Steel sheet and component

A steel sheet with a tailored chemical composition and microstructure addresses formability and impact resistance issues in high-strength steel sheets, enhancing ductility and hole expandability, particularly for automobile suspension parts.

WO2026028896A1 Publication Date: 2026-02-05NIPPON STEEL CORPORATION
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Patent Information

Application Number
PCT/JP2025/026127
Authority / Receiving Office
WO · WO
Patent Type
Applications
Current Assignee / Owner
Priority Date
2024-07-30
Filing Date
2025-07-23
Publication Date
2026-02-05

AI Technical Summary

Technical Problem

High-strength steel sheets used in automobile suspension parts face challenges with insufficient formability, necking, fracture, and reduced impact resistance after pre-straining, while existing solutions like Patent Document 1 do not adequately address workability and impact resistance properties.

Method used

A steel sheet with a specific chemical composition and microstructure, including controlled proportions of elements like C, Si, Mn, Ti, and a tailored metallographic structure with granular and acicular bainite, fresh martensite, tempered martensite, and retained austenite, optimized to enhance ductility, hole expandability, and impact resistance after pre-straining.

Benefits of technology

The proposed steel sheet achieves high strength, excellent ductility, and improved impact resistance after pre-straining, addressing the formability and fracture issues commonly encountered in high-strength steel sheets.

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Abstract

This steel sheet has a predetermined chemical composition, and has a metallographic structure, at a position 1 / 4 of the sheet thickness, comprising, in terms of area%, granular bainite at 30-50%, acicular bainite at 20-50%, at least one selected from fresh martensite, tempered martensite, and retained austenite at 10-30% in total, and at least one selected from ferrite and pearlite at less than 5% in total. The metallographic structure in a surface region of the steel sheet comprises, in terms of area%, at least one selected from fresh martensite, tempered martensite, and retained austenite at 10% or less in total. MA phases, which are composed of the fresh martensite and the retained austenite, and the tempered martensite each have an equivalent circle diameter of 5.0 μm or less.
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