Stainless steel with excellent hydrogen embrittlement resistance, interconnection plate and preparation method

Abstract

The invention provides stainless steel with excellent hydrogen embrittlement resistance, an interconnection plate and a preparation method, and belongs to the field of alloys. The stainless steel comprises the following chemical components: 20%-30% of Cr, 0.6%-5.0% of Al, 3%-5% of Mo, 1%-6.0% of Nb, 0.001%-1.0% of rare earth elements, and Clt. 0.05%, T.O < = 0.002%, and Fe. A stable and dispersed Laves phase is formed by accurately controlling the chemical components in the stainless steel, especially the contents and proportions of Al, Mo, Nb and rare earth elements. As irreversible hydrogen traps, the Laves phases can adsorb hydrogen atoms and inhibit hydrogen diffusion, so that the average hydrogen concentration of the alloy in the loading process is remarkably reduced, and the hydrogen embrittlement tendency of the alloy is inhibited. Meanwhile, due to the addition of the rare earth elements, atomic lattice distortion is generated, the grain boundary is strengthened, the medium-high temperature mechanical property is further improved, the cohesiveness of a surface oxidation film and a base body is improved, and the oxidation resistance is enhanced.

Description

Technical Field

[0001] The present application relates to the field of alloy technology, and in particular to a stainless steel with excellent hydrogen embrittlement resistance, an interconnection plate and a preparation method thereof. Background Art

[0002] High-temperature solid oxide fuel cells (SOFCs) are highly efficient energy conversion devices that convert the chemical energy of fuels into electrical energy without chemical reactions. They can directly use carbon-containing gases such as methane, natural gas and water gas as fuels. The working conditions are 600℃~800℃, and the oxygen partial pressure of the cathode (air electrode) is PO2=2.18×10 4 Pa, water partial pressure is PO2 = 3 × 10 3 Pa, oxygen partial pressure at anode (fuel electrode) PO2 = 4.1 × 10 -17 Pa, water partial pressure is PH2O = 6 × 10 2 Pa~4×10 3 Pa, PH2O = 1 × 10 3 Pa. The metal connector can meet the basic requirements of hydrogen embrittlement resistance, oxidation resistance, mechanical properties, thermal expansion coefficient, etc. at the working temperature. Among them, hydrogen embrittlement performance greatly affects the life of the material. Hydrogen embrittlement is the material in a hydrogen environment, due to the invasion and diffusion of hydrogen atoms, resulting in increased brittleness of the material, decreased strength, and ultimately causing the material to break. This phenomenon is particularly serious under high hydrogen pressure, high temperature and high hydrogen concentration environments. Under SOFC working conditions, even materials with good mechanical properties and corrosion resistance may cause structural failure due to hydrogen embrittlement, posing a safety hazard. After hydrogen atoms are adsorbed into the alloy, they easily diffuse to dislocations, holes, and microcracks in the alloy, thereby reducing the bonding force of the alloy and causing it to fail due to hydrogen embrittlement. Diffusible hydrogen is considered to be the main factor causing hydrogen embrittlement in the alloy. The diffusion rate of hydrogen in ferrite is faster than that in austenite, so the hydrogen embrittlement problem of ferrite alloys is more prominent.

[0003] Until now, due to the restriction of thermal expansion coefficient at high temperature, the expansion coefficient of the solid electrolyte has been (9-11)×10 -6 / K, the current common practice is to use ferritic stainless steel connectors. Such as the commercial alloys Crofer22APU, SUS430, X10CrAl18 and ZMG232. Although the above alloys have excellent performance, there are still bottlenecks in commercial use. Although Fe-Cr-based alloys have suitable thermal expansion coefficients and oxidation resistance, the long-term use of hydrogen-containing fuel gas and the hydrogen embrittlement resistance of interconnect materials are technical problems that restrict the life of solid oxide fuel cell interconnect materials. Therefore, it is urgent to develop interconnect materials with excellent hydrogen embrittlement resistance. Summary of the invention

[0004] The present application provides a stainless steel with excellent hydrogen embrittlement resistance, an interconnection plate and a preparation method to solve the following technical problem: how to improve the hydrogen embrittlement resistance of a fuel cell interconnection plate.

[0005] In a first aspect, the present application provides a stainless steel having excellent hydrogen embrittlement resistance, wherein the stainless steel comprises the following chemical components by mass fraction: Cr: 20% to 30%, Al: 0.6% to 5.0%, Mo: 3% to 5%, Nb: 1% to 6.0%, rare earth elements: 0.001% to 1.0%, C<0.05%, TO≤0.002% and Fe. ;

[0006] Wherein, the rare earth elements include: one or more of Ce, La, Sc and Y.

[0007] Optionally, the stainless steel also includes the following chemical components: W: 1% to 6.0%, Si: 0.05% to 3.0%.

[0008] Optionally, the chemical composition satisfies the following relationship:

[0009] 0.5≤([Al]+0.25×[Cr]) / ([Mo]+[Nb])≤5

[0010] In the formula, [Al] represents the mass fraction of Al, [Cr] represents the mass fraction of Cr, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

[0011] Optionally, the chemical composition satisfies the following relationship:

[0012] 0.1<[R] / (0.08×[Mo]+0.12×[Nb])<1.5

[0013] In the formula, [R] represents the mass fraction of the rare earth element, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

[0014] Optionally, the alloy cast structure of the stainless steel includes, by volume fraction, ferrite phase ≧85%, and Laves phase ≤15%.

[0015] 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:

[0016] 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 Al, Mo, Nb and rare earth elements is added to the molten steel to obtain an alloyed molten steel;

[0017] The alloyed steel liquid is poured to obtain the stainless steel.

[0018] In a third aspect, the present application provides a fuel cell interconnect, wherein the fuel cell interconnect plate is made of the stainless steel described in any one of the embodiments of the first aspect, and the alloy cast structure of the fuel cell interconnect plate includes, by volume fraction: ferrite phase ≧85%, 2% ≤ Laves phase ≤5%.

[0019] Optionally, the fuel cell interconnection plate meets at least one of the following properties:

[0020] Tensile strength Rm≥250MPa at 900℃;

[0021] Yield strength Rp0.2≥210MPa at 900℃;

[0022] The thickness of the oxide film oxidized at 900℃ for 1000h is ≤1.5μm;

[0023] The tensile strain after electrochemical hydrogen charging for 24 hours is ≥35.0%, the yield strength is ≥260MPa, and the tensile strength is ≥210MPa.

[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; the cold rolling reduction ratio is ≧40%.

[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 excellent hydrogen embrittlement resistance, which includes the following chemical components by mass fraction: Cr: 20% to 30%, Al: 0.6% to 5.0%, Mo: 3% to 5%, Nb: 1% to 6.0%, rare earth elements: 0.001% to 1.0%, C < 0.05%, TO ≤ 0.002% and Fe. ; Wherein, the rare earth elements include: one or more of Ce, La, Sc and Y. By precisely controlling the chemical composition in the stainless steel, especially the content and proportion of Al, Mo, Nb and rare earth elements, a stable and dispersed Laves phase is formed. These Laves phases, as irreversible hydrogen traps, can adsorb hydrogen atoms and inhibit hydrogen diffusion, thereby significantly reducing the average hydrogen concentration of the alloy during loading and inhibiting the hydrogen embrittlement tendency of the alloy. At the same time, the addition of rare earth elements not only produces atomic lattice distortion, but also strengthens the grain boundaries, further improves the medium and high temperature mechanical properties, improves the adhesion between the surface oxide film and the matrix, and enhances the oxidation resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[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 excellent hydrogen embrittlement resistance, which comprises the following chemical components by mass fraction: Cr: 20% to 30%, Al: 0.6% to 5.0%, Mo: 3% to 5%, Nb: 1% to 6.0%, rare earth elements: 0.001% to 1.0%, C<0.05%, TO≤0.002% and Fe. ;

[0037] Wherein, the rare earth elements include: one or more of Ce, La, Sc and Y.

[0038] In some embodiments, the stainless steel further comprises the following chemical components: W: 1% to 6.0%, Si: 0.05% to 3.0%.

[0039] The functions of each element are as follows:

[0040] Cr: A basic element to ensure the oxidation resistance and thermal expansion performance of stainless steel. If the content is less than 20%, the oxidation resistance in a strong oxidizing atmosphere of the present invention cannot be achieved. Due to the solid solution treatment effect of Cr, if it is higher than 30%, the expansion coefficient will be too large, which is too different from the expansion coefficient of the solid electrolyte, and the conductivity will deteriorate, reducing the battery life. Exemplarily, the mass fraction of Cr can be 20%, 21%, 22%, 23%, 24%, 26%, 28%, 30%, etc.

[0041] 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. A more important role in the embodiments of the present application: at an operating temperature of 600-900°C, the diffusion rate of Al is accelerated, and it can replace Fe or Cr, (Fe, Cr)2(Mo, Nb) to improve the stability of the Laves phase, while improving the medium and high temperature mechanical properties. Exemplarily, the mass fraction of Al can be 0.6%, 1%, 2%, 3%, 4%, 5.0%, etc.

[0042] Mo: a solution treatment strengthening element that can improve alloy strength and corrosion resistance. It is also a Laves phase forming element. When the content is lower than 3%, Laves phase cannot be formed. When the content is higher than 5%, Mo will enter the oxide layer under oxidation conditions, causing the oxide layer to peel off. At the same time, it cooperates with Al and Nb to form a Laves phase structure with a B2A structure. Exemplarily, the mass fraction of Mo can be 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0043] Nb: a solution treatment strengthening element that can improve the strength of the alloy; it is also a Laves phase forming element. In the embodiment of the present application, it cooperates with Al and Mo to form a Laves phase structure with a B2A structure. Exemplarily, the mass fraction of Nb can be 0.05%, 1%, 2%, 3%, 4%, 5%, 6.0%, etc.

[0044] Rare earth elements: The addition of rare earth elements can act as elements with a larger atomic radius than iron, producing lattice distortion in the ferrite matrix. At the same time, rare earth elements can be concentrated at grain boundaries, strengthen grain boundaries, and improve medium and high temperature mechanical properties; in addition, rare earth elements can improve the adhesion between the surface oxide film and the matrix and improve oxidation resistance. Exemplarily, the mass fraction of the rare earth element can be 0.001%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1.0%, etc.

[0045] 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 constituent element of A in Laves phase B2A, which further enhances the strength and corrosion resistance of stainless steel. Exemplarily, the W content can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, etc.

[0046] Si: As a deoxidizer, Si 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 0.05%, 0.1%, 0.15%, 0.2%, 0.5%, 1.0%, 2.0%, 3.0%, etc.

[0047] It should be noted that TO is the total oxygen content.

[0048] 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.

[0049] In some embodiments, the chemical composition satisfies the following relationship:

[0050] 0.5≤([Al]+0.25×[Cr]) / ([Mo]+[Nb])≤5

[0051] In the formula, [Al] represents the mass fraction of Al, [Cr] represents the mass fraction of Cr, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

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

[0053] 0.1<[R] / (0.08×[Mo]+0.12×[Nb])<1.5

[0054] In the formula, [R] represents the mass fraction of the rare earth element, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

[0055] The introduction of rare earth elements, since the atomic radius of rare earth elements is larger than that of Fe, produces atomic lattice distortion in the ferrite matrix. Through the synergistic relationship between rare earth elements and Mo and Nb, combined with the large atomic lattice distortion, dislocation hydrogen traps located in the crystal are caused, forming dispersed hydrogen traps throughout the crystal and subgrain boundaries. When [R] / (0.08×[Mo]+0.12×[Nb]) is lower than 0.1, the dislocation density in the crystal is lower than the subgrain boundary, and the precipitated Laves phase is unevenly distributed; when [R] / (0.08×[Mo]+0.12×[Nb]) is higher than 1.5, the dislocation density in the crystal is higher than the subgrain boundary, and the precipitated Laves phase is also unevenly distributed. By controlling 0.1<[R] / (0.08×[Mo]+0.12×[Nb])<1.5, a uniformly dispersed Laves phase is formed. When ([Al]+0.25×[Cr]) / ([Mo]+[Nb])>5, Al cannot enter Laves completely. The remaining aluminum diffuses to the surface in an oxidizing atmosphere to form Al2O3, which reduces the conductivity of the oxide film. When ([Al]+0.25×[Cr]) / ([Mo]+[Nb])<0.5, Al does not reach the critical concentration and cannot enter the Laves phase to improve the stability of the structure. By controlling the coordination of Al, Mo, and Nb, and controlling 0.5≤([Al]+0.25×[Cr]) / ([Mo]+[Nb])≤5, Al can enter the Laves stable phase completely and replace the position of B in the B2A structure, stabilizing the phase composition and forming a stable diffuse irreversible hydrogen trap. For example, the value of ([Al]+0.25×[Cr]) / ([Mo]+[Nb]) can be 0.5, 1, 2, 3, 4, 5, etc., and the value of [R] / (0.08×[Mo]+0.12×[Nb]) can be 0.1, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, etc.

[0056] In some embodiments, the alloy cast structure of the stainless steel includes, by volume fraction, ferrite phase ≧85%, and Laves phase ≤15%.

[0057] The embodiment of the present application forms a stable and dispersed Laves phase by precisely controlling the chemical composition of stainless steel, especially the content and ratio of Al, Mo, Nb and rare earth elements. For example, the volume fraction of the ferrite phase can be 85%, 87%, 89%, 90%, 92%, 95%, etc., and the volume fraction of the Laves phase can be 5%, 7%, 9%, 10%, 12%, 14%, 15%, etc.

[0058] Figure 1 A schematic flow chart of a method for preparing stainless steel provided in an embodiment of the present application.

[0059] like Figure 1 As shown, 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:

[0060] S1, vacuum refining the molten steel, and when the TO of the molten steel is ≤0.002%, adding an alloy containing Al, Mo, Nb and rare earth elements to the molten steel to obtain an alloyed molten steel;

[0061] S2, pouring the alloyed steel liquid to obtain the stainless steel.

[0062] 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.

[0063] In some embodiments, when the vacuum refining time is 0.6×T to 0.8×T, an alloy containing Al, Mo, Nb and Ce 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 conductivity and oxidation resistance of the product will be uneven.

[0064] 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.

[0065] Based on a general inventive concept, the present application provides a fuel cell interconnect, wherein the fuel cell interconnect plate is made of the stainless steel described in any one of the embodiments of the first aspect, and the alloy cast structure of the fuel cell interconnect plate includes, by volume fraction: ferrite phase ≧85%, 2% ≤ Laves phase ≤5%.

[0066] In some embodiments, the fuel cell interconnect plate satisfies at least one of the following properties:

[0067] Tensile strength Rm≥250MPa at 900℃;

[0068] Yield strength Rp0.2≥210MPa at 900℃;

[0069] The thickness of the oxide film oxidized at 900℃ for 1000h is ≤1.5μm;

[0070] The tensile strain after electrochemical hydrogen charging for 24 hours is ≥35.0%, the yield strength is ≥260MPa, and the tensile strength is ≥210MPa.

[0071] As a key component in the fuel cell system, the performance of the fuel cell interconnection plate directly affects the stability and service life of the entire system. The interconnection plate has good resistance to hydrogen embrittlement and oxidation during fuel cell operation, which increases the service life of the fuel cell.

[0072] High temperature tensile strength and yield strength: Tensile strength Rm ≥ 250MPa at 900°C: This means that the interconnection plate can still maintain sufficient strength at high temperatures to resist external loads and ensure the structural integrity of the fuel cell stack. Yield strength Rp0.2 ≥ 210MPa at 900°C: Yield strength is the maximum stress of a material before plastic deformation begins. High yield strength indicates that the interconnection plate has good deformation resistance at high temperatures. Exemplarily, the tensile strength Rm at 900°C can be 250MPa, 255MPa, 260MPa, 265MPa, 270MPa, 275MPa, etc. Exemplarily, the yield strength Rp0.2 at 900°C can be 210MPa, 215MPa, 220MPa, 225MPa, 230MPa, 235MPa, 240MPa, etc.

[0073] Oxidation resistance: The thickness of the oxide film oxidized at 900°C for 1000 hours is ≤ 1.5 μm: This indicator reflects the oxidation resistance of the interconnection board at high temperatures. A thinner oxide film means that the interconnection board can resist oxidation corrosion more effectively, thereby extending its service life. For example, the thickness of the oxide film oxidized at 900°C for 1000 hours can be 1.5 μm, 1.4 μm, 1.3 μm, 1.2 μm, 1.1 μm, 1.0 μm, 0.9 μm, etc.

[0074] Hydrogen embrittlement resistance: Tensile strain ≥ 35.0%, yield strength ≥ 260MPa, tensile strength ≥ 210MPa after 24h of electrochemical hydrogenation: These indicators evaluate the interconnection plate's ability to resist embrittlement in a hydrogen environment. High tensile strain and high yield strength and tensile strength indicate that the interconnection plate can still maintain good mechanical properties and toughness under hydrogenation conditions, thereby avoiding failure caused by hydrogen embrittlement. Exemplarily, the tensile strain after electrochemical hydrogen charging for 24 hours can be 35.0%, 35.2%, 35.4%, 35.6%, 35.8%, 36%, 36.4%, 37%, etc., the yield strength can be 260MPa, 262MPa, 265MPa, 268MPa, 270MPa, 275MPa, 280MPa, etc., and the tensile strength can be 210MPa, 215MPa, 220MPa, 225MPa, 230MPa, 235MPa, 240MPa, etc.

[0075] 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:

[0076] 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.

[0077] In some embodiments, the cold rolling reduction ratio is ≧40%.

[0078] In some embodiments, the solution treatment includes the following parameters: temperature of 1000°C to 1100°C, holding time of 30min to 45min, hydrogen injection volume of ≥20m 3 / h.

[0079] The cold rolling reduction ratio is ≥40%, which produces a large number of subgrain boundaries. Therefore, the existence of these substructures provides channels for the diffusion of Mo and Nb during the solid solution process. The substructure promotes the segregation of Mo and Nb elements. When the element enrichment concentration reaches the critical value of precipitation, the B2A structure Laves phase, namely (Fe, Cr) 2 (Mo, Nb), begins to precipitate. After the solid solution, water cooling is used to accelerate the cooling rate. The Laves phase size is concentrated at 5nm. A large number of fine and uniform Laves phases are precipitated at the evenly distributed dislocations, becoming irreversible hydrogen traps, absorbing hydrogen atoms and inhibiting hydrogen diffusion, thereby reducing the average hydrogen concentration of the alloy during the load process and inhibiting the hydrogen embrittlement tendency of the alloy. The solid solution temperature is 1000℃~1100℃, the holding time is 30min~45min, and water cooling is used after the holding to ensure that the second phase particles Laves will not grow in time to form dispersed and fine second phase particles as irreversible hydrogen traps. During the solid solution treatment, hydrogen spraying is used, and the hydrogen spraying amount is ≥20m 3 / h to prevent oxidation of stainless steel during heat treatment. Exemplary, the reduction rate of cold rolling is 40%, 42%, 45%, 48%, 50%, 52%, 55%, etc. The temperature of the solution treatment can be 1000℃, 1020℃, 1040℃, 1060℃, 1080℃, 1100℃, etc., the holding time can be 30min, 32min, 35min, 40min, 42min, 45min, etc., and the hydrogen injection amount can be 20m 3 / h、22m 3 / h、25m 3 / h、28m 3 / h、30m 3 / h, etc.

[0080] 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.

[0081] The advantages of the embodiments of the present application are mainly reflected in the following aspects:

[0082] (1) Excellent resistance to hydrogen embrittlement: By precisely controlling the chemical composition of stainless steel, especially the content and proportion of Al, Mo, Nb and rare earth elements, a stable and dispersed Laves phase is formed. These Laves phases act as irreversible hydrogen traps, which can adsorb hydrogen atoms and inhibit hydrogen diffusion, thereby significantly reducing the average hydrogen concentration of the alloy during loading and inhibiting the hydrogen embrittlement tendency of the alloy. At the same time, the addition of rare earth elements not only produces atomic lattice distortion, but also strengthens the grain boundaries, further improves the medium and high temperature mechanical properties, and improves the adhesion between the surface oxide film and the matrix, thereby enhancing the oxidation resistance.

[0083] (2) Good anti-oxidation performance: The Cr element in stainless steel ensures its basic anti-oxidation and thermal expansion performance. By optimizing the Cr content, the expansion coefficient caused by excessive Cr is avoided, thereby maintaining good matching with the solid electrolyte and ensuring the conductivity and service life of the fuel cell. At the same time, the Al element, as a strong deoxidizer, not only improves the oxidation resistance and high-temperature strength of the alloy, but also reduces the density of the alloy, achieving lightweight materials.

[0084] (3) Precise preparation process: vacuum refining and precise alloy addition timing reduce the risk of alloy oxidation, improve alloy yield, and ensure precise control of the chemical composition of stainless steel. At the same time, the cold rolling reduction rate is ≥40%, which produces a large number of subgrain boundaries, providing channels for the diffusion of Mo and Nb, promoting the precipitation of Laves phase, and forming small and uniform hydrogen traps. In addition, the solution treatment parameters (temperature is 1000℃~1100℃, holding time is 30min~45min, hydrogen spray volume is ≥20m 3 / h) to ensure that the second phase particles Laves have no time to grow, forming dispersed and fine second phase particles, further enhancing the hydrogen embrittlement resistance.

[0085] (4) Efficient production process: From steel liquid refining to the preparation of the final interconnection plate, the entire process goes through multiple steps such as hot rolling, cold rolling, stamping, solution treatment and water cooling. Each step has been carefully designed and optimized to ensure the dual improvement of production efficiency and product quality.

[0086] (5) Broad application prospects: The obtained fuel cell interconnect plate meets a series of strict performance requirements, such as high-temperature tensile strength and yield strength, oxidation resistance, and hydrogen embrittlement resistance, making it a key component in the fuel cell system.

[0087] The good performance of the interconnection plate in the operation of the fuel cell helps to increase the service life of the fuel cell and promote the commercialization and sustainable development of fuel cell technology.

[0088] In summary, this method achieves a significant improvement in the hydrogen embrittlement resistance of stainless steel by precisely controlling the chemical composition and optimizing the preparation process, while maintaining good oxidation resistance and production efficiency, providing an efficient and reliable method for the preparation of fuel cell interconnect plates.

[0089] 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.

[0090] The present application embodiment provides a method for preparing an interconnection board, and the specific process is as follows:

[0091] 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, and the vacuum refining temperature, the time of adding the alloy containing Al, Mo, Nb and Ce, and the TO at that time are shown in Table 1;

[0092] Step 2, after pouring and crystallizing the molten steel in step 1, a stainless steel alloy ingot as shown in Table 2 and Table 3 is obtained, and the stainless steel alloy ingot is heated at 1100° C., forged and tempered for multiple times to obtain a flat slab;

[0093] Step 3, hot rolling, annealing, softening, grinding and welding the flat slab to obtain a hot-rolled strip;

[0094] Step 4: performing blanking, cold rolling, intermediate grinding, edge trimming and solution treatment on the hot-rolled strip to obtain a strip.

[0095] 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 reduction rate is 40%, the second hot rolling reduction rate is 60%, and the third hot rolling reduction rate is 70%. The final rolling temperature is 910°C. After rolling, the steel is water-cooled to room temperature.

[0096] The cold rolling includes: a first cold rolling, a second cold rolling and a third cold rolling, the first cold rolling has a reduction rate of 50%, the second cold rolling has a reduction rate of 60%, and the third cold rolling has a reduction rate of 70%.

[0097] Step 5: Stamping: Heat treatment to 300°C, spray hydrogen volume 5m 3 / h, keep warm for 20min, and press.

[0098] Step 6: subjecting the steel plate formed by stamping in step S5 to solution treatment, and then cooling it to room temperature with water to obtain a fuel cell interconnection plate. The parameters of cold rolling and solution treatment are shown in Table 4.

[0099] Table 1 Vacuum refining temperature, time of adding alloy containing Al, Mo, Nb and Ce, and TO at that time

[0100]

[0101] Table 2 Chemical composition of stainless steel alloy ingots (wt, %), the remainder is Fe and unavoidable impurities

[0102] serial number Al Cr Mo Nb Ce Si W C TO Example 1 0.6 25 0.1 2 0.04 0.5 1.0 0.025 0.0015 Example 2 5 13 0.5 1 0.2 0.2 2.0 0.020 0.0016 Example 3 2 20 1 4 0.5 0.5 2.5 0.030 0.0014 Example 4 4 30 1.5 6 1 1 4.0 0.025 0.0015 Example 5 0.6 13 2 6 0.5 0.5 6.0 0.030 0.0014 Comparative Example 1 1.0 13 1 1 0.001 1 3 0.030 0.0014 Comparative Example 2 5 30 1 0.05 1 1 3 0.030 0.0014 Comparative Example 3 2 20 1 4 0.5 0.2 2.0 0.020 0.0016 Comparative Example 4 4 30 1.5 6 1 0.5 2.5 0.030 0.0014

[0103] Table 3 Relationship between chemical compositions of stainless steel alloy ingots

[0104] serial number ([Al]+0.25×[Cr]) / ([Mo]+[Nb]) [Ce] / (0.08×[Mo]+0.12×[Nb]) Example 1 4.88 0.16 Example 2 4.83 1.25 Example 3 1.80 0.89 Example 4 1.53 1.19 Example 5 0.91 0.57 Comparative Example 1 3.63 0.01 Comparative Example 2 10.95 11.63 Comparative Example 3 1.80 0.89 Comparative Example 4 1.53 1.19

[0105] Table 4 Parameters of cold rolling and solution treatment

[0106]

[0107]

[0108] The interconnection plates prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were charged with hydrogen by electrochemical method on the tensile specimens. The solution used was a mixed aqueous solution of 0.2 mol / L NaOH and 3 g / L NH4SCN. The current density was 50 mA / cm 2 The hydrogen filling time is 24h, 72h and 120h. After the hydrogen filling is completed, the tensile test is immediately carried out on the tensile specimen to measure the tensile strain, yield strength and tensile strength respectively. The atmosphere for the determination of the oxidation resistance is the oxygen partial pressure PO2 = 2.18×10 4 Pa, water partial pressure is PO2 = 3 × 10 3 Pa, oxidized at 900℃ for 1000h, and then the oxide film thickness was measured. The results are shown in Table 5.

[0109] Table 5 Performance of interconnection boards prepared in Examples 1 to 5 and Comparative Examples 1 to 4

[0110]

[0111] As shown in Table 1, the room temperature tensile plasticity of the interconnection plates of Examples 1 to 5 decreases slightly after hydrogen charging, and the tensile strength and yield strength are slightly improved, and the alloy has excellent hydrogen embrittlement resistance. The oxide film thickness is ≤1.5 μm.

[0112] In Comparative Example 1, [Ce] / (0.08×[Mo]+0.12×[Nb]) does not meet the scope of the present invention, in Comparative Example 2, ([Al]+0.25×[Cr]) / ([Mo]+[Nb]) does not meet the scope of the present invention, in Comparative Example 3, the cold reduction rate does not meet the scope of the present invention, and in Comparative Example 4, the solution temperature does not meet the scope of the present invention. After hydrogen charging, the room temperature tensile plasticity of the obtained interconnected plate decreases significantly, the tensile strength and yield strength are both reduced, the oxide film thickness is large, and the alloy's hydrogen embrittlement resistance is poor.

[0113] In addition, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0114] In an embodiment of the present invention, a method for preparing a hydrogen embrittlement-resistant solid oxide fuel cell interconnect is provided. By rationally designing the chemical composition, the prepared material has excellent hydrogen embrittlement resistance, oxidation resistance and mechanical properties at a service temperature of 600 to 800°C, meeting the requirements for the design and use of solid oxide fuel cells.

[0115] In the embodiment of the present invention, by introducing Mo and Nb, using warm rolling, and controlling the cold rolling parameters, a large number of subgrain boundaries are generated. The existence of these substructures provides channels for the diffusion of Mo and Nb. Therefore, the substructure promotes the segregation of Mo and Nb elements during the solid solution process. When the element enrichment concentration reaches the critical value of precipitation, the B2A structure Laves phase, namely (Fe, Cr) 2 (Mo, Nb), begins to precipitate. After the solid solution, water cooling is performed to accelerate the cooling rate. The Laves phase size is concentrated at 5nm. A large number of fine and uniform Laves phases are precipitated at the evenly distributed dislocations, which become irreversible hydrogen traps, adsorb hydrogen atoms and inhibit hydrogen diffusion, thereby reducing the average hydrogen concentration of the alloy during the load process and inhibiting the hydrogen embrittlement tendency of the alloy. Ce is introduced. Since the atomic radius of Ce is larger than that of Fe, atomic lattice distortion is generated in the ferrite matrix. By synergizing the relationship between Ce and Mo and Nb, combined with the large atomic lattice distortion, dislocation hydrogen traps located in the crystal are caused, forming diffusely distributed hydrogen traps throughout the crystal and subgrain boundaries.

[0116] 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 excellent hydrogen embrittlement resistance, wherein the stainless steel comprises the following chemical components by mass fraction: Cr: 20% to 30%, Al: 0.6% to 5.0%, Mo: 3% to 5%, Nb: 0.05% to 6.0%, rare earth elements: 0.001% to 1.0%, C<0.05%, TO≤0.002% and Fe; in, The rare earth elements include one or more of Ce, La, Sc and Y.

2. The stainless steel according to claim 1, characterized in that The stainless steel also includes the following chemical components: W: 1% to 6.0%, Si: 0.05% to 3.0%.

3. The stainless steel according to claim 1, characterized in that The chemical composition satisfies the following relationship: 0.5≤([Al]+0.25×[Cr]) / ([Mo]+[Nb])≤5 In the formula, [Al] represents the mass fraction of Al, [Cr] represents the mass fraction of Cr, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

4. The stainless steel according to claim 1, characterized in that The chemical composition satisfies the following relationship: 0.1<[R] / (0.08×[Mo]+0.12×[Nb])<1.5 In the formula, [R] represents the mass fraction of the rare earth element, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

5. The stainless steel according to claim 4, characterized in that Measured by volume fraction, the alloy cast structure of the stainless steel includes: ferrite phase ≥ 85%, Laves phase ≤ 15%.

6. A method for preparing the stainless steel according to any one of claims 1 to 5, 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 Al, Mo, Nb and rare earth elements is added to the molten steel to obtain an alloyed molten steel; The alloyed steel liquid is poured to obtain the stainless steel.

7. A fuel cell interconnect, wherein the fuel cell interconnect plate is made of the stainless steel according to any one of claims 1 to 5, and the alloy cast structure of the fuel cell interconnect plate comprises, by volume fraction: Ferrite phase ≧85%, 2%≤Laves phase≤5%.

8. The fuel cell interconnect according to claim 7, characterized in that: The fuel cell interconnection plate meets at least one of the following properties: Tensile strength Rm≥250MPa at 900℃; Yield strength Rp0.2≥210MPa at 900℃; The oxide film thickness after oxidation at 900℃ for 1000h is ≤1.5μm; The tensile strain after electrochemical hydrogen charging for 24 hours is ≥35.0%, the yield strength is ≥260MPa, and the tensile strength is ≥210MPa.

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 5 is sequentially subjected to hot rolling, cold rolling, stamping, solution treatment and water cooling to obtain a fuel cell interconnection plate; the cold rolling reduction ratio is ≥ 40%.

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

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