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High uniform elongation properties of the high-strength low-yield ratio steel with, its production method, and high-strength low-yield ratio welded steel pipe
High uniform elongation properties of the high-strength low-yield ratio steel with, its production method, and high-strength low-yield ratio welded steel pipe
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机译:高强度低屈强比钢管的高均匀伸长率及其生产方法和高强度低屈强比焊接钢管
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摘要
PROBLEM TO BE SOLVED: To provide a steel which has a TS (Tensile Strength) of ≥550 MPa and has a low yield ratio and highly uniform elongation, that is, has an YR (Yield Ratio) of ≤80% YP and a product of the TS and the uniform elongation of ≥7,500 MPa×%, to provide a method of producing the steel and to provide a high strength low yield ratio welded steel pipe.;SOLUTION: The steel contains, by mass%, 0.03 to 0.14% C, 0.01-0.5% Si, 1.0-4.0% Mn, 0.003-0.08% Al, 0.01-0.08% Nb, 0.005-0.025% Ti and further, one or more elements among Cu, Ni, Mo, Cr, V, B, Ca, REM, Zr and Mg, and the steel has microscopic structure including: a host phase mainly comprising ferrite or bainite; and MA (Martensite-Austenite constituents) which disperses in the host phase and has an average aspect ratio of ≤2.0 and an area ratio of 5-20%, wherein 90% or more of the MA is present at a ferritic granular boundary or a prior austenitic granular boundary. The method of producing the high strength low yield ratio steel with highly uniform elongation characteristics comprises: heating the steel having the above composition to Ac3 or higher, then hot-rolling the steel at a finish-rolling temperature of Ar3 point or higher; and air-cooling or accelerated-cooling the hot-rolled steel at a cooling stop temperature of 500°C, then reheating the steel at Ac1 -Ac3. The welded steel pipe uses the above steel as the basic material part and is provided with weld metal having a specific composition.;COPYRIGHT: (C)2012,JPO&INPIT
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