High Chromium Ferritic Stainless Steel for Solid Oxide Fuel Cell Interconnects

Abstract

The present invention relates to a steel sheet containing, as chemical components, C≦0.030 mass%, N≦0.030 mass%, Si 0.15 to 0.40 mass%, Mn 0.30 to 0.60 mass%, Cr 23.0 to 26.0 mass%, Nb 0.20 to 0.40 mass%, W 2.0 to 4.0 mass%, Mo≦0.50 mass%, Al≦0.10 mass%, one or more of rare earth elements La, Ce, Y, and Hf in a total amount of 0.05 to 0.20 mass%, the balance being Fe and unavoidable impurities, and 12≦(4w Nb +w W ) / w Si ≦20, provided that w Nb , w W , and w Si discloses a high-chromium ferritic stainless steel for solid oxide fuel cell interconnects, each containing Nb, W, and Si by mass percentage. The high-chromium ferritic stainless steel for solid oxide fuel cell interconnects of the present invention uses a high-chromium ferritic stainless steel as a matrix material and contains elements such as Si, Nb, and W in reasonable amounts. After oxidation at high temperatures of 600 to 900°C, a continuous, dense, and adherent oxide layer is formed on the surface of the stainless steel. Since the oxide layer does not contain Nb or Si oxides, excellent oxidation resistance and good electrical conductivity can be achieved simultaneously, and the requirements for use in solid oxide fuel cells can be met.

Description

[Technical Field]

[0001] The present invention relates to the technical field of stainless steel, and in particular to high chromium ferritic stainless steel for solid oxide fuel cell interconnects. [Background technology]

[0002] Solid oxide fuel cells (SOFCs) are power generation devices that directly convert the chemical energy of fuel into electrical energy. Their advantages are as follows: The system is not subject to the limitations of the Carnot cycle and achieves an energy conversion rate of 45-65%, significantly exceeding conventional power generation methods. They are environmentally friendly, emitting virtually no chlorine oxides or sulfur oxides and reducing carbon dioxide emissions by more than 40% compared to conventional power plants. They are highly adaptable to a variety of fuels, including hydrogen gas, petroleum liquefaction gas, natural gas, and coal gas. Other advantages of SOFCs include simple system design, high scalability, and a long lifespan. SOFCs can be used in large-scale fixed power plants, small-scale distributed combined heat and power plants, and auxiliary power systems for vehicles. They are an important strategic technology tool for mitigating environmental and energy crises and achieving a transition in the energy structure.

[0003] In SOFCs, interconnectors are a core component that ensures efficient and stable output of electrical energy. Solid oxide fuel cell interconnectors have two primary roles: first, to provide a pathway for electron transport adjacent to the cathode and anode of each cell, respectively; and second, to supply fuel gas and oxygen to the adjacent anode and cathode, respectively. During stack operation, a series of by-products are generated by electrode reactions, and the interconnector also serves to discharge these reaction products. To ensure smooth and efficient stack operation, interconnectors must possess certain physical and electrical properties. These properties include excellent oxidation resistance, a thermal expansion coefficient that matches the electrode electrolyte material, low surface resistance, and good mechanical properties. The first solid oxide fuel cell interconnects were made of LaCrO3 ceramic, but ceramic materials are expensive and difficult to process. With the development of SOFC technology, the operating temperature of SOFC systems is expected to fall below 900°C, making it possible to use stainless steel materials.

[0004] Currently, stainless steel for solid oxide fuel cell interconnectors has the following main problems:

[0005] First, solid oxide fuel cells (SOFCs) have a power generation temperature range of 600–900°C and a long operating time of 40,000 hours, making surface oxidation inevitable. Current alloys lack sufficient oxidation resistance, resulting in significant weight gain due to oxidation. Furthermore, the oxide layer peels off after prolonged oxidation, affecting system stability. Most steels used at such high temperatures contain Nb and Mo. However, after high-temperature oxidation, Nb forms Nb oxides (NbO / NbO2 / Nb2O5) between the oxide layer and the matrix. The Nb oxides diffuse through the oxide layer to the surface of the oxide layer, destabilizing the oxide layer's structure and increasing weight gain due to oxidation. Furthermore, because Mo oxide is volatile, the oxide layer of Mo-containing steels is prone to peeling, posing potential hazards and risks to the long-term use of SOFC systems.

[0006] Second, the conductivity of the oxide layer after high-temperature oxidation of the interconnector material is insufficient. Currently, Al and Si elements are generally added to alloys that require oxidation resistance, but when oxidized, a dense Al2O3 and SiO2 oxide layer is formed on the alloy surface. However, Al2O3 and SiO2 have very high resistivity at high temperatures (Al2O3: 5 x 10 at 700°C). 8 Ω·cm; SiO2: 7×10 at 600℃ 6 Ω·cm), the contact resistance between the interconnect and adjacent components increases dramatically, resulting in a significant drop in the power of the entire stack.

[0007] Therefore, it is a technical challenge that those skilled in the art must urgently solve to develop a stainless steel for solid oxide fuel cell interconnects that can form a continuous, dense, and adherent oxide layer on the surface of the product, and that has excellent oxidation resistance and good conductivity, thereby ensuring the operational stability of solid oxide fuel cell systems by not containing oxides of Nb or Si in the structure of the oxide layer. Summary of the Invention

[0008] In order to solve the above technical problems, the inventors have systematically studied the effects of the content of elements such as Cr, Mn, Si, Nb, and W on the microstructure and oxide layer structure of steel materials, and have provided a high-chromium ferritic stainless steel for solid oxide fuel cell interconnects by using high-chromium ferritic stainless steel as the matrix material and optimizing the element composition ratio.

[0009] Solid oxide fuel cells operate at temperatures between 600 and 900°C. To improve their oxidation resistance, the present invention uses high-chromium ferritic stainless steel as the matrix material. The higher the chromium content, the thinner the oxide layer and the better the oxidation resistance. However, due to its semiconducting properties, Cr2O3 does not meet the required electrical conductivity at high temperatures. Research by the inventors has shown that manganese oxides have good electrical conductivity, but manganese is more easily oxidized than chromium. Adding an appropriate amount of manganese to the alloy can form a (Mn,Cr)3O4 spinel structure in the outermost oxide layer, thereby improving electrical conductivity.

[0010] Ferritic stainless steels precipitate a second phase, the Laves phase, i.e., (Fe, Cr)2M (where M represents a metal element, such as Nb, W, Ti, or V), in the temperature range of 600 to 900°C. Research by the present inventors has shown that after oxidizing ferritic stainless steels at 600 to 900°C, a Laves phase forms in the matrix, but no second phase precipitates within a few hundred microns of the surface. Metal elements M, especially Nb, diffuse outward to the surface to form oxides, consuming Nb in the matrix, eliminating the conditions for Laves phase formation. Further research has revealed that under oxidizing conditions, there is a competitive relationship between the second phase precipitation process and the metal oxidation process within a few hundred microns of the surface of ferritic stainless steels. If the Laves phase formation rate is faster than that of the oxide, the Laves phase will form; otherwise, metal oxide will form.

[0011] Through long-term studies, the inventors have made the following two important discoveries.

[0012] First, the addition of Si element can increase the precipitation temperature of Laves phase, increase the nucleation sites of Laves phase, and promote the nucleation of Laves phase, and the combination of both can significantly accelerate the formation rate of Laves phase, thereby inhibiting the oxidation of metal element M (especially Nb).

[0013] Second, Si element replaces a part of metal element M to form a (Fe,Cr)2(M,Si) type Laves phase. Nb +w W +0.5(w Ti +w V )] / w Si <12, during long-term operation of SOFC, not all Si elements are dissolved in the Laves phase, and SiO2 oxide is formed in the oxide layer, resulting in a significant decrease in the conductivity of the interconnect material. Nb +w W +0.5(w Ti +w V )] / w Si When the condition 12≦[4w is satisfied, the content of Si element is insufficient, so that Nb element in the surface matrix preferentially forms oxide, leading to a large weight gain due to oxidation, and at the same time, the low Si content is not enough to support the deoxidation process, resulting in a large total oxygen content in the steel. Therefore, in the present invention, the contents of elements such as Si, Nb, and W are adjusted so that the Si element and the metal element M satisfy the condition 12≦[4w Nb +w W +0.5(w Ti +w V )] / w Si By rationally blending them so as to satisfy the condition of ≦20, all of the Si and Nb are formed in the Laves phase during oxidation, and do not exist on the surface to form oxides.

[0014] As described above, the present invention provides a high-chromium ferritic stainless steel for solid oxide fuel cell interconnects that combines excellent oxidation resistance and good electrical conductivity, is capable of forming a continuous, dense, and adherent oxide layer on the surface of the product, does not contain oxides of Nb or Si in the structure of the oxide layer, and can ensure the operational stability of the solid oxide fuel cell system.

[0015] Specifically, the high chromium ferritic stainless steel for a solid oxide fuel cell interconnector of the present invention contains, as chemical components, C≦0.030 mass%, N≦0.030 mass%, Si 0.15 to 0.40 mass%, Mn 0.30 to 0.60 mass%, Cr 23.0 to 26.0 mass%, Nb 0.20 to 0.40 mass%, W 2.0 to 4.0 mass%, Mo≦0.50 mass%, Al≦0.10 mass%, one or more of rare earth elements La, Ce, Y, and Hf in total 0.05 to 0.20 mass%, the balance being Fe and unavoidable impurities, and 12≦(4w Nb +w W ) / w Si ≦20, provided that w Nb , w W , and w Si indicates the mass percentage contents of Nb, W and Si, respectively.

[0016] Furthermore, the high chromium ferritic stainless steel for a solid oxide fuel cell interconnector further contains, as a chemical component, either or both of 0.02 to 0.10 mass % of Ti and 0.02 to 0.10 mass % of V, and has a Cr content of 12≦[4w Nb +w W +0.5(w Ti +w V )] / w Si ≦20, and (w Nb +w Ti +w V ) / (w C +w N ) ≧ 10, where w Ti , w V , w C , and w N indicates the mass percentage contents of Ti, V, C and N, respectively.

[0017] Furthermore, the above-mentioned high chromium ferritic stainless steel for a solid oxide fuel cell interconnector further contains, as chemical components, either or both of Mg≦0.0010 mass % and Ca≦0.0015 mass %.

[0018] Furthermore, the above-mentioned high chromium ferritic stainless steel for a solid oxide fuel cell interconnector further contains, as chemical components, either or both of Ni≦1.0 mass % and Co≦1.0 mass %.

[0019] Furthermore, the total oxygen content T[O] in the high chromium ferritic stainless steel for a solid oxide fuel cell interconnector is controlled to ≦50 ppm.

[0020] The high chromium ferritic stainless steel for solid oxide fuel cell interconnects of the present invention has the following advantages and beneficial effects:

[0021] The high chromium ferritic stainless steel for solid oxide fuel cell interconnects of the present invention uses high chromium ferritic stainless steel as a matrix material and rationalizes the content ratio of elements such as Si, Nb, and W, thereby simultaneously achieving excellent oxidation resistance and good electrical conductivity. After high-temperature oxidation at 600 to 900°C, which is the operating temperature range of solid oxide fuel cells, a continuous, dense, adhesive, and non-peeling oxide layer is formed on the surface, and the oxide layer structure does not contain oxides of Nb or Si. After oxidation in air for 1,000 hours, the weight gain due to oxidation is 1.5 mg / cm. 2 and a surface resistance of less than 40 mΩ cm 2 This ensures stable operation of the solid oxide fuel cell system.

[0022] In the present invention, by rationally controlling the contents of elements such as Si, Nb, and W, Si functions as a deoxidizing element, and it becomes possible to mass-produce the high chromium ferritic stainless steel for solid oxide fuel cell interconnects of the present invention on a conventional industrial production line using industrial raw materials through the process route of hot metal pretreatment, converter smelting, VOD refining, LF furnace refining, mold casting, blooming, hot rolling, annealing, pickling, cold rolling, and heat treatment, thereby significantly reducing production costs and improving production efficiency. It also makes it possible to manufacture finished high chromium ferritic stainless steel for solid oxide fuel cell interconnects with a thickness of 0.2 to 3.0 mm, which meets the thickness and performance requirements of interconnects in various design proposals for solid oxide fuel cell stacks and promotes the development of the solid oxide fuel cell industry. [Brief explanation of the drawings]

[0023] In order to more clearly describe the embodiments of the present invention or the technical solutions of the prior art, the following will briefly describe the drawings that need to be used in the description of the embodiments or the prior art. The drawings described in the following description are only some embodiments of the present invention, and it is obvious that those skilled in the art can derive other drawings from these drawings without any creative efforts.

[0024] [Figure 1] FIG. 1 is a surface scanning diagram of a cross-sectional component of an oxide layer of a high-chromium ferritic stainless steel for a solid oxide fuel cell interconnector according to Example 1 of the present invention. [Figure 2] FIG. 1 is a surface scanning diagram of a cross-sectional component of an oxidation layer of a stainless steel for a solid oxide fuel cell interconnector according to Comparative Example 1 as a conventional technique. [Figure 3] FIG. 10 is a surface scanning diagram of the cross-sectional components of the oxide layer of a stainless steel for a solid oxide fuel cell interconnector according to Comparative Example 4 as a conventional technique. DETAILED DESCRIPTION OF THE INVENTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described clearly and completely below with reference to specific embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, and are not all of the embodiments. Based on the embodiments of the present invention, all other embodiments that can be obtained by those skilled in the art without any creative efforts fall within the scope of protection of the present invention.

[0026] As described above, the high chromium ferritic stainless steel for a solid oxide fuel cell interconnector of the present invention contains, as chemical components, C≦0.030 mass%, N≦0.030 mass%, Si 0.15 to 0.40 mass%, Mn 0.30 to 0.60 mass%, Cr 23.0 to 26.0 mass%, Nb 0.20 to 0.40 mass%, W 2.0 to 4.0 mass%, Mo≦0.50 mass%, Al≦0.10 mass%, one or more of rare earth elements La, Ce, Y, and Hf in a total amount of 0.05 to 0.20 mass%, the balance being Fe and unavoidable impurities, and 12≦(4w Nb +w W ) / w Si ≦20, provided that w Nb , w W , and w Si indicates the mass percentage contents of Nb, W, and Si, respectively. The principle and effects of using the above-mentioned compounding ratios of chemical components in the present invention will be explained in detail as follows (the content "%" of each element represents mass percentage).

[0027] Both C and N deteriorate the oxidation resistance of stainless steel, so their upper limits should be limited. Taking into consideration the overall capacity and smelting costs, the range for both is controlled to ≦0.030%.

[0028] Cr plays a crucial role in the oxidation resistance of ferritic stainless steels, and increasing the chromium content improves the steel's oxidation resistance. In oxidizing environments, a dense oxide film, primarily composed of Cr2O3, forms on the steel surface, providing protective properties. Because SOFCs have a long operating time of 40,000 hours, the Cr content must be controlled to 23.0% or higher for oxidation resistance. However, if the Cr content exceeds 26.0%, the plasticity, toughness, and workability of ferritic stainless steels are significantly reduced, while the evaporation of Cr elements after high-temperature oxidation becomes severe, resulting in SOFC cathode poisoning. For this reason, the Cr content is controlled between 23.0 and 26.0%.

[0029] Because Mn oxidizes more easily than Cr, a Mn-rich (Mn,Cr)3O4 spinel structure is formed on the outside of Cr2O3 during the oxidation process, which significantly reduces electrical resistance and prevents, to some extent, cathode poisoning caused by evaporation of Cr. To form a continuous, dense (Mn,Cr)3O4 oxide layer, the minimum Mn content must be 0.30%. However, if the Mn content is too high, the oxide layer thickness increases rapidly, resulting in excessive weight gain due to oxidation. To avoid this, the upper limit is set at 0.60%.

[0030] Silicon is added as a deoxidizing element, making it possible to produce steel using industrial raw materials on standard industrial production lines. However, under the actual conditions of use, it raises the precipitation temperature of the Laves phase, promotes its nucleation, and dissolves in the Laves phase to form (Fe,Cr)2(M,Si). This prevents the formation of SiO2, which would reduce electrical conductivity, while suppressing the oxidation of elements such as metallic Nb on the surface of the material and ensuring the stability of the oxide film structure. Taking both of these functions into consideration, the silicon content is controlled to 0.15-0.40%.

[0031] Nb is added to ferritic stainless steels as an element that stabilizes C and N and is also significantly effective in improving high-temperature properties. In the present invention, Nb forms Laves phases at the operating temperatures of SOFCs, improving the high-temperature creep properties of steel materials. At the same time, the Laves phases segregate to grain boundaries, inhibiting atomic diffusion and slowing the oxidation rate. Taking both of these functions of Nb into consideration, the Nb content must be maintained at 0.20% or more. However, if the Nb content is too high, the coarsening rate of the Laves phases increases. Furthermore, after high-temperature oxidation, Nb forms oxides (NbO / NbO2 / Nb2O5) between the oxide layer and the matrix, which destabilizes the oxide film and increases the weight gain due to oxidation. Therefore, the upper limit of the Nb content is set at 0.40%.

[0032] W has a large atomic size and dissolves in ferrite as a substitute, improving the strength and hardness of the material. W increases the diffusion activation energy and can slow the diffusion of Cr at high temperatures, thereby improving oxidation resistance. In addition, W and Nb together promote the formation of the Laves phase, forming (Fe, Cr)2(Nb, W, Si). Adding W can suppress the coarsening rate of the Laves phase and ensure structural stability during long-term operation. To achieve the above two objectives, the W content is set to 2.0 to 4.0%.

[0033] Mo can promote the formation of Laves phase, but after high-temperature oxidation, Mo is likely to cause the oxide layer of the steel to peel off, worsening the adhesion between the oxide layer and the matrix, posing a significant risk to the stable operation of the system. Therefore, the Mo content must be kept below 0.50%.

[0034] Al is a strong deoxidizing element and forms needle-like Al2O3 in the matrix near the oxide layer at the operating temperature of SOFC. Al2O3 has a very high electrical resistance, which seriously affects the efficiency of SOFC stacks. Therefore, in this invention, the upper limit of Al content should be 0.10%.

[0035] Rare earth elements such as La, Ce, Y, and Hf can reduce the oxidation rate of steel, increase the density of the oxide layer, and improve the adhesion of the matrix, significantly improving the high-temperature oxidation resistance of steel. To ensure effective oxidation resistance, the lower limit of rare earth elements is 0.05%. If the rare earth content exceeds 0.20%, a large number of inclusions will form in the steel, which will affect the cold and hot workability of the steel.

[0036] Ti and V are added to steel as stabilizing elements, primarily to immobilize C and N. Because Ti and V carbonitrides exist stably at the operating temperature of SOFCs, the adverse effects of C and N on oxidation performance are suppressed. Ti and V also have the effect of promoting the precipitation of Laves phases. Taking these factors into consideration, the optimal control ranges for Ti and V are Ti: 0.02-0.10% and V: 0.02-0.10%, respectively.

[0037] Both Ni and Co are austenite-forming elements and are advantageous for improving the plasticity and toughness of steel. However, if the content is too high, the thermal expansion coefficient of the steel increases. Therefore, in the present invention, the upper limit of the Ni and Co elements is set to 1.0%.

[0038] Mg and Ca are both deoxidizing elements in ferritic stainless steel, and exist in the form of metal oxides in stainless steel sheets. To reduce the impact of inclusions on corrosion resistance, it is preferable to have low Mg and Ca contents, but considering smelting costs, Mg may be set to ≦0.0010% and Ca to ≦0.0015%. This allows the combined deoxidation with Si, Al, Mg, and Ca elements to control the total oxygen content T[O] in the steel to 50 ppm or less, minimize oxide-based inclusions, and allow rare earth elements to exist in the steel in solid solution as much as possible, thereby ensuring excellent oxidation resistance.

[0039] Furthermore, in order to reduce the adverse effect of Nb, Ti or V on the oxidation performance of C and N to a more desirable level, the content of the related elements is (w Nb +w Ti +w V ) / (w C +w N)≧10.

[0040] Furthermore, to prevent Si and Nb from forming oxides on the surface during oxidation, the content of related elements must be 12≦[4w Nb +w W +0.5(w Ti +w V )] / w Si Satisfy ≦20.

[0041] By rationally controlling the content of elements such as Si, Nb, and W, the precipitation temperature of the intermetallic Laves phase can be adjusted to ensure stable formation of the Laves phase in the stainless steel matrix within the operating temperature range. After oxidation for 1,000 hours in an air atmosphere (600-900°C), the structure of the oxide layer can be further controlled to prevent the formation of Si and Nb oxides in the oxide layer, which would affect the oxidation resistance and electrical conductivity of the material. In addition, by rationally controlling the contents of elements such as Si, Nb, and W, it is possible to produce the high chromium ferritic stainless steel for solid oxide fuel cell assemblies of the present invention using industrial raw materials on a conventional industrial production line through the process route of hot metal pretreatment, converter smelting, VOD refining, LF furnace refining, mold casting, blooming, hot rolling, annealing, pickling, cold rolling, and heat treatment.It also becomes possible to manufacture finished high chromium ferritic stainless steel for solid oxide fuel cell interconnects with a thickness of 0.2 to 3.0 mm, which can meet the thickness and performance requirements of interconnects in various design proposals for solid oxide fuel cell stacks.

[0042] According to the above-mentioned blending ratio of components, the high chromium ferritic stainless steel for solid oxide fuel cell interconnects has a continuous, dense oxide film without peeling after oxidation in an air atmosphere (600-900°C) for 1000 hours, and has good oxidation resistance and electrical conductivity, with no Nb or Si oxides present in the oxide layer. Furthermore, even after oxidation in air for 1000 hours, the weight gain due to oxidation is 1.5 mg / cm. 2 and a surface resistance of less than 40 mΩ cm 2 is less than.

[0043] Hereinafter, the high chromium ferritic stainless steel for a solid oxide fuel cell interconnector of the present invention will be described with reference to specific examples and comparative examples.

[0044] Table 1 below shows the chemical compositions of the high chromium ferritic stainless steels for solid oxide fuel cell interconnectors of Examples 1 to 6 of the present invention, and the chemical compositions of the stainless steels for solid oxide fuel cell interconnectors of Comparative Examples 1 to 4 as prior art.

[0045] [Table 1]

[0046] Table 2 shows the relationship between the contents of Nb, W, Ti, V, and Si in the high chromium ferritic stainless steel for solid oxide fuel cell interconnectors according to Examples 1 to 6 of the present invention [4w Nb +w W +0.5(w Ti +w V )] / w Si and the relational expression [4w Nb +w W +0.5(w Ti +w V )] / w Si In Examples 1 to 6 of the present invention, the contents of Nb, W, Ti, V, and Si are 12≦[4w Nb +w W +0.5(w Ti +w V )] / w Si ≦20, and in Comparative Examples 1 and 2, the contents of Nb, W, Ti, V, and Si are [4w Nb +w W +0.5(w Ti +w V )] / w Si >20, and in Comparative Examples 3 and 4, the contents of Nb, W, Ti, V, and Si were [4w Nb +w W +0.5(w Ti +w V )] / w Si<12 was found to be satisfied.

[0047] [Table 2]

[0048] The ten test steels for Examples 1-6 and Comparative Examples 1-4 were all produced using industrial raw materials on an industrial production line that included hot metal pretreatment, converter smelting, VOD refining, LF furnace refining, mold casting, blooming, hot rolling, annealing, pickling, cold rolling, and heat treatment. All 2.0 mm thick stainless steel products for solid oxide fuel cell interconnects were obtained. Three samples were prepared for each component, each measuring 30 mm x 15 mm. The ten test steel samples were oxidized in air at 900°C for 1,000 hours. The weights were measured before and after oxidation to calculate the weight gain due to oxidation (the average value of the three samples was taken). The surface resistance of the oxide layer on each sample was measured using a DC four-probe method. The samples were mechanically ground and polished perpendicular to the thickness direction, and the cross-sections of the oxide layer were observed using a scanning electron microscope to determine the compositional structure of the oxide layer. For the quantification parameters (weight gain due to oxidation, surface resistance of the oxide layer, and composition structure of the oxide layer) of the 10 types of test steels according to Examples 1 to 6 of the present invention and Comparative Examples 1 to 4, see Table 3 below. For the surface scan diagrams of the cross-sectional components of the oxide layers of the test steels according to Example 1 of the present invention, Comparative Example 1, and Comparative Example 4, see Figures 1, 2, and 3, respectively.

[0049] [Table 3]

[0050] When the structures and compositions of the oxide layers after high-temperature oxidation of alloys with different compositions shown in Figures 1 to 3 are compared with the experimental results in Tables 1, 2, and 3, it is clear that the weight gain due to oxidation is similar in Examples 1 to 6 of the present invention and Comparative Examples 3 and 4, but the weight gain due to oxidation is significantly higher in Comparative Examples 1 and 2. This is because the content of element Si in Comparative Examples 1 and 2 is insufficient, resulting in the formation of Nb oxide, Nb2O5, in the oxide layer, while the oxygen content in the steel increases significantly, causing more of the rare earth elements in the steel to exist in the form of oxides and not be able to dissolve in the matrix, thereby weakening the oxidation resistance.

[0051] Furthermore, in Examples 1 to 6, the oxide layer contains only (Mn, Cr)3O4 / Cr2O3, resulting in low surface resistance; in Comparative Examples 1 and 2, the oxide layer contains Nb2O5 in addition to (Mn, Cr)3O4 / Cr2O3, resulting in increased surface resistance; and in Comparative Examples 3 and 4, the oxide layer contains SiO2 in addition to (Mn, Cr)3O4 / Cr2O3, resulting in extremely high surface resistance, which is extremely detrimental to conductivity.

[0052] Comparing the data parameters in Figures 1 to 3 and Tables 1, 2, and 3, the results of the above comparison tests show that the high-chromium ferritic stainless steel for solid oxide fuel cell interconnects according to the embodiments of the present invention has both excellent oxidation resistance and electrical conductivity.

[0053] The high-temperature oxidation test of the above samples can be performed in accordance with GB / T 13303 "Test Method for Antioxidation of Steels." The above test standard is not the only standard, and other standards may be used for the test. However, the present invention does not limit the specific test method.

[0054] As described above, the high-chromium ferritic stainless steel for a solid oxide fuel cell interconnector of the present invention has the following advantages and beneficial effects compared to the prior art.

[0055] (1) The high-chromium ferritic stainless steel for solid oxide fuel cell interconnectors of the present invention uses high-chromium ferritic stainless steel as a matrix material and rationalizes the content ratio of elements such as Si, Nb, and W, thereby simultaneously achieving excellent oxidation resistance and good electrical conductivity. After high-temperature oxidation at 600 to 900°C, which is the operating temperature range of solid oxide fuel cells, a continuous, dense, and adherent oxide layer that does not peel off is formed on the surface, and the oxide layer structure does not contain oxides of Nb or Si. After oxidation for 1,000 hours in air, the weight gain due to oxidation is 1.5 mg / cm. 2 and a surface resistance of less than 40 mΩ cm 2 less than 1000 kJ / s, thereby ensuring the operational stability of the solid oxide fuel cell system.

[0056] (2) In the present invention, by rationally controlling the contents of elements such as Si, Nb, and W, Si functions as a deoxidizing element, and it becomes possible to mass-produce the high chromium ferritic stainless steel for solid oxide fuel cell interconnects of the present invention on an industrial scale using industrial raw materials in accordance with the process route of hot metal pretreatment, converter smelting, VOD refining, LF furnace refining, mold casting, blooming, hot rolling, annealing, pickling, cold rolling, and heat treatment on a conventional industrial production line, thereby significantly reducing production costs and improving production efficiency. It also makes it possible to manufacture finished high chromium ferritic stainless steel for solid oxide fuel cell interconnects with a thickness of 0.2 to 3.0 mm, which meets the thickness and performance requirements of interconnects in various design proposals for solid oxide fuel cell stacks and promotes the development of the solid oxide fuel cell industry.

[0057] It should be noted that, as used herein, the terms "comprise," "contain," or any other variation thereof, are intended to cover a non-exclusive inclusion, whereby a process, method, article, or apparatus comprising a set of elements is intended to include not only those elements but also other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0058] Furthermore, the above embodiments are only used to explain the technical solutions of the present invention, and do not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, it should be understood that those skilled in the art can modify the technical solutions described in the above embodiments or equally replace some technical features thereof, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. The chemical composition is C≦0.030 mass%, N≦0.030 mass%, Si 0.15 to 0.40 mass%, Mn 0.30 to 0.60 mass%, Cr 23.0 to 26.0 mass%, Nb 0.20 to 0.40 mass%, W 2.0 to 4.0 mass%, Mo≦0.50 mass%, Al≦0.10 mass%, one or more of rare earth elements La, Ce, Y and Hf in total 0.05 to 0.20 mass%, the balance being Fe and unavoidable impurities, and 12≦(4w Ｎｂ +w Ｗ ) / w Ｓｉ ≦20, provided that w Ｎｂ , w Ｗ , and w Ｓｉ A high-chromium ferritic stainless steel for a solid oxide fuel cell interconnect, characterized in that: indicates the mass percentage contents of Nb, W and Si, respectively.

2. The high chromium ferritic stainless steel has the following chemical composition: Further containing either one or both of Ti 0.02 to 0.10 mass% and V 0.02 to 0.10 mass%, And 12≦[4w Ｎｂ +w Ｗ +0.5 (w Ｔｉ +w Ｖ )] / w Ｓｉ ≦20, and (w Ｎｂ +w Ｔｉ +w Ｖ ) / (w Ｃ +w Ｎ ) ≧10, provided that w Ｔｉ , w Ｖ , w Ｃ , and w Ｎ 2. The high chromium ferritic stainless steel for a solid oxide fuel cell interconnect according to claim 1, wherein * denotes the mass percentage contents of Ti, V, C and N, respectively.

3. The high chromium ferritic stainless steel has the following chemical composition:

2. The high-chromium ferritic stainless steel for a solid oxide fuel cell interconnector according to claim 1, further containing either or both of Mg≦0.0010 mass % and Ca≦0.0015 mass %.

4. The high chromium ferritic stainless steel has the following chemical composition:

2. The high-chromium ferritic stainless steel for a solid oxide fuel cell interconnector according to claim 1, further containing either or both of Ni≦1.0 mass % and Co≦1.0 mass %.

5. The high chromium ferritic stainless steel for a solid oxide fuel cell interconnector according to any one of claims 1 to 4, characterized in that a total oxygen content T[O] in the high chromium ferritic stainless steel is controlled to ≦50 ppm.

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