The present invention is a production method of a hot-dip galvanized steel sheet including annealing a belt-shaped steel sheet having a Si content of greater than or equal to 0.2% by mass, wherein the annealing is continuously carried out using an annealing furnace having an oxidation heating zone and a reduction heating zone in this order, while the steel sheet is fed using rollers. The annealing includes oxidizing a surface of the steel sheet in the oxidation heating zone at a temperature at which roll pickup does not occur and reducing an iron oxide layer, formed by the oxidizing, in the reduction heating zone before the iron oxide layer reaches an initial roller in the reduction heating zone.

A hot-dip galvanized steel sheet including: a hot-dip galvanizing layer on at least one side of a base steel sheet, wherein the hot-dip galvanizing layer has a Fe content of more than 0% and 3.0% or less and an Al content of more than 0% and 1.0% or less, the hot-dip galvanized steel sheet including: a FeAl alloy layer provided on an interface between the hot-dip galvanizing layer and the base steel sheet, the FeAl alloy layer having a thickness of 0.1 m to 2.0 m, and a difference between a maximum value and a minimum value of the thickness of the FeAl alloy layer in a width direction of the base steel sheet being within 0.5 m; and a fine-grain layer provided in the base steel sheet and directly in contact with the FeAl alloy layer, the fine-grain layer having an average thickness of 0.1 m to 5.0 m, the fine-grain layer including a ferrite phase with an average grain diameter of 0.1 m to 3.0 m, the fine-grain layer containing oxides of one or more out of Si and Mn, a maximum diameter of the oxides being 0.01 m to 0.4 m, and a difference between a maximum value and a minimum value of the thickness of the fine-grain layer in the width direction of the base steel sheet being within 2.0 m.

Provided is an alloyed hot-dip galvanized steel sheet including a base steel sheet, the base steel sheet containing a given amount of C, Si, Mn, and other elements. The alloyed hot-dip galvanized steel sheet is provided with an alloyed hot-dip galvanized layer on a surface of the base steel sheet, the alloyed hot-dip galvanized layer containing, in mass %, Fe: more than or equal to 5% and less than or equal to 15%, and having a thickness of more than or equal to 3 m and less than or equal to 30 m. The alloyed hot-dip galvanized steel sheet includes an A layer immediately under the surface of the base steel sheet, the A layer being formed in the base steel sheet and having a thickness of more than or equal to 2 m and less than or equal to 20 m from the surface of the base steel sheet, containing more than or equal to 50 vol % of a ferrite structure, and containing more than or equal to 90 mass % of unoxidized Fe, less than or equal to 10 mass % of a total of contents of oxides of Fe, Si, Mn, P, S, and Al, and less than 0.05 mass % of C.

A high-strength hot-dip galvanized steel sheet excellent in impact resistance and worked portion corrosion resistance including a hot-dip galvanized plating layer on a steel sheet base material whose tensile strength is 590 MPa or more, wherein the plating layer includes projecting alloy layers being in contact with the steel sheet base material, a number density of the projecting alloy layers is 4 pieces/mm or more, wherein the steel sheet base material includes: a miniaturized layer being directly in contact with the interface between the steel sheet base material and the plating layer; a decarburized layer being in contact with the miniaturized layer; and an inner layer other than the miniaturized layer and the decarburized layer, and one or more kinds of oxides of Si and Mn are contained in layers of the miniaturized layer, the decarburized layer, and the projecting alloy layers.

A method for producing a high-strength galvanized steel sheet having excellent fatigue resistance properties. The method includes an oxidation processing in which a steel sheet is heated at a temperature of 400 to 750 C. in an atmosphere having an O.sub.2 concentration of 1000 ppm by volume or more and a H.sub.2O concentration of 1000 ppm by volume or more, and the steel sheet is heated at a temperature of 600 to 850 C. in an atmosphere having an O.sub.2 concentration of less than 1000 ppm by volume and a H.sub.2O concentration of 1000 ppm by volume or more. The method also includes reduction-annealing in which the steel sheet is heated at a heating rate of 0.1 C./sec or more to a temperature of 650 to 900 C. in an atmosphere having a H.sub.2 concentration of 5 to 30 vol % and a H.sub.2O concentration of 10 to 1000 ppm by volume.

A method for manufacturing a high-strength galvanized steel sheet having excellent strength-elongation balance, coating adhesiveness, and surface appearance. The method includes: (i) a first heating process of heating a steel sheet having a predetermined chemical composition, (ii) a first pickling process of pickling the steel sheet which was subjected to the first heating process in an oxidizing acidic aqueous solution, (iii) a second pickling process of pickling the steel sheet which was subjected to the first pickling process in a non-oxidizing acidic aqueous solution, (iv) a second heating process of holding the steel sheet, which was subjected to the second pickling process, at a temperature range of 700 C. or higher and 900 C. or lower in a hydrogen-containing atmosphere for 20 seconds or more and 300 seconds or less, and (v) performing a galvanizing treatment on the steel sheet which was subjected to the second heating process.

A method comprises: annealing a steel sheet by conveying the steel sheet through a heating zone, a soaking zone, and a cooling zone in the stated order in an annealing furnace; and then applying a hot-dip galvanized coating onto the steel sheet discharged from the cooling zone. Reducing or non-oxidizing humidified gas and reducing or non-oxidizing dry gas are supplied into the soaking zone. A CO gas concentration is measured using a CO gas concentration meter provided in an exhaust portion for gas in the soaking zone. A decarburized layer thickness of the steel sheet is calculated from the measured CO gas concentration. At least one of a flow rate and a dew point of the humidified gas is controlled so that the calculated decarburized layer thickness is less than or equal to a predetermined thickness.

A method for producing a zinc or zinc-alloy coated steel sheet with a tensile strength higher than 900 MPa, for the fabrication of resistance spot welds containing in average not more than two Liquid Metal Embrittlement cracks per weld having a depth of 100 m or more, with steps of providing a cold-rolled steel sheet, heating cold-rolled steel sheet up to a temperature T1 between 550 C. and Ac1+50 C. in a furnace zone with an atmosphere (A1) containing from 2 to 15% hydrogen by volume, so that the iron is not oxidized, then adding in the furnace atmosphere, water steam or oxygen with an injection flow rate Q higher than (0.07%/h), being equal to 1 if said element is water steam or equal to 0.52 if said element is oxygen, at a temperature TT1, so to obtain an atmosphere (A2) with a dew point DP2 between 15 C. and the temperature Te of the iron/iron oxide equilibrium dew point, then heating the sheet from temperature T.sub.1 up to a temperature T.sub.2 between 720 C. and 1000 C. in a furnace zone under an atmosphere (A2) of nitrogen containing from 2 to 15% hydrogen and more than 0.1% CO by volume, with an oxygen partial pressure higher than 10.sup.21 atm., wherein the duration t.sub.D of heating of the sheet from temperature T.sub.1 up to the end of soaking at temperature T.sub.2 is between 100 and 500s., soaking the sheet at T.sub.2, then cooling the sheet at a rate between 10 and 400 C./s, then coating the sheet with zinc or zinc-alloy coating.

A high-strength surface-coated steel sheet includes a base steel sheet having a composition by mass of C: 0.01 to 0.20%, Si: 0.01 to 0.50%, Mn: 0.10 to 2.50%, P: 0.005 to 0.050%, B: 0.0005 to 0.010%, Ti: 0.01 to 0.20%, Nb: 0 to 0.10%, Mo: 0 to 0.50%, Cr: 0 to 0.50%, Al: 0.01 to 0.10%, and the balance of Fe and inevitable impurities; and a ZnAlMg-based coating layer disposed on a surface of the base steel sheet, The steel sheet has a diffusible hydrogen concentration in the base steel sheet of 0.30 ppm or less and having a time until occurrence of red rust of 7000 hours or more as measured by a salt spray test. The high-strength hot-dip ZnAlMg-based-plated steel sheet has a significantly lowered in-steel concentration of hydrogen which has entered the steel in a plating line and exhibits excellent corrosion resistance.

A method and arrangement for manufacturing hot dip galvanized rolled high strength steel product is presented. The method comprises providing a rolled steel product, heating and annealing the rolled steel product for creating a layer of iron oxide on the surface of the rolled steel product, cooling the rolled steel product, having the iron oxide layer, in a first cooling step to a temperature in a temperature range of 560-600 C. and holding for 3-10 seconds, quenching said rolled steel product, covered with the layer of iron oxide, in a second cooling step by immersing it into a zinc bath comprising aluminium and having a temperature between 440-450 C. for 1-5 seconds and cooling the rolled steel product in a third cooling step to room temperature. An arrangement for implementing the method is also presented.