jet nozzle located between a tundish and a continuous casting mould. The nozzle includes, in its upper part, a dome for deflecting the liquid metal arriving at the inlet of the nozzle towards the internal wall of the nozzle, defining an internal volume with no liquid metal. A simultaneous step of injecting powder through a hole of the dome occurs. The powder has a particle size of 200 ?m or less. The dome includes a first device to inject the powder without any contact with the dome and a second device to avoid sticking or sintering of the powder onto the first device.

The present invention relates to steel sheet realizing both formability and weldability. The steel sheet of the present invention is characterized in that at a surface layer part of a region down to 30 ?m from the surface of the steel sheet in the sheet thickness direction, Al oxide grains are present in 3000 to 6000/mm.sup.2 in number density, the natural logarithms of the particle sizes of the Al oxide grains measured in ?m units are on the average ?5.0 to ?3.5, the standard error is 0.6 or less, and the number of Al oxide grains with deviations of the natural logarithms of the particle sizes from the average larger than 2 times the standard error is 5% or less of the total number of Al oxide grains and at a position of ? of the thickness of the steel sheet, the number density of the Al oxide grains is 1000/mm.sup.2 or less.

A method for improving smooth running of casting of rare earth stainless steel using pulse current includes the following steps: setting corresponding initial pulse voltage, pulse current, and pulse frequency in accordance with difference of rare earth element content in molten steel; and adjusting the pulse voltage, pulse current, and pulse frequency according to position change of stopper rod until the end of continuous casting. The method can stably improve the clogging of immersion nozzle during continuous casting, the smooth running of continuous casting and production efficiency, and decrease production cost.

A method for improving smooth running of casting of rare earth stainless steel using pulse current includes the following steps: setting corresponding initial pulse voltage, pulse current, and pulse frequency in accordance with difference of rare earth element content in molten steel; and adjusting the pulse voltage, pulse current, and pulse frequency according to position change of stopper rod until the end of continuous casting. The method can stably improve the clogging of immersion nozzle during continuous casting, the smooth running of continuous casting and production efficiency, and decrease production cost.

For continuously casting an ingot of titanium or titanium alloy, molten titanium or titanium alloy is poured into a top opening of a bottomless mold with a circular cross-sectional shape, the solidified molten metal in the mold is pulled downward from the mold, a plurality of plasma torches disposed on an upper side of molten metal in the mold such that their centers are located directly vertically above the molten metal in the mold, are operated to generate plasma arcs that heat the molten metal in the mold, and the plasma torches are moved in a horizontal direction above a melt surface of the molten metal in the mold, along a trajectory located directly vertically above the molten metal in the mold, while keeping a mutual distance between the respective plasma torches such that the plasma torches do not interfere with each other.

For continuously casting an ingot of titanium or titanium alloy, molten titanium or titanium alloy is poured into a top opening of a bottomless mold with a circular cross-sectional shape, the solidified molten metal in the mold is pulled downward from the mold, a plurality of plasma torches disposed on an upper side of molten metal in the mold such that their centers are located directly vertically above the molten metal in the mold, are operated to generate plasma arcs that heat the molten metal in the mold, and the plasma torches are moved in a horizontal direction above a melt surface of the molten metal in the mold, along a trajectory located directly vertically above the molten metal in the mold, while keeping a mutual distance between the respective plasma torches such that the plasma torches do not interfere with each other.

Systems and methods may utilize magnetic rotors to heat molten metal in the corner regions of a mold during casting (e.g., casting of an ingot, billet, or slab). The magnetic rotors are positioned adjacent to the corners of the mold and heat the molten metal in the corner region to increase the temperature of the molten metal adjacent the corners. The increased temperature of the molten metal in the mold corners can prevent intermetallics from forming in the molten metal or otherwise reduce such formation.

Provided are a molten steel treatment apparatus and a molten steel treatment method capable of quickly measuring an inclusion adhesion state inside a nozzle during an operation. The molten steel treatment apparatus includes a container, a nozzle equipped in a molten steel tap hole of the container, a liner disposed on a portion of an inner circumferential surface of the nozzle and formed of an ion-conductive material, a power supply for applying electric power to the molten steel and the liner, and a measuring unit for measuring a voltage value or a current value between the molten steel and the liner. The molten steel treatment method includes measuring a voltage value or current value between the molten steel and the liner; and determining a thickness of an inclusion adhering to an interface between the molten steel and the liner by using the voltage value or the current value.

Provided are a molten steel treatment apparatus and a molten steel treatment method capable of quickly measuring an inclusion adhesion state inside a nozzle during an operation. The molten steel treatment apparatus includes a container, a nozzle equipped in a molten steel tap hole of the container, a liner disposed on a portion of an inner circumferential surface of the nozzle and formed of an ion-conductive material, a power supply for applying electric power to the molten steel and the liner, and a measuring unit for measuring a voltage value or a current value between the molten steel and the liner. The molten steel treatment method includes measuring a voltage value or current value between the molten steel and the liner; and determining a thickness of an inclusion adhering to an interface between the molten steel and the liner by using the voltage value or the current value.