High strength hot rolled steel products for line-pipes excellent in low temperature toughness and production method of the same

Abstract

The invention provides a high-strength hot-rolled steel plate for line pipes which is excellent in low-temperature toughness and a process for the production of the same. A steel plate which contains by mass C: 0.01 to 0.1%, Si: 0.05 to 0.5%, Mn: 1 to 2%, P: 0.03% or below, S: 0.005% or below, O: 0.003% or below, Al: 0.005 to 0.05%, N: 0.0015 to 0.006%, Nb: 0.005 to 0.08%, and Ti: 0.005 to 0.02% with the proviso that relationships: N-14 / 48xTi>0% et Nb-93 / 14x(N-14 / 48xTi)>0.005% are satisfied and with the balance consisting of Fe and unavoidable impurities, characterized in that the microstructure is a continuous cooling transformation structure, that the reflected X-ray intensity ratio between {211} plane and {111} plane which are parallel to the plate face, {211} / {111} ratio, in the texture in the thicknesswise central part of the plate is 1.1 or above, and that the density of carbonitride precipitate of Nb and / or Ti in the grains is 10<17> to 10<18 >pieces / cm<3>.

Description

technical field [0001] The present invention relates to a high-strength hot-rolled steel sheet for line pipe using a hot coil excellent in low-temperature toughness as a raw material and a manufacturing method thereof. Background technique [0002] In recent years, the development of energy resources such as crude oil and natural gas has expanded to cold areas such as the North Sea, Siberia, North America, and Sakhalin, as well as areas with harsh natural environments such as the North Sea, the Gulf of Mexico, the Black Sea, the Mediterranean Sea, and the Indian Ocean. In addition, from the viewpoint of emphasizing the global environment, it is required to increase the development of natural gas, and at the same time, from the viewpoint of economical efficiency of the pipeline system, it is required to reduce the weight of steel and increase the pressure of the working pressure. In response to these changes in environmental conditions, the properties required for line pipes ...

AI Technical Summary

Problems solved by technology

However, although increasing the separation improves the low-temperature toughness, on the other hand, it reduces the absorbed energy, so there is a problem that the resistance to unstable ductile failure is deteriorated.

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