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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. [Relational formula 1] (Mn/Si) #3 (weight ratio) [Relational formula 2] (Ni/Si) #1 (weight ratio)

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First Claim