Provided is a method for manufacturing a steel sheet, the method including: reheating a steel slab at a temperature of 1200° C. to 1350° C., the steel slab including, 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 a balance of iron (Fe) and inevitable impurities; finish hot rolling the reheated steel slab under predetermined conditions to obtain a hot-rolled steel sheet; cooling the hot-rolled steel sheet at a cooling rate of 10° C./s to 100° C./s to a temperature of 400° C. to 500° C. after the finish hot rolling; and coiling the steel sheet at a temperature of 400° C. to 500° C. after the cooling.

Provided is super duplex stainless steel having excellent yield strength and impact toughness, wherein a reduction ratio and a heat treatment temperature are controlled so as to improve mechanical properties. The super duplex stainless steel having excellent yield strength and impact toughness is thick super duplex stainless steel having a thickness of 30 mm or greater, and includes, in weight %, Cr: 24% to 26%, Ni: 6.0% to 8.0%, Mo: 3.5% to 5.0%, N: 0.24% to 0.32%, and the remainder being Fe and inevitable impurities, wherein a microstructure includes a ferrite phase, an austenite phase and a secondary austenite phase, and grain size is 25 μm or less.

A multilayer flat steel product may include a multitude of mutually bonded steel alloy layers. A steel of a first steel alloy may be provided in at least one of the steel alloy layers, and a steel of a second steel alloy different than the first steel alloy may be provided in at least one of the other steel alloy layers. The steel of the first steel alloy may have high strength, and the steel of the second steel alloy may have lower strength and lower carbon content. To enable function-optimized modelling of local material properties in all directions, at least one steel of the first steel alloy and at least one steel of the second steel alloy may be present at least within one layer of the flat steel product. Further, a component, such as for a motor vehicle body, may be comprised of a corresponding flat steel product.

This invention relates to prevention of delayed cracking of metal alloys during drawing which may occur from hydrogen attack. The alloys find applications in parts or components used in vehicles, such as bodies in white, vehicular frames, chassis, or panels.

A steel sheet for a crown cap having sufficient strength and formability suitable for forming crown caps even when reduced in gauge, and a method for producing the steel sheet for a crown cap. The steel sheet for a crown cap having a composition that includes, in terms of % by mass: C: 0.002% or more and 0.010% or less, Si: 0.05% or less, Mn: 0.05% or more and 0.30% or less, P: 0.030% or less, S: 0.020% or less, Al: less than 0.0100%, N: 0.0050% or less, and the balance being Fe and unavoidable impurities. The C content is more than 0.003% when the Al content is 0.005% or more. The yield strength in the rolling direction is 500 MPa or more. The average Lankford value is 1.3 or more.

Provided is a high-strength hot-dip galvanized steel sheet having excellent plating adhesion, formability, and hole expandability with an ultimate tensile strength of 980 MPa or more, the hot-dip galvanized steel sheet comprising a hot-dip galvanized layer formed on a surface of a base steel sheet. The base steel sheet contains, by mass %, C: 0.05% to 0.4 %; Si: 0.01% to 3.0%; Mn: 0.1% to 3.0%; Al: 0.01 to 2.0%; in which Si+Al >0.5%, P: limited to 0.04% or less; S: limited to 0.05% or less; N: limited to 0.01% or less; and a balance including Fe and inevitable impurities, a microstructure of the base steel sheet contains 40% or more by total volume fraction of martensite and bainite, 8% or more by volume fraction of residual austenite, and a balance of the microstructure being ferrite or ferrite and 10% or less by volume fraction of pearlite. The martensite contains 10% or more by total volume fraction of two or more kinds of three kinds of martensites (1), (2), and (3), and the hot-dip galvanized layer contains less than 7 mass % of Fe.

This invention relates to prevention of delayed cracking of metal alloys during drawing which may occur from hydrogen attack. The alloys find applications in parts or components used in vehicles, such as bodies in white, vehicular frames, chassis, or panels.

Provided is a high-strength cold rolled steel sheet, a high-strength hot-dip galvanized steel sheet manufactured using the cold rolled steel sheet, and manufacturing methods therefor, the high-strength cold rolled steel sheet comprising, by wt %, 0.17-0.21% of carbon (C), 0.3-0.8% of silicon (Si), 2.7-3.3% of manganese (Mn), 0.3-0.7% of chromium (Cr), 0.01-0.3% of aluminum (Al), 0.01-0.03% of titanium (Ti), 0.001-0.003% of boron (B), 0.04% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.01% or less of nitrogen (N) and the balance of iron (Fe) and other inevitable impurities, wherein the amounts of carbon (C), silicon (Si) and aluminum (Al) satisfy the following mathematical relation (1). [Mathematical relation (1)] [C]+([Si]+[Al])/5≤0.35% (wherein [C], [Si] and [Al] respectively mean the wt % of C, Si and Al.)

A welded component having mechanical properties in a welding seam region comparable or better to those in the non-influenced base material via a method including producing a hot-rolled steel product made of a high-strength air-hardenable steel with a material thickness of at least 1.5 mm having a chemical composition by mass in one embodiment of: C: 0.03 to 0.4; Mn: 1.0 to 4.0; Si: 0.09 to 2.0; Al: 0.02 to 2.0; P<=0.1; S<=0.1; N: 0.001 to 0.5; Ti: 0.01 to 0.2; Cr: 0.05 to 2.0; B: 0.001 to 0.1; Mo: 0.01 to 1.0; V: 0.01 to 0.2; optionally: Ni: 0.02 to 1.0; Nb: 0.01 to 0.1; and residual iron including conventional steel-accompanying elements, subsequently air hardening the produced hot-rolled steel product, then deforming the hot-rolled steel product in the air-hardened state to form a component, and producing welding connections using a fusion welding process on the component.

Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing as high as TS: 1780 MPa or more, and excellent indentation peeling strength at projection welds by properly adjusting its chemical composition and its microstructure such that a prior austenite average grain size is 7 μm or less within a range of 50 μm or less in a thickness direction from a surface of the member, a volume fraction of martensite is 90% or more, and an average intergrain distance of Nb and Ti carbonitrides having a grain size of less than 0.10 μm within a depth range of 20 μm to 100 μm in the thickness direction from the surface of the member is 5 μm or less.