| 摘要 |
PROBLEM TO BE SOLVED: To provide a pipe bend having a tensile strength of≥750 MPa and having excellent base material and weld zone toughness, and to provide its production method. SOLUTION: The ultrahigh strength pipe bend has a composition comprising, by mass, 0.03 to 0.12% C, 0.01 to 0.2% Si, 0.8 to 2.0% Mn,≤0.009% P,≤0.003% S, 0.1 to 1.5% Ni, 0.003 to 0.05% Nb, 0.05 to 1.2% Mo, 0.005 to 0.03% Ti,≤0.005% N and 0.002 to 0.07% Al, and the balance Fe with inevitable impurities, and has a microstructure where a tempered martensitic structure of≥3% is incorporated into a tempered bainitic structure with a mean packet grain size of≤20μm. The pipe bend may further comprises 0.005 to 0.1% V and/or one or more kinds of metals selected from 0.1 to 1.4% Cu, 0.1 to 1.2% Cr, 0.0005 to 0.006% Ca and 0.0001 to 0.003% Mg. In its production, after heating at 820 to 1,050°C, bending is performed, thereafter, accelerated cooling is performed to≤400°C at a cooling rate of≥5°C/s, and subsequently, tempering treatment is performed in the temperature range of 350 to 750°C. COPYRIGHT: (C)2006,JPO&NCIPI
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