Disclosed herein is a high-strength plated steel sheet having a plated layer on the surface of a base steel sheet and containing predetermined steel components. The steel sheet includes, in the order from the interface of the base steel sheet and the plated layer towards the base steel sheet: a soft layer having a Vickers hardness that is 90% or less of the Vickers hardness at a portion t/4 of the base steel sheet, where t is a sheet thickness of the base steel sheet; and a hard layer consisting of a structure which is mainly composed of martensite and bainite and in which the average grain size of prior austenite is 20 μm or less. The average depth D of the soft layer is 20 μm or greater, and the average depth d of an internal oxide layer is 4 μm or greater and smaller than D.

Disclosed herein is a high-strength plated steel sheet containing an internal oxidized layer, a soft layer including the internal oxidized layer, and a hard layer including a structure having metallic structure containing a low-temperature-transformation produced phase in a proportion of 70% or more by area of the whole of the metallic structure, in which polygonal ferrite is in a proportion of 0% or more by area, and 10% or less by area of the same, and retained austenite is in a proportion of 5% or more by volume of the same. The high-strength plated steel sheet satisfies the average depth D of the soft layer is 20 μm or more, the average depth d of the internal oxidized layer is 4 μm or more and less than D, and a tensile strength of 980 MPa or more.

A bolt of the present invention has a composition comprising: 0.50 mass % or greater and 0.65 mass % or less of carbon (C), 1.5 mass % or greater and 2.5 mass % or less of silicon (Si), 1.0 mass % or greater and 2.0 mass % or less of chromium (Cr), 0.2 mass % or greater and 1.0 mass % or less of manganese (Mn), 1.5 mass % or greater and 5.0 mass % or less of molybdenum (Mo), wherein a total amount of phosphorous (P) and sulfur (S) as impurities is 0.03 mass % or less, the remaining is iron (Fe), and the bolt comprises an iron based oxide film with a film thickness of 3 μm or greater and 20 μm or less on the surface thereof. The bolt has excellent delayed fracture resistance and reliably provides a fastening axial force.

A cold rolled and heat-treated steel sheet having a composition including, by weight percent C: 0.12-0.25% Mn: 3.0-8.0%, Si: 0.70-1.50%, Al: 0.3-1.2%, B: 0.0002-0.004%, S≤0.010%, P≤0.020%, N≤0.008%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting, and having a microstructure consisting of, in surface fraction: between 5% and 45% of ferrite, between 25% and 85% of partitioned martensite, the partitioned martensite having a carbides density strictly less than 2×10.sup.6/mm.sup.2, between 10% and 30% of retained austenite, less than 8% of fresh martensite, a part of the fresh martensite being combined with retained austenite in the shape of martensite-austenite islands in total surface fraction less than 10%.

Disclosed in the present invention is a manufacturing method for a carbon steel and austenitic stainless-steel rolling clad plate, comprising the steps of: (1) obtaining a blank material of a carbon steel layer and a blank material of a stainless-steel layer; (2) assembling blank materials; (3) cladding and rolling; (4) cold rolling; (5) first annealing; and (6) second annealing. The carbon steel and austenitic stainless-steel rolling clad plate has two unique annealing processes, so that the clad plate has the performance advantages of the austenitic stainless-steel and the carbon steel. In addition, further disclosed in the present invention is a carbon steel and austenitic stainless-steel rolling clad plate manufactured by this method.

Disclosed are thermoformed component having excellent coating adhesion and a method for manufacturing the same. The thermoformed component comprises a substrate layer and an aluminum coating coated on at least one surface of the substrate layer, wherein the average roughness Ra of a surface of the thermoformed component is between 1.0 μm and 3.0 μm, the peak height and the peak-to-valley height Rt are between 8 μm and 30 μm, and the roughness peak count Rpc is greater than or equal to 50. The thermoformed component has good paintability, good coating adhesion and good corrosion resistance, and is very suitable for automotive parts.

A high-performance thermoformed component provided with a coating, and a manufacturing method therefor. The thermoformed component comprises a substrate and a coating thereon. The substrate comprises the following ingredients in percentage by weight: 0.01-0.8% of C, 0.05-1.0% of Si, 0.1-5% of Mn, 0.001-0.3% of P, 0.001-0.1% of S, 0.001-0.3% of Al, 0.001-0.5% of Ti, 0.0005-0.1% of B, 0.001-0.5% of Nb, 0.001-0.5% of V, and the remainder being Fe and other unavoidable impurities. The appearance of the thermoformed component has no color difference and no mottling. The surface oxygen content of the thermoformed component is 0.1-20 wt. %, and the ratio of the standard deviation to the average value of the surface oxygen content satisfies: 0<standard deviation of oxygen content/average value of oxygen content ≤0.3. In the manufacturing method, a coated steel plate that has undergone heat treatment, transfer processing, and hot stamping is not treated with oil.

The present disclosure relates to a zinc plated steel sheet having excellent fatigue strength of electrical resistance spot welds and a method for manufacturing the same. According to an aspect of the present disclosure, a zinc plated steel sheet includes a base steel sheet and a zinc-based plating layer formed on a surface of the base steel sheet, wherein a concentration profile of one or two of oxygen, and silicon and manganese measured in a depth direction from the surface of the base steel sheet has a maximum point in the depth direction from the surface, and an absolute value of a difference between a depth at which the maximum point of the concentration profile of oxygen is formed and a depth at which the maximum point of the concentration profile of one of silicon and manganese is formed is 0.5 μm or less.

This steel sheet has a specific chemical composition, the tensile strength is 1300 MPa or more, the ratio (R/t) of the limit bend radius to the sheet thickness is less than 3.5, when a depth position of 30 μm from the surface in the sheet thickness direction is defined as a position A and a depth position of ¼ of the sheet thickness from the surface in the sheet thickness direction is defined as a position B, the number density of AIN at the position A is 3000 pieces/mm.sup.2 or more and 6000 pieces/mm.sup.2 or less, a metallographic structure at the position B includes 90% or more of martensite by volume percentage, and the hardness at the position A is 1.20 times or higher than the hardness at the position B.

This hot-rolled steel sheet has a predetermined chemical composition, a microstructure includes 80% or more of tempered martensite by a volume percentage and a remainder consisting of one or more of ferrite, pearlite, bainite, fresh martensite, and residual austenite, the tempered martensite includes 5×10.sup.9 pieces/mm.sup.3 or more of precipitates containing Ti and having an equivalent circle diameter of 5 nm or less per unit volume, in a surface layer region that is a range from a surface to a 1/10 position of a sheet thickness, a sum of an average pole density of a crystal orientation group consisting of {211}<111> to {111}<112> and a pole density in a crystal orientation of {110}<001> is 6.0 or less, and a tensile strength is 980 MPa or more.