Steel plate for line pipes with excellent strength and ductility and process for production of same

Abstract

Provided is a steel plate for line pipes which exhibits excellent strength and ductility. Also provided is a process for the production of the steel plate. The steel plate is characterized by: having a steel composition which contains, by mass, 0.04 to 0.15% of C, 0.05 to 0.60% of Si, 0.80 to 1.80% of Mn, at most 0.020% of P, at most 0.010% of S, 0.01 to 0.08% of Nb, and 0.003 to 0.08% of Al with the balance being iron and unavoidable impurities, and which has a Ceq value of 0.48 or lower as defined by formula (1); having a mixed structure which is composed either of ferrite and pearlite or of ferrite and bainite-containing pearlite and which has a ferrite fraction of 60 to 95%; and exhibiting a yield strength of 450MPa or higher and a hydrogen content of 0.1ppm or lower. Ceq = C + Mn / 6 +(Cu + Ni) / 15 + (Cr + Mo + Nb + V + Ti) / 5 + 5B (1).

Description

technical field [0001] The present invention relates to a high-toughness, high-strength, and high-ductility steel plate for line pipe (pipeline steel pipe; line pipe) having sufficient strength as a steel plate for welded structures, excellent ductility properties, and excellent low-temperature toughness, and a manufacturing method thereof, In particular, it relates to a steel plate for line pipes that requires strength at low temperature toughness and good ductility in cold regions, and a method of manufacturing the same. Background technique [0002] In recent years, steel for line pipes has been required to be higher in strength in order to improve safety and / or improve work efficiency by increasing the pressure of transported gas, etc., and to reduce costs by reducing the use of steel materials. . In addition, the area of ​​use of this steel is expanding to areas with harsh natural environments such as cold areas, and strict toughness characteristics are required. In a...

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Problems solved by technology

However, if the carbon equivalent is simply increased, the ductility and toughness will be reduced.

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