Fe-Ni-Co-based low-expansion high-temperature alloy bar and preparation method thereof

Abstract

The invention discloses a Fe-Ni-Co-based low-expansion high-temperature alloy bar and a preparation method thereof, and belongs to the technical field of high-temperature alloy preparation. Through the multi-channel rapid diffusion annealing process, the size and number of primary segregation phases are effectively reduced, favorable conditions are provided for precipitation of subsequent secondary phases, it is guaranteed that the bar has excellent strength and notch sensitivity resistance, and meanwhile the oxidation loss of the alloy bar is reduced; by controlling the multi-heating-number upsetting and drawing process, the density of the alloy bar is improved, a bar with 7-8-grade grains is obtained, the precipitation density of a secondary phase at a grain boundary is increased, and the strength of the bar is improved; through standard heat treatment, secondary phases are uniformly distributed in the grain boundary and the grain of the bar, and the strength, the notch sensitivity resistance and the performance stability are improved; by means of the method, the production efficiency can be improved, the energy consumption can be reduced, and the alloy bar with the uniform structure and the excellent comprehensive performance can be obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature alloy preparation, in particular to an Fe-Ni-Co based low expansion high-temperature alloy rod and a preparation method thereof. Background Art

[0002] Due to its small thermal expansion coefficient and almost constant elastic modulus, Fe-Ni-Co based low expansion high temperature alloy can effectively control the gap between the stator and the rotating parts, improve fuel efficiency, and is mainly used in parts that need to control the gap, such as aircraft engine casings. And due to the addition of 5.5% Cr, it has excellent oxidation resistance, does not have the problem of notch sensitivity caused by stress-accelerated grain boundary oxygen embrittlement, and can be used for a long time at 650℃ without a protective layer. However, the Nb content of this alloy is relatively high. In actual production, Nb segregation often leads to uneven organization and unstable performance, notch sensitivity caused by insufficient precipitation of grain boundary precipitation phase, and unqualified strength caused by incomplete elimination of primary phase. The above factors will significantly reduce the yield rate of the bar. At the same time, the Nb segregation of this alloy is difficult to eliminate. On the one hand, it will cause serious oxidation loss of the alloy bar, and on the other hand, it will lead to low production efficiency and high energy consumption of the alloy bar. Summary of the invention

[0003] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a Fe-Ni-Co based low expansion high temperature alloy rod and a preparation method thereof. The present invention effectively reduces the size and amount of the primary segregation phase through a multi-channel rapid diffusion annealing process, provides favorable conditions for the subsequent precipitation of the secondary phase, ensures that the rod has excellent strength and resistance to notch sensitivity, and reduces the oxidation loss of the alloy rod; by controlling the multi-fire upsetting process, the density of the alloy rod is improved, and a rod with 7 to 8 grade grains is obtained, the precipitation density of the secondary phase at the grain boundary is increased, and the strength of the rod is improved; through standard heat treatment, the secondary phase is uniformly distributed at the grain boundary and in the grain of the rod, and the strength and resistance to notch sensitivity and performance stability are improved; through this method, both the production efficiency can be improved and the energy consumption can be reduced, and an alloy rod with uniform structure and excellent comprehensive performance can be obtained.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] The invention provides a Fe-Ni-Co based low expansion high temperature alloy bar, the chemical composition and mass percentage of which are: Ni: 23.50%-25.50%, Co: 28.00%-30.00%, Nb: 4.50%-5.20%, Ti: 0.7%-1.00%, Si: 0.20%-0.30%, P: ≤0.015%, C: ≤0.05%, B: ≤0.010%, Al: 0.30%-0.60%, Cr: 5.00%-6.00%, and the balance is Fe and inevitable impurities.

[0006] Based on the above technical solution, further, the area percentage of the primary Laves phase of the alloy rod is 2.53% to 3.61%, the average size is 2.69μm to 3.22μm, the average size of the secondary Laves is 0.81μm to 0.85μm, and the average grain size is 25.28μm to 56.23μm; there is no notch sensitivity, the notch endurance life is higher than 100h, the room temperature yield strength is higher than 900MPa, the elongation is higher than 18%, the 650℃ yield strength is higher than 815MPa, and the elongation is higher than 20%.

[0007] Another aspect of the present invention provides a method for preparing the above-mentioned Fe-Ni-Co based low expansion high temperature alloy rod, comprising the following steps:

[0008] (1) After VIM smelting process, ingots are obtained. The refining temperature of vacuum induction melting is 1520℃~1535℃ to ensure that the raw materials can be melted and prevent the crucible from increasing oxygen. The melting time is 3~4h to ensure that the raw materials can be completely melted and the oxygen and nitrogen content can be better controlled. The pouring temperature is 1485℃~1500℃ to ensure the fluidity of liquid metal during pouring. Fe, Co, Ni, and Cr elements have high oxygen partial pressures and are relatively difficult to oxidize. They also have high melting points. Therefore, they are first loaded into the furnace for melting. The charge needs to be loose at the top and tight at the bottom. The C element is added at the beginning of smelting. The addition of Nb in the refining period can achieve the best effect of removing O and N elements; Nb is a strong nitrogen-fixing element, so it is added in the refining period, and the refining time before and after the addition of Nb is more than 30 minutes to fully remove O and N; Al, Ti, and Si are added after the refining period to prevent burning, and the power needs to be turned off before adding to form a film; Due to the smelting under vacuum environment, the vapor pressure of B is high and it is easy to volatilize, so argon gas needs to be added when B is added, and the gas pressure of argon gas should be higher than the vapor pressure of B, and it is selected to be added in the form of B-Fe master alloy in the later stage of alloying;

[0009] (2) Multi-channel rapid diffusion annealing process: The ingot is subjected to a tempering free forging to break up the dendrites and primary Laves phase and introduce a large number of diffusion channels. It is then heated to 1180-1200°C and kept at this temperature for 10-30 hours to reduce the size and amount of the primary segregation phase, providing favorable conditions for the subsequent precipitation of the secondary phase, ensuring that the rod has excellent strength and resistance to notch sensitivity, while reducing the oxidation loss of the alloy rod;

[0010] (3) Upsetting and drawing process: The upsetting and drawing temperature is 1035-1100℃, and the deformation amount per pass is >50% to improve the density of the alloy rod and obtain rods with 7-8 grains, increase the precipitation density of the secondary phase at the grain boundary and improve the strength of the rod; the surface temperature is lower than 800℃ and then reheated to prevent cracking of the ingot surface, and then air cooled;

[0011] (4) Standard heat treatment process: heat the forged rod to 1090-1100℃ and keep it for 0.5-2h, and air cool it to release the residual stress and avoid the precipitation of needle-like phase; then heat it to 710-730℃ and keep it for 5-10h, cool it to 610-630℃ and keep it for 5-10h, and air cool it to promote the full precipitation of the intragranular strengthening phase γ' phase to ensure that the alloy has high strength, as well as the dispersed precipitation of the secondary phase at the grain boundary to ensure that the alloy is not notch sensitive and has high plasticity.

[0012] Based on the above technical solution, further, the forging temperature of the first tempering free forging described in step (2) is 1040-1060°C, the deformation amount per pass is ≥40%, and the surface temperature is lower than 800°C for furnace heating.

[0013] Based on the above technical solution, further, in step (2), the heating temperature is controlled at 1189-1195° C., and the insulation time is controlled at 12-24 h.

[0014] Based on the above technical solution, further, the number of upsetting and drawing in step (3) is 3 to 4 times, the upsetting deformation is 20 to 35%, and the drawing deformation is 25 to 45%.

[0015] Based on the above technical solution, further, the specific process of step (4) is: heating the forged rod to 1093°C and keeping it warm for 1 hour, air cooling, then heating it to 720°C and keeping it warm for 8 hours, cooling it to 620°C with the furnace and keeping it warm for 8 hours, and air cooling.

[0016] The beneficial effects of the present invention compared with the prior art are as follows:

[0017] The preparation method of the Fe-Ni-Co based low expansion high temperature alloy rod of the present invention effectively reduces the size and quantity of the primary segregation phase through a multi-channel rapid diffusion annealing process, provides favorable composition conditions for the subsequent precipitation of the secondary phase, ensures that the rod has excellent strength and notch sensitivity resistance, and reduces the oxidation loss of the alloy rod; by controlling the multi-fire upsetting process, the density of the alloy rod is improved, and a rod with 7-8 grade grains is obtained, the precipitation density of the secondary phase at the grain boundary is increased, and the strength of the rod is improved; through standard heat treatment, the secondary phase is evenly distributed at the grain boundary and in the grain of the rod, and the strength and notch sensitivity resistance and performance stability are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0019] Figure 1 The grain structure and precipitation phase diagram of the alloy rod prepared in Example 1.

[0020] Figure 2 The grain structure and precipitation phase diagram of the alloy rod prepared in Example 5. DETAILED DESCRIPTION

[0021] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0022] Example 1

[0023] The present embodiment provides a method for preparing a Fe-Ni-Co based low expansion high temperature alloy rod, wherein the chemical composition and mass percentage of the alloy rod are: Ni: 24.31%, Co: 29.18%, Nb: 4.50%, Ti: 0.70%, Si: 0.24%, P: 0.004%, C: 0.0079%, B: 0.0061%, Al: 0.44%, Cr: 5.00%, and the balance is Fe and unavoidable impurities;

[0024] The steps include:

[0025] (1) The alloy rod is subjected to a VIM smelting process to obtain an ingot, the refining temperature of the vacuum induction melting is 1531°C, the melting time is 3.8h, and the pouring temperature is 1485°C; Fe, Co, Ni, Cr, and C elements are first charged into a furnace for melting, and Nb element is added during the refining period, and the refining period is 30min before and after the addition of Nb element; Al, Ti, and Si elements are added after the refining period, and the power is turned off before the addition; B is added in the form of a B-Fe master alloy in the later stage of alloying, and argon gas is filled when it is added, and the gas pressure of argon gas is higher than the vapor pressure of B;

[0026] (2) Multi-channel rapid diffusion annealing process: The ingot is subjected to a single tempering free forging to break up the dendrites and primary Laves phase and introduce a large number of diffusion channels. The forging temperature of the single tempering free forging is 1040°C, the deformation per pass is 41.5%, and the surface temperature is lower than 800°C for reheating to prevent the surface cracking of the ingot. Then it is heated to 1190°C and kept for 12 hours before cooling to reduce the size and amount of the primary segregation phase, providing favorable conditions for the subsequent precipitation of the secondary phase, ensuring that the rod has excellent strength and notch sensitivity resistance, while reducing the oxidation loss of the alloy rod. The cooling method is air cooling;

[0027] (3) Multi-fire upsetting and drawing process: The upsetting and drawing temperature is 1035℃, and the deformation per pass is 60% to improve the density of the alloy rod, increase the precipitation density of the secondary phase at the grain boundary and improve the strength of the rod; the surface temperature is lower than 800℃ and then reheated to prevent cracking on the surface of the ingot, and then air-cooled; the number of upsetting and drawing times is 4 times, the upsetting deformation is 20%, and the drawing deformation is 25%.

[0028] (4) Standard heat treatment process: heat the forged rod to 1093℃ and keep it for 1h, then air cool it to release the residual stress and avoid the precipitation of needle-like phase; then heat the rod to 720℃ and keep it for 8h, then furnace cool it to 620℃ and keep it for 8h, then air cool it to promote the full precipitation of the intragranular strengthening phase γ' phase to ensure that the alloy has high strength, as well as the dispersed precipitation of the secondary phase at the grain boundary to ensure that the alloy is not notch sensitive and has high plasticity.

[0029] After the alloy rod is prepared by the above process, the grain structure and precipitation phase are uniform. Figure 1 The area percentage of the primary Laves phase is 3.61%, the average size is 3.22μm, the average size of the secondary Laves phase is 0.81μm, the average grain size is 25.28μm, and the comprehensive performance is excellent, that is, there is no notch sensitivity, the notch endurance life is 100.3h, the room temperature yield strength is 932MPa, the elongation is 22%, the 650℃ yield strength is 827MPa, and the elongation is 26%.

[0030] Example 2

[0031] The present embodiment provides a method for preparing a Fe-Ni-Co based low expansion high temperature alloy rod, wherein the chemical composition and mass percentage of the alloy rod are: Ni: 25.50%, Co: 30.00%, Nb: 4.80%, Ti: 0.82%, Si: 0.25%, P: 0.003%, C: 0.0075%, B: 0.0060%, Al: 0.45%, Cr: 5.27%, and the balance is Fe and unavoidable impurities;

[0032] The steps include:

[0033] (1) The alloy rod is subjected to a VIM smelting process to obtain an ingot, the refining temperature of the vacuum induction melting is 1520°C, the melting time is 4 hours, and the pouring temperature is 1500°C; Fe, Co, Ni, Cr, and C elements are first charged into a furnace for melting, and Nb element is added during the refining period, and the refining time before and after the addition of Nb element is 30 minutes; Al, Ti, and Si elements are added after the refining period, and the power is turned off before the addition; B is added in the form of a B-Fe master alloy in the later stage of alloying, and argon gas is filled when it is added, and the gas pressure of argon gas is higher than the vapor pressure of B;

[0034] (2) Multi-channel rapid diffusion annealing process: The ingot is subjected to a single tempering free forging to break up the dendrites and primary Laves phase and introduce a large number of diffusion channels. The forging temperature of the single tempering free forging is 1045°C, the deformation amount per pass is 42%, and the surface temperature is lower than 800°C before being returned to the furnace for heating. It is then heated to 1190°C and kept at this temperature for 15 hours, and then air-cooled.

[0035] (3) Multi-fire upsetting and drawing process: the upsetting and drawing temperature is 1055℃, the deformation per pass is 66%, the surface temperature is lower than 800℃, the steel is reheated in the furnace, and then air-cooled; the number of upsetting and drawing times is 3 times, the upsetting deformation is 31%, and the drawing deformation is 43%.

[0036] (4) Standard heat treatment process: heat the forged bar to 1093℃ and keep it for 1 hour, air cool it, then heat the bar to 720℃ and keep it for 8 hours, then furnace cool it to 620℃ and keep it for 8 hours, and air cool it.

[0037] After the alloy rod is prepared by the above process, the grain structure and precipitation phase are uniform, the area percentage of the primary Laves phase is 3.45%, the average size is 3.05μm, the average size of the secondary Laves phase is 0.82μm, and the average grain size is 28.32μm. The comprehensive performance is excellent, that is, there is no notch sensitivity, the notch endurance life is 108.3h, the room temperature yield strength is 946MPa, the elongation is 20%, the 650℃ yield strength is higher than 831MPa, and the elongation is 24%.

[0038] Example 3

[0039] The present embodiment provides a method for preparing a Fe-Ni-Co based low expansion high temperature alloy rod, wherein the chemical composition and mass percentage of the alloy rod are: Ni: 24.42%, Co: 28.98%, Nb: 4.82%, Ti: 0.84%, Si: 0.26%, P: 0.002%, C: 0.0073%, B: 0.0059%, Al: 0.30%, Cr: 5.46%, and the balance is Fe and unavoidable impurities;

[0040] The steps include:

[0041] (1) The alloy rod is subjected to a VIM smelting process to obtain an ingot, the refining temperature of the vacuum induction melting is 1528°C, the melting time is 3.4h, and the pouring temperature is 1490°C; Fe, Co, Ni, Cr, and C elements are first charged into a furnace for melting, and Nb element is added during the refining period, and the refining period is 30min before and after the addition of Nb element; Al, Ti, and Si elements are added after the refining period, and the power is turned off before the addition; B is added in the form of a B-Fe master alloy in the later stage of alloying, and argon is filled when it is added, and the gas pressure of argon is higher than the vapor pressure of B;

[0042] (2) Multi-channel rapid diffusion annealing process: The ingot is subjected to a single tempering free forging to break up the dendrites and primary Laves phase and introduce a large number of diffusion channels. The forging temperature of the single tempering free forging is 1060°C, the deformation per pass is 46%, the surface temperature is lower than 800°C, it is returned to the furnace for heating, and then it is heated to 1190°C and kept warm for 18 hours, and then air-cooled; (3) Multi-fire upsetting process: The upsetting temperature is 1050°C, the deformation per pass is 65%, the surface temperature is lower than 800°C, it is returned to the furnace for heating, and then air-cooled; the number of upsetting times is 3 times, the upsetting deformation is 27%, and the drawing deformation is 38%.

[0043] (4) Standard heat treatment process: heat the forged bar to 1093℃ and keep it for 1 hour, air cool it, then heat the bar to 720℃ and keep it for 8 hours, then furnace cool it to 620℃ and keep it for 8 hours, and air cool it.

[0044] After the alloy rod is prepared by the above process, the grain structure and precipitation phase are uniform, the area percentage of the primary Laves phase is 3.21%, the average size is 2.98μm, the average size of the secondary Laves is 0.82μm, the average grain size is 34.12μm, and the comprehensive performance is excellent, that is, there is no notch sensitivity, the notch endurance life is 114.7h, the room temperature yield strength is 964MPa, the elongation is 19.5%, the 650℃ yield strength is 860MPa, and the elongation is 23%.

[0045] Example 4

[0046] The present embodiment provides a method for preparing a Fe-Ni-Co based low expansion high temperature alloy rod, wherein the chemical composition and mass percentage of the alloy rod are: Ni: 25.16%, Co: 29.79%, Nb: 4.93%, Ti: 0.89%, Si: 0.20%, P: 0.003%, C: 0.0076%, B: 0.0061%, Al: 0.53%, Cr: 5.53%, and the balance is Fe and unavoidable impurities;

[0047] The steps include:

[0048] (1) The alloy rod is subjected to a VIM smelting process to obtain an ingot, the refining temperature of the vacuum induction melting is 1534°C, the melting time is 4 hours, and the pouring temperature is 1498°C; Fe, Co, Ni, Cr, and C elements are first charged into a furnace for melting, and Nb element is added during the refining period, and the refining period is 30 minutes before and after the addition of Nb element; Al, Ti, and Si elements are added after the refining period, and the power is turned off before the addition; B is added in the form of a B-Fe master alloy in the later stage of alloying, and argon is filled when it is added, and the gas pressure of argon is higher than the vapor pressure of B;

[0049] (2) Multi-channel rapid diffusion annealing process: The ingot is subjected to a single tempering free forging to break up the dendrites and primary Laves phase and introduce a large number of diffusion channels. The forging temperature of the single tempering free forging is 1055°C, the deformation amount per pass is 44.5%, and the surface temperature is lower than 800°C before being returned to the furnace for heating. It is then heated to 1190°C and kept at this temperature for 21 hours, and then air-cooled.

[0050] (3) Multi-fire upsetting and drawing process: the upsetting and drawing temperature is 1045℃, the deformation per pass is 63%, the surface temperature is lower than 800℃, the steel is reheated in the furnace, and then air-cooled; the number of upsetting and drawing is 4 times, the upsetting deformation is 23%, and the drawing deformation is 33%.

[0051] (4) Standard heat treatment process: heat the forged bar to 1093℃ and keep it for 1 hour, air cool it, then heat the bar to 720℃ and keep it for 8 hours, then furnace cool it to 620℃ and keep it for 8 hours, and air cool it.

[0052] After the alloy rod is prepared by the above process, the grain structure and precipitation phase are uniform, the area percentage of the primary Laves phase is 2.83%, the average size is 2.73μm, the average size of the secondary Laves is 0.84μm, the average grain size is 41.44μm, and the comprehensive performance is excellent, that is, there is no notch sensitivity, the notch endurance life is 132h, the room temperature yield strength is 970MPa, the elongation is 19.25%, the 650℃ yield strength is higher than 858MPa, and the elongation is 22.5%.

[0053] Example 5

[0054] The present embodiment provides a method for preparing a Fe-Ni-Co based low expansion high temperature alloy rod, wherein the chemical composition and mass percentage of the alloy rod are: Ni: 23.50%, Co: 28.00%, Nb: 5.20%, Ti: 1.00%, Si: 0.3%, P: 0.005%, C: 0.0075%, B: 0.0050%, Al: 0.6%, Cr: 6.0%, and the balance is Fe and unavoidable impurities;

[0055] The steps include:

[0056] (1) The alloy rod is subjected to a VIM smelting process to obtain an ingot, the refining temperature of the vacuum induction melting is 1525°C, the melting time is 3.2h, and the pouring temperature is 1489°C; Fe, Co, Ni, Cr, and C elements are first charged into a furnace for melting, and Nb element is added during the refining period, and the refining period is 30min before and after the addition of Nb element; Al, Ti, and Si elements are added after the refining period, and the power is turned off before the addition; B is added in the form of a B-Fe master alloy in the later stage of alloying, and argon gas is filled when it is added, and the gas pressure of argon gas is higher than the vapor pressure of B;

[0057] (2) Multi-channel rapid diffusion annealing process: The ingot is subjected to a single tempering free forging to break up the dendrites and primary Laves phase and introduce a large number of diffusion channels. The forging temperature of the single tempering free forging is 1050°C, the deformation per pass is 43%, the surface temperature is lower than 800°C, it is returned to the furnace for heating, and then it is heated to 1190°C and kept warm for 24 hours, and then air-cooled; (3) Multi-fire upsetting process: The upsetting temperature is 1100°C, the deformation per pass is 70%, the surface temperature is lower than 800°C, it is returned to the furnace for heating, and then air-cooled; the number of upsetting times is 3 times, the upsetting deformation is 35%, and the drawing deformation is 45%.

[0058] (4) Standard heat treatment process: heat the forged bar to 1093℃ and keep it for 1 hour, air cool it, then heat the bar to 720℃ and keep it for 8 hours, then furnace cool it to 620℃ and keep it for 8 hours, and air cool it.

[0059] After the alloy rod is prepared by the above process, the grain structure and precipitation phase are uniform. Figure 2 The area percentage of the primary Laves phase is 2.53%, the average size is 2.69μm, the average size of the secondary Laves phase is 0.85μm, the average grain size is 56.23μm, and the comprehensive performance is excellent, that is, there is no notch sensitivity, the notch endurance life is 156h, the room temperature yield strength is 985MPa, the elongation is 18.5%, the 650℃ yield strength is higher than 877MPa, and the elongation is 21.5%.

[0060] 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 with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Fe-Ni-Co based low expansion high temperature alloy rod, characterized in that: Its chemical composition and mass percentage are: Ni: 23.50%-25.50%, Co: 28.00%-30.00%, Nb: 4.50-5.20%, Ti: 0.7%-1.00%, Si: 0.20%-0.30%, P: ≤0.015%, C: ≤0.05%, B: ≤0.010%, Al: 0.30%-0.60%, Cr: 5.00%-6.00%, and the balance is Fe and unavoidable impurities; the alloy rod The area percentage of the primary Laves phase of the material is 2.53% to 3.61%, the average size is 2.69μm to 3.22μm, the average size of the secondary Laves phase is 0.81μm to 0.85μm, and the average grain size is 25.28μm to 56.23μm; there is no notch sensitivity, the notch endurance life is higher than 100h, the room temperature yield strength is higher than 900MPa, the elongation is higher than 18%, the 650℃ yield strength is higher than 815MPa, and the elongation is higher than 20%.

2. The method for preparing the Fe-Ni-Co based low expansion high temperature alloy rod according to claim 1, characterized in that: The steps include: (1) After VIM smelting process, an ingot is obtained, the refining temperature of vacuum induction melting is 1520°C to 1535°C, the melting time is 3 to 4 hours, and the pouring temperature is 1485°C to 1500°C; (2) Multi-channel rapid diffusion annealing process: The ingot is subjected to a single tempering free forging to break up the dendrites and primary Laves phase and introduce a large number of diffusion channels, and then heated to 1180-1200 °C and kept at this temperature for 10-30 h; (3) Upsetting and drawing process: The upsetting and drawing temperature is 1035-1100℃, and the deformation amount per pass is >50% to improve the density of the alloy rod and obtain a rod with 7-8 grains, increase the precipitation density of the secondary phase at the grain boundary and improve the strength of the rod; the surface temperature is lower than 800℃ and then heated in the furnace and then air cooled; (4) Standard heat treatment process: heat the forged bar to 1090-1100℃ and keep it for 0.5-2h, air cool, then heat to 710-730℃ and keep it for 5-10h, cool to 610-630℃ and keep it for 5-10h, air cool.

3. The preparation method according to claim 2, characterized in that: In step (1), Fe, Co, Ni, Cr and C elements are first charged into a furnace for melting, Nb element is added during the refining period, and refining is required for more than 30 minutes before and after the addition of Nb element; Al, Ti and Si elements are added after the refining period, and the power is turned off before addition; B is added in the form of B-Fe intermediate alloy in the later stage of alloying, and argon gas is filled when it is added, and the gas pressure of argon gas is higher than the vapor pressure of B.

4. The preparation method according to claim 2, characterized in that: The forging temperature of the free forging with one tempering in step (2) is 1040-1060° C., the deformation amount per pass is ≥40%, and the surface temperature is lower than 800° C. for reheating.

5. The preparation method according to claim 2, characterized in that: In step (2), the heating temperature is controlled at 1189-1195° C., and the insulation time is controlled at 12-24 h.

6. The preparation method according to claim 2, characterized in that: The number of upsetting and drawing in step (3) is 3 to 4 times, the upsetting deformation is 20 to 35%, and the drawing deformation is 25 to 45%.

7. The preparation method according to claim 2, characterized in that: The specific process of step (4) is: heating the forged rod to 1093°C and keeping it at that temperature for 1 hour, air cooling, then heating it to 720°C and keeping it at that temperature for 8 hours, cooling it to 620°C with the furnace and keeping it at that temperature for 8 hours, and air cooling it.

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