High-temperature alloy for molten chloride heat transfer and heat storage and preparation method and use thereof

Abstract

This invention relates to the field of metallic materials technology, specifically to a high-temperature alloy for chloride molten salt heat transfer and storage, its preparation method, and its applications. Based on the total weight of the high-temperature alloy, it comprises: 20%–25% Cr, 25%–30% Fe, 1.8%–3.0% Al, 0.1%–0.5% Si, 1.5%–2.5% Ti, 3%–5% Mo, 0.5%–1% W, 0.5%–1% Mn, 0.01%–0.05% Hf, <0.1% C, and the balance Ni. The high-temperature alloy provided by this invention possesses good corrosion resistance, meeting the corrosion resistance requirements of chloride molten salt environments at 400℃–750℃. Furthermore, this high-temperature alloy also exhibits good mechanical strength, weldability, and cold and hot working properties, making it easy to process into plates and pipes.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, specifically to a high-temperature alloy for heat transfer and storage using chloride molten salt, its preparation method, and its applications. Background Technology

[0002] In the field of renewable energy, concentrated solar thermal power generation technology has received widespread attention. However, due to unpredictable weather and diurnal cycles, thermal energy storage is a significant challenge hindering the development of concentrated solar thermal power generation. To address this issue, molten salt-based thermal storage media have been widely adopted.

[0003] Currently, molten salts used as heat storage media mainly include eutectic salts such as fluorides, chlorides, nitrates, carbonates, and sulfates. These eutectic salts can melt at 400-800℃, thus storing energy, and transferring heat during charge-discharge cycles through phase transitions between the solid and liquid phases of the molten salt. Although concentrated solar thermal power generation has gradually begun commercialization, it has not yet fully realized its potential. One obstacle is that in molten salt environments, power generation systems often operate at temperatures exceeding 600℃, and components in these systems face severe corrosion at high temperatures, thus affecting the entire system.

[0004] As one of the most promising next-generation high-temperature thermal storage technologies, molten salt thermal storage technology using chloride mixed salts can increase the maximum operating temperature of existing commercial molten salts from 550°C to over 800°C, thereby significantly improving the thermoelectric conversion efficiency of power cycle systems. Compared to other thermal storage media, chloride molten salts possess suitable melting points, good thermal properties (low vapor pressure, high thermal stability), and low material costs. Although molten salts operate at atmospheric pressure and do not require complex high-pressure systems, it is still desirable for alloy components to possess good mechanical properties and corrosion resistance in order to avoid bulky components and improve the overall economics of molten salt stacks.

[0005] In alloy design, Cr is an important means to improve the oxidation resistance of alloys. Studies have shown that as the Cr content increases, the corrosion resistance of the alloy improves, and in Ni-Fe based alloys, the required Cr content for corrosion resistance also increases with the increase of Fe content. However, increasing the Cr content in the alloy will lead to a decrease in the microstructure stability of Ni-Fe based alloys, resulting in a deterioration in mechanical properties. For example, in the Ni-Cr-Al-Fe alloy system, when the Fe content is 10 wt%, the γ / γ′ two-phase region shrinks with increasing Cr content, while when the Cr content reaches 22 wt%, the γ / γ′ two-phase region disappears. In particular, in Ni-Fe based alloy systems with high Fe content (>30 wt%), when the Cr content is greater than 20 wt%, α-Cr phase will precipitate in the alloy. Therefore, although a high Cr content can enable Ni-Fe based alloys to have the required corrosion resistance, it will reduce the long-term microstructure stability and mechanical properties of the alloy to a certain extent.

[0006] In addition, Al in the alloy is an important component for forming γ′ phase reinforcement. A higher Al content in the alloy has a positive effect on improving the corrosion resistance of the alloy. In particular, when the alloy contains both Cr and Al, the synergistic effect of the two will make the corrosion resistance of the alloy more significantly improved. However, excessive Al content will reduce the hot working performance and weldability of the alloy.

[0007] Therefore, alloy components used for heat transfer and storage in chloride molten salts in related technologies cannot simultaneously possess both good mechanical properties and corrosion resistance. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to overcome the defect that alloy components used for chloride molten salt heat transfer and heat storage in the prior art are difficult to have both good mechanical properties and corrosion resistance, thereby providing a high-temperature alloy for chloride molten salt heat transfer and heat storage, its preparation method and application.

[0009] Therefore, the present invention provides a high-temperature alloy for chloride molten salt heat transfer and storage, wherein, based on the total weight of the high-temperature alloy, the high-temperature alloy comprises:

[0010] 20wt%–25wt% Cr, 25wt%–30wt% Fe, 1.8wt%–3.0wt% Al, 0.1wt%–0.5wt% Si, 1.5wt%–2.5wt% Ti, 3wt%–5wt% Mo, 0.5wt%–1wt% W, 0.5wt%–1wt% Mn, 0.01wt%–0.05wt% Hf, <0.1wt% C, and the balance Ni.

[0011] Optionally, in the high-temperature alloy, the weight percentage of Al is 2.0 wt% to 2.5 wt%.

[0012] And / or, the weight percentage of Cr is 20wt% to 22wt%;

[0013] And / or, the weight percentage of Ti is 2.0 wt% to 2.5 wt%;

[0014] And / or, the weight percentage of Si is 0.3wt% to 0.5wt%.

[0015] Optionally, the high-temperature alloy does not contain Co.

[0016] Optionally, the high-temperature alloy can be used in a chloride molten salt environment at 400°C to 750°C.

[0017] Optionally, the chloride molten salt includes at least one of sodium chloride, potassium chloride, and magnesium chloride.

[0018] Optionally, the high-temperature alloy has a yield strength of not less than 500 MPa, a tensile strength of not less than 900 MPa, and a microhardness of 300–370 HV.

[0019] The present invention also provides a method for preparing the above-mentioned high-temperature alloy, comprising the following steps:

[0020] Take the alloy raw materials, melt and cast them under vacuum conditions to obtain casting ingots;

[0021] The casting ingot is subjected to heat treatment.

[0022] Optionally, the heat treatment includes a primary heat treatment, a secondary heat treatment, and a tertiary heat treatment; wherein,

[0023] The conditions for the primary heat treatment include: holding at 1160–1200℃ for 0.5–2.5 hours followed by air cooling;

[0024] The conditions for the secondary heat treatment include: holding at 750–800℃ for 5–10 hours followed by air cooling;

[0025] The conditions for the three heat treatments include: holding at 650–700°C for 15–18 hours and then air cooling.

[0026] The present invention also provides the use of the above-described high-temperature alloy in the preparation of components for chloride molten salt heat transfer and storage.

[0027] Optionally, the component is a component for focused solar thermal power generation.

[0028] The technical solution of this invention has the following advantages:

[0029] 1. The high-temperature alloy provided by the present invention has good corrosion resistance and can meet the corrosion resistance requirements of chloride molten salt environment at 400℃~750℃. At the same time, the high-temperature alloy also has good mechanical strength, weldability and cold and hot working performance, and is easy to process into plates and pipes.

[0030] Specifically, the high-temperature alloy provided by this invention contains 20wt% to 25wt% Cr, which ensures that the high-temperature alloy has good corrosion resistance in chloride molten salt environments below 750℃. At the same time, the high-temperature alloy also contains 1.8wt% to 3.0wt% Al and 0.1wt% to 0.5wt% Si. Cr, Al and Si work together to make full use of the third element effect, which can reduce the consumption rate of Cr. The Al2O3 and SiO2 products generated by internal oxidation also help to prevent element diffusion during the oxidation process, thereby achieving the effect of improving the corrosion resistance of the high-temperature alloy and reducing the corrosion rate of the alloy in high-temperature chloride molten salt environments.

[0031] The high-temperature alloy also contains 3wt% to 5wt% Mo, 0.5wt% to 1wt% W, and 0.01wt% to 0.05wt% Hf. These three elements work synergistically as solid solution strengthening elements, which can effectively improve the high-temperature mechanical strength of the high-temperature alloy. Moreover, thanks to the high melting points of Mo, Hf, W and their precipitated phases, the dissolution rate of the high-temperature alloy in chloride molten salt environments below 750℃ can be further reduced, which means that the corrosion resistance of the high-temperature alloy in high-temperature (400℃ to 750℃) chloride molten salt environments can be further improved.

[0032] The high-temperature alloy also contains 1.5wt% to 2.5wt% Ti, which acts as a precipitate strengthening element and can further improve the high-temperature mechanical strength of the high-temperature alloy. The alloy also contains 0.5wt% to 1wt% Mn. Within this content range, Mn can replace Ni to form stable austenite, solidify S in the high-temperature alloy, and will not reduce the corrosion resistance of the high-temperature alloy.

[0033] This high-temperature alloy also contains 25wt% to 30wt% Fe, which helps to reduce the cost of the high-temperature alloy. On the other hand, Fe helps to improve the processing performance and weldability of the alloy, thereby increasing the yield when using the high-temperature alloy to make plates and pipes. Controlling the content of C in this high-temperature alloy to <0.1wt% can effectively prevent C from forming carbides with Hf, Cr, Ti, W and other elements in the alloy and reducing the alloy's corrosion resistance.

[0034] In addition, to effectively ensure the ratio of the γ / γ′ dual-phase region and avoid the precipitation of the α-Cr phase, the Cr content in the high-temperature alloy should be in an appropriate ratio with the Fe content, thereby solving the problem of poor long-term microstructure stability and mechanical properties of the alloy under conditions of high Fe and Cr content.

[0035] 2. The high-temperature alloy provided by the present invention further optimizes the content of Al, Cr, Ti and Si, so that the weight percentage of Al is 2.0wt% to 2.5wt%, the weight percentage of Cr is 20wt% to 22wt%, the weight percentage of Ti is 2.0wt% to 2.5wt%, and the weight percentage of Si is 0.3wt% to 0.5wt%. Within this content range, the corrosion resistance of the high-temperature alloy is further improved.

[0036] 3. The high-temperature alloy provided by this invention, through formula optimization, coordinates the components in the formula so that the alloy does not contain Co, which can significantly reduce the cost of alloy raw materials without affecting the performance of the high-temperature alloy, and further reduce the engineering construction cost for large-scale application.

[0037] 4. The high-temperature alloy preparation method provided by the present invention employs a specific heat treatment procedure, which can significantly improve the grain size of the alloy, control the precipitated phases in the alloy, make the austenite in the alloy more prominent, and thus effectively improve the mechanical strength of the alloy. Attached Figure Description

[0038] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 This is the equilibrium phase diagram of the high-temperature alloy prepared in Example 3 of the present invention;

[0040] Figure 2 This is a microstructure diagram of the high-temperature alloy prepared in Example 3 of the present invention;

[0041] Figure 3 This is a graph showing the morphological characteristics of the high-temperature alloy prepared in Example 3 of this invention after corrosion resistance testing. Detailed Implementation

[0042] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0043] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0044] Examples 1-12

[0045] The high-temperature alloys of Examples 1-12 were prepared according to the following methods:

[0046] (1) Weigh each raw material according to the amount shown in Table 1, place it in a vacuum induction furnace for melting, and cast it into an ingot under vacuum conditions to obtain a casting ingot.

[0047] (2) Take the casting ingot obtained in step (1), first place it in an environment of 1180℃ for 1 hour and then air cool it to room temperature, then place it in an environment of 780℃ for 8 hours and air cool it to 680℃, and finally place it in an environment of 680℃ for 16 hours and air cool it to room temperature to obtain a high temperature alloy.

[0048] Table 1. Amount of each raw material used in Examples 1-10 (wt%)

[0049] alloy C Cr Al Ti Si Mo Hf W Mn Fe Ni Example 1 0.08 20.31 2.08 2.13 0.32 3.21 0.02 0.52 0.58 25.62 margin Example 2 0.07 20.22 2.50 2.03 0.33 3.31 0.01 0.53 0.51 25.32 margin Example 3 0.08 20.11 2.01 2.49 0.32 3.35 0.01 0.54 0.55 25.71 margin Example 4 0.07 21.45 2.34 2.29 0.31 4.01 0.02 0.53 0.56 27.92 margin Example 5 0.07 21.95 2.08 2.03 0.33 3.98 0.02 0.56 0.55 27.99 margin Example 6 0.08 21.89 2.28 2.02 0.48 4.99 0.02 0.78 0.97 28.03 margin Example 7 0.08 21.95 2.27 2.03 0.48 4.97 0.02 0.98 0.60 30.00 margin Example 8 0.08 21.95 2.28 2.01 0.49 3.98 0.03 0.61 0.68 29.89 margin Example 9 0.08 21.85 2.30 2.02 0.44 3.88 0.02 0.55 0.69 29.56 margin Example 10 0.09 21.88 2.30 2.03 0.31 4.01 0.05 0.58 0.94 29.77 margin Example 11 0.08 20 3.0 1.5 0.5 3.0 0.03 0.65 0.80 28.85 margin Example 12 0.08 25 1.8 2.5 0.1 5.0 0.03 0.65 0.79 28.82 margin

[0050] Thermodynamic phase diagram calculations and metallographic analysis were performed on the high-temperature alloy prepared in Example 3. The test results are as follows: Figure 1 and Figure 2 As shown, where, Figure 1 The equilibrium phase diagram of the high-temperature alloy prepared in Example 3 shows that the alloy has a γ / γ′ dual-phase structure with no α-Cr phase precipitation, indicating that the Cr content and Fe content in the high-temperature alloy of the present invention are in an appropriate ratio, thereby solving the problem of poor long-term structural stability and mechanical properties of the alloy under high Fe and Cr content conditions. Figure 2 The diagram shows the microstructure of the high-temperature alloy prepared in Example 3. It can be seen that the high-temperature alloy has an austenitic structure with a small amount of carbide precipitates distributed at the grain boundaries and within the grains.

[0051] Comparative Examples 1-5

[0052] High-temperature alloys of Comparative Examples 1-5 were prepared according to the following methods:

[0053] (1) Weigh each raw material according to the amount shown in Table 2 (Comparative Example 1 is commercial Incoloy 800 corrosion-resistant alloy), place it in a vacuum induction furnace for melting, and cast it into an ingot under vacuum conditions to obtain a cast ingot.

[0054] (2) Take the casting ingot obtained in step (1), first place it in an environment of 1180℃ for 1 hour and then air cool it to room temperature, then place it in an environment of 780℃ for 8 hours and air cool it to 680℃, and finally place it in an environment of 680℃ for 16 hours and air cool it to room temperature to obtain a high temperature alloy.

[0055] Table 2 shows the amount (wt%) of each raw material used in Comparative Examples 1-5.

[0056] alloy C Cr Al Ti Si Mo Hf W Mn Fe Ni Comparative Example 1 0.10 22.13 0.52 0.57 0.98 / / / 1.52 margin 34.72 Comparative Example 2 0.08 / 2.08 2.13 0.32 3.21 0.02 0.52 0.58 25.62 margin Comparative Example 3 0.08 20.31 / 2.13 0.32 3.21 0.02 0.52 0.58 25.62 margin Comparative Example 4 0.08 20.31 2.08 / 0.32 3.21 0.02 0.52 0.58 25.62 margin Comparative Example 5 0.08 20.31 2.08 2.13 / 3.21 0.02 0.52 0.58 25.62 margin

[0057] Experimental Example 1

[0058] This embodiment is used to verify the corrosion resistance of various high-temperature alloys in a high-temperature chloride molten salt environment.

[0059] Three anhydrous chlorides, NaCl, KCl, and MgCl2 (all with a purity >99.8 wt%), were weighed and prepared into a ternary chloride mixed salt at a weight ratio of MgCl2:KCl:NaCl = 55:20.5:24.5. This mixed molten salt was then used to test the corrosion resistance of various high-temperature alloys. The corrosion resistance tests were conducted in a high-purity argon atmosphere at 750℃ for 200 hours. The maximum corrosion depth was used to characterize the corrosion resistance of the alloys. The test results are shown in Table 4.

[0060] Table 4. Maximum corrosion depth of each alloy after corrosion resistance test.

[0061] alloy Maximum corrosion depth, μm alloy Maximum corrosion depth, μm Example 1 88.5 Example 10 62.3 Example 2 86.5 Example 11 58.6 Example 3 84.5 Example 12 78.8 Example 4 68.6 Comparative Example 1 101.8 Example 5 73.2 Comparative Example 2 >500 Example 6 77.5 Comparative Example 3 135.5 Example 7 76.1 Comparative Example 4 115.3 Example 8 65.5 Comparative Example 5 119.8 Example 9 60.3

[0062] The morphological characteristics of the high-temperature alloy prepared in Example 3 after corrosion resistance testing are as follows: Figure 3 As shown. Tests revealed that the outermost layer is a corrosion layer, mainly enriched with small amounts of Ti, Al, and Fe oxides. The next outermost layer is an Al-enriched oxide film, and the innermost layer is a Ni-enriched oxide film, forming a protective layer with corrosion resistance. Ti is enriched inside the alloy. Based on the alloy composition and phase analysis results, it can be determined that the main components of the corrosion product layer are NiCr2O4, Al2O3, and Cr2O3.

[0063] Experiment Example 2

[0064] This experimental example is used to verify the mechanical properties of various high-temperature alloys.

[0065] (1) In accordance with GB / T 228.1-2010 Metallic Materials - Tensile Testing - Part 1, room temperature tensile tests were conducted on various high-temperature alloys using the room temperature test method, with a strain rate of 0.0025 s⁻¹. -1 ;

[0066] (2) Vickers hardness test was performed on each high-temperature alloy. The load of the Vickers hardness tester was 25g and the loading time was 10s.

[0067] The test results are shown in Table 5.

[0068] Table 5. Mechanical property test results of various high-temperature alloys

[0069]

[0070]

[0071] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A high-temperature alloy for heat transfer and storage in chloride molten salt, characterized in that, Based on the total weight of the high-temperature alloy, the high-temperature alloy comprises: 20 wt%–25 wt% Cr, 25 wt%–30 wt% Fe, 1.8 wt%–3.0 wt% Al, 0.1 wt%–0.5 wt% Si, 1.5 wt%–2.5 wt% Ti, 3 wt%–5 wt% Mo, 0.5 wt%–1 wt% W, 0.5 wt%–1 wt% Mn, 0.01 wt%–0.05 wt% Hf, <0.1 wt% C and the balance Ni; The high-temperature alloy is used in a chloride molten salt environment at 750°C. The method for preparing the high-temperature alloy includes the following steps: Take the alloy raw materials, melt and cast them under vacuum conditions to obtain casting ingots; The casting ingot is subjected to heat treatment; The heat treatment includes primary heat treatment, secondary heat treatment, and tertiary heat treatment; wherein... The conditions for the primary heat treatment include: holding at 1160–1200℃ for 0.5–2.5 hours followed by air cooling; The conditions for the secondary heat treatment include: holding at 750–800℃ for 5–10 hours and then air cooling; The conditions for the three heat treatments include: holding at 650–700°C for 15–18 hours and then air cooling.

2. The high-temperature alloy according to claim 1, characterized in that, In the high-temperature alloy, the weight percentage of Al is 2.0 wt% to 2.5 wt%. And / or, the weight percentage of Cr is 20 wt% to 22 wt%; And / or, the weight percentage of Ti is 2.0 wt% to 2.5 wt%; And / or, the weight percentage of Si is 0.3 wt% to 0.5 wt%.

3. The high-temperature alloy according to claim 1, characterized in that, The high-temperature alloy does not contain Co.

4. The high-temperature alloy according to any one of claims 1 to 3, characterized in that, The chloride molten salt includes at least one of sodium chloride, potassium chloride, and magnesium chloride.

5. The high-temperature alloy according to any one of claims 1 to 3, characterized in that, The high-temperature alloy has a yield strength of not less than 500 MPa, a tensile strength of not less than 900 MPa, and a microhardness of 300–370 HV.

6. Use of the high-temperature alloy according to any one of claims 1 to 5 in the preparation of components for chloride molten salt heat transfer and storage.

7. The use according to claim 6, characterized in that, The component is used for focused solar thermal power generation.

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