| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel plate that has high functional properties in which sour resistance, reduction of variations in HAZ toughness and HAZ hardness are satisfied and that is suitable for a steel product for energy, such as a line pipe.SOLUTION: A steel plate contains, by mass%, 0.02 to 0.20% of C, 0.02 to 0.50% of Si, 0.6 to 2.0% of Mn, 0 to 0.030% of P, 0 to 0.004% of S, 0.010 to 0.08% of Al, 0.001 to 0.01% of N, 0.002 to 0.05% of Nb, 0 to 0.0040% of O, 0.0002 to 0.05% of REM and 0.0003 to 0.020% of Zr with the balance being Fe and inevitable impurities and satisfies the relationship: 10,000×[Nb]+31×Di-82≥0. Inclusions which are contained in the steel and which have widths of 1 μm or more, have a composition that comprises: 1 to 40% of Zr; 5 to 50% of REM; 3 to 30% of Al; and more than 0 to less than 20% of S. |
