Steel Sheet for Cans with Nb Precipitates
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Solution Overview
Problem
High-strength steel sheets for cans require a balance between strength, ductility, and uniform deformability to prevent local deformation and ensure dimensional accuracy, particularly in complex shapes like can lids, while existing methods often compromise on these properties.
Innovation Solution
A steel sheet composition with specific chemical elements (C, Si, Mn, P, S, Al, N, Nb, and Cr) and microstructure, optimized through precipitation strengthening and solid solution strengthening, to achieve an upper yield stress of 500 MPa or more and total elongation of 10% or more, with a Nb content fraction of less than 20 nm precipitates at 40% or more and an average precipitate interval of 30 nm or less, ensuring uniform deformability and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If secondary cold rolling with 20% or more reduction is performed to increase strength, then upper yield stress increases to 500 MPa or more, but total elongation decreases to below 10% and local deformation occurs
Solution Approach 1:
The patent changes the microstructural parameters by controlling precipitate size (3-20 nm) and distribution, ferrite grain size (5-15 μm), and phase composition. These parameter changes allow the steel to achieve high strength through precipitation strengthening while maintaining ductility through controlled grain structure, avoiding the need for aggressive cold rolling that causes local deformation
Solution Approach 2:
The patent creates a composite microstructure consisting of ferrite phase with dispersed precipitates (Nb, Ti, B carbonitrides). This composite structure at the microscale provides both strength from the precipitates and ductility from the ferrite matrix, enabling uniform deformability without compromising strength
2Loss of substance
If steel sheet thickness is reduced to lower can material costs, then can production cost decreases, but can body strength decreases
Solution Approach 1:
The patent changes the material parameters by achieving ultrafine precipitates (3-20 nm) with high density (10^23 particles/m³) and controlling ferrite grain size to 5-15 μm. These parameter changes enable the steel to achieve tensile strength of 500 MPa or more in ultra-thin forms (0.2-0.5 mm), maintaining can body strength while reducing material usage
Solution Approach 2:
The patent segments the strengthening mechanism into multiple components: precipitation strengthening from nanoscale particles, grain boundary strengthening from fine ferrite grains, and solid solution strengthening from alloying elements. This multi-component approach allows achieving high strength in thin sheets without relying on a single mechanism
3Strength
If high-strength steel sheet is used to ensure can body strength, then can body strength increases, but formability in complex shapes deteriorates and cracks occur
Solution Approach 1:
The patent optimizes microstructural parameters including ferrite grain size (5-15 μm), precipitate size (3-20 nm), and phase composition to achieve a balance between strength and formability. The controlled microstructure allows the steel to undergo complex forming operations for can lids and beaded cans without cracking, while maintaining high strength
Solution Approach 2:
The patent creates local quality variations through non-uniform precipitate distribution and grain structure that accommodate local deformation requirements. The microstructure is designed to provide different properties in different regions, allowing high strength in critical areas while maintaining formability in regions requiring deformation
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 exhibits high strength, ductility, and uniform deformability, preventing local deformation and maintaining corrosion resistance, even in thin forms, suitable for complex can shapes and high-deformation processes like beading or flanging, with improved dimensional accuracy and formability.
Implementation Method 1
a microstructure including a ferrite phase and Nb-based carbides as precipitates
Implementation Method 2
optimized through precipitation strengthening and solid solution strengthening
Data Source
AI summary
Provided is a steel sheet for cans that has uniform deformability and excellent formability in addition to high strength and excellent ductility. A steel sheet for cans comprises a chemical composition containing, in mass%, C: 0.020-0.130 %, Si: ≤ 0.04 %, Mn: 0.10-1.20 %, P: 0.007-0.100 %, S: ≤ 0.030 %, Al: 0.001-0.100 %, N: > 0.0120 % and ≤ 0.0200 %, Nb: 0.0060-0.0300 %, and Cr: ≤ 0.040 %, with a balance being Fe and inevitable impurities, wherein a ratio of Nb content in precipitates of < 20 nm in size to Nb content in all precipitates is ≥ 40 %, an average interval of all precipitates is ≤ 30 nm, an upper yield stress is 500-640 MPa and a total elongation is ≥ 10 % after heat treatment at 210 °C for 10 min.