Steel sheet for use at lower temperatures, and method for producing same

Abstract

Provided are: a steel sheet for use at lower temperatures, which has high strength, excellent toughness at lower temperatures and excellent brittle crack propagation arrest properties; and a method for producing the steel sheet. A steel sheet for use at lower temperatures, which has tensile strength of 700 MPa or more, excellent toughness at lower temperatures and excellent brittle crack propagation arrest properties, has a structure which has a specified chemical composition, and which is composed of tempered martensite having retained austenite dispersed therein, and which has such properties that the amount of the retained austenite is 2.2 to 14% by volume inclusive at a position located at a thickness of (1 / 4)t, the average grain diameter of prior austenite grains is 10 to 60 mum inclusive and the average aspect ratio of the prior austenite grains is 4.0 or less in a cross section that is parallel to the rolling direction at a position located at a thickness of (1 / 4)t, the degree of accumulation of {110} plane that is parallel to the surface of the sheet is 1.3 or more and the degree of accumulation of {100} plane that is parallel to the surface of the sheet is 0.90 or less at a position located at a thickness of 1 mm in the thickness direction from the surface of the steel sheet, and the degree of accumulation of {111} plane that is parallel to the surface of the sheet is 1.2 to 2.5 inclusive at a position located at a thickness of (1 / 2)t in the steel sheet.

Description

technical field [0001] The present invention relates to a low-temperature steel plate suitable for applications such as LNG storage tanks, having high strength, excellent low-temperature toughness, and brittle crack growth arresting properties, and a method for producing the same. Background technique [0002] In recent years, the increase in energy demand worldwide and the accompanying deterioration of the global environment have become problems, and the demand for natural gas (LNG), which is a source of green energy, has increased rapidly. Along with this, the construction of LNG storage tanks is being actively promoted at home and abroad, and the demand for low-temperature steel plates used for the main body of the tanks is also increasing. [0003] Since LNG storage tanks generally require a high level of safety, the low-temperature steel plates used for the main body of the tank are required to have excellent toughness and high brittle crack growth at the temperature at...

AI Technical Summary

Problems solved by technology

[0007] Generally, when the Ni content of low-temperature steel sheets is reduced, steel sheet properties such as low-temperature toughness deteriorate, and it becomes difficult to secure the high level of safety required for LNG storage tanks

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