| 摘要 |
<p>Disclosed are an extremely thick steel sheet capable of increasing weldability and improving low temperature toughness of a central portion of a thickness by controlling an alloying constituent and a process condition; and a manufacturing method thereof. According to the present invention, the extremely thick steel sheet comprises: 0.04-0.08 wt% of C, 0.1-0.3 wt% of Si, 1.2-1.8 wt% of Mn, 0.05 wt% or less of P, 0.005 wt% or less of S, 0.2 wt% or less of Cr, 0.02-0.06 wt% of S_Al, 0.15-0.50 wt% of Cu, 0.020-0.045 wt% of Nb, 0.3-1.0 wt% of Ni, 0.01-0.03 wt% of Ti, 0.001-0.005 wt% of Ca, and the remainder consisting of iron (Fe) and inevitable impurities. The final microstructure has a composite structure including acicular ferrite and bainite. The acicular ferrite structure has a cross-sectional area fraction of 70-80 wt%.</p> |
