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Low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness

a high-strength steel and low yield ratio technology, applied in the field of low yield ratio and high-strength steel, can solve the problems of degrading stress corrosion cracking (scc) resistance, low economical efficiency of steel for manufacturing gas tanks, etc., and achieve excellent stress corrosion cracking resistance and low temperature toughness. , the effect of low yield ratio

Inactive Publication Date: 2018-12-27
POHANG IRON & STEEL CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

The patent text describes a method to create a strong and corrosion-resistant steel with good low-temperature toughness. By controlling the alloy composition and microstructure, this method produces a low yield ratio and high-strength steel that can withstand stress corrosion cracking and has low temperature toughness. This results in a high-quality steel that can be utilized in various applications.

Problems solved by technology

In particular, since gas tanks are basically required to be enlarged in size, it may be difficult to remove stress by the PWHT method and most shipbuilders prefer the MSR method, and thus, steel for manufacturing gas tanks is required to have low yield ratio characteristics.
In this manner, in the tanks in which the LPG and the LAG coexist, it is a significant issue to achieve both low temperature toughness and a low yield ratio accompanying the regulation of an upper limit of yield strength from liquid ammonia.
However, in general, if a large amount of Ni is added, a large amount of austenite phases having an FCC lattice structure, which is easily deformed due to a narrow interatomic gap, may be formed, and if repeated stress and a corrosive environment are applied to the easily deformed FCC lattice structure, corrosion may easily occur to cause cracking.
Therefore, Patent document 1 has a problem of low economical efficiency due to high-priced Ni content and has a problem of degrading stress corrosion cracking (SCC) resistance.
This technique, however, may achieve low temperature toughness and low yield ratio separately but cannot obtain both low temperature toughness and low yield ratio together.
However, yield strength based on grain refinement may be increased to exceed 440 MPa, a yield strength upper limit, at which ammonia stress corrosion (SCC) occurs, and it is difficult to obtain low-yield ratio.

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  • Low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness
  • Low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness
  • Low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness

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Embodiment Construction

[0026]Hereinafter, preferred embodiments of the present disclosure will be described. However, the embodiments of the present disclosure may be modified into various other forms, and the scope of the present disclosure is not limited to the embodiments described below. Embodiments of the present invention are provided so that those skilled in the art may more completely understand the present invention.

[0027]The inventors of the present application recognized that it is difficult to make both ammonia stress corrosion cracking resistance and low temperature toughness excellent and have studied to solve the problem.

[0028]As a result, the inventors confirmed that it is possible to provide a low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness by controlling an alloy composition and a microstructure and a manufacturing method thereof, thereby completing the present disclosure.

[0029]Hereinafter, a low yield ratio and ...

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Abstract

An aspect of the present invention relates to a low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness, the steel comprising, by weight, 0.02-0.10% of carbon (C), 0.5-2.0% of manganese (Mn), 0.05-0.5% of silicon (Si), 0.05-1.0% of nickel (Ni), 0.005-0.1% of titanium (Ti), 0.005-0.5% of aluminum (Al), 0.005% of less of niobium (Nb), 0.015% or less of phosphorus (P), 0.015% or less of sulfur (S), and the balanced amount of Fe and inevitable impurities, the microstructure of which comprises: by area, 60% or more of acicular ferrite and a balanced amount of one or more phases of bainite, polygonal ferrite and martensite-austenite constituent (MA).

Description

TECHNICAL FIELD[0001]The present disclosure relates to a low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness.BACKGROUND ART[0002]Although varied according to types of a liquefied gas, a temperature for liquefying a gas is generally low (−52° C. in the case of LPG) at normal pressure, and thus, steel used in a liquefied gas storage tank has been required to have excellent low temperature toughness in a welded part, as well as in a base material.[0003]It is known that liquid ammonia (LAG) causes stress corrosion cracking (SCC) of steel, and thus, IGC CODE (International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk) regulates operating conditions at the time of manufacturing, such as oxygen partial pressure, temperature, and the like, limits the Ni content of steel to 5% or less, and defines actual yield strength to 440 MPa or less.[0004]In addition, when a gas tank is manufactu...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C22C38/14C21D8/02C22C38/12C22C38/08C22C38/06C22C38/04C22C38/02C21D6/00
CPCC22C38/14C21D8/0205C22C38/12C22C38/08C22C38/06C22C38/04C22C38/02C21D6/008C21D6/005C21D6/001C21D2211/002C21D2211/005C21D2211/008C21D8/02
Inventor JANG, SUNG-HOLEE, HAK-CHEOL
Owner POHANG IRON & STEEL CO LTD
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