Ultralow Carbon Steel Sheet for Three-Piece Welded Cans
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Solution Overview
Problem
Existing steel sheets for three-piece beverage cans face issues with insufficient ductility and strength in the direction perpendicular to the rolling direction, leading to cracking during flange forming and inadequate strength for retort sterilization, particularly when using double-reduced materials.
Innovation Solution
A high-workability steel sheet is developed by adding boron to ultralow carbon steel and controlling the second cold rolling reduction, ensuring sufficient fracture elongation and hardenability to prevent cracking, with a composition optimized for carbon, silicon, manganese, phosphorus, sulfur, aluminum, nitrogen, and boron content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If double-reduced materials are used to reduce steel sheet thickness, then material cost is reduced and thickness can be more easily reduced, but the steel sheet may crack near the weld in flange forming due to insufficient ductility in the direction perpendicular to the rolling direction
Solution Approach 1:
The patent applies parameter changes by precisely controlling the composition parameters (carbon content ≤0.005%, boron content 0.0005-0.0050%, silicon content 0.03-0.15%, manganese content 0.10-0.60%) and processing parameters (second rolling reduction ratio 5-15%, annealing temperature 550-750°C) to achieve the optimal balance between thickness reduction and prevention of cracking during flange forming
Solution Approach 2:
The patent creates a composite microstructure through controlled rolling and annealing processes, forming a refined grain structure with specific crystallographic orientation that combines the benefits of thin gauge capability with enhanced ductility perpendicular to the rolling direction, effectively creating a functionally optimized material system
2Strength
If the second rolling reduction is increased to improve strength, then tensile strength is improved, but fracture elongation deteriorates leading to cracking in flange forming
Solution Approach 1:
The patent resolves this contradiction by optimizing the second rolling reduction ratio to a specific range (5-15%) and combining it with controlled annealing temperature (550-750°C) to achieve a microstructure that simultaneously provides high tensile strength (400 MPa or more) and sufficient fracture elongation (15% or more) in the direction perpendicular to the rolling direction
Solution Approach 2:
The patent applies local quality by creating anisotropic material properties through controlled rolling and annealing, where the microstructure is specifically optimized to provide enhanced ductility and strength in the direction perpendicular to the rolling direction (the critical direction for flange forming) while maintaining appropriate properties in other directions
3Reliability
If boron is added to improve hardenability and prevent cracking, then weldability is improved, but the complexity of composition control increases
Solution Approach 1:
The patent manages composition control complexity by establishing a well-defined parameter space with specific ranges (boron: 0.0005-0.0050%, silicon: 0.03-0.15%, manganese: 0.10-0.60%) and clear interaction rules between elements, transforming an open-ended compositional problem into a controlled optimization task with predictable outcomes
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 steel sheet achieves a tensile strength of 400 MPa or more in the direction perpendicular to the rolling direction and excellent flange formability, enabling reliable can forming without cracking and withstanding retort sterilization pressure.
Implementation Method 1
adding boron to an ultralow carbon steel to impart hardenability while maintaining its softness
Implementation Method 2
first cold rolling with a rolling reduction of 86 % and a second cold rolling with a rolling reduction of 10% to 35%
Implementation Method 3
single cold rolling process followed by annealing and temper rolling
Data Source
AI summary
A practical high-workability steel sheet for three-piece welded cans contains, in percent by mass, more than 0.0015% to 0.0030% of carbon, 0.10% or less of silicon, 0.20% to 0.80% of manganese, 0.001% to 0.020% of phosphorus, 0.001% to 0.020% of sulfur, more than 0.040% to 0.100% of aluminum, 0.030% or less of nitrogen, and 0.0002% to 0.0050% of boron, the balance being iron and incidental impurities, and has a tensile strength of 400 MPa or more in a direction perpendicular to a rolling direction and a fracture elongation of 15% or more in the direction perpendicular to the rolling direction. This steel sheet can be produced by hot-rolling a steel having the above composition at a finish rolling temperature of the Ar3 transformation temperature to 960°C and a coiling temperature of 560°C to 750°C; subjecting the steel sheet to first cold rolling at a rolling reduction of 89% to 93%; annealing the steel sheet at 600°C to 790°C; and subjecting the steel sheet to second cold rolling at a rolling reduction of more than 6.0% to less than 10.0%.