Steel plate and its manufacturing method

A steel sheet with optimized alloying elements and controlled manufacturing process ensures minimal strength variation and high toughness before and after PWHT, addressing the challenges of conventional materials in liquefied gas tanks.

JP2026523210APending Publication Date: 2026-07-13POHANG IRON & STEEL CO LTD
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Patent Information

Application Number
JP2025574996
Authority / Receiving Office
JP · JP
Patent Type
Applications
Current Assignee / Owner
Priority Date
2023-06-23
Filing Date
2024-05-20
Publication Date
2026-07-13

AI Technical Summary

Technical Problem

Conventional steel materials used in liquefied gas tanks face challenges in maintaining strength and toughness before and after post-weld heat treatment (PWHT), with significant strength differences leading to stress concentration and reduced impact toughness, especially at low temperatures.

Method used

A steel sheet composition containing specific alloying elements (C, Mn, Si, Al, Ni, Ti, Nb, Mo, P, S) and a manufacturing process involving reheating, rough rolling, finish rolling, and controlled cooling to achieve fine-grained microstructure with acicular ferrite or granular bainite, ensuring minimal strength difference and high toughness before and after PWHT.

Benefits of technology

The steel sheet maintains yield strength of 500 MPa or more, tensile strength of 610 MPa or more, and impact toughness of 100 J or more at -60°C, with a tensile strength difference of 50 MPa or less before and after PWHT, suitable for cryogenic environments.

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Abstract

The present invention provides a steel plate with excellent strength and toughness even after post-weld heat treatment, and a method for manufacturing the same, minimizing the difference in strength before and after post-weld heat treatment, and providing a steel plate with excellent toughness before and after post-weld heat treatment, and a method for manufacturing the same. [Solution] The steel sheet of the present invention contains, by weight %, C: 0.03~0.06%, Mn: 1.8~2.1%, Si: 0.05~0.2%, Al: 0.01~0.04%, Ni: 0.5~1.0%, Ti: 0.01~0.018%, Nb: 0.01~0.03%, Mo: 0.2~0.4%, P: 0.008% or less, S: 0.002% or less, with the remainder being Fe and unavoidable impurities. The average size of crystal grains with a boundary angle of 15° or more (effective crystal grains), measured using electron backscatter diffraction, is 20 μm or less. The steel sheet is characterized in that the main phase is either acicular ferrite, granular bainite, or a mixture thereof.
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