Steel Sheet for Cans with Graded Ferrite Grain Structure
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Solution Overview
Problem
Current methods face challenges in manufacturing a steel sheet for cans that simultaneously achieves high deep drawing workability, ironing workability, and surface roughening resistance, while also being cost-effective and requiring minimal sophisticated control techniques.
Innovation Solution
A steel sheet with a composition of 0.0040 to 0.01% C, 0.05% or less Si, more than 0.3 to 0.6% Mn, 0.02% or less P, 0.02% or less S, 0.01 to 0.10% Al, 0.0015 to 0.0050% N, and 0.02 to 0.12% Nb, with a Nb/C ratio less than 0.8, is produced through hot rolling, cooling, pickling, cold rolling, and continuous annealing to achieve fine grains in the surface layer and coarse grains in the center, optimizing grain size and chemical composition for enhanced workability and surface roughening resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the average grain size of the steel sheet is made finer to suppress surface roughening, then surface roughening resistance is improved, but working energy increases and deep drawing workability deteriorates
Solution Approach 1:
The invention creates a non-uniform grain size distribution where the surface layer has fine grains (7-15 μm) for roughening resistance while the center portion has coarse grains for softness and low working energy. This local differentiation resolves the contradiction by assigning different grain sizes to different regions based on their functional requirements.
Solution Approach 2:
The steel sheet is segmented into two distinct regions with different grain characteristics: a surface layer region (0-1/4 thickness) with fine grains and a center portion region (1/4 thickness to center) with coarse grains. This segmentation allows each region to independently fulfill its specific functional requirement without compromising the other.
2Reliability
If the grain size is made fine only on the surface region to suppress roughening, then surface roughening resistance is improved, but deep drawing workability and ironing workability deteriorate due to excessive hardness
Solution Approach 1:
The invention applies local quality by making the surface layer (0-1/4 thickness) fine-grained for roughening resistance while keeping the center portion (1/4 thickness to center) coarse-grained for softness. This ensures the surface has the required hardness for film adhesion while the bulk material remains soft enough for deep drawing and ironing operations.
3Reliability
If the average grain size is made finer to ensure favorable adhesiveness with film, then surface roughening resistance is improved, but manufacturing cost increases due to higher working energy and more sophisticated control techniques
Solution Approach 1:
The invention reduces manufacturing cost by applying fine grains only where necessary (surface layer for film adhesion) rather than throughout the entire sheet. The center portion maintains coarse grains that require less working energy during forming, thereby reducing overall manufacturing costs while still achieving the required surface properties.
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 resulting steel sheet exhibits excellent deep drawing and ironing workability, along with superior surface roughening resistance, reducing manufacturing costs and eliminating the need for complex control techniques, making it suitable for can production.
Implementation Method 1
the steel sheet having the composition which contains by mass% 0.0040 to 0.01% C, 0.05% or less Si, more than 0.3 to 0.6% Mn, 0.02% or less P, 0.02% or less S, 0.01 to 0.10% Al, 0.0015 to 0.0050% N, 0.02 to 0.12% Nb and a balance of Fe and unavoidable impurities, wherein a Nb/C ratio is less than 0.8, an average ferrite grain size in a cross section in the rolling direction in a region ranging from a surface layer of the steel sheet to a position 1/4 of a sheet thickness away from the surface layer of the steel sheet is set to 7 μm or more and 10 μm or less, the average ferrite grain size in a cross section in the rolling direction in a region ranging from the position 1/4 of a sheet thickness away from the surface layer of the steel sheet to a sheet thickness center portion of the steel sheet is set to 15 μm or less
Implementation Method 2
a method of manufacturing the steel sheet for cans having excellent surface roughening resistance according to the above-mentioned [1], wherein a steel slab having the composition which contains by mass% 0.0040 to 0.01% C, 0.05% or less Si, more than 0.3 to 0.6% Mn, 0.02% or less P, 0.02% or less S, 0.01 to 0.10% Al, 0.0015 to 0.0050% N, 0.02 to 0.12% Nb and a balance of Fe and unavoidable impurities, wherein a Nb/C ratio is less than 0.8, subjected to hot rolling, a hot-rolled steel sheet is cooled at a cooling rate of 50 to 100°C/s within 1 second after final finish rolling, is wound at a winding temperature of 500°C to 600°C, is subsequently subjected to pickling treatment, thereafter, is subjected to cold rolling at a reduction rate of 90% or more, and is subjected to continuous annealing at a temperature of equal to or more than a recrystallization temperature to 800°C or below
Data Source
AI summary
Provided is a steel sheet having excellent surface roughening resistance and a manufacturing method thereof. The steel sheet for cans contains 0.0040 to 0.01% C and 0.02 to 0.12% Nb. An average ferrite grain size in a cross section in the rolling direction in a region ranging from a surface layer of the steel sheet to a position 1/4 of a sheet thickness away from the surface layer of the steel sheet is set to 7 µm or more and 10 µm or less, and the average ferrite grain size in a cross section in the rolling direction in a region ranging from the position 1/4 of a sheet thickness away from the surface layer of the steel sheet to a sheet thickness center portion of the steel sheet is set to 15 µm or less. The average ferrite grain size in the cross section in the rolling direction in the region ranging from the surface layer of the steel sheet to the position 1/4 of a sheet thickness away from the surface layer of the steel sheet is set smaller than the average ferrite grain size in the cross section in the rolling direction in a region ranging from the position 1/4 of a sheet thickness away from the surface layer of the steel sheet to the sheet thickness center portion of the steel sheet. The steel sheet for cans is obtained by cooling a steel sheet at 50 to 100°C/s within 1 second after final finish rolling, is wound at 500°C to 600°C, is subsequently subjected to pickling treatment, is subjected to cold rolling at a reduction rate of 90% or more, and is subjected to continuous annealing at a temperature of equal to or more than a recrystallization temperature to 800°C or below.