Steel sheet, member, and production methods for same
EP4660346A4Pending Publication Date: 2026-06-03JFE STEEL CORP
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2024-03-14
- Publication Date
- 2026-06-03
AI Technical Summary
Technical Problem
High-strength steel sheets with tensile strength of 980 MPa or more face issues with ductility, stretch flangeability, and axial crash properties, leading to press cracking and inadequate energy absorption during collisions.
Method used
A steel sheet with a specific chemical composition and controlled heat treatment process, including hot-rolling, cold-rolling, annealing, and controlled cooling to achieve a microstructure with controlled ferrite, martensite, and austenite fractions, enhancing ductility and crash properties.
Benefits of technology
The steel sheet achieves tensile strength of 980 MPa with improved ductility, stretch flangeability, and axial crash properties, suitable for energy-absorbing members in automobiles.
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Abstract
Provided is a steel sheet and a member having a tensile strength (TS) of 980 MPa or more, high ductility and stretch flangeability, and excellent axial crash properties, and methods for producing the same. A steel sheet has a chemical composition with specified C, Si, Mn, P, S, sol. Al, and N contents and has a steel microstructure containing, in area fractions, ferrite: 15% or less, tempered martensite: 30% or more and 80% or less, bainite: 10% or more and 40% or less, retained austenite: 5% or more, fresh martensite: 10% or less. The average C concentration in the retained austenite is 0.60 mass% or more. In a region within 100 µm from a steel sheet surface in a thickness direction, a content of Fe element present as carbides in the tempered martensite is 0.20 mass% or less on average.
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