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 delayed fracture resistance after projection welding by properly adjusting its chemical composition and its microstructure such that at least 5 Ti-based precipitates having a grain size of 0.10 m or less are present on average per 100 m.sup.2 of a cross section parallel to a thickness direction of the member within a range of 100 m in a thickness direction from a surface of the member, a volume fraction of martensite is 95% to 100% within a depth range of 20 m to 100 m in the thickness direction from the surface of the member, and at least 10 cementite grains having a grain size of less than 0.20 m are present on average in a prior austenite grain.

A low-cost and high-formability 1180 MPa grade cold-rolled annealed dual-phase steel plate and a manufacturing method thereof are provided. The dual-phase steel plate has the following chemical composition by mass percentages: C: 0.1%-0.125%, Si: 0.4%-0.8%, Mn: 2.6%-2.9%, Al: 0.01%-0.05%, Nb: 0.01%-0.03%, and Ti: 0.01%-0.03%, the remainder being Fe and unavoidable impurities. By reasonable design of alloy elements and manufacturing processes, the dual-phase steel plate of the invention achieves a strength of 1180 MPa grade at a low cost, obtains a fine and uniform martensite-ferrite dual-phase structure that ensures excellent elongation rate and cold bending performance, and has good formability. The dual-phase steel plate has a yield strength of more than 850 MPa, a tensile strength of more than 1180 MPa, an elongation rate of 8% or more, and a parameter (R/t), characterizing the 90-degree cold bending performance, of 2.5 or less.

An aspect of the present disclosure relates to a high-strength steel material having enhanced resistance to crack initiation and propagation at low temperature.

A steel with high hardness and excellent toughness contains, in mass %, 0.40-1.00% C, 0.10-2.00% Si, 0.10-1.00% Mn, 0.030% or less P, 0.030% or less S, 1.10-3.20% Cr, 0.010-0.10% Al, and 0.15-0.50% V, and further contains at least one or two of 2.50% or less Ni and 1.00% or less Mo, with an amount of (C+V) being 0.60% or more in mass %, with the balance consisting of Fe and unavoidable impurities. The steel has a microstructure which is a martensitic structure with finely dispersed Fe-based carbides, with its prior austenite grain size being 20 m or less.

A steel with high hardness and excellent toughness contains, in mass %, 0.40-1.00% C, 0.10-2.00% Si, 0.10-1.00% Mn, 0.030% or less P, 0.030% or less S, 1.10-3.20% Cr, 0.010-0.10% Al, and 0.15-0.50% V, and further contains at least one or two of 2.50% or less Ni and 1.00% or less Mo, with an amount of (C+V) being 0.60% or more in mass %, with the balance consisting of Fe and unavoidable impurities. The steel has a microstructure which is a martensitic structure with finely dispersed Fe-based carbides, with its prior austenite grain size being 20 m or less.

High strength precipitation hardening stainless steel alloy is disclosed. The steel alloy has a composition by weight %, about: 30.0% max nickel (Ni), 0.0 to 15.0% cobalt (Co), 25.0% max chromium (Cr), 5.0% max molybdenum (Mo), 5.0% max titanium (Ti), 5.0% max vanadium (V), and iron (Fe) and inevitable impurities are in balance. The steel alloy is predominantly hardened (strengthened) by precipitates: two or more binary intermetallic phases Ni.sub.3Ti and Ni.sub.3V and complex intermetallic phases (Ni, Me1).sub.3(Ti, Me2) and (Ni, Me1).sub.3(V, Me2), wherein M1 is one or more elements of Ni-site substitution and M2 is one or more elements of Ti and V-site substitutions. The disclosed steel alloy provides a unique combination of corrosion resistance, strength and toughness.

High strength precipitation hardening stainless steel alloy is disclosed. The steel alloy has a composition by weight %, about: 30.0% max nickel (Ni), 0.0 to 15.0% cobalt (Co), 25.0% max chromium (Cr), 5.0% max molybdenum (Mo), 5.0% max titanium (Ti), 5.0% max vanadium (V), and iron (Fe) and inevitable impurities are in balance. The steel alloy is predominantly hardened (strengthened) by precipitates: two or more binary intermetallic phases Ni.sub.3Ti and Ni.sub.3V and complex intermetallic phases (Ni, Me1).sub.3(Ti, Me2) and (Ni, Me1).sub.3(V, Me2), wherein M1 is one or more elements of Ni-site substitution and M2 is one or more elements of Ti and V-site substitutions. The disclosed steel alloy provides a unique combination of corrosion resistance, strength and toughness.

Disclosed are a hot dip coated steel and a method for manufacturing the same, the hot dip coated steel comprising a hot rolled steel and a hot dip coated layer formed on the surface of the hot rolled steel, wherein the hot rolled steel comprises: by wt %, 0.05-0.15% of C, 0.5% or less of Si (excluding 0%), 0.5-1.5% of Mn, 0.01-0.05% of Nb, 0.005-0.05% of V, 0.03% or less of P (excluding 0%), 0.015% of S or less (excluding 0%), 0.05% or less of Al (excluding 0%), 0.01% or less of N (excluding 0%), and the balance of Fe and inevitable impurities; 90 area % or more of ferrite as the microstructure thereof; and 5,000-15,000/m.sup.2 of V-based precipitates.

The present invention relates to a maraging steel containing C: 0.02% (means mass %, hereinafter the same) or less, Si: 0.3% or less, Mn: 0.3% or less, Ni: 7.0 to 15.0%, Cr: 5.0% or less, Co: 8.0 to 12.0%, Mo: 0.1 to 2.0%, Ti: 1.0 to 3.0%, and Sol.Al: 0.01 to 0.2%, where the balance includes Fe and unavoidable impurities of P: 0.01% or less, S: 0.01% or less, N: 0.01% or less, and O: 0.01% or less. The parent phase of the maraging steel includes a martensitic phase. The parent phase contains a martensitic phase obtained by reverse transformation from a martensitic phase to an austenitic phase and then transformation from the austenitic phase, in an area fraction of 25% to 75%.

Nickel-iron-cobalt based alloys are disclosed having sufficient castability for centrifugal casting essentially free from casting defects, cracking, and microstructure variability, and coefficients of thermal expansion up to about 910.sup.6/ C. for about 100-400 C. and increasing from about 400-500 C. to up to about 1010.sup.6/ C., or up to about 610.sup.6/ C. between about 100-300 C. and increasing from about 300-500 C. to up to about 1010.sup.6/ C. Articles are disclosed including unitary cast structures free of internal welds, brazing, and bolting, essentially annular conformations, diameters of at least about 500 mm, cross-sectional wall areas of at least about 2,000 mm.sup.2, and compositions including nickel-iron-cobalt based alloys. Methods for forming the articles are disclosed including rotating centrifugal molds with the compositions in molten states, forming the articles in near net shape.