| 摘要 |
PROBLEM TO BE SOLVED: To provide steel for a line pipe excellent in high temperature strength and toughness without using refining treatment and controlled rolling requiring expensive alloy elements. SOLUTION: This steel has a composition containing 0.04 to 0.16% C, <=0.5% Si, 0.8 to 1.7% Mn, <=0.015% P, <=0.003% S, <=0.04% Ti, 0.001 to 0.07% Al, <=0.01% N, and the balance Fe with inevitable impurities and moreover satisfying the following inequality, Al×(N-Ti/3.4)<=0.00015 and has a structure containing martensite and bainite in which the austenite average grain size is 50 to 250μm or a tempered structure thereof.
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