POSCO Holdings Inc.
HIGH STRENGTH HOT ROLLED STEEL SHEET HAVING EXCELLENT ELONGATED AND METHOD FOR MANUFACTURING THE SAME

Abstract:

The present invention provides a high strength hot rolled steel sheet and a method for manufacturing same, the steel sheet containing, in weight percentage, 0.11-0.14% of C, 0.20-0.50% of Si, 1.8-2.0% of Mn, 0.03% or less of P, 0.02% or less of S, 0.01-0.04% of Nb, 0.5-0.8% of Cr, 0.01-0.03% of Ti, 0.2-0.4% of Cu, 0.1-0.4% of Ni, 0.2-0.4% of Mo, 0.007% or less of N, 0.001-0.006% of Ca, 0.01-0.05% of Al, a balance of Fe and inevitable impurities, wherein relational expressions 1 to 3 below are satisfied, and a microstructure includes, by area percentage, 88% or more of bainite, 10% or less of ferrite, 2% or less of pearlite, and 0.8% or less of island martensite. [Relational Expression 1] 7.ltoreq.(Mo/93)/(P/31).ltoreq.16. [Relational Expression 2] 1.6.ltoreq.Cr+3Mo+2Ni.ltoreq.2. [Relational Expression 3] 6.ltoreq.(3C/12+Mn/55).times.100.ltoreq.7.