A method for controlling β grains of TC21 titanium alloy thin web die forgings
By establishing the relationship between forging ratio and initial β grain size and grain growth model, the β grain size of TC21 titanium alloy thin web die forging is solved, and the problem of difficult control of β grain size during forging is realized, and the forging mechanics is achieved Performance stability and design requirements.
Patent Information
- Application Number
- CN202311172229.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-12
- Publication Date
- 2025-01-03
- Estimated Expiration
- 2043-09-12
AI Technical Summary
During the forging of aircraft structural parts, the β grain size of TC21 titanium alloy thin web die forging is difficult to effectively control, resulting in unstable mechanical properties, especially during the forging process, the cross-section has accumulated deformation, which affects fracture toughness and fatigue resistance. performance.
By establishing the forging relationship between TC21 titanium alloy in the two-phase region and the single-phase region, fit the expression of the forging ratio and the initial β grain size, and combining the grain growth kinetic model, the insulation time in the single-phase region is determined, Control the β grain size to ensure that the mechanical properties of the forging meet the requirements.
The controllable growth of the β grain size of TC21 titanium alloy thin web die forgings is achieved, ensuring the stable mechanical properties of the forgings, meeting design requirements, and improving the fracture toughness and fatigue resistance of the forgings.
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Figure CN117123708B_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of hot processing of nonferrous metals, and in particular to a method for controlling β grains of a TC21 titanium alloy thin web die forging. Background Art
[0002] TC21 titanium alloy is a damage tolerant titanium alloy. It is widely used in aircraft structural parts due to its good fracture toughness and fatigue crack resistance. Figure 1 As shown, titanium alloy has a phase transition point T β Temperature, at the phase transition point T β Temperature, there are two kinds of grains, α and β, in titanium alloy, so at the phase transition point T β The temperature is called the two-phase region; when the titanium alloy is heated to the phase transition point T β When the temperature rises, the α grains in the titanium alloy will transform into β grains, which makes the phase transition point T β When the temperature is high, only β grains exist in the titanium alloy, so at the phase transition point T β The temperature is called the single-phase zone. At present, the design thickness of some aircraft structural parts is relatively thin (the web thickness is 30-80mm). Such forgings usually use bars for billet making and die forging during the forging process. Therefore, there is a large cumulative deformation of the cross section, that is, the forging ratio is large, which makes the β grain size of the forging seriously broken. According to the metallurgy of titanium alloys, the β grain size of TC21 titanium alloy has an important influence on key mechanical indicators of forgings such as fracture toughness and cross-sectional shrinkage. Therefore, controlling the β grain size of thin web type TC21 titanium alloy die forgings is of great significance to the stability of the mechanical properties of the forgings. Summary of the invention
[0003] The technical problem to be solved by the present invention is to provide a method for controlling the beta grains of a TC21 titanium alloy thin web die forging, so as to control the beta grain size of the thin web type TC21 titanium alloy die forging and ensure the mechanical property requirements of the forging.
[0004] The technical solution adopted by the present invention to solve the technical problem is a method for controlling β grains of a TC21 titanium alloy thin web die forging, comprising the following steps:
[0005] S1: Establish the relationship between the forging ratio of TC21 forgings after forging in the two-phase region and the initial β grain size when heated in the single-phase region;
[0006] S11. Samples are taken from the core of TC21 titanium alloy die forgings at different forging ratios and heated to T β Above the temperature, the two-phase region structure is statically recrystallized to transform the α grains into the β grains. After the β grains are completely formed, water quenching is performed immediately, and the initial β grain size of forgings with different forging ratios is tested by metallographic method.
[0007] S12, the relationship between the fitting forging ratio and the initial β grain size is expressed as expression (1):
[0008] d=393-94.5x
[0009] Where d is the initial β grain size when static recrystallization is just completed, x is the forging ratio, x<4.15;
[0010] S2: Test the time-dependent change of β grain size when TC21 titanium alloy is heated in the single-phase region;
[0011] S21, TC21 titanium alloy in the single phase region β + Δt temperature for the first time, and then quickly quench after the holding time is reached, Δt is 15-25℃;
[0012] S22, performing microstructure testing on the quenched sample and counting the β grain size thereof;
[0013] S23. According to the change of β grain size with holding time, the grain growth kinetic model is obtained and the grain growth relationship expression (2) is formed:
[0014] lnΔd=nlnt+lnK
[0015] Where Δd is the single-phase region T β +Δt temperature, TC21 titanium alloy β The β grain size after the first time of holding at +Δt is different from that just after heating to T β The difference in initial β grain size at +Δt; t is the holding time, n and lnK are coefficients; Δt is 15-25℃;
[0016] S3: The forging ratio of TC21 thin web forging after two-phase zone billet forming is completed, and expressions (1) and (2) are used to determine the forging ratio of T according to the required β grain size of the forging. β + Holding time at Δt temperature; Δt is 15-25℃;
[0017] S4: Die Forging
[0018] The rough block is placed according to the T in step S3. β +Δt temperature and holding time are processed, and then die forging is carried out on the die forging press, with Δt being 15-25℃;.
[0019] Furthermore, the first time in step S21 is 20-120 minutes.
[0020] Further, in step S2, Δt is 15-25°C.
[0021] Further, in step S11, the forging ratio of the TC21 forging after forging in the two-phase region is 1.5-3.5.
[0022] Furthermore, in step S11, when heating in the single-phase region, it is ensured that all α grains are completely dissolved and the α grains are completely transformed into β grains.
[0023] Furthermore, when the β grain size was tested by metallographic method, 5 intercepts were tested along different directions for a single β grain and the average value was calculated.
[0024] Furthermore, the holding time calculated in step S3 refers to the holding time after the core of the forging has reached the temperature when it is heated in the single-phase region and the α grains are completely transformed into equiaxed β grains.
[0025] Compared with the prior art, the embodiments of the present application have the following advantages:
[0026] 1. The present invention establishes the relationship between the β grain size of the forged part and the holding time when the TC21 titanium alloy is forged in the single-phase region, and realizes the prediction of the β grain size of the TC21 titanium alloy when the TC21 titanium alloy is forged in the single-phase region.
[0027] 2. The present invention establishes the relationship between the forging ratio and the initial β grain size of the forging when the TC21 titanium alloy is made in the two-phase region, and combines it with the growth model of the β grains. It can directly determine the holding time of the TC21 titanium alloy thin web forging in the single-phase region, which can ensure that the β grain size growth of the forging is controllable and meet the mechanical property requirements of the forging. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:
[0029] Figure 1 Schematic diagram of the phase transition point of TC21 titanium alloy;
[0030] Figure 2 It is to convert TC21 titanium alloy into T β Schematic diagram of β grain size at different holding times at +20℃;
[0031] Figure 3 It is a schematic diagram of the microstructure of TC21 titanium alloy thin web forging. DETAILED DESCRIPTION
[0032] In order to make the technical solutions and advantages in the embodiments of the present application more clearly understood, the exemplary embodiments of the present application are further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than an exhaustive list of all the embodiments.
[0033] A method for controlling β grains of a TC21 titanium alloy thin web die forging comprises the following steps:
[0034] S1: Establish the relationship between the forging ratio of TC21 forgings after forging in the two-phase region and the initial β grain size when heated in the single-phase region;
[0035] S11, sampling the core of TC21 titanium alloy die forgings at different forging ratios, heating to a temperature above Tβ, and immediately water quenching after the two-phase region structure is statically recrystallized so that α grains are transformed into β grains and the β grains are completely formed, and the initial β grain size of the forgings at different forging ratios is tested by metallographic method;
[0036] S12, the relationship between the fitting forging ratio and the initial β grain size is expressed as expression (1):
[0037] d=393-94.5x
[0038] Where d is the initial β grain size when static recrystallization is just completed, x is the forging ratio, x<4.15;
[0039] S2: Test the time-dependent change of β grain size when TC21 titanium alloy is heated in the single-phase region;
[0040] S21, TC21 titanium alloy in the single phase region β + Δt temperature for the first time, and then quickly quench after the holding time is reached; Δt is 15-25℃;
[0041] S22, performing microstructure testing on the quenched sample and counting the β grain size thereof;
[0042] S23. According to the change of β grain size with holding time, the grain growth kinetic model is obtained and the grain growth relationship expression (2) is formed:
[0043] lnΔd=nlnt+lnK
[0044] Where Δd is the single-phase region T β +Δt temperature, TC21 titanium alloy β The β grain size after the first time of holding at +Δt is different from that just after heating to T β The difference in initial β grain size at +Δt; t is the holding time, n and lnK are coefficients; Δt is 15-25℃;
[0045] S3: The forging ratio of TC21 thin web forging after two-phase zone billet forming is completed, and expressions (1) and (2) are used to determine the forging ratio of T according to the required β grain size of the forging. β + Holding time at Δt temperature; Δt is 15-25℃;
[0046] S4: Die Forging
[0047] The rough block is placed according to the T in step S3. β +Δt temperature and holding time are processed, and then die forging is carried out on the die forging press, with Δt being 15-25℃.
[0048] Furthermore, the first time in step S21 is 20-120 minutes.
[0049] Further, in step S2, Δt is 15-25°C.
[0050] Further, in step S11, the forging ratio of the TC21 forging after forging in the two-phase region is 1.5-3.5.
[0051] Furthermore, in step S11, when heating in the single-phase region, it is ensured that all α grains are completely dissolved and the α grains are completely transformed into β grains.
[0052] Furthermore, when the β grain size was tested by metallographic method, 5 intercepts were tested along different directions for a single β grain and the average value was calculated.
[0053] Furthermore, the holding time calculated in step S3 refers to the holding time after the core of the forging has reached the temperature when it is heated in the single-phase region and the α grains are completely transformed into equiaxed β grains.
[0054] Embodiment 1
[0055] In this embodiment, the TC21 titanium alloy web has a thickness of 90 mm and is forged using a 300 mm diameter rod. The holding temperature is T β +20℃, the main steps are as follows:
[0056] S1: Establish the relationship between the forging ratio of TC21 forgings after forging in the two-phase region and the initial β grain size when heated in the single-phase region;
[0057] S11. Samples are taken from the core of TC21 titanium alloy die forgings at different forging ratios and heated to T β Above the temperature, the two-phase region structure is statically recrystallized to transform the α grains into the β grains. After the β grains are completely formed, water quenching is performed immediately, and the initial β grain size of forgings with different forging ratios is tested by metallographic method.
[0058] S12, the relationship between the fitting forging ratio and the initial β grain size is expressed as expression (1):
[0059] d =393-94.5 x
[0060] In the formula d is the initial β grain size when static recrystallization is just completed, xis the forging ratio, x<4.15;
[0061] The thickness of the web blank of the forging is 90 mm, and the forging ratio of the forging is determined to be 1.8 according to the process. According to expression (1), when the forging ratio of the forging is 1.8, the initial size d of the β grains of the forging heated in the single-phase region is 222.9 μm.
[0062] S2: Test the time-dependent change of β grain size when TC21 titanium alloy is heated in the single-phase region;
[0063] S21, TC21 titanium alloy in the single phase region T β Keep at +20°C for 20min, 40min, 60min, 80min, 100min, 120min and quench to room temperature;
[0064] S22, performing microstructure testing on the quenched sample and counting the β grain size thereof;
[0065] The statistical results are as follows Figure 2 As shown, according to the change of β grain size with holding time, the grain growth kinetic model is obtained to fit the grain growth relationship. According to the fitting results, the values of n and lnK are determined, so expression (2) can be refined as follows:
[0066] lnΔd =0.326 lnt +2.805
[0067] In the formula Δd In the single-phase region T β +20℃ temperature, TC21 titanium alloy β The β grain size after the first time of holding at +20℃ is similar to that just after heating to T β The difference in initial β grain size at +20°C;
[0068] S3: The forging ratio of TC21 thin web forging after two-phase zone billet forming is completed, and expressions (1) and (2) are used to determine the forging ratio of T according to the required β grain size of the forging. β Holding time at +20℃;
[0069] When the required β grain size of the forging is 400μm, the initial β grain size of the forging is 222.9μm. Δd According to the above refined formula (2), it is calculated that the time required for the β grain size to grow from 222.9 μm to 400 μm is 1444 seconds.
[0070] S4: Die Forging
[0071] The blank is heated according to the temperature and time in step S3, and then die forged on a die forging press.
[0072] The rough block is placed in T β +20℃, and keep the blank warm for 1444 seconds, then quickly transfer it to the die forging press for die forging.
[0073] The microstructure of the TC21 titanium alloy thin web forging manufactured in the embodiment of the present application is as follows: Figure 3 As shown in Table 1, it can be shown that the grain size of the forging is very close to 400μm. Its mechanical test is shown in Table 1. The tensile properties and fracture toughness of the forging meet the standard requirements.
[0074] Table 1
[0075]
Claims
1. A method for controlling β grains of TC21 titanium alloy thin web die forgings, characterized in that: The following steps are involved: S1: Establish the relationship between the forging ratio of TC21 forgings after forging in the two-phase region and the initial β grain size when heated in the single-phase region; S11. Samples are taken from the core of TC21 titanium alloy die forgings at different forging ratios and heated to T β Above the temperature, the two-phase region structure is statically recrystallized to transform the α grains into the β grains. After the β grains are completely formed, water quenching is performed immediately, and the initial β grain size of forgings with different forging ratios is tested by metallographic method. S12, the relationship between the fitting forging ratio and the initial β grain size is expressed as expression (1): d =393-94.5 x In the formula d is the initial β grain size when static recrystallization is just completed, x is the forging ratio, x<4.15; S2: Test the time-dependent change of β grain size when TC21 titanium alloy is heated in the single-phase region; S21, TC21 titanium alloy in the single phase region T β + Δt temperature for the first time, and then quickly quench after the holding time is reached, Δt is 15-25℃; S22, performing microstructure testing on the quenched sample and counting the β grain size thereof; S23. According to the change of β grain size with holding time, the grain growth kinetic model is obtained and the grain growth relationship expression (2) is formed: lnΔd=nlnt+lnK In the formula Δd In the single-phase region T β +Δt temperature, TC21 titanium alloy β The β grain size after the first time of holding at +Δt is different from that just after heating to T β The difference in initial β grain size at +Δt; t is the holding time, n and lnK are coefficients; Δt is 15-25℃; S3: The forging ratio of TC21 thin web forging after two-phase zone billet forming is completed, and expressions (1) and (2) are used to determine the forging ratio of T according to the required β grain size of the forging. β + Holding time at Δt temperature, Δt is 15-25℃; S4: Die Forging The rough block is placed according to the T in step S3. β +Δt temperature and holding time are processed, and then die forging is carried out on the die forging press, with Δt being 15-25℃.
2. The method for controlling β grains of a TC21 titanium alloy thin web die forging according to claim 1, characterized in that: The first time in step S21 is 20-120 minutes.
3. The method for controlling β grains of a TC21 titanium alloy thin web die forging according to claim 1, characterized in that: In step S11, the forging ratio of the TC21 forging after forging in the two-phase region is 1.5-3.
5.
4. The method for controlling β grains of a TC21 titanium alloy thin web die forging according to claim 3, characterized in that: In step S11, when heating in the single-phase region, it is ensured that all α grains are completely dissolved and completely transformed into β grains.
5. The method for controlling β grains of a TC21 titanium alloy thin web die forging according to claim 1, characterized in that: When the β grain size is tested by metallographic method, 5 intercepts are tested along different directions for a single β grain and the average value is calculated.
6. The method according to claim 1, characterized in that The holding time calculated in step S3 refers to the holding time after the core of the forging reaches the temperature when it is heated in the single-phase region and the α grains are completely transformed into equiaxed β grains.