| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a method for separately manufacturing a 490 MPa class rolled H-shaped steel having an area ratio of bainite of 30% or less and a plate thickness less than 50 mm and a 550 MPa class rolled H-shaped steel having an area ratio of bainite of 40 to 100% and a plate thickness less than 50 mm, and a rolled raw steel therefor. <P>SOLUTION: A chemical composition is prepared so as to include one or more kinds of C: 0.11 to 0.20%, Si: 0.01 to 0.60%, Mn: 0.5 to 2.0%, Ti: 0.005 to 0.04%, B: 0.0005 to 0.0030%, sol. Al: 0.005 to 0.090%, N: 0.0020 to 0.0090%, and further, Cu: 0.01 to 1.5%, Ni: 0.01% to 1.5%, Cr: 0.01% to 1.5%, Mo: 0.01 to 1.5%, V: 0.001 to 0.100%, and Nb: 0.001 to 0.100%, and the balance of Fe and impurities, and have a ratio of amount of Ti to amount of N (Ti/N): 1.0 to 3.0, a value of Fn in the following expression (1): 0.0010 to 0.0040%, and a value of Pcm in the following expression (2): 0.20 to 0.30% wherein, (1): Fn=N-(Ti/3.4) and (2): Pcm=C+(Si/30)+(Mn/20)+(Cu/20)+(Ni/60)+(Cr/20)+(Mo/15)+(V/10)+5B. <P>COPYRIGHT: (C)2012,JPO&INPIT |
