A short-process same-grade recycling method for waste nickel-based superalloy

Abstract

This invention provides a short-process, same-level recycling method for waste nickel-based superalloys. The method includes the steps of remelting the waste nickel-based superalloy with calcium to obtain alloy ingots, followed by heat treatment. By remelting the waste nickel-based superalloy with calcium and then subjecting it to heat treatment, this invention effectively removes oxide inclusions, significantly improving the plasticity of the remelted alloy. This achieves same-level utilization while maintaining a short-process recycling of waste nickel-based superalloys. In summary, this invention enables the recycling and reuse of valuable metals, saving resources and reducing pollution; shortens the recycling cycle of nickel-based superalloys and simplifies the process; and improves the performance of the remelted alloy, achieving plasticity equal to or higher than that of standard alloys, while maintaining a short-process approach.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, and in particular to a short-process, same-level recycling method for waste nickel-based superalloys. Background Technology

[0002] Nickel-based superalloys (Ni-based alloys for short) are a class of alloys that exhibit high strength and certain resistance to oxidation and corrosion at high temperatures of 650–1000℃. Because they contain large amounts of valuable metallic elements such as nickel and chromium, they still have significant utilization value after being scrapped from high-temperature service. Directly discarding them not only wastes resources but also pollutes the environment. Therefore, the recycling and reuse of waste nickel-based superalloys is of great importance.

[0003] Traditional methods for recycling nickel-based alloys mainly include pyrometallurgical, hydrometallurgical, and combined pyrometallurgical-hydrometallurgical processes. Pyrometallurgical processes primarily consist of stages such as washing, drying, roasting, smelting, and refining. Hydrometallurgical processes typically include steps such as leaching, chemical pre-removal, extraction, and elemental separation. Combined processes are used for alloys with complex compositions. However, these methods for recycling nickel-based superalloy waste are lengthy, complex, and difficult to reuse at the same level.

[0004] To simplify the recycling process, some researchers have used vacuum induction melting technology to recycle waste nickel-based superalloys through direct remelting. However, this method cannot remove oxide inclusions in the waste alloy, resulting in a decrease in the plasticity of the remelted alloy, making it unsuitable for reuse at the same level. Summary of the Invention

[0005] This invention provides a short-process, same-level recycling method for waste nickel-based superalloys, which solves the defects of existing technologies such as long recycling processes, complex processes, and inability to utilize at the same level, and realizes short-process recycling of waste nickel-based superalloys.

[0006] This invention provides a short-process same-level recycling method for waste nickel-based superalloys, which includes the steps of adding calcium to the waste nickel-based superalloy, remelting it to obtain alloy ingots, and then performing heat treatment.

[0007] To achieve same-level utilization based on short-process recycling, this invention employs remelting and heat treatment, adding calcium during the remelting process to reduce oxides. Comparison of the chemical composition, microstructure, and mechanical properties of standard alloys and directly remelted alloys reveals that adding calcium effectively removes oxide inclusions, significantly improving the plasticity of the remelted alloy, thus achieving same-level utilization based on short-process waste alloy recycling.

[0008] In some embodiments of the present invention, calcium is added in the form of metallic calcium with a purity of 99.5%, and the added mass of metallic calcium is 2-5 times the total oxygen content in the waste nickel-based superalloy.

[0009] In a specific embodiment, the total oxygen content in the waste nickel-based superalloy can be obtained by detecting its chemical composition.

[0010] In some embodiments of the present invention, the step of calcium addition and remelting includes:

[0011] Vacuuming reduces the vacuum level to 10. -2 Pa; heat until the waste nickel-based superalloy is completely melted; cool down to 1450-1480℃, add metallic calcium to reduce the oxide; heat up to above 1482℃, let stand, so that the calcium oxide floats to the surface of the molten metal, and remove the residual calcium at the same time; cool, and cast into ingots.

[0012] In the above steps, cooling down first is to prevent calcium from volatilizing during the addition of metallic calcium, which would affect its effect on removing oxide inclusions. Heating up after oxide reduction is to allow excess calcium to volatilize.

[0013] Furthermore, electromagnetic stirring is continuously used during the oxide reduction process for 30-60 minutes.

[0014] In some embodiments of the present invention, the heat treatment steps include forging and solution treatment.

[0015] In some embodiments of the present invention, the forging includes forging at 1000-1200°C at a forging ratio of 2:1-3:1.

[0016] In some embodiments of the present invention, the solution treatment includes holding at 1100-1200°C for 30-60 minutes followed by immediate water quenching.

[0017] In some embodiments of the present invention, before the calcium-added remelting, the waste nickel-based superalloy is pretreated to remove oxide scale and oil stains from its surface. Specifically, commonly used removal methods in the art, such as turning, can be used for removal.

[0018] The waste nickel-based superalloys described in this invention include waste nickel-based 690 alloy, waste nickel-based 600 alloy, waste nickel-based 617 alloy, waste nickel-based 625 alloy, waste nickel-based 718 alloy, and other waste nickel-based superalloys.

[0019] In some embodiments of the present invention, the waste nickel-based superalloy is waste nickel-based 690 alloy. Nickel-based 690 alloy uses nickel (Ni) and chromium (Cr) as the main alloying elements, and this alloy has excellent oxidation resistance, corrosion resistance, and high-temperature strength. The short-process same-level recycling method for the waste nickel-based superalloy includes the following steps:

[0020] (a) Pretreatment of waste nickel-based superalloys: The oxide scale and oil stains on the surface of the waste nickel-based superalloys are removed by turning.

[0021] (b) The pretreated waste nickel-based superalloy is placed in a crucible and remelted using vacuum induction melting technology. The specific steps are as follows: ① Vacuum is drawn, and the vacuum level is reduced to 10. -2 Pa; ② Heating, the heating temperature is controlled at 100℃-150℃ higher than that of nickel-based 690 alloy, that is, 1477℃-1527℃ to ensure that the waste alloy is completely melted; ③ Adding metallic calcium, cooling to 1450℃, adding metallic calcium to reduce oxides, using electromagnetic stirring during the reduction process to make the reduction reaction more complete, the time is 30min; ④ Standing, heating to 1500℃, standing for 15min, so that calcium oxide floats to the surface of the molten metal, and at the same time removing residual calcium; ⑤ Cooling, the molten liquid in the crucible is slowly poured into the mold to form ingots.

[0022] (c) Heat treatment of the alloy ingot obtained by remelting, the specific steps are as follows: ① Forging treatment, forging at 1200℃ at a forging ratio of 2:1; ② Solution treatment, then holding at 1100℃ for 30 minutes and then water quenching immediately.

[0023] The present invention also provides a reusable nickel-based superalloy, which is obtained by the above-mentioned short-process same-level recycling method for waste nickel-based superalloys. The reusable nickel-based superalloy has better strength and plasticity than the standard alloy at room temperature and 650°C.

[0024] This invention provides a short-process, same-stage recycling method for waste nickel-based superalloys. By adding calcium and remelting the waste nickel-based superalloy followed by heat treatment, oxide inclusions can be effectively removed, significantly improving the plasticity of the remelted alloy. This achieves same-stage utilization while maintaining a short-process recycling of waste nickel-based superalloys. In summary, this invention enables the recycling and reuse of valuable metals, saving resources and reducing pollution; shortens the recycling cycle of nickel-based superalloys and simplifies the process; and improves the performance of remelted alloys based on a short process, achieving plasticity equal to or higher than that of standard alloys. Attached Figure Description

[0025] Figure 1 These are the microstructures of different types of 690 alloys (a: standard alloy; b: direct remelted alloy; c: carbon-added remelted alloy; d: calcium-added remelted alloy);

[0026] Figure 2 The room temperature tensile fracture morphologies of different types of 690 alloys are shown (a: standard alloy; b: direct remelted alloy; c: carbon-added remelted alloy; d: calcium-added remelted alloy).

[0027] Figure 3 The fracture morphology of different types of 690 alloys at 650℃ is shown in the tensile test (a: standard alloy; b: direct remelting alloy; c: carbon-added remelting alloy; d: calcium-added remelting alloy). Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0030] Example 1

[0031] This embodiment provides a short-process, same-level recycling method for waste nickel-based 690 alloy (simulating the preparation of waste nickel-based 690 alloy by placing a standard alloy of nickel-based 690 alloy in a muffle furnace and serving it at 850°C for 360 hours in an air atmosphere). The specific steps are as follows:

[0032] (1) Machine off 1 mm from the surface of the waste alloy to remove the oxide scale and oil stains;

[0033] (2) 6800g of waste alloy was selected, and fragments were randomly taken from 6 different locations of the waste alloy to test the oxygen content. The average value was 223ppm.

[0034] (3) Load the waste alloy into the vacuum induction melting furnace and evacuate it to 10°C. -2 Pa, heating to 1500℃ to completely melt the waste alloy;

[0035] (4) Cool down to 1450℃, add 5.04g of metallic calcium (purity 99.5%), and stir electromagnetically for 30min;

[0036] (5) Heat to 1500℃ and let stand for 15 minutes;

[0037] (6) Pour the ingot slowly and evenly, and cut off the riser;

[0038] (7) Forge the ingot at 1200℃ at a forging ratio of 2:1;

[0039] (8) After holding at 1100℃ for 30 minutes, the calcium-added remelted alloy was immediately water-quenched.

[0040] Example 2

[0041] This embodiment provides a short-process, same-level recycling method for waste nickel-based 617 alloy, the specific steps of which are as follows:

[0042] (1) Machining 1mm off the surface of 6000g of waste 617 alloy to remove surface oxide scale and oil stains;

[0043] (2) The oxygen content was tested by randomly taking debris from 6 different locations in the waste alloy. The average value was 205 ppm.

[0044] (3) Load the waste 617 alloy into a vacuum induction melting furnace and evacuate it to 10°C. -2 Pa, heating to 1500℃ to completely melt the waste alloy;

[0045] (4) Cool down to 1450℃, add 5g of metallic calcium (purity 99.5%), and stir electromagnetically for 30min;

[0046] (5) Heat to 1500℃ and let stand for 15 minutes;

[0047] (6) Pour the ingot slowly and evenly, and cut off the riser;

[0048] (7) Forge the ingot at 1200℃ at a forging ratio of 2:1;

[0049] (8) After holding at 1150℃ for 30 minutes, the calcium-added remelted 617 alloy was immediately water-quenched.

[0050] Comparative Example 1

[0051] This comparative example provides a method for direct remelting of waste nickel-based 690 alloy, the specific steps of which are as follows:

[0052] (1) Machining 1cm off the surface of 6000g of waste alloy to remove surface oxide scale and oil stains;

[0053] (2) Load the waste alloy into the vacuum induction melting furnace and evacuate it to 10°C. -2 Pa, heating to 1500℃ to completely melt the waste alloy;

[0054] (3) Stir electromagnetically for 30 minutes;

[0055] (4) Pour the casting into an ingot at a uniform and slow speed, and cut off the riser;

[0056] (5) Forge the ingot at 1200℃ at a forging ratio of 2:1;

[0057] (6) After holding at 1100℃ for 30 minutes, the alloy was immediately water-quenched to obtain a direct remelted alloy.

[0058] Comparative Example 2

[0059] This comparative example provides a method for recycling waste nickel-based 690 alloy, and the specific steps are as follows:

[0060] (1) Remove oil stains from the surface of the waste alloy;

[0061] (2) 6600g of waste alloy was selected, and fragments were randomly taken from 6 different locations of the waste alloy to test the oxygen content. The average value was 130ppm.

[0062] (3) Load the waste alloy into the vacuum induction melting furnace and evacuate it to 10°C. -2 Pa, heating to 1500℃ to completely melt the waste alloy;

[0063] (4) Add 2.2g of carbon block (purity 99.9%) and stir electromagnetically for 30min;

[0064] (5) Pour the casting into an ingot at a uniform and slow speed, and cut off the riser;

[0065] (6) Forge the ingot at 1200℃ at a forging ratio of 2:1;

[0066] (7) After holding at 1100℃ for 30 minutes, the carbon-added remelted alloy was immediately water-quenched.

[0067] Performance testing

[0068] The calcium-added remelted alloy prepared in Example 1, after chemical composition analysis, showed that its main constituent elements were basically consistent with those of the standard alloy, but the oxygen content was lower than that of the standard alloy and the direct remelted alloy. The aluminum content was also lower than that of the standard alloy, the direct remelted alloy, and the carbon-added remelted alloy. Mechanical property testing showed that, while maintaining a strength no lower than that of the standard alloy, the calcium-added remelted alloy exhibited higher room-temperature and high-temperature plasticity. A comparison of the chemical composition and mechanical properties of the calcium-added remelted alloy with the standard alloy, the direct remelted alloy, and the carbon-added remelted alloy is shown in Tables 1 and 2.

[0069] The standard alloy is made from high-purity nickel, chromium, iron, and carbon blocks (purity higher than 99%), melted in a vacuum induction melting furnace at 1500℃, and then forged and solution treated. The forging temperature is 1100℃, the forging ratio is 2:1, the solution treatment temperature is 1100℃, and the holding time is 30 minutes.

[0070] Table 1. Chemical composition (wt.%) of different 690 alloys

[0071] type Ni Cr Fe Al C O Standard alloy Bal. 29.94 8.98 0.014 0.0150 0.0130 direct remelted alloy Bal. 29.65 7.64 0.032 0.0135 0.0225 Carbide remelted alloy Bal. 28.82 7.15 0.053 0.0430 0.0088 Calcium-added remelted alloy Bal. 29.82 8.80 <0.001 0.0130 0.0120

[0072] Table 2 Mechanical properties of different 690 alloys

[0073]

[0074] Figure 1 These are the microstructures of different types of 690 alloy; Figure 2 These are the room temperature tensile fracture morphologies of different types of 690 alloy; Figure 3 These are the tensile fracture morphologies of different types of 690 alloy at 650℃.

[0075] like Figure 1 As shown in (a), the foreign inclusion phase alumina is introduced during the preparation of the standard alloy. Figure 1 As shown in (d), the calcium-added remelted alloy matrix is ​​clean and free of inclusions. Figure 1 As shown in (b), the direct remelted alloy matrix contains large-sized chromium oxide particles. Figure 1 As shown in (c), although the carbide-added remelted alloy does not contain chromium oxide inclusions, it does contain alumina inclusions and carbide precipitates. The results indicate that the calcium-added remelting method can effectively remove chromium oxide and alumina inclusions from waste alloys.

[0076] Depend on Figure 2 The results show that the fracture microstructure of the calcium-added remelted alloy is similar to that of the standard alloy and the carbide-added remelted alloy, mainly consisting of dimples, but some differences exist. The standard alloy has larger dimples, the carbide-added remelted alloy has smaller dimples but contains pores, while the calcium-added remelted alloy has small dimples and no pores. The fracture microstructure of the direct remelted alloy mainly consists of cleavage steps and shallow dimples. This indicates that the calcium-added remelted alloy exhibits the best plasticity at room temperature.

[0077] Depend on Figure 3 The results show that the microstructures of the high-temperature fracture surfaces of the four 690 alloys differ significantly. The standard alloy has very few dimples and exhibits tearing characteristics. The direct remelted alloy has no dimples and contains a large amount of debris. The carbide-added remelted alloy has very few dimples, mainly consisting of cleavage planes. Although the calcium-added remelted alloy has cleavage planes, it has more and smaller dimples. This indicates that the calcium-added remelted alloy exhibits the best plasticity at 650℃.

[0078] Through the same testing and verification, the calcium-added remelted 617 alloy of Example 2 also showed better performance than the directly remelted 617 alloy.

[0079] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0080] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "specific implementation," or "some specific implementations," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for short process, same grade recycling of spent nickel-based superalloy, characterized in that, This includes the steps of remelting waste nickel-based superalloys with calcium to obtain alloy ingots, followed by heat treatment; The calcium-addition and remelting step includes: Vacuuming reduces the vacuum level to 10. -2 Pa; Heat until the waste nickel-based superalloy is completely melted; Cool down to 1450-1480℃, add metallic calcium to reduce the oxide; Heat up to above 1500℃, let stand, so that the calcium oxide floats to the surface of the molten metal, and remove the residual calcium at the same time; Cool, and cast into ingots. Electromagnetic stirring is continuously used during the oxide reduction process for 30-60 minutes.

2. The spent nickel-base superalloy short process peer-to-peer recycling method of claim 1, wherein, Calcium is added in the form of metallic calcium with a purity of 99.5%, and the mass of the added metallic calcium is 2-5 times the total oxygen content in the waste nickel-based superalloy.

3. The short process scrap nickel-base superalloy sibling recycling method according to claim 1 or 2, characterized in that, The heat treatment steps include forging and solution treatment.

4. The short process scrap nickel-base superalloy sibling recycling method according to claim 3, characterized in that, The forging process includes forging at 1000-1200℃ with a forging ratio of 2:1-3:

1.

5. The short process scrap nickel-base superalloy sibling recycling method according to claim 3, wherein, The solution treatment includes holding at 1100-1200℃ for 30-60 minutes followed by immediate water quenching.

6. The short-process, same-stage recycling method for waste nickel-based superalloys according to claim 1 or 2, characterized in that, Before the calcium-added remelting, the waste nickel-based superalloy is pretreated to remove the oxide scale and oil stains from its surface.

7. The short-process, same-stage recycling method for waste nickel-based superalloys according to claim 6, characterized in that, The scrap nickel-based superalloys are scrap nickel-based 690 alloy, scrap nickel-based 600 alloy, scrap nickel-based 617 alloy, scrap nickel-based 625 alloy, or scrap nickel-based 718 alloy.

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