| 摘要 |
PROBLEM TO BE SOLVED: To provide a low-alloy ferritic heat-resisting steel having both of creep rupture strength and toughness in a weld heat-affected zone after creep at 550°C for 100,000 hours. SOLUTION: The low-alloy ferritic heat-resisting steel having superior high-temperature creep strength in the weld heat-affected zone comprises, by mass%, 0.12-0.15% C, 0.01-0.10% Si, 0.30-0.60% Mn, 2.00-2.50% Cr, 0.90-1.20% Mo, 0.01-0.06% Nb, 0.20-0.35% V, 0.05-0.25% Ni, 0.005-0.040% Al, 0.0003-0.0020% B, N limited to 0.010% or less, P limited to 0.02% or less, S limited to 0.005% or less, a specified quantity of one or more elements among Ti, Y, Ce, La, Ca, Mg, Ba, Zr and Cu, as needed, and the balance Fe with unavoidable impurities; controls the amount of B in a solution state to 0.0003% or more, in order to make a ratio of (Mo, V) C mainly containing V among carbides existing in crystal grains in the weld heat-affected zone in creep to be 50% or higher; and has a FB value of 0.0003 or more in the following expression: FB=(B%)-0.78×ä(N%)-(Al%)/4-(Ti%)/3}-ä2×(Mn%)+(Ni%)}/1,000. COPYRIGHT: (C)2005,JPO&NCIPI
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