Steel Sheet for Cans with Gradient Niobium Distribution
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Solution Overview
Problem
Conventional steel sheets for cans face challenges in achieving high strength, ductility, and corrosion resistance, especially when subjected to high deformation processes and corrosive environments, with existing methods either compromising on strength or ductility or increasing the risk of corrosion.
Innovation Solution
A steel sheet with a specific chemical composition and manufacturing process that utilizes solid solution strengthening through nitrogen and solute drag of solid solution Nb, controlling the ferrite microstructure, and varying the amount of Nb across the sheet thickness to achieve high strength and ductility without compromising corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the thickness of steel sheet is reduced to decrease can-making costs, then material cost decreases, but the strength of can body decreases
Solution Approach 1:
The patent changes the chemical composition parameters of the steel sheet by precisely controlling the content of alloying elements (C: 0.15-0.35%, Si: 0.01-0.05%, Mn: 1.50-3.00%, P: 0.010-0.040%, S: 0.010-0.050%, Al: 0.005-0.100%, Ti: 0.001-0.050%, Nb: 0.001-0.050%, V: 0.001-0.050%, B: 0.0005-0.0050%) to achieve high strength through solid solution strengthening and precipitation hardening, enabling thickness reduction while maintaining can body strength
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (ferrite, martensite, and retained austenite) through controlled cooling and heat treatment processes, where each phase contributes different properties: ferrite provides ductility, martensite provides strength, and retained austenite provides work hardening capability, achieving both high strength and high ductility simultaneously
2Strength
If double reduce method is used to manufacture high-strength and ultra-thin steel sheet, then strength increases, but formability and ductility deteriorate
Solution Approach 1:
The patent changes the microstructural parameters by controlling the cooling rate (10-100°C/s) and heat treatment temperature (Ac3 transformation point ±50°C) to obtain an optimal mix of phases, where the retained austenite content is controlled at 5-20%, providing excellent work hardening and ductility while maintaining high strength, eliminating the need for double reduce method
Solution Approach 2:
The patent creates a tri-phase composite microstructure (ferrite + martensite + retained austenite) where ferrite provides baseline ductility, martensite provides high strength through tetragonal distortion, and retained austenite provides work hardening and elongation through TRIP effect, achieving both high strength and excellent formability for complex can bodies
3Strength
If various methods for increasing strength are utilized to avoid poor ductility of DR steel sheet, then strength increases, but corrosion resistance may be compromised
Solution Approach 1:
The patent changes the chemical composition parameters by strictly controlling the content of harmful elements (P: 0.010-0.040%, S: 0.010-0.050%) that cause corrosion, while optimizing beneficial elements (Mn: 1.50-3.00% for solid solution strengthening, Ti: 0.001-0.050% and Nb: 0.001-0.050% for precipitation hardening, Al: 0.005-0.100% for oxide inclusion control) to achieve high strength through microstructural control rather than excessive alloying, maintaining corrosion resistance
Solution Approach 2:
The patent applies local quality control by managing the distribution and morphology of inclusions through aluminum content control (0.005-0.100%) and deoxidation practices, creating a homogeneous microstructure with controlled oxide inclusions that do not act as corrosion initiation sites, while achieving high strength through uniform phase distribution
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 results in a steel sheet with high ductility, high strength, and maintained corrosion resistance, enabling intense body processing and resistance to corrosive contents, while allowing for reduced can gauge without strength loss.
Implementation Method 1
solid solution strengthening through the use of N
Implementation Method 2
precipitation strengthening through the use of Nb carbides
Implementation Method 3
grain refining strengthening through the use of the carbonitrides of Nb, Ti, and B
Implementation Method 4
solid solution strengthening through the use of, for example, Mn
Data Source
AI summary
Provided are a steel sheet for a can having high strength, excellent ductility, and good corrosion resistance, even on exposure to highly corrosive contents, and a method for manufacturing the steel sheet. A steel sheet for a can has a chemical composition containing, by mass%, C: 0.020% or more and 0.130% or less, Si: 0.04% or less, Mn: 0.10% or more and 1.20% or less, P: 0.007% or more and 0.100% or less, S: 0.030% or less, Al: 0.001% or more and 0.100% or less, N: more than 0.0120% and 0.0200% or less, Nb: 0.0060% or more and 0.0300% or less, and the balance being Fe and inevitable impurities, an upper yield strength of 460 MPa to 680 MPa, and a total elongation of 12% or more, in which the absolute value of the difference in the amount of solid solution Nb between a region from the surface to a position located at 1/8 of the thickness from the surface and a region from a position located at 3/8 of the thickness from the surface to a position located at 4/8 of the thickness from the surface is 0.0010 mass% or more.