Iron-chromium alloy with excellent medium-high temperature strength, interconnection plate and preparation method

Abstract

The invention provides an iron-chromium alloy with excellent medium-high temperature strength, an interconnection plate and a preparation method, and belongs to the field of iron-chromium alloys. The iron-chromium alloy comprises the following chemical components: 12%-30% of Cr, 0.5%-3.5% of Cu, 1.0%-1.2% of Ni, 1%-3% of W, less than or equal to 0.015% of C + N, 0.05%-0.3% of Y, 0.001%-0.005% of Th, less than or equal to 0.002% of T.O, less than or equal to 0.2% of Si, 0.1%-0.8% of Mn, less than or equal to 0.2% of Al and Fe. By designing reasonable alloy element addition and proportion, the element Y is added into the alloy, and the influence possibly brought by high Cr on plasticity is counteracted. Th precipitation strengthening is adopted, Th oxide is dispersed by adding a Y element, and the medium-high-temperature mechanical property is improved. The proportion of Y, Cu and W elements is reasonably adjusted, and the dispersion strengthening effect of the Cu and W elements in the alloy is promoted. Therefore, the medium-high temperature strength performance of the alloy material is improved.

Description

Technical Field

[0001] The present application relates to the technical field of ferrochromium alloys, and in particular to an ferrochromium alloy with excellent medium and high temperature strength, an interconnection plate, and a preparation method thereof. Background Art

[0002] Fuel cells are mainly composed of proton exchange membranes, catalyst layers, air diffusion layers and interconnection plates. As the core component of fuel cells, the interconnection plate plays many important roles in the fuel cell, including supporting the membrane electrode structure, separating hydrogen and oxygen, collecting electrons, conducting heat, providing hydrogen and oxygen channels, discharging water generated by the reaction, and providing coolant channels. The battery interconnection plate accounts for more than 80% of the weight of the battery stack.

[0003] The operating temperature of the fuel cell during operation is between 600℃ and 1000℃. Under medium and high temperature conditions, large thermal and mechanical stresses will be generated inside the fuel cell. If the medium and high temperature strength of the material is insufficient, it is easy to deform, crack or even fail, thus affecting the stability and life of the fuel cell. At the same time, the fuel cell will be exposed to corrosive gases such as hydrogen, oxygen and water vapor during operation. These corrosive gases have a more significant corrosive effect on the material at high temperatures. Therefore, the strength performance of alloy materials at medium and high temperatures is crucial. Summary of the invention

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

[0005] In the first aspect, the present application provides an iron-chromium alloy with excellent medium and high temperature strength. The iron-chromium alloy includes the following chemical components, measured by 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%, TO≤0.002%, Si≤0.2%, Mn: 0.1% to 0.8%, Al≤0.2% and Fe.

[0006] Optionally, the chemical composition satisfies the following relationship:

[0007] 10≤[Y] / [Th]≤300

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

[0009] Optionally, the chemical composition satisfies 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, Th oxide is dispersed in the iron-chromium alloy, and the particle size of the oxide is less than 2 μm.

[0013] In a second aspect, the present application provides a method for preparing an iron-chromium alloy as described in any one embodiment of the first aspect, the method comprising:

[0014] The molten steel is subjected to high-temperature refining, and the timing of adding raw materials is controlled during the high-temperature refining process to obtain alloyed molten steel;

[0015] The alloyed steel liquid is poured and crystallized to obtain the iron-chromium alloy.

[0016] Optionally, controlling the timing of adding raw materials during the high-temperature refining process includes:

[0017] Controlling the timing of adding raw materials during the high temperature refining process;

[0018] Before the high-temperature refining, adding C to the molten steel;

[0019] When the high temperature refining time t<0.2T, adding Si and Mn to the molten steel;

[0020] When the high temperature refining time t is 0.2T to 0.6T, Al is added to the molten steel, and then Cr, Cu and Ni are added, and the amount of C added is determined according to the O content in the molten steel;

[0021] 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

[0022] When the high temperature refining time t is 0.8T to 0.95T and TO≤0.002%, Y is added to the molten steel;

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

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

[0025] m=(0.5~0.7)×([O]-20)

[0026] Wherein, m is the mass percentage of the added amount of C in the molten steel, in ppm; [O] is the mass percentage of O in the molten steel, in ppm

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

[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 present application provides a fuel cell interconnector, which is made of the iron-chromium alloy described in any one of the embodiments of the first aspect, and the fuel cell interconnector satisfies at least one of the following performances:

[0033] The tensile strength Rm ≥ 450 MPa at 600 °C;

[0034] The yield strength Rp0.2 ≥ 360 MPa at 600 °C;

[0035] The tensile strength Rm ≥ 250 MPa at 900 °C;

[0036] The yield strength Rp0.2 ≥ 210 MPa at 900 °C.

[0037] In a fourth aspect, the present application provides a preparation method of a fuel cell interconnector described in the embodiment of the third aspect, and the method includes:

[0038] Successively heating, forging and multi-pass tempering the iron-chromium alloy ingot described in any one of claims 1 to 4 to obtain a flat blank;

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

[0040] Performing intermediate heat treatment, multi-pass cold rolling and solution treatment on the hot-rolled strip blank to obtain a strip; the intermediate heat treatment includes the following parameters: the temperature is 900 °C to 1100 °C, the heat preservation time is 5 min to 15 min, and the hydrogen spraying amount ≥ 20 m 3 / h;

[0041] Performing stamping on the strip to obtain a fuel cell interconnector; 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 spraying amount ≥ 5 m 3 / h.

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

[0043] The present application provides an iron-chromium alloy with excellent medium and high temperature strength, which includes 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%, TO≤0.002%, Si≤0.2%, Mn: 0.1% to 0.8%, Al≤0.2% and Fe. By designing reasonable alloy element addition and proportion, the element Y is added to the alloy to offset the influence of high Cr on plasticity. Since the Y element is segregated at the grain boundary, it plays a role in grain boundary strengthening, delaying the formation and expansion of cracks, thereby significantly improving the durability of the alloy. Th precipitation strengthening is adopted. Th is added in the late stage of refining, when TO is 20-25ppm. Y is introduced after all high melting point oxides are formed. The addition time is when TO is lower than 20ppm. By adding Y elements in coordination, Th oxides are dispersed, and the oxide particle size is controlled to be less than 2μm. The Orowan mechanism is used to hinder dislocation movement and improve medium and high temperature mechanical properties. Cr and W elements have a solid solution strengthening effect. Reasonable adjustment of the proportion of Y, Cu, and W elements promotes the dispersion strengthening effect of Cu and W elements in the alloy, effectively improves the strength of the alloy, and makes the alloy stable at a service temperature of about 900℃. Thereby improving the medium and high temperature strength performance of the alloy material. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] 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.

[0045] 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.

[0046] Figure 1 A schematic flow chart of a method for preparing an iron-chromium alloy provided in an embodiment of the present application;

[0047] Figure 2 A schematic flow chart of a method for preparing a fuel cell interconnect plate provided in an embodiment of the present application. DETAILED DESCRIPTION

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The present application provides an iron-chromium alloy with excellent medium and high temperature strength. The iron-chromium alloy includes the following chemical components, measured by 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%, TO≤0.002%, Si≤0.2%, Mn: 0.1% to 0.8%, Al≤0.2% and Fe.

[0053] The functions of each component are mainly reflected in:

[0054] Cr: Cr is a basic element to ensure the oxidation resistance and thermal expansion performance of the iron-chromium alloy. If the Cr content is less than 12%, the oxidation resistance of the present invention cannot be achieved; if the Cr content is higher than 30%, the thermal expansion performance cannot be satisfied. For example, the Cr content can be 12% to 30%, etc.

[0055] Cu: Cu can improve the alloy properties through solid solution strengthening and aging strengthening, and at the same time form a dense oxide film on the alloy surface 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 Cu content 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 between ThO2 and the metal liquid and prevents the aggregation of ThO2 oxides. At the same time, the rare earth element Y has a good effect of reducing the oxidation rate, and can be enriched at the Cr2O3 interface to organize 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°C and a density of 9.86 g / cm 3 , after oxidation, it disperses in the alloy, hinders dislocation movement, and strengthens the mechanical properties at medium and high temperatures; however, Th has radioactive properties, and its content needs to be strictly controlled, so that the beneficial and harmful effects can be combined. For example, the Th content can be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc.

[0058] W: W is a solid solution strengthening element, but W accelerates medium and high temperature corrosion, produces harmful phases during long-term service, and reduces the strength and toughness of the alloy. Reasonable adjustment of the ratio of Y and W elements promotes the dispersion strengthening effect of W elements in the alloy, effectively improves the strength of the alloy, eliminates the deterioration effect on corrosion performance, and increases the service temperature of the alloy to about 900°C. Exemplarily, the W content can be 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0059] Si: Si is a deoxidizer that can improve the oxidation resistance and high temperature strength of the alloy. Excessive addition will form SiO2 on the surface of the alloy during the oxidation process, affecting the conductivity. Exemplarily, the Si content 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 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.

[0061] Al: Al 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. Excessive addition affects the tensile properties and welding properties. For example, the Al content can be 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, etc.

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

[0063] Ni is a matrix element. The specific content / content range of Ni can be obtained through the upper and lower limit formula of the component, 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 value of other components ≤ 100; the lower limit value of a component + the upper limit value of other components ≥ 100.

[0064] In some embodiments, the chemical composition satisfies the following relationship:

[0065] 10≤[Y] / [Th]≤300

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

[0067] Y is an active rare earth element, which can reduce the wetting angle between ThO2 and the metal liquid and prevent the aggregation of ThO2 oxides. The mass fraction of [Y] / [Th] is controlled to satisfy 10≤[Y] / [Th]≤300, Y and Th act synergistically, Y disperses Th oxides, and thus controls the particle size of Y oxides to be less than 2 μm. Exemplarily, the value of [Y] / [Th] can be 10, 50, 100, 150, 200, 250, 300, etc.

[0068] In some embodiments, the chemical composition satisfies 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 effect of controlling the mass fraction of Y and Cu to satisfy [Y]>0.006×[Cu]+0.032×[W] is as follows: Rationally adjusting the ratio of Y, Cu and W elements promotes the dispersion strengthening effect of Cu element in the alloy, effectively improves the strength of the alloy, and increases the service temperature of the alloy to about 950℃.

[0072] In some embodiments, Th oxide is dispersed in the iron-chromium alloy, and the particle size of the oxide is less than 2 μm.

[0073] Y and Th work together, and Y disperses the oxide of Th, thereby controlling the particle size of the oxide of Y to be less than 2 μm. For example, the particle size of the oxide of Th 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 adds element Y to the alloy by designing reasonable alloy element addition and ratio, offsetting the possible influence of high Cr on plasticity. Since the Y element is segregated at the grain boundary, it plays a role in grain boundary strengthening, delaying the formation and expansion of cracks, and thus significantly improving the durability of the alloy. Th precipitation strengthening is adopted. Th is added in the late refining period, when TO is 20-25ppm. Y is introduced after all high melting point oxides are formed. The addition time is when TO is lower than 20ppm. By adding Y element in coordination, Th oxide is dispersed, and the oxide particle size is controlled to be less than 2μm. The Orowan mechanism is used to hinder dislocation movement and improve medium and high temperature mechanical properties. Cr and W elements have a solid solution strengthening effect. Reasonable adjustment of the ratio of Y, Cu, and W elements promotes the dispersion strengthening effect of Cu and W elements in the alloy, effectively improves the strength of the alloy, and makes the alloy stable at a service temperature of about 900℃.

[0075] Figure 1 A schematic flow chart of a method for preparing an iron-chromium alloy provided in an embodiment of the present application.

[0076] Based on a general inventive concept, see Figure 1 The present application also provides a method for preparing the iron-chromium alloy as described in any one of the above embodiments, the method comprising:

[0077] S11, subjecting the molten steel to high-temperature refining, and controlling the timing of adding raw materials during the high-temperature refining process to obtain alloyed molten steel;

[0078] S12, pouring and crystallizing the alloyed steel liquid 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 adding raw materials during the high temperature refining process includes:

[0081] Controlling the timing of adding raw materials during the high temperature refining process;

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

[0083] When the high temperature refining time t<0.2T, adding Si and Mn 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, and then Cr, Cu and Ni are added, 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, and T is 0.5h to 0.7h.

[0088] The present application ensures the quality and uniformity of alloyed molten steel by high-temperature refining and precisely controlling the timing of adding raw materials. Carbon is added before refining to remove the oxygen brought in by the raw materials; when the refining time t<0.2T, Si and Mn are added for composite deoxidation. 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 in the molten steel; 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 an important influence on the properties of the alloy. At the same time, according to the oxygen content in the molten steel, it is determined whether carbon elements need to be added 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, which plays a role in precipitation strengthening; 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 is added. Yttrium segregates at the grain boundaries, which can play a role in grain boundary strengthening and improve the durability of the alloy. At the same time, the content of TO is controlled to increase the yield of expensive rare earth elements.

[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 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 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 alloying 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 prepared 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≥360MPa at 600℃;

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

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

[0104] The present invention improves the strength performance of the iron-chromium alloy at medium and high temperature operating temperatures of 600 to 900°C by designing reasonable alloy element addition and ratio and optimizing process preparation technology.

[0105] Figure 2 A schematic flow chart of a method for preparing a fuel cell interconnect plate provided in an embodiment of the present application.

[0106] See also Figure 2 The present application provides a method for preparing the fuel cell interconnection plate described in the above embodiment, the method comprising:

[0107] S21, sequentially heating, forging and multi-pass tempering the iron-chromium alloy ingot described in any one of the above items to obtain a slab;

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

[0109] S22, performing multiple hot rolling and annealing to soften the slab to obtain a hot-rolled strip;

[0110] 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 20% to 50%, the second hot rolling deformation is 30% to 60%, and the third hot rolling deformation is 40% to 70%. The final rolling temperature is higher than 900°C. After rolling, the steel is water-cooled to room temperature.

[0111] S23, subjecting the hot-rolled strip to intermediate heat treatment, multiple cold rolling and solution treatment to obtain a strip; the intermediate heat treatment includes the following parameters: temperature of 900°C to 1100°C, holding time of 5min to 15min, hydrogen injection volume ≥ 20m 3 / h;

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

[0113] S24. Stamp the strip to form a fuel cell interconnector; 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 volume ≥ 5 m 3 / h.

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

[0115] The following will further illustrate the present application 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 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 interconnector, 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 a ferrochromium alloy ingot with a set chemical composition after crystallization; wherein, 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 ferrochromium 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 addition timing of the 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. Perform hot rolling, annealing softening, and grinding and welding on 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 blanking, intermediate heat treatment, cold rolling, intermediate grinding, trimming and solution treatment to obtain a strip. The cold rolling includes: a first cold rolling, a second cold rolling and a third cold rolling. The deformation of the first cold rolling is 40%, the deformation of the second cold rolling is 40%, and the deformation of the third cold rolling is 60%. The temperature of the intermediate heat treatment is 1000°C, the holding time of the intermediate heat treatment is 10 minutes, and the amount of hydrogen sprayed during the intermediate heat treatment is 20m 3 / h.

[0121] Step 5, surface finishing, cleaning and plate shape correction of the strip, the specific process of the surface finishing is: using a polishing wheel with a particle size of 1000 mesh for rough polishing, and then using a polishing wheel with a particle size of 3000 mesh for fine polishing.

[0122] Step 6: stamping the strip: heat treatment to 300°C, spraying hydrogen at a rate of 5m 3 / h, keep warm for 60min, and punch to obtain the fuel cell interconnection plate.

[0123] Table 1 Chemical composition of Fe-Cr alloy ingot

[0124] serial number Cr Cu Ni W C+N Y Th TO Si Mn Al Example 1 12 0.5 1 1 0.01 0.05 0.005 0.002 0.2 0.1 0.2 Example 2 15 1 1.1 1.5 0.015 0.1 0.002 0.0015 0.15 0.2 0.15 Example 3 20 2 1.2 2 0.01 0.15 0.003 0.001 0.1 0.4 0.1 Example 4 25 3 1 2.5 0.009 0.2 0.004 0.0015 0.15 0.6 0.15 Example 5 30 3.5 1 3 0.013 0.3 0.001 0.002 0.15 0.8 0.1 Comparative Example 1 15 1 1.1 2 0.01 0.3 0.0005 0.0015 0.15 0.4 0.15 Comparative Example 2 20 0.5 1.1 3 0.01 0.1 0.002 0.0025 0.15 0.4 0.15 Comparative Example 3 25 1 1.1 4 0.01 0.1 0.003 0.0015 0.15 0.4 0.15 Comparative Example 4 20 2 1.2 2 0.01 0.15 0.003 0.001 0.1 0.4 0.1

[0125] Table 2 Relationship between the chemical compositions of ferrochromium alloy ingots

[0126] serial number [Y] / [Th] 0.006×[Cu]+0.032×[W] Example 1 10 0.035 Example 2 50 0.054 Example 3 50 0.076 Example 4 50 0.098 Example 5 300 0.117 Comparative Example 1 600 0.07 Comparative Example 2 50 0.099 Comparative Example 3 33.3 0.134 Comparative Example 4 50 0.076

[0127] Table 3 Timing of adding raw materials during high temperature refining

[0128]

[0129]

[0130] The fuel cell interconnection plates prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were tested for mechanical properties. The results are shown in Table 4.

[0131] Table 4 Mechanical properties of fuel cell interconnection plates

[0132]

[0133] As can be seen from Table 4, the ratio of Y / Th in Comparative Example 1 does not meet the requirements, the content of the target component TO in Comparative Example 2 does not meet the requirements, the chemical composition of Comparative Example 3 does not meet the requirements of Y>0.006×Cu+0.032×W, the timing of adding Th in Comparative Example 4 does not meet the requirements of>0.7×T, and the TO content at the time of adding Th does not meet the requirements of 0.002% to 0.0025%, and the mechanical properties of the fuel cell interconnection plates at 600°C and 900°C of Comparative Examples 1 to 4 do not meet the requirements.

[0134] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0135] In the embodiments of the present application, the technical problem of poor strength performance of existing alloys at medium and high temperature operating temperatures of 600 to 900°C is solved by designing reasonable alloy element additions and ratios and optimizing process preparation technology.

[0136] In the embodiment of the present application, through vacuum melting + multi-pass tempering + rolling, the connector obtained has less harmful impurity elements, high purity, less internal defects, and good uniformity of composition and structure. Through solution process control, the prepared product has excellent medium and high temperature strength.

[0137] In the embodiment of the present application, the prepared fuel cell interconnection plate has a tensile strength Rm≥450MPa at 600°C, a yield strength Rp0.2≥360MPa at 600°C, a tensile strength Rm≥250MPa at 900°C, and a yield strength Rp0.2≥210MPa at 900°C.

[0138] In the embodiments of the present application, the alloy has low cost and simple preparation process, which reduces energy consumption, shortens the production cycle, improves production efficiency, and is suitable for promotion and application in industrial production.

[0139] In the examples of the present application, the cost of the prepared iron-based material is more than 50% lower than the cost of general high-temperature nickel-based alloys.

[0140] 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. An iron-chromium alloy with excellent medium and high temperature strength. By 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.

2. The iron-chromium alloy according to claim 1, characterized in that The chemical components satisfy the following relational expressions: 10 ≤ [Y] / [Th] ≤ 300 In the formula, [Y] represents the mass fraction of Y, and [Th] represents the mass fraction of Th.

3. The iron-chromium alloy according to claim 1, characterized in that The chemical components satisfy the following relational expressions: [Y] > 0.006×[Cu] + 0.032×[W] 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.

4. The iron-chromium alloy according to claim 1, characterized in that The iron-chromium alloy has Th oxide dispersed therein, and the particle size of the oxide is < 2 μm.

5. A method for preparing an iron-chromium alloy as claimed in any one of claims 1 to 4, 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.

6. The method according to claim 5, characterized in that 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 is < 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 additional 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%; Wherein, T is the total time of the high-temperature refining, and T is 0.5 h - 0.7 h.

7. The method according to claim 6, characterized in that The O content in the molten steel and the additional 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 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.

8. The method according to claim 5, 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; Wherein, T is the total time of the high-temperature refining, and T is 0.5 h - 0.7 h.

9. A fuel cell interconnection plate, characterized in that: The fuel cell interconnector is made of the iron-chromium alloy according to any one of claims 1 to 4, and the fuel cell interconnector satisfies at least one of the following performances: The tensile strength Rm ≥ 450 MPa at 600 °C; Yield strength Rp0.2≥360MPa at 600℃; Tensile strength Rm≥250MPa at 900℃; The yield strength Rp0.2≥210MPa at 900℃.

10. A method for preparing a fuel cell interconnection plate according to claim 9, characterized in that: The method comprises: The ferrochromium alloy ingot according to any one of claims 1 to 4 is sequentially heated, forged and tempered multiple times to obtain a slab; The slab is subjected to multiple hot rolling and annealing to obtain a hot-rolled strip; The hot-rolled strip is subjected to intermediate heat treatment, multiple cold rolling and solution treatment to obtain a strip; the intermediate heat treatment includes the following parameters: temperature of 900°C to 1100°C, holding time of 5min to 15min, hydrogen injection volume of ≥20m 3 / h; The strip is stamped to obtain a fuel cell interconnection plate; the stamping includes the following parameters: a heating temperature of 200°C to 400°C, a heat preservation time of 20min to 120min, a hydrogen injection volume of ≥5m 3 / h.

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