| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a method for producing a steel material for high heat input welding, in which the toughness of a weld heat affected zone is not reduced even by the welding of an amount of welding heat input of 300 kJ/cm or more, on the assumption that it is produced by TMCP. <P>SOLUTION: The component composition of steel includes, by mass, 0.005 to 0.02% of C, Si, Mn, P, S, Al, Ni, Nb, and Ti, and 0.0035 to 0.0070% of N, and Ca and B, and satisfies Ceq≤0.36. The steel material is heated and then rolled at a cumulative rolling reduction of 40% or more at a steel sheet surface temperature of 850°C or less. Finishing temperature: FT(°C) is FT(°C)≥790°C when Ti/N≤2.2, and FT(°C)≥(1065-125×Ti/N) and FT(°C)≥Ar<SB POS="POST">3</SB>transformation point when Ti/N>2.2. Subsequently, accelerated cooling is performed at a cooling start-up temperature of (Ar<SB POS="POST">3</SB>-30)°C and a cooling shut-down temperature in the range of 300 to 500°C. <P>COPYRIGHT: (C)2013,JPO&INPIT</p> |
