| 摘要 |
PROBLEM TO BE SOLVED: To improve toughness at low temperatures by a specific composition which consists of C, Si, Mn, P, S, Ni, Mo, Nb, Ti, Al, N, O, and the balance Fe with inevitable impurities and in which respective component values satisfy a specific relation and further providing a microstructure containing specific amounts of bainite. SOLUTION: This bent pipe has a composition consisting of, by weight, 0.03-0.10% C, <=0.6% Si, 1.8-2.5% Mn, <=0.015% P, <=0.003% S, 0.20-1.0% Ni, 0.25 0.60% Mo, 0.01-0.10% Nb, 0.005-0.030% Ti, <=0.06% Al, 0.001-0.006% N, <=0.005% O, and the balance Fe with inevitable impurities. Moreover, the value of P1 defined by equation is regulated to 2.5-3.8. Further, this bent pipe has a microstructure containing bainite of <=10μm average grain size, transformed from austenite, by >=70% by volume fraction.
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