Nickel-based wrought superalloy and preparation method thereof

Abstract

The invention belongs to the field of high-temperature alloys, and particularly relates to a nickel-based wrought high-temperature alloy and a preparation method thereof. On the premise that chemical components of the nickel-based wrought superalloy are not changed, the dilemma of medium-temperature brittleness of the nickel-based wrought superalloy is relieved, and the adverse effect on the alloy performance caused by regulation and control of the content of microelements is avoided. The preparation method of a triple smelting process, hot working deformation, short-time annealing treatment and solid solution aging treatment is adopted; according to the nickel-based wrought superalloy, the grain size double-peak structure is constructed, meanwhile, a solid solution double aging treatment mode is adopted for promoting gamma'phase precipitation, the precipitation strengthening effect is improved, the tensile elongation of the prepared nickel-based wrought superalloy within the temperature range of 600-800 DEG C is larger than or equal to 15%, and further preferably, the tensile elongation can be larger than or equal to 20%; the yield strength of the alloy at 700 DEG C is not less than 1050 MPa, and the tensile strength is not less than 1500 MPa; and at 750 DEG C, the yield strength is not less than 1000 MPa, and the tensile strength is not less than 1400 MPa.

Description

Technical Field

[0001] The present invention belongs to the field of superalloys, and particularly relates to a nickel-based wrought superalloy and a preparation method thereof. Background Art

[0002] Nickel-based wrought superalloys face the problem of "mid-temperature brittleness" during service. "Mid-temperature brittleness" refers to the phenomenon that the plasticity of alloy materials drops significantly when deformed in the mid-temperature range. For nickel-based wrought alloys, the "mid-temperature brittleness" range is 650 - 850 °C, which highly coincides with their service temperature range. Therefore, solving the "mid-temperature brittleness" dilemma is the key path to improving the service stability of key components prepared from nickel-based wrought superalloys and even extending their service life.

[0003] Existing solutions to "mid-temperature brittleness" mainly focus on improving the grain boundary bonding force of nickel-based wrought superalloys, alleviating the mid-temperature brittleness of the alloy by strengthening the grain boundaries. The mainstream approach is to strengthen the grain boundaries by adding various grain boundary strengthening elements, and the most common grain boundary strengthening elements are C element and B element. For example, CN115449670B discloses a high-strength nickel-based wrought superalloy without mid-temperature brittleness, including: Cr, Fe, Co, W, Ti, Al, B, Zr, C, and the balance is Ni. Solid solution strengthening is formed by elements such as Cr and W, and the intragranular is strengthened by γ′(Ni3(Ti, Al)) precipitation phase. At the same time, fine and discontinuous M 23 C6-type carbides strengthen the grain boundaries, and elements such as C, B, and Zr are further regulated to ensure the strength of the grain boundaries.

[0004] However, the addition of grain boundary strengthening elements will not only affect the grain boundary strength but also have a comprehensive impact on the microstructure and organization such as precipitation phases. For example, when the content of C element increases, it will promote the precipitation of coarse MC-type carbides, damaging the alloy strength; when the content of B element increases, it will promote the continuous precipitation of grain boundary borides, which is not conducive to the stability of alloy properties. Summary of the Invention

[0005] The present invention provides a nickel-based wrought superalloy with improved mid-temperature brittleness and a preparation method thereof. The main purpose is to alleviate its "mid-temperature brittleness" dilemma and make it have good mid-temperature strength and plasticity matching performance on the premise of not changing the chemical composition of the nickel-based wrought superalloy. This is specifically achieved through the following technical solutions.

[0006] The present application provides a nickel-based wrought superalloy, which includes a bimodal grain structure, wherein the coarse grain size is ASTM 4 - 6 grade, and the fine grain size is ASTM 8 - 9 grade;

[0007] By mass percentage, the elemental composition of the above nickel-based wrought superalloy includes: Cr 9.0 - 11.0 wt.%, Al + Ti 6.0 - 8.0 wt.%, and the balance is Ni.

[0008] Further, it is characterized in that, by mass percentage, the elemental composition includes: C 0.03 - 0.08 wt%, Cr 9.0 - 11.0 wt%, Al + Ti 6.0 - 8.0 wt%, Nb 2.0 - 3.5 wt%, W 2.5 - 3.5 wt%, Co

[0009] 13.0 - 14.5 wt%, V 0.5 - 0.8 wt%, Mo 3.0 - 4.5 wt%, and the balance is Ni.

[0010] Further, it is characterized in that, by mass percentage, the elemental composition includes: C 0.04 - 0.06 wt%, Cr 10.0 - 11.0 wt%, Al + Ti 6.0 - 8.0 wt%, Nb 3.0 - 3.5 wt%, W 2.5 - 3.0 wt%, Co

[0011] 13.0 - 14.0 wt%, V 0.5 - 0.7 wt%, Mo 3.0 - 4.0 wt%, and the balance is Ni.

[0012] The present invention provides a method for preparing a nickel-based wrought superalloy with improved intermediate-temperature brittleness, comprising the following steps:

[0013] Step 1) Prepare raw materials and smelt and prepare an alloy ingot;

[0014] Step 2) Perform hot working deformation on the ingot;

[0015] Step 3) Perform short-time annealing heat treatment on the alloy after hot working deformation;

[0016] Step 4) Perform solution aging treatment on the alloy after short-time annealing heat treatment.

[0017] Further, the preparation of the alloy ingot adopts a triple melting process of vacuum induction melting, protective atmosphere electroslag remelting, and vacuum consumable melting;

[0018] Further, the temperature of hot working deformation is 1100 - 1190 °C;

[0019] Further, the annealing temperature of the short-time annealing treatment is 950 - 1050 °C, and the annealing time is 0.5 - 1.0 h;

[0020] Further, the annealing temperature and time are adjusted according to the deformation amount of hot working deformation: for every 0.5% increase in the deformation amount, the annealing time is shortened by 10 min, and the total annealing time is not less than 0.5 h;

[0021] Furthermore, the microstructure of the alloy after short-time annealing heat treatment contains a bimodal grain structure, that is, it contains two grain sizes of fine grains and coarse grains. Among them, the coarse grain size meets ASTM 4-6 levels, and the coarse grain diameter range is 44-88 μm. The fine grain size meets ASTM 8-9 levels, and the fine grain diameter range is 16-22 μm.

[0022] Furthermore, the solution aging treatment includes the following steps:

[0023] Conduct solution treatment on the alloy: heat the alloy to the solution temperature and hold it, and then rapidly cool it. The rapid cooling method is selected from one of water quenching or oil quenching;

[0024] Conduct double aging treatment on the alloy after the above solution treatment: heat the alloy to the primary aging temperature, hold it, and then cool it; heat the alloy after the primary aging treatment to the secondary aging temperature, hold it, and then cool it.

[0025] Furthermore, in the solution treatment, the solution temperature is 1100-1160 °C, the holding time is 3-4 h, the rapid cooling rate ≥ 80 °C / min, and it is cooled to room temperature;

[0026] Furthermore, in the double aging treatment, the primary aging temperature is 830-880 °C, the holding time after heating to the primary aging temperature is 6-7 h, and it is cooled to room temperature; the secondary aging temperature is 730-780 °C, the holding time after heating to the secondary aging temperature is 16-18 h, and it is cooled to room temperature; the cooling method is air cooling.

[0027] Furthermore, a large amount of precipitated secondary γ' phase should be contained in the alloy after the above solution aging treatment, and its content is between 43-48 wt.%, and its size is between 100-200 nm.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The technical solution of this application alleviates the "mid-temperature brittleness" dilemma of nickel-based wrought superalloys without changing the chemical composition of nickel-based wrought superalloys, avoids the adverse effects on the alloy properties caused by adjusting the content of trace elements, and enables it to have good mid-temperature strength and plasticity matching performance. By using the preparation method of this application, the tensile elongation of nickel-based wrought superalloys in the range of 600-800 °C ≥ 15%, and the further preferably tensile elongation can reach ≥ 20%; the yield strength of the alloy at 700 °C ≥ 1050 MPa, and the tensile strength ≥ 1500 MPa; the yield strength at 750 °C ≥ 1000 MPa, and the tensile strength ≥ 1400 MPa. Description of the Drawings

[0030] Figure 1 Schematic diagram of bimodal grain structure with coexisting coarse and fine grains of nickel-based wrought superalloy prepared for this application;

[0031] Figure 2 Tensile curve of the nickel-based wrought superalloy prepared in Example 1 at 700 °C;

[0032] Figure 3 Tensile curve of the nickel-based wrought superalloy prepared in Example 2 at 750 °C;

[0033] Figure 4 Tensile curve of the nickel-based wrought superalloy prepared in Comparative Example 1 at 700 °C;

[0034] Figure 5 Tensile curve of the nickel-based wrought superalloy prepared in Comparative Example 2 at 750 °C. Detailed implementation manners

[0035] In this application, a bimodal grain size structure is constructed by heat treatment, and a solution + double aging treatment method is adopted to promote the precipitation of γ' phase. As Figure 1 shown, due to the existence of the bimodal grain size structure in the alloy, during deformation, the fine grain region provides strength and the coarse grain region provides plasticity, enabling the material to have good strength-plasticity matching at medium temperature, thereby alleviating the "medium temperature brittleness" dilemma; at the same time, the solution + double aging treatment of the deformed alloy is to dissolve the large primary γ' phase in the alloy after melting into the matrix (solution), and re-precipitate to form a large number of secondary γ' phases with smaller sizes (double aging). At the same time, the size of the secondary γ' phase should be between 100-200 nm to further improve the strength of the alloy and enhance the precipitation strengthening effect. While ensuring the strength of the alloy, the medium temperature brittleness problem is alleviated, enabling the alloy to have excellent mechanical properties.

[0036] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following combines the drawings and preferred embodiments to detail the specific implementation manners, structures, features and their effects of the application according to the present invention. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0037] The present invention provides a method for improving the "medium temperature brittleness" dilemma of nickel-based wrought superalloys without changing the alloy chemical composition. The main solutions are as follows:

[0038] First, a billet with relatively high purity is prepared through triple smelting. Subsequently, hot working deformation and short-time annealing heat treatment are carried out on the billet to prepare a bimodal structure in which coarse grains and fine grains coexist in the alloy. Then, solution double aging treatment is carried out on the alloy to promote the precipitation of nanoscale secondary γ' phase and improve the precipitation strengthening effect of the alloy. Compared with the prior art, this method does not change the chemical composition of the alloy. Only by means of deformation and heat treatment, a bimodal structure of grain size is designed, and by combining the characteristics of good plasticity in the coarse grain region and high strength in the fine grain region, the purpose of achieving a strong-plasticity matching of nickel-based deformed superalloy in the medium temperature region is realized.

[0039] It should be noted that the composition of the nickel-based alloy applicable to the method of the present invention is not limited to the regulations given in the present invention, but is applicable to a series of deformed superalloys, including but not limited to GH4151, GH4068, etc.

[0040] The following further illustrates the method of the present invention through specific examples:

[0041] Example 1

[0042] The preparation steps of the nickel-based deformed superalloy are as follows:

[0043] Prepare alloy raw materials with the composition of C 0.05wt%, Cr 10.5wt%, Al+Ti 7.5wt%, Nb 3.3wt%, W 2.8wt%, Co 13.4wt%, V 0.54wt%, Mo 3.6wt%, and the balance being Ni.

[0044] Step 1) Prepare an alloy ingot by using vacuum induction melting, electroslag remelting under protective atmosphere, and vacuum consumable melting.

[0045] Step 2) Carry out preliminary forging deformation on the material prepared in Step 1 at 1180°C, and then carry out final forging deformation at 1110°C.

[0046] Step 3) First carry out short-time annealing treatment on the material forged in Step 2, with the annealing temperature of 1000°C and the annealing time of 0.5h.

[0047] Step 4) Carry out solution treatment on the alloy obtained in the above steps at a temperature of 1160°C, with a holding time of 4h, and water quench to room temperature; then carry out double aging treatment: the first-stage aging temperature is 850°C, the holding time is 7h, air cool to room temperature, the second-stage aging temperature is 760°C, the holding time is 18h, and air cool to room temperature.

[0048] After preparation, carry out a high-temperature tensile test on the nickel-based deformed superalloy at 700°C, and the results are as Figure 2 shown. At 700°C, its yield strength is 1078MPa, the tensile strength is 1528MPa, and the elongation is 20.8%.

[0049] Example 2

[0050] The preparation steps of the nickel-based wrought superalloy are as follows:

[0051] Prepare alloy raw materials with the composition of C 0.06wt%, Cr 9.8wt%, Al+Ti 7.8wt%, Nb 2.8wt%, W 3.0wt%, Co 13.8wt%, V 0.7wt%, Mo 4.3wt%, and the balance being Ni.

[0052] Step 1) Prepare alloy ingots by using vacuum induction melting, electroslag remelting under protective atmosphere, and vacuum consumable melting.

[0053] Step 2) Perform preliminary forging deformation on the material prepared in Step 1 at 1150°C, and then perform final forging deformation at 1120°C.

[0054] Step 3) First perform short-time annealing treatment on the material forged in Step 2, with the annealing temperature of 960°C and the annealing time of 0.5h.

[0055] Step 4) Perform solution treatment on the alloy obtained in the above steps, with the temperature of 1120°C and the holding time of 3h. Quench in oil to room temperature; then perform double aging treatment: the first-stage aging temperature is 830°C, the holding time is 6h, cool to room temperature, the second-stage aging temperature is 730°C, the holding time is 16h, and cool to room temperature.

[0056] After preparation, perform high-temperature tensile test on the nickel-based wrought superalloy at 750°C, and the results are as Figure 3 shown. At 750°C, its yield strength is 1162MPa, the tensile strength is 1515MPa, and the elongation is 18%.

[0057] Comparative Example 1

[0058] The preparation steps of the nickel-based alloy are as follows:

[0059] Its composition is the same as that of Example 1.

[0060] Step 1) Prepare alloy ingots by using vacuum induction melting, electroslag remelting under protective atmosphere, and vacuum consumable melting.

[0061] Step 2) Perform preliminary forging deformation on the material prepared in Step 1 at 1180°C, and then perform final forging deformation at 1110°C.

[0062] Step 3) Solution treatment is carried out on the alloy obtained in the above steps at a temperature of 1130 °C for 3 h, and then cooled to room temperature; then double aging treatment is carried out: the first-stage aging temperature is 850 °C for 6 h, cooled to room temperature, the second-stage aging temperature is 740 °C for 16 h, and cooled to room temperature.

[0063] After preparation, a high-temperature tensile test of the nickel-based wrought superalloy is carried out at 700 °C, and the results are as Figure 4 shown. At 700 °C, its yield strength is 1112 MPa, tensile strength is 1416 MPa, and elongation is 14.4%.

[0064] Comparative Example 2

[0065] The preparation steps of the nickel-based alloy are as follows:

[0066] Its composition is the same as that of Example 2.

[0067] Step 1) Alloy ingots are prepared by vacuum induction melting, electroslag remelting under protective atmosphere and vacuum consumable melting.

[0068] Step 2) The material prepared in Step 1 is subjected to preliminary forging deformation at 1150 °C, and then final forging deformation at 1120 °C.

[0069] Step 3) Solution treatment is carried out on the alloy obtained in the above steps at a temperature of 1120 °C for 3 h; then double aging treatment is carried out: the first-stage aging temperature is 830 °C for 6 h, and the second-stage aging temperature is 730 °C for 16 h.

[0070] After preparation, a high-temperature tensile test of the nickel-based wrought superalloy is carried out at 750 °C, and the results are as Figure 5 shown. At 750 °C, its yield strength is 1160 MPa, tensile strength is 1458 MPa, and elongation is 13.8%.

[0071] It should be noted that the above are only preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A nickel-based wrought superalloy, characterized in that, It contains a bimodal grain structure, where the coarse grain size is ASTM 4 - 6 grades and the fine grain size is ASTM 8 - 9 grades; By mass percentage, the elemental composition of the nickel - based wrought superalloy includes: Cr 9.0 - 11.0 wt.%, Al + Ti 6.0 - 8.0 wt.%, and the balance is Ni.

2. The nickel-based wrought superalloy according to claim 1, characterized in that, By mass percentage, the elemental composition includes: C 0.03 - 0.08 wt.%, Cr 9.0 - 11.0 wt.%, Al + Ti 6.0 - 8.0 wt.%, Nb 2.0 - 3.5 wt.%, W 2.5 - 3.5 wt.%, Co 13.0 - 14.5 wt.%, V 0.5 - 0.8 wt.%, Mo 3.0 - 4.5 wt.%, and the balance is Ni.

3. The nickel-based wrought superalloy according to claim 1 or 2, characterized in that, By mass percentage, the elemental composition includes: C 0.04 - 0.06 wt.%, Cr 10.0 - 11.0 wt.%, Al + Ti 6.0 - 8.0 wt.%, Nb 3.0 - 3.5 wt.%, W 2.5 - 3.0 wt.%, Co 13.0 - 14.0 wt.%, V 0.5 - 0.7 wt.%, Mo 3.0 - 4.0 wt.%, and the balance is Ni.

4. A method for preparing a nickel-based wrought superalloy according to any one of claims 1-3, characterized in that, It includes the following steps: Prepare an alloy ingot; Perform hot working deformation on the alloy ingot; Perform short - time annealing heat treatment on the alloy after hot working deformation; Perform solution aging treatment on the alloy after short - time annealing heat treatment.

5. The preparation method according to claim 4, wherein The preparation of the alloy ingot adopts a triple melting process of vacuum induction melting, electroslag remelting under protective atmosphere, and vacuum consumable melting.

6. The preparation method according to claim 4, characterized in that, The temperature of the hot working deformation is 1100 - 1190 °C.

7. The preparation method according to claim 4, characterized in that, The annealing temperature of the short - time annealing treatment is 950 - 1050 °C, and the annealing time is 0.5 - 1.0 h.

8. The preparation method according to claim 4, characterized in that, The solution aging treatment includes the following steps: Perform solution treatment on the alloy: heat the alloy to the solution temperature and hold, then cool; Perform double aging treatment on the alloy after solution treatment: heat the alloy to the primary aging temperature, hold, then cool; heat the alloy after primary aging treatment to the secondary aging temperature, hold, then cool.

9. The preparation method according to claim 8, wherein In the solution treatment, the solution temperature is 1100 - 1160 °C, the holding time is 3 - 4 h, the cooling rate ≥ 80 °C / min, and it is cooled to room temperature.

10. The preparation method according to claim 9, characterized in that, The cooling method is selected from one of water quenching or oil quenching.

11. The preparation method according to claim 8, characterized in that, In the double aging treatment, the primary aging temperature is 830 - 880 °C, the holding time after heating to the primary aging temperature is 6 - 7 h, and it is cooled to room temperature; the secondary aging temperature is 730 - 780 °C, the holding time after heating to the secondary aging temperature is 16 - 18 h, and it is cooled to room temperature.

12. The preparation method according to claim 11, characterized in that, The cooling method is air cooling.

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