C-HRA-2 nickel-based heat-resistant alloy, heat treatment method and application thereof

Abstract

The application discloses C-HRA-2 nickel-based heat-resistant alloy and a heat treatment method and application thereof, wherein the heat treatment method comprises the following steps: heating the forged C-HRA-2 nickel-based heat-resistant alloy to 1150-1170 DEG C for solid solution and heat preservation for 0.5-2h, and then water cooling to room temperature after the solid solution and heat preservation; determining the aging temperature and the heat preservation time according to the yield strength level and a formula; heating the C-HRA-2 nickel-based heat-resistant alloy to the determined aging temperature and heat preserving for the corresponding time, and then air cooling to room temperature after the heat preservation is finished. The application realizes accurate and rapid preparation of C-HRA-2 nickel-based heat-resistant alloys with different strength levels, the finished product is stable and reliable in performance, and is suitable for commercial application.

Description

TECHNICAL FIELD

[0001] The present application relates to heat treatment of heat-resistant alloy, in particular to a heat treatment method of C-HRA-2 nickel-based heat-resistant alloy, C-HRA-2 nickel-based heat-resistant alloy prepared by the heat treatment method, and application of the C-HRA-2 nickel-based heat-resistant alloy. BACKGROUND

[0002] At present, the development and construction of ultra-supercritical coal-fired power plants in China leads the world, and the 630℃ ultra-supercritical demonstration project has been started. The ultra-supercritical coal-fired power generating unit means that the high-temperature superheater outlet header, the high-temperature reheater outlet header, and the main steam and reheater hot section pipeline elements need to withstand higher temperature and pressure, so higher requirements are put forward for the element materials.

[0003] C-HRA-2 nickel-based heat-resistant alloy has application prospects in large thick-walled pipes such as boiler system main steam pipes and headers at 650-680℃. However, the rapid coarsening of the γ' phase of C-HRA-2 nickel-based heat-resistant alloy in long-time high-temperature environment makes its microstructure and performance stability insufficient, hindering the development of commercial application. On the other hand, the application of C-HRA-2 nickel-based heat-resistant alloy requires adjusting it to a specific strength level, and there is no such solution in the prior art.

[0004] In summary, it is of great significance to research and develop C-HRA-2 nickel-based heat-resistant alloy without γ' phase precipitation, so that it can be truly applied to commercial application. SUMMARY

[0005] The first object of the present application is to provide a heat treatment method of C-HRA-2 nickel-based heat-resistant alloy which can obtain different strength levels conveniently and quickly and ensure performance; the second object of the present application is to provide C-HRA-2 nickel-based heat-resistant alloy prepared by the heat treatment method; and the third object of the present application is to provide application of the C-HRA-2 nickel-based heat-resistant alloy.

[0006] Technical scheme: The heat treatment method of C-HRA-2 nickel-based heat-resistant alloy provided by the present application comprises:

[0007] (1) heating the forged C-HRA-2 nickel-based heat-resistant alloy to 1150-1170℃ for solid solution and holding for 0.5-2h, and then cooling to room temperature after solid solution and holding;

[0008] (2) determining the aging temperature and holding time according to the yield strength level of the C-HRA-2 nickel-based heat-resistant alloy and formulas (1) and (2);

[0009] σ s = 812 ± 5 - 0.504T (1)

[0010] t = 3.813 x 10 11 exp(-0.03062T) + 3.88 (2)

[0011] wherein σ s represents the peak yield strength / MPa, T represents the aging temperature / ℃, and t represents the aging time / h;

[0012] (3) heating the C-HRA-2 nickel-based heat-resistant alloy treated in step (1) to the aging temperature determined in step (2) and holding for a corresponding time, and cooling to room temperature after holding.

[0013] Although the C-HRA-2 nickel-based heat-resistant alloy does not have the precipitation strengthening of γ' phase, the strength of the C-HRA-2 alloy after solid solution treatment can be greatly improved after aging treatment at a certain temperature and time, because the needle / rod-shaped M 23 C6 can be precipitated in the grain, hindering the movement of dislocations and thus improving the yield strength.

[0014] Further, in step (1), the C-HRA-2 nickel-based heat-resistant alloy is a forged alloy bar.

[0015] Further, the C-HRA-2 nickel-based heat-resistant alloy comprises, in terms of mass percentage: C: 0.04-0.07%, Cr: 21-23%, Co: 11-13%, Mo: 8-9%, Nb: 0.02-0.04%, B: 0.004-0.006%, W: 0.1-0.3%, Zr: 0.01%-0.03%, Mn: ≤0.3%, Si: ≤0.15%, and the balance of Ni.

[0016] Further, in step (1), the grain size after solid solution holding is 2-3 levels.

[0017] Further, in step (1), water cooling is used for cooling. In step (1), water cooling is used for cooling, which aims to prevent the precipitation of the second phase precipitates before aging, so as to affect the precipitation strengthening effect of the intragranular long strip-shaped M23C6 during aging.

[0018] Further, in step (2), the peak yield strength σ s is 400-500 MPa, the aging temperature is 600-800℃, and the aging time is 20-5000h.

[0019] Further, in step (3), air cooling is used for cooling. In step (3), air cooling is used for cooling, which aims to reduce the generation of thermal stress during cooling and prevent the alloy from failing prematurely and reducing the service life.

[0020] A C-HRA-2 nickel-based heat-resistant alloy prepared by the heat treatment method.

[0021] Application of the C-HRA-2 nickel-based heat-resistant alloy to a large-thick-wall pipeline.

[0022] Further, the large-thick-wall pipeline includes a boiler system main steam pipeline and a header of a 650-680 DEG C grade.

[0023] Beneficial effects: Compared with the prior art, the present application has the following remarkable advantages:

[0024] In step (1), the solid solution treatment temperature and time are controlled to improve the diffusion ability and effect of elements, ensure that the second phase precipitates are basically dissolved into the matrix, and make the as-forged structure recrystallize and grain grow, reduce the defect density in the material, reduce the interface energy, homogenize the austenite, reduce the system energy and tend to be in a stable state. 23 Intrinsic yield strength increase behavior of the C-HRA-2 alloy in the aging process is due to intragranular and grain boundary precipitation strengthening of C6, especially whether long strip / rod-shaped M 23 C6 can be formed in the intragranular. The lower the aging temperature, the slower the speed of forming long strip-shaped M 23 C6, the higher the dislocation density after entanglement of M 23 C6, the higher the peak yield strength, and the longer the duration of the peak strength.

[0025] The present application realizes precise and rapid preparation of C-HRA-2 nickel-based heat-resistant alloys of different strength grades, and the finished product has stable and reliable performance and is suitable for commercial application. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a control relationship between the peak yield strength and the aging temperature in step (2);

[0027] Figure 2 is a control relationship between the aging temperature and the aging time required to reach the peak yield strength in step (2);

[0028] Figure 3 is a microstructure diagram after step (1) in Example 1;

[0029] Figure 4 is a microstructure diagram after step (3) in Example 1;

[0030] Figure 5 is an intragranular strip / rod-shaped M 23 C6 microstructure after step (3) in Example 1;

[0031] Figure 6 is the intracrystalline strip / rod-shaped M 23 C6 microstructure. DETAILED DESCRIPTION

[0032] The application will be further described below with reference to the accompanying drawings.

[0033] A heat treatment method of C-HRA-2 nickel-based heat-resistant alloy, specifically comprising the following steps:

[0034] (1) taking a forged C-HRA-2 alloy rod with a diameter of 15-30 mm, heating the alloy rod to 1150-1170℃ for solid solution and holding for 0.5-2h, and then water cooling to room temperature after the solid solution holding is completed, so as to ensure that the grain size of the alloy is 2-3 grade.

[0035] (2) determining the aging temperature and holding time according to the yield strength grade of the C-HRA-2 nickel-based heat-resistant alloy and formulas (1) and (2);

[0036] σ s = 812 ± 5 - 0.504T (1)

[0037] t = 3.813 × 10 11 · exp(-0.03062T) + 3.88 (2)

[0038] wherein σ s represents the peak yield strength / MPa, T represents the aging temperature / ℃, and t represents the aging time / h;

[0039] The parameter value range is: the peak yield strength σ s is 400-500MPa, the aging temperature is 600-800℃, and the aging time is 20-5000h;

[0040] Figure 1 The control relationship between the peak yield strength and the aging temperature is shown in FIG. 1, Figure 2 The control relationship between the aging temperature and the aging time required to reach the peak yield strength is shown in FIG. 2.

[0041] (3) heating the C-HRA-2 nickel-based heat-resistant alloy treated in step (1) to the aging temperature determined in step (2) and holding for the corresponding time, and then air cooling to room temperature after the holding is completed.

[0042] In the following Examples 1-3 and Comparative Examples 1-4, the components of the C-HRA-2 nickel-based heat-resistant alloy rod are as shown in Table 1 (in wt.%):

[0043] Table 1

[0044] C Mn Si Cr Co Mo B Nb W Zr Ni 0.06 0.004 0.05 22 12 8.6 0.005 0.03 0.2 0.02 Bal.

[0045] Example 1

[0046] (1) Take the composition of Table 1 and the diameter of 18 mm of C-HRA-2 nickel-based heat-resistant alloy in forged state to 1160℃ for 1h, and water-cooled to room temperature after holding, to complete the solid solution treatment. The microstructure of the sample after solid solution treatment is shown in Figure 3 , the average grain size is 180μm, and the grain size is 2 grade, at this time the room temperature tensile yield strength test result is 300-305MPa.

[0047] (2) Determine the aging temperature of C-HRA-2 alloy of 400MPa grade as 800℃, and the aging time as 20-30h.

[0048] (3) The C-HRA-2 nickel-based heat-resistant alloy rod after step (1) is heated to 800℃ in the furnace, and held for 30h, and after completion, it is taken out of the furnace and air-cooled to room temperature, and the obtained microstructure is shown in Figure 4 and Figure 5 .

[0049] It can be seen from Figure 4 and Figure 5 that after the treatment of step (3), the nickel-based alloy has a large amount of M 23 C6 carbide precipitated in the grain boundary and in the grain, and no γ' phase, and the M 23 C6 carbide in the grain is mostly short rod-shaped with a length of 100-200nm, which pins a certain number of dislocations. The average value of the room temperature tensile yield strength test result of the alloy after step (3) is 416MPa.

[0050] Comparative Example 1

[0051] (1) Take the composition of Table 1 and the diameter of 18 mm of C-HRA-2 nickel-based heat-resistant alloy in forged state to 1160℃ for 1h, and water-cooled to room temperature after holding, to complete the solid solution treatment. The microstructure of the sample after solid solution treatment is shown in Figure 3 , the average grain size is 180μm, and the grain size is 2 grade, at this time the room temperature tensile yield strength test result is 300-305MPa.

[0052] (2) Determine the aging temperature of C-HRA-2 alloy of 400MPa grade as 800℃, and the aging time as 20-30h.

[0053] (3) The C-HRA-2 nickel-based heat-resistant alloy rod after step (1) is heated to 800℃ in the furnace, and held for 500h, and after completion, it is taken out of the furnace and air-cooled to room temperature.

[0054] The average value of the room temperature tensile yield strength test result of the alloy after step (3) is 415MPa, which proves that the aging time in Example 1 has reached the peak strength.

[0055] Example 2

[0056] (1) A forged C-HRA-2 nickel-based heat-resistant alloy with the composition shown in Table 1 and a diameter of 18 mm was heated to 1160℃ and held for 1 hour. After holding, it was water-cooled to room temperature to complete the solution treatment. The microstructure of the sample after solution treatment is as follows: Figure 3 As shown, the average grain size is 180 μm, the grain size is grade 2, and the room temperature tensile yield strength test result is 300-305 MPa.

[0057] (2) The aging temperature of the 500MPa grade C-HRA-2 alloy is determined to be 600℃ and the aging time is 4000-5000h.

[0058] (3) The C-HRA-2 nickel-based heat-resistant alloy rod treated in step (1) is heated to 600℃ in the furnace and held for 5000h. After completion, it is removed from the furnace and air-cooled to room temperature. The resulting microstructure is as follows. Figure 6 As shown.

[0059] from Figure 6 It can be seen that the M in the nickel-based alloy crystals after step (3) treatment 23 C6 carbides are mostly elongated strips with a length of 200-500 nm, pinning a large number of dislocations. The average room temperature tensile yield strength of the alloy after step (3) was 521 MPa.

[0060] Comparative Example 2

[0061] (1) A forged C-HRA-2 nickel-based heat-resistant alloy with the composition shown in Table 1 and a diameter of 18 mm was heated to 1160℃ and held for 1 hour. After holding, it was water-cooled to room temperature to complete the solution treatment. The microstructure of the sample after solution treatment is as follows: Figure 3 As shown, the average grain size is 180 μm, the grain size is grade 2, and the room temperature tensile yield strength test result is 300-305 MPa.

[0062] (2) The aging temperature of the 500MPa grade C-HRA-2 alloy is determined to be 600℃ and the aging time is 4000-5000h.

[0063] (3) The C-HRA-2 nickel-based heat-resistant alloy rod treated in step (1) was heated to 600°C in the furnace and held for 3000 hours. After completion, it was removed from the furnace and air-cooled to room temperature. The average value of the room temperature tensile yield strength test of the alloy treated in step (3) was 365 MPa, which proved that the aging time in Comparative Example 2 had not yet reached the peak strength, while the aging time in Example 2 had reached the peak strength.

[0064] Example 3

[0065] (1) Take the composition of Table 1 and the diameter of 18 mm of C-HRA-2 nickel-based heat-resistant alloy in the forged state to 1160℃ for 1h, and water-cooled to room temperature after holding, complete the solid solution treatment. The microstructure of the sample after solid solution treatment is shown in Figure 3 , the average grain size is 180μm, and the grain size is 2 grade, at this time the room temperature tensile yield strength test result is 300-305MPa.

[0066] (2) Determine the aging temperature of C-HRA-2 alloy of 470MPa grade as 675℃, and the aging time as 400-500h.

[0067] (3) The C-HRA-2 nickel-based heat-resistant alloy rod after step (1) is heated to 675℃ in the furnace, and held for 500h, and after completion, it is taken out of the furnace and air-cooled to room temperature. The average value of the room temperature tensile yield strength test result of the alloy after step (3) is 478MPa.

[0068] Comparative Example 3

[0069] (1) Take the composition of Table 1 and the diameter of 18 mm of C-HRA-2 nickel-based heat-resistant alloy in the forged state to 1160℃ for 1h, and water-cooled to room temperature after holding, complete the solid solution treatment. The microstructure of the sample after solid solution treatment is shown in Figure 3 , the average grain size is 180μm, and the grain size is 2 grade, at this time the room temperature tensile yield strength test result is 300-305MPa.

[0070] (2) Determine the aging temperature of C-HRA-2 alloy of 470MPa grade as 675℃, and the aging time as 400-500h.

[0071] (3) The C-HRA-2 nickel-based heat-resistant alloy rod after step (1) is heated to 675℃ in the furnace, and held for 100h, and after completion, it is taken out of the furnace and air-cooled to room temperature. The average value of the room temperature tensile yield strength test result of the alloy after step (3) is 331MPa, which proves that the aging time in the comparative example 3 has not reached the peak strength, while the aging time in the example 3 has reached the peak strength.

[0072] Comparative Example 4

[0073] (1) Take the composition of Table 1 and the diameter of 18 mm of C-HRA-2 nickel-based heat-resistant alloy in the forged state to 1160℃ for 1h, and water-cooled to room temperature after holding, complete the solid solution treatment. The microstructure of the sample after solid solution treatment is shown in Figure 3 , the average grain size is 180μm, and the grain size is 2 grade, at this time the room temperature tensile yield strength test result is 300-305MPa.

[0074] (2) The aging temperature required for the C-HRA-2 alloy of 470 MPa grade was determined to be 675 °C, and the aging time was 400-500 h.

[0075] (3) The C-HRA-2 nickel-based heat-resistant alloy rod after step (1) was heated to 675 °C in the furnace, and the heat preservation time was 1000 h. After completion, it was taken out of the furnace and air-cooled to room temperature. The average value of the room temperature tensile yield strength test result of the alloy after step (3) was 480 MPa, which was basically consistent with the yield strength result in Example 3, proving that the aging time in Example 3 had reached the peak strength.

Claims

1. A heat treatment method of a C-HRA-2 nickel-based heat-resistant alloy, characterized by, The C-HRA-2 nickel-based heat-resistant alloy comprises, in mass percentage, C: 0.04-0.07%, Cr: 21-23%, Co: 11-13%, Mo: 8-9%, Nb: 0.02-0.04%, B: 0.004-0.006%, W: 0.1-0.3%, Zr: 0.01-0.03%, Mn: ≤0.3%, Si: ≤0.15%, and the balance of Ni; and the heat treatment method comprises: (1) heating the forged C-HRA-2 nickel-based heat-resistant alloy to 1150-1170°C for solution treatment for 0.5-2h, and then cooling to room temperature; (2) determining the aging temperature and the holding time according to the yield strength grade of the C-HRA-2 nickel-based heat-resistant alloy and formulas (1) and (2); （1） （2） wherein, represents peak yield strength / MPa, represents aging temperature / °C, represents aging time / h; (3) heating the C-HRA-2 nickel-based heat-resistant alloy treated in step (1) to the aging temperature determined in step (2) and holding for the corresponding time, and then cooling to room temperature.

2. The heat treatment method according to claim 1, characterized by, In step (1), the C-HRA-2 nickel-based heat-resistant alloy is in a forged state.

3. The heat treatment method according to claim 1, characterized by, In step (1), the grain size after solution treatment is 2-3.

4. The heat treatment method according to claim 1, characterized by, In step (1), the cooling is performed by water cooling.

5. The heat treatment method according to claim 1, characterized by, In step (2), the peak yield strength is 400-500 MPa, the aging temperature is 600-800 °C, and the aging time is 20-5000 h.

6. The heat treatment method according to claim 1, characterized by, In step (3), the cooling is performed by air cooling.

7. A C-HRA-2 nickel-based heat-resistant alloy prepared by the heat treatment method of any one of claims 1 to 6.

8. Use of the C-HRA-2 nickel-based heat-resistant alloy of claim 7 in a large thick-walled pipe.

9. Use according to claim 8, characterized in that, The large thick-walled pipe comprises a boiler system main steam pipe and a header at a temperature of 650-680°C.

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