| 摘要 |
<p>Disclosed are an ultra-thick steel sheet and a manufacturing method thereof, wherein the steel sheet can have a tensile strength (TS) of 500-650 MPa and a yield ratio of 0.7-0.8 by an alloy element control and a process condition control. The ultra-thick steel sheet according to the present invention comprises: 0.05-0.12 wt% of C, 0.05-0.30 wt% of Si, 1.2-2.0 wt% of Mn, 0.01-0.03 wt% of Al, at most 0.015 wt% of P, at most 0.005 wt% of S, 0.01-0.04 wt% of Nb, 0.02-0.05 wt% of Ti, 0.01-0.20 wt% of Mo, 0.001-0.003 wt% of Ca, at most 0.005 wt% of N, and remnants of Fe and inevitable impurities; and has a composite structure of which the final fine structure contains an acicular ferrite phase, a bainite phase, and a martensite-austenite constituent (MA) phase which has an average grain size of at most 10μm. [Reference numerals] (AA) Secondary phase</p> |
