Method for improving the uniformity of dual-state structure of TC4 special-grade disc forgings

Abstract

The present invention discloses a method for improving the uniformity of the dual-state structure of TC4 special-grade disc-type forgings, comprising the following steps: S1. determining the α-phase content ω% and the β-phase transformation point temperature t in the TC4 raw material; S2. blanking to obtain a billet with a diameter of D0 and an initial height of H0; S3. heating the billet: the billet is placed in a furnace for heating below 800°C, and the heating temperature t1 after entering the furnace satisfies the following conditions: heating to temperature t1 and then keeping the temperature; S4. die forging the billet after it is taken out of the furnace: during the die forging process, each hammer presses down the height H0. n and hammering time interval T n Design is performed; S5. The forging obtained in S4 is quenched at a temperature above the two-phase region and then tempered. The present invention determines a reasonable forging heating temperature based on the primary α-phase content and the β-phase transformation temperature of the material. By designing the number of forging hammer blows, the hammer blow interval, and the amount of reduction per hammer blow, a foundation is laid for the internal microstructure transformation of the forging. Finally, the forging is quenched at a temperature above the two-phase region. As the heat is maintained, the primary α-phase in the forging microstructure transforms into a high-temperature β-phase, resulting in a dual-structure forging with an α-phase content that meets technical requirements and a uniform distribution of the α-phase throughout the microstructure.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy part forging, and in particular to a method for improving the uniformity of the dual-state structure of TC4 super-grade disc-type forgings. Background Art

[0002] TC4 super-grade titanium alloy is an important structural material already used in aviation and aerospace applications. Its excellent overall performance is closely linked to its microstructure. This TC4 super-grade material is often used to make disc-type components for use in aircraft engines. For example, a TC4 super-grade axial impeller disc in an aircraft engine requires a dual-modal microstructure at high magnification due to the specific working location of this component. This means that unconnected primary α particles (primary α phase + secondary α phase) are distributed within a β-transformed matrix. The primary α particle content should be 15% to 25%.

[0003] The above TC4 special axial flow impeller disc is shown in the attached manual. Figure 2 As shown in the figure, the traditional preparation process is as follows: the blank is heated at the upper temperature of the two-phase zone, forged using a CNC die forging hammer, then quenched at the two-phase zone temperature, and tempered at a medium temperature to obtain the forging. Since the upper heating temperature of the two-phase zone and the solid solution temperature of the two-phase zone are constant, while the α phase content and β phase transformation point of the raw material fluctuate, when the β phase transformation point of the raw material is low, the temperature rise of the core of the blank during the forging process is obvious, resulting in the final forging temperature of the core being close to the β phase transformation point, and the microstructure after forging is a basket weft structure, see the attached manual. Figure 3 As shown in the figure; when the raw material α phase content is too high and the β phase transformation point is too high, it is equivalent to the heating temperature being much lower than the β phase transformation point. After forging, the α phase content in the organization is likely to be too high. See the attached manual. Figure 4 Therefore, currently, there is no effective countermeasure for the preparation of this TC4 special-grade axial flow impeller disc to obtain the uniform bimodal structure with a primary α particle content of 15% to 25%.

[0004] The patent with publication number CN112760581A discloses a forging and rolling composite processing and heat treatment process for a near-α-type high-temperature titanium alloy. First, the β-phase region is forged to obtain a Widmanstätten structure high-temperature titanium alloy. The alloy is kept at 980°C below its β / (α+β) phase transformation point for 20 minutes to make the internal temperature uniform. After the temperature is uniform, the alloy is then hot-rolled. There are three passes in total. The first pass has a 10% reduction, the second pass has a 20% reduction, and the third pass has a 25% reduction. Each pass is kept warm for 5 minutes. After rolling, air cooling annealing is performed. The total deformation is 46%, and a large amount of α is obtained. p and a very small amount of α s The high temperature titanium alloy sheet with equiaxed microstructure of β and β is obtained by heat treatment.

[0005] Although the above patent points out that the α p The content accounts for 27%, but it is not aimed at the TC4 special grade titanium alloy required by the present invention, and the patent obtains titanium alloy plates through hot rolling process, which cannot be used to produce parts with complex structures. Therefore, it cannot be applied to the production of disc parts proposed in the present invention. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for improving the uniformity of the dual-state structure of TC4 special-grade disc forgings, which can effectively ensure that the microstructure and α phase content of the forgings are within the technical requirements, in response to the defects of the existing technology.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for improving the uniformity of dual-state microstructure of TC4 special-grade disc forgings, comprising the following steps:

[0009] S1. Determine the α-phase content ω% and the β-phase transition temperature t in the TC4 raw material, where ω∈[35,60], t∈[980,1005];

[0010] S2. Cutting the material to obtain a blank with a diameter of D0 and an initial height of H0;

[0011] S3. Billet heating: The billet is heated in a furnace below 800°C. The heating temperature t1 after entering the furnace satisfies: Heat to temperature t1 and keep warm;

[0012] S4. Die forging after the billet is taken out of the furnace: During the die forging process, each hammer presses down the height H n satisfy:

[0013]

[0014] Hammering time interval T n satisfy:

[0015]

[0016] Where H1 is the height of the forging after die forging, n is the number of hammer blows, n≤16;

[0017] S5. Quench the forging obtained in S4 at the upper temperature of the two-phase region and then temper it.

[0018] Furthermore, the measurement of the α-phase content in S1 requires that the raw material samples be first subjected to solution heat treatment, wherein the solution heat treatment is as follows: keeping at 955±10°C followed by water cooling, and then keeping at 700±10°C followed by air cooling.

[0019] Furthermore, the β phase transition point temperature is measured using a metallographic method.

[0020] Furthermore, the aspect ratio of the blank in S2 is

[0021] Furthermore, there is a blank spraying step S20 between S2 and S3: spraying a lubricant on the surface of the blank, and the spraying thickness h of the lubricant satisfies:

[0022] Where μ is the thickness coefficient, μ∈[0.4,0.5].

[0023] Furthermore, the shortest insulation time T1 in S3 satisfies: T1 = k × D0, where k is the insulation coefficient, k∈[0.6,0.8].

[0024] Furthermore, the quenching temperature t2 in S5 satisfies:

[0025] Furthermore, the tempering temperature in S5 is 700-750°C.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention determines a reasonable forging heating temperature based on the content of the primary α phase and the β phase transformation point temperature of the TC4 special-grade material. By designing the number of hammer blows, the hammer blow time interval, and the amount of reduction per hammer during the forging process, a foundation is laid for the transformation of the internal structure of the forging. Finally, the forging is quenched at the upper temperature of the two-phase region. As the heat preservation continues, the primary α phase in the forging structure transforms into the high-temperature β phase, successfully obtaining a dual-structure forging with an α phase content that meets the technical requirements and a uniform distribution of the α phase in the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a micrograph of the dual-state structure of the core of the axial flow impeller forging described in Example 1 of the present invention;

[0029] Figure 2 A cross-sectional view of the axial flow impeller forging according to Example 1 of the present invention (showing the core sampling position);

[0030] Figure 3 This is a micrograph of the basket structure at the core of an axial flow impeller forging obtained by a traditional preparation method;

[0031] Figure 4 This is a micrograph of the α phase in the center of the axial flow impeller forging obtained by another traditional preparation method. DETAILED DESCRIPTION

[0032] In order to clearly illustrate the technical features of this solution, the technical solution is described in detail below through specific implementation methods and in conjunction with the accompanying drawings.

[0033] In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present application is not limited to the specific embodiments disclosed below.

[0034] In addition, in the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, features defined as "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0035] In this application, unless otherwise expressly specified or limited, terms such as "installed," "connected," "connect," and "fixed" should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0036] In this application, unless otherwise expressly specified and limited, a first feature "above" or "below" a second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples.

[0037] Example 1

[0038] A method for improving the uniformity of dual-state microstructure of TC4 super-grade axial flow impeller disk forgings comprises the following steps:

[0039] S1. Determination of α-phase content ω% and β-phase transition temperature t in TC4 special raw materials,

[0040] The specific operation is: first take samples of the raw materials for solution heat treatment, the solution heat treatment process: keep at 955±10℃ for about 1h and water cool, then age at 700±10℃ for about 2h and air cool, then check the α phase content ω% in the microstructure, and require ω∈[35,60].

[0041] The β phase transition point temperature is measured by metallographic method, requiring t∈[980,1005].

[0042] S2. Cutting: Use a circular saw to machine a blank with a diameter of D0 and an initial height of H0 (unit: mm) on the raw material, and use a lathe to machine both ends of the blank and fillet the corners. The height-to-diameter ratio of the blank is required to be D0∈[70,150].

[0043] S3. Billet heating: Place the billet in a heating furnace for heating. The temperature inside the furnace must be lower than 800°C. The heating temperature t1 after entering the furnace must meet the following requirements: Heat to temperature t1 and keep warm.

[0044] The shortest holding time T1 must satisfy: T1 = k × D0 to ensure that the billet is burned through and the internal temperature of the billet is consistent with the surface temperature, where k is the insulation coefficient. When D0∈[70,100], k=0.8~0.7; when D0∈(100,150], k=0.7~0.6. Here, k takes the active value to reduce energy consumption.

[0045] The forging heating temperature t1 in this embodiment is determined based on the phase transformation temperature t and the α-phase content ω in the bar. Heating temperature t1 represents the forging temperature in the two-phase region of the TC4 premium grade material. Forging at this temperature is intended to produce an equiaxed forging. Subsequent solutionization at the upper temperature of the two-phase region successfully achieves a dual-state structure.

[0046] In addition, forging at temperature t1 can obtain an appropriate content of α phase, that is, when the phase transformation point temperature t and the α phase content ω in the bar are relatively high, according to the formula, the heating temperature t1 is higher, and the forging process can increase the transformation of the primary α phase, reduce the α phase content in the organization, and make the α phase in the organization meet the requirements.

[0047] S4. Billet forging: After the billet is taken out of the furnace, it is forged on a 3T CNC die forging hammer. During the die forging process, each hammer presses down a height of H n (Unit: mm)

[0048]

[0049] Hammering time interval T n (unit s) satisfies:

[0050]

[0051] Where T n Refers to the time interval between the nth hammer strike and the n+1th hammer strike, H1 is the height of the forging after die forging, n is the number of hammer strikes, n≤16.

[0052] During the die forging process, the temperature rise in the core of the billet causes a microstructure transformation or affects the α-phase content in the microstructure. In order to control the temperature rise fluctuation in the core of the billet, this embodiment controls the billet reduction amount per hammer and the time interval between hammer strikes, thereby controlling the reasonable fluctuation of the temperature in the core of the billet in the two-phase region, avoiding a significant impact on the primary α-phase content in the microstructure, and ensuring that the microstructure after forging is an equiaxed microstructure with a moderate α-phase content.

[0053] At this point, the two-phase zone forging of the billet has been completed and the equiaxed structure has been obtained.

[0054] S5. Quench the forging obtained in S4 at the upper temperature of the two-phase region and then temper it to obtain a dual-state structure.

[0055] The quenching temperature t2 satisfies: The tempering temperature is 700-750℃.

[0056] The quenching temperature t2 of the forging is the upper temperature of the two-phase region. As the tempering and heat preservation proceed, the primary α phase in the organization transforms into the high-temperature β phase, and finally a dual-state organization with good uniformity is obtained.

[0057] Example 2

[0058] A method for improving the uniformity of dual-state microstructure of TC4 special-grade disc forgings, comprising the following steps:

[0059] S1. Determination of α-phase content ω% and β-phase transition temperature t in TC4 raw materials,

[0060] The specific operation is: first take samples of the raw materials for solution heat treatment. The solution heat treatment process is: keep warm at 955±10℃ for about 1h and then cool with water. Then keep warm at 700±10℃ for about 2h and then cool with air. Then check the α phase content ω% in the microstructure, and require ω∈[35,60].

[0061] The β phase transition point temperature is measured by metallographic method, requiring t∈[980,1005].

[0062] S2. Cutting: Use a circular saw to machine a blank with a diameter of D0 and an initial height of H0 (unit: mm) on the raw material, and use a lathe to machine both ends of the blank and fillet the corners. The height-to-diameter ratio of the blank is required to be D0∈[70,150].

[0063] This embodiment adds step S20 on the basis of embodiment 1. Blank spraying: spraying lubricant on the surface of the blank, and the spraying thickness h (unit: mm) of the lubricant satisfies the following conditions:

[0064] Where μ is the thickness coefficient. When D0∈[70,100], μ is 0.4, and when D0∈(100,150], μ is 0.5.

[0065] The spraying method of the lubricant is atomized spraying, and the spraying process includes preheating, spraying and drying the blank in sequence.

[0066] Spraying lubricant on the billet surface has the following purposes: on the one hand, it has a heat preservation effect to prevent the billet surface temperature from dropping too quickly, especially the part of the billet in contact with the forging die; on the other hand, it has a lubricating effect to reduce the flow resistance of the billet during plastic forming.

[0067] S3. Billet heating: Place the billet in a heating furnace for heating. The temperature inside the furnace must be lower than 800°C. The heating temperature t1 after entering the furnace must meet the following requirements: Heat to temperature t1 and keep warm.

[0068] The shortest holding time T1 must satisfy: T1 = k × D0 to ensure that the billet is burned through and the internal temperature of the billet is consistent with the surface temperature, where k is the insulation coefficient. When D0∈[70,100], k=0.8~0.7; when D0∈(100,150], k=0.7~0.6. Here, k takes the active value to reduce energy consumption.

[0069] The forging heating temperature t1 in this embodiment is determined based on the phase transformation temperature t and the α-phase content ω in the bar. Heating temperature t1 represents the forging temperature in the two-phase region of the TC4 premium grade material. Forging at this temperature is intended to produce an equiaxed forging. Subsequent solutionization at the upper temperature of the two-phase region successfully achieves a dual-state structure.

[0070] In addition, forging at temperature t1 can obtain an appropriate content of α phase, that is, when the phase transformation point temperature t and the α phase content ω in the bar are relatively high, according to the formula, the heating temperature t1 is higher, and the forging process can increase the transformation of the primary α phase, reduce the α phase content in the organization, and make the α phase in the organization meet the requirements.

[0071] S4. Billet forging: After the billet is taken out of the furnace, it is forged on a 3T CNC die forging hammer. During the die forging process, each hammer presses down a height of H n (Unit: mm)

[0072]

[0073] Hammering time interval T n (unit s) satisfies:

[0074]

[0075] Where T n Refers to the time interval between the nth hammer strike and the n+1th hammer strike, H1 is the height of the forging after die forging, n is the number of hammer strikes, n≤16.

[0076] During the die forging process, the temperature rise in the core of the billet causes a microstructure transformation or affects the α-phase content in the microstructure. In order to control the temperature rise fluctuation in the core of the billet, this embodiment controls the billet reduction amount per hammer and the time interval between hammer strikes, thereby controlling the reasonable fluctuation of the temperature in the core of the billet in the two-phase region, avoiding a significant impact on the primary α-phase content in the microstructure, and ensuring that the microstructure after forging is an equiaxed microstructure with a moderate α-phase content.

[0077] At this point, the two-phase zone forging of the billet has been completed and the equiaxed structure has been obtained.

[0078] S5. Quench the forging obtained in S4 at the upper temperature of the two-phase region and then temper it to obtain a dual-state structure.

[0079] The quenching temperature t2 satisfies: The tempering temperature is 700-750℃.

[0080] The quenching temperature t2 of the forging is the upper temperature of the two-phase region. As the tempering and heat preservation proceed, the primary α phase in the organization transforms into the high-temperature β phase, and finally a dual-state organization with good uniformity is obtained.

[0081] Example 3

[0082] This embodiment limits the type of lubricant in Example 2, and preferably uses glass lubricant for the best effect.

[0083] Obviously, the above embodiments are merely examples for the purpose of clearly illustrating the technical solutions of the present invention, and are not intended to limit the implementation methods of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for improving the uniformity of dual-state structure of TC4 special-grade disc forgings, characterized in that , including the following steps: S1. Determination of TC4 raw materials Phase content and Phase transition temperature , the unit is ℃, where , ; S2. Cutting, the diameter is , unit is mm, initial height is , the unit is mm of the blank; S3. Billet heating: The billet is heated in the furnace below 800℃. The heating temperature after entering the furnace is , in °C, satisfies: , heating to temperature After insulation; S4. Die forging after the billet is taken out of the furnace: During the die forging process, each hammer presses down the height , in mm, satisfies: ， Hammering time interval , in units of s, satisfies: ， in is the height of the forging after die forging, is the number of hammer blows, ; S5. Quench the forging obtained in S4 at the upper temperature of the two-phase region and then temper it.

2. The method for improving the dual-state microstructure uniformity of TC4 super-grade disc forgings according to claim 1, characterized in that: S1 The measurement of phase content requires that the raw material samples be first subjected to solution heat treatment, wherein the solution heat treatment is as follows: keeping at 955±10°C followed by water cooling, and then keeping at 700±10°C followed by air cooling.

3. The method for improving the dual-state microstructure uniformity of TC4 super-grade disc forgings according to claim 1, characterized in that: The phase transition point temperature was measured by metallographic method.

4. The method for improving the dual-state microstructure uniformity of TC4 super-grade disc forgings according to claim 1, characterized in that: The height-to-diameter ratio of the blank in S2 is .

5. The method for improving the dual-state microstructure uniformity of TC4 special-grade disc forgings according to claim 1 or 4, characterized in that: There is also a blank spraying step S20 between S2 and S3: spraying lubricant on the surface of the blank, the spraying thickness of the lubricant is , in mm, satisfies: ,in is the thickness coefficient, .

6. The method for improving the dual-state microstructure uniformity of TC4 super-grade disc forgings according to claim 5, characterized in that: The lubricant is sprayed by atomized spraying.

7. The method for improving the dual-state microstructure uniformity of TC4 special-grade disc forgings according to claim 5, characterized in that: Blank spraying includes the steps of preheating, spraying and drying the blank in sequence.

8. The method for improving the dual-state microstructure uniformity of TC4 special-grade disc forgings according to claim 1, characterized in that: S5 quenching temperature , in °C, satisfies: .

9. The method for improving the dual-state microstructure uniformity of TC4 special-grade disc forgings according to claim 1, characterized in that: The tempering temperature in S5 is 700-750°C.

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