| 摘要 |
PROBLEM TO BE SOLVED: To provide a seamless steel pipe having≥483 MPa yield stress and excellent HIC resistance and suitable for a pipeline. SOLUTION: The high strength seamless steel pipe having≥483 MPa yield stress and excellent HIC resistance has a composition containing, by mass, 0.03 to 0.11% C, 0.05 to 0.5% Si, 0.8 to 1.6% Mn,≤0.025% P,≤0.003% S, 0.002 to 0.017% Ti, 0.001 to 0.10% Al, 0.05 to 0.5% Cr, 0.02 to 0.3% Mo, 0.02 to 0.20% V, 0.0005 to 0.005% Ca,≤0.008% N and≤0.004% O (oxygen) and also has a structure which is composed of bainite or/and martensite and in which ferrite is precipitated at the grain boundaries. Further, it is desirable to incorporate either or both of 0.05 to 0.5 mass% Cu and 0.05 to 0.5 mass% Ni for securing high strength. In order to manufacture the above steel pipe, it is necessary to limit starting temperature of quenching after finish rolling, cooling rate and tempering temperature. COPYRIGHT: (C)2004,JPO
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