An oxide layer thickness measurement device according to the present invention stores, for each of layer thickness measurement sub-ranges constituting a layer thickness measurement range, layer thickness conversion information representing a correlation between a layer thickness and an emissivity where a ratio of a change in the emissivity to a change in the layer thickness in the layer thickness measurement sub-range falls within a set extent. Emitting light luminances of a surface of a steel sheet are measured at respective measurement wavelengths different from each other, and a temperature of the surface of the steel sheet is measured to thereby calculate the emissivity at each of the measurement wavelengths. Calculated in connection with the emissivity calculated at each of the measurement wavelength are the layer thickness corresponding to the emissivity at the measurement wavelength, and a ratio at the layer thickness by using the layer thickness conversion information corresponding to the measurement wavelength. The calculated thickness is extracted as a candidate value for an actual layer thickness when the calculated ratio is within the preset extent assigned for the layer thickness conversion information.

The present invention has as its object the provision of a coated steel member and coated steel sheet excellent in hydrogen embrittlement resistance in a corrosive environment and methods for manufacturing the same. The coated steel member of the present invention is provided on its surface with an Al-Fe-based coating containing Cu and one or more of Mo, Ni, Mn, and Cr in a total by mass % of 0.12% or more by heating, cooling, and manufacturing a coated steel sheet having a layer containing Cu on its surface under predetermined conditions.

This coated steel member includes: a steel sheet substrate having a predetermined chemical composition; and a coating formed on a surface of the steel sheet substrate and containing Al and Fe, in which the coating has a low Al content region having an Al content of 3 mass % or more and less than 30 mass % and a high Al content region formed on a side closer to a surface than the low Al content region and having an Al content of 30 mass % or more, a maximum C content of the high Al content region is 25% or less of a C content of the steel sheet substrate, a maximum C content of the low Al content region is 40% or less of the C content of the steel sheet substrate, and a maximum C content in a range from an interface between the steel sheet substrate and the coating to a depth of 10 μm on a side of the steel sheet substrate is 80% or less of the C content of the steel sheet substrate.

A method manufacturing a steel strip, including the subsequent steps of hot rolling the strip into a hot rolled strip, cold rolling the hot rolled strip and hot dip coating the cold rolled strip with a Zn based coating by leading the strip through a bath including molten zinc and wiping the strip after the coating using a gas knife having a knife slot from which a wiping gas is projected and the steel strip is cold rolled to a final cold rolled thickness of between 0.40 mm and 1.00 mm in a multi-stand cold rolling mill, and the coated steel sheet includes a steel substrate provided with a hot dip metal coating.

Provided is a highly corrosion-resistant plated steel sheet having plating adhesion and resistance to liquid metal embrittlement. A highly corrosion-resistant plated steel sheet comprises a base steel sheet and a plated layer, which sequentially comprises an Fe—Al alloy layer and an MgZn.sub.2 layer from an interface with the base steel sheet.

Equipment for the continuous hot dip-coating of a metal strip 9 including an annealing furnace, a tank 2 containing a liquid metal bath 3, a snout connecting the annealing furnace and tank 2, through which the metal strip 9 runs in a protective atmosphere and the lower part of the snout, the sabot 5, is at least partly immersed in the liquid metal bath 3 in order to define with the surface of the bath, and inside this snout, a liquid seal 6, an overflow 7 not connected to the snout, the overflow 7 including at least one tray 8, placed in the vicinity of the strip 9 when entering the liquid metal bath 3 and encompassed by liquid seal 6.

Provided are a plated steel sheet for hot press forming including: a base steel sheet containing, by wt%, 0.14 to 0.5% of C, 0.001 to 1% of Si, 0.3 to 4% of Mn, 0.001 to 0.015% of P, 0.0001 to 0.02% of S, 0.001 to 0.1% of Al, 0.001 to 1% of Cr, 0.001 to 0.02% of N, 0.1% or less of Ti, 0.01% or less of B, 0.005 to 0.1% of Sb, and a balance of Fe and unavoidable impurities; an aluminum or aluminum alloy plating layer provided on at least one surface of the base steel sheet; and a Sb-rich layer provided between the base steel sheet and the plating layer, wherein the plated steel sheet for hot press forming satisfies the following Relational Expressions 1-1 and 1-2, a hot press formed member manufactured using the same, and methods for manufacturing the plated steel sheet for hot press forming and the hot press formed member.

[00001]$\begin{array}{cc}\frac{S{b}_{\max }}{S{b}_{coat}}\ge 1.2& \text{­­­[Relational Expression 1-1]}\end{array}$

[00002]$\begin{array}{cc}\frac{\left(S{b}_{\max }-S{b}_{coat}\right)}{2}\times \text{Δ}t\ge 0.008& \text{­­­[Relational Expression 1-2]}\end{array}$

[In Relational Expressions 1-1 and 1-2, Sb.sub.coat represents an average content of Sb in the plating layer, and a unit thereof is wt%, Sb.sub.max represents a maximum value of a content of Sb in the Sb-rich layer, and a unit thereof is wt%, and Δt represents a linear distance from a boundary between the plating layer and the Sb-rich layer to a point where Sb.sub.max is measured, and a unit thereof is .Math.m.]

Provided is a low-density clad steel sheet having excellent formability and fatigue properties, including a base material; and cladding materials provided on both side surfaces of the base material, wherein the base material is a lightweight steel sheet including, by weight, C: 0.3 to 1.0%, Mn: 4.0 to 16.0%, Al: 4.5 to 9.0%, and a remainder of Fe and inevitable impurities, and each of the cladding materials is martensitic carbon steel including, by weight, C: 0.1 to 0.45%, Mn: 1.0 to 3.0%, and a remainder of Fe and inevitable impurities.

A rolled steel sheet, for press hardening is provided, having a chemical composition where Ti/N>3.42, and the carbon, manganese, chromium and silicon contents satisfy:

[00001]$2.6C+\frac{\mathrm{Mn}}{5.3}+\frac{\mathrm{Cr}}{13}+\frac{\mathrm{Si}}{15}\ge 1.1\%.$

The sheet has a nickel content Ni.sub.surf at any point of the steel in the vicinity of the surface over a depth Δ, such that: Ni.sub.surf>Ni.sub.nom, Ni.sub.nom denoting the nominal nickel content of the steel, and such that, Ni.sub.max denoting the maximum nickel content within Δ:

[00002]$\frac{\left({\mathrm{Ni}}_{\max }+{\mathrm{Ni}}_{\mathrm{nom}}\right)}{2}\times \left(\Delta \right)\ge 0.6,$

and such that:

[00003]$\frac{\left({\mathrm{Ni}}_{\max }-{\mathrm{Ni}}_{\mathrm{nom}}\right)}{\Delta }\ge 0.01$

and the surface density of all of the particles D.sub.i , and the surface density of the particles D.sub.(>2 μm) larger than 2 micrometers satisfy, at least to a depth of 100 micrometers in the vicinity of the surface of said sheet:

D.sub.i+6.75 D.sub.(>2 μm)<270

D.sub.i and D.sub.(>2 μm) being expressed as number of particles per square millimeter, and said particles denoting all the oxides, sulfides, and nitrides, either pure or combined such as oxysulfides and carbonitrides, present in the steel matrix.

Provided is a hot-dip galvanized steel sheet to be used for home appliances, vehicles, and the like, and having excellent surface appearance and low-temperature bonding brittleness. The hot-dip galvanized steel sheet includes: a base steel sheet; and a hot-dip galvanized layer formed on the base steel sheet. A surface of the base steel sheet has a centerline average roughness (Ra) of 0.3 or more, a roughness skewness (Rsk) of −1 or less, and a roughness kurtosis (Rku) of 6 or more.