POSCO Holdings Inc.
PRECIPITATION-HARDENING HOT ROLLED STEEL SHEET HAVING EXCELLENT MATERIAL UNIFORMITY AND HOLE EXPANDABILITY, AND MANUFACTURING METHOD THEREFOR

Abstract:

Provided is a precipitation-hardening hot rolled steel sheet, having excellent material uniformity and hole expandability, comprising, by weight, 0.02% to 0.05% of C, 0.01% to 0.3% of Si, 1.0% to 1.6% of Mn, 0.04% to 0.1% of Ti, 0.01% to 0.05% of Nb, 0.008% or less of N, and a remainder of Fe and inevitable impurities, satisfying Relationship 1, wherein a microstructure of the precipitation-hardening hot rolled steel sheet comprises 95 area % or more of ferrite and (Ti, Nb)C complex precipitates, the number of (Ti, Nb)C complex precipitates having a diameter of 10 nm or less is five or more times the number of (Ti, Nb)C complex precipitates having a diameter greater than 10 nm. Relationship 1: 0.35.ltoreq.(Ti+Nb+V+Mo)/(C+N) 0.70.