HIGH STRENGTH STEEL SHEET HAVING EXCELLENT RESISTANCE TO POST WELD HEAT TREATMENT AND METHOD FOR MANUFACTURING SAME

摘要

Provided are a steel sheet having excellent Post Weld Heat Treatment (PWHT) resistance of which strength and toughness are not deteriorated even after performing PWHT for a lengthy period of time, and a method for manufacturing the steel sheet. The steel sheet has a composition comprising by weight percent: 0.1 to 0.3% of C; 0.15 to 0.50% of Si; 0.6 to 1.2% of Mn; 0.035% or less of P; 0.020% or less of S; 0.001 to 0.05% of Al; 0.01 to 0.35% of Cr; 0.005 to 0.2% of Mo; 0.005 to 0.05% of V; 0.001 to 0.05% of Nb; 0.001 to 0.05% of Ti; 0.0005 to 0.005% of Ca; 0.05 to 0.5% of Ni; one or more selected from the group consisting of 0.005 to 0.5% of Cu, 0.005 to 0.2% of Co and 0.005 to 0.2% of W; and Fe as well as unavoidable impurities.