Low-density stainless steel, fuel cell interconnection plate and preparation method

Abstract

The invention provides low-density stainless steel, a fuel cell interconnection plate and a preparation method, and belongs to the field of alloys. The stainless steel comprises the following chemical components: 13%-30% of Cr, 8%-12% of Al, 0.25%-0.5% of V, 0.01%-0.5% of B, 0.4%-1.0% of Zr, and Clt. The alloy comprises the following components in percentage by weight: 0.008% of Si, 0.008% or less of T.O, 0.001% or less of N, 0.15-0.3% of Si, 0.1-0.8% of Mn and Fe. The chemical components of stainless steel are reasonably designed. Al is introduced to reduce the alloy density, and a low-density FeAl intermetallic compound is separated out in the aging process, so that the mechanical property at medium and high temperatures is improved. The comprehensive performance of the alloy at the medium temperature of 600-900 DEG C can be improved through the comprehensive effect of B and Zr. And meanwhile, V is introduced to occupy the Al position of the intermetallic compound, so that the stability of the Fe-Al intermetallic compound is improved. Therefore, on the basis that the fuel cell interconnection plate has high strength, high toughness and oxidation resistance, the density of the fuel cell interconnection plate is reduced.

Description

Technical Field

[0001] The present application relates to the field of alloy technology, and in particular to a low-density stainless steel, a fuel cell interconnection plate and a preparation method thereof. Background Art

[0002] The urgent need to reduce greenhouse gas emissions and control global warming has attracted widespread attention from the industry. From the perspective of high-end material development, lightweighting can greatly reduce energy consumption and reduce carbon dioxide emissions. There are two main weight reduction ideas. One is to reduce the thickness of the material by increasing its strength to achieve the purpose of overall structural weight reduction. The other is to achieve lightweighting by developing low-density materials. Taking electric vehicles as an example, for every 10% reduction in the weight of an electric vehicle, its driving range can be increased by 5.5%. The "three-electric" system of new energy vehicles accounts for about 1 / 4 of the curb weight of the vehicle, and lightweighting is the key to solving this problem.

[0003] Light elements can expand the lattice constant of steel and reduce its density by virtue of low atomic weight. But at the same time, they bring a series of problems. Light elements have a significant impact on the thermodynamic stability of steel allotropes. For example, excessive use of aluminum without carbon compensation will cause the ferrite phase to be able to exist stably at different temperatures below the solidus, thus eliminating the possibility of organizational optimization through heat treatment. In addition, the precipitation of brittle phases is not conducive to the mechanical properties of materials. In solid fuel cells, the connector material accounts for more than 80% of the total weight. At present, the ferritic stainless steel connectors that have been studied more carefully for solid oxide fuel cells are Crofer 22APU, SUS430, X10CrAl18 and ZMG232. The more representative ferritic Fe-Cr alloys are ZMG232 developed by Hitachi Metals and Crofer22 APU alloy announced by ThyssenKrupp VDM in 2003. After optimization in the later period, ZMG232L and Crofer22H were further developed. Although the performance of the four alloys is excellent, the density of the above alloys is 7.8g / cm 3 ~8.0g / cm 3 Therefore, how to reduce the density of the fuel cell interconnection plate while ensuring that the fuel cell interconnection plate has high strength, high toughness and oxidation resistance is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application provides a low-density stainless steel, a fuel cell interconnection plate and a preparation method to solve the following technical problem: how to reduce the density of the fuel cell interconnection plate while ensuring that the fuel cell interconnection plate 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 method for preparing the stainless steel according to any one of the first aspect, the method comprising:

[0013] Vacuum refining the molten steel, and 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;

[0014] Casting 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] 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 first aspects.

[0021] Optionally, the fuel cell interconnection plate meets at least one of the following properties:

[0022] Alloy density is 7.0g / cm 3 ~7.2g / cm 3 ;

[0023] In O2-H2O atmosphere, the total thickness of the oxide film after oxidation at 900℃ for 30000h is less than 15μm;

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

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

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

[0027] In a fourth aspect, the present application provides a method for preparing the fuel cell interconnection plate according to the third aspect, the method comprising:

[0028] The stainless steel according to any one of the embodiments of the first aspect is sequentially heated, forged and tempered multiple times to obtain a slab;

[0029] The slab is subjected to multiple hot rolling and annealing to obtain a hot-rolled strip;

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

[0031] The strip is subjected to stamping and aging treatment to obtain a fuel cell interconnection plate.

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

[0033] Optionally, the aging treatment includes the following parameters: temperature of 400°C to 500°C, holding time of 60min to 90min, and hydrogen injection volume ≥ 20m 3 / h.

[0034] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0035] The present application provides a low-density stainless steel, which includes the following chemical components by mass fraction: Cr: 13% to 30%, Al: 8% to 12%, V: 0.25% to 0.5%, B: 0.01% to 0.5%, Zr: 0.4% to 1.0%, C < 0.008%, TO ≤ 0.002%, N ≤ 0.001%, Si: 0.15% to 0.3%, Mn: 0.1% to 0.8% and Fe. The chemical composition of the stainless steel is reasonably designed. By introducing Al to reduce the density of the alloy, the low-density FeAl intermetallic compound precipitated during the aging process has the effect of improving the mechanical properties at medium and high temperatures. At the same time, the Fe-Al intermetallic compound is brittle, which reduces the plasticity of the alloy. B is concentrated at the grain boundary, improving the grain boundary bonding force. The appropriate addition can improve the brittleness of the phase. Zr can improve the room temperature plasticity of the Fe-Al intermetallic compound and the medium temperature plasticity of the alloy. The combined effect of B and Zr can improve the comprehensive performance of the alloy at 600℃ to 900℃ and improve the processing performance of the alloy. At the same time, the introduction of V to occupy the Al position of the intermetallic compound improves the stability of the Fe-Al intermetallic compound, reduces the brittleness, and improves the medium temperature processability of the alloy. In this way, the density of the fuel cell interconnection plate is reduced on the basis of meeting the requirements of high strength, high toughness and oxidation resistance of the fuel cell interconnection plate. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0037] 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.

[0038] Figure 1 A schematic diagram of a process for preparing stainless steel provided in an embodiment of the present application;

[0039] Figure 2 A schematic flow chart of a method for preparing a fuel cell interconnection plate provided in an embodiment of the present application;

[0040] Figure 3 This is a metallographic structure diagram of stainless steel provided in Example 1 of the present application. DETAILED DESCRIPTION

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

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

[0046] The functions of each component are mainly reflected in:

[0047] Cr: A basic element to ensure the oxidation resistance and thermal expansion performance of the present invention. If the content is less than 12%, the oxidation resistance of the present invention cannot be achieved, and if the content is more than 30%, the thermal expansion performance cannot be satisfied. For example, the content of Cr can be 13%, 15%, 18%, 20%, 25%, 28%, 30%, etc.

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

[0049] B: reduces alloy density and is also a grain boundary strengthening element. It can increase alloy plasticity, is beneficial to the coordinated deformation of grain boundaries during hot working, and can improve the oxidation resistance and creep resistance of the alloy. If the B content is too high, large-sized B-containing precipitates will form at the grain boundaries, deteriorating the performance. For example, the B content can be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0050] Al: Aluminum is a strong deoxidizer, which can improve the oxidation resistance and high temperature strength of the alloy. In addition, it can also reduce the density of the alloy, achieving the advantages of lightweight and low cost of the material; excessive addition affects the tensile properties and welding properties. In the present invention, Al is introduced to form Fe-Al intermetallic compounds, which have the advantages of low density, high specific strength, good resistance to high temperature oxidation and corrosion resistance, etc., but the disadvantage is that it is brittle and unstable. Exemplarily, the content of Al can be 8%, 9%, 10%, 11%, 12%, etc.

[0051] Zr: Purifies grain boundaries, and is added in combination with B to enhance grain boundary bonding and maintain high temperature strength. Anti-oxidation, improves oxide film structure, inhibits inward diffusion of oxygen, and enhances the bonding between oxide film and stainless steel matrix. Excessive addition will deteriorate hot working properties. Exemplarily, the Zr content can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0052] Si: deoxidizer, can improve the oxidation resistance and high temperature strength of the alloy. Excessive addition will form SiO2 on the surface of the alloy during oxidation, affecting the conductivity. Exemplarily, the content of Si can be 0.15%, 0.2%, 0.25%, 0.3%, etc.

[0053] Mn: deoxidizer, can improve the oxidation resistance and high temperature strength of the alloy. Excessive addition will increase the thermal expansion coefficient of the alloy. Exemplarily, the content of Mn 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 is the total oxygen content.

[0055] 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.

[0056] In some embodiments, the chemical composition satisfies the following relationship:

[0057] 24≤[Al] / [V]≤32

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

[0059] In some embodiments, the chemical composition satisfies 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] At present, relevant research is being carried out both at home and abroad. The main direction is to reduce the density of the material by adding a certain amount of Al, Mn, and C elements. Such alloys are generally called low-density alloys or light alloys. The degree of density reduction depends on the addition amount of Al, Mn, and C light elements. Among them, Al has the greatest impact on the density of the material. Every 1% addition can reduce the density of the alloy by 0.101g / cm 3 The technical difficulty is that the higher the content of alloying elements such as Al, the more severe the brittleness caused by grain boundary weakening, the poorer the processing performance and mechanical properties, and the easier it is to produce cracks during the rolling process. Therefore, the technical problems of low density, high strength and toughness, and oxidation resistance in the production process of fuel cells need to be solved urgently.

[0063] Therefore, the embodiment of the present application reduces the density of the alloy by introducing Al; the low-density FeAl intermetallic compound precipitated during the aging process has the effect of improving the mechanical properties at medium and high temperatures, while the Fe-Al intermetallic compound is brittle, which reduces the plasticity of the alloy. B is concentrated at the grain boundary, improving the grain boundary bonding force, and adding an appropriate amount can improve the brittleness of the phase. Zr can improve both the room temperature plasticity of the Fe-Al intermetallic compound and the medium-temperature plasticity of the alloy. The combined effect of B and Zr can improve the comprehensive performance of the alloy at 600℃ to 900℃ and improve the processing performance of the alloy.

[0064] The introduction of V to occupy the Al position of the intermetallic compound improves the stability of the Fe-Al intermetallic compound, reduces brittleness, and improves the medium-temperature machinability of the alloy; when [Al] / [V]≧32, Al precipitates too much from the intermetallic compound. Under the oxidation conditions of the oxide fuel cell material, the precipitated Al will quickly diffuse the outer layer of Cr2O3 to form Al2O3, deteriorating the conductivity and reducing the battery life; when [Al] / [V]≤24, due to the low concentration ratio, it cannot replace the position of Al. Exemplarily, 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 A schematic flow chart of a method for preparing stainless steel provided in an embodiment of the present application.

[0066] like Figure 1 As shown, the present application provides a method for preparing the stainless steel described in any one of the above, the method comprising:

[0067] S11. vacuum refining the molten steel, and when the TO of the molten steel is less than or equal to 0.002%, adding an alloy containing Al, V, B and Zr to the molten steel to obtain an alloyed molten steel;

[0068] 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.

[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, that is, added before steel is tapped in the late refining stage, 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 medium-temperature mechanical properties and oxidation resistance of the product will be unstable.

[0070] S12, pouring the alloyed steel liquid 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 1Pa~5Pa;

[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 the 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 alloying 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 ≤ 20 ppm in the alloy, 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 alloying 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, and the fuel cell interconnect plate is made of the stainless steel according to any one of the first aspect.

[0080] In some embodiments, the fuel cell interconnect plate 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≥210MPa at 900℃;

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

[0086] Alloy density: The alloy density required for the fuel cell interconnection plate is 7.0g / cm 3 ~7.2g / cm 3 . This density range has an important influence on ensuring the weight, strength and corrosion resistance of the interconnection board. Oxide film thickness: In an O2-H2O atmosphere, the total thickness of the oxide film on the interconnection board after oxidation at 900°C for 30,000 hours should be less than 15μm. This requirement is intended to ensure the long-term stability and durability of the interconnection board in a high-temperature oxidizing environment. Tensile strength and yield strength: At 900°C, the tensile strength Rm of the interconnection board should not be less than 250MPa, and the yield strength Rp0.2 should not be less than 210MPa. These strength requirements are critical to ensuring the structural integrity and load-bearing capacity of the interconnection board in a high-temperature environment. Thermal expansion coefficient: The thermal expansion coefficient of the interconnection board at 600°C to 900°C is 11×10 -6 / K~13×10 -6 / K. This requirement helps ensure the dimensional stability and compatibility of the interconnect board with other components in high temperature operating environments.

[0087] The low-density solid oxide fuel cell interconnect provided in the embodiment of the present application has an alloy prepared by rationally designing the chemical composition, which has excellent mechanical properties and oxidation resistance under 900°C medium-temperature oxidation conditions, as well as a stable low thermal expansion coefficient, meeting the design and use requirements of solid oxide fuel cells. For example, the alloy density can be 7.0 g / cm 3 , 7.05g / cm 3 , 7.1g / cm 3 , 7.15g / cm 3 , 7.2g / cm 3 etc.; in O2-H2O atmosphere, the total thickness of the oxide film oxidized at 900℃ for 30000h 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 thermal expansion coefficient at 600℃~800℃ can be 11×10 -6 / K, 11.5×10 -6 / K, 12×10-6 / K, 12.5×10 -6 / K, 13×10 -6 / K, etc.

[0088] Figure 2 A schematic flow chart of a method for preparing a fuel cell interconnect plate provided in an embodiment of the present application.

[0089] like Figure 2 As shown, the present application provides a method for preparing a fuel cell interconnection plate according to the third aspect, the method comprising:

[0090] S21, sequentially heating, forging and multi-pass tempering the stainless steel described in any one of the above embodiments to obtain a flat slab;

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

[0092] S22, performing multiple hot rolling and annealing to soften the slab to obtain a hot-rolled strip;

[0093] The slab is subjected to multiple hot rolling processes to further improve the plasticity and deformability of the material, followed by annealing and softening to reduce the hardness of the material and increase its toughness in preparation for subsequent cold rolling.

[0094] In some embodiments, the temperature of the multiple hot rolling is 1000°C to 1150°C. The multiple hot rolling includes: a first hot rolling, a second hot rolling, and a third hot rolling, the first hot rolling deformation is 30% to 50%, the second hot rolling deformation is 40% to 60%, and the third hot rolling deformation is 50% to 80%. The final rolling temperature is higher than 900°C. After rolling, water cooling is performed to room temperature.

[0095] S23, subjecting the hot-rolled strip to intermediate heat treatment, multiple cold rolling and solution treatment to obtain a strip;

[0096] The hot-rolled strip is subjected to intermediate heat treatment to adjust its microstructure and mechanical properties. Then it is subjected to multiple cold rolling processes to obtain the required plate thickness and precision. Finally, solid solution treatment is performed to eliminate the internal stress and structural defects generated during the cold rolling process, and to improve the corrosion resistance and oxidation resistance of the material.

[0097] In some embodiments, the multiple cold rolling passes include: a first cold rolling pass, a second cold rolling pass and a third cold rolling pass, the deformation of the first cold rolling pass is 50% to 70%, the deformation of the second cold rolling pass is 60% to 80%, and the deformation of the third cold rolling pass is 70% to 80%.

[0098] S24, stamping and aging the strip to obtain a fuel cell interconnection plate.

[0099] The strip is subjected to a stamping process to obtain the desired shape and size of the interconnection plate, and then an aging treatment is performed to further stabilize the microstructure and mechanical properties of the material and improve the long-term stability and durability of the interconnection plate.

[0100] In some embodiments, the stamping forming includes the following parameters: heating temperature is 200°C to 400°C, holding time is 20min to 120min, hydrogen injection volume is ≥5m 3 / h.

[0101] The heating temperature is controlled between 200℃ and 400℃. This temperature range helps to reduce the deformation resistance of the material and improve its plasticity, which is conducive to the stamping process. At the same time, the appropriate heating temperature can also reduce defects such as cracks and deformation generated during the stamping process. The insulation time is controlled between 20min and 120min. The length of the insulation time depends on the thickness of the material and the degree of microstructural change required. The appropriate insulation time can ensure that the material is fully and evenly heated during the heating process and reaches the required microstructural state. The amount of hydrogen spraying should not be less than 5m 3 / h. Hydrogen spray treatment helps to eliminate the internal stress and structural defects of the material generated during the stamping process, and improve the mechanical properties and corrosion resistance of the material. At the same time, hydrogen spray treatment can also promote the uniform deformation and flow of the material, which is conducive to obtaining interconnected plates with high shape and dimensional accuracy. Exemplarily, the heating temperature can be 200°C, 220°C, 250°C, 280°C, 300°C, 340°C, 360°C, 400°C, etc., the holding time can be 20min, 40min, 60min, 80min, 100min, 120min, etc., and the hydrogen spray volume can be 5m 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°C to 500°C, holding time of 60min to 90min, and hydrogen injection volume of ≥20m 3 / h.

[0103] During 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 process, 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 interconnector plate is the above-mentioned fuel cell interconnector plate. The chemical composition and microstructure of the fuel cell interconnector plate prepared by the preparation method of the fuel cell interconnector plate can refer to the above embodiments. Since the preparation method of the fuel cell interconnector plate adopts some or all of the technical solutions of the fuel cell interconnector plate embodiment, it has at least all the beneficial effects brought by the technical solutions of the fuel cell interconnector plate embodiment, which will not be elaborated one by one here.

[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 interconnector plate, 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 alloyed molten steel; the alloyed molten steel is cast, 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: heating, forging and multi-pass tempering the stainless steel alloy ingot to obtain a flat slab, wherein the heating temperature is 1100°C.

[0109] Step 3, hot rolling, annealing, softening, grinding and welding the flat slab to obtain a hot-rolled strip; the hot rolling temperature is 1100°C. The hot rolling includes: a first hot rolling, a second hot rolling and a third hot rolling. The first hot rolling deformation is 40%, the second hot rolling deformation is 50%, and the third hot rolling deformation is 60%. The final rolling temperature is 900°C. After rolling, water cooling to room temperature.

[0110] Step 4, subjecting the hot-rolled strip to blanking, intermediate heat treatment, cold rolling, intermediate grinding, trimming and solution treatment to obtain a strip; the cold rolling includes: a first cold rolling pass, a second cold rolling pass and a third cold rolling pass, the first cold rolling pass has a deformation of 60%, the second cold rolling pass has a deformation of 70%, and the third cold rolling pass has a deformation of 80%.

[0111] Step 5, surface finishing, cleaning and plate shape correction of the strip, the specific process of the surface finishing is: firstly use a polishing wheel with a particle size of 1000 mesh for rough polishing, and then use a polishing wheel with a particle size of 3000 mesh for fine polishing.

[0112] Step 6: stamping and aging the strip to obtain a fuel cell interconnection plate; the stamping includes the following parameters: heating temperature of 200°C to 400°C, insulation time of 20min to 120min, hydrogen injection volume ≥5m 3 / h; the aging treatment includes the following parameters: temperature of 400℃~500℃, holding time of 60min~90min and hydrogen injection volume ≥20m 3 / h. The parameters of the preparation method of the fuel cell interconnection plate are shown in Table 3.

[0113] Table 1 Chemical composition of stainless steel alloy ingot (wt, %), the balance is Fe and unavoidable impurities

[0114] serial number Cr Al V B Zr C N TO Si Mn Example 1 13 8 0.25 0.01 0.4 0.007 0.001 0.0018 0.15 0.1 Example 2 20 10 0.35 0.1 0.6 0.006 0.0009 0.0019 0.2 0.3 Example 3 25 11 0.4 0.3 0.8 0.007 0.001 0.0020 0.3 0.5 Example 4 30 12 0.5 0.5 1 0.006 0.009 0.0018 0.2 0.7 Example 5 15 9 0.3 0.05 0.5 0.007 0.008 0.0018 0.2 0.8 Comparative Example 1 20 10 0.3 0.1 0.6 0.007 0.001 0.0018 0.15 0.4 Comparative Example 2 20 3 0.25 0.5 1 0.006 0.0009 0.0019 0.2 0.5 Comparative Example 3 20 8 0.25 0.05 0.2 0.006 0.001 0.0018 0.3 0.6 Comparative Example 4 25 11 0.4 0.3 0.8 0.007 0.001 0.0030 0.3 0.5

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

[0116] serial number [Al] / [V] ([Zr]+1.1[B]) / ([Al]+[V]) Example 1 32.00 0.05 Example 2 28.57 0.069 Example 3 27.50 0.099 Example 4 24.00 0.124 Example 5 30.00 0.060 Comparative Example 1 33.33 0.069 Comparative Example 2 12.00 0.477 Comparative Example 3 32.00 0.031 Comparative Example 4 27.50 0.099

[0117] Table 3 Parameters of the preparation method of the fuel cell interconnection plate

[0118]

[0119]

[0120] The fuel cell interconnection plates 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.

[0121] Table 4 Performance of fuel cell interconnection board

[0122]

[0123] As shown in Table 4, Examples 1 to 5 meet the process parameter range of this patent, and the alloy density reaches 7.0 g / cm3 to 7.2 g / cm3; the total thickness of the oxide film oxidized at 900 ° C for 30000 h in O2-H2O atmosphere is less than 15 μm; the tensile strength Rm at 900 ° C is ≥ 250 MPa; the yield strength Rp0.2 at 900 ° C is ≥ 210 MPa; the thermal expansion coefficient at 600 ° C to 900 ° C is 11×10 -6 / K~13×10 -6 / K.

[0124] In Comparative Example 1, [Al] / [V]≧32, and Al precipitates too much from the intermetallic compound, deteriorating the high-temperature mechanical properties. Under the oxidation conditions of the oxide fuel cell material, the precipitated Al will quickly diffuse the outer layer of Cr2O3 to form Al2O3, and the thickness of the oxide film is too large.

[0125] 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 the density cannot be reduced; the high-temperature mechanical properties and oxidation properties deteriorate, the tensile strength and yield strength at high temperature are lower than those of Examples 1 to 5, the thickness of the oxide film increases, and the battery performance deteriorates.

[0126] In Comparative Example 3, the Zr content is lower than 0.4%, which fails to effectively improve the medium and high temperature mechanical properties.

[0127] In Comparative Example 4, TO is higher than 0.0020%, and part of the added alloying elements participates in oxidation, failing to effectively play the role of alloying, thereby deteriorating the high-temperature mechanical properties and oxidation resistance.

[0128] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0129] In the embodiment of the present application, Al is introduced to reduce the density of the alloy; the low-density FeAl intermetallic compound precipitated during the aging process has the effect of improving the mechanical properties at medium and high temperatures, while the Fe-Al intermetallic compound is brittle, which reduces the plasticity of the alloy. B is concentrated at the grain boundary, improving the grain boundary bonding force, and adding an appropriate amount can improve the brittleness of the phase. Zr can improve both the room temperature plasticity of the Fe-Al intermetallic compound and the medium-temperature plasticity of the alloy. The combined effect of B and Zr can improve the comprehensive performance of the alloy at 600℃ to 900℃ and improve the processing performance of the alloy.

[0130] In the embodiments of the present application, V is introduced to occupy the Al position of the Fe-Al intermetallic compound, so that the stability of the Fe-Al intermetallic compound is improved, while the brittleness is reduced and the medium-temperature machinability of the alloy is improved.

[0131] 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 low-density stainless steel, by 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.

2. The stainless steel according to claim 1, characterized in that 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.

3. The stainless steel according to claim 1, characterized in that 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.

4. A preparation method of the stainless steel according to any one of claims 1 - 3, the method comprising: 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; Casting the alloyed molten steel to obtain the stainless steel.

5. The method according to claim 4, 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; 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 - 0.7 h.

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

7. The fuel cell interconnect according to claim 6, characterized in that: The fuel cell interconnect plate satisfies at least one of the following performances: Alloy density is 7.0g / cm 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 thermal expansion coefficient at 600℃~900℃ is 11×10 -6 / K~13×10 -6 / K.

8. A preparation method of the fuel cell interconnect plate according to claim 6 or 7, the method comprising: Successively heating, forging and multi-pass tempering the stainless steel according to any one of claims 1 - 3 to obtain a flat blank; Performing multi-pass hot rolling and annealing softening on the flat blank to obtain a hot-rolled strip blank; Performing intermediate heat treatment, multi-pass cold rolling and solution treatment on the hot-rolled strip blank to obtain a strip; Performing stamping forming and aging treatment on the strip to obtain a fuel cell interconnect plate.

9. The method according to claim 8, characterized in that The stamping forming includes the following parameters: heating temperature is 200℃~400℃, holding time is 20min~120min, hydrogen injection volume is ≥5m 3 / h.

10. The method according to claim 8, characterized in that The aging treatment includes the following parameters: temperature of 400°C to 500°C, holding time of 60min to 90min, and hydrogen injection volume of ≥20m 3 / h.

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