Ni3Al-based alloy, test bar, turbine disc and preparation method of Ni3Al-based alloy

Abstract

The invention relates to the technical field of alloys, in particular to a Ni3Al-based alloy, a test bar, a turbine disc and a preparation method of the Ni3Al-based alloy. The invention discloses a Ni3Al-based alloy which comprises the following components in percentage by mass: 7%-9% of Al, 7%-8.5% of Cr, 0.13%-0.24% of C, 0.5%-2% of Ti, 3%-6% of Mo, 1%-3% of W, 1%-2% of Hf, 0.005%-0.03% of B and the balance of Ni. According to the Ni3Al-based alloy disclosed by the invention, all the elements are coordinated and matched, so that the Ni3Al-based alloy has a long-range ordered crystal structure, a stable high-temperature phase structure and excellent oxidation resistance, mechanical property and high-temperature property.

Description

Technical Field

[0001] The present invention relates to the technical field of alloys, and in particular to a Ni 3 Al-based alloy, test rod, turbine disk and preparation method thereof. Background Art

[0002] The turbine disk is a core component with key characteristics in aircraft engines. The service application temperature is usually 600~800℃. The uniformity of its organizational mechanical properties and medium and low temperature fatigue performance are extremely high. Therefore, the turbine disk often requires uniform fine-grained organizational control. Compared with traditional deformation, powder and other high-temperature alloy fine-grained turbine disks, integral casting fine-grained turbine disks not only have higher service temperatures, but also have low preparation costs. Using fine-grained casting technology, Mod5A, Mar-M247, IN713C and IN718 high-temperature alloy integral fine-grained casting turbine disks have been successfully manufactured, which are used for aircraft emergency or auxiliary power small-sized integral fine-grained turbine disks. With the increase in the flight speed and climbing altitude of the new generation of aircraft, the auxiliary power unit is lighter, smaller in size, and has a higher power-to-weight ratio. Therefore, the integral fine-grained casting turbine disk used is required to have a lower specific gravity, higher temperature resistance, and higher stress load level. The existing traditional high-temperature alloy integral casting fine-grained turbine disk can no longer meet the application requirements of the new generation of aircraft.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] One object of the present invention is to provide a Ni 3 Al-based alloy, which has a long-range ordered crystal structure, a stable high-temperature phase structure and excellent oxidation resistance.

[0005] Another object of the present invention is to provide a test rod.

[0006] Another object of the present invention is to provide a turbine disk having excellent mechanical properties and anti-oxidation properties.

[0007] Another object of the present invention is to provide a method for preparing a turbine disk.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted: A Ni 3 Al-based alloy, calculated by mass percentage, includes: Al 7%~9%, Cr 7%~8.5%, C 0.13%~0.24%, Ti 0.5%~2%, Mo 3%~6%, W 1%~3%, Hf 1%~2%, B 0.005%~0.03%, and the balance is Ni.

[0009] In some embodiments, the composition includes, by mass percentage, Al 7.6% to 8.5%, Cr 7.5% to 8.2%, C 0.13% to 0.2%, Ti 1.1% to 1.7%, Mo 3.5% to 5%, W 1.5% to 2.5%, Hf 1.2% to 1.8%, B 0.009% to 0.02%, and the balance is Ni. The mass ratio of Al to Ti is 4.471 to 7.72.

[0010] In some embodiments, the Ni 3 The microstructure of the Al-based alloy includes: a dendrite trunk γ / γ′ two-phase region, a eutectic phase γ-γ′, and carbides distributed between dendrites, wherein the carbides include TiC, MoC and HfC; the volume proportion of the eutectic phase γ-γ′ is 2% to 3%, and the volume proportion of the carbides is 1.4% to 1.9%.

[0011] A test rod, comprising the Ni 3 Al-based alloys; In some embodiments, the Ni 3 The tensile properties of Al-based alloy test bars at 850°C meet the following requirements: b 835~900MPa, δ 5 It is 6.8%~10%.

[0012] In some embodiments, the Ni 3 The endurance performance of Al-based alloy test rods at 975℃ and 196MPa meets the following requirements: 5 It is 6.8%~12%.

[0013] A turbine disk, comprising the Ni 3 Al-based alloy.

[0014] In some embodiments, the average grain size of the turbine disk is 1-1.5 mm.

[0015] In some embodiments, the density of the turbine disk is 5-7.6 g / cm 3 .

[0016] In some embodiments, the tensile properties of the turbine disk at 850° C. satisfy: σb is 800-1000 MPa, and δ5 is 5%-12%. In some embodiments, the durability of the turbine disk at 850° C. and 441 MPa is 40 to 80 hours.

[0017] The method for preparing the turbine disk as described above comprises the following steps: (A) According to Ni 3The proportions of the elements of the Al-based alloy are adjusted to prepare a master alloy bar, and the master alloy bar is remelted to obtain a remelted liquid; (B) obtaining a mold shell and preheating the mold shell; (C) pouring the remelted liquid into the shell mold, followed by cooling and post-processing.

[0018] In some implementations, the method for preparing the master alloy bar specifically comprises: 1) Heat nickel, chromium, tungsten, molybdenum and ferroboron. When the nickel is red hot, the first power of 50-80KW is used for 8-12 minutes to remove hydrogen. The second power of 150-200KW is used for full melting, and then refining is performed. The refining temperature is 1500-1550℃, the time is 10-45 minutes, and the refining vacuum is less than 5Pa. 2) After refining, add electrode graphite, then cool to 1380~1400℃ and add aluminum and sponge titanium; 3) After melting aluminum and sponge titanium, fill with argon and add hafnium. When the liquid surface is clean, stir for 1~2 minutes at a power of 150~200KW.

[0019] In some implementations, the preheating temperature is 800-920° C., and the preheating time is 4-8 hours.

[0020] In some embodiments, the pouring temperature is 1370-1510°C.

[0021] In some implementations, the pouring speed is 15-20 Kg / s.

[0022] In some embodiments, the post-treatment includes heat treatment and machining; the temperature of the heat treatment is 900-1170° C., the time of the heat treatment is 2-6 hours, and furnace cooling is adopted after the heat treatment.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) Ni of the present invention 3 Al-based alloys can control the relative content of γ′ and γ phases by reasonably adjusting the Al content; solid solution strengthening of the matrix can be achieved by using appropriate amounts of W and Mo elements; room temperature and medium temperature plasticity of the material can be improved by using appropriate amounts of B and Cr elements; and appropriate amounts of Hf can not only significantly improve the medium temperature endurance strength and plasticity of the cast high temperature alloy, but also the Hf-rich melt in the late solidification period has excellent wettability and fluidity, which can give full play to the shrinkage feeding effect of the capillary between the dendrites and significantly improve the casting process performance of the alloy; through the coordination of various elements, Ni 3 Al-based alloys have long-range ordered crystal structures, stable high-temperature phase structures, excellent oxidation resistance, mechanical properties and high-temperature properties.

[0024] (2) The test rod of the present invention has excellent mechanical properties, anti-oxidation properties and high temperature properties.

[0025] (3) The turbine disk of the present invention has a suitable average grain size, uniform grain size, suitable density, excellent mechanical properties, anti-oxidation properties and high temperature properties.

[0026] (4) The preparation method of the turbine disk of the present invention adopts the rapid low superheat pouring control technology, which controls the pouring temperature of the alloy liquid, reduces the heat storage, increases the cooling rate, shortens the dendrite growth time, inhibits the grain growth space, and achieves the purpose of low-multiple grain structure refinement control. Through the coordination of various steps, the obtained Ni 3 The Al-based alloy integrally cast fine-grained turbine disk has uniform grain structure, excellent mechanical properties, good oxidation resistance and good high-temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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.

[0028] Figure 1 Ni of Example 1 3 Microstructure diagram of Al-based alloy, a represents the eutectic phase γ-γ′, b represents the carbide, and c represents the dendrite trunk γ / γ′ two-phase region; Figure 2 For you 3 Macroscopic grain structure of Al-based alloy integrally cast fine-grained turbine disk; Figure 3 d is a microstructure diagram of the alloy of Comparative Example 1, d represents the eutectic phase γ-γ′, e represents the carbide, and f represents the dendrite stem γ / γ′ two-phase region; Figure 4 is the microstructure diagram of the alloy in Comparative Example 2; Figure 5 : is the microstructure diagram of the alloy in Comparative Example 3, g represents the eutectic phase γ-γ′, and h represents the dendrite trunk γ / γ′ two-phase region. DETAILED DESCRIPTION

[0029] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0030] According to one aspect of the present invention, the present invention relates to a Ni 3 Al-based alloy, calculated by mass percentage, includes: Al 7%~9%, Cr 7%~8.5%, C 0.13%~0.24%, Ti 0.5%~2%, Mo 3%~6%, W 1%~3%, Hf 1%~2%, B 0.005%~0.03%, and the balance is Ni.

[0031] The high specific strength Ni 3 Al-based alloys can control the relative content of γ′ and γ phases by reasonably adjusting the Al equivalent, achieve solid solution strengthening of the matrix by adjusting the appropriate amount of W and Mo elements, and improve the room temperature and medium temperature plasticity of the material by adjusting the appropriate amount of B and Cr elements. The appropriate amount of Hf can not only significantly improve the medium temperature endurance strength and plasticity of the cast high-temperature alloy, but also the Hf-rich melt in the late solidification period has excellent wettability and fluidity, which can give full play to the shrinkage feeding effect of the capillary between the dendrites and significantly improve the casting process performance of the alloy. Through the coordination of various elements, Ni 3 Al-based alloys have long-range ordered crystal structures, stable high-temperature phase structures, and excellent oxidation resistance and mechanical properties.

[0032] In some embodiments, Al is 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, etc., or any range therebetween, in terms of mass percentage. Element Al is γ′ phase Ni 3 (Al, Ti) forming elements, by adjusting the Al content can control the relative ratio of γ′ and γ phases in the alloy, thus affecting the mechanical properties of the material; in addition, the appropriate content of Al allows the alloy to form a dense and stable Al surface when oxidized at high temperature. 2 O 3 Film, the Al 2 O 3 The film protects the alloy from further oxidation, thereby improving the high temperature oxidation resistance of the alloy. Therefore, the Al content in the material of the present invention is controlled to be 7% to 9% to ensure that the γ′ and γ phases have a suitable relative ratio and coordinate the mechanical properties and oxidation resistance.

[0033] In some embodiments, Cr is 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, etc., or any range therebetween, in terms of mass percentage. 3 In Al, the element Cr can occupy the Ni position or the Al position. Cr can form Cr 2 O 3 The protective film has good anti-oxidation effect below 1000℃, making Ni 3 The medium temperature plasticity of Al-based alloys is significantly improved, which can effectively overcome the 3 The medium-temperature brittleness of Al alloy. The present invention controls the Cr content in the material to 7% to 8.5%, which is beneficial to ensure the oxidation resistance and medium-temperature plasticity of the alloy.

[0034] In some embodiments, in terms of mass percentage, C is 0.13%, 0.15%, 0.18%, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, etc., or any range between the two. 3 In the Al crystal structure, C occupies the body-centered interstitial position. 3 Below the Al peak temperature, adding C can increase the Ni 3 In addition, C is a carbide-forming element, which forms (Ti, Mo) C and HfC dispersion strengthening phases in the alloy of the present invention. 3 It plays a role of dispersion strengthening in Al alloy.

[0035] In some embodiments, Ti is 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc., or any range therebetween, in terms of mass percentage. Ti is γ′ phase Ni 3 (Al, Ti) and carbide-forming elements play the role of adjusting the γ′ phase content in the alloy and forming partial carbides to strengthen the alloy. Properly increasing the Ti content can reduce the consumption of Mo content when forming (Ti, Mo)C carbides, ensuring a sufficient amount of Mo for solid solution strengthening.

[0036] In some embodiments, in terms of mass percentage, Mo is 3%, 3.2%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, etc., or any range between the two. W is 1%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc., or any range between the two. Mo and W have similar electronic structures to Al and can replace Ni. 3The Al element in Al has a solid solution strengthening effect. The addition of W and Mo with large atomic radius causes γ / γ´ lattice distortion and changes the lattice parameters of γ and γ´ phases. When W and Mo elements are not added to the alloy, the lattice constants of γ and γ′ phases are 3.5680Å and 3.5691Å, respectively, and the mismatch is 0.031%. 3 When W and Mo elements are added to the Al-based alloy, the lattice constants of the γ and γ′ phases are 3.5905Å and 3.5772Å, respectively, and the mismatch is -0.370%. When the lattice mismatch changes from a positive value to a negative value, the bonding strength between the γ′ phase and the γ phase increases, which can greatly improve the mismatch of γ / γ´, thereby effectively strengthening the alloy. In some embodiments, the mass ratio of Mo to W is (2~3):1, such as 2:1, 2.2:1, 2.5:1 or 3:1, etc.

[0037] In some embodiments, Hf is 1.0%, 1.2%, 1.5%, 1.8%, or 2.0%, or any range between the two, in terms of mass percentage. The addition of an appropriate amount of Hf element is an important innovation of the present invention. Hf has multiple roles in high-temperature alloys. First, Hf is a γ′-forming element, and most of the Hf dissolves into the γ′ phase to strengthen γ′; second, Hf can form an oxide film with O, adhere to the surface of the alloy, hinder the further diffusion of O atoms, and improve the oxidation resistance of the alloy; third, Hf is a carbide-forming element, forming carbides between grain boundaries and dendrites, changing the grain boundaries from straight to curved. For straight grain boundaries, the intragranular deformation is always less than the total deformation, indicating that the grain boundary deformation accounts for a certain proportion. For curved grain boundaries, the intragranular deformation is basically equal to the total creep deformation, indicating that the grain boundaries are strengthened and the grain boundary deformation is very small. Therefore, the creep rupture life and plasticity of the alloy can be improved by bending the grain boundaries; fourthly, Hf added to the alloy also has the effect of purifying the grain boundaries. Hf has a high affinity for S and can produce high-melting-point sulfides that can be removed, thereby preventing S from causing grain boundary embrittlement and strengthening the alloy. Finally, the addition of Hf expands the solid-liquid phase temperature range, and maintains the connectivity of the micro-liquid pools between dendrites over a wide temperature range in the late solidification period, allowing the liquid to have good fluidity and wettability, and low viscosity, which can give full play to the capillary action between dendrites and improve the casting process performance of the alloy. The appropriate amount of Hf element in the present invention can work synergistically with other elements to improve Ni 3 Mechanical properties, oxidation resistance and high temperature properties of Al-based alloys.

[0038] In some embodiments, in terms of mass percentage, B is 0.005%, 0.008%, 0.01%, 0.015%, 0.02%, 0.025%, 0.028% or 0.03%, or any range between the two. Boron is an element that improves Ni 3Boron is an essential element for the room temperature plasticity of Al alloy. Adding an appropriate amount of boron to the composition of the material of the present invention can effectively strengthen the grain boundary and improve the dislocation slip on the grain boundary, prevent hydrogen from diffusing along the grain boundary, and avoid the possibility of environmental hydrogen embrittlement inside the material, thereby improving the plasticity of the alloy. However, if the B content is too high (greater than 0.03%), it will form a low-melting-point boride with Mo, thereby reducing the initial melting temperature of the alloy, which is not conducive to the high-temperature service of the alloy. In addition, it will consume the Mo content and weaken the solid solution strengthening effect of Mo.

[0039] In some embodiments, the Ni 3 Al-based alloy includes: Al 7.6%~8.5%, Cr7.5%~8.2%, C 0.13%~0.2%, Ti 1.1%~1.7%, Mo 3.5%~5%, W 1.5%~2.5%, Hf 1.2%~1.8%, B0.009%~0.02%, and the balance is Ni.

[0040] The present invention controls the mass ratio of Al to Ti (Al / Ti) to be less than 8), and can control the interdendritic eutectic γ-γ′ phase in the microstructure to be smooth plate-shaped, and the dendrite stem γ′ to be block-shaped, and improves the high temperature stability of the γ′ phase, so that the alloy has high medium and high temperature mechanical properties above 800°C. In some embodiments, the mass ratio of Al to Ti is 4.471 to 7.72, such as 4.471, 5, 5.5, 6, 7, 7.5, 7.72, etc.

[0041] In some embodiments, the Ni 3 The microstructure of the Al-based alloy includes: a dendrite trunk γ / γ′ two-phase region, a smooth plate-like eutectic phase γ-γ′ between dendrites, and carbides distributed between dendrites, wherein the carbides include TiC, MoC and HfC; the volume proportion of the eutectic phase γ-γ′ is 2%~3% (for example, 2%, 2.2%, 2.5%, 2.7%, 3%, etc.), and the volume proportion of the carbide is 1.4%~1.9% (1.4%, 1.5%, 1.7%, 1.9%, etc.).

[0042] According to another aspect of the present invention, the present invention relates to a Ni 3 Preparation method of Al-based alloy, using vacuum induction melting furnace for Ni 3The preparation of Al-based alloy master alloy includes: a) selecting electrolytic nickel, metal aluminum, metal chromium, sponge titanium, ferroboron, metal molybdenum, metal tungsten, electrode graphite, and metal hafnium as raw materials, and weighing the raw materials in proportion for use; b) heating nickel, chromium, tungsten, molybdenum, and ferroboron, and after the nickel is red hot, supplying electricity at a first power of 50-80KW for 8-12 minutes to remove hydrogen, and then supplying electricity at a second power of 150-200KW until it is fully melted, and then refining, the refining temperature is 1500-1550°C, the time is 10-45 minutes, and the refining vacuum is less than 5Pa; c) after refining, adding electrode graphite, and then cooling to add aluminum and sponge titanium when it is rapidly solidified, and the adding temperature is 1380-1400°C; d) after the aluminum and sponge titanium are melted, argon is filled and hafnium is added, and after the liquid surface is clean, stirring is performed at a power of 150-200KW for 1-2 minutes.

[0043] In some embodiments, electrolytic nickel and metallic chromium are placed at the bottom of the crucible, metallic molybdenum and metallic tungsten are placed at the top of the crucible, ferroboron is also placed in the crucible, and other elements are added from a hopper.

[0044] In some embodiments, Ni 3 The Al-based alloy is remelted, poured, cooled and post-processed. The remelting temperature is heated to 80~100℃ (such as 80℃, 90℃, 100℃, etc.) above the melting point of the alloy, and refined for 10~20min (such as 10min, 15min or 20min, etc.) under the condition of heat preservation power of 100~150KW (100KW, 110KW, 150KW, etc.), and the pouring temperature is 1370~1510℃; post-processing includes heat treatment, and the heat treatment temperature is 900~1170℃.

[0045] According to another aspect of the present invention, the present invention relates to a test rod, comprising the Ni 3 Al-based alloy. The test rod has excellent mechanical properties and oxidation resistance. 3 The tensile properties of Al-based alloy test bars at 850°C meet the following requirements: b 835~900MPa (e.g. 835MPa, 840MPa, 845MPa, 850MPa, 880MPa, 900MPa, etc.), δ 5 is 6.8% to 10% (e.g., 6.8%, 7%, 7.5%, 8%, 8.5%, 9% or 10%, etc.); the Ni 3 The endurance performance of Al-based alloy test rods at 975℃ and 196MPa meets the following requirements: 5 It is 6.8%~12% (6.8%, 7%, 8%, 9%, 10%, 11%, 12%, etc.).

[0046] The present invention also relates to a method for preparing a test rod, comprising the following steps: (1) According to Ni 3 The chemical composition ratio of Al-based alloy is selected from electrolytic nickel, metal aluminum, metal chromium, sponge titanium, ferroboron, metal molybdenum, metal tungsten, electrode graphite, and metal hafnium. The raw materials are weighed in proportion and set aside. Electrolytic nickel and metal chromium are placed at the bottom of the crucible, metal molybdenum and metal tungsten are placed at the top of the crucible, ferroboron is also placed in the crucible, and other elements are added from the hopper. Ni is melted in a vacuum induction furnace. 3 The preparation of Al-based alloy master alloy comprises the following specific steps: 1) heating nickel, chromium, tungsten, molybdenum and ferroboron, and after the nickel is red hot, supplying power at a first power of 50-80KW for 8-12 minutes to remove hydrogen, and then supplying power at a second power of 150-200KW until it is fully melted, and then refining, the refining temperature is 1500-1550°C, the time is 10-45 minutes, and the refining vacuum is less than 5Pa; 2) after refining, adding electrode graphite, and then cooling to a fast solidification state, and then adding aluminum and sponge titanium; 3) after melting the aluminum and sponge titanium, filling with argon and adding hafnium, and stirring for 1-2 minutes at a power of 150-200KW until the liquid surface is clean.

[0047] (2) Mold shell preparation: The mold shell is prepared by the investment casting method; the mold shell is insulated by filling with sand; the investment casting mold shell sand box is placed in a muffle furnace, and the temperature is raised to 890~910℃ (for example, 890℃, 900℃, 905℃, 910℃, etc.) with the furnace, and the temperature is kept for 4~8h (4h, 5h, 6h, 7h, 8h, etc.) for preheating. After the preheating is completed, it is directly and quickly transferred to the vacuum induction casting furnace.

[0048] (3) Remelting and casting of master alloy: The master alloy is remelted in a vacuum induction casting furnace. The master alloy remelting temperature is 80~100℃ (e.g. 80℃, 90℃, 100℃, etc.) above the melting point of the alloy. The alloy is refined for 10~20min (e.g. 10min, 15min or 20min, etc.) under the condition of heat preservation power of 100~150KW (100KW, 110KW, 150KW, etc.). After molten metal is cleared, the alloy liquid is cast into the mold shell at a casting temperature of 1390~1510℃ (1390℃, 1400℃, 1420℃, 1450℃, 1500℃ or 1510℃, etc.). The mold shell is air-cooled in the sand box outside the furnace. After the sand box is cooled to room temperature, the shell is cleared to obtain a nickel-based cast high-temperature alloy test bar.

[0049] (4) Heat treatment: The test bar is heat treated at 1100~1170℃ (1100℃, 1120℃, 1150℃, 1170℃, etc.) for 2~5h (2h, 3h, 4h, 5h, etc.), and air-cooled to obtain the heat-treated Ni 3 Al-based alloy mechanical test bar.

[0050] According to another aspect of the present invention, the present invention relates to a turbine disk, comprising the Ni 3 Al-based alloy.

[0051] The turbine disk of the present invention has a suitable average grain size, a uniform grain size, a suitable density, and excellent mechanical properties and anti-oxidation properties.

[0052] In some embodiments, the average grain size of the turbine disk is between 1 and 1.5 mm, such as 1 mm, 1.2 mm, 1.3 mm, 1.5 mm, etc., or any range between the two.

[0053] In some embodiments, the density of the turbine disk is 5-7.6 g / cm 3 , for example 5g / cm 3 , 5.5g / cm 3 , 6g / cm 3 、6.5g / cm 3 , 7g / cm 3 etc., or any range between them.

[0054] In some embodiments, the tensile properties of the turbine disk at 850° C. satisfy: σb is 800-1000 MPa, such as 800 MPa, 850 MPa, 900 MPa, 950 MPa, 1000 MPa, etc., or any range between them. δ5 is 5%, 6%, 7%, 8%, 9%, 10%, etc., or any range between them. In some embodiments, the durability of the turbine disk at 850° C. and 441 MPa is 40 to 80 hours, such as 40 hours, 45 hours, 50 hours, 55 hours, 60 hours, 70 hours, 80 hours, etc., or any range value therebetween.

[0055] According to another aspect of the present invention, the present invention relates to a method for preparing the turbine disk as described above, comprising the following steps: (A) According to the present invention, Ni 3The proportion of each element of the Al-based alloy is used to prepare a master alloy rod, specifically comprising: 1) heating nickel, chromium, tungsten, molybdenum and ferroboron, and after the nickel is red hot, the first power of 50-80KW is supplied for 8-12min (for example, 8min, 10min, 12min) to remove hydrogen, and then the second power of 150-200KW is supplied until it is fully melted, and then refining is performed, the refining temperature is 1500-1550°C (for example, 1500°C, 1520°C, 1530°C, 1550°C, etc.), the time is 10-45min (10min, 20min, 30min or 45min, etc.), and the refining vacuum is less than 5Pa (for example, 2Pa, 3Pa, 4Pa, etc.); 2) After refining, electrode graphite is added, and then aluminum and sponge titanium are added when the temperature is lowered to rapid solidification, and the adding temperature is 1380-1400°C; 3) After the aluminum and titanium sponge are melted, argon is filled and hafnium is added. When the liquid surface is clean, stirring is performed for 1 to 2 minutes at a power of 150 to 200 kW. The master alloy bar is remelted to obtain a remelted liquid. (B) obtaining a mold shell and preheating the mold shell; (C) pouring the remelted liquid into the shell mold, followed by cooling and post-processing.

[0056] The method for preparing the turbine disk of the present invention adopts a fast low superheat casting control technology to carry out Ni 3 The preparation of Al-based alloy integral fine-grained turbine disks achieves the purpose of low-multiple grain structure refinement control by controlling the pouring temperature of the alloy liquid, reducing the heat storage, and increasing the cooling rate, shortening the dendrite growth time, and inhibiting the grain growth space. 3 The Al-based alloy integrally cast fine-grained turbine disk has uniform grain structure, excellent mechanical properties, and good oxidation resistance, meeting the application requirements of turbine disks for auxiliary power units of new-generation aircraft engines.

[0057] In some embodiments, electrolytic nickel, metallic aluminum, metallic chromium, sponge titanium, ferroboron, metallic molybdenum, metallic tungsten, electrode graphite, and metallic hafnium are selected as raw materials, and the raw materials are weighed in proportion. Electrolytic nickel and metallic chromium are placed at the bottom of the crucible, metallic molybdenum and metallic tungsten are placed at the top of the crucible, ferroboron is also placed in the crucible, and other elements are added from the hopper.

[0058] In some embodiments, the remelting of the master alloy specifically includes: after the surface of the master alloy bar is polished, the master alloy is remelted in a 50 kg vacuum induction melting furnace, Ni 3The material of Al-based alloy integral fine-grained turbine disk master alloy is 20~40Kg / furnace, such as 20Kg / furnace, 25Kg / furnace, 30Kg / furnace, 35Kg / furnace, 40Kg / furnace, etc. The master alloy remelting temperature is heated to 80~100℃ (such as 80℃, 90℃, 100℃, etc.) above the melting point of the alloy, and refined for 10~20min (such as 10min, 15min or 20min, etc.) under the condition of heat preservation power of 100~150KW (100KW, 120KW, 150KW, etc.).

[0059] In some embodiments, the preheating temperature is 800-920°C, such as 800°C, 820°C, 850°C, 880°C, 900°C, 920°C, etc., or any range between the two. The preheating time is 4-8h, such as 4h, 5h, 6h, 7h, 8h, etc. A silica sol shell for investment casting is used, and the shell is placed in a muffle furnace together with a fixed tooling for preheating. The shell preheating method is to heat from room temperature to 800-920°C, and the insulation time is 4-8h. The preheated shell is sent to a vacuum induction melting furnace for casting fine-grained turbine disks.

[0060] In some embodiments, after the master alloy is fully melted, the casting of the overall fine-grained turbine disk begins. 3 The casting of Al-based alloy integral fine-grained turbine disk adopts low superheat fine-grain control technology, that is, the pouring temperature is controlled to be between 10 and 30°C above the melting point of the alloy, specifically 1370~1510°C (for example, 1370°C, 1380°C, 1390°C, 1400°C, 1500°C, etc.). In addition, in order to improve its filling capacity, the steel liquid is filled by fast pouring, and the pouring speed is controlled to be 15~20Kg / s (for example, 15Kg / s, 16Kg / s, 17Kg / s, 18Kg / s, 20Kg / s, etc.). After the casting is completed, the casting is taken out of the vacuum induction melting furnace together with the shell, and placed in room temperature environment for strong cooling control by air cooling.

[0061] In some embodiments, the post-processing includes heat treatment and machining; the turbine disk casting blank is cast, the riser is cut off by wire cutting, and after heat treatment, Ni is processed according to the design requirements. 3 Processing and forming of Al-based alloy turbine disks. The heat treatment temperature is 900-1170°C, such as 900°C, 920°C, 950°C, 980°C, 1000°C, 1100°C, 1170°C, etc., and the heat treatment time is 2-6h, such as 2h, 2.5h, 3h, 4h, 5h, 6h, etc.

[0062] The following is further explained in conjunction with specific embodiments and comparative examples.

[0063] Example 1 A Ni 3 The Al-based alloy test bar comprises, by mass percentage, Al 8.2%, Cr 7.8%, C 0.15%, Ti1%, Mo 4%, W 2%, Hf 1.3%, B 0.01%, and the balance is Ni.

[0064] Ni 3 The method for preparing an Al-based alloy test rod comprises the following steps: (1) Preparation of master alloy: According to the above element ratio, select electrolytic nickel, metal aluminum, metal chromium, sponge titanium, ferroboron, metal molybdenum, metal tungsten, electrode graphite, and metal hafnium as raw materials, weigh the raw materials in proportion and set aside. Electrolytic nickel and metal chromium are placed at the bottom of the crucible, metal molybdenum and metal tungsten are placed at the top of the crucible, ferroboron is also placed in the crucible, and other elements are added from the hopper. Use a vacuum induction melting furnace to carry out Ni 3 The preparation of Al-based alloy master alloy specifically includes: a) heating nickel, chromium, tungsten, molybdenum and ferroboron, and after the nickel is red hot, the first power of 70KW is supplied for 10 minutes to remove hydrogen, and then the second power of 180KW is supplied until it is fully melted, and then refining is performed, the refining temperature is 1520℃, the time is 30min, and the refining vacuum is 4Pa; b) after refining, electrode graphite is added, and then aluminum and sponge titanium are added when the temperature is lowered to fast solidification, and the adding temperature is 1400℃; c) after the aluminum and sponge titanium are melted, argon is filled and hafnium is added, and when the liquid surface is clean, stirring is performed with a power of 200KW for 1.5min.

[0065] (2) Mold shell preparation: The mold shell is prepared by the investment casting method; the mold shell is insulated by filling with sand; the investment casting mold shell sand box is placed in a muffle furnace, heated to 900°C with the furnace, and kept warm for 5 hours for preheating. After preheating, it is directly and quickly transferred to the vacuum induction casting furnace.

[0066] (3) Remelting and casting the master alloy of step (1): remelting the master alloy in a vacuum induction casting furnace, heating the master alloy to 90°C above the melting point of the alloy, refining for 15 minutes under a power of 120KW, casting the alloy liquid into the mold shell at a casting temperature of 1470°C after purifying, and air cooling the mold shell in the sand box outside the furnace. After the sand box is cooled to room temperature, the shell is purged to obtain a nickel-based cast high-temperature alloy test bar.

[0067] (4) Heat treatment: The alloy test bar was heat treated at 1160℃ for 2.5h and air cooled to obtain Ni 3 Al-based alloy test rod.

[0068] Example 2 A Ni 3The Al-based alloy test bar comprises, by mass percentage, Al 8.5%, Cr 7.8%, C 0.2%, Ti 1%, Mo 4%, W 2%, Hf 1.5%, B 0.01%, and the balance is Ni.

[0069] Ni 3 The preparation method of Al-based alloy test rod is as follows: 3 The element ratio of the Al-based alloy test rod and other conditions are the same as those in Example 1.

[0070] Example 3 A Ni 3 The Al-based alloy test bar comprises, by mass percentage, Al 7.8%, Cr 7.8%, C 0.13%, Ti1%, Mo 4%, W 2%, Hf 1.3%, B 0.01%, and the balance is Ni.

[0071] Ni 3 The preparation method of Al-based alloy test rod is as follows: 3 The element ratio of the Al-based alloy test rod and other conditions are the same as those in Example 1.

[0072] Example 4 A turbine disk comprises, by mass percentage, 8.2% Al, 7.8% Cr, 0.15% C, 1% Ti, 4% Mo, 2% W, 1.3% Hf, 0.01% B, and the balance is Ni.

[0073] A Ni with a diameter of φ120mm 3 The method for preparing an Al-based alloy integrally cast fine-grained turbine disk comprises the following steps: (1) Preparation of master alloy: According to the composition ratio of the turbine disc, select electrolytic nickel, metal aluminum, metal chromium, sponge titanium, ferroboron, metal molybdenum, metal tungsten, electrode graphite, and metal hafnium as raw materials, and weigh the raw materials in proportion for use. Electrolytic nickel and metal chromium are placed at the bottom of the crucible, metal molybdenum and metal tungsten are placed at the top of the crucible, ferroboron is also placed in the crucible, and other elements are added from the hopper. Use a vacuum induction melting furnace to carry out Ni 3 The preparation of Al-based alloy master alloy specifically includes: a) heating nickel, chromium, tungsten, molybdenum and ferroboron, and after the nickel is red hot, supplying power at a first power of 70KW for 10 minutes to remove hydrogen, and then supplying power at a second power of 180KW until it is fully melted, and then refining, the refining temperature is 1520°C, the time is 30 minutes, and the refining vacuum is 4Pa; b) after refining, adding electrode graphite, and then cooling to the rapid solidification time to add aluminum and sponge titanium, and the adding temperature is 1400°C; c) after melting the aluminum and sponge titanium, filling with argon and adding hafnium, and when the liquid surface is clean, stirring with a second power of 200KW for 1.5 minutes.

[0074] (2) Shell preheating: Use a silica sol shell for investment casting, put the shell together with the fixed tooling into a muffle furnace for preheating. The shell preheating method is to heat from room temperature to 800℃, and the holding time is 6 hours. The preheated shell is sent to a vacuum induction melting furnace for casting fine-grained turbine disks.

[0075] (3) Remelting of master alloy: After the surface of the master alloy bar is polished, the master alloy is remelted in a 50Kg vacuum induction melting furnace, with 30Kg of master alloy material per furnace. The master alloy remelting temperature is 90°C above the melting point of the alloy, and the refining is carried out for 15 minutes under the condition of 120KW insulation power.

[0076] (4) Fine grain casting: Ni begins after the alloy is fully melted. 3 The casting of Al-based alloy fine-grained turbine disk adopts low overheat fine-grained control technology to control Ni 3 The pouring temperature of Al-based alloy fine-grained turbine disk is 1380℃. At the same time, in order to improve its filling capacity, the fast pouring method is used to complete the steel liquid filling. 3 The pouring speed of the Al-based alloy fine-grained turbine disk is 18 Kg / s. After the casting is completed, the casting together with the shell is taken out from the vacuum induction melting furnace and placed under room temperature environment for strong cooling control by air cooling.

[0077] (5) Post-processing: The turbine disk casting blank is cut off by wire cutting, and then heat treated at 950℃ for 4h. After furnace cooling, Ni 3 Processing and forming of Al-based alloy turbine disks.

[0078] Example 5 A turbine disk comprises, by mass percentage, 8.5% Al, 7.8% Cr, 0.2% C, 1% Ti, 4% Mo, 2% W, 1.5% Hf, 0.01% B, and the balance is Ni.

[0079] In this embodiment, a Ni with a diameter of φ120 mm 3 The method for preparing the Al-based alloy integrally cast fine-grained turbine disk is the same as Example 4 except for adjusting the component ratio of the turbine disk.

[0080] Example 6 A turbine disk comprises, by mass percentage, 7.8% Al, 7.8% Cr, 0.13% C, 1% Ti, 4% Mo, 2% W, 1.3% Hf, 0.01% B, and the balance is Ni.

[0081] In this embodiment, a Ni with a diameter of φ120 mm 3The method for preparing the Al-based alloy integrally cast fine-grained turbine disk is the same as Example 4 except for adjusting the component ratio of the turbine disk.

[0082] Example 7 A turbine disk comprises, by mass percentage, 7% Al, 8.5% Cr, 0.24% C, 2% Ti, 3% Mo, 1% W, 1% Hf, 0.005% B, and the balance is Ni.

[0083] In this embodiment, a Ni with a diameter of φ120 mm 3 The method for preparing the Al-based alloy integrally cast fine-grained turbine disk is the same as Example 4 except for adjusting the component ratio of the turbine disk.

[0084] Example 8 A turbine disk comprises, by mass percentage, Al 9%, Cr 7%, C 0.13%, Ti 0.5%, Mo 6%, W3%, Hf 2%, B 0.03%, and the balance is Ni.

[0085] In this embodiment, a Ni with a diameter of φ120 mm 3 The method for preparing the Al-based alloy integrally cast fine-grained turbine disk is the same as Example 4 except for adjusting the component ratio of the turbine disk.

[0086] Comparative Example 1 A Ni 3 The Al-based alloy test bar comprises, by mass percentage, Al 8.2%, Cr 7.8%, C 0.1%, Ti 1%, Mo 4%, W 2%, Hf 0.5%, B 0.01%, and the balance is Ni.

[0087] Ni 3 The preparation method of Al-based alloy test rod is as follows: 3 The element ratio of the Al-based alloy test rod and other conditions are the same as those in Example 1.

[0088] Comparative Example 2 A Ni 3 The Al-based alloy test bar comprises, by mass percentage, Al 8.2%, Cr 7.8%, C 0.15%, Ti1%, Mo 4%, W 2%, Hf 2.1%, B 0.01%, and the balance is Ni.

[0089] Ni 3 The preparation method of Al-based alloy test rod is as follows: 3 The element ratio of the Al-based alloy test rod and other conditions are the same as those in Example 1.

[0090] Comparative Example 3 A Ni 3 The Al-based alloy test bar comprises, by mass percentage, Al 9%, Cr 7.8%, C 0.1%, Ti 1%, W2%, Hf 0.5%, B 0.02%, and the balance is Ni.

[0091] Ni 3 The preparation method of Al-based alloy test rod is as follows: 3 The element ratio of the Al-based alloy test rod and other conditions are the same as those in Example 1.

[0092] Comparative Example 4 A method for preparing a high-temperature alloy K417G integrally cast fine-grained turbine disk with a diameter of φ120 mm, wherein the K417G alloy is currently used for high-temperature alloy fine-grained turbines, comprises the following steps: (1) Preparation of master alloy: The master alloy is melted in a vacuum induction furnace. The specific chemical composition includes: C 0.15%, Cr 9%, Co 10%, Mo 3%, Al 5.5%, Ti 4.5%, V 0.8%, B 0.02%, and the balance is Ni.

[0093] (2) Shell preheating: Use a silica sol shell for investment casting, put the shell together with the fixed tooling into a muffle furnace for preheating. The shell preheating method is to heat from room temperature to 800℃, and the holding time is 6 hours. The preheated shell is sent to a vacuum induction melting furnace for casting fine-grained turbine disks.

[0094] (3) Remelting of master alloy: After the surface of the master alloy bar is polished, the master alloy is remelted in a 50 kg vacuum induction melting furnace, with the master alloy material being 30 kg / furnace.

[0095] (4) Fine-grain casting: After the alloy is fully melted, the K417G alloy fine-grain turbine disk is poured. The low superheat fine-grain control technology is used to control the pouring temperature to 20°C above the melting point of the alloy and the pouring speed to 18Kg / s. After the casting is completed, the casting and the shell are taken out of the vacuum induction melting furnace and placed in a room temperature environment for strong cooling control by air cooling.

[0096] (5) Post-processing: The riser of the cast turbine disk casting is cut off by wire cutting, and then heat treated at "950℃, 4h, furnace cooling" to produce a K417G alloy integral fine-grained turbine disk.

[0097] Experimental example 1. Ni 3 Mechanical properties test of Al-based alloy test bar The Ni in Examples 1-3 and Comparative Examples 1-3 3The Al-based alloy test bars were subjected to tensile property tests at room temperature and 850°C. The test bar tensile test standard is GB / T 228.2-2015; the high temperature endurance test standard is GB / T 2039-2012. The tensile property test results are shown in Table 1.

[0098] Table 1 Ni 3 Tensile properties test results of Al-based alloy test bars

[0099] The Ni in Examples 1-3 and Comparative Examples 1-3 3 The Al-based alloy test rods were subjected to high temperature durability tests. The test results are shown in Table 2.

[0100] Table 2 Ni 3 High temperature durability test results of Al-based alloy test bars

[0101] It can be seen from Table 1 and Table 2 that the Ni 3 The Al-based alloy not only has better room temperature and 850°C tensile properties than the alloys of Comparative Examples 1-3, but also has significantly better medium and high temperature endurance properties than the alloys of Comparative Examples 1-3. Therefore, the change in composition has a greater impact on the performance of the alloy of the present invention. The difference in mechanical properties of the alloys in this embodiment is further analyzed in combination with the microstructure. The microstructure diagram of the alloy of Example 1 of the present invention is shown in FIG. Figure 1 As shown ( Figure 1 a represents the eutectic phase γ-γ′, b represents the carbide, and c represents the dendrite stem γ / γ′ two-phase region). The microstructure diagram of comparative example 1 is shown in FIG. Figure 3 As shown ( Figure 3 In the figure, d represents the eutectic phase γ-γ′, e represents the carbide, and f represents the dendrite stem γ / γ′ two-phase region). As the content of C and Hf elements in Comparative Example 1 decreases, the main changes in the organizational morphology are as follows: On the one hand, as Ni 3 The γ-γ′ eutectic phase, an important strengthening phase under high temperature conditions in Al-based alloys, is reduced. On the other hand, the amount of carbides that play a role in grain boundary strengthening is reduced. Under the above effects, the mechanical properties of Comparative Example 1 are significantly reduced from room temperature to 850°C compared with the alloy of the present invention. In Comparative Example 2, when the Hf content is increased to 2.1%, a small amount of Ni 7 M 2 Low melting point phase (see Figure 4), resulting in a significant decrease in the rupture performance of the alloy under 975℃ / 196MPa conditions, so the Hf element content in the alloy of the present invention cannot be controlled to exceed 2.0%. Comparative Example 3 Due to the excessively high Al content, the content of the γ-γ′ eutectic phase of the alloy and the size of the dendrite stem γ′ phase increased, but with the decrease of W and Mo content, the γ / γ′ mismatch and lattice distortion decreased, and the γ′ morphology changed from block to cellular (see Figure 5 ), which seriously affects the strengthening effect of the γ′ phase, resulting in a significant decrease in the medium and high temperature mechanical properties of the alloy of Comparative Example 3.

[0102] Combined with microstructural observation and analysis, the phase composition of several alloys has not changed significantly, including γ phase, γ′ phase, carbide and boride. In the microstructure of the alloy in Example 1, the volume of the eutectic γ-γ′ phase accounts for 2.1%, and the volume of the carbide accounts for 1.8%.

[0103] 2. Performance test of turbine disc Example 4 Preparation of Ni 3 The low-magnification grain structure of the Al-based alloy integral fine-grained turbine disk is shown in Figure 2 As shown, the average grain size is less than 1.5 mm and the grain structure is uniform.

[0104] The turbine disks in the embodiments and the K417G alloy turbine disks of comparative example 4 were sampled and tested for performance. The test results are shown in Table 3.

[0105] Table 3 Ni 3 Results of sampling performance test of Al-based composite disc body

[0106] From the above, it can be seen that the fine-grained and densified Ni 3 The Al-based alloy turbine has excellent medium and high temperature fatigue performance, and its tensile performance is better than that of the formed test bar. In terms of endurance performance, the fine-grained densified cast turbine disk is equivalent to the formed test bar, giving full play to the Ni 3 Performance potential of Al-based alloy materials.

[0107] The K417G alloy turbine disk body of the comparative example 4 and the Ni 3 Compared with the bulk performance of the fine-grained turbine of the Al-based alloy, the tensile properties of the fine-grained turbine disk of the K417G alloy of the comparison alloy 7 at room temperature are comparable to those of the alloy of the present invention, but the tensile properties at 850°C under service conditions are significantly lower, reflecting the Ni 3 Al-based alloy fine-grained turbine disks can better meet the application requirements of small-sized integral fine-grained turbine disks for emergency or auxiliary power of the new generation of aircraft.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Ni3Al-based alloy, characterized in that: Calculated by mass percentage, it includes: Al 7%~9%, Cr 7%~8.5%, C0.13%~0.24%, Ti 0.5%~2%, Mo 3%~6%, W 1%~3%, Hf 1%~2%, B 0.005%~0.03%, and the balance is Ni.

2. The Ni3Al-based alloy according to claim 1, characterized in that Contains at least one of the following features (1) to (2): (1) In terms of mass percentage, it comprises: Al 7.6% to 8.5%, Cr 7.5% to 8.2%, C 0.13% to 0.2%, Ti 1.1% to 1.7%, Mo 3.5% to 5%, W 1.5% to 2.5%, Hf 1.2% to 1.8%, B 0.009% to 0.02%, and the balance is Ni; the mass ratio of Al to Ti is 4.471 to 7.72; (2) The microstructure of the Ni3Al-based alloy includes: a dendrite trunk γ / γ′ two-phase region, a eutectic phase γ-γ′, and carbides distributed between dendrites, wherein the carbides include TiC, MoC and HfC; the volume proportion of the eutectic phase γ-γ′ is 2% to 3%, and the volume proportion of the carbides is 1.4% to 1.9%.

3. A test rod, characterized in that: Including the Ni3Al-based alloy described in claim 1 or 2.

4. The test rod according to claim 3, characterized in that Contains at least one of the following features (1) to (2): (1) The tensile properties of the Ni3Al-based alloy test bar at 850°C satisfy: σ b is 835~900MPa, δ5 is 6.8%~10%; (2) The endurance performance of the Ni3Al-based alloy test rod at 975°C and 196 MPa satisfies: δ5 is 6.8%~12%.

5. A turbine disc, characterized in that: Including the Ni3Al-based alloy described in claim 1 or 2.

6. The turbine disk according to claim 5, characterized in that Contains at least one of the following features (1) to (2): (1) The average grain size of the turbine disc is 1 to 1.5 mm; (2) The density of the turbine disc is 5~7.6g / cm 3 .

7. The turbine disk according to claim 5, characterized in that Contains at least one of the following features (1) to (2): (1) The tensile properties of the turbine disk at 850°C satisfy: σb is 800-1000 MPa, δ5 is 5%-12%; (2) The durability of the turbine disc under the conditions of 850°C and 441 MPa is 40 to 80 hours.

8. The method for preparing a turbine disk according to any one of claims 5 to 7, characterized in that: The following steps are involved: (A) preparing a master alloy bar according to the ratio of each element of the Ni3Al-based alloy, and remelting the master alloy bar to obtain a remelted liquid; (B) obtaining a mold shell and preheating the mold shell; (C) pouring the remelted liquid into the shell mold, followed by cooling and post-processing.

9. The method for preparing a turbine disk according to claim 8, characterized in that: The method for preparing the master alloy bar specifically comprises: 1) Heat nickel, chromium, tungsten, molybdenum and ferroboron. When the nickel is red hot, the first power of 50-80KW is used for 8-12 minutes to remove hydrogen. The second power of 150-200KW is used for full melting, and then refining is performed. The refining temperature is 1500-1550℃, the time is 10-45 minutes, and the refining vacuum is less than 5Pa. 2) After refining, add electrode graphite, then cool to 1380~1400℃ and add aluminum and sponge titanium; 3) After melting aluminum and sponge titanium, fill with argon and add hafnium. When the liquid surface is clean, stir for 1~2 minutes at a power of 150~200KW.

10. The method for preparing a turbine disk according to claim 8, characterized in that: Contains at least one of the following features (1) to (4): (1) The preheating temperature is 800-920°C and the preheating time is 4-8 hours; (2) The pouring temperature is 1370~1510℃; (3) The pouring speed is 15-20 kg / s; (4) The post-treatment includes heat treatment and machining; the temperature of the heat treatment is 900-1170°C, and the time of the heat treatment is 2-6 hours.

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