Cold-Rolled Steel Sheet for Backlight Chassis with Low Yield Elongation
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Solution Overview
Problem
Conventional techniques fail to achieve the required workability and shape fixability for large-size liquid crystal display television backlight chassis, leading to issues with rigidity, flatness, and surface appearance, particularly due to high yield strength and Lankford values in low-carbon steels.
Innovation Solution
A cold-rolled steel sheet with a specific composition and manufacturing process, including a ferrite microstructure with grains larger than 7 µm, controlled Lankford values, and annealing conditions to reduce yield strength and elongation, ensuring shape fixability and surface quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional low-carbon steel is used to ensure workability, then elongation is sufficient, but yield strength is too high causing poor shape fixability and springback
Solution Approach 1:
The invention changes the chemical composition parameters by adding boron (0.0005-0.0050 wt%) and adjusting aluminum content (0.01-0.10 wt%), along with controlling rolling reduction (50-85%) and annealing temperature (600-800°C), to achieve a balance between yield strength and shape fixability that conventional low-carbon steels cannot provide
2Strength
If machining is performed to ensure rigidity by forming beads or bending, then rigidity is improved, but flatness deteriorates and twist increases due to poor shape fixability
Solution Approach 1:
By optimizing the chemical composition (adding boron, controlling aluminum) and processing parameters (rolling reduction 50-85%, annealing temperature 600-800°C), the invention achieves a steel sheet with improved shape fixability that maintains flatness during machining operations while providing the rigidity needed for structural applications
3Adaptability or versatility
If conventional steel sheet is used for large-size backlight chassis, then material is available, but uneven feed during drawing causes twist and poor flatness
Solution Approach 1:
The invention modifies the steel sheet properties by adding boron (0.0005-0.0050 wt%) and controlling aluminum content (0.01-0.10 wt%), along with specific rolling reduction (50-85%) and annealing temperature (600-800°C), to achieve uniform elongation characteristics that prevent uneven feed during drawing operations for large-size components
4Ease of manufacture
If conventional steel sheet is shaped, then forming is complete, but stretcher strains appear causing poor flatness and appearance
Solution Approach 1:
By adding boron (0.0005-0.0050 wt%) and controlling aluminum content (0.01-0.10 wt%), along with optimizing rolling reduction (50-85%) and annealing temperature (600-800°C), the invention suppresses stretcher strain formation while maintaining excellent formability for complex shaping operations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a steel sheet with low yield elongation, high elongation, and low yield strength, enabling effective drawing, bending, and stretching while maintaining excellent formability and surface appearance, suitable for large-size parts like backlight chassis.
Implementation Method 1
performing heating to an annealing temperature of 700°C or higher from 600°C or higher at an average heating rate of 1 to 30 °C/s, holding the annealing temperature with a soaking time in the range of 30 s to 200 s and then performing cooling to 600°C at an average cooling rate of 3 °C/s to 30° C/s
Data Source
AI summary
In low-carbon steel, a cold-rolled steel sheet and a method for manufacturing the same are provided. The cold-rolled steel sheet can satisfy both workability and shape fixability; can be subjected to drawing, bending, and stretching; can ensure shapes required for large-size parts; have high flatness; is free from appearance defects; and is excellent in formability, shape fixability, and surface appearance. The cold-rolled steel sheet has a composition of 0.030% to 0.060% C, 0.05% or less Si, 0.1% to 0.3% Mn, 0.05% or less P, 0.02% or less S, 0.02% to 0.10% Al, and 0.005% or less N on a mass basis, the remainder being iron and unavoidable impurities. The Lankford value thereof is 0.7 to 1.4 in a rolling direction and a direction perpendicular to the rolling direction. The in-plane anisotropy (Δr) of the Lankford value thereof satisfies the inequality -0.2 ≤ Δr ≤ 0.2. The mean yield strength thereof is 230 MPa or less and the mean elongation thereof is 40% or more in three directions: the rolling direction, a direction at 45 degrees to the rolling direction, and a direction perpendicular to the rolling direction. The yield elongation of the cold-rolled steel sheet held at 170°C for 60 minutes is 2% or less in each of the three directions.