High chromium ferritic stainless steel for solid oxide fuel cell interconnects

Abstract

The present invention discloses a high chromium ferrite stainless steel for a solid oxide fuel cell connector, comprising the following chemical components by mass percentage: C≤0.030%, N≤0.030%, Si: 0.15-0.40%, Mn: 0.30-0.60%, Cr: 23.0-26.0%, Nb: 0.20-0.40%, W: 2.0-4.0%, Mo≤0.50%, Al≤0.10%, and a total amount of 0.05-0.20% of one or more of the rare earth elements La, Ce, Y and Hf, with the remainder being Fe and unavoidable impurities, and 12≤(4w Nb +w W ) / w Si ≤20, where w Nb 、w W and w Si The high-chromium ferritic stainless steel for a solid oxide fuel cell interconnect of the present invention uses high-Cr ferritic stainless steel as a base material. By rationally matching the contents of elements such as Si, Nb, and W, a continuous, dense, and well-adhesive oxide layer forms on the stainless steel surface after high-temperature oxidation at 600 to 900°C. The oxide layer contains no Nb and Si oxides, achieving both excellent oxidation resistance and good electrical conductivity, meeting the requirements for use in solid oxide fuel cells.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel, and in particular relates to a high-chromium ferrite stainless steel for a solid oxide fuel cell connector. Background Art

[0002] Solid oxide fuel cells (SOFCs) are power generation devices that convert the chemical energy of fuel directly into electrical energy. They offer the following advantages: The system is not constrained by the Carnot cycle, and the energy conversion rate can reach 45-65%, significantly higher than traditional power generation methods. They are environmentally friendly, emitting virtually no chlorine oxides and sulfur oxides, and reducing carbon dioxide emissions by over 40% compared to conventional power plants. They are also highly adaptable to fuels, operating not only with hydrogen but also with a variety of other gases, including liquefied petroleum gas, natural gas, and coal gas. Furthermore, SOFCs offer advantages such as simple system design, scalability, and a long lifespan. SOFCs can be used in a variety of applications, from large-scale stationary power plants to small, distributed combined heat and power units and auxiliary power systems for vehicles. They are a strategically important technological tool for alleviating environmental and energy crises and achieving energy transition.

[0003] In SOFCs, the interconnect is a core component for achieving efficient and stable power output. Solid oxide fuel cell interconnects have two primary functions: first, they are adjacent to the cathode and anode of a single cell, providing a pathway for electron transfer; second, they provide fuel gas and oxygen to the adjacent anode and cathode, respectively. During stack operation, electrode reactions produce a series of byproducts, and the interconnect also serves to remove these byproducts. To ensure smooth and efficient stack operation, the interconnect must possess certain physical and electrical properties: excellent oxidation resistance, a thermal expansion coefficient that matches the electrode and electrolyte materials, low surface resistance, and good mechanical properties. Initial solid oxide fuel cell interconnects used LaCrO3 ceramic, but ceramics are expensive and difficult to process. With the advancement of SOFC technology, the operating temperature of SOFC systems has dropped below 900°C, paving the way for the use of stainless steel.

[0004] There are currently several major problems with stainless steel used in solid oxide fuel cell connectors:

[0005] First, the temperature range of solid oxide fuel cell power generation is 600-900℃, and the operating time is as long as 40,000 hours, so surface oxidation is inevitable. Currently, the alloy's oxidation resistance is insufficient, oxidation weight gain is large, and after long-term oxidation, the oxide layer peels off, affecting the stability of the system. Most of this type of steel, which serves for a long time at high temperatures, contains Nb and Mo elements in its composition design. After high-temperature oxidation, Nb will form Nb oxide (NbO / NbO2 / Nb2O5) between the oxide layer and the matrix. Nb oxide will even diffuse through the oxide layer to the surface of the oxide scale, resulting in an unstable oxide scale structure and increased oxidation weight gain. Mo oxide is volatile, so the oxide scale of Mo-containing steel is extremely easy to peel off, posing hidden dangers and risks to the long-term use of solid oxide fuel cell systems.

[0006] Second, the conductivity of the oxide layer of the interconnect material after high-temperature oxidation is insufficient. Currently, Al and Si elements are often added to alloys that require oxidation resistance. After oxidation, dense Al2O3 and SiO2 oxide layers are formed on the alloy surface. However, the resistivity of Al2O3 and SiO2 is very high at high temperatures (Al2O3: 5×10 at 700°C). 8 Ω·cm; SiO2: 7×10 at 600℃ 6 Ω·cm), which causes the contact resistance between the connector and the adjacent components to increase sharply, thereby significantly attenuating the power of the entire battery stack.

[0007] Therefore, developing a stainless steel for solid oxide fuel cell connectors that has both excellent antioxidant properties and good electrical conductivity, where a continuous, dense, and well-adhesive oxide layer can be formed on the surface of the product, and where the oxide layer structure does not contain Nb and Si oxides, thereby ensuring the stability of the operation of the solid oxide fuel cell system, has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0008] To solve the above technical problems, the inventors systematically studied the effects of the contents of elements such as Cr, Mn, Si, Nb and W on the microstructure and oxide layer structure of steel. Using high-Cr ferritic stainless steel as the matrix material and through a reasonable element ratio, they provided a high-chromium ferritic stainless steel for solid oxide fuel cell connectors.

[0009] The operating temperature range of solid oxide fuel cells is 600-900°C. To improve its oxidation resistance, the present invention uses high-Cr ferritic stainless steel as the base material. The higher the Cr content, the thinner the oxide layer and the better the oxidation resistance. However, Cr2O3 has semiconductor properties and its conductivity at high temperatures cannot meet the requirements. The inventors have found that Mn oxide has better conductivity and Mn is more easily oxidized than Cr. Adding an appropriate amount of Mn to the alloy can form a (Mn,Cr)3O4 spinel structure in the outermost layer of the oxide layer, thereby improving the conductivity.

[0010] Ferritic stainless steel will precipitate a second phase in the temperature range of 600-900°C: the Laves phase, i.e., (Fe,Cr)2M, where M represents metal elements such as Nb, W, Ti, and V. The inventors have found that after ferritic stainless steel is oxidized at 600-900°C, a Laves phase forms in the matrix, while no second phase precipitates within a few hundred microns of the surface. The metal element M, especially Nb, diffuses outward to the surface to form oxides, consuming the Nb in the matrix, and therefore does not have the conditions for the formation of the Laves phase. Further research has shown that under oxidizing conditions, within a few hundred microns of the surface of ferritic stainless steel, the second phase precipitation process and the metal oxidation process compete with each other. If the formation rate of the Laves phase is greater than that of the oxide, the Laves phase is formed; otherwise, a metal oxide is formed.

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

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

[0013] Second, Si will partially replace the metal element M to form a (Fe,Cr)2(M,Si) type Laves phase. When Si and metal element M meet the conditions [4w Nb +w W +0.5(w Ti +w V )] / w Si When the Si element is less than 12, during the long-term operation of SOFC, the Si element cannot be completely dissolved in the Laves phase, and SiO2 oxide will be formed in the oxide layer, resulting in a significant decrease in the conductive properties of the interconnect material; when the Si element and the metal element M meet the conditions [4w Nb +w W +0.5(w Ti +w V )] / w SiWhen the Si content is relatively insufficient, the Nb element in the surface matrix preferentially forms oxides, which increases the oxidation weight gain. At the same time, the low Si content is insufficient to support the deoxidation process, resulting in a high total oxygen content in the steel. Therefore, the present invention makes a reasonable ratio of the content of Si, Nb, W and other elements, so that the Si element and the metal element M meet the condition 12≤[4w Nb +w W +0.5(w Ti +w V )] / w Si ≤20, therefore, during oxidation, Si and Nb can all be formed in the Laves phase without forming oxides on the surface.

[0014] In summary, the present invention provides a high-chromium ferritic stainless steel for a solid oxide fuel cell connector. The high-chromium ferritic stainless steel has both excellent antioxidant properties and good electrical conductivity. A continuous, dense, and well-adhesive oxide layer can be formed on the surface of the product. At the same time, the oxide layer structure does not contain Nb and Si oxides, thereby ensuring the stability of the operation of the solid oxide fuel cell system.

[0015] Specifically, the high chromium ferritic stainless steel for solid oxide fuel cell connector of the present invention contains the following chemical composition by mass percentage: C≤0.030%, N≤0.030%, Si: 0.15-0.40%, Mn: 0.30-0.60%, Cr: 23.0-26.0%, Nb: 0.20-0.40%, W: 2.0-4.0%, Mo≤0.50%, Al≤0.10%, and one or more of the rare earth elements La, Ce, Y and Hf with a total amount of 0.05-0.20%, and the rest is Fe and unavoidable impurities, and 12≤(4w Nb +w W ) / w Si ≤20, where w Nb 、w W and w Si represent the mass percentage contents of Nb, W and Si respectively.

[0016] Furthermore, the high chromium ferrite stainless steel for the solid oxide fuel cell connector further comprises any one or two of the following chemical components by mass percentage: Ti: 0.02-0.10%, V: 0.02-0.10%, 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, where w Ti 、w V 、w C and w N Represent the mass percentage contents of Ti, V, C and N respectively.

[0017] Furthermore, the high chromium ferrite stainless steel for the solid oxide fuel cell interconnect further comprises any one or two of the following chemical components in percentage by mass: Mg≤0.0010%, Ca≤0.0015%.

[0018] Furthermore, the high chromium ferrite stainless steel for the solid oxide fuel cell interconnect further comprises any one or two of the following chemical components in percentage by mass: Ni≤1.0%, Co≤1.0%.

[0019] Furthermore, the total oxygen content T[O] in the high chromium ferrite stainless steel for the solid oxide fuel cell interconnect is controlled to be T[O]≤50ppm.

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

[0021] The high-chromium ferritic stainless steel for the solid oxide fuel cell connector of the present invention uses high-Cr ferritic stainless steel as the base material. By rationally matching the contents of elements such as Si, Nb, and W, it can simultaneously achieve excellent oxidation resistance and good electrical conductivity. After high-temperature oxidation in the operating temperature range of 600-900°C for the solid oxide fuel cell, a continuous, dense, well-adhesive, and non-flaking oxide layer is formed on the surface. The oxide layer structure does not contain Nb and Si oxides. Moreover, after oxidizing in air for 1000 hours, the oxidation weight gain is less than 1.5 mg / cm 2 , surface resistance is less than 40mΩ·cm 2 , thereby ensuring the stability of the operation of the solid oxide fuel cell system;

[0022] The present invention rationally controls the contents of elements such as Si, Nb, and W, and can use Si as a deoxidizing element, so that the high-chromium ferritic stainless steel for the solid oxide fuel cell connector of the present invention can be industrially produced in batches on a conventional industrial production line using industrial raw materials according to a process route of molten iron pretreatment, converter smelting, VOD refining, LF furnace refining, die casting, cogging, hot rolling, annealing, pickling, cold rolling, and heat treatment. This can significantly reduce production costs, improve production efficiency, and realize the preparation of high-chromium ferritic stainless steel products for the solid oxide fuel cell connector with a thickness of 0.2 to 3.0 mm, meeting the requirements of different solid oxide fuel cell stack design schemes for connector thickness and performance, and promoting the development of the solid oxide fuel cell industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide a further understanding of the embodiments of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0024] Figure 1 This is a scanning diagram of the cross-sectional composition of the oxide layer of high-chromium ferrite stainless steel used in the solid oxide fuel cell interconnect according to an embodiment of the present invention;

[0025] Figure 2 A scanning diagram of the cross-sectional composition of the oxide layer of stainless steel for a solid oxide fuel cell interconnector according to Comparative Example 7 of the prior art;

[0026] Figure 3 This is a scanning diagram of the cross-sectional composition of the oxide layer of stainless steel used for a solid oxide fuel cell interconnector in comparative example 10 of the prior art. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] As described above, the high chromium ferritic stainless steel for the solid oxide fuel cell interconnect of the present invention contains the following chemical composition by mass percentage: C≤0.030%, N≤0.030%, Si: 0.15-0.40%, Mn: 0.30-0.60%, Cr: 23.0-26.0%, Nb: 0.20-0.40%, W: 2.0-4.0%, Mo≤0.50%, Al≤0.10%, and one or more of the rare earth elements La, Ce, Y and Hf in a total amount of 0.05-0.20%, the remainder being Fe and unavoidable impurities, and 12≤(4w Nb +w W ) / w Si ≤20, where w Nb 、w W and w Si The principle and effect of the above chemical composition ratios of the present invention are described in detail as follows (the content of each element "%" represents the mass percentage):

[0029] Both C and N deteriorate the oxidation resistance of stainless steel, and their upper limits should be controlled. Taking into account equipment capacity and smelting costs, the control range of both is ≤0.030%.

[0030] Cr plays a decisive role in the oxidation resistance of ferritic stainless steel. As the chromium content increases, the steel's oxidation resistance gradually improves. In an oxidizing environment, a dense, protective oxide film composed primarily of Cr2O3 forms on the steel surface. Because SOFCs operate for up to 40,000 hours, the Cr content needs to be controlled above 23.0% for oxidation resistance. However, above 26.0% Cr significantly reduces the ductility, toughness, and processing properties of ferritic stainless steel. Furthermore, high-temperature oxidation accelerates Cr evaporation, leading to SOFC cathode poisoning. Therefore, the Cr content is controlled between 23.0 and 26.0%.

[0031] Mn is more easily oxidized than Cr. During the oxidation process, it forms a Mn-rich (Mn,Cr)3O4 spinel structure on the outside of the Cr2O3, significantly reducing resistance and, to a certain extent, preventing Cr evaporation and cathode poisoning. To form a continuous, dense (Mn,Cr)3O4 oxide layer, a minimum Mn content of 0.30% is required. However, excessive Mn content causes the oxide layer thickness to increase rapidly, resulting in excessive oxidation weight gain. To avoid this, the upper limit is set at 0.60%.

[0032] On the one hand, Si acts as a deoxidizing element, enabling the production of steel using industrial raw materials on conventional industrial production lines. On the other hand, under actual operating conditions, Si increases the precipitation temperature of the Laves phase, promoting its nucleation. It then dissolves in the Laves phase to form (Fe, Cr)2(M, Si), preventing the formation of SiO2 that reduces electrical conductivity. It also inhibits the oxidation of metallic elements like Nb on the surface of the material, ensuring the stability of the oxide scale structure. To balance these two aspects of Si's role, the Si content should be controlled between 0.15% and 0.40%.

[0033] In ferritic stainless steel, Nb is added as a stabilizing element for C and N, and secondly, Nb has a significant effect in improving high-temperature performance. In the present invention, Nb forms a Laves phase at the SOFC operating temperature, which improves the high-temperature creep performance of the steel. At the same time, the Laves phase segregates at the grain boundaries, which can hinder atomic diffusion and play a role in slowing down the oxidation rate. Taking into account the two effects of the Nb element, the Nb element content needs to be maintained at more than 0.20%. However, if the Nb content is too high, the Laves phase will coarsen too quickly. In addition, after high-temperature oxidation, Nb will form oxides (NbO / NbO2 / Nb2O5) between the oxide layer and the matrix, resulting in unstable oxide scale structure and increased oxidation weight gain. Therefore, the upper limit of Nb content is 0.40%.

[0034] W, due to its large atomic size, dissolves in ferrite by substitution, increasing the material's strength and hardness. W increases the diffusion activation energy and slows the diffusion of Cr at high temperatures, thereby improving oxidation resistance. Furthermore, W and Nb jointly promote the formation of the Laves phase, forming (Fe,Cr)2(Nb,W,Si). The addition of W inhibits the coarsening rate of the Laves phase, thereby ensuring structural stability during long-term operation. To achieve these two objectives, the W content is controlled between 2.0 and 4.0%.

[0035] Mo promotes the formation of Laves phase, but after high-temperature oxidation, Mo can easily cause the steel oxide layer to flake off, deteriorating the adhesion between the oxide layer and the substrate, and posing a significant risk to the stable operation of the system. Therefore, the Mo content must be controlled below 0.50%.

[0036] Al is a strong deoxidizing element. At SOFC operating temperatures, Al forms needle-shaped Al2O3 in the matrix near the oxide layer. This Al2O3 has very high resistance, seriously affecting the efficiency of the SOFC stack. Therefore, in the present invention, the upper limit of its content is controlled to 0.10%.

[0037] 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 the adhesion of the substrate, and significantly improve the steel's high-temperature oxidation resistance. To ensure effective oxidation resistance, the lower limit of rare earth elements is 0.05%. When the rare earth content exceeds 0.20%, a large number of inclusions will form in the steel, affecting the steel's cold and hot working properties.

[0038] Ti and V are added to steel as stabilizing elements, primarily to fix carbon and nitrogen. Their carbonitrides are stable at SOFC operating temperatures, suppressing the adverse effects of carbon and nitrogen on oxidation resistance. Ti and V also promote the precipitation of Laves phases. Taking all these factors into account, the optimal control ranges for Ti and V are 0.02-0.10% for Ti and 0.02-0.10% for V, respectively.

[0039] Both Ni and Co are austenite-forming elements, which contribute to the ductility and toughness of steel. However, excessive Ni and Co contents can increase the thermal expansion coefficient of steel. Therefore, in the present invention, the upper limit of Ni and Co is 1.0%.

[0040] Mg and Ca are both deoxidizing elements in ferritic stainless steel. In stainless steel plates, Mg and Ca exist in the form of metal oxides. To reduce the impact of inclusions on corrosion resistance, the lower the Mg and Ca content, the better. However, considering smelting costs, Mg can be controlled to ≤ 0.0010% and Ca ≤ 0.0015%, respectively. Therefore, through the composite deoxidation of Si, Al, Mg, and Ca elements, the total oxygen content T[O] in the steel is controlled below 50ppm, oxide inclusions are minimized, and rare earth elements are present in the steel in a solid solution state as much as possible, thus ensuring excellent oxidation resistance.

[0041] Furthermore, in order to reduce the adverse effects of C and N on the antioxidant properties to a more ideal level through Nb, Ti or V, the contents of the relevant elements meet the following requirements (w Nb +w Ti +w V ) / (w C +w N )≥10.

[0042] Furthermore, in order to ensure that Si and Nb do not form oxides on the surface during oxidation, the content of related elements satisfies 12≤[4w Nb +w W +0.5(w Ti +w V )] / w Si ≤20.

[0043] Thus, by rationally controlling the contents of elements such as Si, Nb, and W, the precipitation temperature of the intermetallic compound Laves phase is adjusted, the Laves phase is stably formed in the stainless steel matrix within the service temperature range, and after oxidation at (600-900)°C in an air atmosphere for 1000h, the oxide layer structure is further controlled to prevent the formation of Si and Nb oxides in the oxide layer from affecting the material's oxidation resistance and electrical conductivity. Furthermore, by rationally controlling the contents of elements such as Si, Nb, and W, the high-chromium ferritic stainless steel for the solid oxide fuel cell interconnect of the present invention can be produced using industrial raw materials on a conventional industrial production line in the order of molten iron pretreatment, converter smelting, VOD refining, LF furnace refining, die casting, cogging, hot rolling, annealing, pickling, cold rolling, and heat treatment. Furthermore, the preparation of a finished high-chromium ferritic stainless steel product for the solid oxide fuel cell interconnect with a thickness of 0.2 to 3.0 mm can be achieved, meeting the requirements for interconnect thickness in different solid oxide fuel cell stack designs.

[0044] Based on the above composition ratio, after the high chromium ferrite stainless steel used for the solid oxide fuel cell connector is oxidized at (600-900)℃ in air for 1000h, the oxide scale is continuous and dense without peeling, and there is no Nb and Si oxide in the oxide layer, which has good oxidation resistance and electrical conductivity. In addition, after oxidizing in air for 1000h, the oxidation weight gain is less than 1.5mg / cm 2 , surface resistance is less than 40mΩ·cm 2 .

[0045] The high chromium ferrite stainless steel for the solid oxide fuel cell interconnect of the present invention is described below with reference to specific examples and comparative examples.

[0046] Table 1 below shows the chemical compositions of high chromium ferrite stainless steel for solid oxide fuel cell interconnects according to Examples 1 to 6 of the present invention and the chemical compositions of stainless steel for solid oxide fuel cell interconnects according to Comparative Examples 1 to 4 of the prior art.

[0047] Table 1 Content of various elements in stainless steel for solid oxide fuel cell connectors (unit: mass percentage)

[0048]

[0049] Table 2 shows the relationship between the contents of Nb, W, Ti, V, and Si in the high chromium ferrite stainless steel for the interconnects of solid oxide fuel cells of Examples 1 to 6 of the present invention [4w Nb +w W +0.5(w Ti +w V )] / w Si The specific values ​​of and the content relationship formula of Nb, W, Ti, V, and Si in the stainless steel for solid oxide fuel cell interconnects of comparative examples 1 to 4 of the prior art [4w Nb +w W +0.5(w Ti +w V )] / w Si It can be seen that in Examples 1 to 6 of the present invention, the contents of Nb, W, Ti, V, and Si satisfy 12≤[4w Nb +w W +0.5(w Ti +w V )] / w Si ≤20, in Comparative Examples 1-2, the contents of Nb, W, Ti, V, and Si satisfy [4w Nb +w W +0.5(w Ti +w V )] / w Si>20, in Comparative Examples 3-4, the contents of Nb, W, Ti, V, and Si satisfy [4w Nb +w W +0.5(w Ti +w V )] / w Si <12.

[0050] Table 2 Relationship between the contents of Nb, W, Ti, V, and Si in stainless steel for solid oxide fuel cell connectors

[0051]

[0052]

[0053] The ten test steels of 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, die casting, cogging, hot rolling, annealing, pickling, cold rolling, and heat treatment. The resulting stainless steel products for solid oxide fuel cell interconnects each had a thickness of 2.0 mm. Three samples of each component were prepared, each measuring 30 mm x 15 mm. The ten test steel samples were oxidized in air at 900°C for 1000 h. The weights before and after oxidation were measured, and the oxidation weight gain was calculated (the average of the three samples was taken). The sheet resistance of the oxide layer of the samples was measured using a DC four-terminal method. The samples were mechanically ground and polished perpendicular to the thickness of the samples, and then the oxide layer cross-sections were observed using a scanning electron microscope to provide the composition and structure of the oxide layer. The quantitative parameters (oxidation weight gain, oxide layer resistance, oxide layer composition structure) of the 10 test steels of Examples 1 to 6 of the present invention and Comparative Examples 1 to 4 are shown in Table 3 below. The cross-sectional composition scanning diagrams of the oxide layers of the test steels of Example 1, Comparative Example 7 and Comparative Example 10 of the present invention are shown in Table 3 below. Figure 1 、 Figure 2 and Figure 3 .

[0054] Table 3 Quantitative parameters of stainless steel for solid oxide fuel cell connectors

[0055]

[0056] from Figures 1 to 3From the structures and compositions of the oxide layers of the alloys with different compositions shown above after high-temperature oxidation, combined with the experimental results in Tables 1, 2, and 3, it can be seen that the oxidation weight gains of Examples 1 to 6 of the present invention and Comparative Examples 3 to 4 are comparable, while the oxidation weight gains of Comparative Examples 1 to 2 are significantly increased. This is because the Si content in Comparative Examples 1 to 2 is insufficient. On the one hand, Nb oxide Nb2O5 is formed in the oxide layer. On the other hand, the oxygen content in the steel is significantly increased, causing more rare earth elements in the steel to exist in the form of oxides and unable to be dissolved in the matrix, resulting in weakened oxidation resistance.

[0057] In addition, the oxide layers of Examples 1 to 6 only contain (Mn,Cr)3O4 / Cr2O3, and the surface resistance is relatively low; in addition to (Mn,Cr)3O4 / Cr2O3, the oxide layers of Comparative Examples 1 to 2 also contain Nb2O5, which significantly increases the surface resistance; in addition to (Mn,Cr)3O4 / Cr2O3, the oxide layers of Comparative Examples 3 to 4 also form SiO2, which is very unfavorable to the conductive performance due to its high resistance.

[0058] Combine Figures 1 to 3 Combined with the comparison of the data parameters in Table 1, Table 2 and Table 3, the above comparative test results show that the high chromium ferritic stainless steel for the solid oxide fuel cell connector according to the embodiment of the present invention can have both excellent oxidation resistance and electrical conductivity.

[0059] It should be noted that the high-temperature oxidation test of the above-mentioned specimens can be conducted in accordance with GB / T 13303, "Test Method for Oxidation Resistance of Steel." It should also be noted that the above-mentioned test standard is not exclusive and other standards may be used for the test. This invention does not limit the specific test method.

[0060] In summary, compared with the prior art, the high chromium ferrite stainless steel for the solid oxide fuel cell interconnect of the present invention has the following advantages and beneficial effects:

[0061] (1) The high-chromium ferritic stainless steel for the solid oxide fuel cell connector of the present invention uses high-Cr ferritic stainless steel as the base material. By rationally matching the contents of Si, Nb, W and other elements, it can simultaneously achieve excellent oxidation resistance and good electrical conductivity. After high-temperature oxidation in the operating temperature range of 600-900°C of the solid oxide fuel cell, a continuous, dense, well-adhesive and non-flaking oxide layer is formed on the surface. At the same time, the oxide layer structure does not contain Nb and Si oxides. Moreover, after oxidation in air for 1000 hours, the oxidation weight gain is less than 1.5 mg / cm 2 , surface resistance is less than 40mΩ·cm 2 , thereby ensuring the stability of the operation of the solid oxide fuel cell system.

[0062] (2) The present invention reasonably controls the content of elements such as Si, Nb, and W, and can use Si as a deoxidizing element so that the high chromium ferritic stainless steel for the solid oxide fuel cell connector of the present invention can be mass-produced on a conventional industrial production line using industrial raw materials according to the process route of molten iron pretreatment, converter smelting, VOD refining, LF furnace refining, die casting, blanking, hot rolling, annealing, pickling, cold rolling and heat treatment. This can significantly reduce production costs, improve production efficiency, and achieve the preparation of high chromium ferritic stainless steel products for solid oxide fuel cell connectors with a thickness of 0.2 to 3.0 mm, meeting the requirements of different design schemes of solid oxide fuel cell stacks on connector thickness and performance, and promoting the development of the solid oxide fuel cell industry.

[0063] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A high chromium ferrite stainless steel for a solid oxide fuel cell connector, characterized in that: The high chromium ferritic stainless steel contains the following chemical components by mass percentage: C≤0.030%, N≤0.030%, Si: 0.15-0.40%, Mn: 0.30-0.60%, Cr: 23.0-26.0%, Nb: 0.20-0.40%, W: 2.0-4.0%, Mo≤0.50%, Al≤0.10%, Ti: 0.02-0.10%, V: 0.02-0.10%, and one or more of the rare earth elements La, Ce, Y and Hf in a total amount of 0.05-0.20%, and the rest is Fe and unavoidable impurities; And 12≤(4w Nb +w W ) / w Si ≤20, where w Nb 、w W and w Si Represent the mass percentage contents of Nb, W and Si respectively; 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, where w Ti 、w V 、w C and w N Represent the mass percentage contents of Ti, V, C and N respectively; The solid oxide fuel cell connector is made of high chromium ferrite stainless steel and oxidized in air at 600-900°C for 1000 hours. The oxide scale is continuous and dense without peeling, Si and Nb are completely transformed into Laves phase, and there is no Nb and Si oxide in the oxide layer. The connector has good oxidation resistance and electrical conductivity. Moreover, after oxidizing in air for 1000 hours, the oxidation weight gain is less than 1.5 mg / cm 2 , surface resistance is less than 40mΩ·cm 2 .

2. The high chromium ferrite stainless steel for a solid oxide fuel cell interconnect according to claim 1, characterized in that: The high chromium ferritic stainless steel further comprises any one or two of the following chemical components by mass percentage: Mg≤0.0010%, Ca≤0.0015%.

3. The high chromium ferrite stainless steel for a solid oxide fuel cell interconnect according to claim 1, characterized in that: The high chromium ferritic stainless steel further comprises any one or two of the following chemical components by mass percentage: Ni≤1.0%, Co≤1.0%.

4. The high chromium ferrite stainless steel for a solid oxide fuel cell interconnect according to any one of claims 1 to 3, characterized in that: The total oxygen content T[O] in the high chromium ferrite stainless steel is controlled to be T[O]≤50ppm.

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