POSCO Holdings Inc.
ULTRA HIGH STRENGTH HOT-ROLLED STEEL SHEET HAVING EXCELLENT DUCTILITY AND METHOD FOR MANUFACTURING SAME

Abstract:

Provided is an ultra high strength hot-rolled steel sheet including, in percentage by weight: 0.15-0.25% of C, 0.6-2.0% of Si, 1.5-3.0% of Mn, 0.01-0.1% of Al, 0.01-0.5% of Cr, 0.005-0.2% of Mo, 0.001-0.05% of P, 0.001-0.05% of S, 0.001-0.01% of N, 0.003-0.1% of Nb, 0.003-0.1% of Ti, 0.003-0.1% of V, and the remainder being Fe and other unavoidable impurities, and satisfying following relational expressions (1) and (2). [Relational Expression 1] 4.5.ltoreq.[Mn]+12[sol.C]+2.5[Mo]+2[Cr]+300[B]+[V].ltoreq.5.3. [Relational Expression 2] [sol.C]=[C]-(0.25[Ti]+0.13[Nb]+0.125[Mo]), 0.17.ltoreq.[sol.C].ltoreq.0.22. (In relational expressions 1 and 2, each element symbol represents the content of each element in wt %.)