Nippon Steel Corporation

Masaaki Uranaka

Takuya Mitsunobu

Jun Maki

Hiroshi Takebayashi

Keitaro Matsuda

Kohei Tokuda

Masahiro Matsuba

To further improve electrodeposition coating properties in a weld bead zone. A welded joint according to the present invention includes: a first steel sheet and a second steel sheet; and a weld bead zone formed by arc welding or laser welding, wherein at least one of the first steel sheet or the second steel sheet has a plating layer composed of a predetermined component and an oxide layer located on the plating layer in a non-heat-affected zone, and the weld bead zone has a weld metal and a slag layer formed on part of a surface of the weld metal, and the slag layer contains, by mass % when oxygen is excluded, Al: 1.0 to 45.0% and Mg: 1.0 to 30.0%, with the balance composed of Fe, easily oxidizable metallic elements, and impurities.

Welded joint

This plated steel sheet includes a steel sheet, and a plated layer disposed on a surface of the steel sheet, in which the plated layer has a chemical composition containing, in mass %, Al: 10.0 to 25.0%, Mg: 3.0 to 10.0%, Fe: 0.01 to 2.0%, and Si: more than 0 to 2.0%, with a remainder including Zn and impurities, and a number density of MgSi phases having a major axis of 2 μm or more exposed on the surface of the plated layer is 3 to 150 per area of 10,000 μm.

Plated steel sheet

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 ([Al—O]+[Mg—O])/[Zn—O]) calculated from intensity of peaks respectively attributed to an Al—O bond, an Mg—O bond, and a Zn—O bond is 5.0 or more.

High strength plated steel sheet having high hydrogen embrittlement resistance, that is, alloyed hot dip galvannealed steel sheet including steel sheet containing C: 0.05 to 0.40%, Si: 0.2 to 3.0%, Mn: 0.1 to 5.0%, and sol. Al: 0.4 to 1.50% and a alloyed hot dip galvannealed layer deposited on at least one surface of the steel sheet to 10 to 100 g/mand containing Fe: 5.0 to 15.0% and Al: 0.01 to 1.0%, having an internal oxidation layer including grain boundary oxides in a surface layer of the steel sheet, when examining a cross-section of a surface layer of the steel sheet, a Ratio A of the length of the grain boundary oxides projected an interface of the steel sheet and the alloyed hot dip galvannealed layer to the length of interface is 50% or more and 100% or less, and a surface depleted layer with a steel composition not including the grain boundary oxides which satisfies, by mass %, Si≤0.6% and Al≥0.05% is included at a depth of ½ of the average depth of the internal oxidation layer.

Alloyed hot dip galvannealed steel sheet

High strength steel sheet and plated steel sheet having high plateability, LME resistance, and hydrogen embrittlement resistance, that is, steel sheet containing C: 0.05 to 0.40%, Si: 0.2 to 3.0%, Mn: 0.1 to 5.0%, and sol. Al: 0.4 to 1.50%, having an internal oxidation layer including fine granular oxides, coarse granular oxides, and grain boundary oxides in a surface layer of the steel sheet, a number density of fine granular oxides in the internal oxidation layer being 4.0/μmor more, a number density of coarse granular oxides in the internal oxidation layer being 4.0/25 μmor more, having a Ratio A of the length of the grain boundary oxides projected on the surface of the steel sheet to the length of the surface of the steel sheet when examining a cross-section of the surface layer of the steel sheet being 50% or more and 100% or less, and including a surface depleted layer with a steel composition not including oxides which satisfies, by mass %, Si≤0.6% and Al≥0.05% at a depth of ½ of the average depth of the internal oxidation layer calculated from the cross-sectional SEM image of the steel sheet, and a plated steel sheet using the same.

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Tokyo, Japan

Masaaki Uranaka