Abstract: A method by which an extremely low nitrogen concentration range can be stably reached in a short time without use of a top-blown gas is proposed. A molten steel denitrification method is a denitrification process in which CaO-and-Al2O3-containing slag formed by a combination of an Al addition step of adding a metal-Al-containing substance to molten steel to deoxidize and turn the molten steel into Al-containing molten steel and a CaO addition step of adding a CaO-containing substance to the molten steel is brought into contact with the Al-containing molten steel to remove nitrogen in the molten steel, in which the molten steel is stirred at a stirring power density ? of 60 W/t or higher. It is preferable that, in the denitrification process, a surface of the molten steel or the slag is subjected to an atmosphere of 1.0×105 Pa or lower. In a steel production method, the obtained molten steel is cast after the components are adjusted.

Abstract: There is provided a raw material cold-rolled steel sheet with Fe-based coating film excellent in primary rust prevention property or plating appearance. The raw material cold-rolled steel sheet with Fe-based coating film comprises: a base steel sheet having a chemical composition containing C of 0.80 mass % or less, Si of 0.10 mass % or more and 3.00 mass % or less, Mn of 1.50 mass % or more and 3.50 mass % or less, P of 0.100 masse or less; S of 0.0300 mass % or less, Al of 0.100 mass % or less, with a remaining part consisting of Fe and inevitable impurities; and a P-adhered Fe-based coating film containing an Fe-based coating film disposed on at least one surface of the base steel sheet and a P-containing substance adhered to a surface of the Fe-based coating film, and an adhesion amount of the P-containing substance in terms of P is 0.2 mg/m2 or more.

Abstract: To provide a grain-oriented electrical steel sheet with good processing accuracy in rounding while maintaining excellent magnetic properties, and a producing method thereof. Disclosed is the method including: subjecting a steel material to heating to 1300° C. or higher and hot rolling, subjecting the resulting sheet directly, or after subjection to hot-rolled sheet annealing, to at least two cycles of cold rolling with intermediate annealing therebetween, decarburization annealing, application of an annealing separator to a surface of the sheet, final annealing, in which maximum arrival temperatures in the first and second cycles of the cold rolling satisfy a predetermined relation, total rolling reductions in the first and second cycles of the cold rolling satisfy a predetermined relation, and in the final annealing, an average heating rates in temperature ranges from 50° C. to 1000° C. and from 1000° C. to (maximum arrival temperature—50° C.) satisfy a predetermined relation.

Abstract: There is provided a ferritic stainless steel which has a composition containing, in % by mass, C: 0.003 to 0.030%, Si: 0.01 to 1.00%, Mn: 0.05 to 0.30%, P: 0.050% or less, S: 0.020% or less, Cr: 24.0 to 30.0%, Ni: 1.50 to 3.00%, Mo: 1.00 to 3.00%, Al: 0.001 to 0.020%, Nb: 0.20 to 0.80%, and N: 0.030% or less, the balance being Fe and incidental impurities. The composition satisfies certain inequalities.

Abstract: In the production of a grain-oriented electrical steel sheet by heating a steel slab containing, in mass %, C: 0.02 to 0.10%, Si: 2.5 to 5.5%, Mn: 0.01 to 0.30%, S: 0.0010 to 0.040%, Se: 0 to 0.040%, sol. Al: 0.010 to 0.040%; and N: 0.004 to 0.020% to 1300° C. or higher; subsequently performing hot rolling, hot-band annealing as necessary, cold rolling, and primary recrystallization annealing which also serves as decarburization annealing; applying an annealing separator on the surface of the steel sheet; and performing finishing annealing, edge cracks that may occur in the hot rolling are effectively prevented by keeping a slab lateral face temperature at a time of starting rough rolling during the hot rolling equal to or lower than a temperature Te defined by the following Expression Te=?120000 [% S]2+1400 (1) and carrying out width reduction after at least one pass in the rough rolling.

Abstract: An automotive member and a resistance spot welding method. The automotive member includes a resistance spot weld formed by resistance-spot-welding a plurality of steel sheets including at least one high strength steel sheet. The high strength steel sheet has a specific chemical composition. The microstructure in the vicinity of the edge of the nugget of the resistance spot weld is a composite microstructure containing ferrite at a volume fraction of 1 to 30%, martensite at a volume fraction of 1 to 50%, and tempered martensite at a volume fraction of 20% or more. The average number density of Nb-based precipitate grains having a grain diameter less than 0.09 ?m and Ti-based precipitate grains having a grain diameter less than 0.09 ?m is 10 or more grains per 100 ?m2 in a sheet cross section.

Abstract: A high-strength hot-rolled steel sheet according to the present invention has a specific chemical composition and a steel microstructure including, as main phases, 80% to 100% of martensite and bainite in terms of total area fraction. An entire area fraction of the martensite dispersed in the bainite is 2% to 20%. Among the martensite dispersed in the bainite, an area fraction of martensite each having an orientation difference of 15° or more between a crystal orientation of the martensite and a crystal orientation of at least one of bainite adjacent to the martensite is more than 50% relative to the whole martensite dispersed in the bainite. When regions surrounded by boundaries between adjacent crystals having an orientation difference of 15° or more are defined as crystal grains, an average aspect ratio of the crystal grains present in a region extending from a surface of the steel sheet to a depth of 5 ?m is 2.0 or less.

Abstract: In determining the conditions for final annealing, information on the concentration of enriched components over the entire length and width of the steel sheet after decarburization annealing is obtained, the optimum function of product properties in the relationship between enriched components and control conditions for final annealing is obtained in advance, and the distribution of the control conditions for final annealing within the coil were considered while determining the control conditions for final annealing such that the area where the deviation of the product properties from the above optimum function is within a range of ±? is maximized over the entire length and width.

Abstract: A moving inspection device inspecting an inspection target while realizing the simplification of the configuration and significant size reduction/weight reduction of the device, a moving inspection method, and a method for manufacturing a steel material. The device includes a moving inspection device body configured to inspect an inspection target for defects while moving over its surface. The moving inspection device body includes: a carriage that moves by at least two wheels that rotate forward and backward over the surface; and at least one inspection sensor on the front end side or the rear end side of the carriage. An inspection region of the inspection target is divided into two divided regions across a straight line, and the carriage is configured to move when the inspection sensor is directed to side edges sides of the divided regions facing the straight line in each of the two divided regions.

Abstract: A steel sheet having a specified chemical composition and a method for producing the steel sheet. The steel sheet has a microstructure comprising ferrite: 5% or less, and at least one of upper bainite, fresh martensite, tempered martensite, lower bainite, and retained ?: 95% to 100%, and retained ?: 5% to 20%. Retained ?UB has a specified area percentage S?UB, retained ?LB has a specified distribution number N?LB, and at least one of (i) fresh martensite has a specified equivalent circular grain diameter and aspect ratio and (ii) retained ? grains has a specified equivalent circular grain diameter and aspect ratio.

Abstract: A high-yield-ratio high-strength electrogalvanized steel sheet having an electrogalvanized coating layer formed on a surface of a base steel sheet, in which the base steel sheet has a certain chemical composition, and a steel microstructure, in which a total area fraction of one or both of bainite containing carbides having an average grain diameter of 50 nm or less and tempered martensite containing carbides having an average grain diameter of 50 nm or less is 90% or more in the whole of the steel microstructure, and in which a total area fraction of one or both of the bainite containing and the tempered martensite containing carbides is 80% or more in a region from the surface of the base steel sheet to a position located at ? of a thickness of the base steel sheet, and diffusible hydrogen in steel in an amount of 0.20 mass ppm or less.

Abstract: A high-ductility, high-strength electrolytic zinc-based coated steel sheet includes an electrolytic zinc-based coating on a base steel sheet, in which the base steel sheet has a predetermined composition and a steel microstructure in which the total area percentage of one or two of martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less is 90% or more in the entire steel microstructure, the total area percentage of one or two of the martensite containing a carbide having an average particle size of 50 nm or less and the bainite containing a carbide having an average particle size of 50 nm or less is 80% or more in a region extending from the surface of the base steel sheet to a depth of ? of the thickness of the base steel sheet.

Abstract: Provided is a slag component analysis method capable of quickly and accurately measuring slag components generated during refining of molten iron. The method comprises: irradiating a surface of slag to be analyzed with a pulse laser a plurality of times to turn part of the slag into plasma; dispersing excitation light obtained from the slag turned into plasma and acquiring an emission spectrum of an element contained in the slag per one pulse laser irradiation or per a plurality of pulse laser irradiations; and deriving a target component concentration or component amount ratio from the acquired emission spectrum, wherein the slag to be analyzed is slag generated in a converter-type refining furnace, and in the process of turning part of the slag into plasma, the pulse laser is applied from a side of the converter-type refining furnace tilted to remove the slag generated in the converter-type refining furnace.

Abstract: A resistance spot welding method in which a high strength zinc-based coated steel sheet used in a sheet set has an equivalent carbon content of 0.20% or more and a tensile strength of 780 MPa or more. The method includes performing a first energization step such that a current value at the end of the energization, a current value Is at the start of the energization, and a thickness of the thinnest steel sheet among steel sheets overlapping each other satisfy specified relationships. The method includes performing a second energization step in which a cooling step of holding a non-energization state for 10 ms or longer and shorter than 160 ms and performing energization at a current value equal to or more than the current value at the end of the first energization step for 20 ms or longer and shorter than 200 ms are repeated.

Abstract: To provide a method of producing a grain-oriented electrical steel sheet whereby greater purification of an inhibitor-strengthening element can be promoted by improvement of an annealing separator and, as a result, iron loss can be effectively improved. The annealing separator contains 1 to 10 parts by mass of a composite oxide, relative to 100 parts by mass of MgO, the composite oxide containing at least one selected from a Group 1: Fe, Mn, Al and Ca, and at least one of a Group 2: Zr, Ta, Mo and Nb.

Abstract: To provide a method for producing a grain-oriented electrical steel sheet that can solve the problem of cracking in steel sheets during final cold rolling and that can stably produce a grain-oriented electrical steel sheet with low iron loss. A production method includes predetermined steps, wherein the conditions: T??4000×A+440, and T?360 are satisfied, where A denotes an average C content in mass % in a predetermined region of the steel sheet after subjection to annealing preceding final cold rolling and before subjection to the final cold rolling, and T denotes a time in hours from just after the completion of the annealing preceding the final cold rolling to just before the start of the final cold rolling, and after the final cold rolling and before the decarburization annealing, pickling treatment is performed with a predetermined treatment solution.

Abstract: Provided is a grain-oriented electrical steel sheet that achieves both low iron loss and low magnetostriction and has excellent transformer properties. The grain-oriented electrical steel sheet has a thermal strain-imparted region extending in a direction crossing the rolling direction, where the steel sheet has a closure domain inside the thermal strain-imparted region, the thermal strain-imparted region has maximum points of tensile strain on both outer sides in the rolling direction of the closure domain, and in a strain distribution in the rolling direction of the thermal strain-imparted region, the strain at both outer sides of the closure domain is tensile strain larger than the strain at the center between the maximum points.

Abstract: A method of estimating a surface tension of coal includes subjecting a surface tension, a physical property value representing a coal rank, and a total inert content of each of different brands of coal to multiple regression analysis to determine in advance a regression equation including the surface tension of coal as an objective variable and the physical property value and the total inert content as explanatory variables; and measuring the physical property value and the total inert content of a coal of which the surface tension is to be estimated, and calculating the surface tension of the coal with the measured physical property value and the measured total inert content, and the regression equation.

Abstract: A method includes: forming either one or both of convex and concave bead portions at surface portions corresponding to sites of a side wall portion on both sides of a convex curve site and to sites of a side wall portion on both sides of a concave curve site; and squashing the bead portions, wherein the bead portions formed on both sides of the convex curve site are tilted such that an end part of the bead portion positioned on the convex curve site side is farther from a baseline and the other end part is closer to the baseline; and the bead portions formed on both sides of the concave curve site are tilted such that an end part of the bead portion positioned on the concave curve site side is closer to the baseline and the other end part is farther from the baseline.

Abstract: A method for producing a steel material for line pipes including heating a steel having a specific composition to a temperature of 1000° C. to 1200° C.; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature +20° C.) or less is 50% or more, and a rolling finish temperature is the Ar3 transformation point or more and 790° C. or less; subsequently performing accelerated cooling from a temperature of the Ar3 transformation point or more, at a cooling rate of 10° C./s or more, to a cooling stop temperature of 200° C. to 450° C.; and then performing reheating such that the temperature of a surface of the steel plate is 350° C. to 550° C. and the temperature of the center of the steel plate is less than 550° C.