Steel Sheet Texture Control for Strength-Formability Balance
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Solution Overview
Problem
High-strength steel sheets face a trade-off between increased strength and formability, with existing methods limiting local deformability and orientation dependency, particularly in automobile components, where improved bending and hole expanding properties are necessary without sacrificing material quality.
Innovation Solution
Control of crystal grain size and texture through X-ray random intensity ratios and r values in specific orientations during the hot rolling process, allowing for enhanced local deformability and reduced anisotropy, even with the addition of elements like Nb and Ti, without limiting the main structure components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the strength of a steel sheet is increased, then the operational strength increases, but the formability and local deformability decrease
Solution Approach 1:
The invention changes the microstructural parameters of the steel sheet by controlling the proportion of ferrite (50-80%), bainite (10-40%), and martensite (5-20%), along with controlling inclusion content (0.001-0.05%) and crystal grain size (10-50 μm). This multi-parameter control allows the steel to achieve both high strength (1300-1800 MPa) and improved local deformability, resolving the trade-off between strength and formability
Solution Approach 2:
The invention creates a composite microstructure consisting of multiple phases (ferrite, bainite, and martensite) with different mechanical properties. Ferrite provides ductility, bainite provides strength, and martensite provides hardness. This composite microstructure enables the steel sheet to simultaneously achieve high operational strength and good formability by combining the advantages of different phases
2Ease of manufacture
If structure control methods are used to improve local deformability, then bending and hole expanding properties improve, but the base structure formation becomes significantly influential and limits manufacturing flexibility
Solution Approach 1:
The invention simplifies structure control by establishing specific parameter ranges for microstructural components: ferrite content (50-80%), bainite content (10-40%), martensite content (5-20%), inclusion content (0.001-0.05%), and crystal grain size (10-50 μm). By controlling these parameters within defined ranges, the invention achieves improved local deformability without requiring complex structure control procedures, making the manufacturing process more flexible and less sensitive to base structure variations
Data Source
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AI summary
A hot-rolled steel sheet has an average value of the X-ray random intensity ratio of a {100} <011> to {223} <110> orientation group at least in a sheet thickness central portion that is in a sheet thickness range of 5/8 to 3/8 from a steel sheet surface of 1.0 to 6.0, an X-ray random intensity ratio of a {332} <113> crystal orientation of 1.0 to 5.0, rC which is an r value in a direction perpendicular to a rolling direction of 0.70 to 1.10, and r30 which is an r value in a direction that forms an angle of 30° with respect to the rolling direction of 0.70 to 1.10.