A method for producing a high-temperature alloy rod having high density and uniformly distributed grains

Abstract

The application discloses a method for preparing a high-temperature alloy rod with high compactness and uniformly distributed grains, and belongs to the technical field of high-temperature alloy rod processing. The application finds a hole closure interval by studying Thermo-Span low-expansion high-temperature alloy hot deformation parameters, makes the holes closed through high-temperature large deformation, makes the rod fully recrystallized through multi-fire free forging, obtains a uniform equiaxed fine-grain structure, and the grain size is 7-8 levels, which provides a nucleation position for subsequent secondary phase precipitation and contributes to the strengthening alloy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature alloy rod processing, and particularly relates to a method for preparing high-temperature alloy rods with high density and uniformly distributed grains. BACKGROUND

[0002] With the increase of the service temperature of an aero-engine, the aero-engine material, i.e., a high-temperature alloy, is required to have higher high-temperature strength and endurance life. In order to improve the high-temperature strength of the high-temperature alloy, a material designer adds many strengthening elements to the high-temperature alloy. High alloying brings about serious segregation and a large amount of precipitation of harmful phases, which significantly reduces the hot working and mechanical properties of the alloy, and thus long-time high-temperature diffusion annealing is needed to eliminate element segregation and segregation phases. However, some high-temperature alloys have less addition of anti-oxidation elements such as Al, Cr and Si elements, and the oxidation loss is serious during long-time high-temperature diffusion annealing. In order to reduce the oxidation loss and alleviate the segregation, a pre-deformation treatment is usually added before high-temperature diffusion annealing, aiming to introduce a large number of rapid diffusion channels (dislocations, grain boundaries, vacancies, etc.) to promote element diffusion. However, although this method can quickly eliminate segregation and reduce the oxidation loss of the alloy, due to the Kirkendall effect, more pores are left in the alloy matrix. The pores are crack nucleation points and crack propagation sources, which lead to the reduction of the performance of the alloy rod and the failure to meet the delivery standard. SUMMARY

[0003] In view of this, the purpose of the present application is to provide a method for preparing high-temperature alloy rods with high density and uniformly distributed grains. The present application finds a pore closure interval by studying the hot deformation parameters of Thermo-Span low-expansion high-temperature alloy, closes the pores through high-temperature large deformation, and makes the rod fully recrystallize through multi-fire free forging to obtain a uniform equiaxed fine-grained structure, thereby providing nucleation sites for subsequent secondary phase precipitation and contributing to the strengthening of the alloy.

[0004] The purpose of the present application is achieved by the following means:

[0005] The present application provides a method for preparing high-temperature alloy rods with high rod density and uniformly distributed grains, comprising the following steps:

[0006] (1) After the VIM smelting process, a cast ingot is obtained. The refining temperature of vacuum induction melting is 1520-1535 DEG C to ensure that the raw materials can be melted and the crucible can be prevented from increasing oxygen. The melting time is 3-4 h 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 DEG C to ensure the fluidity of the liquid metal during pouring;

[0007] (2) multi-channel fast diffusion annealing process: the ingot is once tempered free forging to break the dendrite and primary Laves phase, and introduce a large number of diffusion channels, and then heated to 1180-1200℃ and kept for 10-30h;

[0008] (3) the obtained rod is subjected to hot working simulation test, the deformed structure is analyzed, the hot working interval of hole closure and the hot working interval of recrystallization are determined, and the forging process is determined in combination with the hot working interval of hole closure and the hot working interval of recrystallization.

[0009] Based on the above technical scheme, further, the chemical composition and mass percentage of the high-temperature alloy rod 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.

[0010] Based on the above technical scheme, further, in step (1), Fe, Co, Ni and Cr elements have high oxygen partial pressure and are relatively difficult to oxidize, and have high melting points, so they are first charged into the furnace and melted, and the charging needs to be loose at the top and tight at the bottom; C element is added in the early stage of smelting to achieve the best effect of removing O and N elements; Nb element is a strong nitrogen element, so it is added in the refining period, and the refining time before and after the addition of Nb element is more than 30 minutes, so as to fully remove O and N; Al, Ti and Si elements are added after the refining period to prevent burning loss, and need to be stopped before adding; since smelting is carried out in a vacuum environment, the vapor pressure of B is high and easy to volatilize, so argon gas needs to be filled when B is added, the gas pressure of argon gas needs to be higher than the vapor pressure of B, and B-Fe intermediate alloy is selected to be added in the late alloying period.

[0011] Based on the above technical scheme, further, in step (2), the forging temperature of the once tempered free forging is 1030-1060℃, the pass deformation is 40-45%, and the surface temperature is lower than 800℃ for reheat heating.

[0012] Based on the above technical scheme, further, in step (2), the heating temperature is controlled at 1189-1195℃, and the holding time is controlled at 12-24h.

[0013] Based on the above technical scheme, further, in step (3), the hot working simulation test is Gleeble hot compression test, the deformation temperature interval is 880℃-1130℃, the strain rate is 1s -1 ~ 10s -1The deformation amount is 30% to 60%, and the cooling mode is helium cooling.

[0014] According to the technical scheme, the forging process in step (3) is free forging, and two-time free forging is performed: in the first forging, the deformation temperature is 1030-1100 DEG C, the deformation amount is 75%-80%, and the surface temperature is lower than 800 DEG C tempering; in the second forging, the deformation temperature is 1030-1100 DEG C, the deformation amount is 60%-75%, and the surface temperature is lower than 800 DEG C tempering; in the third forging, the deformation temperature is 1030-1100 DEG C, the deformation amount is 45%-56%, and the surface temperature is lower than 800 DEG C tempering.

[0015] The present application has the following beneficial effects compared with the prior art:

[0016] The present application closes the holes through high-temperature large deformation, and makes the bar completely recrystallize through multi-time upsetting and drawing deformation to obtain uniform equiaxed fine grain structure, provides nucleation sites for subsequent secondary phase precipitation and contributes to strengthening the alloy, and improves the quality of the bar. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application, the drawings involved in the embodiments will be briefly introduced below.

[0018] Figure 1 The microstructure of a vacuum induction ingot alloy subjected to a multi-channel rapid diffusion annealing process at 880 DEG C for 1s -1 Hot compression cross-section microstructure under a 30% deformation process.

[0019] Figure 2 The microstructure of a vacuum induction ingot alloy subjected to a multi-channel rapid diffusion annealing process at 1130 DEG C for 1s -1 Hot compression cross-section microstructure under a 30% deformation process.

[0020] Figure 3 The microstructure of a vacuum induction ingot alloy subjected to a multi-channel rapid diffusion annealing process at 1130 DEG C for 1s -1 Hot compression cross-section microstructure under a 60% deformation process.

[0021] Figure 4 The microstructure of a vacuum induction ingot alloy subjected to a multi-channel rapid diffusion annealing process at 1130 DEG C for 10s -1 Hot compression cross-section microstructure under a 60% deformation process.

[0022] Figure 5 The microstructure of a vacuum induction ingot alloy subjected to a multi-channel rapid diffusion annealing process at 1130 DEG C for 10s

[0023] Figure 6Longitudinal section structure of the vacuum induction ingot after two heating times of free forging in Example 2 subjected to the multi-channel rapid diffusion annealing process. DETAILED DESCRIPTION

[0024] The application will be described in detail below with examples, but the embodiments of the application are not limited thereto. It is obvious that the examples described below are only some of the embodiments of the application, and other similar embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0025] Example 1

[0026] The present example provides a preparation of a vacuum induction ingot subjected to a vacuum induction melting and multi-channel rapid diffusion annealing process, the chemical composition and mass percentage of the vacuum induction ingot are as follows: Ni: 24.10%, Co: 28.56%, Nb: 4.93%, Ti: 0.87%, Si: 0.30%, Al: 0.45%, Cr: 5.32%, P: ≤0.005%, C: 0.0073%, B: 0.0063%, and the balance is Fe and inevitable impurities.

[0027] The method comprises the following steps:

[0028] (1) After the VIM smelting process, a cast ingot is obtained, the refining temperature of the vacuum induction melting is 1535℃, the melting time is 4h, and the pouring temperature is 1500℃; Fe, Co, Ni, Cr, and C elements are first melted in the furnace, Nb element is added during the refining period, and 30min of refining is required before and after the addition of Nb element; Al, Ti, and Si elements are added after the refining period and need to be stopped before the film is added; B is added in the form of B-Fe inter alloy in the alloying period, argon gas is filled when adding, and the argon gas pressure should be higher than the vapor pressure of B;

[0029] (2) Multi-channel rapid diffusion annealing process: the cast ingot is once tempered and free forged, the forging temperature of the once tempered free forging is 1040℃, the deformation amount of the pass is 41.5%, the surface temperature is lower than 800℃, and the ingot is reheated to prevent the surface cracking of the ingot, then the ingot is heated to 1190℃ and kept for 24h before cooling, and the cooling mode is air cooling;

[0030] The prepared vacuum induction ingot is processed into a standard Gleeble hot compression sample, and hot compression test is carried out at 880℃, 930℃, 980℃, 1030℃, 1080℃, and 1130℃ respectively after keeping for 5min, the strain rate is 1s -1 ~10s -1 , the deformation amount is 30%~60%, and the cooling mode is helium cooling.

[0031] Figures 1-4The hot compression section microstructure diagram under different temperature, strain rate and deformation amount. It can be seen from the diagram that under the condition of low temperature and small deformation amount, the hole size in the uniform deformation zone in the middle of the sample is large, while under the condition of high temperature and large deformation amount, the hole in the uniform deformation zone in the middle of the sample is hardly observed, which shows that high temperature and large deformation amount is beneficial to hole closure, and the effect of strain rate on hole closure is not obvious. According to statistics, under the experimental conditions, the alloy undergoes incomplete recrystallization, the recrystallization starts at 980℃, the higher the temperature, the larger the deformation amount, the higher the strain rate, the more easily the alloy recrystallizes. Therefore, in order to make the alloy rod completely recrystallize, it needs multiple high temperature and large deformation amount, and in order to prevent the recrystallized grains from growing too large, the deformation temperature should not be too high.

[0032] Example 2:

[0033] The vacuum induction ingot subjected to the multi-channel rapid diffusion annealing process in Example 1 is subjected to two times of free forging: the first time of forging, the deformation temperature is 1040℃, the deformation amount is 78%, and the surface temperature is lower than 800℃ tempering. The second time of forging, the deformation temperature is 1045℃, the deformation amount is 60%, and the surface temperature is lower than 800℃ tempering. The third time of forging, the deformation temperature is 1040℃, the deformation amount is 50%, and the surface temperature is lower than 800℃ tempering.

[0034] Figure 5 The microstructure of the vacuum induction ingot subjected to the multi-channel rapid diffusion annealing process. Figure 6 The forged state microstructure of the vacuum induction ingot subjected to the multi-channel rapid diffusion annealing process in this example after two times of free forging. By comparing Figure 5 and Figure 6 it can be seen that the vacuum induction ingot subjected to the multi-channel rapid diffusion annealing process has a large number of micron-sized holes distributed on the substrate, and after two times of free forging, the holes on the substrate are completely closed, and the rod has completely recrystallized, obtaining a uniform equiaxed fine grain structure, and the grain size is 7-8 grade.

[0035] Example 3:

[0036] The vacuum induction ingot subjected to the multi-channel rapid diffusion annealing process in Example 1 is subjected to two times of free forging: the first time of forging, the deformation temperature is 1035℃, the deformation amount is 75%, and the surface temperature is lower than 800℃ tempering. The second time of forging, the deformation temperature is 1030℃, the deformation amount is 60%, and the surface temperature is lower than 800℃ tempering. The third time of forging, the deformation temperature is 1030℃, the deformation amount is 45%, and the surface temperature is lower than 800℃ tempering.

[0037] Example 4:

[0038] The vacuum induction ingot subjected to the multi-pass rapid diffusion annealing process in Example 1 was subjected to two-pass free forging: the first pass was at a deformation temperature of 1050°C, a deformation of 80%, and tempering at a surface temperature of less than 800°C. The second pass was at a deformation temperature of 1060°C, a deformation of 69%, and tempering at a surface temperature of less than 800°C. The third pass was at a deformation temperature of 1055°C, a deformation of 53%, and tempering at a surface temperature of less than 800°C.

[0039] Example 5:

[0040] The vacuum induction ingot subjected to the multi-pass rapid diffusion annealing process in Example 1 was subjected to two-pass free forging: the first pass was at a deformation temperature of 1105°C, a deformation of 80%, and tempering at a surface temperature of less than 800°C. The second pass was at a deformation temperature of 1100°C, a deformation of 75%, and tempering at a surface temperature of less than 800°C. The third pass was at a deformation temperature of 1090°C, a deformation of 56%, and tempering at a surface temperature of less than 800°C.

[0041] Example 6:

[0042] The vacuum induction ingot subjected to the multi-pass rapid diffusion annealing process in Example 1 was subjected to two-pass free forging: the first pass was at a deformation temperature of 1100°C, a deformation of 76%, and tempering at a surface temperature of less than 800°C. The second pass was at a deformation temperature of 1100°C, a deformation of 73%, and tempering at a surface temperature of less than 800°C. The third pass was at a deformation temperature of 1100°C, a deformation of 51%, and tempering at a surface temperature of less than 800°C.

[0043] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art will understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent replacements to some or all of the technical features; and 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 application.

Claims

1. A method of producing a high temperature alloy bar having a high density and a uniform distribution of grains, characterized by, It comprises the following steps: (1) obtaining ingot through VIM smelting process, the refining temperature of vacuum induction melting is 1520-1535℃, the melting time is 3-4h, and the pouring temperature is 1485-1500℃; (2) multi-channel rapid diffusion annealing process: the ingot is once tempered and free forged to break the dendrite and primary Laves phase, and a large number of diffusion channels are introduced, then the ingot is heated to 1180-1200℃ and kept for 10-30h; (3) the obtained rod is subjected to hot working simulation test, the deformation structure is analyzed, the hot working interval of hole closure and the hot working interval of recrystallization are determined, and the forging process is determined in combination with the hot working interval of hole closure and the hot working interval of recrystallization; In step (1), Fe, Co, Ni, Cr and C elements are first loaded into the furnace and melted, Nb element is added during refining, and more than 30 minutes of refining is required before and after the addition of Nb element; Al, Ti and Si elements are added after the refining period and need to be stopped for film formation before addition; B is added in the form of B-Fe intermediate alloy in the later alloying period, argon gas is charged when adding, and the argon gas pressure should be higher than the vapor pressure of B; In step (2), the forging temperature of the once tempered free forging is 1030-1060℃, the pass deformation is 40-45%, and the surface temperature is lower than 800℃ for reheat heating; In step (3), the forging process is free forging, and two times of free forging are carried out: the first forging, the deformation temperature is 1030-1100℃, the deformation amount is 75%-80%, and the surface temperature is lower than 800℃ for tempering; the second forging, the deformation temperature is 1030-1100℃, the deformation amount is 60%-75%, and the surface temperature is lower than 800℃ for tempering; the third forging, the deformation temperature is 1030-1100℃, the deformation amount is 45%-56%, and the surface temperature is lower than 800℃ for tempering; The grain size grade of the high-temperature alloy rod is 7-8 grade.

2. The method of claim 1, wherein, The chemical composition and mass percentage of the high-temperature alloy rod are as follows: 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.

3. The method of claim 1, wherein, In step (2), the heating temperature is controlled at 1189-1195℃, and the holding time is controlled at 12-24h.

4. The method of claim 1, wherein, The thermal processing simulation test described in step (3) is a Gleeble thermal compression test, the deformation temperature range is 880°C to 1130°C, the strain rate is 1 s -1 ~ 10 s -1 , the deformation amount is 30% to 60%, and the cooling method is helium cooling.

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