POSCO Holdings Inc.
HOT-ROLLED STEEL SHEET HAVING EXCELLENT IMPACT RESISTANCE, STEEL PIPE, MEMBER, AND MANUFACTURING METHODS THEREFOR

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).gtoreq.3 (weight ratio) [Relational formula 2] (Ni+Cu)/(C+Mn).gtoreq.0.2 (weight ratio) [Relational formula 3] (Ni/Si).gtoreq.(weight ratio).