Abstract: There is provided a high-strength galvanized steel sheet and a relatively low-strength galvanized steel sheet that undergoes complex forming, a galvanized steel sheet that exhibits consistently excellent press formability and that generates no hazardous fumes during welding as well as a manufacturing method therefor. The galvanized steel sheet has an oxide layer on the surface, where the oxide layer has an average thickness of 20 nm or more, and the oxide layer contains 30 mg/m2 or more of Zn, 1.0 mg/m2 or more of S, and 50 mg/m2 or more and 1,000 mg/m2 or less of polyethylene particles having an average particle size of 5.0 ?m or less.

Abstract: A method is provided for producing a hot-pressed member including heating a Ni-based coated steel sheet, which includes, on a surface thereof, a Zn—Ni alloy coating layer containing 13% by mass or more of Ni, in a temperature region of an Ac3 transformation point to 1200° C.; and then hot-pressing the steel sheet.

Abstract: Provided is a high-strength cold-rolled steel sheet has a chemical composition containing, by mass %, C: 0.10% or more and 0.6% or less, Si: 1.0% or more and 3.0% or less, Mn: more than 2.5% and 10.0% or less, P: 0.05% or less, S: 0.02% or less, Al: 0.01% or more and 1.5% or less, N: 0.005% or less, Cu: 0.05% or more and 0.50% or less, and the balance being Fe and inevitable impurities, and a tensile strength of 1180 MPa or more, in which a steel sheet surface coverage of oxides mainly containing Si is 1% or less, a steel sheet surface coverage of iron-based oxides is 40% or less, CuS/CuB is 4.0 or less, and a tensile strength is 1180 MPa or more, where CuS denotes a Cu concentration in a surface layer of a steel sheet and CUB denotes a Cu concentration in base steel.

Abstract: Provided are a high-yield-ratio high-strength galvanized steel sheet that includes a Mn-containing steel sheet serving as a base material, and a production method therefor. The high-yield-ratio high-strength galvanized steel sheet includes a steel sheet having a specific composition and a metallographic structure including, by area percentage, 20% or less ferrite, 40% or more in total of bainite and tempered martensite, and 60% or less as-quenched martensite, the bainite having an average grain size of 6.0 ?m or less, and a coated layer arranged on the steel sheet, the coated layer having a coating weight per side of 20 to 120 g/m2 and having a Mn content of 0.05 g/m2 or less, in which the high-yield-ratio high-strength galvanized steel sheet has a yield ratio of 65% or more and a tensile strength of 950 MPa or more.

Abstract: Provided are a high-yield-ratio high-strength galvanized steel sheet and a method for manufacturing thereof. The high-yield-ratio high-strength galvanized steel sheet has a steel sheet having a specified chemical composition and a metallographic structure including, in terms of area ratio, in terms of area ratio, 15% or less of ferrite, 20% or more and 50% or less of martensite, and bainite and tempered martensite in a total amount of 30% or more, and a galvanized layer formed on the steel sheet having a coating weight of 20 g/m2 to 120 g/m2 per side, in which a yield strength ratio is 65% or more, a tensile strength is 950 MPa or more, and Mn oxides are contained in the galvanized layer in an amount of 0.015 g/m2 to 0.050 g/m2.

Abstract: A Si-containing high-strength cold rolled steel sheet has a chemical composition comprising C: 0.02˜0.3 mass %, Si: 0.8˜2.0 mass %, Mn: 1.0˜5.0 mass % and the remainder being Fe and inevitable impurities with a ratio of Si content to Mn content (Si/Mn) exceeding 0.4, and has a tensile strength TS of not less than 780 MPa, wherein a metallic structure of the steel sheet surface contains polygonal ferrite and/or bainitic ferrite having a Si concentration of not more than 3.0 mass % and a grain size of not more than 10 ?m and does not have a Si-containing oxide layer on the steel sheet surface.

Abstract: A high-strength hot-dip coated hot-rolled steel sheet excellent in terms of surface appearance quality and coating adhesiveness and a method for manufacturing. The method includes performing hot rolling followed by pickling on steel to form a pickled steel sheet, the steel having a chemical composition containing, by mass %, C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.3% or more and 2.5% or less, P: 0.08% or less, S: 0.02% or less, Al: 0.001% or more and 0.20% or less, and Fe and inevitable impurities. The method further includes performing rolling with a rolling reduction ratio of 1% or more and 10% or less, and a hot-dip coating treatment. The obtained steel sheet has an arithmetic average roughness Ra of 2.0 ?m or less on the surface of the steel sheet, and a tensile strength of 590 MPa or more.

Abstract: A method of producing a cold rolled steel strip includes: subjecting a steel strip that has been cold rolled and subsequently continuously annealed to pickling by continuously feeding the steel strip into a mixed acid solution containing a first acid that is oxidizing and a second acid that is non-oxidizing to immerse the steel strip; and subsequently subjecting the steel strip to repickling by continuously feeding the steel strip into an acid solution containing a third acid that is non-oxidizing to immerse the steel strip. The concentration of the first acid in the mixed acid solution is lowered and the concentration of the second acid in the mixed acid solution is raised as the iron ion concentration in the mixed acid solution rises.

Abstract: A hot-pressed member includes a steel sheet, a Ni-diffusion region present in a surface layer of the steel sheet, and an intermetallic compound layer and a ZnO layer which are provided in order on the Ni-diffusion region, the intermetallic compound layer corresponding to a ? phase present in a phase equilibrium diagram of a Zn—Ni alloy, wherein a spontaneous immersion potential indicated in a 0.5 M NaCl aqueous air-saturated solution at 25° C.±5° C. is ?600 to ?360 mV based on a standard hydrogen electrode.

Abstract: A cold-rolled steel sheet has excellent chemical convertibility and excellent corrosion resistance after coating. A method of manufacturing a cold-rolled steel sheet includes first pickling applied to a steel sheet which is continuously annealed after cold rolling, second pickling applied to the steel sheet subsequently and, thereafter, neutralizing treatment applied to the steel sheet using an alkaline solution.

Abstract: A method for producing a hot-pressed member includes heating a coated steel sheet, which includes, on a surface thereof, a Zn—Ni alloy coating layer containing 10% by mass or more and less than 13% by mass of Ni at a coating weight of over 50 g/m2 per side of the steel sheet, in a temperature region of an Ac3 transformation point to 1200° C. at an average heating rate of 12° C./second or more, and then hot-pressing the steel sheet.

Abstract: This invention provides methods and apparatuses which can manufacture Si-containing cold rolled steel sheets exhibiting excellent chemical conversion properties even if a chemical conversion treatment solution is used at a lower temperature while minimally suppressing the generation of sludge as well as reducing running costs. The method includes steps of cold rolling a steel containing 0.5 to 3.0 mass % Si, continuously annealing the cold rolled steel sheet, pickling the surface of the continuously annealed cold rolled steel sheet, and repickling the surface of the pickled steel sheet with a non-oxidative acid. The repickling is performed such that a repickling solution is sampled continuously or periodically, an acid concentration in the sampled solution is measured, and the acid concentration in the repickling solution is regularly controlled within a prescribed concentration range.

Abstract: A hot-pressed member includes a steel sheet, a Ni-diffusion region present in a surface layer of the steel sheet, and an intermetallic compound layer and a ZnO layer which are provided in order on the Ni-diffusion region, the intermetallic compound layer corresponding to a ? phase present in a phase equilibrium diagram of a Zn—Ni alloy, wherein a spontaneous immersion potential indicated in a 0.5 M NaCl aqueous air-saturated solution at 25° C.±5° C. is ?600 to ?360 mV based on a standard hydrogen electrode.

Abstract: A hot-pressed member includes a steel sheet, a Ni-diffusion region present in a surface layer of the steel sheet, and an intermetallic compound layer and a ZnO layer which are provided in order on the Ni-diffusion region, the intermetallic compound layer corresponding to a ? phase present in a phase equilibrium diagram of a Zn—Ni alloy, wherein a spontaneous immersion potential indicated in a 0.5 M NaCl aqueous air-saturated solution at 25° C.±5° C. is ?600 to ?360 mV based on a standard hydrogen electrode.

Abstract: A Si-containing high-strength cold rolled steel sheet has a chemical composition comprising C: 0.0˜20.3 mass %, Si: 0.8˜2.0 mass %, Mn: 1.0˜5.0 mass % and the remainder being Fe and inevitable impurities with a ratio of Si content to Mn content (Si/Mn) exceeding 0.4, and has a tensile strength TS of not less than 780 MPa, wherein a metallic structure of the steel sheet surface contains polygonal ferrite and/or bainitic ferrite having a Si concentration of not more than 3.0 mass % and a grain size of not more than 10 ?m and does not have a Si-containing oxide layer on the steel sheet surface.

Abstract: In a method for prevention of yellowing on a surface of a steel sheet subjected to re-pickling, washing with water and drying after a surface of a continuously annealed steel sheet is pickled to remove Si-containing oxide layer from a surface layer of the steel sheet, the surface of the steel sheet is held at a wet state between the pickling and the re-pickling and between the re-pickling and the washing, and more preferably the washing is carried out with water having an iron ion concentration decreased to not more than 20 g/L, whereby the yellowing on the surface of the steel sheet after the pickling is prevented. Thus, cold rolled steel sheets being excellent in not only the appearance quality but also the phosphatability and corrosion resistance after painting are manufactured stably.

Abstract: A hot-pressed member includes a steel sheet, a Ni-diffusion region present in a surface layer of the steel sheet, and an intermetallic compound layer and a ZnO layer which are provided in order on the Ni-diffusion region, the intermetallic compound layer corresponding to a ? phase present in a phase equilibrium diagram of a Zn—Ni alloy, wherein a spontaneous immersion potential indicated in a 0.5 M NaCl aqueous air-saturated solution at 25° C.±5° C. is ?600 to ?360 mV based on a standard hydrogen electrode.

Abstract: A hot-pressed member includes a steel sheet, a Ni-diffusion region present in a surface layer of the steel sheet, and an intermetallic compound layer and a ZnO layer which are provided in order on the Ni-diffusion region, the intermetallic compound layer corresponding to a ? phase present in a phase equilibrium diagram of a Zn—Ni alloy, wherein a spontaneous immersion potential indicated in a 0.5 M NaCl aqueous air-saturated solution at 25° C.±5° C. is ?600 to ?360 mV based on a standard hydrogen electrode.

Abstract: A hot-pressed member includes a steel sheet, a Ni-diffusion region present in a surface layer of the steel sheet, and an intermetallic compound layer and a ZnO layer which are provided in order on the Ni-diffusion region, the intermetallic compound layer corresponding to a ? phase present in a phase equilibrium diagram of a Zn—Ni alloy, wherein a spontaneous immersion potential indicated in a 0.5 M NaCl aqueous air-saturated solution at 25° C.±5° C. is ?600 to ?360 mV based on a standard hydrogen electrode.

Abstract: A zinc-based metal plated steel sheet is excellent in tribological properties during press forming. An oxide layer containing crystalline 3Zn(OH)2·ZnSO4·xH2O is formed on a plated surface. The oxide layer has a thickness of 10 nm or more. The crystalline oxide layer is composed of 3Zn(OH)2·ZnSO4·3-5H2O.