A process for manufacturing a flat steel product having a prealloyed corrosion-resistant coating, comprises providing a coated flat steel product comprising a steel substrate having, at least on one side of the steel substrate, and an aluminum-based corrosion-resistant coating. The coated flat steel product is heat-treated, comprising the following substeps: Heating the coated flat steel product in a furnace at a furnace temperature T of between 950° C. and 1150° C. with a furnace dwell time tv of between 40 seconds and 150 seconds, the furnace temperature being chosen such that the heating rate of the coated flat steel product in the temperature range from 500° C. to 700° C. is more than 10 K/s. The coated flat steel product is held at a temperature above Ac3 for a hold time of between 20 seconds and 60 seconds.

A ferritic stainless steel sheet comprises a chemical composition containing, in mass %, C: 0.030% or less, Si: 3.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.010% or less, Cr: 11.0% to 30.0%, Al: 8.0% to 20.0%, Ni: 0.05% to 0.50%, N: 0.020% or less, and at least one selected from the group consisting of Zr: 0.01% to 0.20% and Hf: 0.01% to 0.20%, with a balance consisting of Fe and inevitable impurities.

A press hardened coated steel part with high resistance to delayed fracture, the coating containing (Fe.sub.x—Al.sub.y) intermetallic compounds resulting from the diffusion of iron into an aluminum or an aluminum-based alloy, or an aluminum alloy of a precoating, wherein the chemical composition of the steel includes, in weight: 0.16%≤C≤0.42%, 0.1%≤Mn≤3%, 0.07%≤Si≤1.60%, 0.002%≤Al≤0.070%, 0.02%≤Cr≤1.0%, 0.0005≤B≤0.005%, 0.002%≤Mg≤0.007%, 0.002%≤Ti≤0.11%, 0.0008%≤O≤0.005%, wherein (Ti)×(O).sup.2×10.sup.7≤2, 0.001%≤N≤0.007%, 0.001%≤S≤0.005%, 0.001%≤P≤0.025% and optionally one or more elements selected from the list of: 0.005%≤Ni≤0.23%, 0.005%≤Nb≤0.060%, the remainder being Fe and unavoidable impurities, and wherein the microstructure includes at least 95% martensite.

A press hardened steel part is provided. The steel of the part has a chemical composition including, in weight: 0.062%≤C≤0.095%, 1.4%≤Mn≤1.9%, 0.2%≤Si≤0.5%, 0.020%≤Al≤0.070%, 0.02%≤Cr≤0.1%, wherein: 1.5%≤(C+Mn+Si+Cr)≤2.7%, 0.040%≤Nb≤0.060%, 3.4×N≤Ti≤8×N wherein: 0.044%≤(Nb+Ti)≤0.090%, 0.0005≤B≤0.004%, 0.001%≤N≤0.009%, 0.0005%≤S≤0.003%, 0.001%≤P≤0.020%, optionally: 0.0001%≤Ca≤0.003%, and the remainder being Fe and unavoidable impurities. The microstructure of the part includes, in a majority of the part, in surface fractions: less than 40% of bainite, less than 5% of austenite, less than 5% of ferrite, and a remainder being martensite. The martensite is fresh martensite and self-tempered martensite.

A steel sheet has a predetermined chemical composition, and a surface exhibits an absorption peak at which a reflectance is not less than 50% nor more than 85% in a range of wave numbers of 1200 cm.sup.−1 to 1300 cm.sup.−1 by a Fourier transform-infrared spectroscopy analysis by a reflection absorption spectrometry method, and does not exhibit an absorption peak in a range of wave numbers of 1000 cm.sup.−1 to 1100 cm.sup.−1, or exhibits an absorption peak at which a reflectance is 85% or more in the range of wave numbers of 1000 cm.sup.−1 to 1100 cm.sup.−1, wherein Ni of 3 mg/m.sup.2 to 100 mg/m.sup.2 adheres to the surface.

Provided are a high-strength galvanized steel sheet having excellent delayed fracture resistance by reducing the diffusible hydrogen content in the steel and a method for producing the same. The high-strength galvanized steel sheet includes a steel sheet having a prescribed composition and a microstructure including martensite and tempered martensite, the total area fraction of the martensite and the tempered martensite being 30% or more, and a galvanizing layer formed on the surface of the steel sheet. The diffusible hydrogen content in the high-strength galvanized steel sheet is 0.50 wt. ppm or less. The half-width of the hydrogen release peak of the high-strength galvanized steel sheet is 70° C. or less. The diffusible hydrogen content and the half-width of the hydrogen release peak are determined by a prescribed analysis method.

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 hot-rolled steel sheet has a predetermined chemical composition, and in a case where the thickness is denoted by t, the metallographic structure at a t/4 position from the surface contains one or both of tempered martensite and lower bainite at a volume percentage of 90% or more, the tensile strength is 980 MPa or more, and the average Ni concentration on the surface is 7.0% or more.

Provided is a high-strength hot-rolled coated steel sheet having a TS of 980 MPa or more, excellent bulging formability and stretch flange formability, and excellent coatability. The high-strength hot-rolled coated steel sheet includes a steel sheet having a chemical composition containing, by mass %, C: 0.03% to 0.09%, Si: 0.01% to 1.60%, Mn: 2.20% to 3.60%, P: 0.100% or less, S: 0.0100% or less, Ti: 0.05% to 0.18%, B: 0.0005% to 0.0050%, Al: 0.005% to 0.40%, N: 0.010% or less, and a balance of Fe and inevitable impurities, in which a CSM value expressed by the equation 33.8[% C][% Mn]+12.4[% Si]/[% Mn] is 3.3 to 12.0, and a steel microstructure containing bainite in an amount of 85% or more in terms of area fraction and martensite in an amount of 2.0% or more and 15.0% or less in terms of area fraction and includes a coating layer or an alloyed coating layer on a surface of the steel sheet.

Disclosed is a steel composition including specified ranges of Ni; Mo; Co; Mo+Co+Si+Mn+Cu+W+V+Nb+Zr+Ta+Cr+C; Co+Mo; Ni+Co+Mo; and traces of Al; Ti; N; Si; Mn; C; S; P; B; H; O; Cr; Cu; W; Zr; Ca; Mg; Nb; V; and Ta in specified ranges; the remainder being iron and impurities. The inclusion population, as observed by image analysis over a polished surface measuring 650 mm.sup.2 if hot-formed or hot-rolled; and measuring 800 mm.sup.2 if cold-rolled, does not contain non-metallic inclusions of diameter>10 μm, and, in the case of a hot-rolled sheet, does not contain more than four non-metallic inclusions of diameter 5-10 μm over 100 mm.sup.2, the observation being performed by image analysis over a polished surface measuring 650 mm.sup.2.