Steel plate having excellent pwht resistance for low-temperature pressure vessel and method for manufacturing same

Abstract

The present disclosure relates to a steel plate having excellent PWHT resistance and low-temperature toughness for a low-temperature pressure vessel and a method for manufacturing the same, wherein the steel plate comprises, in terms of wt %, 0.07-0.17% of C, 0.15-0.40% of Si, 0.3-0.7% of Mn, 0.012% or less of P, 0.015% or less of S, 3.0-4.0% of Ni, 0.03-0.25% of W, and a balance of Fe and inevitable impurities, has a micro-structure comprising 25-80 area % of tempered bainite and the balance of tempered martensite, and has a tensile strength of 600 MPa or more.

Description

TECHNICAL FIELD[0001]The present disclosure relates to a thick steel plate used in a low-temperature pressure vessel, a ship, a storage tank, a structural steel, and the like, and a method for manufacturing the same, and more particularly, to a steel plate having excellent PWHT resistance and low-temperature toughness for a low-temperature pressure vessel in which a tensile strength is 600 MPa or more, and a method for manufacturing the same.BACKGROUND ART[0002]As a thick plate steel material having high strength for low-temperature uses, a mixed structure including ferrite, a martensite structure, and a bainite structure, or a nearly single-phase structure mainly consisting of bainite and ferrite, or the like, is widely known.[0003]It is necessary to have high strength, since the steel material itself is usable as a structural material at the time of construction. Meanwhile, this high strength structural steel material is required to have excellent PWHT resistance.[0004]The high st...

AI Technical Summary

Benefits of technology

[0021]As set forth above, according to an exemplary embodiment in the present disclosure, a steel plate having excellent PWHT resistance for a low-temperature pressure vessel, stably usable at a low temperature of about −110° C. while satisfying a tensile strength of 600 MPa or more, may be effective provided.

[0022]Hereinafter, the present disclosure will be described in detail.

[0023]First, a steel plate having excellent PWHT resistance for a low-temperature pressure vessel of the present disclosure is described.

[0024]The steel plate of the present disclosure includes, in terms of wt %, 0.07-0.17% of C, 0.15-0.40% of Si, 0.3-0.7% of Mn, 0.012% or less of P, 0.015% or less of S, 3.0-4.0% of Ni, 0.03-0.25% of W, and a balance of Fe and inevitable impurities, and specific steel composition components and reasons for limiting the components are as follows.

[0025]In the present disclosure, C is preferably limited to a content of 0.07-0.17%. When the content is less than 0.07%, a self-strength of a matrix may be deteriorated. When the content is more than 0.17%, weldability of the steel plate may be greatly deteriorated.

[0026]Si is a component to be added for a deoxidation effect, a solid-solution strengthening effect and an impact transition temperature increasing effect, and is preferably added in a content of 0.15% or more in order to achieve these additive effects. However, when the content of Si is more than 0.40%, the weldability is lowered and an oxide film is excessively formed on a surface of the steel plate, such that the content thereof is preferably limited to 0.15-0.40%.

Problems solved by technology

However, when a PWHT treatment is performed in a subsequent process of a steel material having the structure, a carbide is formed along a grain boundary, and thus, strength and toughness of the steel material are lowered, failing to guarantee physical properties required for PWHT.

However, since the invention disclosed in the above-described publication is a steel material manufactured through general normalizing, there is a problem in that deterioration of strength and toughness of the steel material after PWHT treatment is not avoidable even in the case that Ni, or the like, is added.