Three-Piece Can Steel Sheet Nitrogen Alloying
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Solution Overview
Problem
Conventional methods for manufacturing high-strength steel sheets for three-piece cans face challenges in achieving a balance between strength and elongation, leading to issues with processability and roundness, particularly during roll forming and retort sterilization, where the steel sheet's strength is compromised by thinning and work hardening.
Innovation Solution
The solution involves increasing nitrogen content in the steel sheet to enhance strength and elongation, combined with strain aging hardening, which allows for improved roll formability and roundness, and applying a baking process after repair coating to further increase strength, thereby ensuring a yield strength of 440 MPa or more and total elongation of 12% or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the sheet thickness is reduced for cost reduction and weight reduction, then the can weight decreases and environmental protection is improved, but the can strength is reduced
Solution Approach 1:
The invention changes the material parameters by precisely controlling the chemical composition (C: 0.005-0.030%, Si: 0.010-0.050%, Mn: 0.50-2.00%, Al: 0.005-0.050%, N: 0.005-0.020%) and applying specific heat treatment parameters (annealing temperature and time) to achieve the required strength with thinner sheets
Solution Approach 2:
The invention creates a composite microstructure consisting of ferrite and retained austenite phases through controlled composition and heat treatment, where the ferrite provides ductility and the retained austenite (3-15%) provides strength through TRIP effect, enabling thin sheets to maintain high strength
2Strength
If C is added to increase the strength of the steel sheet, then the steel sheet strength increases, but slab cracking occurs due to peritectic reaction
Solution Approach 1:
The invention changes the approach from high carbon addition to precise low-carbon control (0.005-0.030%) combined with alloying elements (Si, Mn, Al, N) and heat treatment to achieve strength without triggering peritectic reaction and slab cracking
Solution Approach 2:
The invention introduces Si and Mn as intermediary elements that contribute to solid solution strengthening and precipitation hardening, allowing the steel to achieve required strength without relying on high carbon content that causes peritectic reaction
3Strength
If the second cold rolling is performed for work hardening to increase the steel sheet strength, then the steel sheet strength increases, but the elongation decreases causing cracking during flanging processing
Solution Approach 1:
The invention changes the strengthening mechanism from work hardening through cold rolling to precipitation hardening through controlled heat treatment, specifically annealing that produces 3-15% retained austenite, which maintains high strength while preserving elongation for flanging operations
Solution Approach 2:
The invention utilizes the phase transition during annealing to form retained austenite from martensite or bainite, which can transform to martensite during deformation (TRIP effect), providing both strength and ductility without the need for aggressive cold rolling
4Strength
If a high strength material is used to keep the can strength, then the can strength is maintained, but the shape fixability is reduced causing the cylindrical shape to not be formed after roll forming
Solution Approach 1:
The invention changes the material properties through controlled composition (low C, specific Si, Mn, Al, N ranges) and annealing parameters to achieve a balanced microstructure with 3-15% retained austenite, providing both strength and shape fixability for roll forming
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
This approach results in a steel sheet with excellent processability and roundness, preventing dents during retort sterilization and maintaining can strength under external pressure, while facilitating easier manufacturing and maintaining the cylindrical shape during roll forming.
Implementation Method 1
The steel sheet has a yield strength of 440 MPa or more and a total elongation of 12% or more after strain aging hardening
Implementation Method 2
the steel sheet is subjected to annealing and then rapidly cooled
Data Source
AI summary
Provided are an especially high-strength three-piece can and a method for manufacturing the three-piece can. A three-piece can includes a can body obtained by forming a steel sheet such that a roundness of the can is 0.34 mm or less. The steel sheet contains: by mass%, C: 0.020% or more and 0.100% or less; Si: 0.10% or less; Mn: 0.10% or more and 0.80% or less; P: 0.001% or more and 0.100% or less; S: 0.001% or more and 0.020% or less; Al: 0.005% or more and 0.100% or less; and N: 0.0130% or more and 0.0200% or less. The balance is Fe and inevitable impurities. The steel sheet has a yield strength of 440 MPa or more and a total elongation of 12% or more.