A medium-high temperature iron-chromium alloy with excellent strength, an interconnection board and a preparation method

Abstract

The application provides a high-temperature iron-chromium alloy with excellent strength, an interconnection board and a preparation method, and belongs to the field of iron-chromium alloys. The iron-chromium alloy comprises the following chemical components: Cr: 12-30%, Cu: 0.5-3.5%, Ni: 1.0-1.2%, W: 1-3%, C+N≤0.015%, Y: 0.05-0.3%, Th: 0.001-0.005%, T.O≤0.002%, Si≤0.2%, Mn: 0.1-0.8%, Al≤0.2% and Fe. By designing reasonable alloy element addition and proportioning, the element Y is added in the alloy to offset the influence of high Cr on plasticity. Th precipitation strengthening is adopted, and by adding Y elements in cooperation, the dispersion of Th oxides is improved, and the high-temperature mechanical properties are improved. The proportion of Y, Cu and W elements is reasonably adjusted to promote the dispersion strengthening effect of Cu and W elements in the alloy. Therefore, the high-temperature strength performance of the alloy material is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of iron-chromium alloys, in particular to an iron-chromium alloy with excellent medium-high temperature strength, an interconnection plate and a preparation method. BACKGROUND

[0002] A fuel cell mainly comprises a proton exchange membrane, a catalyst layer, an air diffusion layer and an interconnection plate. As a core component of the fuel cell, the interconnection plate plays important roles in supporting a membrane electrode structure, separating hydrogen and oxygen, collecting electrons, conducting heat, providing hydrogen and oxygen channels, discharging water generated in reaction, providing a cooling liquid flow channel and the like. The amount of the interconnection plate accounts for more than 80% of the weight of the fuel cell stack.

[0003] The fuel cell operates at a medium-high temperature of 600-1000 DEG C. Under the medium-high temperature condition, a large thermal stress and mechanical stress are generated inside the fuel cell. If the medium-high temperature strength of the material is insufficient, deformation, cracking and even failure are likely to occur, thereby affecting the stability and service life of the fuel cell. Meanwhile, the fuel cell is in contact with corrosive gases such as hydrogen, oxygen and water vapor during operation, and the corrosion of the material by the corrosive gases is more significant at high temperatures. Therefore, the strength performance of the alloy material under the medium-high temperature is crucial. SUMMARY

[0004] The application provides an iron-chromium alloy with excellent medium-high temperature strength, an interconnection plate and a preparation method, so as to solve the technical problem of how to improve the medium-high temperature strength performance of the alloy material.

[0005] In a first aspect, the application provides an iron-chromium alloy with excellent medium-high temperature strength. The iron-chromium alloy comprises the following chemical components in terms of mass fraction: Cr: 12%-30%, Cu: 0.5%-3.5%, Ni: 1.0%-1.2%, W: 1%-3%, C+N≤0.015%, Y: 0.05%-0.3%, Th: 0.001%-0.005%, T.O≤0.002%, Si≤0.2%, Mn: 0.1%-0.8%, Al≤0.2% and Fe.

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

[0007] 10≤[Y] / [Th]≤300

[0008] In the formula, [Y] represents the mass fraction of Y, and [Th] represents the mass fraction of Th.

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

[0010] [Y]>0.006×[Cu]+0.032×[W]

[0011] In the formula, [Y] represents the mass fraction of Y, [Cu] represents the mass fraction of Cu, and [W] represents the mass fraction of W.

[0012] Optionally, the iron-chromium alloy dispersively distributes oxides of Th, and the particle size of the oxides is less than 2 μm.

[0013] In a second aspect, the present application provides a preparation method of the iron-chromium alloy according to any one of the embodiments of the first aspect, and the method comprises:

[0014] carrying out high-temperature refining on the molten steel, and controlling the adding time of raw materials during the high-temperature refining to obtain an alloyed molten steel;

[0015] carrying out pouring and crystallization on the alloyed molten steel to obtain the iron-chromium alloy.

[0016] Optionally, the controlling the adding time of raw materials during the high-temperature refining comprises:

[0017] controlling the adding time of raw materials during the high-temperature refining;

[0018] adding C into the molten steel before the high-temperature refining;

[0019] adding Si and Mn into the molten steel at a time t of 0.2T-0.6T during the high-temperature refining;

[0020] adding Al into the molten steel at a time t of 0.2T-0.6T during the high-temperature refining, then adding Cr, Cu and Ni, and determining the additional amount of C according to the O content in the molten steel;

[0021] adding Th into the molten steel at a time t of 0.6T-0.8T and T.O of 0.002%-0.0025% during the high-temperature refining; and

[0022] adding Y into the molten steel at a time t of 0.8T-0.95T and T.O≤0.002% during the high-temperature refining.

[0023] wherein T is the total time of the high-temperature refining, and T is 0.5h-0.7h.

[0024] Optionally, the O content in the molten steel and the additional amount of C satisfy the following relationship:

[0025] m=(0.5-0.7)×([O]-20)

[0026] In the formula, m is the additional amount of C in the molten steel, and the unit is ppm; and [O] is the mass percentage of O in the molten steel, and the unit is ppm.

[0027] Optionally, the pressure P of the high-temperature refining satisfies the following relationship with the time t of the high-temperature refining:

[0028] When t < 0.2T, P is 1 Pa to 5 Pa;

[0029] When 0.2T < t < 0.6T, P is 0.1 Pa to 0.5 Pa;

[0030] When t > 0.6T, P is 1 Pa to 2 Pa;

[0031] Wherein, T is the total time of the high-temperature refining, and T is 0.5 h to 0.7 h.

[0032] In a third aspect, the application provides a fuel cell interconnection plate made of the ferrum-chromium alloy according to any one of the embodiments of the first aspect, and the fuel cell interconnection plate satisfies the following performances:

[0033] Tensile strength Rm at 600℃ is ≥450 MPa;

[0034] Yield strength Rp0.2 at 600℃ is ≥360 MPa;

[0035] Tensile strength Rm at 900℃ is ≥250 MPa;

[0036] Yield strength Rp0.2 at 900℃ is ≥210 MPa.

[0037] In a fourth aspect, the application provides a preparation method of the fuel cell interconnection plate according to the third aspect, and the method comprises:

[0038] Heating, forging and multi-pass tempering are sequentially performed on a ferrum-chromium alloy ingot to obtain a flat blank;

[0039] Multi-pass hot rolling and annealing softening are performed on the flat blank to obtain a hot-rolled strip blank;

[0040] Intermediate heat treatment, multi-pass cold rolling and solid solution treatment are performed on the hot-rolled strip blank to obtain a strip, and the intermediate heat treatment comprises the following parameters: temperature is 900℃ to 1100℃, holding time is 5 min to 15 min, and hydrogen spraying amount is ≥20 m 3 / h;

[0041] Punch forming is performed on the strip to obtain a fuel cell interconnection plate, and the punch forming comprises the following parameters: heating temperature is 200℃ to 400℃, holding time is 20 min to 120 min, and hydrogen spraying amount is ≥5 m 3 / h.

[0042] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art.

[0043] The present application provides a high-temperature strength excellent iron-chromium alloy, which comprises the following chemical components: Cr: 12% to 30%, Cu: 0.5% to 3.5%, Ni: 1.0% to 1.2%, W: 1% to 3%, C+N≤0.015%, Y: 0.05% to 0.3%, Th: 0.001% to 0.005%, T.O≤0.002%, Si≤0.2%, Mn: 0.1% to 0.8%, Al≤0.2% and Fe. By designing reasonable alloy element addition and proportioning, the element Y is added in the alloy, which offsets the influence of high Cr on plasticity. Since the Y element is segregated at the grain boundary, it further plays a grain boundary strengthening role, delays the formation and expansion of cracks, and thus significantly improves the endurance performance of the alloy. Th precipitation strengthening is adopted, the Th addition timing is in the late refining stage, T.O is 20 to 25 ppm, Y is introduced after all high-melting-point oxides are formed, the addition timing is when T.O is lower than 20 ppm, by the addition of Y element, the dispersion of Th oxides is controlled to be less than 2 microns, the Orowan mechanism is used to hinder dislocation movement, and the high-temperature mechanical properties are improved. Cr and W elements have solid solution strengthening effect, the proportion of Y, Cu and W elements is reasonably adjusted, the dispersion strengthening effect of Cu and W elements in the alloy is promoted, the strength of the alloy is effectively improved, and the performance of the alloy is stable at a service temperature of about 900 DEG C. Thus the high-temperature strength performance of the alloy material is improved. BRIEF DESCRIPTION OF DRAWINGS

[0044] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows, and obviously, other drawings can also be obtained by those skilled in the art without any creative labor.

[0046] Figure 1 A flowchart of a preparation method of an iron-chromium alloy provided by the embodiments of the present application is shown in the figure.

[0047] Figure 2 A flowchart of a preparation method of a fuel cell interconnection plate provided by the embodiments of the present application is shown in the figure. DETAILED DESCRIPTION

[0048] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0049] Various embodiments of the present application can exist in a range of forms; it should be understood that the description in a range of forms is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has disclosed all possible sub-ranges and single values in the range. For example, it should be considered that the range description from 1 to 6 has 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 values in the described range, such as 1, 2, 3, 4, 5 and 6, which is applicable to any range. In addition, whenever a numerical range is indicated in the present application, it refers to any cited number (fraction or integer) in the indicated range.

[0050] In addition, in the description of the present application, the terms "comprise", "contain" and the like mean "comprise but not limited to". In this paper, such as "first" and "second" and other relational terms 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 the entities or operations. In this paper, "and / or", the association relationship between the associated objects, means that there can be three kinds of relationships, for example, A and / or B, can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone. Where A, B can be singular or plural. In this paper, "at least one" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or similar expressions means any combination of these items, including any combination of single item (s) or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple. "Parts representation method" such as weight parts, mass parts and the like represents the proportional relationship between the components. In the proportional relationship involved in this paper, the parameters that need to be described by proportion should be understood as the former in the proportional form according to the order of description, and the proportional number is understood as the latter in the proportional form, 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 be in the proportional form according to the description order and the proportional number one by one, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0051] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0052] The present application provides an iron-chromium alloy with excellent high-temperature strength, which comprises the following chemical components in mass fraction: Cr: 12% to 30%, Cu: 0.5% to 3.5%, Ni: 1.0% to 1.2%, W: 1% to 3%, C+N≤0.015%, Y: 0.05% to 0.3%, Th: 0.001% to 0.005%, T.O≤0.002%, Si≤0.2%, Mn: 0.1% to 0.8%, Al≤0.2%, and Fe.

[0053] The main effects of each component are as follows:

[0054] Cr: Cr is a basic element to ensure the oxidation resistance and thermal expansion performance of the ferrochrome alloy. If the Cr content is less than 12%, the oxidation resistance performance of the present application cannot be achieved; if the Cr content is higher than 30%, the thermal expansion performance cannot be met. Exemplarily, the content of Cr can be 12% to 30%, etc.

[0055] Cu: Cu can improve the alloy performance through solid solution strengthening and aging strengthening, while forming a dense oxide film on the surface of the alloy to improve the corrosion resistance of the alloy. If the Cu content is higher than 3.5%, it will cause brittle fracture of the alloy. Exemplarily, the content of Cu can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, etc.

[0056] Y: Y is an active rare earth element, which reduces the wetting angle of ThO2 and the metal liquid, and prevents ThO2 oxide from gathering. At the same time, the rare earth element Y has the effect of reducing the oxidation rate, and can enrich in the Cr2O3 interface organization Cr to diffuse outward. Exemplarily, the content of Y can be 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc.

[0057] Th: ThO2 has a melting point of 3390℃, a density of 9.86g / cm 3 , and after oxidation, it is dispersed in the alloy to hinder dislocation movement and strengthen the mechanical properties at medium and high temperatures; however, Th has a radioactive property, and the content needs to be strictly controlled, so as to comprehensively consider the beneficial and harmful effects. Exemplarily, the content of Th can be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc.

[0058] W: W is a solid solution strengthening element, however, W accelerates corrosion at medium and high temperatures, produces harmful phases during long-term service, and reduces the strength and toughness of the alloy. By reasonably adjusting the proportion of Y and W elements, the dispersion strengthening effect of W element in the alloy is promoted, the strength of the alloy is effectively improved, the adverse effect on the corrosion performance is eliminated, and the service temperature of the alloy is increased to about 900℃. Exemplarily, the content of W can be 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0059] Si: Si is a deoxidizer, which 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 electrical conductivity. Exemplarily, the content of Si can be 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, etc.

[0060] Mn: Mn is a deoxidizer that can improve 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.

[0061] Al: Al is a strong deoxidizer that can improve the oxidation resistance and high-temperature strength of alloys. In addition, it can reduce the density of alloys, achieving the advantages of lightweight materials and low cost. Excessive addition will affect tensile properties and weldability. For example, the content of Al can be 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, etc.

[0062] It should be noted that TO represents the total oxygen content.

[0063] Ni is the matrix element. The specific content / range of Ni can be obtained by the formula for the upper and lower limits of the components. That is, the sum of the percentages of each component in a composition should be equal to 100%, and 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.

[0064] In some embodiments, the chemical components satisfy the following relationship:

[0065] 10≤[Y] / [Th]≤300

[0066] In the formula, [Y] represents the mass fraction of Y, and [Th] represents the mass fraction of Th.

[0067] Y is an active rare earth element that can reduce the wetting angle between ThO2 and molten metal, preventing the aggregation of ThO2 oxides. By controlling the mass fraction of [Y] / [Th] to satisfy 10 ≤ [Y] / [Th] ≤ 300, Y and Th work synergistically, with Y dispersing Th oxides, thereby controlling the particle size of Y oxides to be less than 2 μm. For example, the value of [Y] / [Th] can be 10, 50, 100, 150, 200, 250, 300, etc.

[0068] In some embodiments, the chemical components satisfy the following relationship:

[0069] [Y] > 0.006 × [Cu] + 0.032 × [W]

[0070] In the formula, [Y] represents the mass fraction of Y, [Cu] represents the mass fraction of Cu, and [W] represents the mass fraction of W.

[0071] The positive effects of controlling the mass fractions of Y and Cu to satisfy [Y]>0.006×[Cu]+0.032×[W] are: rationally adjusting the proportions of Y, Cu and W elements promotes the dispersion strengthening effect of Cu element in the alloy, effectively improves the alloy strength, and increases the service temperature of the alloy to about 950℃.

[0072] In some embodiments, the iron-chromium alloy contains dispersed Th oxides with a particle size <2 μm.

[0073] Y and Th work synergistically, with Y dispersing Th oxides, thereby controlling the particle size of Y oxides to be less than 2 μm. For example, the particle size of Th oxides can be 0.5 μm, 0.7 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.9 μm, etc.

[0074] In summary, this application, through the design and reasonable addition and proportion of alloying elements, incorporates element Y to offset the potential impact of high Cr on plasticity. Because Y segregates at grain boundaries, it exerts a grain boundary strengthening effect, delaying crack formation and propagation, thereby significantly improving the alloy's creep resistance. Th precipitation strengthening is employed, with Th added in the later stages of refining when TO is 20-25 ppm. Y is introduced after all high-melting-point oxides have formed, at a TO level below 20 ppm. This synergistic addition of Y disperses the Th oxides, controlling the oxide particle size to less than 2 μm, and using the Orowan mechanism to hinder dislocation movement, thus improving medium- and high-temperature mechanical properties. Cr and W elements have solid solution strengthening effects. Reasonably adjusting the ratio of Y, Cu, and W elements promotes the dispersion strengthening effect of Cu and W elements in the alloy, effectively improving the alloy's strength and ensuring stable performance at service temperatures around 900℃.

[0075] Figure 1 This is a schematic flowchart illustrating a method for preparing an iron-chromium alloy, as provided in an embodiment of this application.

[0076] Based on a general inventive concept, please refer to... Figure 1 This application also provides a method for preparing an iron-chromium alloy as described in any of the above embodiments, the method comprising:

[0077] S11. The molten steel is refined at high temperature, and the timing of adding raw materials is controlled during the high-temperature refining process to obtain alloyed molten steel.

[0078] S12. The alloyed steel liquid is poured and crystallized to obtain the iron-chromium alloy.

[0079] In some embodiments, the vacuum refining temperature is 1500°C to 1600°C.

[0080] In some embodiments, controlling the timing of raw material addition during the high-temperature refining process includes:

[0081] Control the timing of raw material addition during the high-temperature refining process;

[0082] Before the high-temperature refining, C is added to the molten steel;

[0083] When the high-temperature refining time t < 0.2T, Si and Mn are added to the molten steel;

[0084] When the high-temperature refining time t is 0.2T to 0.6T, Al is added to the molten steel, followed by Cr, Cu and Ni, and the amount of C added is determined according to the O content in the molten steel.

[0085] When the high-temperature refining time t is 0.6T to 0.8T and TO is 0.002% to 0.0025%, Th is added to the molten steel; and

[0086] When the high-temperature refining time t is 0.8T to 0.95T and TO ≤ 0.002%, Y is added to the molten steel;

[0087] Wherein, T is the total time of the high-temperature refining, which is 0.5h to 0.7h.

[0088] This application ensures the quality and uniformity of alloyed molten steel through high-temperature refining and precise control of the timing of raw material addition. Carbon is added before refining to remove oxygen introduced by the raw materials. When the refining time t < 0.2T, a Si-Mn composite deoxidizer is added. Silicon and manganese are commonly used deoxidizers; they can combine with oxygen in the molten steel to form silicates and manganese oxides, thereby reducing the oxygen content. When the refining time t is between 0.2T and 0.6T, aluminum is added for deep deoxidation. Aluminum is a strong deoxidizer that can further reduce the oxygen content in the molten steel. Subsequently, elements such as chromium (Cr), copper (Cu), and nickel (Ni) are added. These elements are the main alloying elements of iron-chromium alloys and have a significant impact on the alloy's performance. Simultaneously, based on the oxygen content in the molten steel, it is determined whether additional carbon is needed to maintain the stability of the alloy composition. When the refining time t is between 0.6T and 0.8T, and the oxygen content (TO) in the molten steel is between 0.002% and 0.0025%, thorium is added. Thorium can form high-melting-point oxides at high temperatures, acting as precipitation strengthening. Yttrium is added when the refining time (t) is between 0.8T and 0.95T, and the oxygen content (TO) in the molten steel is less than or equal to 0.002%. Yttrium segregates at grain boundaries, acting as grain boundary strengthening and improving the alloy's creep resistance. Simultaneously, controlling the TO content increases the yield of this expensive rare earth element.

[0089] In some embodiments, the O content in the molten steel and the additional amount of C satisfy the following relational expression:

[0090] m=(0.5~0.7)×([O]-20)

[0091] In the formula, m is the mass percentage of the additional amount of C in the molten steel, with the unit of ppm; [O] is the mass percentage of O in the molten steel, with the unit of ppm.

[0092] In some embodiments, the pressure P of the high-temperature refining and the time t of the high-temperature refining satisfy the following relationship:

[0093] When t < 0.2T, P is 1 Pa to 5 Pa;

[0094] When 0.2T < t < 0.6T, P is 0.1 Pa to 0.5 Pa;

[0095] When t > 0.6T, P is 1 Pa to 2 Pa;

[0096] Wherein, T is the total time of the high-temperature refining, and T is 0.5 h to 0.7 h.

[0097] 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 conducive 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 helps to maintain the stability of the molten steel and prevent 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.

[0098] The preparation product of the preparation method of this ferrochromium alloy is the above ferrochromium alloy. The chemical composition and microstructure of the ferrochromium alloy obtained by the preparation method of this ferrochromium alloy can refer to the above embodiments. Since the preparation method of this ferrochromium alloy adopts some or all of the technical solutions of the ferrochromium alloy embodiments, it has at least all the beneficial effects brought by the technical solutions of the ferrochromium alloy embodiments, which will not be elaborated here one by one.

[0099] Based on a general inventive concept, the present application provides a fuel cell interconnector plate, which is made of the ferrochromium alloy described in any one of the above embodiments, and the fuel cell interconnector plate satisfies at least one of the following performances:

[0100] The tensile strength Rm ≥ 450 MPa at 600 °C;

[0101] Yield strength Rp0.2 at 600℃ ≥ 360MPa;

[0102] Tensile strength Rm ≥ 250 MPa at 900℃;

[0103] The yield strength Rp0.2 at 900℃ is ≥210MPa.

[0104] This application improves the strength performance of ferrochromium alloys at medium and high temperature operating temperatures of 600~900℃ by designing reasonable alloy element additions and proportions and optimizing process preparation technology.

[0105] Figure 2 This is a schematic flowchart illustrating a method for fabricating a fuel cell interconnect plate according to an embodiment of this application.

[0106] Please see Figure 2 This application provides a method for preparing the fuel cell interconnect plate described in the above embodiments, the method comprising:

[0107] S21. The iron-chromium alloy ingot described in any one of the above items is sequentially heated, forged, and tempered in multiple passes to obtain a flat billet.

[0108] In some embodiments, the heating temperature is 1050°C to 1200°C.

[0109] S22. The flat billet is subjected to multiple hot rolling passes and annealing softening to obtain a hot-rolled strip billet;

[0110] 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 20%~50%, the deformation amount of the second hot rolling pass is 30%~60%, and the deformation amount of the third hot rolling pass is 40%~70%. The final rolling temperature is above 900℃. After rolling, the material is water-cooled to room temperature.

[0111] S23. The hot-rolled strip is subjected to intermediate heat treatment, multiple cold rolling passes, and solution treatment to obtain strip material; the intermediate heat treatment includes the following parameters: temperature of 900℃~1100℃, holding time of 5min~15min, and hydrogen injection rate ≥20m³. 3 / h;

[0112] 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 of the first cold rolling is 20% to 60%, the deformation of the second cold rolling is 30% to 60%, and the deformation of the third cold rolling is 40% to 70%.

[0113] S24. Stamp the strip to form a fuel cell interconnect plate. The stamping includes the following parameters: the heating temperature is 200°C to 400°C, the heat preservation time is 20 min to 120 min, and the hydrogen injection amount is ≥5 m 3 / h.

[0114] The product prepared by the preparation method of this fuel cell interconnect plate is the above-mentioned fuel cell interconnect plate. The chemical composition and microstructure of the fuel cell interconnect plate prepared by the preparation method of this fuel cell interconnect plate can refer to the above embodiments. Since the preparation method of this fuel cell interconnect plate adopts some or all of the technical solutions of the fuel cell interconnect plate embodiment, it has at least all the beneficial effects brought by the technical solutions of the fuel cell interconnect plate embodiment, which will not be elaborated here one by one.

[0115] The following will further elaborate on this application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. The experimental methods without specific conditions in the following embodiments are usually measured according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0116] This embodiment provides a preparation method of a fuel cell interconnect plate, which specifically may include the following steps:

[0117] Step 1. Vacuum melt, high-temperature refine, and pour the raw materials proportioned according to the ratio, and obtain an iron-chromium alloy ingot with a set chemical composition after crystallization. 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 iron-chromium alloy ingot is shown in Table 1, the relationship between the chemical compositions of the nickel-based alloy ingots is shown in Table 2, and the timing of adding raw materials during the high-temperature refining process is shown in Table 3;

[0118] Step 2. Heat, forge, and perform multi-pass tempering on the alloy ingot to obtain a flat blank, and the heating temperature is 1100°C;

[0119] Step 3. Hot-roll, anneal and soften, and grind and weld the flat blank to obtain a hot-rolled strip blank. The hot-rolling temperature is 1100°C. The hot-rolling includes: the first hot-rolling, the second hot-rolling, and the third hot-rolling. The deformation amount of the first hot-rolling is 30%, the deformation amount of the second hot-rolling is 50%, and the third deformation amount is 60%. The final rolling temperature is 950°C. After rolling, it is water-cooled to room temperature;

[0120] Step 4: The hot-rolled strip is subjected to billet preparation, intermediate heat treatment, cold rolling, intermediate grinding, edge trimming, and solution treatment to obtain the strip. Cold rolling includes a first cold rolling pass, a second cold rolling pass, and a third cold rolling pass. The deformation amount of the first cold rolling pass is 40%, the deformation amount of the second cold rolling pass is 40%, and the deformation amount of the third cold rolling pass is 60%. The intermediate heat treatment temperature is 1000℃, the holding time of the intermediate heat treatment is 10 minutes, and the hydrogen injection rate of the intermediate heat treatment is 20 mg / L. 3 / h.

[0121] Step 5: Perform surface finishing, cleaning, and shape correction on the strip. The specific process of surface finishing is as follows: rough polishing is performed using a 1000-mesh polishing wheel, followed by fine polishing using a 3000-mesh polishing wheel.

[0122] Step 6: Stamp the strip into shape: heat treatment to 300°C, hydrogen injection rate is 5m. 3 / h, heat preservation for 60min, stamping, to obtain fuel cell interconnect plate.

[0123] Table 1 Chemical composition of iron-chromium alloy ingots

[0124]

[0125] Table 2 Relationship between the chemical compositions of iron-chromium alloy ingots

[0126]

[0127] Table 3 Timing of Raw Material Addition During High-Temperature Refining

[0128]

[0129] The mechanical properties of the fuel cell interconnect plates prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were tested, and the results are shown in Table 4.

[0130] Table 4 Mechanical properties of fuel cell interconnect panels

[0131]

[0132] As shown in Table 4, in Comparative Example 1, the Y / Th ratio does not meet the requirements; in Comparative Example 2, the target component TO content does not meet the requirements; in Comparative Example 3, the chemical composition does not meet the requirement of Y > 0.006 × Cu + 0.032 × W; in Comparative Example 4, the timing of Th addition does not meet the requirement of > 0.7 × T, and the TO content at the time of Th addition does not meet the requirement of 0.002%~0.0025%. The mechanical properties of the fuel cell interconnect plates of Comparative Examples 1~4 at 600℃ and 900℃ do not meet the requirements.

[0133] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0134] In this embodiment of the application, by designing reasonable alloy element additions and proportions and optimizing the process preparation technology, the technical problem of poor strength performance of existing alloys at medium and high temperature (600~900℃) has been solved.

[0135] In this embodiment, the composite material prepared by vacuum melting, multi-pass tempering, and rolling has fewer harmful impurities, higher purity, fewer internal defects, and better uniformity in composition and structure. Through solution treatment control, the prepared product exhibits excellent medium- and high-temperature strength.

[0136] In this embodiment, the prepared fuel cell interconnect plate has a tensile strength Rm ≥ 450 MPa at 600°C and a yield strength Rp0.2 ≥ 360 MPa at 600°C. At 900°C, the tensile strength Rm ≥ 250 MPa and the yield strength Rp0.2 ≥ 210 MPa.

[0137] In this embodiment, the alloy is inexpensive, has a simple preparation process, reduces energy consumption, shortens the production cycle, and improves production efficiency, making it suitable for widespread application in industrial production.

[0138] In this embodiment, the cost of the prepared iron-based material is reduced by more than 50% compared to the cost of a typical high-temperature nickel-based alloy.

[0139] 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. An iron-chromium alloy with excellent medium and high temperature strength. In terms of mass fraction, the iron-chromium alloy comprises the following chemical components: Cr: 12% - 30%, Cu: 0.5% - 3.5%, Ni: 1.0% - 1.2%, W: 1% - 3%, C + N ≤ 0.015%, Y: 0.05% - 0.3%, Th: 0.001% - 0.005%, T.O ≤ 0.002%, Si ≤ 0.2%, Mn: 0.1% - 0.8%, Al ≤ 0.2% and Fe; in, The chemical components satisfy the following relational expressions: 10 ≤ [Y] / [Th] ≤ 300, [Y] > 0.006×[Cu] + 0.032×[W] In the formula, [Y] represents the mass fraction of Y, [Th] represents the mass fraction of Th, [Cu] represents the mass fraction of Cu, and [W] represents the mass fraction of W; The iron-chromium alloy has Th oxide dispersed therein, and the particle size of the oxide is < 2 μm.

2. A method for preparing the iron-chromium alloy as described in claim 1, characterized in that, The method includes: Performing high-temperature refining on the molten steel and controlling the addition timing of raw materials during the high-temperature refining to obtain alloyed molten steel; Pouring and crystallizing the alloyed molten steel to obtain the iron-chromium alloy; Among them, controlling the addition timing of raw materials during the high-temperature refining includes: Controlling the addition timing of raw materials during the high-temperature refining; Adding C to the molten steel before the high-temperature refining; Adding Si and Mn to the molten steel when the time t of the high-temperature refining < 0.2T; Adding Al to the molten steel when the time t of the high-temperature refining is 0.2T - 0.6T, then adding Cr, Cu and Ni, and determining the supplementary addition amount of C according to the O content in the molten steel; Adding Th to the molten steel when the time t of the high-temperature refining is 0.6T - 0.8T and T.O is 0.002% - 0.0025%; and Adding Y to the molten steel when the time t of the high-temperature refining is 0.8T - 0.95T and T.O ≤ 0.002%; Among them, T is the total time of the high-temperature refining, and T is 0.5 h - 0.7 h.

3. The method according to claim 2, characterized in that, The O content in the molten steel and the supplementary addition amount of C satisfy the following relational expression: m = (0.5 - 0.7)×([O] - 20) In the formula, m is the mass percentage of the supplementary addition amount of C in the molten steel, with the unit of ppm; [O] is the mass percentage of O in the molten steel, with the unit of ppm.

4. The method according to claim 2, characterized in that, 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 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; Among them, T is the total time of the high-temperature refining, and T is 0.5 h - 0.7 h.

5. A fuel cell interconnect plate, characterized in that, The fuel cell interconnector is made of the iron-chromium alloy described in claim 1, and the fuel cell interconnector satisfies the following properties: The tensile strength Rm ≥ 450 MPa at 600°C; The yield strength Rp0.2 ≥ 360 MPa at 600°C; The tensile strength Rm ≥ 250 MPa at 900°C; The yield strength Rp0.2 at 900℃ is ≥210MPa.

6. A method for preparing the fuel cell interconnect plate according to claim 5, characterized in that, The method includes: The iron-chromium alloy ingot is heated, forged, and tempered in multiple passes to obtain a flat billet. The flat billet is subjected to multiple hot rolling passes and annealing softening to obtain a hot-rolled strip billet. The hot-rolled strip is subjected to intermediate heat treatment, multiple cold rolling passes, and solution treatment to obtain strip material. The intermediate heat treatment includes the following parameters: temperature of 900℃~1100℃, holding time of 5min~15min, and hydrogen injection rate ≥20m³. 3 / h; The strip is stamped to obtain a fuel cell interconnect plate; the stamping includes the following parameters: heating temperature of 200℃~400℃, holding time of 20min~120min, and hydrogen injection rate ≥5m³. 3 / h.

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