| 摘要 |
PROBLEM TO BE SOLVED: To provide a thick steel plate excellent in fatigue characteristic without increasing static strength for maintaining flexure processability and weld workability similar to conventional steels.SOLUTION: There is provided a thick steel plate having a chemical composition containing, by mass%, C:0.01 to 0.10%, Si:0.04 to 0.60%, Mn:0.50 to 1.50%, P:0.025% or less, S:0.020% or less, N:over 0.0080% and 0.0250% or less, Sol.Al:0.003 to 0.045%, Ti:0.002 to 0.040%, Zr:0.020% or less, Nb:0.020% or less, V:0.020% or less, B:0.0050% or less, O:0.0030% or less, Cr:0 to 1.0%, Mo:0 to 0.8%, Cu:0 to 0.7%, Ni:0 to 3.0%, Ca:0 to 0.007%, Mg:0 to 0.007%, Ce:0 to 0.007%, Y:0 to 0.5%, Nd:0 to 0.5% and the balance Fe with impurity and having free nitrogen index Nrepresented by [N=N-14×(Sol.Al/27+Ti/47.9+Zr/91.2+Nb/92.9+V/50.9+B/10.8)] of -0.0009 or more and a metallographic structure contains, by area%, a bainite structure of 80% or more and total of the bainite structure and a ferrite structure having average crystal grain diameter of 30 μm or less of 95% or more.SELECTED DRAWING: None |
