Method for improving homogeneity of two-state structure of TC4 special-grade disc forgings

Abstract

The invention discloses a method for improving the uniformity of a two-state structure of a TC4 special-grade disc forging. The method comprises the following steps that S1, the alpha phase content omega% and the beta phase transformation point temperature t in a TC4 raw material are measured; s2, blanking is conducted, and a blank with the diameter being D0 and the initial height being H0 is obtained; s3, blank heating is conducted, specifically, the blank is put into a furnace to be heated at the temperature below 800 DEG C, and the heating temperature t1 after the blank is put into the furnace meets the condition that # imgabs0 # is heated to the temperature t1 and then subjected to heat preservation; s4, die forging is conducted after the blank is discharged out of the furnace, and in the die forging process, the pressing height Hn of each hammer and the hammering time interval Tn are designed; and S5, the forge piece obtained in the step S4 is subjected to temperature quenching on the upper portion of the two-phase region and then tempered. According to the method, the reasonable forging heating temperature is determined according to the primary alpha-phase content and the beta-phase transformation point temperature of the material, the forging hammering frequency, the hammering time interval and the rolling reduction per hammer are designed, a foundation is laid for internal structure transformation of the forge piece, and finally the forge piece is subjected to temperature quenching at the upper portion of a two-phase region; and a primary alpha phase in a forging structure is converted into a high-temperature beta phase, and the double-state structure forging with the alpha phase content meeting technical regulations and the alpha phase evenly distributed in the structure is obtained.

Description

Technical Field

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

[0002] TC4 special grade titanium alloy is an important structural material, which has been applied in the fields of aviation and aerospace. Its excellent comprehensive performance is inseparable from its microstructure. This kind of TC4 special grade material is often used to make disc parts for use in aircraft engines. For example, a certain aircraft engine TC4 special grade axial flow impeller disc requires a dual-state microstructure at high magnification due to the particularity of the working part of the part, that is, on the matrix of the β transformation structure, there are primary α particles (primary α phase + secondary α phase) that are not connected to each other, and the content of primary α particles should be 15% to 25%.

[0003] The above TC4 special axial flow impeller disc is attached to the instruction manual. Figure 2 As shown in the figure, the traditional preparation process is: the billet is heated at the upper temperature of the two-phase zone, forged by a CNC die forging hammer, and then quenched at the temperature of the two-phase zone, and the forging is obtained after medium-temperature tempering. Since the upper heating temperature of the forging two-phase zone and the solid solution temperature of the two-phase zone are constant values, and 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 billet is obvious during the forging process, resulting in the final forging temperature of the core close to the β phase transformation point, and the structure 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 to obtain the uniform dual-state structure with the primary α particle content of 15% to 25% in the preparation of the TC4 special axial flow impeller disc.

[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 high-temperature titanium alloy with a Widmanstatten structure. 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 pressure of 10%, the second pass has a pressure of 20%, and the third pass has a pressure of 25%. Each pass is kept warm for 5 minutes. After the rolling is completed, 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 structure 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 produce parts with complex structures, and therefore 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 prescribed range, in view of the defects of the prior art.

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

[0008] A method for improving the uniformity of dual-state structure 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 up to temperature t1 and then keep warm;

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

[0013]

[0014] Hammer 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 first taking samples of the raw materials and subjecting them to a solution heat treatment, wherein the solution heat treatment is as follows: water cooling after insulation at 955±10°C, and then air cooling after insulation at 700±10°C.

[0019] Furthermore, the β phase transition point temperature is measured by 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 according to the content of the primary α phase and the β phase transformation point temperature of the TC4 special grade material, lays a foundation for the transformation of the internal structure of the forging by designing the number of hammering, the hammering time interval and the pressing amount of each hammer during the forging process, and finally the forging is quenched at the upper temperature of the two-phase region. As the heat preservation is carried out, the primary α phase in the forging structure is transformed into the high-temperature β phase, and a dual-state structure forging is successfully obtained in which the α phase content meets the technical specification range and the α phase is evenly distributed 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 an axial flow impeller forging according to Example 1 of the present invention (showing the sampling position of the core);

[0030] Figure 3 This is a micrograph of the basket structure at the center 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 an axial flow impeller forging obtained by another traditional preparation method. DETAILED DESCRIPTION

[0032] In order to clearly illustrate the technical features of the present solution, the present 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", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying 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 only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0035] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0036] In the present application, unless otherwise clearly 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 structure of TC4 super-grade axial flow impeller disk forgings, comprising the following steps:

[0039] S1. Determine the 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 is: keep at 955±10℃ for about 1h and water cool, then age at 700±10℃ for about 2h and air cool, and then check the α phase content ω% in the microstructure, requiring 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 process a blank with a diameter of D0 and an initial height of H0 (in mm) on the raw material, and use a lathe to process both ends of the blank and chamfer 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 in the heating furnace must be lower than 800°C. The heating temperature t1 after entering the furnace satisfies: Heat to temperature t1 and then 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, where k takes the active value to reduce energy consumption.

[0045] The forging heating temperature t1 in this embodiment is determined according to the phase transformation point temperature t and the α phase content ω in the bar. The heating temperature t1 is the two-phase region forging temperature of the TC4 special grade material. Forging at this heating temperature is to obtain an equiaxed structure forging. Subsequently, solid solution is performed at the upper temperature of the two-phase region to smoothly obtain 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 high, according to the formula, the heating temperature t1 is high, 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) meets the following requirements:

[0048]

[0049] Hammer time interval T n (Unit s) satisfies:

[0050]

[0051] Where T n It 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, and n≤16.

[0052] During the die forging process, the temperature rise in the core of the billet causes the transformation of the structure or affects the α phase content in the structure. In order to control the temperature rise fluctuation in the core of the billet, this embodiment controls the billet pressing amount per hammer and the hammering time interval, thereby controlling the reasonable fluctuation of the temperature in the core of the billet in the two-phase region, avoiding a large impact on the primary α phase content in the structure, so as to ensure that the structure after forging is an equiaxed structure 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. The forging obtained in S4 is quenched at the upper temperature of the two-phase region, and then tempered 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 zone. As the tempering and insulation 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 structure of TC4 special-grade disc forgings, comprising the following steps:

[0059] S1. Determine the 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 air cool. Then check the α phase content ω% in the microstructure. The requirement is 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 process a blank with a diameter of D0 and an initial height of H0 (in mm) on the raw material, and use a lathe to process both ends of the blank and chamfer the corners; the height-to-diameter ratio of the blank is required to be D0∈[70,150].

[0063] Based on Example 1, this embodiment adds step S20. Blank spraying: spraying lubricant on the surface of the blank, and the spraying thickness h (unit mm) of the lubricant meets 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 the steps of preheating, spraying and drying the blank in sequence.

[0066] Spraying lubricant on the surface of the billet has the following purposes: on the one hand, it has a heat-insulating effect to prevent the temperature of the billet surface 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 in the heating furnace must be lower than 800°C. The heating temperature t1 after entering the furnace satisfies: Heat to temperature t1 and then 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, where k takes the active value to reduce energy consumption.

[0069] The forging heating temperature t1 in this embodiment is determined according to the phase transformation point temperature t and the α phase content ω in the bar. The heating temperature t1 is the two-phase region forging temperature of the TC4 special grade material. Forging at this heating temperature is to obtain an equiaxed structure forging. Subsequently, solid solution is performed at the upper temperature of the two-phase region to smoothly obtain 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 high, according to the formula, the heating temperature t1 is high, 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) meets the following requirements:

[0072]

[0073] Hammer time interval T n (Unit s) satisfies:

[0074]

[0075] Where T n It 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, and n≤16.

[0076] During the die forging process, the temperature rise in the core of the billet causes the transformation of the structure or affects the α phase content in the structure. In order to control the temperature rise fluctuation in the core of the billet, this embodiment controls the billet pressing amount per hammer and the hammering time interval, thereby controlling the reasonable fluctuation of the temperature in the core of the billet in the two-phase region, avoiding a large impact on the primary α phase content in the structure, so as to ensure that the structure after forging is an equiaxed structure 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. The forging obtained in S4 is quenched at the upper temperature of the two-phase region, and then tempered 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 zone. As the tempering and insulation 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 Embodiment 2, and preferably uses glass lubricant for the best effect.

[0083] Obviously, the above embodiments are merely examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation methods here. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope 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. 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]; S2. Cutting the material to obtain a blank with a diameter of D0 and an initial height of H0; S3. Billet heating: The billet is heated in a furnace below 800°C. The heating temperature t1 after entering the furnace satisfies: Heat up to temperature t1 and then keep warm; S4. Die forging after the billet is taken out of the furnace: During the die forging process, each hammer presses down to a height of H n satisfy: Hammer time interval T n satisfy: Where H1 is the height of the forging after die forging, n is the number of hammer blows, n≤16; 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 uniformity of dual-state structure of TC4 special-grade disc forgings according to claim 1 is characterized in that: The measurement of the α phase content in S1 requires that the raw material be sampled and subjected to solution heat treatment, wherein the solution heat treatment is: heat preservation at 955±10°C followed by water cooling, and then heat preservation at 700±10°C followed by air cooling.

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

4. The method for improving the uniformity of dual-state structure of TC4 special-grade disc forgings according to claim 1 is characterized in that: The height-to-diameter ratio of the blank in S2 is 5. The method for improving the uniformity of dual-state structure 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, and the spraying thickness h of the lubricant satisfies: Where μ is the thickness coefficient, μ∈[0.4,0.5].

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

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

8. The method for improving the uniformity of dual-state structure of TC4 special-grade disc forgings according to claim 1, characterized in that: The shortest insulation time T1 in S3 satisfies: T1 = k × D0, where k is the insulation coefficient, k∈[0.6,0.8].

9. The method for improving the uniformity of dual-state structure of TC4 special-grade disc forgings according to claim 1, characterized in that: The quenching temperature t2 in S5 satisfies:

10. The method for improving the uniformity of dual-state structure 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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