A high strength steel sheet having excellent surface quality and formability with a tensile strength of 980 MPa or more and a TS-El balance of 30000 MPa % or more is provided. A high strength steel sheet comprises: a chemical composition containing C: 0.08% to 0.30%, Si: 2.0% or less, Mn: more than 3.0% and 10.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 1.5% or less, Ti: 0.010% to 0.300%, and N: 0.0020% to 0.0100% in a range satisfying 1.1(Ti+Mn.sup.1/2/400)/(0.01+5N)6.0; and a microstructure including a retained austenite phase and a ferrite phase, wherein a ratio Mn/Mn of an average Mn concentration (Mn) of the retained austenite phase to an average Mn concentration (Mn) of the ferrite phase is 1.5 or more.

A material-property-value estimating method of estimating a material-property-value of a target steel-strip product manufactured via at least one of a reheating process, a rolling process, and a cooling process, which are performed while a target material is being conveyed along a conveyance route, the material-property-value estimating method includes an estimating step of estimating a material-property-value of each of meshes dividing the target steel-strip product based on a measured value that has been measured once or more by a measuring device installed on the conveyance route, the measured value including at least a temperature of the target material; and a chemical composition per component of the target steel-strip product.

A material-property-value estimating method of estimating a material-property-value of a target steel-strip product manufactured via at least one of a reheating process, a rolling process, and a cooling process, which are performed while a target material is being conveyed along a conveyance route, the material-property-value estimating method includes an estimating step of estimating a material-property-value of each of meshes dividing the target steel-strip product based on a measured value that has been measured once or more by a measuring device installed on the conveyance route, the measured value including at least a temperature of the target material; and a chemical composition per component of the target steel-strip product.

A casting device in which refrigerant is pressure-fed to a cooling passage formed in a die, leakage of refrigerant in the die can be reliably detected in a short time without a significant modification applied to the conventional device. A casting device includes a pressure-feed device that pressure-feeds refrigerant to a cooling passage formed in a die, and a release agent coating applicator that applies a release agent to the die, and further includes a unit that mixes a fluorescent agent into the refrigerant (fluorescent agent tank), a unit that irradiates the die surface of the die with black light while the refrigerant containing the fluorescent agent mixed therein is pressure-fed to the die, and an imaging device that captures an image of the die surface. The imaging device is integrally assembled with the release agent coating applicator.

A casting device in which refrigerant is pressure-fed to a cooling passage formed in a die, leakage of refrigerant in the die can be reliably detected in a short time without a significant modification applied to the conventional device. A casting device includes a pressure-feed device that pressure-feeds refrigerant to a cooling passage formed in a die, and a release agent coating applicator that applies a release agent to the die, and further includes a unit that mixes a fluorescent agent into the refrigerant (fluorescent agent tank), a unit that irradiates the die surface of the die with black light while the refrigerant containing the fluorescent agent mixed therein is pressure-fed to the die, and an imaging device that captures an image of the die surface. The imaging device is integrally assembled with the release agent coating applicator.

A spray apparatus for cooling a metal strand in a continuous casting machine, wherein at least one multiple-nozzle head and at least one switching valve are provided, wherein the multiple-nozzle head has at least a first and a second nozzle, wherein the switching valve is arranged upstream of the multiple-nozzle head, and wherein the switching valve is flow-connected to all the second nozzles in the multiple-nozzle head, in order to enable or to shut off a supply of spray liquid to all the second nozzles.

A continuous casting mold according to the present invention has plural separate portions filled with a metal of low thermal conductivity formed by filling a metal having a thermal conductivity of 30% or less of that of copper into circular concave grooves having a diameter of 2 to 20 mm which are formed in the region of the inner wall surface of the copper mold from an arbitrary position higher than a meniscus to a position 20 mm or more lower than the meniscus, in which the filling thickness of the metal in the portions filled with the metal of low thermal conductivity is equal to or less than the depth of the circular concave grooves and satisfies the relationship with the diameter of the portions filled with the metal of low thermal conductivity expressed by expression (1) below:
0.5Hd(1).

A steel for induction hardening according to an aspect includes, as a chemical composition, predetermined amounts of alloy elements and a remainder including Fe and impurities, in which AlN is 0.000330 to 0.000825, Mn/S is 4.6 to 14.0, a machinability index M is 15.5 to 25.65, an area fraction of AlN having an equivalent circle diameter of more than 200 nm at a position of a diameter of the steel is 20% or less of an area fraction of all AlN having an equivalent circle diameter of 40 nm or more, and a number density of Mn sulfide-based inclusions having a maximum diameter of 0.3 m or more and 10 m or less at the position of the diameter is 100 pieces/mm.sup.2 or more and 2500 pieces/mm.sup.2 or less.

A casting of metal strip by continuous casting in a twin roll caster is provied. In a twin roll caster, molten metal is introduced between a pair of counter-rotated horizontal casting rolls that are cooled so that metal shells solidify on the moving roll surfaces. The twin roll caster is capable of continuously producing cast strip from molten steel through a sequence of ladles positioned on a turret. In casting thin strip by twin roll caster, the crown of the casting surfaces of the casting rolls varies during a casting campaign. The crown of the casting surfaces of the casting rolls in turn determines the strip thickness profile.

A casting of metal strip by continuous casting in a twin roll caster is provied. In a twin roll caster, molten metal is introduced between a pair of counter-rotated horizontal casting rolls that are cooled so that metal shells solidify on the moving roll surfaces. The twin roll caster is capable of continuously producing cast strip from molten steel through a sequence of ladles positioned on a turret. In casting thin strip by twin roll caster, the crown of the casting surfaces of the casting rolls varies during a casting campaign. The crown of the casting surfaces of the casting rolls in turn determines the strip thickness profile.