A high-strength structural steel material having excellent fatigue crack propagation inhibitory characteristics according to an aspect of the present invention contains, by weight, 0.02-0.12% of C, 1.7-2.5% of Mn, 0.01-0.8% of Si, 0.005-0.5% of Al, and the balance Fe and unavoidable impurities, wherein a microstructure of the structural steel sheet material is divided into a surface layer portion outside and a central portion inside along a thickness direction; the surface layer portion comprises tempered bainite as a matrix structure, fresh martensite as a second structure, and austenite as a residual structure; and the central portion comprises lath bainite.

Provided is a high-strength steel sheet having high impact resistance. The steel sheet includes: by weight %, carbon (C): 0.05% to 0.14%, silicon (Si): 0.01% to 1.0%, manganese (Mn): 1.5% to 2.5%, aluminum (Al): 0.01% to 0.1%, chromium (Cr): 0.005% to 1.0%, phosphorus (P): 0.001% to 0.05%, sulfur (S): 0.001% to 0.01%, nitrogen (N): 0.001% to 0.01%, niobium (Nb): 0.005% to 0.06%, titanium (Ti): 0.005% to 0.11%, and the balance of iron (Fe) and inevitable impurities. The steel sheet has a microstructure comprising ferrite and bainite in a total area fraction of 90% or more. The steel sheet has a value of 0.05 to 1.0 as a shear texture ({110}<112>, {112}<111>) area ratio of a center region (ranging deeper than 1/10t to ½t in a thickness direction, t refers to thickness (mm)) and a surface region (ranging from a surface to 1/10t in the thickness direction).

An method of manufacturing a hot press-formed member comprises heating a blank of an aluminum-based plated steel sheet in a heating furnace, removing the heated blank from the heating furnace and conveying the removed blank between an upper mold portion and a lower mold portion of a mold, mounted on a press, to be seated; and performing a forming process after the upper mold portion of the mold is in contact with the seated blank.

A method of producing a high performance stainless steel exhibiting corrosion resistance even under a very severe corrosion environment at temperatures of equal to or higher than 180° C., for example, 220° C., while maintaining strength and toughness by improving the corrosion resistance of a conventional martensitic stainless steel with high strength. The martensitic stainless steel includes, in mass %, C: 0.005% to 0.05%, Si: equal to or less than 1.0%, Mn: equal to or less than 2.0%, Cr: 16 to 18%, Ni: 2.5 to 6.5%, Mo: 1.5 to 3.5%, W: equal to or less than 3.5%, Cu: equal to or less than 3.5%, V: 0.01 to 0.08%, Sol.Al: 0.005 to 0.10%, N: equal to or less than 0.05%, and Ta: 0.01 to 0.06%, and the balance Fe with inevitable impurities.

A method for manufacturing a grain-oriented electrical steel sheet, according to an embodiment of the present invention includes: heating a slab, based on 100 wt % of a total composition thereof, including N at 0.0005 wt % to 0.015 wt %, Ti at 0.0001 wt % to 0.020 wt %, V at 0.0001 wt % to 0.020 wt %, Nb at 0.0001 wt % to 0.020 wt %, B at 0.0001 wt % to 0.020 wt %, and the remaining portion including Fe and other impurities, and then hot rolling it to prepare a hot-rolled steel sheet; annealing the hot-rolled steel sheet; after the hot-rolled steel sheet is annealed, cooling the hot-rolled steel sheet, and then cold rolling it to prepare a cold-rolled steel sheet; decarburization-annealing the cold-rolled steel sheet and then nitriding-annealing it, or simultaneously performing the decarburization-annealing and the nitriding-annealing; and final-annealing the decarburization-annealed and nitriding-annealed steel sheet.

A grain-oriented electrical steel sheet that includes a base coating with a high TiN ratio advantageous for the application of tension to the steel sheet and has excellent magnetic property is provided. The grain-oriented electrical steel sheet includes: a base coating having a peak value PTiN of TiN in the form of osbornite, observed in a range of 42°<2θ<43° and a peak value PMg.sub.2SiO.sub.4 of Mg.sub.2SiO.sub.4 in the form of forsterite, observed in a range of 35°<2θ<36° of both more than 0 and satisfying a relationship PTiN≧PMg.sub.2SiO.sub.4, in thin-film X-ray diffraction analysis; and an iron loss W.sub.17/50 of 1.0 W/kg or less.

A high strength galvanized steel sheet having excellent surface qualities, plating adhesion, and formability is provided, wherein a galvanized layer is formed on a cold-rolled steel sheet comprising 0.1-0.3 wt % of C, 1-2.5 wt % of Si, 2.5-8 wt % of Mn, 0.001-0.5 wt % of sol. Al, at most 0.04 wt % of P, at most 0.015 wt % of S, at most 0.02 wt % of N (excluding 0 wt %), 0.1-0.7 wt % of Cr, at most 0.1 wt % of Mo, (48/14)*[N] to 0.1 wt % of Ti, 0.005-0.5 wt % of Ni, 0.01-0.07 wt % of Sb, at most 0.1 wt % of Nb, and at most 0.005 wt % of B, with the remainder being Fe and other inevitable impurities.

Provided are a high-strength steel sheet and a method for manufacturing the steel sheet. The high-strength steel sheet has a specified chemical composition with the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 30% or more of a ferrite phase, 40% to 65% of a bainite phase and/or a martensite phase, and 5% or less of cementite, in which, in a surface layer that is a region within 50 μm from the surface in the thickness direction, the area ratio of a ferrite phase is 40% to 55% and the total area ratio of a bainite phase having a grain diameter of more than 5 μm and/or a martensite phase having a grain diameter of more than 5 μm is 20% or less, and a tensile strength is 980 MPa or more.

A high-strength galvanized steel sheet that includes a chemical composition containing, by mass %, C: 0.15% or more and 0.25% or less, Si: 0.50% or more and 2.5% or less, Mn: 2.3% or more and 4.0% or less, P: 0.100% or less, S: 0.02% or less, Al: 0.01% or more and 2.5% or less, and Fe and inevitable impurities. The steel sheet having a microstructure containing, by an area percentage basis, a tempered martensite phase: 30% or more and 73% or less, a ferrite phase: 25% or more and 68% or less, a retained austenite phase: 2% or more and 20% or less, and other phases: 10% or less (including 0%), the other phases containing a martensite phase: 3% or less (including 0%) and a bainitic ferrite phase: less than 5% (including 0%).

Provided are a high-strength steel sheet and a method for manufacturing the steel sheet. The high-strength steel sheet has a specified chemical composition with the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 25% or less of a ferrite phase, 75% or more of a bainite phase and/or a martensite phase, and 5% or less of cementite, in which, in a surface layer that is a region within 50 μm from the surface in the thickness direction, the area ratio of a ferrite phase is 5% to 20%, and a tensile strength is 1180 MPa or more.