POSCO Holdings Inc.
HIGH STRENGTH STEEL PLATE AND MANUFACTURING METHOD THEREFOR

Abstract:

A high strength steel plate according to an aspect of the present disclosure includes, by weight: 0.05 to 0.20% of C, 0.15 to 0.55% of Si, 0.9 to 1.75% of Mn, 0.001 to 0.05% of Al, 0.03% or less of P, 0.03% or less of S, 0.05 to 0.3% of Cr, 0.05 to 0.6% of Ni, 0.005 to 0.35% of Cu, 0.05 to 0.2% of Mo, 0.005 to 0.07% of V, 0.005 to 0.04% of Nb, 0.0005 to 0.005% of Ca, 0.005 to 0.025% of Ti, 0.002 to 0.006% of N, less than 0.0005% of B, and a balance of Fe, with inevitable impurities, satisfies relationships of Cu+Ni+Cr+Mo: 1.5% or less, Cr+Mo: 0.4% or less, V+Nb: 0.1% or less, and Ca/S: 1.0 or higher, and includes a combined structure of tempered martensite and tempered bainite as a microstructure.