| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a thick steel sheet having superior fatigue resistance properties in the sheet thickness direction which is favorable for a welded steel structure such as a pressure vessel, and to provide a method for producing the same. <P>SOLUTION: The thick steel sheet has an aggregate structure having an x-ray intensity ratio of at least 2.0 in the (110) plane parallel to the sheet surface in at least the range from the position 2 mm in the direction of sheet thickness from one or both of the rolled surfaces of the steel sheet to the 3/10 position of the sheet thickness, and has a structure having an average value for the compressive residual stress in the direction of sheet thickness of at least 160 MPa, having an x-ray intensity ratio in the (100) plane parallel to the sheet surface of no greater than 1.1, and containing: C, Si, and Mn; Ti and/or Nb; and, as needed, one or at least two of Cu, Ni, Cr, Mo, V, W, Zr, B, and Al, the remainder comprising Fe and unavoidable impurities. The method for producing the thick steel sheet includes: subjecting the steel having this composition as described above to hot rolling including a first rolling in which the cumulative rolling reduction is 10% or more in a temperature region of the austenite partial recrystallization temperature or more, and a second rolling in which the average rolling reduction of each pass is less than 3.5% and the cumulative rolling reduction is 50% or more in a temperature region where the range from a 2 mm position to a 3/10 position of the sheet thickness in the thickness direction from both sides or one side of the rolling surfaces has a two phase structure; and completing the hot rolling at 600°C or more, followed by accelerated cooling at a cooling rate of 1°C/s or more. <P>COPYRIGHT: (C)2013,JPO&INPIT |
