A method of manufacturing a steel sheet plated with an Al—Fe alloy for hot forming. The method includes: aluminum-plating and coiling a base steel sheet to obtain an aluminum-plated steel sheet, where an amount of the aluminum-plating is 30 to 200 g/m.sup.2 based on one surface of the base steel sheet, and tension in the coiling is 0.5 to 5 kg/mm.sup.2; after the aluminum-plating, performing cooling to 250° C. at a rate of 20° C./sec or less; annealing the aluminum-plated steel sheet to obtain the steel sheet plated with the Al—Fe alloy; and cooling the steel sheet plated with the Al—Fe alloy. The annealing is carried out for 30 minutes to 50 hours within a heating temperature range of 550 to 750° C. in a batch annealing furnace.

A high-strength steel sheet has a specific composition and a microstructure. In the microstructure, the area fraction of elongated ferrite phase grains having an aspect ratio of 3 or more is 1% or less, the average crystal grain size of martensite included in a region extending 50 μm from a surface of the steel sheet is 20 μm or less, the content of oxide particles having a minor axis length of 0.8 μm or less in the region extending 50 μm from the surface of the steel sheet is 1.0×10.sup.10 particles/m.sup.2 or more, and the content of coarse oxide particles having a minor axis length of more than 1 μm in the region extending 50 μm from the surface of the steel sheet is 1.0×10.sup.8 particles/m.sup.2 or less. The content of hydrogen trapped in the steel sheet is 0.05 ppm by mass or more.

Provided is a plated steel to be used for automobiles, electric home appliances, building materials and the like and, more specifically, to a zinc alloy-plated steel having excellent corrosion resistance and surface smoothness, and a method for manufacturing the same.

This coated steel member includes: a steel sheet substrate having a predetermined chemical composition; and a coating formed on a surface of the steel sheet substrate and containing Al and Fe, in which the coating has a low Al content region having an Al content of 3 mass % or more and less than 30 mass % and a high Al content region formed on a side closer to a surface than the low Al content region and having an Al content of 30 mass % or more, a maximum C content of the high Al content region is 25% or less of a C content of the steel sheet substrate, a maximum C content of the low Al content region is 40% or less of the C content of the steel sheet substrate, and a maximum C content in a range from an interface between the steel sheet substrate and the coating to a depth of 10 μm on a side of the steel sheet substrate is 80% or less of the C content of the steel sheet substrate.

An embodiment of the present disclosure provides a hot dip alloy coated steel material having high corrosion resistance, the hot dip alloy coated steel material including: a base steel sheet; and a hot dip alloy coating layer formed on the base steel sheet, wherein the hot dip alloy coating layer includes, by wt %, Al: from greater than 8% to 25%, Mg: from greater than 4% to 12%, and a balance of Zn and other inevitable impurities, wherein a surface of the hot dip alloy coating layer has a surface X-ray diffraction intensity satisfying Condition 1 below: [Condition 1] 2000 cps≤X-ray diffraction intensity≤20000 cps where the X-ray diffraction intensity refers to M−N, M refers to a greatest peak intensity within a 2θ range of 20.00° to lower than 21°, and N refers to a peak intensity at 2θ=20.00°.

A method of forming a coating of an Al—Zn—Si—Mg alloy on a steel strip to form an Al—Zn—Mg—Si coated steel strip is disclosed. The method includes the steps of dipping steel strip into a bath of molten Al—Zn—Si—Mg alloy and forming a coating of the alloy on exposed surfaces of the steel strip and cooling the coated strip with cooling water. The cooling step includes controlling the p H of cooling water to be in a range of pH 5-9. Particular embodiments focus on Al—Zn—Si—Mg alloys that contain the following elements in % by weight: Zn: 2 to 19, Si: 0.01 to 2, Mg: 1 to 10, and Balance Al and unavoidable impurities.

The invention relates to a method for coating a steel sheet or steel strip to which an aluminium-based coating is applied in a dip-coating process and the surface of the coating is freed of a naturally occurring aluminium oxide layer. In order to provide a low-cost method for coating steel sheets or steel strips that makes the steel sheets or steel strips outstandingly suitable for the production of components by means of press hardening and for the further processing thereof, it is proposed that transition metals or transition metal compounds are subsequently deposited on the freed surface of the coating to form a top layer. The invention also relates to a method for producing press-hardened components from the aforementioned steel sheets or steel strips with an aluminium-based coating.

Provided is a thermal-insulated multi-walled pipe for superconducting power transmission that highly prevents intrusion of external heat due to radiation and has excellent thermal insulation property without using a superinsulation. A thermal-insulated multi-walled pipe for superconducting power transmission comprises: a superconducting cable; and a multi-walled pipe that houses the superconducting cable, wherein the multi-walled pipe is composed of a plurality of straight pipes, and at least one of the plurality of straight pipes has, at a surface thereof, a zinc or zinc alloy-plated layer having an average spangle size of 2.0 mm or less.

Provided is a steel sheet by weight percentage (wt %), carbon (C): 0.005 to 0.08%, manganese (Mn): 1.25% or less (excluding 0%), phosphorus (P): 0.03% or less (excluding 0%), sulfur (S): 0.01% or less (excluding 0%), nitrogen (N): 0.01% or less (excluding 0%), soluble aluminum (sol.Al): 0.01 to 0.06%, chromium (Cr): 1.15 to 2.5%, antimony (Sb): 0.1% or less (excluding 0%), at least one selected from the group consisting of nickel (Ni): 0.3% or less (excluding 0%), silicon (Si): 0.3% or less (excluding 0%), molybdenum (Mo): 0.2% or less (excluding 0%), and boron (B): 0.003% or less (excluding 0%), and a remainder of iron (Fe) and other unavoidable impurities, satisfying Expression 1: 1.3≤Mn(wt %)+Cr(wt %)/1.5+Sb(wt %)≤2.7, where Mn, Cr, and Sb refer to contents (wt %) of corresponding elements, respectively; and 1 to 5% of martensite and a remainder of ferrite by an area percentage (area %).

The present invention provides a steel sheet plated with aluminum-iron and a preparation method therefor, the steel sheet comprising: a base steel sheet; and a plated layer formed on the surface of the base steel sheet and comprising: an alloyed layer containing at least one of Fe3Al, FeAl(Si), Fe2Al5, and FeAl3; and an aluminum layer formed on the alloyed layer and having a thickness less than 10% of that of the plated layer, wherein the plated layer is 20-35 μm in thickness and contains 1-20 wt % of Mg as measured by GDS at a position 0.1 μm deep from the surface of the plated layer and 10 wt % of oxygen as measured by GDS at a position 0.1 μm deep from the surface of the plated layer.