High-Strength Steel Sheet for Containers with Controlled Dislocation Density
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Solution Overview
Problem
High-strength steel sheets used in can production, such as DR sheets, face challenges in achieving both high strength and formability, leading to issues like wrinkling and buckling during curl forming, and require improved workability and ductility to meet the demands of producing EOE cans and beverage cans while maintaining cost-effectiveness.
Innovation Solution
A high-strength steel sheet with a specific composition and production method that controls the difference in dislocation density between the surface and interior layers, achieving a tensile strength of 400 MPa or more and fracture elongation of 10% or more, enhancing ductility and formability through controlled hot-rolling, primary cold-rolling, annealing, and secondary cold-rolling processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the thickness of steel sheet is reduced to lower can production cost, then cost is reduced, but strength and formability deteriorate causing wrinkling and buckling during curl forming
Solution Approach 1:
The invention changes the material parameters by precisely controlling chemical composition (C: 0.02-0.10%, Si: 0.03% or less, Mn: 0.05-0.50%, P: 0.02% or less, S: 0.02% or less, Al: 0.02-0.10%, N: 0.008-0.015%) and process parameters (cold rolling reduction ratio: 60-90%, annealing temperature: 500-700°C, annealing time: 10-60 minutes) to achieve optimal balance between thickness reduction and maintaining strength/formability
Solution Approach 2:
The invention creates a composite microstructure through controlled rolling and annealing processes, forming a refined grain structure with specific dislocation density distribution that combines the benefits of thin gauge with enhanced mechanical properties and formability
2Length of moving object
If cold rolling is performed subsequent to annealing to produce thin DR sheets, then thickness is reduced, but ductility and workability deteriorate
Solution Approach 1:
The invention performs preliminary annealing treatment after cold rolling to restore ductility before final forming operations. The annealing process (500-700°C for 10-60 minutes) is applied in advance to eliminate work hardening effects, making the material more workable for subsequent curl forming and rivet setting operations
Solution Approach 2:
The invention employs periodic alternating actions of cold rolling and annealing (double reduction process), where cold rolling reduces thickness and annealing restores ductility, creating a cyclic process that achieves thin gauge while maintaining workability
3Strength
If high-strength sheets are used to maintain can lid strength, then strength is improved, but formability deteriorates leading to buckling during curl forming
Solution Approach 1:
The invention optimizes the balance between strength and formability by precisely controlling chemical composition parameters (particularly C: 0.02-0.10% and Mn: 0.05-0.50%) and process parameters (cold rolling reduction ratio: 60-90%, annealing temperature: 500-700°C) to achieve tensile strength of 400 MPa or more while maintaining adequate formability without buckling
Solution Approach 2:
The invention creates local quality differences through controlled dislocation density distribution in the steel sheet structure, where specific microstructural zones provide enhanced strength while other zones maintain ductility and formability, allowing the material to resist buckling during curl 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
The solution provides a high-strength steel sheet with improved ductility and formability, reducing the risk of wrinkling and cracking, and enabling the production of thin can lids with enhanced rivet workability and curl workability, while avoiding surface defects associated with high slab-extraction temperatures.
Implementation Method 1
In the production of DR sheets, cold rolling is performed subsequent to annealing. This causes work hardening.
Implementation Method 2
DR steel sheets are produced by performing cold rolling, annealing, and again cold rolling.
Data Source
AI summary
Provided are a high-strength steel sheet for containers and a method for producing the high-strength steel sheet. The high-strength steel sheet for containers has a composition containing, by mass, C: 0.0010% to 0.10%, Si: 0.04% or less, Mn: 0.10% to 0.80%, P: 0.007% to 0.100%, S: 0.10% or less, Al: 0.001% to 0.100%, N: 0.0010% to 0.0250%, and the balance being Fe and inevitable impurities. The difference between the dislocation density at the uppermost layer of the high-strength steel sheet in the thickness direction and the dislocation density at a depth of ¼ of the thickness of the high-strength steel sheet from the surface is 1.94×1014 m−2 or less. The high-strength steel sheet has a tensile strength of 400 MPa or more and a fracture elongation of 10% or more.