Provided are coated steel sheets, production methods therefor, and so forth, the coated steel sheets having a tensile strength of 440 MPa or more, good formability, and good aging resistance. A steel sheet of the present invention includes a specific component composition and a steel microstructure having an area fraction of a ferrite phase of 80% or more and 95% or less, an area fraction of pearlite of 5% or more and 20% or less, and an average ferrite grain size of 5 m or more and 20 m or less, in which in a ferrite grain size histogram, the average grain size of the largest 20% of ferrite grains in terms of grain size is 10 m or more, and the pearlite has an average lamellar spacing of 200 nm or less, the area fraction, the average ferrite grain size, and the lamellar spacing being determined by microstructure observation.

A zinc-plated steel sheet for hot stamping according to an aspect of the present invention includes a steel substrate and a plated layer provided on a surface of the steel substrate, in which the steel substrate contains, in % by mass, C: 0.10 to 0.5%, Si: 0.7 to 2.5%, Mn: 1.0 to 3%, and Al: 0.01 to 0.5%, with the balance being iron and inevitable impurities, and the steel substrate has, in the inside thereof, an internal oxide layer consists of an oxide containing at least one of Si and Mn having a thickness of 1 m or more, and a decarburized layer having a thickness of 20 m or less from an interface with the plated layer toward an internal direction of the steel substrate.

A zinc-coated steel may be produced by performing a pre-alloying heat treatment after galvannealing the steel and prior to the hot stamping the steel. The pre-alloying heat treatment is conducted at a temperature between about 850 F. and about 950 F. in an open coil annealing process. The pre-alloying heat treatment allows for shorter time at the austenitization temperature to form a desired -Fe phase in the coating by increasing the concentration of iron. This also decreases the loss of zinc, and a more adherent oxide exists after hot stamping.

A hot pressed part comprises: a predetermined chemical composition; and a steel microstructure that is a gradient microstructure in which, in a thickness direction, a surface layer is a soft layer, an inside is a hard layer, and a layer between the soft layer and the hard layer is a transition layer.

A hot stamped steel includes a base material, a plated layer that is formed on a surface of the base material, and an oxide film that is formed on a surface of the plated layer; chemical composition of the plated layer contains 20.00 to 45.00 mass % of Al, 10.00 to 45.00 mass % of Fe, 4.50 to 15.00 mass % of Mg, 0.10 to 3.00 mass % of Si, 0.05 to 3.00 mass % of Ca, 0 to 0.50 mass % of Sb, 0 to 0.50 mass % of Pb, 0 to 1.00 mass % of Cu, 0 to 1.00 mass % of Sn, 0 to 1.00 mass % of Ti, 0 to 0.50 mass % of Sr, 0 to 1.00 mass % of Cr, 0 to 1.00 mass % of Ni, and 0 to 1.00 mass % of Mn with a remainder of Zn and impurities; and chemical composition of the oxide film contains 20.0 to 55.0 at % of Mg, 0.5 to 15.0 at % of Ca, 0 to 15.0 at % of Zn, and 0 at % or more and less than 10.0 at % of Al with a remainder of O and a total of 5.0 at % or less of impurities, and the adhesion amount of the oxide film per one surface is in a range of 0.01 to 10 g/m.sup.2.

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 ZnNi 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.

A steel sheet for hot pressing includes a specific chemical composition and further includes a steel structure in which an area ratio of ferrite in a region ranging from a surface to 100 m in depth is 30% to 90% and an area ratio of pearlite including an average grain diameter of 5 m or more in a region excluding the region ranging from the surface to 100 m in depth is 10% to 70%.

A hot-pressed steel sheet member includes a specific chemical composition and further includes a steel structure in which an area ratio of ferrite in a surface layer portion ranging from a surface to 15 m in depth is greater than 1.20 times an area ratio of ferrite in an inner layer portion being a portion excluding the surface layer portion, and the inner layer portion contains a steel structure represented, in area %, ferrite: 10% to 70%, martensite: 30% to 90%, and a total area ratio of ferrite and martensite: 90% to 100%. A tensile strength of the hot-pressed steel sheet member is 980 MPa or more.

Provided are coated steel sheets, production methods therefor, and so forth, the coated steel sheets having a tensile strength of 440 MPa or more, good formability, and good aging resistance.

A steel sheet of the present invention includes a specific component composition and a steel microstructure having an area fraction of a ferrite phase of 80% or more and 95% or less, an area fraction of pearlite of 5% or more and 20% or less, and an average ferrite grain size of 5 m or more and 20 m or less, in which in a ferrite grain size histogram, the average grain size of the largest 20% of ferrite grains in terms of grain size is 10 m or more, and the pearlite has an average lamellar spacing of 200 nm or less, the area fraction, the average ferrite grain size, and the lamellar spacing being determined by microstructure observation.

Disclosed is a method of manufacturing a blank for hot stamping, which includes forming a plated layer on a steel plate by immersing the steel plate in a plating bath including aluminum and silicon; and heating the steel plate on which the plated layer is formed at a first temperature for a first time period.