The present invention provides an aluminum-iron-plated steel sheet, having excellent mold wear resistance, for hot press forming, and a manufacturing method thereof.

A steel sheet has a specific chemical composition and has a structure represented by, by area ratio, ferrite: 5 to 60%, and bainite: 40 to 95%. When a region that is surrounded by a grain boundary having a misorientation of 15 or more and has a circle-equivalent diameter of 0.3 m or more is defined as a crystal grain, the proportion of crystal grains each having an intragranular misorientation of 5 to 14 to all crystal grains is 20 to 100% by area ratio. A precipitate density of Ti(C,N) and Nb(C,N) each having a circle-equivalent diameter of 10 nm or less is 10.sup.10 precipitates/mm.sup.3 or more. A ratio (Hvs/Hvc) of a hardness at 20 m in depth from a surface (Hvs) to a hardness of the center of a sheet thickness (Hvc) is 0.85 or more.

This invention provides process for manufacturing a galvanized metal three-dimensional object with a shape including multiple edges, said process comprising, in the following order, the steps of: (A) providing and cutting a metal sheet matrix with a thickness within a range from 0.8 mm to 6 mm, the shape of said metal sheet matrix including multiple free edges, (B) batch-wise hot dipping said metal sheet matrix into a molten zinc alloy galvanizing bath, (C) cold-forming the galvanized metal sheet matrix into a desired three-dimensional shape including multiple adjacent metal edges, and (D) cold-forming a series of joining points for fastening together said multiple adjacent metal edges, to form said galvanized metal three-dimensional object.

Provided is a method for producing a galvanized steel sheet that includes an oxide layer forming step of bringing a galvanized steel sheet into contact with an acidic solution containing sulfate ions, then holding the galvanized steel sheet in contact for 1 to 60 seconds, and then washing the galvanized steel sheet with water; and a neutralization treatment step of holding a surface of an oxide layer, which has been formed in the oxide layer forming step, in contact with an alkaline aqueous solution for 0.5 seconds or longer, and then performing washing with water and drying. The alkaline aqueous solution contains 0.1 g/L or more of carbonate ions.

[Object] There are provided automobile parts and a method for manufacturing the automobile parts. The automobile parts have an excellent corrosion resistance after coated with a electrodeposition paint with smaller thickness, improve formability and productivity in hot pressing, and also improve chemical conversion treatability after hot press-forming.

[Solution] An automobile part according to the present invention includes: a formed steel sheet having an intermetallic compound layer formed on a surface of the steel sheet, the intermetallic compound layer being formed of AlFe intermetallic compound having a thickness of 10 m or more and 50 m or less, the intermetallic compound layer including a diffusion layer positioned in closest proximity to the steel sheet, the diffusion layer having a thickness of 10 m or less; a surface coating layer provided on a surface of the intermetallic compound layer, the surface coating layer including a coating containing ZnO and a zinc phosphate coating and having a surface roughness of 3 m or more and 20 m or less as a maximum profile height Rt in accordance with JIS B0601 (2001); and an electrodeposition paint film provided on a surface of the surface coating layer and having a thickness of 6 m or more and less than 15 m.

A method of manufacturing a hot press formed part by hot pressing a coated steel sheet that is obtained by forming a Zn-based coating layer on a surface of a steel sheet includes: heating the coated steel sheet to a temperature range of 750 C. or more and 1000 C. or less; cooling a surface of the coated steel sheet; and hot press forming the coated steel sheet under a condition that a surface temperature of the coated steel sheet is 400 C. or less and an average temperature of the coated steel sheet is 500 C. or more or a temperature of a center position of the coated steel sheet in a thickness direction is 530 C. or more.

The present invention provides a plated steel material having excellent processability and corrosion resistance, the plated steel material comprising: a base iron; and a hot-dip alloy-plated layer formed on the base iron, the hot-dip alloy-plated layer comprising, in wt %, 5-30% of Al, 2-10% of Mg, and a balance of Zn and other inevitable impurities, wherein, in a cross-section in the hot-dip alloy-plated layer, the area fraction of a MgZn2 phase is 20-70%, and the ratio of the area fraction of an Al-containing phase to the area fraction of the MgZn2 phase is 1-70%.

A metallic flat product is disclosed which is subjected to surface finishing by hot-dip coating and which is preferably composed of steel. The metallic flat product includes a metallic alloy layer (11) and a metallic surface layer (12), which metallic alloy layer and metallic surface layer differ from one another in terms of their chemical composition. The two layers (11, 12) are produced in a one process step and define a continuous transition region (13) in which a mixture of the two different chemical compositions is present. The metallic alloy layer (11) has a thickness of less than 8 m, preferably less than 6 m, and the surface layer (12) is formed from aluminum or zinc. The flat product has an improved coating, by means of which the flat product more effectively satisfies the requirements with regard to good deformability and has good anti-corrosion protection.

A hot stamped steel according to the present invention satisfies an expression of (5[Si]+[Mn])/[C]>11 when [C] represents an amount of C by mass %, [Si] represents an amount of Si by mass %, and [Mn] represents an amount of Mn by mass %, a metallographic structure after hot stamping includes 40% to 90% of a ferrite and 10% to 60% of a martensite in an area fraction, a total of an area fraction of the ferrite and an area fraction of the martensite is 60% or more, a hardness of the martensite measured with a nanoindenter satisfies an H2/H1<1.10 and HM<20, and TS, which is a product of a tensile strength TS and a hole expansion ratio is 50000 MPa.Math.% or more.

To more reliably suppress LME and blowhole formation while maintaining excellent corrosion resistance.

A plated steel sheet according to the present invention, includes: a steel sheet as a base material; a plating layer located on at least part of a surface of the steel sheet; and an oxide layer located on a surface of the plating layer, where a chemical composition of the plating layer is made up of prescribed components, and Zn and impurities as the balance, and when a position at a depth of 5 nm from an uppermost surface of the oxide layer is observed by X-ray photoelectron spectroscopy (XPS), a value of an intensity ratio ([AlO]+[MgO])/[ZnO]) calculated from intensity of peaks respectively attributed to an AlO bond, an MgO bond, and a ZnO bond is 5.0 or more.