A heat treatment process for nickel-based high-temperature alloy and its application

Abstract

A heat treatment process for a nickel-based superalloy and its application, belonging to the technical field of heat treatment of heat-resistant alloys, overcomes the defect that the tensile properties and creep properties cannot be improved simultaneously in the prior art. The heat treatment process for the nickel-based superalloy of the present invention comprises the following steps: (1) heating the as-rolled nickel-based superalloy in a furnace at a heating rate not higher than 20 °C / min to a temperature 180 - 250 °C below the liquidus temperature of the alloy, holding for 0.5 - 3 h, and after the holding is completed, air-cooling to room temperature; (2) heating the nickel-based superalloy treated in step (1) in a furnace at a heating rate not higher than 20 °C / min to a temperature 120 - 150 °C below the temperature at which the grain boundary second phase M6C starts to precipitate, performing high-temperature aging treatment, and then air-cooling to room temperature; (3) heating the nickel-based superalloy treated in step (2) in a furnace at a heating rate not higher than 20 °C / min to a temperature 200 - 250 °C below the temperature at which the γ' phase starts to precipitate, performing low-temperature aging treatment, and then air-cooling to room temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment of heat-resistant alloys, and in particular relates to a heat treatment process for a nickel-based high-temperature alloy and an application thereof. Background Art

[0002] In my country's energy consumption structure, coal accounts for more than 70% of primary energy, and thermal power generation accounts for more than 75% of the country's total power generation. Based on the current situation of my country's energy structure and energy consumption, in order to alleviate the increasingly severe environmental pressure and achieve sustainable development of nature, economy and society, it is particularly important for my country to develop 700℃ ultra-supercritical coal-fired power generation technology. The development of high-parameter ultra-supercritical units is largely subject to the development of material technology in terms of design and parameter selection. The key high-temperature components of the boiler require not only heat-resistant alloys with high high-temperature strength, resistance to flue gas corrosion, and resistance to steam oxidation corrosion, but also good high-temperature plasticity. The key components of the boiler are subject to greater stress and higher temperatures. If the heat-resistant high-temperature alloy has higher high-temperature tensile strength and endurance strength, it can significantly improve the safety and economy of the operation of the thermal power unit. For the key components of the ultra-supercritical power station, the superheater / reheater, the traditional steel grades can no longer meet the requirements, and precipitation-strengthened nickel-based and iron-nickel-based alloys with stronger temperature bearing capacity must be used.

[0003] Nickel-based high-temperature alloys for 700℃ boilers are mainly precipitation-strengthened high-temperature alloys. The strength of these alloys is closely related to the microstructural characteristic parameters of the γ′ phase. When the γ′ phase particle size is small, the alloy has excellent tensile strength, low tensile plasticity, and poor endurance strength. When the particle size is large, the alloy has high endurance strength and high plasticity, which often leads to a decrease in the high-temperature tensile strength of the alloy. Summary of the invention

[0004] Therefore, in order to overcome the defect in the prior art that the tensile properties and the endurance properties cannot be improved simultaneously, the present invention provides a heat treatment process for a nickel-based high-temperature alloy and its application.

[0005] To this end, the present invention provides the following technical solutions.

[0006] A heat treatment process for a nickel-based high-temperature alloy comprises the following steps:

[0007] (1) heating the rolled nickel-based high-temperature alloy to 180-250°C below the alloy liquidus temperature at a heating rate of no more than 20°C / min, and then keeping the temperature for 0.5-3h, and cooling the alloy to room temperature after the temperature is kept constant;

[0008] (2) heating the nickel-based high-temperature alloy treated in step (1) at a heating rate of no more than 20° C. / min to a temperature 120-150° C. below the precipitation temperature of the second phase M6C carbide at the grain boundary, performing high-temperature aging treatment, and then cooling to room temperature;

[0009] (3) The nickel-based high-temperature alloy treated in step (2) is heated in a furnace at a heating rate of no more than 20°C / min to 200-250°C below the precipitation temperature of the γ′ phase, subjected to low-temperature aging treatment, and then cooled to room temperature.

[0010] Furthermore, the nickel-based high-temperature alloy includes, by mass percentage, C: 0.04-0.08%, Cr: 19-21%, Co: 9-11%, Mo: 8-9%, Ti: 1.9-2.3%, Al: 1.3-1.7%, Fe: ≤1.5%, Mn: ≤0.3%, Si: ≤0.15%, B: ≤0.005%, and the balance is Ni.

[0011] Furthermore, in step (1), the nickel-based high-temperature alloy is a nickel-based high-temperature alloy rod with a diameter of 140-160 mm.

[0012] Furthermore, in step (2), the high temperature aging treatment time is 1-3 hours.

[0013] Furthermore, in step (3), the low-temperature aging treatment time is 24-48 hours.

[0014] Furthermore, in step (1) and / or (2), cooling is performed by air cooling.

[0015] Furthermore, in step (3), cooling is performed by air cooling.

[0016] An alloy after the above heat treatment process.

[0017] Furthermore, the grain size of the alloy is 100-130 μm, the average size of γ′ phase particles is 45-55 nm, and the volume fraction of γ′ phase is 18-19.5%.

[0018] The above alloy is used in 700℃ grade boilers.

[0019] The technical solution of the present invention has the following advantages:

[0020] 1. The heat treatment process of the nickel-based high-temperature alloy provided by the present invention comprises the following steps: (1) heating the rolled nickel-based high-temperature alloy in a furnace to 180-250°C below the alloy liquidus temperature at a heating rate not higher than 20°C / min, keeping the temperature for 0.5-3h, and cooling to room temperature after the insulation is completed; (2) heating the nickel-based high-temperature alloy treated in step (1) in a furnace to 120-150°C below the starting precipitation temperature of the second phase M6C at the grain boundary at a heating rate not higher than 20°C / min, performing high-temperature aging treatment, and then cooling to room temperature; (3) heating the nickel-based high-temperature alloy treated in step (2) in a furnace to 200-250°C below the starting precipitation temperature of the γ′ phase at a heating rate not higher than 20°C / min, performing low-temperature aging treatment, and then cooling to room temperature.

[0021] The control of the solution treatment temperature in step (1) is to ensure the solubility of the matrix to the elements and activate the diffusion capacity of the elements. The control of the solution treatment time is to dissolve the precipitated phase precipitated in the grains during the hot working process into the matrix, so that the rolled structure undergoes recrystallization and grain growth, eliminates segregation, and simultaneously dissolves the second phases in the grains and grain boundaries into the matrix. The purpose of step (2) high temperature aging is to promote the sufficient precipitation of the precipitated phase at the grain boundaries, improve the strength of the phase interface, prevent the alloy from cracking along the grain boundaries, and ensure that the heat-resistant alloy has good tensile plasticity; the purpose of step (3) low temperature aging is to promote the sufficient precipitation and growth of the γ′ phase particles, the main strengthening phase of the alloy, to improve the strength of the alloy. The average size of the γ′ phase particles of the alloy obtained by the heat treatment process of the present invention is about 45-55nm, and the volume fraction of the precipitated phase is 18-19.5%, while improving the high temperature tensile strength, tensile plasticity, and endurance strength of the alloy.

[0022] The slow heating at a heating rate of no more than 20°C / min in the present invention is to reduce the thermal stress during the heating process, thereby inhibiting the precipitation of harmful phases at the grain boundaries, preventing grain boundary cracking, and thus improving the tensile plasticity of the alloy.

[0023] 2. In the heat treatment process provided by the present invention, in step (1), the nickel-based high-temperature alloy is a nickel-based high-temperature alloy rod with a diameter of 140-160 mm. The use of a larger nickel-based high-temperature alloy can promote the rapid growth of γ′ phase particles at the grain boundary and within the grain during heating and cooling, thereby improving the strength and plasticity of the alloy.

[0024] 3. The heat treatment process provided by the present invention adopts air cooling to reduce the thermal stress induced in the cooling process and thus inhibit the precipitation of harmful phases at the grain boundaries, and provide nucleation points for the precipitation of precipitated phases in the aging process, promote the precipitation and growth of γ′ phase particles, and ensure that the average size of the γ′ phase particles is between 45-55nm.

[0025] Through aging treatment, fine and continuous precipitation phases are precipitated in the alloy matrix and grain boundaries, which improves the strength of the alloy and makes the grain boundaries and the grains have good performance matching, ensuring that the alloy has good plasticity during deformation, and the tensile and endurance strengths are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 This is the macroscopic tissue structure after processing in step 1 of Example 1;

[0028] Figure 2 The grain boundary structure after the treatment in step 2 of Example 1;

[0029] Figure 3 The γ / γ′ microstructure in the alloy crystal after the treatment in step 3 of Example 1;

[0030] Figure 4 This is the grain boundary structure after the treatment in step 2 of comparative example 1;

[0031] Figure 5 This is the intracrystalline γ / γ′ microstructure after processing in step 3 of comparative example 1. DETAILED DESCRIPTION

[0032] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0033] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0034] A heat treatment process for a nickel-based high-temperature alloy of the present invention comprises the following steps:

[0035] 1) A rolled nickel-based high-temperature alloy rod with a diameter of 140-160 mm is obtained, wherein the deformed nickel-based high-temperature alloy comprises, by mass percentage, C: 0.04-0.08%, Cr: 19-21%, Co: 9-11%, Mo: 8-9%, Ti: 1.9-2.3%, Al: 1.3-1.7%, Fe: ≤1.5%, Mn: ≤0.3%, Si: ≤0.15%, B: ≤0.005%, and the balance is Ni.

[0036] 2) The alloy rod is heated in the furnace at a temperature not higher than 20°C / min to 180-250°C below the alloy liquidus temperature, kept at this temperature for 0.5-3h, subjected to solution treatment, and then air-cooled to room temperature to ensure that the grain size of the alloy is 100-130μm;

[0037] 3) The nickel-based high-temperature alloy treated in step 2) is heated in a furnace to 120-150° C. below the precipitation temperature of the second phase M6C at the grain boundary, subjected to high-temperature aging treatment, and then air-cooled to room temperature to ensure discontinuous precipitation of carbides at the grain boundary.

[0038] 4) The nickel-based high-temperature alloy treated in step 3) is heated in a furnace to 200-250° C. below the precipitation temperature of the main strengthening phase γ′ phase, subjected to low-temperature aging treatment, and then air-cooled to room temperature to ensure that the average size of the alloy γ′ phase particles is about 45-55 nm and the volume fraction of the γ′ phase is 18-19.5%.

[0039] Table 1 Composition of nickel-based high-temperature alloy rods in Examples 1-4 and Comparative Example 1, wt%

[0040] Ni Cr Co Mo Ti Al Fe Si Mn C B Bal. 20 10 8.5 2.1 1.5 1.2 0.04 0.06 0.06 0.004

[0041] The alloy liquidus temperature is 1346℃, the precipitation temperature of the second phase M6C at the grain boundary is 1151℃, and the precipitation temperature of the γ′ phase is 1005℃.

[0042] Example 1

[0043] This embodiment provides a heat treatment process for a nickel-based high-temperature alloy, comprising the following steps:

[0044] Step 1: Take a rolled nickel-based alloy high-temperature alloy rod with a composition of Table 1 and a diameter of 150 mm, heat it to 1140°C at a heating rate of 18°C / min, keep it warm for 2 hours, and then air cool it to room temperature to complete the solution treatment. The microstructure of the sample after solution treatment is as follows Figure 1 As shown, the average grain size is 120 μm.

[0045] Step 2: The nickel-based high-temperature alloy rod treated in step 1 is heated to 1010°C at a heating rate of 18°C / min, kept at this temperature for 2 hours, and then air-cooled to complete the high-temperature aging heat treatment. The obtained structure is as follows: Figure 2 As shown. Figure 2 It can be seen that the carbides at the grain boundaries of the nickel-based high-temperature alloy treated in step 2 are discontinuously distributed.

[0046] Step 3: The nickel-based high-temperature alloy rod treated in step 1 and step 2 is heated to 760°C in a furnace at a heating rate of 18°C / min, kept at this temperature for 24 hours, and then air-cooled to complete the low-temperature aging heat treatment. The γ / γ′ microstructure inside the alloy grains is as follows: Figure 3 The average size of the γ′ phase particles is 50 nm, and the volume fraction is 19.3%.

[0047] Example 2

[0048] This embodiment provides a heat treatment process for a nickel-based high-temperature alloy, comprising the following steps:

[0049] Step 1: Take a rolled nickel-based high-temperature alloy rod with a composition of Table 1 and a diameter of 150 mm, heat it to 1145°C at a heating rate of 20°C / min, keep it warm for 2 hours, and then air cool it to room temperature to complete the solution treatment. The average grain size of the alloy is 125μm.

[0050] Step 2: The alloy rod treated in step 1 is heated to 1015°C in a furnace at a heating rate of 20°C / min, kept at this temperature for 2 hours, and then air-cooled to complete the high temperature aging heat treatment.

[0051] Step 3: The alloy test bar treated in step 1 and step 2 was heated to 770°C at a heating rate of 20°C / min and kept at this temperature for 24 hours, and then air-cooled to complete the low-temperature aging heat treatment. The average size of the γ′ phase particles was 53nm, and the volume fraction was 19.0%.

[0052] Example 3

[0053] This embodiment provides a heat treatment process for a nickel-based high-temperature alloy, comprising the following steps:

[0054] Step 1: Take a rolled nickel-based high-temperature alloy rod with a composition of Table 1 and a diameter of 140 mm, heat it to 1145°C at a heating rate of 20°C / min, keep it warm for 2 hours, and then air cool it to room temperature to complete the solution treatment. The average size of the alloy grains is 125μm. Step 2: Heat the alloy rod treated in step 1 to 1020°C at a heating rate of 20°C / min, keep it warm for 2 hours, and then air cool it to complete the high-temperature aging heat treatment.

[0055] Step 3: The alloy test bar treated in step 1 and step 2 was heated to 780°C at a heating rate of 20°C / min and kept at this temperature for 36 hours, and then air-cooled to complete the low-temperature aging heat treatment. The average size of the γ′ phase particles was 55nm, and the volume fraction was 18.7%.

[0056] Example 4

[0057] This embodiment provides a heat treatment process for a nickel-based high-temperature alloy, comprising the following steps:

[0058] Step 1: Take a rolled nickel-based high-temperature alloy rod with a composition of Table 1 and a diameter of 140 mm, heat it to 1145°C at a heating rate of 20°C / min, keep it warm for 2 hours, and then air cool it to room temperature to complete the solution treatment. The average grain size of the alloy is 125±5μm.

[0059] Step 2: The alloy rod treated in step 1 is heated to 1018°C in a furnace at a heating rate of 20°C / min, kept at this temperature for 2 hours, and then air-cooled to complete the high temperature aging heat treatment.

[0060] Step 3: The alloy test bar treated in step 1 and step 2 was heated to 770°C at a heating rate of 20°C / min and kept at this temperature for 24 hours, and then air-cooled to complete the low-temperature aging heat treatment. The average size of the γ′ phase particles was 53nm, and the volume fraction was 19.0%.

[0061] Comparative Example 1

[0062] This comparative example provides a heat treatment process for a nickel-based high-temperature alloy, comprising the following steps:

[0063] Step 1: Take a rolled nickel-based alloy high-temperature alloy rod with a composition of Table 1 and a diameter of 150 mm, directly put it into a 1140℃ heat treatment furnace, keep it warm for 2 hours, and then water cool it to room temperature to complete the solution treatment. The microstructure of the sample after solution treatment is as follows Figure 4 The average grain size of the alloy is 120±5μm.

[0064] Step 2: Place the alloy rod treated in step 1 directly into a 1010℃ heat treatment furnace, keep it warm for 2h, and then water cool it to room temperature to complete the high temperature aging heat treatment, and obtain the structure at the grain boundary as shown in Figure 4 shown.

[0065] Step 3: Place the alloy test bar treated in steps 1 and 2 at 788℃ for 8 hours, then air cool it to complete the low-temperature aging heat treatment. Figure 5 The average size of the γ′ phase particles is 21 nm, and the volume fraction is 18.7%.

[0066] Test example

[0067] The tensile strength and tensile plasticity of the alloys treated in the examples and comparative examples at 760° C. are tested. The test results are shown in Table 2.

[0068] Table 2 Tensile plasticity and strength test results of alloy at 760℃

[0069] Tensile strength / MPa Yield strength / MPa Tensile elongation at fracture / % Example 1 880 660 34 Example 2 875 625 31 Comparative Example 1 821 598 21

[0070] The endurance life (i.e., the time until fracture) of the alloys treated in the examples and comparative examples was tested at 760°C / 386MPa. The test results are shown in Table 3.

[0071] Table 3 Stress resistance of alloy at 760℃ / 386MPa

[0072]

[0073]

[0074] By comparing Example 1 with Comparative Example 1, it can be seen that the microstructure of the heat-resistant alloy obtained by the process of the present invention has a high-temperature yield strength of 62MPa at 760°C, a tensile strength of 59MPa, and a high-temperature elongation of more than 61%; under the condition of 760°C / 386MPa, the alloy's endurance life is increased by more than 103%, ensuring that the alloy has excellent tensile plasticity while improving high-temperature strength.

[0075] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A heat treatment process for a nickel-based high-temperature alloy, characterized in that: The following steps are involved: (1) heating the rolled nickel-based high-temperature alloy to 180-250°C below the alloy liquidus temperature at a heating rate of no more than 20°C / min, and then keeping the temperature for 0.5-3h, and then cooling the alloy to room temperature after the temperature is kept at the end of the heating; (2) heating the nickel-based high-temperature alloy treated in step (1) at a heating rate of no more than 20° C. / min to a temperature 120-150° C. below the precipitation temperature of the second phase M6C carbide at the grain boundary, performing high-temperature aging treatment, and then cooling to room temperature; (3) heating the nickel-based high-temperature alloy treated in step (2) to 200-250° C. below the precipitation temperature of the γ′ phase at a heating rate of no more than 20° C. / min, performing low-temperature aging treatment, and then cooling to room temperature; The nickel-based high-temperature alloy comprises, by mass percentage: C: 0.04-0.08%, Cr: 19-21%, Co: 9-11%, Mo: 8-9%, Ti: 1.9-2.3%, Al: 1.3-1.7%, Fe: ≤1.5%, Mn: ≤0.3%, Si: ≤0.15%, B: ≤0.005%, the balance is Ni.

2. The heat treatment process according to claim 1, characterized in that: In step (1), the nickel-based high-temperature alloy is a nickel-based high-temperature alloy rod with a diameter of 140-160 mm.

3. The heat treatment process according to claim 1 or 2, characterized in that: In step (2), the high temperature aging treatment time is 1-3 hours.

4. The heat treatment process according to claim 1 or 2, characterized in that: In step (3), the low temperature aging treatment time is 24-48 hours.

5. The heat treatment process according to claim 1 or 2, characterized in that: In step (1) and / or (2), cooling is performed by air cooling.

6. The heat treatment process according to claim 1 or 2, characterized in that: In step (3), cooling is performed by air cooling.

7. An alloy after the heat treatment process according to claim 1 or 2.

8. The alloy according to claim 7, characterized in that The grain size of the alloy is 100-130 μm, the average size of γ′ phase particles is 45-55 nm, and the volume fraction of the γ′ phase is 18-19.5%.

9. Use of the alloy according to claim 7 or 8 in a 700°C class boiler.

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