| 摘要 |
PROBLEM TO BE SOLVED: To provide martensitic steel for line pipes which displays sufficient general corrosion resistance and pitting corrosion resistance in the environment of carbon dioxide, excellent resistance to sulfide stress corrosion cracking (SSC resistance) in the environment containing a small amount of hydrogen sulfide and which is excellent in weldability, toughness in weld zone and tensile property at high temp. and whose cost is inexpensive. SOLUTION: This martensitic steel contains, by weight, >0.015 to 0.0l5% C, <=0.5% Si, 0.2-3.0% Mn, 10-14% Cr, 0.2-7.0% Ni, 0.2-5.0% Mo, <=0.1% Al, <=0.07% N, as necessary, one or more kinds of <=2.0% Cu, <=0. 15% Ti, <=0.15% Zr, <=0.15% Ta, <=0.006% Ca and 0. 02-0.20% (0.8Nb+V) of Nb and/or V in a range where (Cr%)+(Mo%)+0.1(Ni%)+3(Cu%)-3(C%)>=12.2, (Cr%)+3.5(Mo%)+10(N%)+0.2×(Ni%)-20(C%)>=14.5 and 150(C%)+100(N%)-(Ni%)-(Mn%)<=4 are satisfied and the balance has a composition of Fe essentially.
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