Titanium alloy bar forging process for improving structure uniformity

Abstract

The invention relates to the technical field of titanium forging, in particular to a titanium alloy bar forging process for improving structure uniformity, which comprises the following steps: cogging and forging: carrying out 1-2 heating number forging on a titanium alloy cast ingot at 280-330 DEG C above a phase transformation point, and then cooling to obtain an intermediate blank; intermediate forging is conducted, specifically, the intermediate blank is heated, subjected to heat preservation, subjected to 2-4 heating number forging and then cooled, and an intermediate bar blank is obtained; meanwhile, through simulation analysis of temperature, stress and strain distribution of each heating number of forging of the bar blank, the local pressing speed of the current bar blank local area of the hydraulic machine is adjusted in real time; and forming and forging: heating the middle bar blank, preserving heat, forging for 1-2 heating times, and cooling to obtain the final finished bar. According to the difference of forging parameters at different positions of the bar blank, the pressing speed of the same pass is finely adjusted, the consistency of the distribution proportion of the alpha phase and the beta phase at different positions of the titanium alloy bar is improved, and the overall structure uniformity of the titanium alloy bar is improved.

Description

Technical Field

[0001] The present application relates to the field of titanium forging technology, and in particular to a titanium alloy bar forging process for improving microstructure uniformity. Background Art

[0002] Additive manufacturing technology places high demands on the quality of titanium alloy powder. The uniformity of the structure and control of internal defects of titanium alloy powder rods are key factors in ensuring the quality of titanium alloy powder. Titanium alloy powder rods with high structural uniformity can ensure the consistency of the composition, microstructure and properties of titanium alloy powder particles produced by the aerosol method, thereby improving the overall performance and reliability of additively manufactured parts. At the same time, the improvement of the structural uniformity of titanium alloy powder rods can avoid the generation of microcracks inside the rods and prevent crack propagation, ensure the fluidity of titanium alloy powder during the powder making process, reduce the introduction of impurities, and facilitate the formation of a high-quality molten pool during the additive manufacturing process, thereby improving the quality of titanium alloy parts.

[0003] Ti-55531 titanium alloy features high tensile strength, excellent fracture toughness, and high hardenability. Ti-55531 titanium alloy products manufactured using additive manufacturing technology are suitable for lightweight load-bearing components and structural parts with high strength requirements. Ti-55531 titanium alloy is composed of α and β phases. During the forging process of Ti-55531 titanium alloy powder rods, the α and β phases within the rods are prone to uneven distribution due to the varying forging deformation of different parts of the rods, resulting in reduced microstructural uniformity within the rods. Furthermore, the different physical and chemical properties of the α and β phases lead to uneven stress distribution at the α / β phase interface, which can easily lead to stress concentration. This uneven distribution of the two phases exacerbates the anisotropy of the titanium alloy rod's mechanical properties, increasing the likelihood of microcracks during the powdering process and reducing the quality of the resulting titanium alloy powder. Therefore, improving the microstructural uniformity of titanium alloy rods during the forging process is a pressing technical challenge. Summary of the Invention

[0004] In order to solve the above technical problems, the present application provides a titanium alloy bar forging process with improved structural uniformity to solve the existing problems.

[0005] A titanium alloy bar forging process for improving microstructure uniformity in this application adopts the following technical solutions:

[0006] One embodiment of the present application provides a titanium alloy bar forging process for improving microstructure uniformity, the process comprising the following steps:

[0007] Open forging: The titanium alloy ingot is forged 1-2 times at 280-330°C above the phase transformation point and then cooled to obtain an intermediate billet;

[0008] Intermediate forging: The intermediate billet is heated and kept warm, forged for 2 to 4 times, and then cooled to obtain an intermediate billet. At the same time, the temperature, stress, and strain distribution of each forging time of the billet are simulated and analyzed to adjust the local pressing speed of the hydraulic press in the current local area of ​​the billet in real time. Specifically:

[0009] Obtain the three-dimensional point cloud data of the billet after each forging, convert it into STL format, and perform finite element analysis to obtain several divided grids. At the same time, set the initial temperature of the billet to the temperature after heating in that firing;

[0010] The initial reduction speed of the current pass is calculated based on the ratio of the current pass's heating temperature to the highest heating temperature of all passes during the intermediate forging process. Within the same pass, the reduction speed reduction rate of the current pass is calculated based on the difference in stress and strain between each pass and its adjacent previous pass in the same grid cell, combined with the temperature mean change of all grid cells of the billet between two adjacent passes, so as to adjust the reduction speed of the current pass.

[0011] Based on the abnormal distribution of temperature, stress, and strain of all grid cells of the billet, the adjustment limit of the current pass reduction speed is calculated; the billet between the upper and lower anvils of the hydraulic press is obtained as the current local area of ​​the billet; based on the difference between the mean values ​​of the three parameters of temperature, stress, and strain of the local area and the entire billet, the local difference characteristic value is calculated; based on the local difference characteristic value and the adjustment limit of the reduction speed, the local reduction speed of the current local area of ​​the billet is calculated;

[0012] Forming forging: The intermediate bar is heated and kept warm, forged 1 to 2 times, and then cooled to obtain the final finished bar.

[0013] Preferably, during the blank forging, 2 to 3 upsettings are completed in each forging fire to obtain a β structure with a grain size of 10 mm to 20 mm; and the cumulative forging ratio of each fire is 9.0 to 11.8.

[0014] Preferably, during the intermediate forging, the intermediate billet that has completed the open forging is subjected to 2 to 4 fire forgings at a temperature of 60°C below the phase transformation point to 140°C above the phase transformation point, with the forging ratio of each fire being 2.8 to 5.2.

[0015] Preferably, the calculation method of the initial pressing speed of the current fire is:

[0016]

[0017] Among them, v1 represents the initial pressing speed of the current fire, that is, the pressing speed of the first pass in the fire; v max Indicates the maximum pressing speed; T indicates the heating temperature of the current fire; T maxIndicates the highest heating temperature of all fires in the intermediate forging process.

[0018] Preferably, the calculation method of the reduction rate of the current pass pressing speed is:

[0019]

[0020] Among them, η i represents the reduction rate of the pressing speed of the i-th pass; T i-1 and T i represent the mean temperature of all grid cells of the billet at the i-1th pass and the i-th pass respectively; It represents the average value of strain difference of all grid cells of the billet in the i-th pass; norm[] represents the normalization function;

[0021] Among them, the strain difference value D of the same grid unit under the i-th pass is i The calculation expression is: Among them, D i represents the strain difference value of the same grid unit under the i-th pass; ε i-1 and ε i Respectively represent the strain magnitude of the same grid unit in the i-1th pass and the i-th pass; σ i-1 and σ i They represent the stress magnitude of the same grid unit in the i-1th pass and the i-th pass respectively.

[0022] Preferably, the method for adjusting the pressing speed of the current pass is:

[0023] v i =v i-1 -η i ×(v i-1 -v min )

[0024] Among them, v i Indicates the pressing speed of the current pass, v min is the preset minimum pressing speed; η i represents the reduction rate of the pressing speed of the i-th pass; v i-1 and v i They represent the pressing speeds of the i-1th pass and the i-th pass respectively.

[0025] Preferably, the calculation method of the adjustment limit of the current pass pressing speed is:

[0026] Th=v×exp(-CV)

[0027] Where Th represents the adjustment limit of the current pass's reduction speed, v represents the current pass's reduction speed, CV represents the average value of the temperature variation coefficient, stress variation coefficient, and strain variation coefficient of all grid cells of the billet before the current forging pass, and exp() represents an exponential function with a natural constant as the base.

[0028] Preferably, the calculation method of the local difference eigenvalue is:

[0029] λ=norm(ΔT)×(sim+δ)

[0030] Where λ represents the local difference characteristic value of the current local area of ​​the billet; ΔT represents the difference between the temperature mean of the grid cells in the current local area of ​​the billet and the temperature mean of all grid cells in the entire billet; norm() represents the normalization function, sim represents the cosine similarity of the parameter characteristic vectors of the local area of ​​the billet and the entire billet, and δ is a preset adjustment parameter;

[0031] Among them, the parameter characteristic vectors of the local area of ​​the billet and the entire billet are respectively composed of the temperature mean, stress mean, and strain mean of all the grid cells therein.

[0032] Preferably, the calculation method of the local pressing speed of the local area of ​​the current billet is:

[0033] va=v+λ×Th

[0034] Among them, va represents the local pressing speed of the local area of ​​the current billet; v represents the pressing speed of the current pass; λ represents the local difference characteristic value of the local area of ​​the current billet; Th represents the adjustment limit of the pressing speed of the current pass.

[0035] Preferably, the forging methods of the blanking forging and the intermediate forging are upsetting, squaring, flattening and chamfering, and the forging methods of the forming forging are straight drawing, chamfering and rounding.

[0036] In the above scheme, the beneficial effects are:

[0037] This application targets the characteristic that the internal phase transformation of Ti-55531 titanium alloy material is sensitive to strain rate. By adjusting the pressing speed of the hydraulic press in real time during the intermediate forging process, the distribution of α phase and β phase tends to be uniform, thereby improving the internal structural uniformity of the titanium alloy bar. This application controls the adjustment degree of the pressing speed of different passes based on the difference in the temperature of the billet under different fires and passes, as well as the influence of different temperature changes and strain rates on the phase transformation of the titanium alloy material, reduces the difference in the strain rate of the billet caused by the fixed pressing speed at different billet temperature passes, and avoids the decrease in the uniformity of the two-phase distribution in the titanium alloy material caused by excessive or too small strain rate. This application fine-tunes the pressing speed of the same pass based on the difference in forging parameters at different positions of the billet, improves the consistency of the distribution ratio of α phase and β phase at different positions of the titanium alloy bar, and improves the overall structural uniformity of the titanium alloy bar. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0039] Figure 1 A flowchart of a titanium alloy bar forging process for improving microstructure uniformity provided in one embodiment of the present application;

[0040] Figure 2 This application provides a flowchart of a specific implementation process for adjusting the local pressing speed of each pass in the local area of ​​the current billet during the intermediate forging process in real time. DETAILED DESCRIPTION

[0041] To further illustrate the technical means and effectiveness of this application's implementation of the intended invention, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effectiveness of a titanium alloy bar forging process for improving microstructure uniformity proposed in this application. In the following description, references to different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0042] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0043] The following describes in detail a specific solution for a titanium alloy bar forging process for improving microstructure uniformity provided by the present application with reference to the accompanying drawings.

[0044] The forging equipment used in this application utilizes a 1600T hydraulic press and a 10T manipulator. The heating equipment is a box-type resistance furnace with Class 3 precision requirements. The forging raw material is a 1T Ti 55531 titanium alloy ingot with a diameter of 380mm, obtained through triple vacuum consumable melting. The forging process for Ti 55531 titanium alloy bars includes three stages: cogging forging, intermediate forging, and forming forging. The resulting Ti 55531 titanium alloy bars have a diameter of 40mm.

[0045] Example 1

[0046] See also Figure 1 , which shows a flowchart of the steps of a titanium alloy bar forging process for improving microstructure uniformity provided in Example 1 of the present application, the process comprising:

[0047] Stage 1: Blank forging.

[0048] The purpose of blank forging is to break up the coarse grain structure in the titanium alloy ingot and improve the internal structure of the material through plastic deformation.

[0049] This application adopts large deformation upsetting to refine the coarse cast grains in the original material; and adopts rounding and inverting operations to improve the forgeability inside the titanium alloy ingot and the deformation uniformity at each position, thereby improving the structural uniformity of the intermediate billet.

[0050] Specifically, this example uses a hydraulic press to forge a Ti-55531 titanium alloy ingot at 280°C above the phase transformation point (i.e., upsetting forging). Each forging cycle completes two upsetting cycles to obtain a β structure with a grain size of 20 mm. The cumulative forging ratio per cycle ranges from 9.0 to 11.8, and the forging methods include upsetting, rounding, and squaring. After forging, surface cracks in the material are polished after air cooling. The initial forging temperature for each cycle is 50°C above the phase transformation point, and the final forging temperature is 20°C below the phase transformation point, resulting in an intermediate billet.

[0051] Stage 2: Intermediate forging.

[0052] Intermediate forging adjusts the proportion and distribution of α-phase and β-phase in the structure by controlling the forging temperature, forging ratio and pressing speed of multiple fires, thereby improving the uniformity of the structure and obtaining ideal mechanical properties.

[0053] This application uses a box-type resistance furnace to heat and maintain the intermediate billet, which is then cooled after 2 to 4 forging passes, with 2 to 5 passes per pass, to produce the intermediate billet. By adjusting the reduction rate of the hydraulic press in real time, the α-phase formation process is controlled, limiting the α-phase content and grain size during hot deformation, and improving the uniformity of the α- and β-phase distribution.

[0054] Specifically, in order to obtain a titanium alloy billet with uniform structure, this embodiment performs four forgings (i.e., upsetting and drawing forging) on ​​the intermediate billet after the blanking forging is completed, which is divided into one heating at a temperature of 60°C below the phase transformation point, one heating at a temperature of 140°C above the phase transformation point, one heating at a temperature of 30°C below the phase transformation point, and one heating at a temperature of 100°C above the phase transformation point; the forging ratio of each fire is 3.1-4.9, the forging method is upsetting, drawing, flattening and inverting, and the cooling method after forging is air cooling. After forging air cooling, the surface cracks of the material are polished to ensure uniform deformation of each part of the billet. The starting forging temperature of each fire in the two-phase region is 60°C below the phase transformation point, and the final forging temperature is 150°C below the phase transformation point; the starting forging temperature of each fire in the single-phase region is 30°C above the phase transformation point, and the final forging temperature is 70°C below the phase transformation point, to obtain an intermediate billet.

[0055] In addition, the size of the pressing speed directly affects the strain rate of the billet during forging. The higher the pressing speed of the hydraulic press, the greater the deformation of the billet per unit time, resulting in a higher strain rate.

[0056] The internal phase transformation of Ti-55531 titanium alloy is sensitive to strain rate. At lower strain rates, the grain size within the billet material is larger, and the distribution of α and β phases is less uniform. However, as the strain rate increases, the billet deformation deepens, the distribution of α and β phases becomes more uniform, the grain size becomes smaller, and the texture becomes more distinct, which promotes a more uniform distribution of α and β phases.

[0057] On the other hand, excessively high strain rates can cause more severe deformation of the billet material, leading to the fragmentation of the α phase. At the same time, excessively high strain rates prevent the heat generated by deformation at high temperatures from dissipating quickly enough, increasing grain size and causing more β phase to form, affecting the uniform distribution of the two phases.

[0058] Furthermore, during the same forging process, the temperature of different locations on the billet varies due to the influence of the forging sequence. At locations with higher temperatures, the titanium alloy's deformation resistance decreases significantly, making it easier for the material to flow and dislocations to move, enhancing its plastic deformation capacity and generating a greater strain rate at the same reduction rate.

[0059] If the same reduction rate is used for forging, the strain rate distribution at different positions of the billet will be quite different, resulting in different distribution ratios of α phase and β phase at different positions, which in turn affects the overall microstructure uniformity of the billet.

[0060] This application uses finite element simulation to obtain the distribution of temperature and strain in the billet. By analyzing the temperature, stress, and strain distribution of each forging cycle, the optimal reduction speed is determined to improve the ratio and uniformity of the α-phase and β-phase in the microstructure during the forging process.

[0061] As attached Figure 2 As shown, the present application provides a specific implementation process flow chart for achieving real-time adjustment of the local pressing speed of each pass in the current local area of ​​the billet during the intermediate forging process, which is as follows:

[0062] S1: Forging simulation.

[0063] First, considering that the shape of the bar billet changes significantly after each forging, in order to reduce the error introduced in the simulation process, the shape of the bar billet is measured after each forging.

[0064] Three identical 3D laser binocular cameras are installed between the hydraulic press and the manipulator, evenly spaced around the object being measured. As the billet completes one forging pass and retreats, each camera captures depth information within its field of view.

[0065] This application utilizes the 3D data model reconstruction method for bar material disclosed in Publication No. CN113379894A. Based on the depth information collected as the bar is withdrawn from the hydraulic press, 3D point cloud data of the bar after each forging cycle is obtained and recorded as the initial 3D point cloud data for the next cycle. The 3D point cloud data for the first cycle of intermediate forging is obtained by measuring the intermediate billet during the final cycle of open forging, when the billet is withdrawn.

[0066] After heating the billet each time, the three-dimensional point cloud data and billet temperature of the billet are adjusted in real time to improve the accuracy of the billet simulation data.

[0067] Specifically, the initial three-dimensional point cloud data of the bar blank from this heat was converted to STL format and imported into the DEFORM-3D finite element system. The bar blank was then meshed using the DEFORM-3D finite element system's built-in tetrahedral elements, with the number of mesh elements set to 200,000. The initial temperature of the bar blank was set to the temperature of the bar blank after heating in this heat.

[0068] The rest of the simulation conditions are set as follows:

[0069] The upper and lower anvils are set to be rigid bodies, the material is 5CrNiMo, and the dimensions of the upper and lower anvils are both 120mm×120mm×30mm; the billet is a plastic body. The outer surface of the billet exchanges heat with the surfaces of the upper and lower anvils and the air. The heat exchange coefficient between the billet and the air is set to 0.02[N / (sec·mm·℃)], and the heat exchange coefficient between the billet and the upper and lower anvils is set to 0.02[N / (sec·mm·℃)]. The ambient temperature is set to 20℃, and the temperature of the upper and lower anvils is set to 350℃. The contact surface between the upper and lower anvils and the billet adopts a shear friction model. This application is set to a non-lubricated condition, and the friction factor is selected as 0.58.

[0070] This application uses the cooperation of a hydraulic press and a manipulator to achieve upsetting, squaring, flattening, and square-squaring of a bar. The control signals of the hydraulic press and manipulator are input into the DEFORM-3D finite element system to complete the bar forging simulation for each press cycle, and to obtain the temperature, stress, and strain distribution of the bar after each press cycle.

[0071] S2: Adjustment of the pressing speed of each pass in each fire.

[0072] The maximum pressing speed of the hydraulic press is set to 25 mm / s and the minimum pressing speed is set to 3 mm / s.

[0073] At high temperatures, titanium alloys have low deformation resistance and enhanced plastic deformation capabilities, allowing for a higher reduction speed. However, at low temperatures, the deformation uniformity of titanium alloys is poor, requiring a reduced reduction speed. Furthermore, when forging in the higher-temperature single-phase region, the reduction speed should not be too low, as this will result in excessive forging time and a large surface temperature drop, affecting the material's fluidity and uniformity. When forging in the lower-temperature two-phase region, the material's deformation uniformity is poor. Therefore, the reduction speed should be appropriately reduced to ensure uniform deformation, consistent strain rates within the material, and improved uniformity of the internal two-phase distribution.

[0074] Based on the influence of temperature on material deformation behavior and microstructure evolution, the initial reduction speed of the current fire is calculated according to the heating temperature of the current fire:

[0075]

[0076] Among them, v1 represents the initial pressing speed of the current fire, that is, the pressing speed of the first pass in the fire; v max represents the maximum pressing speed, which is 25 mm / s in this embodiment; T represents the heating temperature of the current fire; T max It represents the highest heating temperature of all the firings in the intermediate forging process, and in this embodiment, the value is 820°C.

[0077] Within the same forging cycle, the forging temperature decreases with each pass, requiring the reduction rate to be adjusted appropriately based on the temperature changes. During the forging process, the titanium alloy's microstructure undergoes changes, such as grain breakage, recrystallization, and phase transformation. These changes affect the material's strain and stress distribution.

[0078] Comparing the strain under unit stress in different passes can reflect changes in the material structure. If the strain under unit stress in a particular pass changes significantly, it indicates that the titanium alloy material structure in that area has undergone significant deformation or phase transformation, and the material structure has changed dramatically. The reduction rate needs to be reduced to avoid local overheating and ensure a uniform distribution of α and β phases.

[0079] According to the difference in stress and strain between each pass and its adjacent previous pass in the same grid unit, the strain difference value of each pass in the grid unit is calculated:

[0080]

[0081] Among them, D i represents the strain difference value of the grid unit under the i-th pass; ε i-1 and ε i Respectively represent the strain of the grid unit under the i-1th pass and the i-th pass; σ i-1 and σ i They represent the stress of the grid unit under the i-1th pass and the i-th pass respectively.

[0082] By obtaining the change in strain under unit stress, the change in the material structure at the corresponding rod position of the grid cell is reflected. The strain difference value reflects the degree of change in the material structure at the corresponding rod position of the grid cell between two consecutive passes.

[0083] At the same time, the faster the temperature of the billet drops, the more obvious the decrease in the fluidity of the internal material, the increase in strain rate sensitivity, and the deterioration of the structural uniformity. It is necessary to increase the reduction rate of the pressing speed to ensure the stability of the forging process and the uniformity of the material.

[0084] Furthermore, the reduction rate of the current pass speed is calculated:

[0085]

[0086] Among them, η i represents the reduction rate of the pressing speed of the i-th pass; T i-1 and T i represent the mean temperature of all grid cells of the billet at the i-1th pass and the i-th pass respectively; It represents the average value of the strain difference of all grid elements of the bar blank under the i-th pass; norm[] represents the normalization function, and the arc tangent normalization function is used here, and the normalization range is (0,1).

[0087] Finally, calculate the pressing speed v of the current pass i :

[0088] v i =v i-1 -η i ×(v i-1 -v min )

[0089] Among them, v min is the preset minimum pressing speed, which is 3 mm / s; η irepresents the reduction rate of the pressing speed of the i-th pass; v i-1 and v i They represent the pressing speeds of the i-1th pass and the i-th pass respectively.

[0090] S3: Adjustment of the pressing speed of the local position of the billet in each pass.

[0091] During the forging process, the temperature, stress, and strain distributions at different locations within the billet vary, leading to variations in deformation behavior in these areas. To improve the overall structural uniformity of the titanium alloy bar, the local reduction speed is adjusted based on the contrast between the local and overall characteristics of the billet.

[0092] According to the displacement data of the manipulator, the rod blank between the upper and lower anvils of the hydraulic press is obtained through the DEFORM-3D finite element system and recorded as the current local area of ​​the rod blank, whose length is consistent with the length of the upper and lower anvils of the hydraulic press.

[0093] Inhomogeneities in temperature, stress, and strain distributions affect the material's deformation behavior and ultimate microstructure. To ensure uniform deformation and microstructure throughout the billet, the reduction speed must be dynamically adjusted based on these distribution inhomogeneities. When these three distributions are uneven, the adjustment limits need to be increased to allow for flexible adjustment of the reduction speed in different areas, ensuring microstructure uniformity during the forging process.

[0094] According to the abnormal distribution of temperature, stress and strain of all grid cells of the billet, the adjustment limit of the current pass speed is calculated:

[0095] Th=v×exp(-CV)

[0096] Among them, Th represents the adjustment limit of the current pass pressing speed, that is, the maximum adjustment amount of the pressing speed in this pass, v represents the pressing speed of the current pass; CV represents the average value of the temperature variation coefficient, stress variation coefficient, and strain variation coefficient of all grid cells of the bar before the current forging pass; exp() represents an exponential function with a natural constant as the base, which is used to characterize the quantitative change relationship between the mean value of the coefficient of variation of the temperature, stress, and strain of the bar and the adjustment limit of the pressing speed in this pass.

[0097] The parameter feature vector is constructed by taking the mean temperature, mean stress, and mean strain of all grid cells in the local area of ​​the billet. The parameter feature vector of the entire billet is constructed in the same way.

[0098] According to the parameter eigenvectors of the local area of ​​the billet and the entire billet, the local difference eigenvalue is calculated:

[0099] λ=norm(ΔT)×(sim+δ)

[0100] Where λ represents the local difference characteristic value of the local area of ​​the current billet; ΔT represents the difference between the temperature mean of the grid cells in the local area of ​​the current billet and the temperature mean of all grid cells in the entire billet; norm() represents the normalization function, and the hyperbolic tangent function is used here to map ΔT to (-1, 1).

[0101] A larger ΔT indicates a greater temperature difference between the local region and the entire billet, and the calculated local difference characteristic value increases the subsequent adjustment of the reduction speed. Furthermore, when the temperature of the local region is higher than that of the entire billet, the local difference characteristic value and the subsequent adjustment of the reduction speed are positive, increasing the reduction speed. When the temperature of the local region is lower than that of the entire billet, the local difference characteristic value and the subsequent adjustment of the reduction speed are negative, decreasing the reduction speed.

[0102] sim represents the cosine similarity of the parameter feature vectors of the local area of ​​the billet and the entire billet, reflecting the difference in forging parameters between the local area of ​​the billet and the entire billet; δ is a preset adjustment parameter, which is set to 1 in this embodiment, in order to map sim to a positive value.

[0103] The larger the local difference characteristic value, the greater the difference between the forging parameters of the local area of ​​the billet being forged by the hydraulic press and the entire billet, and the greater the adjustment amount of the pressing speed in this area.

[0104] Finally, the local pressing speed of the current local area of ​​the billet is calculated according to the local difference characteristic value and the adjustment limit of the pressing speed, so as to adjust the local pressing speed of the current local area of ​​the billet.

[0105] va=v+λ×Th

[0106] Among them, va represents the local pressing speed of the local area of ​​the current billet; v represents the pressing speed of the current pass; λ represents the local difference characteristic value of the local area of ​​the current billet; Th represents the adjustment limit of the pressing speed of the current pass.

[0107] Stage three: forming and forging.

[0108] As the final stage of forging, the main purpose of forming forging is to ensure that the titanium alloy bar has a precise geometry and size to meet the needs of subsequent processing. At the same time, through the final forming forging, the residual stress in the titanium alloy material can be effectively reduced, avoiding cracking or deformation caused by stress concentration.

[0109] This application uses a box-type resistance furnace to heat and insulate the intermediate bar, followed by cooling after one to two forging passes, with each pass consisting of two to five passes, to produce Ti 55531 titanium alloy bar. A forging method combining straight drawing, chamfering, and rounding, combined with a small forging ratio and appropriate reheating, is employed to achieve uniform metal flow and deformation in all directions during the forging process, thereby preventing a decrease in the uniformity of the intermediate bar's internal structure.

[0110] Specifically, in this embodiment, the intermediate bar blank obtained by the intermediate forging is heated to 40°C below the phase transformation point and the holding time is 7h; then two fire forgings are performed with a forging ratio of 1.0 to 2.0. The forging methods are straight drawing, chamfering and rounding. The shape of the billet changes from a square billet to a round billet. The forging process can be appropriately reheated, and the surface cracks of the material are polished after forging air cooling; the initial forging temperature of each forming forging is 90°C below the phase transformation point, and the final forging temperature is 160°C below the phase transformation point; and then through machining and finishing, a Ф40mm Ti 55531 titanium alloy bar is finally obtained.

[0111] Example 2

[0112] See also Figure 1 , which shows a flowchart of the steps of a titanium alloy bar forging process for improving microstructure uniformity provided in Example 2 of the present application, the process comprising:

[0113] Stage 1: Blank forging.

[0114] In this example, a Ti-55531 titanium alloy ingot was forged using a hydraulic press in two cycles (i.e., upsetting and drawing) at 300°C above the phase transformation point, with three upsetting cycles completed per cycle. This resulted in a β structure with a grain size of 15 mm. The cumulative forging ratio for each cycle ranged from 9.0 to 11.8, with upsetting, rounding, and squaring. After air cooling, surface cracks were polished. Each cycle began at a temperature 100°C above the phase transformation point and ended at a temperature 50°C below the phase transformation point, yielding an intermediate billet.

[0115] Stage 2: Intermediate forging.

[0116] In this embodiment, the intermediate billet after the blanking forging is subjected to three forging cycles (i.e., upsetting and drawing forging), which are divided into one heating cycle with a temperature of 30°C below the phase transformation point, one heating cycle with a temperature of 120°C above the phase transformation point, and one heating cycle with a temperature of 50°C below the phase transformation point; the forging ratio of each fire cycle is 3.1-4.9, the forging methods are upsetting, drawing, flattening, and inverting, and the cooling method after forging is air cooling. After forging air cooling, the surface cracks of the material are polished to ensure uniform deformation of each part of the billet. The starting forging temperature of each fire cycle in the two-phase region is 110°C below the phase transformation point, and the final forging temperature is 200°C below the phase transformation point; the starting forging temperature of each fire cycle in the single-phase region is 50°C above the phase transformation point, and the final forging temperature is 120°C below the phase transformation point, to obtain an intermediate billet.

[0117] Stage three: forming and forging.

[0118] In this embodiment, the intermediate bar blank obtained by the intermediate forging is heated to 45°C below the phase transformation point and the holding time is 7.5 hours; then two fire forgings are performed with a forging ratio of 1.0 to 2.0. The forging methods are straight drawing, chamfering and rounding. The shape of the billet is changed from a square billet to a round billet. The forging process can be appropriately reheated, and the surface cracks of the material are polished after forging air cooling; the initial forging temperature of each forming forging is 130°C below the phase transformation point, and the final forging temperature is 180°C below the phase transformation point; and then through machining and finishing, a Ф40mm Ti 55531 titanium alloy bar is finally obtained.

[0119] The remaining steps are processed in exactly the same manner as in Example 1 of the present application to obtain a titanium alloy wire.

[0120] Example 3

[0121] See also Figure 1 , which shows a flowchart of the steps of a titanium alloy bar forging process for improving microstructure uniformity provided in Example 3 of the present application, the process comprising:

[0122] Stage 1: Blank forging.

[0123] In this example, a Ti-55531 titanium alloy ingot was forged using a hydraulic press at 330°C above the phase transformation point (i.e., upsetting forging). Three upsettings were performed per forging cycle to obtain a β structure with a grain size of 10 mm. The cumulative forging ratio per cycle ranged from 9.0 to 11.8, and the forging methods included upsetting, rounding, and squaring. After air cooling, surface cracks were polished. Each cycle began at a temperature of 150°C above the phase transformation point and ended at a temperature of 100°C below the phase transformation point to produce an intermediate billet.

[0124] Stage 2: Intermediate forging.

[0125] In this embodiment, the intermediate billet after the blanking forging is subjected to two forgings (i.e., upsetting and drawing forging) at 40°C above the phase transformation point, which is divided into one heating at a temperature of 50°C below the phase transformation point and one heating at a temperature of 80°C above the phase transformation point; the forging ratio of each fire is 3.1-4.9, the forging methods are upsetting, drawing, flattening and inverting, and the cooling method after forging is air cooling. After forging air cooling, the surface cracks of the material are polished to ensure uniform deformation of each part of the billet. The starting forging temperature of each fire in the two-phase region is 150°C below the phase transformation point, and the final forging temperature is 250°C below the phase transformation point; the starting forging temperature of each fire in the single-phase region is 80°C above the phase transformation point, and the final forging temperature is 150°C below the phase transformation point, to obtain an intermediate bar billet.

[0126] Stage three: forming and forging.

[0127] In this embodiment, the intermediate bar blank obtained by the intermediate forging is heated to 50°C below the phase transformation point and kept at this temperature for 8 hours. Then, one fire forging is performed with a forging ratio of 1.0 to 2.0. The forging method includes straight drawing, chamfering and rounding. The shape of the billet is changed from a square billet to a round billet. The forging process can be appropriately reheated, and the surface cracks of the material are polished after forging and air cooling. The initial forging temperature of each forming forging is 180°C below the phase transformation point, and the final forging temperature is 200°C below the phase transformation point. Then, through machining and finishing, a Ø40mm Ti 55531 titanium alloy bar is finally obtained.

[0128] The remaining steps are processed in exactly the same manner as in Example 1 of the present application to obtain a titanium alloy wire.

[0129] The various embodiments in this application are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0130] It should be noted that, unless otherwise specified and limited, terms such as "include", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a circuit structure, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, the phrase "including a ..." defines an element, does not exclude the presence of other identical elements in the article or device including the element. In addition, the term "and\or" used herein includes any and all combinations of one or more related listed items.

[0131] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of the present application and include common knowledge or customary techniques in the art not invented herein.

[0132] It will be understood that the present application is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

1. A titanium alloy bar forging process for improving microstructure uniformity, characterized in that: The process includes the following steps: Open forging: The titanium alloy ingot is forged 1-2 times at 280-330°C above the phase transformation point and then cooled to obtain an intermediate billet; Intermediate forging: The intermediate billet is heated and kept warm, forged for 2 to 4 times, and then cooled to obtain an intermediate billet. At the same time, the temperature, stress, and strain distribution of each forging time of the billet are simulated and analyzed to adjust the local pressing speed of the hydraulic press in the current local area of ​​the billet in real time. Specifically: Obtain the three-dimensional point cloud data of the billet after each forging, convert it into STL format, and perform finite element analysis to obtain several divided grids. At the same time, set the initial temperature of the billet to the temperature after heating in that firing; The initial reduction speed of the current pass is calculated based on the ratio of the current pass's heating temperature to the highest heating temperature of all passes during the intermediate forging process. Within the same pass, the reduction speed reduction rate of the current pass is calculated based on the difference in stress and strain between each pass and its adjacent previous pass in the same grid cell, combined with the temperature mean change of all grid cells of the billet between two adjacent passes, so as to adjust the reduction speed of the current pass. Based on the abnormal distribution of temperature, stress, and strain of all grid cells of the billet, the adjustment limit of the current pass reduction speed is calculated; the billet between the upper and lower anvils of the hydraulic press is obtained as the current local area of ​​the billet; based on the difference between the mean values ​​of the three parameters of temperature, stress, and strain of the local area and the entire billet, the local difference characteristic value is calculated; based on the local difference characteristic value and the adjustment limit of the reduction speed, the local reduction speed of the current local area of ​​the billet is calculated; Forming forging: The intermediate bar is heated and kept warm, forged 1 to 2 times, and then cooled to obtain the final finished bar.

2. A titanium alloy bar forging process for improving microstructure uniformity according to claim 1, characterized in that: During the blank forging, 2 to 3 upsettings are completed in each forging process to obtain a β structure with a grain size of 10 mm to 20 mm; the cumulative forging ratio of each fire is 9.0 to 11.

8.

3. A titanium alloy bar forging process for improving microstructure uniformity according to claim 1, characterized in that: During the intermediate forging, the intermediate billet that has completed the open forging is forged at a temperature of 60°C below the phase transformation point to 140°C above the phase transformation point for 2 to 4 fires, with a forging ratio of 2.8 to 5.2 for each fire.

4. A titanium alloy bar forging process for improving microstructure uniformity according to claim 1, characterized in that: The calculation method of the initial pressing speed of the current fire is: Among them, v1 represents the initial pressing speed of the current fire, that is, the pressing speed of the first pass in the fire; v max Indicates the maximum pressing speed; T indicates the heating temperature of the current fire; T max Indicates the highest heating temperature of all fires in the intermediate forging process.

5. The titanium alloy bar forging process for improving microstructure uniformity according to claim 1, wherein: The calculation method of the reduction rate of the current pass speed is: Among them, η i represents the reduction rate of the pressing speed of the i-th pass; T i-1 and T i represent the mean temperature of all grid cells of the billet at the i-1th pass and the i-th pass respectively; It represents the average value of strain difference of all grid cells of the billet in the i-th pass; norm[] represents the normalization function; Among them, the strain difference value D of the same grid unit under the i-th pass is i The calculation expression is: Among them, D i represents the strain difference value of the same grid unit under the i-th pass; ε i-1 and ε i Respectively represent the strain magnitude of the same grid unit in the i-1th pass and the i-th pass; σ i-1 and σ i They represent the stress magnitude of the same grid unit in the i-1th pass and the i-th pass respectively.

6. The titanium alloy bar forging process for improving microstructure uniformity according to claim 1, characterized in that: The method for adjusting the pressing speed of the current pass is: v i =v i-1 -η i ×(v i-1 -v min ) Among them, v i Indicates the pressing speed of the current pass, v min is the preset minimum pressing speed; η i represents the reduction rate of the pressing speed of the i-th pass; v i-1 and v i They represent the pressing speeds of the i-1th pass and the i-th pass respectively.

7. The titanium alloy bar forging process for improving microstructure uniformity according to claim 1, characterized in that: The calculation method of the adjustment limit of the current pass pressing speed is: Th=v×exp(-CV) Where Th represents the adjustment limit of the current pass's reduction speed, v represents the current pass's reduction speed, CV represents the average value of the temperature variation coefficient, stress variation coefficient, and strain variation coefficient of all grid cells of the billet before the current forging pass, and exp() represents an exponential function with a natural constant as the base.

8. The titanium alloy bar forging process for improving microstructure uniformity according to claim 1, wherein: The calculation method of the local difference eigenvalue is: λ=norm(ΔT)×(sim+δ) Where λ represents the local difference characteristic value of the current local area of ​​the billet; ΔT represents the difference between the temperature mean of the grid cells in the current local area of ​​the billet and the temperature mean of all grid cells in the entire billet; norm() represents the normalization function, sim represents the cosine similarity of the parameter characteristic vectors of the local area of ​​the billet and the entire billet, and δ is a preset adjustment parameter; Among them, the parameter characteristic vectors of the local area of ​​the billet and the entire billet are respectively composed of the temperature mean, stress mean, and strain mean of all the grid cells therein.

9. The titanium alloy bar forging process for improving microstructure uniformity according to claim 1, wherein: The calculation method of the local pressing speed of the current local area of ​​the billet is: va=v+λ×Th Among them, va represents the local pressing speed of the local area of ​​the current billet; v represents the pressing speed of the current pass; λ represents the local difference characteristic value of the local area of ​​the current billet; Th represents the adjustment limit of the pressing speed of the current pass.

10. The titanium alloy bar forging process for improving microstructure uniformity according to claim 1, wherein: The forging methods for blank forging and intermediate forging are upsetting, squaring, flattening and chamfering, and the forging methods for forming forging are straight drawing, chamfering and rounding.

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