Optimization method for microstructure abnormality of special TC4 alloy forgings

Abstract

The present application belongs to the field of forging technology, and relates to a kind of optimization method for microstructure abnormality of special TC4 alloy forgings. The method comprises the following steps: step 1: upsetting the bar to obtain a rough shape; step 2: machining the lower end face of the rough shape to a circular arc surface, and the circular arc surface is in contact with the lower die; step 3: heating the rough shape to 950-960 DEG C, and performing die forging on the rough shape, with a deformation rate of 5 mm / s and a deformation amount controlled within 35%-45%, and the process is completed in one heating cycle.

Description

Technical Field

[0001] This invention belongs to the field of forging technology and relates to an optimization method for abnormal microstructure of TC4 alloy forgings. Background Technology

[0002] TC4 alloy (Ti-6Al-4V) is a typical α+β type dual-phase titanium alloy. Its main component is titanium (Ti), with 6% aluminum (Al) and 4% vanadium (V) as the main alloying elements. It also contains small amounts of impurities such as iron (Fe), oxygen (O), hydrogen (H), and nitrogen (N). TC4 alloy possesses excellent mechanical properties, high yield strength and tensile strength, good plasticity and fatigue resistance, and is widely used in rotating components of aerospace engines due to its superior performance. The main difference between special TC4 alloy and TC4 alloy lies in the content of oxygen (O) and hydrogen (H) in their chemical compositions. The O content (peak value: 0.22) in special TC4 alloy is slightly higher than that in TC4 alloy (peak value: 0.20), while the H content (peak value: 0.01) is slightly lower than that in TC4 alloy (peak value: 0.015), indicating that the mechanical properties of special TC4 alloy are significantly superior to those of TC4 alloy.

[0003] A certain TC4 alloy impeller forging is a crucial rotating component of an aero-engine. A key characteristic of this forging is that a mismatch between forging and heat treatment temperatures leads to abnormal microstructure, specifically a large number of coarse, rod-shaped β-transformation structures distributed within the β matrix. This results in brittle fracture of the engine blades during long-term service. This invention proposes an optimization method to address the abnormal microstructure of the TC4 alloy forging. This method eliminates the large number of coarse, rod-shaped β-transformation structures distributed within the β matrix, resulting in a TC4 alloy forging with only fine, uniform, and uniformly distributed primary α-structure within a specific content range within the β matrix. Summary of the Invention

[0004] Purpose of the invention: A method for optimizing the microstructure of special TC4 alloy forgings is provided. The rod-shaped β-transformation structure distributed on the β matrix is ​​removed to obtain a special TC4 alloy forging with only fine and uniform primary α-structure distributed on the β matrix within a certain range. The performance indicators and ultrasonic testing meet the standard requirements.

[0005] Technical solution: An optimization method for microstructure anomalies in TC4 alloy forgings includes: Step 1: Upset the bar stock to obtain a rough shape; Step 2: Machin the lower end face of the rough shape to form an arc surface, which contacts the lower mold. Step 3: Heat the rough shape to 950~960℃, and perform die forging on the rough shape. The deformation rate is 5mm / s, and the deformation amount is controlled at 35%~45%. The process is completed in one forging.

[0006] Furthermore, step 1 is performed using a 16MN free forging press.

[0007] Furthermore, in step 1, the deformation rate is 8~10mm / s, the deformation amount is controlled at 40%~50%, and it is completed in one firing.

[0008] Furthermore, step 1 also includes: The upper surface of the rough shape is pressed into a concave structure with a central arc. The position near the center of the bar stock, which is less than or equal to the outer diameter of the forging hub, forms an inner draft angle with the tooling and is chamfered inward by R20.

[0009] Furthermore, step 3 is performed using a 50MN hydraulic press.

[0010] Furthermore, it also includes: Step 4: After forging, rough machining is performed on the forging before heat treatment to remove the large excess area of ​​the blade body, so as to prevent the forging from having poor heat penetration during heat treatment due to the large thickness of the forging cross section.

[0011] Furthermore, it also includes: Step 5: After processing, the forging is subjected to heat treatment, the heat treatment regime is solution treatment and aging.

[0012] Furthermore, the solution treatment temperature is 960~970℃, the holding time is 60min, and the water cooling time is ≥30min. The transfer time from the forging to the water cooling tank is ≤60s, and the water temperature is controlled at 10~40℃ to prevent the precipitation and coarsening of β-transformation structure in the microstructure of the forging due to excessive transfer time and high water temperature.

[0013] Furthermore, the aging temperature is 690~710℃, the holding time is 120min, and then air-cooled to obtain the final forging.

[0014] Beneficial effects: This invention utilizes a free-forging billet and designs a reasonable rough shape for die forging. First, a special tooling is used to press a specific shape onto the head of the bar stock, followed by forging using a special die. This results in a more rational distribution of deformation in the forging and saves raw materials. During billet preparation and die forging, appropriate billet heating temperatures are selected in conjunction with the heat treatment process parameters. This avoids situations where the forging temperature and heat treatment (solution) temperature are mismatched, preventing the β-transformation structure generated during forging from completely dissolving in the β matrix and forming interlaced lamellar structures along grain boundaries, resulting in coarse β-transformation structures. Consequently, the final microstructure of the forging consists of numerous coarse β-transformation structures within the β matrix. Furthermore, the fixed forging heating temperature prevents fluctuations in forging temperature caused by differences in phase transformation point detection from affecting the final microstructure of the forging. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is the final forging drawing.

[0017] Figure 2 Forge a wasteland for freedom.

[0018] Figure 3 This is a diagram of a die forging material.

[0019] Figure 4 This is an unacceptable organizational chart.

[0020] Figure 5 This is a microstructure diagram of the forging. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0023] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing and simplifying the invention, and should not be construed as limiting the invention. Furthermore, the use of ordinal numbers (e.g., "first and second," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly, encompassing both direct connection and indirect connection via an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0025] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] Analysis of the abnormal microstructure of the forging revealed that the β-transformation structure in the β matrix exhibited elongated rod-like structures, which are unacceptable according to the forging acceptance criteria. The main mechanism causing this microstructure abnormality is as follows: The high forging temperature provides sufficient potential energy for the transformation from α to β phases, resulting in a low content of primary α phase after forging. To maintain phase equilibrium at this temperature, a significant amount of secondary α phase is retained. Simultaneously, a low cooling rate after forging leads to a prolonged residence time in the high-temperature region, further promoting the growth and coarsening of the secondary α phase. Secondly, during heat treatment, when the solution temperature of the forging is lower than the forging temperature, the secondary α phase generated during forging cannot completely dissolve in the β matrix, forming interlaced lamellar structures along grain boundaries, resulting in coarse secondary α phases. This ultimately leads to the final microstructure of the forging consisting of a large amount of coarse β-transformation structure within the β matrix.

[0027] The present invention will be further described in detail below through specific embodiments: This invention provides an optimization method for the microstructure anomalies of TC4 alloy forgings, resulting in forgings with only fine, uniformly distributed primary α-structure within a certain content range on the β matrix, such as... Figure 1 As shown, the TC4 centrifugal impeller forging sequentially includes a hub, a rim, and a blade, with the blade height to the total forging height ratio being 0.6:1. The method includes the following steps: Step 1: Heat the bar stock to 950~960℃, and use a 16MN free forging press to upset the bar stock to a certain height (see...). Figure 2During upsetting, a special tooling is used, placed at the center of the upper end face of the bar stock. The deformation rate is 8~10mm / s, and the deformation amount is controlled at 40%~50%, completed in one pass. The special tooling is used to press the upper end face of the rough shape into a concave structure with a central arc. The position near the center of the bar stock, less than or equal to the outer diameter of the forging hub, forms an inner draft angle with the tooling and is chamfered inward by R20. This increases the deformation effect of the forging hub area and reduces the number of bar stock processing steps, thus saving raw materials.

[0028] Step 2: Position the lower end face of the machined blank with a circular arc. The circular arc surface contacts the lower mold. During blank making, ensure that the blank is in a suitable position in the mold to prevent the blank from being misaligned and affecting the final forming effect.

[0029] Step 3: Heat the rough shape to 950~960℃, place the rough shape in a special mold, and press it with a 50MN hydraulic press until the upper and lower molds fit together (see...). Figure 3 The deformation rate is 5 mm / s, and the deformation amount is controlled at 35%~45%, completed in one pass. During die forging, since the ratio of the rough shape height to the forging height is close to 1:1, and the rough shape is located close to the hub area of ​​the forging, i.e., the center area of ​​the forging, a large number of deformation dead zones will appear in the hub area of ​​the forging during the die pressing process. Therefore, the central arc-shaped concave structure on the upper end face of the rough shape will increase the deformation amount in the hub area of ​​the forging, so that the overall deformation of the forging is uniform. The cooling method is flowing water cooling, and the water temperature is controlled at 20~40℃. Step 4: After forging, perform rough machining on the forging before heat treatment to remove the large excess area of ​​the blade body and prevent poor heat penetration of the forging during heat treatment due to the large thickness of the forging cross section.

[0030] Step 5: After processing, the forging is subjected to heat treatment. The heat treatment regime is solution treatment and aging. The solution treatment temperature is 960~970℃, held for 60min, and then water-cooled (water cooling time ≥30min). The time from when the forging is taken out of the furnace to when it is transferred to the water cooling tank is ≤60s. The water temperature is controlled at 10~40℃ to prevent the precipitation and coarsening of β-transformation structure in the microstructure of the forging due to excessive transfer time and high water temperature. The aging temperature is 690~710℃, held for 120min, and then air-cooled to obtain the final forging.

[0031] Example 1 The present invention discloses a special TC4 alloy impeller forging with a disc outer diameter of Φ268mm, a forging height of 190mm, and a forging weight of 25.7Kg. The rationally designed rough shape increases the deformation of the hub area during subsequent die forging, reduces the deformation dead zone, and saves costs. During billet preparation and die forging, by combining the forging heat treatment process parameters and selecting an appropriate billet forging heating temperature, the large number of coarse rod-shaped β-transformation structures distributed on the β matrix can be effectively eliminated. Figure 4(As an unacceptable structure), the microstructure of the forging is such that only fine, uniform, and primary α structure is distributed on the β matrix with a content within a certain range, and the performance indicators and ultrasonic testing meet the forging standard requirements.

[0032] The manufacturing process is detailed below: 1. Cutting: Sawing machine, cutting size Φ150×360mm; 2. Billet machining: The bar stock is chamfered to R10, and a rounded surface is machined at one end for positioning; 3. Billet Preparation: Forging is performed using a 16MN hydraulic press. The bar stock is preheated to 200~250℃, and then heated to 955℃. The fixture is placed at the center of the upper end face of the bar stock. The deformation rate is 8~10mm / s, and the deformation amount is controlled at 40%~50%. The process is completed in one pass, forming the rough shape required for die forging. A special fixture is used to press the upper end face of the rough shape into a central arc-shaped concave structure. The position near the center of the bar stock, less than or equal to the outer diameter of the forging hub, forms an inner draft angle with the fixture and is chamfered inward by R20. This increases the deformation effect of the upper end face of the forging hub and reduces the number of bar stock processing steps, thus saving raw materials.

[0033] 4. Machining positioning table facilitates rough shape positioning; 5. Die forging: A 50MN hydraulic press is used for die forging. The die preheating temperature is 300℃, and the preheating time is ≥20h. The rough shape is heated to 955℃. Before forging, the bottom groove surface of the rough shape is positioned in contact with the lower die. (See attached...) Figure 3 The billet is placed, and the forging speed is set to a constant 5 mm / s. The deformation is controlled between 25% and 50%. During die forging, the ratio of the blank height to the forging height is close to 1:1, and the blank is positioned close to the center of the forging, i.e., the hub area. This will cause a large number of deformation dead zones in the hub area of ​​the forging during the die pressing process. Therefore, the central arc-shaped concave structure on the upper end face of the blank will increase the deformation of the hub area of ​​the forging, making the overall deformation of the forging more uniform. 6. After forging, rough machining is performed on the forging before heat treatment to remove the large excess area of ​​the blade body, so as to prevent poor heat penetration of the forging during heat treatment due to the large thickness of the forging cross section.

[0034] 7. After processing, the forgings are subjected to heat treatment. The heat treatment regime is solution treatment and aging. The solution treatment temperature is 960~970℃, holding time is 60min, and water cooling is performed (water cooling time ≥30min). The time from the forgings to the water cooling tank is ≤60s, and the water temperature is controlled at 10~40℃ to prevent the precipitation and coarsening of β-transformation structure in the microstructure of the forgings due to excessive transfer time and high water temperature. The aging temperature is 690~710℃, holding time is 120min, and air cooling is performed.

[0035] The TC4 alloy impeller forgings obtained by this forging method, after testing, showed that the microstructure met the standard requirements (see...). Figure 5 ), room temperature tensile strength: σ b =982MPa, σ 0.2 =909MPa, δ5=14.0%, ψ=87%, notched strength σ=1440MPa, notch ratio=1.50, high-temperature tensile strength: σ b =698MPa, σ 0.2 =572MPa, δ5=20.5%, ψ=61%, the microstructure and performance indicators of the forging meet the requirements of the special standard for TC4 alloy.

[0036] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for optimizing the microstructure anomalies of TC4 alloy forgings, characterized in that, include: Step 1: Upset the bar stock to obtain a rough shape; Step 2: Machin the lower end face of the rough shape to form an arc surface, which contacts the lower mold. Step 3: Heat the rough shape to 950~960℃, and perform die forging on the rough shape. The deformation rate is 5mm / s, and the deformation amount is controlled at 35%~45%. The process is completed in one forging.

2. The method according to claim 1, characterized in that, Step 1 is performed using a 16MN free forging press.

3. The method according to claim 1, characterized in that, In step 1, the deformation rate is 8~10mm / s, the deformation amount is controlled at 40%~50%, and it is completed in one firing.

4. The method according to claim 1, characterized in that, Step 1 also includes: The upper surface of the rough shape is pressed into a concave structure with a central arc. The position near the center of the bar stock, which is less than or equal to the outer diameter of the forging hub, forms an inner draft angle with the tooling and is chamfered inward by R20.

5. The method according to claim 1, characterized in that, Step 3 is performed using a 50MN hydraulic press.

6. The method according to claim 1, characterized in that, Also includes: Step 4: After forging, perform rough machining on the forging before heat treatment to remove the large excess area of ​​the blade body and prevent poor heat penetration of the forging during heat treatment due to the large thickness of the forging cross section.

7. The method according to claim 1, characterized in that, It also includes: Step 5: After processing, the forging is heat treated with a solution treatment and aging process.

8. The method according to claim 1, characterized in that, Solution treatment temperature: 960~970℃, holding time: 60min, water cooling time: ≥30min, transfer time from furnace to water cooling tank: ≤60s, water temperature: 10~40℃, to prevent precipitation and coarsening of β-transformation structure in the microstructure of forging due to excessive transfer time and high water temperature.

9. The method according to claim 1, characterized in that, The aging temperature is 690~710℃, the holding time is 120min, and the final forging is obtained by air cooling.

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