Steel Sheet Nitrogen Optimization for Can Lid Strength
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Solution Overview
Problem
Conventional steel sheets for easy open ends of cans face challenges in achieving both high strength and formability, particularly with increasing can lid diameters, where high nitrogen content compromises ductility and leads to slab cracks, and existing methods for improving rivet formability are insufficient for sphere-like bulging.
Innovation Solution
A high strength and high formability steel sheet is developed by optimizing the nitrogen content, restricting carbon content, and applying a resin film layer with appropriate thickness, along with controlled cold rolling and coiling temperatures, to achieve a tensile strength of at least 520 MPa and an Erichsen value of 5.0 mm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If nitrogen content is increased to achieve high strength, then tensile strength is improved, but ductility deteriorates and slab cracks occur during continuous casting
Solution Approach 1:
The patent optimizes the nitrogen content parameter to a specific range (0.0120-0.0250% by mass) rather than simply increasing it. This parameter optimization achieves the necessary tensile strength while preventing excessive nitrogen from causing ductility deterioration and slab cracks during continuous casting
Solution Approach 2:
The patent creates a composite chemical composition system combining multiple elements (C: 0.02-0.10%, Si: ≤0.10%, Mn: ≤1.5%, Al: ≤0.10%, N: 0.0120-0.0250%) that work synergistically. The combination of these elements achieves high strength through nitrogen while other elements help maintain ductility and prevent cracking during processing
2Ease of operation
If carbon content is reduced to improve formability, then rivet formability is enhanced, but tensile strength becomes insufficient for large diameter cans
Solution Approach 1:
The patent optimizes carbon content to a specific range (0.02-0.10% by mass) rather than simply reducing it. This parameter optimization maintains sufficient tensile strength for large diameter cans while preventing excessive carbon from compromising rivet formability
Solution Approach 2:
The patent uses a composite chemical composition where carbon (0.02-0.10%) works synergistically with nitrogen (0.0120-0.0250%) and other alloying elements. This composite approach achieves both adequate strength and good formability that would be difficult to obtain with carbon reduction alone
3Length of moving object
If second cold rolling reduction ratio is increased to achieve thin sheet thickness, then sheet thinning is improved, but work hardening increases and formability deteriorates
Solution Approach 1:
The patent performs annealing treatment before the second cold rolling to restore ductility and reduce work hardening. This preliminary action enables subsequent thinning through second cold rolling while maintaining sufficient formability for rivet formation
Solution Approach 2:
The patent optimizes the second cold rolling reduction ratio to a specific range (5-20%) rather than simply increasing it. This parameter optimization achieves necessary sheet thinning while preventing excessive work hardening that would compromise formability
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 enables the production of steel sheets with enhanced strength and formability, preventing slab cracks and ensuring successful rivet formation without cracking, thereby allowing for significant thinning of steel sheets for easy open ends.
Implementation Method 1
In the DR method, the cold rolling performed again after annealing causes work hardening, and thus although a thin and hard steel sheet can be manufactured
Implementation Method 2
thereafter performing continuous annealing at a soaking temperature of 600 to 700°C for a soaking period of 10 to 50 seconds
Data Source
AI summary
A high strength and high formability steel sheet contains, by mass% of the steel sheet: greater than 0.020% and less than 0.040% of C; not less than 0.003% and not greater than 0.100% of Si; not less than 0.10% and not greater than 0.60% of Mn; not less than 0.001% and not greater than 0.100% of P; not less than 0.001% and not greater than 0.020% of S; not less than 0.005% and not greater than 0.100% of Al; and greater than 0.0130% and not greater than 0.0170% of N, wherein a remainder is Fe and inevitable impurities, and the steel sheet has: a tensile strength in a rolling direction of not lower than 520 MPa; an Erichsen value of not less than 5.0 mm; and a resin film layer at least on a side to be an inner surface of a can.