Stainless steel with stable medium-temperature thermal expansion coefficient, interconnection plate and preparation method

Abstract

The invention provides stainless steel with a stable medium-temperature thermal expansion coefficient, an interconnection plate and a preparation method, and belongs to the field of alloys. The stainless steel comprises the following chemical components: 21%-30% of Cr, 0.05%-0.19% of Al, 0.1%-2.5% of Mn, 0.05%-3% of Nb, 0.02%-0.14% of Si, 0.5%-2.5% of W, 2.1%-7% of Mo, and the balance of Clt. 0.008%, T.O < = 0.002%, N < = 0.001%, and Fe. Through matching and cooperation of alloy elements Al, Cr, Mn, V, Si and Mo, the medium-temperature expansion coefficient is adjusted to be (10-12) * 10 <-6 > / K, and the medium-temperature thermal expansion requirement of the solid oxide fuel cell is met. Different elements have different influences on lattice vibration at medium temperature, and the Mo element obviously reduces the lattice vibration, so that the thermal expansion coefficient of the alloy is effectively reduced, and the thermal expansion coefficient of the alloy at 600-900 DEG C is effectively controlled to be consistent with the thermal expansion coefficient of a solid electrolyte through matching and cooperation of the alloy elements.

Description

Technical Field

[0001] The present application relates to the field of alloy technology, and in particular to stainless steel with a stable medium-temperature thermal expansion coefficient, an interconnecting plate, and a preparation method thereof. Background Art

[0002] High-temperature solid oxide fuel cells are highly efficient energy conversion devices that directly convert the chemical energy of fuel into electrical energy without chemical reactions. They can directly use carbon-containing gases such as methane, natural gas and water gas as fuel. In recent years, improvements in material manufacturing processes and design technologies have enabled the operating temperature of SOFC to be reduced from 1000°C to a medium temperature range of 600 to 900°C, which also makes it possible to use metal connector materials as connector materials. Metal connectors can meet basic requirements such as electrical conductivity, thermal expansion coefficient, thermal conductivity, and oxidation resistance at operating temperatures.

[0003] The thermal expansion coefficient of each component of the solid oxide fuel cell is (10.5~12.5)*10 -6 / K, so the thermal expansion coefficient TEC of the metal interconnect material is required to be close to this to avoid excessive thermal stress that causes rapid degradation of the stack performance. Therefore, at the SOFC operating temperature of 600-900℃, the development of interconnect materials with stable thermal expansion coefficient is crucial. Summary of the invention

[0004] The present application provides stainless steel with a stable medium-temperature thermal expansion coefficient, an interconnection plate and a preparation method to solve the following technical problem: how to stabilize the medium-temperature thermal expansion coefficient of a fuel cell interconnection plate.

[0005] In a first aspect, the present application provides a stainless steel with a stable medium-temperature thermal expansion coefficient, which includes the following chemical components, measured by mass fraction: Cr: 21% to 30%, Al: 0.05% to 0.19%, Mn: 0.1% to 2.5%, Nb: 0.05% to 3%, Si: 0.02% to 0.14%, W: 0.5% to 2.5%, Mo: 2.1% to 7%, C<0.008%, TO≤0.002%, N≤0.001% and Fe.

[0006] Optionally, the stainless steel further includes the following chemical components: rare earth elements: 0.005% to 0.2%, wherein the rare earth elements include one or more of La, Ce, Sc and Y.

[0007] Optionally, the chemical composition satisfies the following relationship:

[0008] 1.0≤([Al]+[Mn]) / (0.02×[Cr] 2 -[Si]-[Mo])≤4.0

[0009] In the formula, [Al] represents the mass fraction of Al, [Mn] represents the mass fraction of Mn, [Cr] represents the mass fraction of Cr, [Si] represents the mass fraction of Si, and [Mo] represents the mass fraction of Mo.

[0010] Optionally, the chemical composition satisfies the following relationship:

[0011] 5%≤[Mo]+[Nb]+3×[Al]+6×[W]≤23%

[0012] In the formula, [Mo] represents the mass fraction of Mo, [Nb] represents the mass fraction of Nb, [Al] represents the mass fraction of Al, and [W] represents the mass fraction of W.

[0013] In a second aspect, the present application provides a method for preparing the stainless steel according to any one embodiment of the first aspect, the method comprising:

[0014] The molten steel is subjected to vacuum refining, and when the TO of the molten steel is less than or equal to 0.002%, an alloy containing a rare earth element is added to the molten steel to obtain an alloyed molten steel;

[0015] The alloyed steel liquid is poured to obtain the stainless steel.

[0016] In a third aspect, the present application provides a fuel cell interconnector, wherein the fuel cell interconnector plate is made of the stainless steel described in any one of the embodiments in the first aspect.

[0017] Optionally, fine Laves phase particles are dispersed in the matrix of the fuel cell interconnector, and the particle size of the Laves phase particles is less than 2 μm, and the total amount of precipitated phase in the matrix of the fuel cell interconnector is less than 2.5%.

[0018] Optionally, the fuel cell interconnection plate meets at least one of the following properties:

[0019] The thermal expansion coefficient at 600℃~900℃ is (10~12)×10 -6 / K;

[0020] 20% O 2 -80% H 2 In O atmosphere, ASR≤0.004Ω·cm after oxidation at 900℃ for 10000h 2 ;

[0021] 20% O 2 -80% H 2 In O atmosphere, oxidation at 900℃ for 30000h, the total thickness of the oxide film is less than 10μm;

[0022] Tensile strength Rm≥260MPa at 900℃;

[0023] The yield strength Rp0.2≥210MPa at 900℃.

[0024] In a fourth aspect, the present application provides a method for preparing the fuel cell interconnection plate according to the embodiment of the third aspect, the method comprising:

[0025] The stainless steel described in any one of the embodiments of the first aspect is sequentially subjected to hot rolling, cold rolling, stamping, solution treatment and water cooling to obtain a fuel cell interconnection plate.

[0026] Optionally, the solution treatment includes the following parameters: heating temperature of 1000°C to 1100°C, holding time of 30min to 45min, hydrogen injection volume of ≥20m 3 / h.

[0027] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0028] The present application provides a stainless steel with a stable coefficient of thermal expansion at medium temperature, which includes the following chemical components by mass fraction: Cr: 21% to 30%, Al: 0.05% to 0.19%, Mn: 0.1% to 2.5%, Nb: 0.05% to 3%, Si: 0.02% to 0.14%, W: 0.5% to 2.5%, Mo: 2.1% to 7%, C < 0.008%, TO ≤ 0.002%, N ≤ 0.001% and Fe. The mechanical performance requirements of solid oxide fuel cells at medium temperature are achieved by reasonable matching of Cr and Mo, and the coefficient of thermal expansion at medium temperature is adjusted to (10 to 12) × 10 by matching and synergizing the alloy elements Al, Cr, Mn, V, Si and Mo. -6 / K, meeting the medium-temperature thermal expansion requirements of solid oxide fuel cells. Different elements have different effects on lattice vibration at medium temperature. Among them, Mo element significantly reduces lattice vibration, thereby effectively reducing the thermal expansion coefficient of the alloy. Therefore, by matching and synergizing the alloy elements, the thermal expansion coefficient of the alloy at 600℃~900℃ is effectively controlled to be consistent with the thermal expansion coefficient of the solid electrolyte. However, the addition of Mo, Nb, W, etc. leads to the precipitation of Laves phase during the solidification process. By controlling the composition and solid solution process parameters of Mo, Nb, Al, and W, the proportion and size of the Laves phase are controlled, and the influence of the Laves phase on thermal expansion properties and mechanical properties at medium temperature is weakened. Thereby stabilizing the medium-temperature thermal expansion coefficient of the fuel cell interconnect plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings herein are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present application, and together with the description, are used to explain the principles of the present application.

[0030] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0031] Figure 1 A schematic flow chart of a method for preparing stainless steel provided in an embodiment of the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0033] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0034] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one-to-one with the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0035] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0036] The present application provides a stainless steel with a stable coefficient of thermal expansion at medium temperature. The stainless steel comprises the following chemical components, measured by mass fraction: Cr: 21% to 30%, Al: 0.05% to 0.19%, Mn: 0.1% to 2.5%, Nb: 0.05% to 3%, Si: 0.02% to 0.14%, W: 0.5% to 2.5%, Mo: 2.1% to 7%, C<0.008%, TO≤0.002%, N≤0.001% and Fe.

[0037] In some embodiments, the stainless steel further comprises the following chemical components: rare earth elements: 0.005% to 0.2%, wherein the rare earth elements include one or more of La, Ce, Sc and Y.

[0038] The functions of each element are as follows:

[0039] Cr: Cr is the main antioxidant element in stainless steel, and its content is between 21% and 30%, which ensures that stainless steel has excellent antioxidant properties in a strong oxidizing atmosphere. At the same time, an appropriate amount of Cr helps to stabilize the thermal expansion coefficient of stainless steel and avoid excessive differences in the expansion coefficient of the solid electrolyte, thereby maintaining good conductivity and battery life. Exemplarily, the Cr content can be 21%, 22%, 23%, 24%, 26%, 28%, 30%, etc.

[0040] Al: Al, as a strong deoxidizer, can significantly reduce the oxygen content in stainless steel and improve the purity and oxidation resistance of the alloy. At the same time, the addition of Al improves the high-temperature strength of stainless steel, allowing it to maintain good mechanical properties under high temperature conditions. In addition, Al has a low density, which helps to reduce the density of stainless steel and achieve lightweight materials. Exemplarily, the Al content can be 0.05%, 0.08%, 0.10%, 0.12%, 0.15%, 0.18%, 0.19%, etc.

[0041] Mo: The Mo element has the effect of significantly reducing the thermal expansion coefficient of stainless steel, which helps to maintain the dimensional stability of the material. At the same time, Mo, as a solid solution strengthening element, can significantly improve the mechanical properties and corrosion resistance of stainless steel. At the same time, during the solidification process, Mo easily forms Laves phases with other elements, which help to further improve the strength and corrosion resistance of stainless steel. Exemplarily, the Mo content can be 2.1%, 2.5%, 3%, 4%, 5%, 6%, 7%, etc.

[0042] Si: Si, as a deoxidizer, can further reduce the oxygen content in stainless steel and improve the purity of the alloy. At the same time, Si is a strong ferrite-forming element, which helps to form a stable ferrite structure and improve the high temperature performance and corrosion resistance of stainless steel. In addition, the addition of Si can also improve the casting characteristics of stainless steel, making it easier to process and form. Exemplarily, the Si content can be 0.02%, 0.04%, 0.06%, 0.08%, 0.10%, 0.12%, 0.14%, etc.

[0043] Nb: Nb can preferentially combine with carbon to form stable carbides, preventing the formation of Cr carbides, thereby preventing intergranular corrosion. At the same time, Nb is also a ferrite-forming element, which helps to form a single ferrite structure with a low thermal expansion coefficient. In addition, Nb is a Laves phase B 2 The constituent elements of A in A, these phases help to improve the strength and corrosion resistance of stainless steel. Exemplarily, the content of Nb can be 0.05%, 0.10%, 0.50%, 0.80%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0044] W: As a solid solution strengthening element, W can significantly improve the mechanical properties and corrosion resistance of stainless steel. At the same time, W is also a Laves phase B 2 The constituent elements of A in A further enhance the strength and corrosion resistance of stainless steel. For example, the content of W can be 0.5%, 1%, 1.5%, 2%, 2.5%, etc.

[0045] C: Reducing the carbon content is one of the most effective measures to prevent intergranular corrosion of stainless steel. By limiting the C content to below 0.008%, the risk of intergranular corrosion can be significantly reduced. Exemplarily, the C content can be 0.004%, 0.005%, 0.006%, 0.007%, etc.

[0046] N: Similar to C, limiting the content of N also helps prevent intergranular corrosion of stainless steel. Exemplarily, the content of N may be 0.0004%, 0.0005%, 0.0006%, 0.0007%, 0.0008%, 0.0009%, 0.001%, etc.

[0047] Mn: Mn is an element that expands and stabilizes austenite. However, in this stainless steel, by precisely controlling the Mn content between 0.1% and 2.5%, a single ferrite structure with a low thermal expansion coefficient can be formed to avoid the generation of austenite structure with a high expansion coefficient. At the same time, the addition of Mn can also improve the strength of stainless steel and increase the solubility of N in steel. Exemplarily, the Mn content can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.2%, 2.5%, etc.

[0048] Rare earth elements (La, Ce, Sc, Y): As purifiers, rare earth elements can reduce the harmful effects of oxygen and sulfur at the grain boundaries, and improve the purity and mechanical properties of stainless steel. At the same time, rare earth elements are concentrated at the grain boundaries, strengthening the grain boundaries and improving the strength and toughness of stainless steel. In addition, during the working process at 600℃~900℃, rare earth elements can inhibit the diffusion of chromium into the steel matrix, reducing Cr 2 O 3 The film formation rate is 2 O 3 A nail wedge structure is formed between the oxide film and the substrate, which improves the adhesion between the oxide film and the substrate, thereby improving the oxidation resistance of the stainless steel. Exemplarily, the content of the rare earth element can be 0.005%, 0.01%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, etc.

[0049] In summary, this stainless steel with stable medium-temperature thermal expansion coefficient achieves optimization and balance of multiple properties, including oxidation resistance, thermal expansion stability, mechanical properties and corrosion resistance, by precisely controlling the content and proportion of each element.

[0050] It should be noted that TO is the total oxygen content.

[0051] Fe is a matrix element. The specific content / content range of Fe can be obtained through the upper and lower limit formulas of the components, that is, the sum of the percentages of the contents of each component in a composition should be equal to 100%, and the content ranges of several components should meet the following conditions: the upper limit value of a component + the lower limit values ​​of other components ≤ 100; the lower limit value of a component + the upper limit values ​​of other components ≥ 100.

[0052] In some embodiments, the chemical composition satisfies the following relationship:

[0053] 1.0≤([Al]+[Mn]) / (0.02×[Cr] 2 -[Si]-[Mo])≤4.0

[0054] In the formula, [Al] represents the mass fraction of Al, [Mn] represents the mass fraction of Mn, [Cr] represents the mass fraction of Cr, [Si] represents the mass fraction of Si, and [Mo] represents the mass fraction of Mo.

[0055] In some embodiments, the chemical composition satisfies the following relationship:

[0056] 5%≤[Mo]+[Nb]+3×[Al]+6×[W]≤23%

[0057] In the formula, [Mo] represents the mass fraction of Mo, [Nb] represents the mass fraction of Nb, [Al] represents the mass fraction of Al, and [W] represents the mass fraction of W.

[0058] The mechanical performance requirements of solid oxide fuel cells at medium temperature are achieved by reasonable matching of Cr and Mo. The expansion coefficient at medium temperature is adjusted to (10~12)×10 -6 / K, meeting the medium-temperature thermal expansion requirements of solid oxide fuel cells. Different elements have different effects on lattice vibration at medium temperature, among which Mo element significantly reduces lattice vibration, thereby effectively reducing the thermal expansion coefficient of the alloy. Therefore, the alloy elements are matched and coordinated to effectively control the thermal expansion coefficient of the alloy at 600℃~900℃ to be consistent with the thermal expansion coefficient of the solid electrolyte. However, the addition of Mo, Nb, W, etc. leads to the precipitation of Laves phase during solidification. By controlling the composition and solid solution process parameters of Mo, Nb, Al, and W, the proportion and size of Laves phase are controlled, and the influence of Laves phase on thermal expansion performance and mechanical properties at medium temperature is weakened. Exemplarily, the value of ([Al]+[Mn]) / (0.02×[Cr]2-[Si]-[Mo]) can be 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, etc. [Mo]+[Nb]+3×[Al]+6×[W] can be 5%, 8%, 10%, 12%, 15%, 20%, 23%, etc.

[0059] Figure 1 A schematic flow chart of a method for preparing stainless steel provided in an embodiment of the present application.

[0060] like Figure 1 Based on a general inventive concept, the present application provides a method for preparing the stainless steel described in any one of the above embodiments, the method comprising:

[0061] S1, vacuum refining the molten steel, and when the TO of the molten steel is ≤0.002%, adding an alloy containing a rare earth element to the molten steel to obtain an alloyed molten steel;

[0062] S2, pouring the alloyed steel liquid to obtain the stainless steel.

[0063] In step S1, when the alloy is added, TO in the molten steel is ≤20ppm. At this time, the molten steel has been completely deoxidized, which can reduce the risk of alloy oxidation and improve the alloy yield.

[0064] In some embodiments, when the vacuum refining time is 0.6×T to 0.8×T, an alloy containing rare earth is added to the molten steel, that is, added before steel is tapped in the late refining period, so that the yield of expensive rare earth elements can be improved. Wherein T is the vacuum refining cycle. If the alloy is added too early, the yield of the alloying elements will be reduced to a certain extent. If the alloy is added too late, it will cause the alloy to be uneven to a certain extent, and the conductivity and oxidation resistance of the product will be uneven.

[0065] The product prepared by the method for preparing stainless steel is the above-mentioned stainless steel. The chemical composition and structure of the stainless steel prepared by the method for preparing stainless steel can refer to the above-mentioned embodiment. Since the method for preparing stainless steel adopts part or all of the technical solutions of the stainless steel embodiment, it at least has all the beneficial effects brought by the technical solutions of the stainless steel embodiment, which will not be described one by one here.

[0066] Based on a general inventive concept, the present application provides a fuel cell interconnector, wherein the fuel cell interconnector plate is made of the stainless steel described in any one of the embodiments in the first aspect.

[0067] In some embodiments, fine Laves phase particles are dispersed in the matrix of the fuel cell interconnector, and the particle size of the Laves phase particles is less than 2 μm, and the total amount of precipitated phase in the matrix of the fuel cell interconnector is less than 2.5%.

[0068] Dispersed fine Laves phase particles can be used as strengthening phases to effectively hinder the movement of dislocations, thereby improving the strength of the material. At the same time, fine particles help to disperse the energy of crack propagation, improve the toughness of the material, and prevent the occurrence of brittle fracture. In addition, because the particles are small and dispersed, they have little effect on the plasticity of the material, and can maintain good plasticity and processing properties. The total amount of precipitated phase refers to the sum of the volume fractions of all precipitated phases (including Laves phases) in the material. The performance of the matrix dominates the overall performance of the material, and the precipitated phase mainly plays a role in strengthening and refining the grains. Exemplarily, the particle size of the Laves phase particles can be 1.9μm, 1.8μm, 1.7μm, 1.6μm, 1.5μm, etc., and the total amount of precipitated phases in the stainless steel matrix can be 2.4%, 2.3%, 2.2%, 2.1%, 2.0%, 1.9%, 1.8%, 1.7%, etc.

[0069] In some embodiments, the fuel cell interconnect plate satisfies at least one of the following properties:

[0070] The thermal expansion coefficient at 600℃~900℃ is (10~12)×10 -6 / K;

[0071] 20% O 2 -80% H 2 In O atmosphere, ASR≤0.004Ω·cm after oxidation at 900℃ for 10000h 2 ;

[0072] 20% O 2 -80% H 2 In O atmosphere, oxidation at 900℃ for 30000h, the total thickness of the oxide film is less than 10μm;

[0073] Tensile strength Rm≥260MPa at 900℃;

[0074] The yield strength Rp0.2≥210MPa at 900℃.

[0075] The interconnection plate provided in the embodiment of the present application has good hydrogen embrittlement resistance and oxidation resistance during operation of the fuel cell, thereby increasing the service life of the fuel cell.

[0076] The thermal expansion coefficient at 600℃~900℃ is (10~12)×10 -6 / K: Ensures dimensional stability of the interconnect at high temperatures. The coefficient of thermal expansion is a measure of the dimensional change of a material as the temperature changes, and it is critical for the interconnect to match the coefficient of thermal expansion of the electrolyte and other components to avoid cracking or deformation due to thermal stress.

[0077] 20% O 2 -80% H 2 In O atmosphere, ASR≤0.004Ω·cm after oxidation at 900℃ for 10000h 2 :ASR (area specific resistance) is an important indicator to measure the conductive performance of the interconnection board. In a long-term high-temperature oxidizing environment, the increase of ASR will lead to a decrease in battery performance. It ensures that the interconnection board has good conductive performance and stability in high temperature, high humidity and oxidizing atmosphere.

[0078] 20% O 2 -80% H 2 O atmosphere, 900℃ oxidation for 30000h, total oxide film thickness <10μm: The formation of oxide film is an inevitable phenomenon of interconnection board in high temperature oxidation environment. However, too thick oxide film will lead to the decline of conductivity and degradation of mechanical properties. The growth rate of oxide film is limited, thus ensuring the stability and reliability of interconnection board during long-term use.

[0079] Tensile strength Rm≥260MPa at 900℃: Tensile strength is an indicator of the material's ability to resist tensile damage. At high temperatures, the tensile strength of the material usually decreases. This ensures that the interconnection board has sufficient strength and load-bearing capacity at high temperatures to avoid damage caused by mechanical stress.

[0080] Yield strength Rp0.2≥210MPa at 900℃: Yield strength is an indicator of the maximum stress that a material can withstand before plastic deformation. At high temperatures, the yield strength of the material will also decrease. This ensures that the interconnection board has sufficient resistance to plastic deformation at high temperatures to avoid failure caused by plastic deformation.

[0081] Based on a general inventive concept, the present application provides a method for preparing the fuel cell interconnection plate described in the above embodiment, the method comprising:

[0082] The stainless steel described in any one of the above embodiments is sequentially subjected to hot rolling, cold rolling, stamping, solution treatment and water cooling to obtain a fuel cell interconnection plate.

[0083] The stainless steel material is made into the desired shape and size by high temperature heating and rolling. The shape and size of the material are further adjusted and the hardness and strength of the material are improved by rolling at room temperature or near room temperature. The stainless steel material is punched into the desired shape and size by a die to prepare the preliminary form of the interconnection plate. The alloy elements in the stainless steel are dissolved into the matrix by heating and heat preservation to form a uniform solid solution. At the same time, the morphology and amount of the precipitated phase can be regulated by controlling the cooling method (such as water cooling). After the solution treatment, water cooling is immediately performed to quickly cool the material, prevent the growth of the precipitated phase, and retain the dispersed fine second phase particles.

[0084] In some embodiments, the solution treatment includes the following parameters: heating temperature of 1000°C to 1100°C, holding time of 30min to 45min, hydrogen injection volume of ≥20m 3 / h.

[0085] Limiting the heating temperature to 1000℃~1100℃ can ensure that the alloying elements in the stainless steel are fully dissolved into the matrix to form a uniform solid solution. Limiting the holding time to 30min~45min can ensure that the alloying elements are fully dissolved while avoiding excessive growth of the precipitate phase. Water cooling is performed immediately after the holding to quickly cool the material. This can prevent the further growth of the precipitate phase and ensure that the Laves phase particles have time to grow in the future to form dispersed and fine second phase particles. These fine particles can improve the strength and toughness of the material. By controlling the parameters of the solution treatment and water cooling treatment, the amount of precipitate phase can be controlled. The total amount of precipitate phase is less than 2.5%, which can ensure good comprehensive performance of the material and avoid excessive hardening and embrittlement. In addition, during the solution treatment process, hydrogen spraying is used, and the hydrogen spraying amount is ≥20m 3 / h. Hydrogen can be used as a reducing gas to prevent stainless steel from being oxidized during heat treatment. At the same time, hydrogen can also promote the dissolution and uniform distribution of alloying elements. For example, the temperature of the solution treatment can be 1000°C, 1020°C, 1040°C, 1060°C, 1080°C, 1100°C, etc., the holding time can be 30min, 32min, 35min, 40min, 42min, 45min, etc., and the hydrogen spraying amount can be 20m 3 / h、22m 3 / h、25m 3 / h、28m 3 / h、30m 3 / h, etc.

[0086] The product prepared by the preparation method of the fuel cell interconnection plate is the above-mentioned fuel cell interconnection plate. The chemical composition and microstructure of the fuel cell interconnection plate prepared by the preparation method of the fuel cell interconnection plate can refer to the above-mentioned embodiment. Since the preparation method of the fuel cell interconnection plate adopts part or all of the technical solutions of the fuel cell interconnection plate embodiment, it at least has all the beneficial effects brought by the technical solutions of the fuel cell interconnection plate embodiment, which will not be repeated here one by one.

[0087] The advantages of the embodiments of the present application are mainly reflected in the following aspects:

[0088] (1) Optimized chemical composition and performance balance: By precisely controlling the content and ratio of each element in stainless steel, the optimization and balance of various properties such as oxidation resistance, thermal expansion stability, mechanical properties and corrosion resistance are achieved. At the same time, especially through the reasonable matching of Cr and Mo, and the synergistic effect of elements such as Al, Mn, Si, Nb, and W, the medium-temperature expansion coefficient is adjusted to meet the medium-temperature thermal expansion requirements of solid oxide fuel cells.

[0089] (2) Stable thermal expansion coefficient: The thermal expansion coefficient of stainless steel is stable at (10-12)×10^-6 / K in the range of 600℃ to 900℃, which matches the thermal expansion coefficient of the solid electrolyte and avoids cracking or deformation caused by thermal stress.

[0090] (3) Good anti-oxidation and anti-hydrogen embrittlement performance: Under high temperature, high humidity and oxidizing atmosphere, stainless steel exhibits good anti-oxidation performance, low ASR value and slow oxide film growth, which ensures the stability and reliability of the interconnection board during long-term use. At the same time, stainless steel also has good anti-hydrogen embrittlement performance, which improves the service life of the fuel cell.

[0091] (4) High strength and yield strength: At high temperatures, stainless steel can still maintain high tensile strength and yield strength, ensuring that the interconnection plate has sufficient strength and bearing capacity at high temperatures, avoiding damage caused by mechanical stress or plastic deformation.

[0092] (5) Fine microstructure: By controlling the parameters of solution treatment and water cooling treatment, fine Laves phase particles are dispersed in the stainless steel matrix, and the total amount of precipitated phase is low, which improves the strength and toughness of the material and prevents the occurrence of brittle fracture.

[0093] (6) Efficient preparation method: Vacuum refining and alloying technology are used to reduce the oxygen content in the molten steel, increase the recovery rate of alloy elements, and ensure the purity and performance of the stainless steel. At the same time, through hot rolling, cold rolling, stamping, solution treatment and water cooling treatment and other process steps, the precise processing and forming of stainless steel materials are achieved.

[0094] (7) Broad application prospects: The prepared fuel cell interconnect plate has excellent comprehensive performance and is suitable for high-temperature working environments such as solid oxide fuel cells, providing strong material support for the development of fuel cell technology.

[0095] In summary, this application achieves the optimization and balance of multiple properties by optimizing the chemical composition and preparation process of stainless steel, provides high-performance material support for the development of fuel cell technology, and has broad application prospects and significant social and economic benefits.

[0096] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0097] The present application embodiment provides a method for preparing an interconnection board, and the specific process is as follows:

[0098] Step 1, add industrial pure iron, Cr alloy, and C into a vacuum induction furnace for vacuum refining, the loading amount of the vacuum induction furnace is 3 tons, the vacuum refining time is 60 minutes, the vacuum refining temperature is 1500°C, the alloy containing La is added at the 40th minute of vacuum refining, and TO at this moment is 0.0015%;

[0099] Step 2, after pouring and crystallizing the molten steel in step 1, a stainless steel alloy ingot as shown in Table 1 and Table 2 is obtained, and the stainless steel alloy ingot is heated at 1100° C., forged and tempered for multiple times to obtain a flat slab;

[0100] Step 3, hot rolling, annealing, softening, grinding and welding the flat slab to obtain a hot-rolled strip;

[0101] Step 4, performing blanking, cold rolling, intermediate grinding, edge trimming and solution treatment on the hot-rolled strip to obtain a strip;

[0102] The hot rolling temperature is 1100°C. The hot rolling includes: the first hot rolling, the second hot rolling and the third hot rolling. The deformation of the first hot rolling is 40%, the deformation of the second hot rolling is 60%, and the deformation of the third hot rolling is 70%. The final rolling temperature is 910°C. After rolling, water cooling to room temperature;

[0103] The cold rolling includes: a first cold rolling, a second cold rolling and a third cold rolling, the deformation amount of the first cold rolling is 50%, the deformation amount of the second cold rolling is 60%, and the deformation amount of the third cold rolling is 70%.

[0104] Step 5, stamping: heat treatment to 300°C, hydrogen spraying rate 5m3 / h, heat preservation for 20min, stamping.

[0105] Step 6: Solution treatment is performed on the steel plate after stamping in step S5, and then water-cooled to room temperature. The parameters of the solution treatment are shown in Table 3.

[0106] Table 1 Chemical composition of stainless steel alloy ingot (wt, %), the balance is Fe and unavoidable impurities

[0107]

[0108]

[0109] Table 2 Relationship between chemical compositions of stainless steel alloy ingots

[0110] serial number <![CDATA[([Al]+[Mn]) / (0.02×[Cr] 2 -[Si]-[Mo])]]> [Mo]+[Nb]+3×[Al]+6×[W] Example 1 2.51 5.35 Example 2 1.82 10.3 Example 3 2.67 15.3 Example 4 2.79 19.95 Example 5 3.99 22.57 Comparative Example 1 6.41 13.3 Comparative Example 2 1.06 25.57 Comparative Example 3 2.67 15.3 Comparative Example 4 2.79 19.95

[0111] Table 3 Parameters of cold rolling and solution treatment

[0112]

[0113]

[0114] The performance of the interconnection boards prepared in Examples 1 to 5 and Comparative Examples 1 to 4 was measured. The thermal expansion coefficient was measured at 600°C-900°C; 2 -80% H 2 O atmosphere, 900℃ oxidation for 10000h, and the ASR was measured; 2 -80% H 2 In an O atmosphere, the steel was oxidized at 900℃ for 30000h, and the total thickness of the oxide film was measured; the tensile strength Rm at 900℃ and the yield strength Rp0.2 at 900℃ were measured. The results are shown in Table 4.

[0115] Table 4 Performance of interconnection boards prepared in Examples 1 to 5 and Comparative Examples 1 to 4

[0116]

[0117] As shown in Tables 1 to 4, Examples 1 to 5 meet the composition and process parameter requirements of the present application, and have excellent thermal expansion performance, oxidation resistance, and mechanical properties. Comparative Example 1 does not meet 1.0≤([Al]+[Mn]) / (0.02×[Cr] 2-[Si]-[Mo])≤4.0, Comparative Example 2 does not meet the requirement of 5%≤[Mo]+[Nb]+3×[Al]+6×[W]≤23%, and the comprehensive performance is lower than that of Examples 1 to 5. The solid solution temperature of Comparative Example 3 is too low, and the solid solution temperature of Comparative Example 4 is too high, and both do not meet the process parameter requirements, and the comprehensive performance is lower than that of Examples 1 to 5.

[0118] In addition, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0119] In the embodiment of the present invention, the thermal expansion coefficient of the fuel cell interconnection plate at 600°C to 900°C is (10-12)×10 -6 / K; 20%O 2 -80% H 2 In O atmosphere, ASR≤0.004Ω·cm after oxidation at 900℃ for 10000h 2 ; 20%O 2 -80% H 2 In O atmosphere, oxidation at 900℃ for 30000h, the total thickness of the oxide film is <10μm; the tensile strength Rm at 900℃ is ≥260MPa; the yield strength Rp0.2 at 900℃ is ≥210MPa.

[0120] In the embodiment of the present invention, the provided interconnection plate has good hydrogen embrittlement resistance and oxidation resistance during operation of the fuel cell, thereby increasing the service life of the fuel cell.

[0121] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A stainless steel with a stable coefficient of thermal expansion at medium temperature, wherein the stainless steel comprises the following chemical components by mass fraction: Cr: 21% to 30%, Al: 0.05% to 0.19%, Mn: 0.1% to 2.5%, Nb: 0.05% to 3%, Si: 0.02% to 0.14%, W: 0.5% to 2.5%, Mo: 2.1% to 7%, C<0.008%, TO≤0.002%, N≤0.001% and Fe.

2. The stainless steel according to claim 1, characterized in that The stainless steel also includes the following chemical components: rare earth elements: 0.005% to 0.2%, wherein the rare earth elements include one or more of La, Ce, Sc and Y.

3. The stainless steel according to claim 1, characterized in that The chemical composition satisfies the following relationship: 1.0≤([Al]+[Mn]) / (0.02×[Cr] 2 -[Yes]-[Mo])≤4.0 In the formula, [Al] represents the mass fraction of Al, [Mn] represents the mass fraction of Mn, [Cr] represents the mass fraction of Cr, [Si] represents the mass fraction of Si, and [Mo] represents the mass fraction of Mo.

4. The stainless steel according to claim 1, characterized in that The chemical composition satisfies the following relationship: 5%≤[Mo]+[Nb]+3×[Al]+6×[W]≤23% In the formula, [Mo] represents the mass fraction of Mo, [Nb] represents the mass fraction of Nb, [Al] represents the mass fraction of Al, and [W] represents the mass fraction of W.

5. A method for preparing the stainless steel according to any one of claims 1 to 4, the method comprising: The molten steel is subjected to vacuum refining, and when the TO of the molten steel is less than or equal to 0.002%, an alloy containing a rare earth element is added to the molten steel to obtain an alloyed molten steel; The alloyed steel liquid is poured to obtain the stainless steel.

6. A fuel cell interconnector, wherein the fuel cell interconnector plate is made of the stainless steel according to any one of claims 1 to 4.

7. The fuel cell interconnect according to claim 6, characterized in that: Fine Laves phase particles are dispersed in the matrix of the fuel cell interconnector, and the particle size of the Laves phase particles is less than 2 μm. The total amount of precipitated phase in the matrix of the fuel cell interconnector is less than 2.5%.

8. The fuel cell interconnect according to claim 6, characterized in that: The fuel cell interconnection plate meets at least one of the following properties: The thermal expansion coefficient at 600℃~900℃ is (10~12)×10 -6 / K; In 20% O2-80% H2O atmosphere, ASR≤0.004Ω·cm after oxidation at 900℃ for 10000h 2 ; In 20% O2-80% H2O atmosphere, oxidized at 900℃ for 30000h, the total thickness of the oxide film is less than 10μm; Tensile strength Rm≥260MPa at 900℃; The yield strength Rp0.2≥210MPa at 900℃.

9. A method for preparing a fuel cell interconnection plate according to claim 7 or 8, the method comprising: The stainless steel according to any one of claims 1 to 4 is sequentially subjected to hot rolling, cold rolling, stamping, solution treatment and water cooling to obtain a fuel cell interconnection plate.

10. The method according to claim 9, characterized in that The solution treatment includes the following parameters: heating temperature is 1000℃~1100℃, holding time is 30min~45min, hydrogen injection volume is ≥20m 3 / h.

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