Austenitic Stainless Steel Foil for Repeated-Bending Fatigue
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Solution Overview
Problem
Existing austenitic stainless steel foils do not adequately address the need for enhanced fatigue strength, particularly in applications involving repeated bending stress, such as foldable smartphones.
Innovation Solution
Austenitic stainless steel foils with specific chemical compositions, including controlled levels of C, Si, Mn, P, S, Cr, Ni, N, and other elements, with a full width at half maximum (Fw) of a {111} plane in an X-ray diffraction profile greater than 0.366°, to enhance fatigue strength through increased dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional austenitic stainless steel foils are used, then manufacturing and processing are straightforward, but fatigue strength under repeated bending stress is insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.03-0.10%, Si: 0.10-2.00%, Mn: 0.10-2.00%, Cr: 16.00-20.00%, Ni: 6.00-10.50%, etc.) and processing parameters (cold rolling reduction ratio: 98% or more, final thickness: 100 μm or less) to achieve the desired fatigue strength while maintaining manufacturability
Solution Approach 2:
The patent applies preliminary action by controlling the size of inclusions to 7 μm or less before final product completion, and by subjecting the steel to repeated cold rolling and annealing processes in advance to control the total rolling reduction ratio to 98% or more, thereby pre-establishing the microstructure needed for high fatigue strength
2Length of moving object
If the foil thickness is reduced to 100 μm or less, then the foil becomes more suitable for electronic equipment applications, but the fatigue strength may be compromised
Solution Approach 1:
The patent simultaneously optimizes multiple parameters: reduces thickness to 100 μm or less while controlling chemical composition (particularly Cr: 16.00-20.00% and Ni: 6.00-10.50%) and processing parameters (rolling reduction ratio: 98% or more) to maintain fatigue strength despite the reduced thickness
Solution Approach 2:
The patent creates a composite microstructure by controlling the phases present in the steel foil, specifically managing the austenitic phase along with controlled amounts of other phases through precise composition control and thermomechanical processing, resulting in a multi-phase microstructure that provides both thinness and fatigue resistance
3Strength
If repeated cold rolling and annealing are performed to control rolling reduction ratio at 98% or more, then fatigue strength is improved, but manufacturing time and energy consumption increase
Solution Approach 1:
The patent applies preliminary action by performing repeated cold rolling and annealing processes during the manufacturing stage to establish the desired microstructure and achieve 98% or more total rolling reduction ratio, so that the fatigue strength is built into the material structure before final product completion, reducing the need for additional post-processing steps
Solution Approach 2:
The patent optimizes the balance between processing intensity and time by controlling the total rolling reduction ratio parameter to 98% or more while managing the chemical composition parameters, achieving high fatigue strength through optimized parameter combinations that reduce the number of processing cycles needed
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 foils exhibit superior fatigue strength and durability under repeated bending stress, minimizing permanent deformation and extending the number of cycles before failure.
Implementation Method 1
in an X-ray diffraction profile obtained using CuKα radiation, a full width at half maximum Fw of a peak of a {111} plane is greater than 0.366°
Data Source
AI summary
An austenitic stainless steel foil according to this disclosure consists of, in mass %, C: 0.150% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.0300% or less, Cr: 16.00 to 20.00%, Ni: 6.00 to 10.50%, N: 0.100% or less, Mo: 0 to 2.50%, Nb: 0 to 0.12%, V: 0 to 1.00%, Ta: 0 to 0.50%, Hf: 0 to 0.10%, Co: 0 to 0.50%, B: 0 to 0.0100%, Ca: 0 to 0.0200%, Mg: 0 to 0.0200%, rare earth metal: 0 to 0.0100%, Al: 0 to 0.010%, Ti: 0 to 0.500%, Zr: 0 to 0.100%, and Cu: 0 to 3.00%, with the balance being Fe and impurities. In an X-ray diffraction profile obtained using CuKα radiation, a full width at half maximum Fw of a peak of a {111} plane is greater than 0.366°.