CN112662974A - Heat treatment method of TC21 alloy forging - Google Patents
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Abstract
The invention belongs to the technical field of metal heat treatment, and discloses a heat treatment method of a TC21 alloy forging, which comprises the following steps: the first step is as follows: primary annealing: heating the TC21 alloy forging to 910 ℃, preserving the heat for a period of time, and then discharging the TC21 alloy forging within 2min to perform scattered air cooling or air cooling; the second step is that: secondary annealing: and heating the TC21 alloy forging to 560-580 ℃, preserving the heat for a period of time, and discharging from the furnace for air cooling. The heat treatment method for the TC21 alloy forging provided by the invention can obtain higher strength, plasticity and fracture toughness meeting the standard requirements, has a simple and stable process and convenient operation, and is suitable for industrial production.
Description
Technical Field
The invention belongs to the technical field of metal heat treatment, and particularly relates to a heat treatment method of a TC21 alloy forging.
Background
In order to adapt to the durability/damage tolerance design of an airplane structure, TC21 damage tolerance type titanium alloy is researched and developed domestically so as to meet the requirements of the airplane structural member on the static strength and the fatigue performance of damaged materials. The TC21 titanium alloy has stable mechanical property, good matching of strength, plasticity and fracture toughness, and is a high-strength high-toughness titanium alloy with wide application prospect.
The TC21 alloy is subjected to beta forging and then is subjected to double annealing heat treatment, so that the good matching of strength, plasticity and fracture toughness can be achieved; however, in actual production, the situation of insufficient strength or insufficient plasticity is often encountered, and detailed analysis is made on the influence of the primary annealing temperature of heat treatment and the like on the performance of the TC21 alloy forging in documents, but no systematic discussion is made on the influence of the cooling speed of forgings with different thicknesses after primary annealing and the influence of different secondary annealing temperatures on the comprehensive performance of the TC21 alloy forging, and the invention provides a heat treatment method to specifically stipulate the primary annealing and secondary annealing processes so as to improve the comprehensive mechanical property of the TC21 alloy forging.
The current specifications determine the parameters of the double annealing heat treatment as follows: primary annealing: 60-80 ℃ below the beta transformation point; secondary annealing: 500 to 650 ℃. The technical indexes are that when the effective thickness is less than or equal to 75 mm: the tensile strength is more than or equal to 1100MPa, the yield strength is more than or equal to 1000MPa, the elongation is more than or equal to 8/6%, and the reduction of area is more than or equal to 15/10%; when the effective thickness is more than 75-150 mm: the tensile strength is more than or equal to 1070MPa, the yield strength is more than or equal to 970MPa, the elongation is more than or equal to 8/6/5%, and the reduction of area is more than or equal to 15/10/10%; effective thickness is more than 150 mm: the tensile strength is more than or equal to 1030MPa, the yield strength is more than or equal to 930MPa, the elongation is more than or equal to 8/6/5%, and the reduction of area is more than or equal to 15/10/10%. The requirement of fracture toughness is more than or equal to 70 MPa.m 1/2.
Through tests and trial production, the effective thickness of the TC21 alloy forging is less than or equal to 75mm and more than 150mm, and the situation that the tensile strength is not qualified is easy to occur. When the effective thickness is 75-150 mm, the strength of the free forging is unqualified easily, and the elongation and the reduction of area are unqualified easily during die forging.
Disclosure of Invention
The invention provides a heat treatment method for improving the comprehensive mechanical property of a TC21 alloy forging, the TC21 alloy forging processed by the method has a microstructure meeting requirements, has higher strength, obtains a plasticity index meeting the requirements and high fracture toughness, and solves the problem that the performance in the prior art can not meet the standard requirements.
A heat treatment method of a TC21 alloy forging comprises the following steps:
the method comprises the following steps: primary annealing, heating the TC21 alloy forging to 910 ℃, preserving heat, and carrying out air cooling or scattered air cooling on the TC21 alloy forging after the heat preservation is finished;
step two: and (4) secondary annealing, namely heating the TC21 alloy forging to 560-580 ℃, preserving heat, and cooling in air after the heat preservation is finished.
Further, in the first step, when the thickness of the forged piece is less than or equal to 50mm, the one-time annealing heat preservation time is equal to the effective thickness multiplied by 0.5min/mm +1 h; when the thickness of the forged piece is larger than 50mm, the one-time annealing heat preservation time is equal to the effective thickness multiplied by 0.5min/mm +/2 h.
Further, in the second step, the secondary annealing and heat preservation time is equal to the effective thickness x (0.8 min/mm-1 min/mm) +240 min.
Further, in the first step, the time from one-time annealing discharging to cooling transfer does not exceed 120 s.
Further, in the first step, the TC21 alloy forging with the effective thickness not more than 75mm is subjected to primary annealing and then is cooled by air blowing.
Further, in the first step, TC21 die forgings with the effective thickness of 75 mm-150 mm are subjected to primary annealing and then dispersed for air cooling; and (3) performing primary annealing on the TC21 free forging with the effective thickness of 75-150 mm, and then cooling by blowing.
Further, in the step one, the TC21 alloy forging with the effective thickness exceeding 150mm is cooled by air blowing after primary annealing.
Further, in the second step, the secondary annealing and heat preservation time is equal to the effective thickness x (0.8 min/mm-1 min/mm) +240 min. .
The invention has the beneficial effects that:
the method provided by the invention has the advantages that the influence of parameters such as heating temperature, heat preservation time and cooling mode of heat treatment on the alloy structure and performance is comprehensively considered, the dual annealing heat treatment process parameters of the TC21 alloy forging are specified, the alloy can obtain higher strength, plasticity and fracture toughness meeting the standard requirements through parameter control, the process is simple and stable, the operation is convenient, and the method is suitable for industrial production.
Drawings
FIG. 1 shows the performance rule of TC21 alloy forgings along with the change of secondary annealing temperature;
FIG. 2 is a schematic representation of the microstructure of an example TC21 alloy forging after double annealing;
FIG. 3 is a schematic view of the microstructure of an example dual TC21 alloy forging after dual annealing.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A heat treatment method for improving comprehensive mechanical properties of a TC21 alloy forging comprises the following steps:
the first step is as follows: primary annealing:
heating the TC21 alloy forging to 910 ℃, preserving the heat for a period of time, and then discharging the TC21 alloy forging within 2min to perform scattered air cooling or air cooling;
the second step is that: and (5) secondary annealing.
And heating the TC21 alloy forging to 560-580 ℃, preserving the heat for a period of time, and discharging from the furnace for air cooling.
Optionally, the one-time annealing heat preservation time is equal to the effective thickness multiplied by 0.5+1h (the thickness is less than or equal to 50mm)/2h (the thickness is more than 50 mm).
Optionally, the secondary annealing and heat preservation time is equal to the effective thickness x (0.8-1) +240 min. And (4) the following steps.
Optionally, the larger the effective thickness of the TC21 alloy forging is, the longer the primary annealing heat preservation time or the secondary annealing heat preservation time is.
Optionally, the TC21 forge piece is subjected to scattered air cooling or air blowing cooling within 2min after primary annealing and discharging.
Optionally, the starting of air cooling or air blowing cooling of the TC21 alloy forging includes:
when the effective thickness of the TC21 alloy forging is less than or equal to 75mm, air blowing is adopted;
when the effective thickness of the TC21 alloy forging is 75-150 mm, if the forging is a die forging, scattered air cooling is adopted, and if the forging is a free forging, air cooling is adopted;
and when the effective thickness of the TC21 alloy forging is larger than 150mm, adopting air blowing and cooling.
Optionally, the secondary annealing includes:
and heating the TC21 alloy forging cooled to room temperature by air cooling or air blowing to 560-580 ℃, and keeping the effective thickness x (0.8-1) +240 min. Air cooling to room temperature; the room temperature is less than or equal to 40 ℃.
Principle of forging
1) The higher annealing temperature 910 ℃ is selected in the primary annealing, the higher room-temperature tensile strength and high-temperature tensile strength can be obtained at the temperature, and the elongation and the reduction of area are slightly reduced because for alpha + beta type dual-phase titanium alloy, the transformation beta relative strength in the alloy plays a role, the primary alpha phase mainly plays a role in plasticity, the primary annealing is high, more metastable beta phases can be obtained, and a larger driving force is provided for the subsequent precipitation of the secondary alpha phase, so that the purpose of improving the strength of the forging is achieved, and the quantity of the primary alpha phase can also meet the requirement on plasticity. However, the solid solution temperature should not exceed 915 deg.C, otherwise the elongation rate has no margin basically. Therefore, the primary annealing temperature is 910 ℃, and the specific test data are shown in Table 1.
2) The cooling mode after primary annealing heat preservation is to carry out the cooling of different modes to the forging of different thickness, guarantees that the whole cooling rate of forging satisfies the performance requirement, in the cooling process, appears beta → alpha and changes, because the grain boundary has higher energy, alpha crystal nucleus is preferred to be formed in grain boundary department, grows along certain direction by the grain boundary to the crystalline interior, and the continuous longitudinal growth of alpha piece of different directions is until meeting with other alpha pieces, forms different alpha and restraints promptly. The larger the cooling speed, the more nucleation positions are, the finer the alpha sheet layer is, the more complex the growth direction of the alpha sheet layer is, the smaller the cluster size formed by the alpha sheet layers in different directions is, and the higher the strength is. The method can ensure that forgings with different thicknesses can generate small alpha sheet layer thickness and alpha bundling size so as to obtain higher tensile strength. Therefore, higher strength can be obtained by air cooling than by air cooling, but the plasticity is slightly reduced. The test data of air cooling and air cooling after the primary annealing are shown in Table 2.
When the effective thickness of the TC21 alloy forging is larger than or equal to 75mm, the standard requirement of the forging is high, and air blowing and cooling are required to be adopted to meet the high strength requirement no matter the die forging or the free forging.
When the effective thickness of the TC21 alloy forging is 75-150 mm, the forging strength standard is reduced to 1070MPa from 1100MPa, the free forging is forged by a press, the deformation process is slow, the temperature rise is small, the structure is fine, the plasticity is good, so the strength of the forging is ensured by air cooling after primary annealing, the die forging is forged by a counter-blow hammer, the deformation process is fast, the temperature rise is large, the structure is coarse, the plasticity is poor, the strength is too high if air cooling is adopted after primary annealing, the elongation and the section shrinkage are unqualified, and the air cooling is needed to be adopted after primary annealing of the die forging to meet the comprehensive requirements of the strength and the plasticity.
When the effective thickness of the TC21 alloy forging is more than 150mm, the strength standard of the forging is reduced to 1030MPa, but the thick size of the forging still needs air cooling to meet the comprehensive requirements of strength and plasticity.
3) The secondary annealing temperature is selected to be 560-580 ℃, the purpose is to generate a short flaky secondary alpha phase on a metastable beta phase matrix, the structure performance is stabilized, the stress is eliminated, a fine dispersion second phase with strong strengthening effect in the titanium alloy just has negative influence on the improvement of plasticity, otherwise, a coarse dispersion second phase plays a certain positive role on the plasticity, so the secondary annealing temperature is selected to be 560-580 ℃, the temperature is too low, the fine dispersion second phase has a good effect on the front strength, but is unfavorable to the plasticity, the temperature is too high, and the coarse dispersion second phase has a bad effect on the strength; comprehensively considering, the alloy performance can be influenced by adjusting the microstructure at 560-580 ℃. The curve variation law is shown in figure 1.
TABLE 1
TABLE 2
Example one
FIG. 2 is a schematic view of the microstructure of TC21 alloy forgings in different cooling manners after primary annealing according to an embodiment of the invention; in the embodiment, a TC21 alloy free forging with the external dimension of 1040 multiplied by 280 multiplied by 85 is adopted, the effective thickness of the forging is 85mm, the forging state microstructure is a basket structure, the phase transformation point is 976 ℃, the alloy is heated to 910 ℃ in the first step, the temperature is kept for 150min, then the forging is dispersed for air cooling within 2min, the forging is heated to 560 ℃ in the second step, the temperature is kept for 240min, and the forging is air cooled.
The room temperature mechanical property parameters of the TC21 alloy forging after the treatment of the embodiment are shown in the following table 3, and the microstructure is shown in FIG. 2. And 20 μm represents a magnification of 500 times.
TABLE 3
Example two
Fig. 3 is a schematic microstructure diagram of a TC21 alloy forged piece after heat treatment according to another embodiment of the present invention, in this embodiment, a TC21 alloy forged piece with an external dimension of 1170 × 260 × 190 is adopted, an effective thickness is 190mm, the forged piece is a thick forged piece, a forging state is a basket structure, a transformation point is 973 ℃, the alloy is heated 910 ℃ in a first step, heat is preserved for 150min, due to the thick dimension, air cooling is selectively dispersed, and the forged piece is heated to 560 ℃, heat is preserved for 360min, and air cooling is performed.
The room temperature mechanical property parameters of the TC21 alloy forging after the treatment of the embodiment are shown in the following table 4, and the microstructure is shown in FIG. 3. And 20 μm represents a magnification of 500 times.
TABLE 4
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive various equivalent modifications or substitutions within the technical scope of the present invention, and these modifications or substitutions should be covered within the scope of the present invention.
Claims (8)
1. A heat treatment method of a TC21 alloy forging is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: primary annealing, heating the TC21 alloy forging to 910 ℃, preserving heat, and carrying out air cooling or scattered air cooling on the TC21 alloy forging after the heat preservation is finished;
step two: and (4) secondary annealing, namely heating the TC21 alloy forging to 560-580 ℃, preserving heat, and cooling in air after the heat preservation is finished.
2. The heat treatment method of the TC21 alloy forging of claim 1, wherein: in the first step, when the thickness of the forged piece is less than or equal to 50mm, the one-time annealing heat preservation time is equal to the effective thickness multiplied by 0.5min/mm +1 h;
when the thickness of the forged piece is larger than 50mm, the one-time annealing heat preservation time is equal to the effective thickness multiplied by 0.5min/mm +/2 h.
3. The heat treatment method of the TC21 alloy forging of claim 1, wherein: in the second step, the secondary annealing and heat preservation time is equal to the effective thickness x (0.8 min/mm-1 min/mm) +240 min.
4. The heat treatment method of the TC21 alloy forging of claim 1, wherein: in the first step, the time from one-time annealing discharging to cooling transfer does not exceed 120 s.
5. The heat treatment method of the TC21 alloy forging of claim 1, wherein: in the first step, the TC21 alloy forging with the effective thickness not more than 75mm is subjected to primary annealing and then is cooled by blowing air.
6. The heat treatment method of the TC21 alloy forging of claim 1, wherein: in the first step, TC21 die forgings with the effective thickness of 75 mm-150 mm are subjected to primary annealing and then dispersed for air cooling; and (3) performing primary annealing on the TC21 free forging with the effective thickness of 75-150 mm, and then cooling by blowing.
7. The heat treatment method of the TC21 alloy forging of claim 1, wherein: in the first step, the TC21 alloy forging with the effective thickness of more than 150mm is subjected to primary annealing and then is cooled by blowing air.
8. The heat treatment method of the TC21 alloy forging of claim 1, wherein: in the second step, the secondary annealing and heat preservation time is equal to the effective thickness x (0.8 min/mm-1 min/mm) +240 min.
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| CN114606455A (en) * | 2022-05-11 | 2022-06-10 | 北京煜鼎增材制造研究院有限公司 | Spray type heat treatment method for large titanium alloy component |
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| CN117926157A (en) * | 2023-12-28 | 2024-04-26 | 中国第二重型机械集团德阳万航模锻有限责任公司 | Microstructure control method in heat treatment cooling process of TC21 titanium alloy die forging |
| CN118222955A (en) * | 2023-12-28 | 2024-06-21 | 中国第二重型机械集团德阳万航模锻有限责任公司 | Microstructure control method of high-strength and high-toughness TC21 titanium alloy oversized rim strip die forging |
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