| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing an electroseamed steel pipe for a line pipe excellent in hydrogen-crack resistance and toughness, which is capable of solving the problem of quality deterioration at pipe-making and taking advantage of a uniform and fine metallic structure of hot-rolled steel sheet before the pipe-making. SOLUTION: A steel raw material comprises specific amounts of C, Si, Mn, P, S, Al, N and O and a specific amount of at least one element chosen from Nb, V, Ti, Mo, B and Ca. The steel raw material is heated to≥1,100°C, subjected to hot-rolling that yields a rolling reduction ratio of≥50% within a non-recrystallization temperature range equal to or above Ar<SB>3</SB>, coiled at≤600°C and processed into the steel pipe through an electroseamed steel pipe process. The steel pipe is heated by high-frequency heating so that the temperature in the coldest part falls within 500-650°C and that the temperature difference between the hottest and coldest parts in the thickness direction becomes≥70°C, held at that temperature or annealed for≤30 s and cooled at an average cooling rate of 5-30°C/s. COPYRIGHT: (C)2005,JPO&NCIPI
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