| 摘要 |
<p>A thick steel plate having a high strength level of about 490 MPa, which is suitable for ships, is provided, a thick steel plate having excellent uniform elongation(equal elongation) is provided, a thick steel plate having excellent weldability(HAZ toughness) also is provided, and a method for manufacturing such thick steel plates is provided. A high-tension thick steel plate is made of steel comprising, by mass percent, 0.02 to 0.20% of C, 0.2 to 0.5% of Si, 1 to 1.8% of Mn, total 0.2 to 1% of Cu and/or Ni, and the balance of Fe and inevitable impurities, wherein the high-tension thick steel plate comprises 80 vol.% or more of a ferrite fraction and 1 vol.% or more of residual austenite fraction, and wherein C is contained in the residual austenite as much as 0.80 to 1.10 mass%. A manufacturing method of a high-tension thick steel plate comprises: a first process of generating 80 vol.% of more of ferrite and 1 vol.% or more of residual austenite; and a second process of controlling the amount of C contained in the residual austenite within a range of 0.80 to 1.10 mass%, wherein the second process is carried out by slowly cooling a workpiece to an optional temperature range of 500 to 300 deg.C at an average cooling rate of 1 deg.C/sec or less for 50 to 3600 seconds, or holding the workpiece in the optional temperature range of 500 to 300 deg.C for 50 to 3600 seconds.</p> |
