Abstract: An embodiment of the present invention provides steel for hot forming, a hot-formed member, and methods for manufacturing same, the steel comprising, by wt %, 0.06-0.1% of C, 0.05-0.6% of Si, 0.6-2% of Mn, 0.05% or less of P, 0.02% or less of S, 0.01-0.1% of Al, 0.01-0.8% of Cr, 0.01-0.5% of Mo, 0.02% or less of N, and the remainder of Fe and inevitable impurities, wherein an alloy factor represented by relational expression 1 below is 7 or more, and the number of carbides having a circular equivalent diameter of 0.5 ?m or greater is 105/mm2 or less. Alloy factor=I(Mn)×I(Si)×I(Cr)×I(Mo)??[Relational expression 1] where the I values for the components are I(Mn)=3.34×Mn+1, I(Si)=0.7×Si+1, I(Cr)=2.16×Cr+1, and I(Mo)=3×Mo+1, respectively, and the content of each component is expressed as wt %.

Abstract: A preferable aspect of the present invention provides: a hot-rolled steel sheet with excellent impact resistance containing, by weight, 0.35-0.55% of C, 0.7-1.5% of Mn, 0.3% or less (excluding 0%) of Si, 0.03% or less (including 0%) of P, 0.004% or less (including 0%) of S, 0.04% or less (excluding 0%) of Al, 0.3% or less (excluding 0%) of Cr, 0.3% or less (excluding 0%) of Mo, one or two of 0.1-1.0% of Ni and 0.1-1.0% of Cu, 0.4% or more of Cu+Ni, 0.006% or less (excluding 0%) of N, and the balance Fe and other impurities, the alloy elements satisfying relational formulas 1 to 3 below, wherein a microstructure of the hot-rolled steel sheet comprises, by volume, 10% or more of ferrite and 90% or less of pearlite; a steel pipe and a member each using the same; and manufacturing methods therefore. (Mn/Si)?3 (weight ratio)??[Relational formula 1] (Ni+Cu)/(C+Mn)?0.2 (weight ratio)??[Relational formula 2] (Ni/Si)?(weight ratio)??[Relational formula 3].

Abstract: Provided is a hot-rolled coated steel sheet having a yield point elongation of less than 4% and a manufacturing method for the same. The hot-rolled steel sheet comprises, by weight, 0.03 to 0.06% of carbon (C), 0.5 to 1.5% of manganese (Mn), 0.01 to 0.25% of silicon (Si), 0.01 to 0.05% of aluminum (Al), 0.001 to 0.02% of phosphorus (P), 0.006% or less of sulfur (S), 0.0001 to 0.02% of titanium (Ti), 0.0001 to 0.03% of niobium (Nb), 0.001 to 0.005% of nitrogen (N), and a balance of iron (Fe) and inevitable impurities, wherein the Ti, Al and N satisfy the following relationship 1, and the Nb, C and N satisfy the following relationship 2: 0.03?(wt % Ti)×(wt % Al)×(wt % N)×106?0.20 (1), and 22?(mol % Nb)/{(mol % C)×(mol % N)}?1826 (2).

Abstract: A preferable aspect of the present invention provides: a hot-rolled steel sheet containing, by weight, 0.35-0.55% of C, 0.7-1.5% of Mn, 0.3% or less of Si, 0.03% or less of P, 0.004% or less of S, 0.04% or less of Al, 0.3% or less (excluding 0%) of Cr, 0.3% or less of Mo, one or two of 0.1-1.0% of Ni and 0.1-1.0% of Cu, 0.4% or more of Cu+Ni, 0.006% or less of N, and the balance Fe and other impurities, the alloy elements satisfying relational formulas 1 to 3 below, wherein a microstructure of the hot-rolled steel sheet comprises, by volume, 10% or more of ferrite and 90% or less of pearlite; a steel pipe and a member each using the same; and manufacturing methods therefore. [Relational formula 1] (Mn/Si)?3 (weight ratio) [Relational formula 2] (Ni+Cu)/(C+Mn)?0.2 (weight ratio) [Relational formula 3] (Ni/Si)?(weight ratio).

Abstract: Provided is a hot-rolled coated steel sheet having a yield point elongation of less than 4% and a manufacturing method for the same. The hot-rolled steel sheet comprises, by weight, 0.03 to 0.06% of carbon (C), 0.5 to 1.5% of manganese (Mn), 0.01 to 0.25% of silicon (Si), 0.01 to 0.05% of aluminum (Al), 0.001 to 0.02% of phosphorus (P), 0.006% or less of sulfur (S), 0.0001 to 0.02% of titanium (Ti), 0.0001 to 0.03% of niobium (Nb), 0.001 to 0.005% of nitrogen (N), and a balance of iron (Fe) and inevitable impurities, wherein the Ti, Al and N satisfy the following relationship 1, and the Nb, C and N satisfy the following relationship 2: 0.03?(wt % Ti)×(wt % Al)×(wt % N)×106?0.20 (1), and 22?(mol % Nb)/{(mol % C)×(mol % N)}?1826 (2).

Abstract: A preferable aspect of the present invention provides: an ultra-high-strength hot-rolled steel sheet containing, by weight, one or two of 0.40-0.60% of C, 0.7-1.5% of Mn, 0.3% or less (excluding 0%) of Si, 0.03% or less (including 0%) of P, 0.004% or less (including 0%) of S, 0.04% or less (excluding 0%) of Al, 0.3% or less (excluding 0%) of Cr, 0.3% or less (excluding 0%) of Mo, 0.9-1.5% of Ni, and 0.9-1.5% of Cu, 1.1% or more of Cu+Ni, 0.04% or less (excluding 0%) of Ti, 0.005% or less (excluding 0%) of B, 0.006% or less (excluding 0%) of N, and the balance Fe and other impurities, the alloy elements satisfying relational formulas 1 and 2 below, wherein a microstructure of the hot-rolled steel sheet comprises, by volume, 7% or more of ferrite and 93% or less of perlite; a steel pipe and a member each using the same; and manufacturing methods therefor.

Abstract: Provided is a tempered martensitic steel having a low yield ratio and an excellent uniform elongation, the tempered martensitic steel: comprising, by wt %, 0.2-0.6% of C, 0.01-2.2% of Si, 0.5-3.0% of Mn, 0.015% or less of P, 0.005% or less of S, 0.01-0.1% of Al, 0.01-0.1% of Ti, 0.05-0.5% of Cr, 0.0005-0.005% of B, 0.05-0.5% of Mo, 0.01% or less of N, and the balance of Fe and inevitable impurities; having a yield ratio of 0.4-0.6; having a product (TS*U-El), of a tensile strength and a uniform elongation, of 10,000 MPa % or more; and having a microstructure containing, by an area fraction, 90% or more of tempered martensite, 5% or less of ferrite and the balance of bainite.