Steel plate for linepipe having ultra-high strength and excellent low temperature toughness and manufacturing method of the same

Abstract

A steel plate for linepipes having ultra-high strength and excellent low temperature toughness, and a method for manufacturing the same are disclosed. The steel plate has a strength of 930 MPa or more and excellent toughness even with much smaller amounts of alloying elements than that of conventional steel plates, and a method for manufacturing the same. The steel includes by weight %: 0.03˜0.10% C; 0˜0.6% Si; 1.6-2.1% Mn; 0˜1.0% Cu; 0-1.0% Ni; 0.02-0.06% Nb; 0-0.1% V; 0.1-0.5% Mo; 0-1.0% Cr; 0.005-0.03% Ti; 0.01-0.06% Al; 0.0005-0.0025% B; 0.001-0.006% N; 0-0.006% Ca; 0.02% or less P; 0.005% or less S; and the balance Fe and unavoidable impurities. The microstructure includes at least about 75 area percent of a mixture of bainitic ferrite and acicular ferrite.

Description

TECHNICAL FIELD[0001]The present invention relates to a steel plate for linepipes having ultra-high strength and excellent low temperature toughness, and a method for manufacturing the same. More particularly, the present invention relates to a steel plate for linepipes that has strength of 930 MPa or more and excellent toughness even with much smaller amounts of alloying elements than that of conventional steel plates, and a method for manufacturing the same.BACKGROUND ART[0002]Linepipes refer to a steel pipe buried in the ground for a long-distance transportation of crude oil and natural gas, and generally experience high pressure caused by a fluid of high pressure gas or crude oil flowing therein.[0003]For increasing transportation efficiency of the linepipes, it is necessary to increase a transportable amount of crude oil or gas (hereinafter, simply referred to as “crude oil and the like”) per hour. For this purpose, the outer diameter of linepipe must be increased to a large si...

AI Technical Summary

Benefits of technology

[0018]The present invention has been made to solve the foregoing problems of the prior art and therefore an aspect of the present invention is to provide a steel plate that has high tensile strength and excellent low temperature toughness without containing a great amount of Mo, and a method of manufacturing the same.

Problems solved by technology

However, Comparative Example 1 was cooled at a too high cooling rate.

In particular, for Comparative Example 3, not only was the reheating temperature excessively high, but the cooling finish temperature was also excessively high.

In particular, for Comparative Example 5, not only was the cooling rate too low, but the cooling finish temperature was also excessively high.

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