The invention relates to battery trays for electric or hybrid vehicles. The bottoms of the battery trays are made of a thin sheet of aluminum alloy having a modulus of elasticity higher than 77 GPa in order to optimize thickness thereof while ensuring resistance to intrusion. The invention also relates to a thin sheet of 4xxx series aluminum alloy whose modulus is higher than 77 GPa and whose yield strength Rp 0.2 is higher than 295 MPa.

Provided is an ultra-high strength steel sheet having excellent ductility including, 0.1 to 0.2% of carbon (C), 0.1 to 1.0% of silicon (Si), 2.0 to 3.0% of manganese (Mn), 1.0% or less of aluminum (Al), 1.0% or less of chromium (Cr), 0.5% or less of molybdenum (Mo), 0.1% or less of titanium (Ti), 0.1% or less of niobium (Nb), 0.1% or less of antimony (Sb), 0.05% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.02% or less of nitrogen (N), and a balance of Fe and unavoidable impurities. The steel sheet satisfies the following: 1110[C]+41.5[Si]+575[Mn]−1092[Al]−3590[Nb]−5181[Ti]+258[Cr]+664 [Mo]≥1380; 2853 [C]+95 [Si]+309 [Mn]−153 [Al]+4661 [Nb]−780[Ti]+210[Cr]+457[Mo]≥1300; and −29[C]+0.6[Si]−7.3[Mn]+7.8[Al]−145.2[Nb]+62.6[Ti]−3.3[Cr]−2.2[Mo]≥−24.

A hot-dip plated steel includes a base steel and a hot-dip plating layer on a surface of the base steel, a chemical composition of the hot-dip plating layer contains, by mass %, Al: 10.00% to 30.00%, Mg: 3.00% to 12.00%, Sn: 0% to 2.00%, Si: 0% to 2.50%, Ca: 0% to 3.00%, Ni: 0% or more and less than 0.25%, Fe: 0% to 5.00%, and the like, a remainder includes Zn and impurities, a metallographic structure of the hot-dip plating layer contains 5 to 45 area % of an α phase having a grain diameter of 0.5 to 2 μm, the metallographic structure of the hot-dip plating layer contains 15 to 70 area % of a MgZn.sub.2 phase, and, among the α phases having the grain diameter of 0.5 to 2 μm, an area ratio of an α phase having a (111)α//(0001)MgZn.sub.2 orientation relationship to the adjacent MgZn.sub.2 phase is 25% to 100%.

A steel sheet according to the present invention has a specific chemical composition and a steel microstructure including, in terms of area fraction, ferrite: 40% or more and 70% or less, a total of bainite and tempered martensite: 5% or more and 30% or less, retained austenite: 4% or more and 18% or less, fresh martensite: 8% or more and 35% or less, and the remainder: 5% or less. Cementite particles are present in the retained austenite, a ratio of an area fraction of the cementite particles in the retained austenite to an area fraction of the retained austenite is 5% or more and 25% or less, and the steel sheet has a tensile strength of 780 MPa or more and less than 980 MPa.

Provided are a high-strength thick hot-rolled steel sheet having excellent elongation and a method for manufacturing same. The high-strength thick hot-rolled steel sheet comprises, by weight %: 0.05-0.15% of C; 0.01-1.0% of Si; 1.0-2.0% of Mn; 0.01-0.1% of Sol. Al; 0.005-1.0% of Cr; 0.001-0.02% of P; 0.001-0.01% of S; 0.001-0.01% of N; 0.005-0.07% of Nb; 0.005-0.11% of Ti; and the remainder of Fe and unavoidable impurities, satisfies relation 1, and has a microstructure comprising, by area %: 25-50% of polygonal ferrite; 30-50% of bainitic ferrite and acicular ferrite; 20% or less of bainite; less than 5% of the sum of area fractions of carbide and pearlite structures having a diameter of 0.5 μm or more, observed within a unit area (1 cm.sup.2); and less than 5% of phase MA (martensitic-austenitic constituents).

A steel sheet according to an aspect of the present invention has a predetermined chemical composition, in which a metallographic structure at a ¼ thickness portion includes, by volume percentage, a total of 50% or more of one or both of martensite and bainite and 8% or more of residual austenite, an average value of aspect ratios of prior austenite grains is 5.0 or more, number density of AlN is 3000 pieces/mm.sup.2 or more and less than 6000 pieces/mm.sup.2 at a depth position of 30 μm from a sheet surface, an internal oxidation layer in which at least a part of a crystal grain boundary is coated with an oxide is provided from the sheet surface to a depth of 5.0 μm or more, grain boundary coverage of the oxide is 60% or more in a region from the sheet surface to a depth of 5.0 μm, and a tensile strength is 980 MPa or more.

A steel sheet for the manufacture of a press hardened part is provided, having a composition of: 0.15%≤C≤0.22%, 3.5%≤Mn<4.2%, 0.001%≤Si≤1.5%, 0.020%≤Al≤0.9%, 0.001%≤Cr≤1%, 0.001%≤Mo≤0.3%, 0.001%≤Ti≤0.040%, 0.0003%≤B≤0.004%, 0.001%≤Nb≤0.060%, 0.001%≤N≤0.009%, 0.0005%≤S≤0.003%, 0.001%≤P≤0.020%. A microstructure has less than 50% ferrite, 1% to 20% retained austenite, cementite, such that the surface density of cementite particles larger than 60 nm is lower than 10{circumflex over ( )}7/mm.sup.2, and a complement of bainite and/or martensite, the retained austenite having an average Mn content of at least 1.1*Mn %. Press-hardened steel part obtained by hot forming the steel sheet, and manufacturing methods thereof.

Provided are plated steel sheets for hot press forming, hot press formed parts, and manufacturing methods thereof, the plated steel sheets comprising: a base steel sheet comprising, in weight %, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5 to 5%, P: 0.001 to 0.015%, S: 0.0001 to 0.02%, Al: 0.01 to 0.1%, Cr: 0.01 to 1%, N: 0.001 to 0.02%, Ti: 0.1% or less, B: 0.01% or less, Sn: 0.01 to 0.1%, and a balance of Fe and inevitable impurities; an aluminum or aluminum alloy plating layer disposed on at least one surface of the base steel sheet; and an Sn-enriched layer provided between the base steel sheet and the plating layer, wherein the Sn-enriched layer satisfies a specific relationship.

A plated steel sheet for automobile structural members has a steel sheet, a plating layer formed on at least a part of a surface of the steel sheet, and an oxide layer formed on at least a part of a surface of the plating layer, the plating layer has a predetermined chemical composition, and when measurement by XPS is performed at a position 5.0 nm below a surface of the oxide layer in a thickness direction. I.sub.Mg/I.sub.MgOx, which is the ratio of a maximum detected intensity of Mg to a maximum detected intensity of an oxide or hydroxide of Mg, is 0.00 or greater and 1.20 or less.

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.