Ferritic Stainless Steel Composition for SOFC Separator Conductivity
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Solution Overview
Problem
Ferritic stainless steels used as separators for solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOEC) face challenges such as high thermal expansion coefficients, decreased electron conductivity due to insulating oxide films, and reduced hot workability from excessive alloying elements.
Innovation Solution
A ferritic stainless steel composition is optimized with specific limits for elements like C, Si, Mn, P, S, Cu, Ni, Cr, Co, Al, Ti, N, La, V, Nb, Ta, and B to achieve a balance of low thermal expansion, high electron conductivity, excellent oxidation resistance, and improved hot workability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of Al is increased to improve oxidation resistance, then oxidation resistance is improved, but the thermal expansion coefficient increases and electron conductivity decreases
Solution Approach 1:
The patent optimizes the Al content parameter within a specific range (0.01-3.00 mass%) rather than using excessive amounts. This parameter optimization resolves the contradiction by finding the optimal balance point where oxidation resistance is sufficient while thermal expansion coefficient and electron conductivity are maintained within acceptable ranges.
Solution Approach 2:
The patent creates a composite alloy system combining multiple elements (Cr, Mn, Si, Mo, Ni, Al, Ti, Nb, V, B) in specific proportions. This composite approach allows the steel to achieve oxidation resistance through synergistic effects of multiple elements rather than relying excessively on Al, thereby avoiding the negative effects of high Al content on thermal expansion and conductivity.
2Reliability
If excessive alloying elements are added to improve oxidation resistance and strength, then oxidation resistance and strength are improved, but hot workability decreases
Solution Approach 1:
The patent optimizes the content parameters of multiple alloying elements within specific ranges rather than using excessive amounts. This parameter optimization resolves the contradiction by achieving sufficient oxidation resistance and strength while maintaining hot workability through balanced composition.
Solution Approach 2:
The patent employs a composite alloy system where multiple elements work synergistically at controlled concentrations. This composite approach achieves the required performance levels with smaller total alloy content, thereby maintaining hot workability while providing adequate oxidation resistance and strength.
3Reliability
If the content of Cr is increased to improve oxidation resistance, then oxidation resistance is improved, but the cost increases and hot workability decreases
Solution Approach 1:
The patent optimizes Cr content within a specific range (18.0-30.0 mass%) rather than using excessive amounts. This parameter optimization resolves the contradiction by achieving sufficient oxidation resistance while maintaining hot workability and controlling cost through balanced alloy design.
Solution Approach 2:
The patent combines Cr with multiple other alloying elements (Mn, Si, Mo, Ni, Al, Ti, Nb, V, B) in specific proportions to create a composite system. This composite approach allows Cr to work synergistically with other elements, reducing the total Cr content needed while maintaining oxidation resistance and improving hot workability.
Data Source
AI summary
The present invention relates to a ferritic stainless steel containing: 0 mass %<C≤0.03 mass %; Si≤0.05 mass %; 0.30 mass %≤Mn≤1.00 mass %; P≤0.05 mass %; S≤0.05 mass %; Cu≤0.10 mass %; Ni≤0.20 mass %; 20.0 mass %≤Cr≤25.0 mass %; Co≤0.10 mass %; Al≤0.10 mass %; 0.01 mass %≤Ti≤0.30 mass %; 0 mass %<N≤0.03 mass %; 0.05 mass %≤La≤0.30 mass %; and at least one element selected from the group consisting of: 0.05 mass %≤V≤2.00 mass %, 0.05 mass %≤Nb≤2.00 mass %, 0.05 mass %≤Ta≤0.30 mass %, and 0.0010 mass %≤B≤0.0100 mass %, with a balance being Fe and unavoidable impurities.