A corrosion-resistant complex alloy material with stable high-temperature structure and a preparation method thereof

Abstract

The present application relates to the field of complex alloy materials, and discloses a corrosion-resistant complex alloy material with stable high-temperature structure and a preparation method thereof. The preparation method comprises: using pure nickel solder to perform surfacing on the surface of Inconel 617 alloy parent material, and during the surfacing, controlling the welding heat input to be 1440-1920 J / mm, the number of surfacing layers ≥ 3 layers, and the total surfacing layer thickness ≥ 3 mm. The implementation method of the present application can significantly improve the molten salt corrosion resistance of the alloy itself while maintaining good high-temperature structure stability.

Description

Technical Field

[0001] The present application relates to the field of complex alloy materials, and in particular to corrosion-resistant complex alloy materials with stable high-temperature structures and preparation technologies thereof. Background Art

[0002] Molten salt reactor is the only liquid fuel reactor among the six types of fourth generation reactors, with unique advantages such as high inherent safety, water-free cooling, and small modularization. The complex environment of molten salt reactors, such as high temperature, strong molten salt corrosion, and strong neutron irradiation, places extremely stringent requirements on reactor materials.

[0003] The currently mature structural material for molten salt reactors is UNS N10003 alloy (70wt.% Ni-16wt.% Mo-7wt.% Cr solid solution nickel-based high-temperature alloy), which has a maximum allowable temperature of 704°C. However, to achieve high-efficiency energy conversion such as high-temperature hydrogen production, the molten salt reactor needs to operate above 800°C. At this time, the mechanical properties of UNS N10003 alloy can no longer meet the requirements. Therefore, the development of alloys for molten salt reactors that can serve for a long time at higher temperatures (≥850°C) has become an urgent problem to be solved. Summary of the invention

[0004] The purpose of the present application is to provide a corrosion-resistant complex alloy material with stable high-temperature structure and a preparation method thereof, which can maintain structural stability in a high-temperature environment (≥850°C) and is resistant to high-temperature molten salt corrosion.

[0005] The present application discloses a method for preparing a corrosion-resistant complex alloy material with stable high-temperature structure, comprising:

[0006] Select Inconel 617 alloy base material and pure nickel solder;

[0007] The pure nickel solder is used to perform surfacing welding on the surface of the Inconel 617 alloy base material. During the surfacing welding, the welding heat input is controlled to be 1440-1920 J / mm, the number of surfacing layers is ≥3 layers, and the total surfacing layer thickness is ≥3 mm.

[0008] In a preferred embodiment, the nickel content in the pure nickel solder is ≥ 93%.

[0009] In a preferred embodiment, the pure nickel solder is ERNi-1 pure nickel welding wire.

[0010] In a preferred example, the welding heat input is 1440-1760 J / mm.

[0011] In a preferred example, the welding heat input is 1760 J / mm.

[0012] In a preferred embodiment, the surfacing welding is performed by tungsten inert gas arc welding.

[0013] In a preferred embodiment, before using the pure nickel solder to perform surfacing welding on the surface of the Inconel 617 alloy base material, the method further comprises:

[0014] If the ambient temperature is lower than 5°C, a non-contact heating method is used to make the surface temperature of the Inconel 617 alloy base material reach 15°C.

[0015] In a preferred embodiment, when the pure nickel solder is used to perform surfacing welding on the surface of the Inconel 617 alloy base material, it also includes:

[0016] Control the interlayer temperature ≤93℃.

[0017] In a preferred embodiment, before using the pure nickel solder to perform surfacing welding on the surface of the Inconel 617 alloy base material, the method further comprises:

[0018] The surface of the Inconel 617 alloy base material is polished to be smooth and have a metallic luster;

[0019] Remove impurities such as moisture, phosphate, halogen and oil on the surface of the Inconel 617 alloy base material.

[0020] The present application also discloses a high-temperature microstructure-stable corrosion-resistant replica alloy material, wherein the high-temperature microstructure-stable corrosion-resistant replica alloy material is prepared according to the preparation method described above.

[0021] In the implementation manner of the present application, at least the following beneficial effects are included:

[0022] Although Inconel 617 is not resistant to high-temperature molten salt corrosion (Cr content exceeds 20%) and pure nickel itself has low strength at high temperatures, the embodiment of the present application is capable of maintaining structural stability and resisting high-temperature molten salt corrosion in a high-temperature environment (≥850°C) by surfacing pure nickel on the surface of Inconel 617 alloy to prepare a complex alloy.

[0023] In addition, the development of new alloys usually requires not only a reasonable ratio of elements, but also the accumulation of data on relevant mechanics, irradiation, etc. in order to obtain permission to enter the reactor, which requires a long period of time and high costs. The implementation method of the present application is to optimize the performance of existing alloys to obtain alloys for molten salt reactors that can serve for a long time at higher temperatures (≥850°C). Compared with the development of new alloys, this greatly shortens the research and development cycle and reduces the research and development costs.

[0024] A large number of technical features are recorded in the specification of this application, which are distributed in various technical solutions. If all possible combinations of technical features of this application (i.e., technical solutions) are to be listed, the specification will be too long. In order to avoid this problem, the various technical features disclosed in the above-mentioned invention content of this application, the various technical features disclosed in the various embodiments and examples below, and the various technical features disclosed in the accompanying drawings can be freely combined with each other to form various new technical solutions (these technical solutions are all deemed to have been recorded in this specification), unless the combination of such technical features is technically infeasible. For example, in one example, feature A+B+C is disclosed, and in another example, feature A+B+D+E is disclosed, and features C and D are equivalent technical means that play the same role. Technically, only one can be used, and it is impossible to use them at the same time. Feature E can be combined with feature C technically. Then, the solution of A+B+C+D should not be deemed to have been recorded because it is technically infeasible, and the solution of A+B+C+E should be deemed to have been recorded. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic flow chart showing a method for preparing a corrosion-resistant complex alloy material with stable high-temperature structure according to the first embodiment of the present application.

[0026] Figure 2 It is a microscopic metallographic picture showing the interface between the pure nickel welding layer and the Inconel617 alloy in the vertical surfacing direction of the complex alloy of Examples 1-8 of the present application.

[0027] Figure 3 It is a schematic diagram showing the results of the complex alloy of Example 6 of the present application after being corroded in LiF-NaF-KF molten salt at 850°C for 400 hours; wherein, (a) is a schematic diagram of the metallographic structure, (b) is a scanning electron microscope image of the base material area, and (c) is a scanning electron microscope image of the top area of ​​the pure nickel solder layer.

[0028] Figure 4 Schematic diagram showing the Cr element distribution curve of the complex alloy of Example 6 of the present application after high-temperature aging at 850° C. for different times.

[0029] Figure 5 2 is a schematic diagram showing the analysis of the precipitated phase composition in the overlay layer of the complex alloy of Example 6 of the present application after high-temperature aging at 850°C for 2000 hours; wherein (a), (b), and (c) respectively represent the first, second, and third layers of the pure nickel weld layer in the unaged sample, and (d), (e), and (f) respectively represent the first, second, and third layers of the pure nickel weld layer in Example 6 after aging for 2000 hours. DETAILED DESCRIPTION

[0030] In the following description, many technical details are provided to help readers better understand the present application. However, those skilled in the art can understand that the technical solution claimed in the present application can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0031] Description of some concepts:

[0032] Interlayer temperature: refers to the real-time measured temperature of the previous adjacent weld bead when welding the subsequent weld bead in multi-layer welding.

[0033] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0034] The first embodiment of the present application relates to a method for preparing a corrosion-resistant complex alloy material with stable high-temperature structure, the preparation method comprising the following steps:

[0035] In step 101, the surface of the Inconel 617 alloy base material is polished to be smooth and have a metallic luster. It should be noted that when cleaning and polishing the surface of the Inconel 617 alloy base material, special tools should be used and it should not be mixed with other alloys.

[0036] Then, step 102 is entered to remove impurities such as moisture, phosphate, halogen and oil on the surface of the Inconel 617 alloy base material. For example, alcohol or the like can be used to wipe the surface to remove moisture, phosphate, oil, grease, oxide, tape, coating, marking raw materials and other carbon-containing substances, halogen and other foreign matter on the surface of the Inconel 617 alloy base material.

[0037] Then, the process proceeds to step 103. If the ambient temperature is lower than 5°C, a non-contact heating method is used to make the surface temperature of the Inconel 617 alloy base material reach 15°C.

[0038] Then, enter step 104, use pure nickel solder to perform surfacing welding on the surface of the Inconel 617 alloy base material. During the surfacing welding, the welding heat input is controlled to be 1440-1920 J / mm, the number of surfacing layers is ≥3 layers, and the total surfacing layer thickness is ≥3 mm.

[0039] Optionally, step 104 further includes: controlling the temperature between layers (lanes) to be ≤ 93° C. For example, an auxiliary cooling method may be used to control the temperature between layers (lanes) to be ≤ 93° C.

[0040] Optionally, the nickel content of the pure nickel solder in step 104 is ≥ 93%. In one embodiment, the pure nickel solder uses ERNi-1 pure nickel welding wire. In other embodiments, other pure nickel solders such as UNS N02201, UNS N02200 (not limited to wire materials) may also be used.

[0041] Optionally, the welding heat input in step 104 may be 1440-1760 J / mm. For example, the welding heat input may be 1440 J / mm, 1600 J / mm or 1760 J / mm.

[0042] Optionally, the cladding may be performed by tungsten inert gas welding, manual electrode welding, metal arc gas shielded welding, plasma powder cladding or other welding methods.

[0043] Optionally, the welding position is, for example, flat welding but not limited to flat welding. After each weld is completed, the weld edge needs to be transitionally smooth, and the weld surface is cleaned of oxide scale by brushing with a stainless steel brush or grinding.

[0044] It should be pointed out that this application is preferably carried out in a well-ventilated, dry, clean and orderly workshop with a wind speed lower than 2m / s, avoiding construction in the same workshop with work that can generate smoke, dust, loud noise, etc., to protect the workpiece from contamination and influence of harmful substances.

[0045] The second embodiment of the present application relates to a corrosion-resistant replica alloy material with stable high-temperature structure. The corrosion-resistant replica alloy material with stable high-temperature structure is prepared according to the preparation method of the first embodiment.

[0046] In order to better understand the technical solution of the present application, the technical solution of the present application and its experimental verification results are described below in conjunction with the following Examples 1-8. Among them, the details in Examples 1-8 are mainly for ease of understanding and are not intended to limit the scope of protection of the present application.

[0047] 1. Surfacing:

[0048] In Example 1-8, ERNi-1 pure nickel welding wire is welded on the surface of Inconel 617 alloy with a thickness of 25 mm by argon tungsten arc welding.

[0049] The surfacing process parameters used in Examples 1-8 are shown in Table 1. The calculation formula for welding heat input is: heat input = current * voltage * 60 / welding speed, the welding speed unit is mm / min, and the heat input unit is J / mm. It should be noted that in Examples 1-8, when the heat input is constant, the current, voltage and welding speed can be changed within a reasonable range.

[0050] Among them, the main chemical composition (mass fraction, %) of Inconel 617 alloy is 22.3% Cr, 9.55% Mo, 12.2% Co, 1.05% Al, 0.09% Si, 0.39% Ti, 0.08% Mn, 0.08% C and Ni Bal. Among them, the main chemical composition of ERNi-1 pure nickel welding wire is 0.03% C, 0.07% Fe, 0.50% Mn, 0.41% Al, 0.36% Si, 2.77% Ti and Ni Bal.

[0051] Table 1

[0052] Example Current A Voltage V Welding speed mm / min Number of cladding layers Heat input J / mm 1 180A 12V 90mm / min 2 1440 2 180A 12V 90mm / min 3 1440 3 200A 12V 90mm / min 2 1600 4 200A 12V 90mm / min 3 1600 5 220A 12V 90mm / min 2 1760 6 220A 12V 90mm / min 3 1760 7 240A 12V 90mm / min 2 1920 8 240A 12V 90mm / min 3 1920

[0053] 2. Test verification results:

[0054] In the above-mentioned Examples 1-8, microscopic metallographic samples were cut in the vertical surfacing direction to observe the three overlapping areas.

[0055] Polish the cross section of the sample and magnify it 200 times for inspection (such as Figure 2 shown), from Figure 2 It can be seen from the test results that there are no microcracks in the welding areas of the samples corresponding to Examples 1-8.

[0056] Generally, the corrosion of high-temperature molten salt on alloys is mainly the corrosion of Cr and Fe elements in the alloys. Therefore, the molten salt corrosion resistance of the alloy after cladding is related to the Cr and Fe content on its surface. If the Cr and Fe content is high, the alloy will suffer from intergranular corrosion. The following Table 2 is a statistical table of the element content (mass fraction, %) on the surface of the pure nickel welding layer of the above-mentioned Examples 1-8.

[0057] Table 2

[0058]

[0059] It can be seen from Table 2 above that: with the increase of heat input, the cladding dilution rate increases, resulting in an increase in the Cr content on the surface of the pure nickel weld layer. At the same time, with the increase of the number of cladding layers, the Cr content on the surface of the pure nickel weld layer decreases.

[0060] At present, the only structural material that can be used maturely in molten salt reactors is UNS N10003 alloy (Hastelloy N alloy), and the content of Cr in this alloy composition is 7%. In the Hastelloy N (UNSN10003) alloy manual of Haynes International, it is clearly pointed out that the alloy has excellent molten salt corrosion resistance in the temperature range of 704-871°C. In the embodiment of the present invention, only when the number of surfacing layers reaches 3 layers, the Cr content on the surface of the pure nickel welding layer is lower than 7%, that is, the content of Cr on the surface of the pure nickel welding layer of the complex alloy in Examples 2, 4, and 6 meets the requirements. Among them, the surface Cr content is the highest when the heat input is 1760J / mm and the number of surfacing layers is 3 layers (Example 6), and it can be inferred that its molten salt corrosion resistance is the weakest one.

[0061] We used LiF-NaF-KF (46.5–11.5–42 mol.%) (FLiNaK) molten salt as the corrosion medium and immersed the samples of Example 6 (3 parallel samples) in the FLiNaK molten salt at 850°C. Figure 3 Schematic diagram of the corrosion results of the complex alloy of Example 6 of the present application in LiF-NaF-KF molten salt at 850°C for 400 hours, wherein 3(a) is the metallographic structure, 3(b) is the scanning electron microscope image of the base material area, and 3(c) is the scanning electron microscope image of the top area of ​​the pure nickel solder layer.

[0062] from Figure 3 It can be seen that: 1) The Inconel 617 base metal area in the complex alloy shows severe intergranular corrosion, and the pure nickel weld layer area close to the base metal side also shows obvious corrosion, while the top area of ​​the weld layer (far away from the base metal area) has no obvious corrosion (such as Figure 3 (a)); 2) Scanning electron microscopy (SEM) was used to further observe the corroded samples, and it was found that there were a large number of corrosion holes near the surface of the parent material area, and the corrosion along the grain boundaries was serious (such as Figure 3 (b)), while there is a layer of corrosion holes in the top area of ​​the pure nickel solder layer, with a thickness of about 25um (e.g. Figure 3 (c)) No obvious corrosion along the grain boundaries was observed in this area.

[0063] Studies have shown (Corros. Sci. 106 (2016) 249-259.) that the corrosion depth of Hastelloy N alloy for molten salt reactors is about 26.5um after being corroded in FLiNaK at 850°C for 400 hours. In comparison, under the same conditions, the thickness of the corrosion layer in the top area of ​​the pure nickel solder layer in the complex alloy material prepared in this application is equivalent to the corrosion depth of Hastelloy N, which shows that: when the heat input is below 1760J / mm, the pure nickel solder layer in this application has excellent molten salt corrosion resistance at 850°C.

[0064] Furthermore, we conducted a long-term aging experiment at 850°C on Example 6 to investigate the structural stability of the complex alloy at high temperatures. The element distribution (perpendicular to the surfacing direction) and precipitated phase composition of Example 6 after long-term aging at high temperatures were analyzed using scanning electron microscope energy spectrum (SEM-EDS). Figure 4 The figure shows the Cr element distribution curve of the complex alloy of Example 6 after high temperature aging at 850°C for different times. Figure 5 The figure shows the analysis diagram of the precipitated phase composition in the overlay layer of the complex alloy of Example 6 after high-temperature aging at 850°C for 2000 hours, wherein 5(a), 5(b), and 5(c) respectively represent the first, second, and third layers of the pure nickel weld layer in the unaged sample, and 5(d), 5(e), and 5(f) respectively represent the first, second, and third layers of the pure nickel weld layer in Example 6 after aging for 2000 hours.

[0065] from Figure 4 and Figure 5 It can be seen that the Cr content and distribution at the surface weld layer and interface after aging for 2000 hours are basically the same as those of the samples without aging treatment (such as Figure 4 ), the precipitated phase in the pure nickel solder layer before aging and after aging for 2000 hours is TiN (such as Figure 5 ), which shows that the composition and structure of the complex alloy are very stable during high temperature aging.

[0066] Therefore, the experimental results of the above-mentioned embodiments 1-8 of the present application show that the composite alloy prepared under the welding parameters of the cladding heat input between 1440 and 1760 J / mm, the cladding layer ≥ 3 layers, and the total cladding layer thickness ≥ 3 mm has a very stable composition and structure at a high temperature of 850°C, and the pure nickel weld layer has excellent resistance to molten salt corrosion.

[0067] It should be noted that the above experiments cannot be completed in a short period of time, because the various characterization processes involved in the experiments require a lot of money and time, and these all require the use of specific equipment and be carried out in a specific environment.

[0068] It should be noted that in the application documents of this patent, relational terms such as first and second 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. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "including one" do not exclude the existence of other identical elements in the process, method, article or device including the elements. In the application documents of this patent, if it is mentioned that an action is performed according to an element, it means that the action is performed at least according to the element, which includes two situations: performing the action only according to the element, and performing the action according to the element and other elements. Expressions such as multiple, multiple, and multiple include 2, 2 times, 2 kinds, and more than 2, more than 2 times, and more than 2 kinds.

[0069] All documents mentioned in this application are considered to be included in the disclosure of this application as a whole, so that they can be used as the basis for modification when necessary. In addition, it should be understood that after reading the above disclosure of this application, those skilled in the art can make various changes or modifications to this application, and these equivalent forms also fall within the scope of protection claimed in this application.

Claims

1. A method for preparing a corrosion-resistant complex alloy material with stable high-temperature structure, characterized in that: include: Using pure nickel solder to perform surfacing welding on the surface of Inconel617 alloy base material, during the surfacing welding, the welding heat input is controlled to be 1440-1760 J / mm, the number of surfacing layers is ≥3 layers, and the total surfacing layer thickness is ≥3 mm; When using pure nickel solder to perform surfacing welding on the surface of Inconel617 alloy base material, it also includes: Control the interlayer temperature ≤93℃.

2. The method for preparing the corrosion-resistant complex alloy material with stable high-temperature structure according to claim 1, characterized in that: The nickel content in the pure nickel solder is ≥93%.

3. The method for preparing a corrosion-resistant complex alloy material with stable high-temperature structure according to claim 2, characterized in that: The pure nickel solder adopts ERNi-1 pure nickel welding wire.

4. The method for preparing a corrosion-resistant complex alloy material with stable high-temperature structure according to claim 3, characterized in that: The welding heat input is 1760 J / mm.

5. The method for preparing the corrosion-resistant complex alloy material with stable high-temperature structure according to claim 1, characterized in that: The surfacing welding adopts tungsten inert gas arc welding.

6. The method for preparing the corrosion-resistant complex alloy material with stable high-temperature structure according to claim 1, characterized in that: Before using pure nickel solder to perform surfacing on the surface of the Inconel617 alloy base material, the method further includes: If the ambient temperature is lower than 5°C, a non-contact heating method is used to make the surface temperature of the Inconel 617 alloy base material reach 15°C.

7. The method for preparing a corrosion-resistant complex alloy material with stable high temperature structure according to any one of claims 1 to 6, characterized in that: Before using pure nickel solder to perform surfacing on the surface of the Inconel617 alloy base material, the method further includes: The surface of the Inconel 617 alloy base material is polished to be smooth and have a metallic luster; The moisture, phosphate, halogen and oil stains on the surface of the Inconel617 alloy base material are removed.

8. A corrosion-resistant complex alloy material with stable high-temperature structure, characterized in that: The corrosion-resistant complex alloy material with stable high-temperature structure is prepared by the preparation method according to any one of claims 1 to 7.

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