| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel having high toughness, most suitable for a steel tube used in a severe oil well environment. SOLUTION: (1) The steel comprises, 0.17 to 0.32% C, 0.1 to 0.5% Si, 0.30 to 2.0% Mn,≤0.030% P,≤0.010% S, 0.10 to 1.01% Cr, 0.01 to 0.30% Mo, 0.001 to 0.100% sol.Al, 0.0001 to 0.0020% B and≤0.0070% N, and the balance Fe with inevitable impurities, has a Mo content [Mo] in carbide precipitated on austenite grain boundaries and an austenite grain size number G satisfying inequality (a) [Mo]≤exp(G-5)+5 and inequality (b) G≤5.5, has a yield strength of 703 to 803 MPa, and is produced by inline heat treatment. (2) It is preferable that the steel in the above (1) contains one or more kinds selected from among 0.005 to 0.04% Ti, 0.005 to 0.04% Nb and 0.03 to 0.30% V. COPYRIGHT: (C)2008,JPO&INPIT
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