Low density stainless steel, fuel cell interconnect and method of making

Abstract

This application provides a low-density stainless steel, a fuel cell interconnect, and a preparation method thereof, belonging to the field of alloys. The stainless steel comprises the following chemical composition: Cr: 13%–30%, Al: 8%–12%, V: 0.25%–0.5%, B: 0.01%–0.5%, Zr: 0.4%–1.0%, C<0.008%, TO≤0.002%, N≤0.001%, Si: 0.15%–0.3%, Mn: 0.1%–0.8%, and Fe. The chemical composition of the stainless steel is rationally designed. By introducing Al to reduce the alloy density, the precipitation of low-density FeAl intermetallic compounds during the aging process improves the mechanical properties at medium and high temperatures. The combined effect of B and Zr improves the overall performance of the alloy at medium temperatures of 600℃–900℃. Simultaneously, the introduction of V to occupy Al sites in the intermetallic compounds improves the stability of the Fe-Al intermetallic compounds. Thus, while satisfying the requirements of high strength, high toughness, and oxidation resistance in the fuel cell interconnect, the density of the fuel cell interconnect is reduced.

Description

Technical Field

[0001] This application relates to the field of alloy technology, and in particular to a low-density stainless steel, a fuel cell interconnect, and a method for its preparation. Background Technology

[0002] The urgent need to reduce greenhouse gas emissions and control global warming worldwide has attracted widespread attention from the industry. From the perspective of advanced materials development, lightweighting can significantly reduce energy consumption and carbon dioxide emissions. There are two main approaches to weight reduction: one is to increase the strength of materials to reduce their thickness, thereby achieving overall structural weight reduction; the other is to develop low-density materials to achieve lightweighting. Taking electric vehicles as an example, for every 10% reduction in the overall weight of an electric vehicle, its driving range can increase by 5.5%. The "three-electric" systems (battery, motor, and electronic control) of new energy vehicles account for approximately one-quarter of the vehicle's curb weight, and lightweighting is key to solving this problem.

[0003] Lighter elements can increase the lattice constant of steel and reduce its density due to their lower atomic weight. However, this also brings a series of problems. Lighter elements have a significant impact on the thermodynamic stability of steel's allotropes. For example, excessive use of aluminum without carbon compensation will cause the ferrite phase to exist stably at different temperatures below the solidus, thus eliminating the possibility of microstructure optimization through heat treatment. In addition, the precipitation of brittle phases is detrimental to the mechanical properties of the material. In solid oxide fuel cells, the interconnect material accounts for more than 80% of the total weight. Currently, the four ferritic stainless steel interconnects for solid oxide fuel cells that have been studied in detail are Crofer 22 APU, SUS430, X10CrAl18, and ZMG232. The more representative ferritic Fe-Cr alloys are ZMG232 developed by Hitachi Metals and the Crofer22 APU alloy announced by ThyssenKrupp VDM in 2003. After later optimization, ZMG232L and Crofer22H were further developed. Although all four alloys exhibit excellent properties, their densities are all around 7.8 g / cm³. 3 ~8.0g / cm 3 Therefore, how to reduce the density of fuel cell interconnects while ensuring they possess high strength, high toughness, and oxidation resistance is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This application provides a low-density stainless steel, a fuel cell interconnect, and a preparation method thereof, to solve the following technical problem: how to reduce the density of the fuel cell interconnect while ensuring that it has high strength, high toughness, and oxidation resistance.

[0005] In a first aspect, the present application provides a low-density stainless steel. In terms of mass fraction, the stainless steel comprises the following chemical components: Cr: 13% - 30%, Al: 8% - 12%, V: 0.25% - 0.5%, B: 0.01% - 0.5%, Zr: 0.4% - 1.0%, C < 0.008%, T.O ≤ 0.002%, N ≤ 0.001%, Si: 0.15% - 0.3%, Mn: 0.1% - 0.8%, and Fe.

[0006] Optionally, the chemical components satisfy the following relationship:

[0007] 24 ≤ [Al] / [V] ≤ 32

[0008] In the formula, [V] represents the mass fraction of V, and [Al] represents the mass fraction of Al.

[0009] Optionally, the chemical components satisfy the following relationship:

[0010] 0.01 ≤ ([Zr] + 1.1[B]) / ([Al] + [V]) ≤ 0.2

[0011] In the formula, [Zr] represents the mass fraction of Zr, [B] represents the mass fraction of B, [V] represents the mass fraction of V, and [Al] represents the mass fraction of Al.

[0012] In a second aspect, the present application provides a preparation method for the stainless steel according to any one of the first aspect. The method includes:

[0013] Vacuum refining the molten steel, and when T.O of the molten steel ≤ 0.002%, adding an alloy containing Al, V, B, and Zr to the molten steel to obtain an alloyed molten steel;

[0014] Pouring the alloyed molten steel to obtain the stainless steel.

[0015] Optionally, the time and pressure of the vacuum refining satisfy the following relationship:

[0016] When t < 0.2T, P is 1 Pa - 5 Pa;

[0017] When 0.2T < t < 0.6T, P is 0.1 Pa - 0.5 Pa;

[0018] When t > 0.6T, P is 1 Pa - 2 Pa;

[0019] Wherein, t represents the time of the vacuum refining, P represents the pressure of the vacuum refining, and T represents the total time of the high-temperature refining, and T is 0.5 h - 0.7 h.

[0020] Thirdly, this application provides a fuel cell interconnect made of stainless steel as described in any one of the first aspects.

[0021] Optionally, the fuel cell interconnect satisfies at least one of the following performance characteristics:

[0022] The alloy density is 7.0 g / cm³. 3 ~7.2g / cm 3 ;

[0023] Under an O2-H2O atmosphere, the total thickness of the oxide film after oxidation at 900℃ for 30,000 hours is <15μm;

[0024] Tensile strength Rm ≥ 250 MPa at 900℃;

[0025] Yield strength Rp0.2 at 900℃ ≥ 210MPa;

[0026] The coefficient of thermal expansion between 600℃ and 900℃ is 11×10⁻⁶. -6 / K~13×10 -6 / K.

[0027] Fourthly, this application provides a method for preparing the fuel cell interconnect described in the third aspect, the method comprising:

[0028] The stainless steel described in any one of the embodiments of the first aspect is sequentially heated, forged, and tempered in multiple passes to obtain a flat billet;

[0029] The flat billet is subjected to multiple hot rolling passes and annealing softening to obtain a hot-rolled strip billet.

[0030] The hot-rolled strip is subjected to intermediate heat treatment, multiple cold rolling passes, and solution treatment to obtain strip material.

[0031] The strip is stamped and aged to obtain a fuel cell interconnect.

[0032] Optionally, the stamping process includes the following parameters: heating temperature of 200℃~400℃, holding time of 20min~120min, and hydrogen injection volume ≥5m³. 3 / h.

[0033] Optionally, the aging treatment includes the following parameters: temperature of 400℃~500℃, holding time of 60min~90min, and hydrogen injection rate ≥20m³. 3 / h.

[0034] The technical solutions provided in this application have the following advantages compared with the prior art:

[0035] This application provides a low-density stainless steel, comprising the following chemical composition by mass fraction: Cr: 13%–30%, Al: 8%–12%, V: 0.25%–0.5%, B: 0.01%–0.5%, Zr: 0.4%–1.0%, C<0.008%, TO≤0.002%, N≤0.001%, Si: 0.15%–0.3%, Mn: 0.1%–0.8%, and Fe. The chemical composition of the stainless steel is rationally designed. By introducing Al to reduce the alloy density, the precipitation of low-density Fe-Al intermetallic compounds during the aging process improves the mechanical properties at medium and high temperatures. Simultaneously, the Fe-Al intermetallic compounds are brittle, reducing the alloy's plasticity. Boron (B) segregates at grain boundaries, improving grain boundary bonding. Appropriate addition can mitigate phase brittleness. Zr improves both the room-temperature and mid-temperature plasticity of the Fe-Al intermetallic compound. The combined effect of B and Zr improves the overall mid-temperature performance of the alloy from 600℃ to 900℃, enhancing its machinability. Simultaneously, the introduction of vanadium (V) to occupy Al sites in the intermetallic compound increases the stability of the Fe-Al intermetallic compound, reduces brittleness, and improves the mid-temperature machinability of the alloy. This allows for a reduction in the density of the fuel cell interconnect while maintaining high strength, high toughness, and oxidation resistance. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 A schematic flowchart illustrating a method for preparing stainless steel provided in this application embodiment;

[0039] Figure 2 A schematic flowchart illustrating the method for fabricating a fuel cell interconnect provided in an embodiment of this application;

[0040] Figure 3 This is a metallographic diagram of a stainless steel provided in Embodiment 1 of this application. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0042] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has 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., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0043] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely 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 document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts representation" such as parts by weight or parts by mass indicates the proportional relationship between components. In the proportional relationships discussed in this article, parameters that need to be described by proportion should be understood as the first term of the proportion in the order of description, while the proportion figure should be understood as the second term. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substances A, B, and C should correspond one-to-one with the proportion figure in the proportion in the order of description, i.e., the mass of substance A : the mass of substance B : the mass of substance C = 1:2:3.

[0044] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0045] This application provides a low-density stainless steel, which, by mass fraction, comprises the following chemical composition: Cr: 13%–30%, Al: 8%–12%, V: 0.25%–0.5%, B: 0.01%–0.5%, Zr: 0.4%–1.0%, C<0.008%, TO≤0.002%, N≤0.001%, Si: 0.15%–0.3%, Mn: 0.1%–0.8%, and Fe.

[0046] The main functions of each component are as follows:

[0047] Cr: A fundamental element ensuring the antioxidant and thermal expansion properties of this invention. A Cr content below 12% will not achieve the antioxidant properties required for this invention, while a content above 30% will fail to meet the thermal expansion performance requirements. For example, the Cr content can be 13%, 15%, 18%, 20%, 25%, 28%, 30%, etc.

[0048] Vanadium (V): Reduces alloy density and is also a strengthening element. Adding vanadium to stainless steel pipes can refine the grain structure, improving strength and toughness. Vanadium carbides formed with carbon can improve resistance to hydrogen corrosion under high temperature and pressure. For example, the V content can be 0.25%, 0.35%, 0.4%, 0.45%, 0.5%, etc.

[0049] Boron (B): Reduces alloy density and acts as a grain boundary strengthening element. It increases alloy plasticity, facilitates coordinated deformation of grain boundaries during hot working, and improves the alloy's oxidation and creep resistance. Excessive B content will lead to large-sized B precipitates at grain boundaries, deteriorating performance. For example, the B content can be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0050] Al (Al): Aluminum is a strong deoxidizer, which can improve the oxidation resistance and high-temperature strength of alloys. It can also reduce the density of alloys, achieving the advantages of lightweight materials and low cost. However, excessive addition affects tensile and weldability. In this invention, Al is introduced to form Fe-Al intermetallic compounds, which have advantages such as low density, high specific strength, good resistance to high-temperature oxidation, and good corrosion resistance. The disadvantages are high brittleness and instability. For example, the Al content can be 8%, 9%, 10%, 11%, 12%, etc.

[0051] Zr: Purifies grain boundaries; when combined with boron (B), it enhances grain boundary bonding and maintains high-temperature strength. It also provides antioxidant protection, improves oxide film structure, inhibits oxygen diffusion inward, and strengthens the bond between the oxide film and the stainless steel substrate. Excessive addition will deteriorate hot working properties. For example, the Zr content can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0052] Si: A deoxidizer that improves the oxidation resistance and high-temperature strength of alloys. Excessive addition can lead to the formation of SiO2 on the alloy surface during oxidation, affecting electrical conductivity. For example, the Si content can be 0.15%, 0.2%, 0.25%, 0.3%, etc.

[0053] Mn: A deoxidizer that improves the oxidation resistance and high-temperature strength of alloys. Excessive addition will increase the coefficient of thermal expansion of the alloy. For example, the Mn content can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc.

[0054] It should be noted that TO represents the total oxygen content.

[0055] Fe is the matrix element. The specific content / range of Fe can be obtained by the formula for the upper and lower limits of the components. That is, the sum of the percentage content of each component in a composition should be equal to 100%. The content range of several components should meet the following conditions: the upper limit of a certain component + the lower limit of other components ≤ 100; the lower limit of a certain component + the upper limit of other components ≥ 100.

[0056] In some embodiments, the chemical components satisfy the following relationship:

[0057] 24≤[Al] / [V]≤32

[0058] In the formula, [V] represents the mass fraction of V, and [Al] represents the mass fraction of Al.

[0059] In some embodiments, the chemical components satisfy the following relationship:

[0060] 0.01≤([Zr]+1.1[B]) / ([Al]+[V])≤0.2

[0061] In the formula, [Zr] represents the mass fraction of Zr, [B] represents the mass fraction of B, [V] represents the mass fraction of V, and [Al] represents the mass fraction of Al.

[0062] Currently, relevant research is being conducted both domestically and internationally. The main direction is to reduce the density of materials by adding certain amounts of Al, Mn, and C elements. These alloys are generally called low-density alloys or lightweight alloys. The degree of density reduction depends on the amount of Al, Mn, and C elements added, with Al having the greatest impact on the material's density; adding 1% Al can reduce the alloy's density by 0.101 g / cm³. 3 The resulting technical challenge is that the higher the content of alloying elements such as Al, the more severe the brittleness caused by grain boundary weakening, resulting in poor processing performance, poor mechanical properties, and a high susceptibility to cracking during the rolling process. Therefore, the technical problems of low density, high strength, high toughness, and oxidation resistance in fuel cell production urgently need to be solved.

[0063] Therefore, the embodiments of this application reduce the alloy density by introducing Al; the precipitation of low-density FeAl intermetallic compounds during the aging process improves the mechanical properties at medium and high temperatures, while the Fe-Al intermetallic compounds are brittle, reducing the alloy's plasticity. Boron segregates at grain boundaries, improving grain boundary bonding strength, and its appropriate addition can improve the brittleness of the phase. Zr can improve both the room temperature plasticity of the Fe-Al intermetallic compounds and the medium-temperature plasticity of the alloy. The combined effect of B and Zr can improve the overall medium-temperature performance of the alloy from 600℃ to 900℃ and improve the alloy's processing performance.

[0064] Introducing V to occupy Al sites in intermetallic compounds improves the stability of Fe-Al intermetallic compounds, reduces brittleness, and improves the alloy's mid-temperature workability. When [Al] / [V] ≥ 32, excessive Al precipitates from the intermetallic compounds. Under oxidation conditions in oxide fuel cell materials, the precipitated Al will rapidly diffuse to the outer layer of Cr2O3 to form Al2O3, deteriorating conductivity and reducing battery life. When [Al] / [V] ≤ 24, the concentration ratio is too low to replace Al sites. For example, the value of [Al] / [V] can be 24, 25, 26, 27, 28, 29, 30, etc. The value of ([Zr]+1.1[B]) / ([Al]+[V]) can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.2, etc.

[0065] Figure 1 This is a schematic flowchart illustrating a method for preparing stainless steel, as provided in an embodiment of this application.

[0066] like Figure 1 As shown, this application provides a method for preparing stainless steel according to any one of the above claims, the method comprising:

[0067] S11. Vacuum refining of molten steel until the TO content of the molten steel is ≤0.002%, adding an alloy containing Al, V, B and Zr to the molten steel to obtain alloyed molten steel.

[0068] In step S1, when the alloy is added, the TO in the molten steel is ≤20ppm. At this time, the molten steel has been completely deoxidized, which can reduce the risk of the alloy being oxidized and improve the alloy yield.

[0069] In some embodiments, when the vacuum refining time is 0.6*T to 0.8*T, an alloy containing Al, V, B, and Zr is added to the molten steel, specifically before tapping the steel in the later stages of refining. This increases the yield of expensive rare earth elements. Here, T represents the vacuum refining cycle. Adding the alloy too early will reduce the yield of the alloying elements to some extent, while adding it too late will lead to alloy inhomogeneity and unstable mid-temperature mechanical properties and oxidation resistance in the product.

[0070] S12. The alloyed steel liquid is poured to obtain the stainless steel.

[0071] In some embodiments, the vacuum refining time and the vacuum refining pressure satisfy the following relationship:

[0072] When t < 0.2T, P is 1 Pa to 5 Pa;

[0073] When 0.2T < t < 0.6T, P is 0.1 Pa to 0.5 Pa;

[0074] When t > 0.6T, P is 1 Pa to 2 Pa;

[0075] Wherein, t represents the time of the vacuum refining, P represents the pressure of the vacuum refining, T represents the total time of the high-temperature refining, and T is 0.5 h to 0.7 h.

[0076] In the initial stage of refining (t < 0.2T), limiting P to 1 Pa to 5 Pa helps to promote the escape of gases (such as hydrogen, oxygen, etc.) in the molten steel, and also helps the rapid melting and uniform mixing of raw materials; in the middle stage of refining (0.2T < t < 0.6T), limiting P to 0.1 Pa to 0.5 Pa helps to reduce the gas content in the molten steel and further improve the purity of the molten steel. At the same time, the lower pressure is also beneficial to promoting the uniform distribution of alloy elements and the progress of chemical reactions; in the later stage of refining (t > 0.6T), limiting P to 1 Pa to 2 Pa ensures that T.O in the alloy ≤ 20 ppm, and helps to maintain the stability of the molten steel, preventing the splashing or spraying of the molten steel caused by too low pressure. At the same time, it also helps to control the further reaction and precipitation of alloy elements.

[0077] In some embodiments, the temperature of the vacuum refining is 1500 °C to 1600 °C.

[0078] The product prepared by the preparation method of this stainless steel is the above-mentioned stainless steel. The chemical composition and structure of the stainless steel prepared by the preparation method of this stainless steel can refer to the above embodiments. Since the preparation method of this stainless steel adopts some or all of the technical solutions of the stainless steel embodiments, it has at least all the beneficial effects brought by the technical solutions of the stainless steel embodiments, which will not be elaborated here one by one.

[0079] Based on a general inventive concept, the present application provides a fuel cell interconnect, which is made of the stainless steel described in any one of the first aspect.

[0080] In some embodiments, the fuel cell interconnect satisfies at least one of the following performances:

[0081] The alloy density is 7.0 g / cm 3 ~7.2 g / cm 3 ;

[0082] In an O2-H2O atmosphere, the total thickness of the oxide film after oxidation at 900 °C for 30000 h < 15 μm;

[0083] The tensile strength Rm ≥ 250 MPa at 900 °C;

[0084] Yield strength Rp0.2 at 900℃ ≥ 210MPa;

[0085] The coefficient of thermal expansion between 600℃ and 900℃ is 11×10⁻⁶. -6 / K~13×10 -6 / K.

[0086] Alloy Density: The required alloy density for fuel cell interconnects is 7.0 g / cm³ to 7.2 g / cm³. This density range significantly impacts the interconnect's weight, strength, and corrosion resistance. Oxide Film Thickness: Under an O₂-H₂O atmosphere, the total oxide film thickness after oxidation at 900°C for 30,000 hours should be less than 15 μm. This requirement ensures the long-term stability and durability of the interconnect in high-temperature oxidizing environments. Tensile Strength and Yield Strength: At 900°C, the tensile strength Rm of the interconnect should be no less than 250 MPa, and the yield strength Rp₀.₂ should be no less than 210 MPa. These strength requirements are crucial for ensuring the structural integrity and load-bearing capacity of the interconnect under high-temperature conditions. Coefficient of Thermal Expansion: The coefficient of thermal expansion of the interconnect between 600°C and 900°C is 11 × 10⁻⁶. -6 / K~13×10 -6 / K. This requirement helps ensure the dimensional stability of interconnects in high-temperature operating environments and their compatibility with other components.

[0087] The low-density solid oxide fuel cell interconnect provided in this application, through rational design of chemical composition, produces an alloy that exhibits excellent mechanical properties and oxidation resistance under medium-temperature oxidation conditions at 900℃, as well as a stable low coefficient of thermal expansion, meeting the design and application requirements of solid oxide fuel cells. For example, the alloy density can be 7.0 g / cm³. 3 7.05g / cm 3 7.1g / cm 3 7.15g / cm 3 7.2g / cm 3 The total thickness of the oxide film after oxidation at 900℃ for 30,000 h under an O2-H2O atmosphere is 5μm, 7μm, 9μm, 10μm, 12μm, 14μm, 14.5μm, etc.; the tensile strength Rm at 900℃ can be 250MPa, 260MPa, 270MPa, 280MPa, 290MPa, 300MPa, etc.; the yield strength Rp0.2 at 900℃ can be 210MPa, 220MPa, 230MPa, 240MPa, 250MPa, etc.; the coefficient of thermal expansion at 600℃~800℃ can be 11×10⁻⁶. -6 / K, 11.5×10 -6 / K, 12×10 -6 / K, 12.5×10-6 / K、13×10 -6 / K etc.

[0088] Figure 2 This is a schematic flowchart illustrating the method for preparing a fuel cell interconnect according to an embodiment of this application.

[0089] like Figure 2 As shown, this application provides a method for preparing a fuel cell interconnect as described in the third aspect, the method comprising:

[0090] S21. The stainless steel described in any of the above embodiments is sequentially heated, forged, and tempered multiple times to obtain a flat billet;

[0091] The microstructure and mechanical properties of the material are improved by heating and forging, while internal stress and structural defects generated during forging are eliminated by multiple tempering processes.

[0092] S22. The flat billet is subjected to multiple hot rolling passes and annealing softening to obtain a hot-rolled strip billet;

[0093] The flat billet undergoes multiple hot rolling passes to further improve the material's plasticity and deformation capacity. It is then subjected to annealing and softening treatment to reduce the material's hardness and increase its toughness, preparing it for subsequent cold rolling.

[0094] In some embodiments, the temperature of the multi-pass hot rolling is 1000℃~1150℃. The multi-pass hot rolling includes: a first hot rolling pass, a second hot rolling pass, and a third hot rolling pass. The deformation amount of the first hot rolling pass is 30%~50%, the deformation amount of the second hot rolling pass is 40%~60%, and the deformation amount of the third hot rolling pass is 50%~80%. The final rolling temperature is higher than 900℃. After rolling, the material is water-cooled to room temperature.

[0095] S23. The hot-rolled strip is subjected to intermediate heat treatment, multiple cold rolling passes, and solution treatment to obtain strip material;

[0096] The hot-rolled strip undergoes intermediate heat treatment to adjust its microstructure and mechanical properties. It is then subjected to multiple cold rolling passes to obtain the desired sheet thickness and precision. Finally, solution treatment is performed to eliminate internal stresses and structural defects generated during cold rolling, and to improve the material's corrosion resistance and oxidation resistance.

[0097] In some embodiments, the multi-pass cold rolling includes: a first cold rolling, a second cold rolling, and a third cold rolling, wherein the deformation amount of the first cold rolling is 50% to 70%, the deformation amount of the second cold rolling is 60% to 80%, and the deformation amount of the third cold rolling is 70% to 80%.

[0098] S24. The strip is stamped and aged to obtain a fuel cell interconnect.

[0099] The strip is stamped to obtain the desired interconnect shape and size. Then, aging treatment is performed to further stabilize the material's microstructure and mechanical properties, improving the long-term stability and durability of the interconnect.

[0100] In some embodiments, the stamping process includes the following parameters: heating temperature of 200℃~400℃, holding time of 20min~120min, and hydrogen injection volume ≥5m³. 3 / h.

[0101] The heating temperature is controlled between 200℃ and 400℃. This temperature range helps reduce the material's resistance to deformation and improve its plasticity, thus facilitating the stamping process. Simultaneously, an appropriate heating temperature can also reduce defects such as cracks and deformation generated during stamping. The holding time is controlled between 20 min and 120 min. The holding time depends on the material thickness and the desired degree of microstructural change. An appropriate holding time ensures that the material is heated sufficiently and uniformly during the heating process and achieves the required microstructural state. The hydrogen spraying rate should not be less than 5 m³ / h. Hydrogen spraying helps eliminate internal stress and structural defects generated during the stamping process and improves the material's mechanical properties and corrosion resistance. Simultaneously, hydrogen spraying promotes uniform deformation and flow of the material, which is beneficial for obtaining interconnects with high shape and dimensional accuracy. For example, the heating temperature can be 200℃, 220℃, 250℃, 280℃, 300℃, 340℃, 360℃, 400℃, etc., the holding time can be 20min, 40min, 60min, 80min, 100min, 120min, etc., and the hydrogen injection rate can be 5m³. 3 / h、7m 3 / h, 10m 3 / h、12m 3 / h, 15m 3 / h etc.

[0102] In some embodiments, the aging treatment includes the following parameters: temperature of 400℃~500℃, holding time of 60min~90min, and hydrogen injection rate ≥20m³. 3 / h.

[0103] In the aging treatment, the solution treatment temperature is limited to 400 °C to 500 °C, and the holding time is 60 min to 90 min, so that the elements in the alloy are fully dissolved in the matrix to form a uniform solid solution. This helps to improve the properties of the alloy such as corrosion resistance, strength and toughness. During the solution treatment, hydrogen spraying treatment is simultaneously adopted to avoid the oxidation of the iron-chromium alloy during the solution treatment. Exemplarily, the solution treatment temperature can be 400 °C, 420 °C, 440 °C, 460 °C, 480 °C, 490 °C, 500 °C, etc., the holding time can be 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, etc., and the hydrogen spraying amount can be 20 m3 / h, 22 m3 / h, 25 m3 / h, 28 m3 / h, 30 m3 / h, etc.

[0104] The preparation product of the preparation method of the fuel cell interconnect is the above-mentioned fuel cell interconnect. The chemical composition and microstructure of the fuel cell interconnect prepared by the preparation method of the fuel cell interconnect can refer to the above embodiments. Since the preparation method of the fuel cell interconnect adopts some or all of the technical solutions of the fuel cell interconnect embodiment, it has at least all the beneficial effects brought by the technical solutions of the fuel cell interconnect embodiment, which will not be elaborated here one by one.

[0105] The following will further elaborate on the present application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0106] This embodiment provides a preparation method of a fuel cell interconnect, which specifically includes the following steps:

[0107] Step 1: Vacuum melting and vacuum refining are carried out on the raw materials proportioned according to the ratio. During the vacuum refining process, when the T.O of the molten steel is ≤ 20 ppm, an alloy containing Al, V, B and Zr is added to the molten steel to obtain an alloyed molten steel; the alloyed molten steel is poured, and after crystallization, a stainless steel alloy ingot with a set chemical composition is obtained; among them, the pressure P of the high-temperature refining and the time t of the high-temperature refining satisfy the following relationship: when t < 0.2T, P varies within the range of 1 Pa to 5 Pa; when 0.2T < t < 0.6T, P varies within the range of 0.1 Pa to 0.5 Pa; when t > 0.6T, P varies within the range of 1 Pa to 2 Pa; the chemical composition of the stainless steel alloy ingot is shown in Table 1, and the relationship between the chemical compositions of the stainless steel alloy ingot is shown in Table 2.

[0108] Step 2: The stainless steel alloy ingot is heated, forged, and tempered multiple times to obtain a flat billet. The heating temperature is 1100℃.

[0109] Step 3: The flat billet is hot-rolled, annealed and softened, and then ground and welded to obtain a hot-rolled strip. The hot rolling temperature is 1100℃. The hot rolling includes a first hot rolling pass, a second hot rolling pass, and a third hot rolling pass. The deformation amount of the first hot rolling pass is 40%, the deformation amount of the second hot rolling pass is 50%, and the deformation amount of the third hot rolling pass is 60%. The final rolling temperature is 900℃. After rolling, the strip is water-cooled to room temperature.

[0110] Step 4: The hot-rolled strip is subjected to billet opening, intermediate heat treatment, cold rolling, intermediate grinding, edge trimming and solution treatment to obtain strip material; the cold rolling includes: first cold rolling, second cold rolling and third cold rolling, the deformation amount of the first cold rolling is 60%, the deformation amount of the second cold rolling is 70%, and the deformation amount of the third cold rolling is 80%.

[0111] Step 5: Perform surface finishing, cleaning, and shape correction on the strip. The specific process of surface finishing is as follows: first, use a 1000-mesh polishing wheel for coarse polishing, and then use a 3000-mesh polishing wheel for fine polishing.

[0112] Step 6: The strip is stamped and aged to obtain a fuel cell interconnect; the stamping includes the following parameters: heating temperature of 200℃~400℃, holding time of 20min~120min, and hydrogen injection rate ≥5m³. 3 / h; the aging treatment includes the following parameters: temperature 400℃~500℃, holding time 60min~90min, and hydrogen injection rate ≥20m³ / h. 3 / h. The parameters for the fabrication method of the fuel cell interconnect are shown in Table 3.

[0113] Table 1. Chemical composition (wt, %) of stainless steel alloy ingots, balance being Fe and unavoidable impurities.

[0114]

[0115] Table 2 Relationship between the chemical compositions of stainless steel alloy ingots

[0116]

[0117] Table 3 Parameters of the fuel cell interconnect fabrication method

[0118]

[0119] The fuel cell interconnects prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were subjected to performance tests, and the results are shown in Table 4.

[0120] Table 4 Performance of fuel cell interconnects

[0121]

[0122] As shown in Table 4, Examples 1-5 meet the process parameter range of this patent, with alloy density reaching 7.0 g / cm³ to 7.2 g / cm³; the total oxide film thickness after oxidation at 900℃ for 30,000 hours in an O₂-H₂O atmosphere is <15 μm; the tensile strength Rm at 900℃ is ≥250 MPa; the yield strength Rp0.2 at 900℃ is ≥210 MPa; and the coefficient of thermal expansion between 600℃ and 900℃ is 11 × 10⁻⁶. -6 / K~13×10 -6 / K.

[0123] In Comparative Example 1, [Al] / [V]≧32, too much Al is precipitated from the intermetallic compound, which deteriorates the high-temperature mechanical properties. Under the oxidation conditions of the oxide fuel cell material, the precipitated Al will rapidly diffuse to the outer layer of Cr2O3 to form Al2O3, resulting in an excessively thick oxide film.

[0124] In Comparative Example 2, the value of ([Zr]+1.1[B]) / ([Al]+[V]) is higher than 0.2, the Al content is lower than 8%, the density increases, and it cannot play a role in reducing the density; it deteriorates the high-temperature mechanical properties and oxidation properties, the tensile strength and yield strength at high temperature are lower than those in Examples 1-5, the oxide film thickness increases, and the battery performance deteriorates.

[0125] In Comparative Example 3, the Zr content was less than 0.4%, which failed to effectively improve the mechanical properties at medium and high temperatures.

[0126] In Comparative Example 4, the TO content was higher than 0.0020%. Some of the added alloying elements participated in oxidation and failed to effectively play an alloying role, which deteriorated the high-temperature mechanical properties and oxidation resistance.

[0127] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0128] In this embodiment, Al is introduced to reduce the alloy density; the aging process precipitates low-density FeAl intermetallic compounds, which improves the mechanical properties at medium and high temperatures. However, the Fe-Al intermetallic compounds are brittle, reducing the alloy's plasticity. Boron segregates at grain boundaries, improving grain boundary bonding strength, and its appropriate addition can improve the brittleness of the phase. Zr can improve both the room temperature plasticity of the Fe-Al intermetallic compounds and the medium-temperature plasticity of the alloy. The combined effect of B and Zr can improve the overall medium-temperature performance of the alloy from 600℃ to 900℃ and improve the alloy's processing performance.

[0129] In this embodiment, V is introduced to occupy the Al sites of the intermetallic compound, which improves the stability of the Fe-Al intermetallic compound, reduces brittleness, and improves the medium-temperature machinability of the alloy.

[0130] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A low-density stainless steel, in terms of mass fraction, the stainless steel contains the following chemical components: Cr: 13% - 30%, Al: 8% - 12%, V: 0.25% - 0.5%, B: 0.01% - 0.5%, Zr: 0.4% - 1.0%, C < 0.008%, T.O ≤ 0.002%, N ≤ 0.001%, Si: 0.15% - 0.3%, Mn: 0.1% - 0.8% and Fe; The chemical components satisfy the following relationship: 24 ≤ [Al] / [V] ≤ 32 In the formula, [V] represents the mass fraction of V, and [Al] represents the mass fraction of Al; The chemical components satisfy the following relationship: 0.01 ≤ ([Zr] + 1.1[B]) / ([Al] + [V]) ≤ 0.2 In the formula, [Zr] represents the mass fraction of Zr, [B] represents the mass fraction of B, [V] represents the mass fraction of V, and [Al] represents the mass fraction of Al.

2. A preparation method of the stainless steel according to claim 1, the method includes: Performing vacuum refining on the molten steel, when the T.O of the molten steel ≤ 0.002%, adding an alloy containing Al, V, B and Zr to the molten steel to obtain an alloyed molten steel; Pouring the alloyed molten steel to obtain the stainless steel.

3. The method according to claim 2, characterized in that, The time and pressure of the vacuum refining satisfy the following relationship: When t < 0.2T, P is 1 Pa - 5 Pa; When 0.2T < t < 0.6T, P is 0.1 Pa - 0.5 Pa; When t > 0.6T, P is 1 Pa - 2 Pa; Where, t represents the time of the vacuum refining, P represents the pressure of the vacuum refining, T represents the total time of the vacuum refining, and T is 0.5 h - 0.7 h.

4. A fuel cell interconnect, the fuel cell interconnect is made of the stainless steel according to claim 1.

5. The fuel cell interconnect according to claim 4, characterized in that, The fuel cell interconnect satisfies at least one of the following performances: The alloy density is 7.0 g / cm³. 3 ~7.2g / cm 3 ; In an O2-H2O atmosphere, the total thickness of the oxide film after oxidation at 900°C for 30000 h < 15 μm; The tensile strength Rm ≥ 250 MPa at 900°C; The yield strength Rp0.2 ≥ 210 MPa at 900°C; The coefficient of thermal expansion between 600℃ and 900℃ is 11×10⁻⁶. -6 / K~13×10 -6 / K.

6. A preparation method of the fuel cell interconnect according to claim 4 or 5, the method includes: Heating, forging and multi-pass tempering the stainless steel according to claim 1 in sequence to obtain a flat billet; Performing multi-pass hot rolling and annealing softening on the flat billet to obtain a hot-rolled strip billet; Performing intermediate heat treatment, multi-pass cold rolling and solution treatment on the hot-rolled strip billet to obtain a strip; Performing stamping forming and aging treatment on the strip to obtain a fuel cell interconnect.

7. The method according to claim 6, characterized in that, The stamping process includes the following parameters: heating temperature of 200℃~400℃, holding time of 20min~120min, and hydrogen injection volume ≥5m³. 3 / h.

8. The method according to claim 6, characterized in that, The aging treatment includes the following parameters: temperature of 400℃~500℃, holding time of 60min~90min, and hydrogen injection rate ≥20m³. 3 / h.

Images