Hot-rolled steel sheet and method for producing same

A hot-rolled steel sheet with controlled composition and manufacturing process addresses the lack of ductility and work hardening in existing sheets, achieving improved formability and safety in automotive applications.

WO2026116406A1PCT designated stage Publication Date: 2026-06-04JFE STEEL CORP
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Patent Information

Authority / Receiving Office
WO · WO
Patent Type
Applications
Current Assignee / Owner
JFE STEEL CORP
Filing Date
2025-11-27
Publication Date
2026-06-04

AI Technical Summary

Technical Problem

Existing hot-rolled steel sheets with tensile strength of 400 MPa or less lack sufficient ductility and work hardening properties, leading to issues such as necking and poor formability during processes like flanging and deep drawing, and prior technologies fail to adequately control ferrite grain growth and cooling patterns.

Method used

A hot-rolled steel sheet with a specific composition and controlled microstructure, including ferrite grains of defined sizes and ratios, and a manufacturing process involving controlled heating, hot-rolling, and multi-stage cooling to achieve uniform elongation and high work hardening properties.

Benefits of technology

The solution results in a steel sheet with tensile strength of 400 MPa or less, exhibiting excellent ductility and work hardening properties, suitable for forming complex parts with improved safety in automotive components.

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Abstract

Provided is a hot-rolled steel sheet which has a tensile strength of not more than 400 MPa and has excellent ductility and work hardening property.　This hot-rolled steel sheet has a component composition which comprises, in mass%, not less than 0.005% to less than 0.050% of C, not more than 0.10% of Si, not less than 0.05% to less than 0.50% of Mn, not more than 0.05% of P, not more than 0.008% of S, 0.01-0.08% of Al, and not more than 0.0080% of N, and in which the contents of Cu, Ni, Cr, and Mo, and Mn satisfy a prescribed relational formula, the remaining portion being Fe and unavoidable impurities. The hot-rolled steel sheet has a tensile strength of not more than 400 MPa, and includes ferrite in which the area proportion of ferrite grains having a grain size of less than 15 µm is not more than 20%, the area proportion of ferrite grains having a grain size of 15-35 µm is 50-100%, and the area proportion of ferrite grains having a grain size of more than 35 µm is not more than 30%.
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