Electric resistance welded steel pipes for line pipes

By optimizing chemical composition and manufacturing processes, the steel pipes achieve high strength, low yield ratio, and improved toughness in both base material and welded joints, overcoming previous limitations in electric resistance welded steel pipes for line pipes.

JP2026099012APending Publication Date: 2026-06-18NIPPON STEEL CORPORATION
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Patent Information

Authority / Receiving Office
JP · JP
Patent Type
Applications
Current Assignee / Owner
NIPPON STEEL CORPORATION
Filing Date
2024-12-06
Publication Date
2026-06-18

AI Technical Summary

Technical Problem

Existing electric resistance welded steel pipes for line pipes face challenges in achieving high strength, low yield ratio, and excellent low-temperature toughness in both the base material and welded joints, particularly due to inappropriate chemical composition and manufacturing methods that lead to deviations in island-shaped martensite area ratio and dislocation density, affecting toughness.

Method used

The steel pipes are formulated with specific chemical compositions and controlled microstructures, including ferrite area ratios, dislocation densities, and controlled reheating and tempering processes to optimize the base material and welded portions, ensuring high strength and low yield ratio with improved toughness.

Benefits of technology

The solution results in electric resistance welded steel pipes with enhanced high strength, low yield ratio, and excellent low-temperature toughness, addressing the limitations of previous technologies by optimizing chemical composition and manufacturing processes.

✦ Generated by Eureka AI based on patent content.

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Abstract

To provide electric resistance welded steel pipes for line pipes that have high strength, low YR, and excellent low-temperature toughness in the base material and electric resistance welded joints. [Solution] The material has a base material portion and an electric resistance welded portion, and in the microstructure of the 1 / 2 × tB portion of the base material, the area ratio of ferrite is 40-80%, the average grain size is 35 μm or less, and the dislocation density is 1.0 × 10 13 ~5.0×10 15 m -2 The electric resistance welded steel pipes used for line pipes are characterized in that, in the microstructure of the 1 / 4 × tS portion of the electric resistance welded joint, the area ratio of ferrite is 40-70%, the area ratio of island martensite is 0.2-10.0%, the average grain size is 35 μm or less, the maximum Vickers hardness is 180-220 HV, the yield stress is 360 MPa or more, and the tensile strength is 465 MPa or more.
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