Titanium alloy bar forging process for improving microstructure uniformity

Abstract

The application relates to the field of titanium forging technology, in particular to a titanium alloy bar forging process for improving the uniformity of the structure, which comprises the following steps: blooming forging: after 1-2 heating times of forging of a titanium alloy ingot above the phase transition point of 280 DEG C-330 DEG C and cooling, intermediate blank is obtained; intermediate forging: after 2-4 heating times of forging of the intermediate blank and cooling, an intermediate bar blank is obtained; meanwhile, through simulation analysis of the temperature, stress and strain distribution of each heating time of the bar blank, the local reduction speed of the current bar blank local area of the hydraulic machine is adjusted in real time; forming forging: after 1-2 heating times of forging of the intermediate bar blank and cooling, the final finished bar material is obtained. According to the difference of the forging parameters of different positions of the bar blank, the reduction speed of the same pass is fine-tuned, the consistency of the distribution proportion of alpha phase and 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 technical field of titanium forging, in particular to a titanium alloy bar forging process for improving microstructure uniformity. BACKGROUND

[0002] Additive manufacturing technology has high requirements for the quality of titanium alloy powder. The control of the microstructure uniformity and internal defects of the titanium alloy bar for powder production is a key factor to ensure the quality of the titanium alloy powder. The titanium alloy bar for powder production with high microstructure uniformity can ensure the consistency of the titanium alloy powder particles in composition, microstructure and performance, thereby improving the overall performance and reliability of the additive manufacturing parts. At the same time, the improvement of the microstructure uniformity of the titanium alloy bar for powder production can avoid the generation of micro-cracks in the bar and prevent the propagation of the cracks, ensure the flowability of the titanium alloy powder during the powder production process, reduce the introduction of impurities, and be conducive to the formation of a high-quality molten pool during the additive manufacturing process, thereby improving the quality of the titanium alloy parts.

[0003] Ti-55531 titanium alloy has high tensile strength, good fracture toughness and high hardenability, and the Ti-55531 titanium alloy product made by additive manufacturing technology can be applied to lightweight load-bearing components and structural components with high strength requirements. Ti-55531 titanium alloy is composed of α phase and β phase. During the forging process of the Ti-55531 titanium alloy bar for powder production, due to the difference in forging deformation of each part of the titanium alloy bar, the α phase and β phase in the bar are more likely to be unevenly distributed, resulting in a decrease in the microstructure uniformity of the bar. At the same time, the α phase and β phase have different physical and chemical properties, and the stress distribution at the α / β phase interface is uneven, which is prone to stress concentration. The uneven distribution of the two phases exacerbates the anisotropy of the mechanical properties of the titanium alloy bar, increases the possibility of generating micro-cracks in the titanium alloy bar during the powder production process, and leads to a decrease in the quality of the titanium alloy powder produced. Therefore, how to improve the microstructure uniformity of the titanium alloy bar during the forging process is a technical problem to be solved at present. SUMMARY

[0004] To solve the above technical problems, the present application provides a titanium alloy bar forging process for improving microstructure uniformity to solve the existing problems.

[0005] The titanium alloy bar forging process for improving microstructure uniformity provided by the present application adopts the following technical scheme:

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

[0007] Blooming forging: after 1-2 heating times of forging the titanium alloy ingot at 280-330℃ above the phase transition point and cooling, an intermediate blank is obtained;

[0008] Intermediate forging: heating, holding, 2-4 fire forging and cooling of intermediate blank to obtain intermediate bar blank; at the same time, through simulation analysis of temperature, stress and strain distribution of each fire forging of the bar blank, the local reduction speed of the current bar blank local area of the hydraulic press is adjusted in real time; specifically:

[0009] The three-dimensional point cloud data of the bar blank after each fire forging is obtained, and the finite element analysis is carried out after being converted into STL format, and a plurality of grids after division are obtained, and the initial temperature of the bar blank is set to the temperature after heating of the fire;

[0010] According to the proportion of the heating temperature of the current fire to the maximum heating temperature of all fires in the intermediate forging process, the initial reduction speed of the current fire is calculated; within the same fire, according to the difference between the stress and strain of each pass and its adjacent previous pass in the same grid unit, and combining the average temperature change of all grid units between the adjacent two passes, the reduction rate of the current pass reduction speed is calculated to adjust the reduction speed of the current pass;

[0011] According to the abnormal distribution of temperature, stress and strain of all grid units of the bar blank, the adjustment limit value of the current pass reduction speed is calculated; the bar blank between the upper and lower anvils of the hydraulic press is obtained as the current bar blank local area; according to the difference between the average values of temperature, stress and strain of the bar blank local area and the whole, the local difference characteristic value is calculated; according to the local difference characteristic value and the adjustment limit value of the reduction speed, the local reduction speed of the current bar blank local area is calculated.

[0012] Forming forging: heating, holding, 1-2 fire forging and cooling of intermediate bar blank to obtain final finished bar material.

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

[0014] Preferably, during the intermediate forging, the intermediate blank after the breakdown forging is forged 2-4 times below 60℃ below the phase transition point to above 140℃ above the phase transition point, and the forging ratio of each fire is 2.8-5.2.

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

[0016]

[0017] Wherein, v1 represents the initial reduction speed of the current fire, that is, the reduction speed of the first pass in the fire; v max represents the maximum reduction speed; T represents the heating temperature of the current fire; T maxrepresents the maximum heating temperature of all heating times in the intermediate forging process.

[0018] Preferably, the method for calculating the down-regulation rate of the current pass reduction speed is:

[0019]

[0020] wherein η i represents the down-regulation rate of the i-th pass reduction speed; T i-1 and T i respectively represent the average value of the temperature of all grid units of the bar blank in the i-1-th pass and the i-th pass; represents the average value of the strain difference value of all grid units of the bar blank in the i-th pass; norm[] represents a normalization function;

[0021] wherein the calculation expression of the strain difference value D i of the same grid unit in the i-th pass is: wherein D i represents the strain difference value of the same grid unit in the i-th pass; ε i-1 and ε i respectively represent the strain size of the same grid unit in the i-1-th pass and the i-th pass; σ i-1 and σ i respectively represent the stress size of the same grid unit in the i-1-th pass and the i-th pass.

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

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

[0024] wherein v i represents the reduction speed of the current pass, v min is a preset minimum reduction speed; η i represents the down-regulation rate of the i-th pass reduction speed; v i-1 and v i respectively represent the reduction speed of the i-1-th pass and the i-th pass.

[0025] Preferably, the method for calculating the adjustment limit value of the current pass reduction speed is:

[0026] Th = v × exp(-CV)

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

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

[0029] λ = norm (ΔT) x (sim + δ)

[0030] Wherein, λ represents the local difference characteristic value of the current local area of the bar; ΔT represents the difference between the temperature average of the grid cells in the current local area of the bar and the temperature average of all grid cells of the entire bar; norm() represents the normalization function, sim represents the cosine similarity of the parameter characteristic vector of the local area of the bar and the entire bar, and δ is a preset adjustment parameter.

[0031] Wherein, the parameter characteristic vectors of the local area of the bar and the entire bar are respectively composed of the temperature average, the stress average and the strain average of all grid cells in the local area.

[0032] Preferably, the calculation method of the local reduction speed of the current local area of the bar is:

[0033] va = v + λ x Th

[0034] Wherein, va represents the local reduction speed of the current local area of the bar; v represents the reduction speed of the current pass; λ represents the local difference characteristic value of the current local area of the bar; Th represents the adjustment limit value of the current pass reduction speed.

[0035] Preferably, the forging modes of the cogging forging and the intermediate forging are upsetting, square drawing, flat square drawing and inverted octagonal drawing, and the forging modes of the forming forging are straight drawing, inverted corner and round rolling.

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

[0037] The present application is aimed at the characteristics of the internal phase transition of Ti-55531 titanium alloy material being sensitive to strain rate, by adjusting the press-down speed of the hydraulic machine in the intermediate forging process in real time, the distribution of alpha phase and beta phase tends to be homogenized, and the internal microstructure uniformity of titanium alloy bar is improved. According to the differences in bar blank temperature under different heating times and passes, and the influence of different temperature changes and strain rates on the phase transition of titanium alloy material, the adjustment degree of the press-down speed of different passes is controlled, the difference in strain rate of the bar blank caused by the fixed press-down speed of different bar blank temperature passes is reduced, and the decline of the internal two-phase distribution uniformity of titanium alloy material caused by excessive or insufficient strain rate is avoided. According to the difference of forging parameters of different positions of the bar blank, the press-down speed of the same pass is fine-tuned, the consistency of the distribution proportion of alpha phase and beta phase at different positions of the titanium alloy bar is improved, and the overall microstructure uniformity of the titanium alloy bar is improved. BRIEF DESCRIPTION OF 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 drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0039] Figure 1 A step flow chart of a titanium alloy bar forging process for improving microstructure uniformity provided by an embodiment of the present application;

[0040] Figure 2 A specific implementation process flow chart of the present application which can adjust the local press-down speed of each pass in the current local area of the bar blank in the intermediate forging process in real time. DETAILED DESCRIPTION

[0041] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the specific embodiments, structure, features and effects of a titanium alloy bar forging process for improving microstructure uniformity according to the present application are described in detail as follows. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

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

[0043] The specific scheme of the titanium alloy bar forging process for improving microstructure uniformity provided by the present application is described in detail below with reference to the drawings.

[0044] The forging equipment of the present application adopts a 1600T hydraulic machine and a 10T manipulator, the heating equipment is a box-type resistance furnace with a three-level precision requirement, and the forging raw material is a Φ380mm, 1T Ti 55531 titanium alloy ingot prepared by three times of vacuum consumable melting. The forging process for the Ti 55531 titanium alloy bar includes three stages of blooming forging, intermediate forging and forming forging, and the Ti 55531 titanium alloy bar prepared by forging has a specification of Φ40mm.

[0045] Example 1

[0046] Referring to Figure 1 which shows a step flow chart of a titanium alloy bar forging process for improving the uniformity of the organization provided by the present application, the process includes:

[0047] Stage one: blooming forging.

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

[0049] The present application adopts large deformation upsetting to refine the coarse as-cast grains in the original material, and adopts rolling and inverted octagonal operation to improve the forging penetration and deformation uniformity of each position in the titanium alloy ingot, and to improve the uniformity of the obtained intermediate material.

[0050] Specifically, the present embodiment adopts a hydraulic machine to perform 2 fire times of forging (i.e. upsetting and drawing) on the Ti-55531 titanium alloy ingot at 280℃ above the phase transition point, and 2 upsetting and drawing are completed for each fire time to obtain β organization with a grain size of 20mm; the cumulative forging ratio for each fire time is 9.0-11.8, the forging mode is upsetting, rolling and inverted octagonal, and the surface cracks of the material are polished after air cooling and forging. The initial forging temperature is 50℃ above the phase transition point, and the final forging temperature is 20℃ below the phase transition point, and the intermediate material is obtained.

[0051] Stage two: intermediate forging.

[0052] Intermediate forging adjusts the proportion and distribution of α phase and β phase in the organization by controlling the forging temperature, forging ratio and reduction speed of multiple fire times, so as to improve the uniformity of the organization and obtain ideal mechanical properties.

[0053] The present application adopts a box-type resistance furnace to heat and keep the intermediate material, and the intermediate bar blank is obtained after 2-4 fire times of forging, each fire time is set with 2-5 passes. By adjusting the reduction rate of the hydraulic machine in real time, the generation process of the α phase is controlled, the α phase content and grain size in the thermal deformation process are limited, and the uniformity of the distribution of the α phase and the β phase is improved.

[0054] Specifically, to obtain a titanium alloy blank with uniform structure, the intermediate blank after finish breakdown forging is forged 4 times (i.e., upsetting and drawing), which is divided into 1 heating at 60°C below the phase transition point, 1 heating at 140°C above the phase transition point, 1 heating at 30°C below the phase transition point, and 1 heating at 100°C above the phase transition point; the forging ratio of each heating is 3.1-4.9, the forging mode is upsetting, drawing, drawing flat square, and inverted square, the cooling mode after forging is air cooling, the surface cracks of the material are polished after air cooling, and the deformation of each part of the blank is ensured to be uniform. The initial forging temperature of each heating in the two-phase region is 60°C below the phase transition point, and the final forging temperature is 150°C below the phase transition point; the initial forging temperature of each heating in the single-phase region is 30°C above the phase transition point, and the final forging temperature is 70°C below the phase transition point, to obtain an intermediate bar blank.

[0055] In addition, the size of the pressing speed directly affects the strain rate of the bar blank during forging. The greater the pressing speed of the hydraulic machine, the greater the deformation amount the bar blank bears in unit time, resulting in a greater strain rate.

[0056] The internal phase transition of Ti-55531 titanium alloy material is relatively sensitive to the strain rate. On the one hand, at a relatively low strain rate, the grain size in the bar blank material is relatively large, and the distribution of the α phase and the β phase is not uniform enough. With the increase of the strain rate, the deformation degree of the bar blank deepens, the distribution of the α phase and the β phase tends to be uniform, the grain size is relatively small, and the texture is obvious, which is beneficial to the uniform distribution of the α phase and the β phase.

[0057] On the other hand, too high a strain rate will make the deformation of the bar blank material more severe, resulting in the fragmentation of the α phase. At the same time, too high a strain rate makes the heat generated by deformation at high temperature not enough and dissipate in time, resulting in the increase of the grain size, causing more β phase to be generated, affecting the uniform distribution of the two phases.

[0058] In addition, during the forging process of the bar blank in the same heating, the temperature of each position of the bar blank is different due to the influence of the forging sequence of different positions of the bar blank. At the position of the bar blank with a higher temperature, the deformation resistance of the titanium alloy decreases significantly, the material is more prone to flow, the dislocation movement is more prone to occur, the plastic deformation ability of the material is enhanced, and the same pressing speed produces a greater strain rate on the bar blank.

[0059] If the same pressing speed is used for forging, the strain rate distribution of different positions of the bar blank will appear a large difference, resulting in different distribution proportions of the α phase and the β phase at different positions, and further affecting the overall uniformity of the structure of the bar blank.

[0060] The present application uses finite element simulation to obtain the distribution of the temperature and strain of the bar blank. By simulating the temperature, stress and strain distribution of the bar blank during each heating, the optimal pressing speed is determined, and the proportion and distribution uniformity of the α phase and the β phase in the structure during the forging process are improved.

[0061] As shown in the accompanying Figure 2 The application gives a specific implementation process flow chart for realizing real-time adjustment of the local reduction speed of each pass in the current local area of the billet in the intermediate forging process, as follows:

[0062] S1: forging simulation.

[0063] Firstly, considering that the shape of the billet changes greatly after each heating and forging, in order to reduce the error introduced in the simulation process, the shape of the billet is measured after each heating and forging.

[0064] Three laser 3D binocular cameras of the same model are installed between the hydraulic press and the manipulator, and are uniformly distributed in a circle around the measured object. When the billet completes a heating and forging and is withdrawn backward, the three laser 3D binocular cameras respectively acquire the depth information of the billet within their respective visual ranges.

[0065] The application adopts the three-dimensional data model reconstruction method for a bar disclosed in publication No. CN113379894A, acquires the three-dimensional point cloud data of the billet after the heating and forging according to the depth information collected when the billet is withdrawn from the hydraulic press, and records it as the initial three-dimensional point cloud data of the billet for the next heating and forging. The three-dimensional point cloud data of the billet for the first heating and forging in the intermediate forging is acquired by measurement when the intermediate billet is withdrawn in the last heating and forging of the blooming forging.

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

[0067] Specifically, the initial three-dimensional point cloud data of the billet for the heating is converted into STL format and input into the DEFORM-3D finite element system, and the tetrahedral element of the DEFORM-3D finite element system is used to divide the grid of the billet, and the number of grid elements is set to 200000. The initial temperature of the billet is set to the temperature of the billet after heating.

[0068] The settings of the remaining simulation conditions are as follows:

[0069] The upper and lower anvils are set as rigid bodies, and the material is 5CrNiMo. The size of the upper and lower anvils is 120mmx120mmx30mm. 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 environmental 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. The application is set to a non-lubricated condition, and the friction factor is selected as 0.58.

[0070] The application realizes upsetting, square bar drawing, flat bar drawing and inverted octagonal bar drawing of the bar blank through cooperation of the hydraulic press and the manipulator. The control signals of the hydraulic press and the manipulator are input into a DEFORM-3D finite element system to complete bar blank forging simulation of each pass pressing scheme, and to obtain temperature, stress and strain distribution of the bar blank after each pressing of the hydraulic press.

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

[0072] The application sets the maximum pressing speed of the hydraulic press as 25 mm / s and the minimum pressing speed as 3 mm / s.

[0073] At high temperature, the deformation resistance of the titanium alloy material is small, and the plastic deformation capacity is enhanced, so that a higher pressing speed can be adopted; at low temperature, the deformation uniformity of the titanium alloy material is poor, so that the pressing speed needs to be appropriately reduced. In addition, when forging in the single-phase zone at high temperature, the pressing speed should not be too low, otherwise the forging time will be too long, the surface temperature will drop too much, and the flowability and uniformity of the material will be affected. When forging in the two-phase zone at low temperature, the deformation uniformity of the material is poor. Therefore, the pressing speed should be appropriately reduced to ensure deformation uniformity and make the internal material have a consistent strain rate, so as to improve the uniformity of the internal two-phase distribution.

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

[0075]

[0076] Wherein, v1 represents the initial pressing speed of the current pass, i.e. the pressing speed of the first pass in the pass; v max represents the maximum pressing speed, and the value in the embodiment is 25 mm / s; T represents the heating temperature of the current pass; T max represents the highest heating temperature of all passes in the intermediate forging process, and the value in the embodiment is 820℃.

[0077] In the same pass, the forging temperature of each pass is constantly decreasing, and the pressing speed needs to be reasonably adjusted according to the temperature change. In the forging process, the microstructure of the titanium alloy material will change, such as grain crushing, recrystallization, phase transformation, etc. These changes will affect the strain and stress distribution of the material.

[0078] By comparing the strain under the unit stress of the bar blank in different passes, the change of the material microstructure can be reflected. If the strain under the unit stress of the pass changes obviously, it indicates that the microstructure of the titanium alloy material in the region has undergone significant deformation or phase change, and the material microstructure changes dramatically, so the pressing speed needs to be reduced to avoid local overheating and ensure uniform distribution of the α phase and the β phase.

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

[0080]

[0081] wherein, D i represents the strain difference value of the grid cell under the i-th pass; ε i-1 and ε i respectively represent the strain size of the grid cell under the i-1-th pass and the i-th pass; σ i-1 and σ i respectively represent the stress size of the grid cell under the i-1-th pass and the i-th pass.

[0082] By obtaining the size change of strain under unit stress, the change of the material organization at the position corresponding to the grid cell of the bar blank is reflected. The strain difference value reflects the degree of change of the material organization at the position corresponding to the grid cell of the bar blank between the continuous two passes.

[0083] At the same time, the faster the temperature of the bar blank decreases, the more obvious the flowability of the internal material decreases, the strain rate sensitivity increases, and the uniformity of the organization deteriorates, so it is necessary to increase the down-regulation rate of the reduction speed to ensure the stability of the forging process and the uniformity of the material.

[0084] Further, the down-regulation rate of the reduction speed of the current pass is calculated:

[0085]

[0086] wherein, η i represents the down-regulation rate of the reduction speed of the i-th pass; T i-1 and T i respectively represent the average value of the temperature of all grid cells of the bar blank under the i-1-th pass and the i-th pass; represents the average value of the strain difference values of all grid cells of the bar blank under the i-th pass; norm[] represents a normalization function, and the inverse tangent normalization function is adopted herein, and the normalization range is (0, 1).

[0087] Finally, the reduction speed v i of the current pass is calculated:

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

[0089] wherein, v min is a preset minimum reduction speed, and the value is 3 mm / s; η irepresents the down rate of the i-th pass reduction speed; v i-1 and v i respectively represent the reduction speed of the i-1-th pass and the i-th pass.

[0090] S3: Adjustment of the local position reduction speed of the rod blank per pass.

[0091] During forging, due to the differences in temperature, stress and strain distribution of different positions of the rod blank, the deformation behavior of the local area is different from the whole. In order to improve the overall microstructure uniformity of titanium alloy rod, according to the comparison between the local and the whole of the rod blank, the local reduction speed is adjusted.

[0092] According to the displacement data of the operating machine, the rod blank between the upper and lower anvils of the hydraulic machine is obtained through the DEFORM-3D finite element system, and it is recorded as the current local area of the rod blank, which has the same length as the upper and lower anvils of the hydraulic machine.

[0093] The unevenness of temperature, stress and strain distribution will affect the deformation behavior and the final microstructure performance of the material. In order to ensure the deformation uniformity and the microstructure uniformity of the whole rod blank, the reduction speed needs to be dynamically adjusted according to the unevenness of these distributions. When the three distributions are uneven, the adjustment limit needs to be increased in order to flexibly adjust the reduction speed in different areas and ensure the microstructure uniformity of the forging process.

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

[0095] Th=v×exp(-CV)

[0096] Where Th represents the adjustment limit of the current pass reduction speed, i.e. the maximum adjustment amount of the reduction speed of this pass, v represents the reduction 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 elements of the rod blank before the current pass forging; exp() represents the exponential function with natural constant as the base, which is used to represent the quantitative change relationship between the average value of the temperature, stress and strain variation coefficients of the rod blank and the adjustment limit of the reduction speed of this pass.

[0097] The temperature average, stress average and strain average of all grid elements in the local area of the rod blank are used to form its parameter feature vector. The parameter feature vector of the whole rod blank is constructed in the same way.

[0098] According to the parameter feature vectors of the local area and the whole rod blank, the local difference characteristic value is calculated:

[0099] λ=norm(ΔT)×(sim+δ)

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

[0101] The larger ΔT is, the greater the temperature difference between the local area of the rod blank and the entire rod blank is, the greater the local difference characteristic value obtained by calculation is, and the adjustment amount of the subsequent reduction speed needs to be increased. At the same time, when the temperature of the local area is higher than the temperature of the entire rod blank, the local difference characteristic value and the subsequent reduction speed adjustment amount are positive, and the reduction speed is increased; when the temperature of the local area is lower than the temperature of the entire rod blank, the local difference characteristic value and the subsequent reduction speed adjustment amount are negative, and the reduction speed is decreased.

[0102] sim represents the cosine similarity of the parameter characteristic vectors of the local area of the rod blank and the entire rod blank, reflecting the difference between the forging parameters of the local area of the rod blank and the entire rod blank; δ is a preset adjustment parameter, which is taken as 1 in this embodiment, and the purpose is to map sim to a positive value.

[0103] The larger the local difference characteristic value is, the greater the difference between the forging parameters of the local area of the rod blank being forged by the current hydraulic press and the entire rod blank is, and the greater the adjustment amount of the reduction speed for the region is.

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

[0105] va = v + λ × Th

[0106] wherein, va represents the local reduction speed of the current local area of the rod blank; v represents the reduction speed of the current pass; λ represents the local difference characteristic value of the current local area of the rod blank; Th represents the adjustment limit value of the reduction speed of the current pass.

[0107] Stage three: forming forging.

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

[0109] The application adopts a box-type resistance furnace to heat and keep warm the intermediate bar blank, and cools after 1-2 times of forging, sets 2-5 passes for each time of forging, and produces Ti 55531 titanium alloy bar. The forging methods of straight drawing, beveling and rounding, combined with small forging ratio and appropriate reheat, can realize the uniform flow and deformation of the metal in all directions in the forging process, and avoid the decline of the internal structure uniformity of the intermediate bar blank.

[0110] Specifically, the intermediate bar blank obtained by intermediate forging is heated to 40℃ below the phase transition point, and the holding time is 7h; then 2 times of forging are performed, the forging ratio is 1.0-2.0, the forging method is straight drawing, beveling and rounding, the blank shape changes from square blank to round bar blank, the reheat can be appropriately used in the forging process, and the surface cracks of the material are polished after air cooling; the initial forging temperature of each forming forging is 90℃ below the phase transition point, and the final forging temperature is 160℃ below the phase transition point; finally, the Ti 55531 titanium alloy bar with a diameter of 40mm is obtained through machining.

[0111] Embodiment 2

[0112] Please refer to Figure 1 which shows a step flow chart of a titanium alloy bar forging process for improving the structure uniformity provided by the embodiment 2 of the application, and the process comprises:

[0113] Stage one: blooming forging.

[0114] In this embodiment, the Ti-55531 titanium alloy ingot is forged at 300℃ above the phase transition point by 2 times of upsetting and drawing (i.e. upsetting and drawing forging) by a hydraulic machine, 3 upsetting and drawing are completed for each time of forging, so as to obtain β structure with a grain size of 15mm; the cumulative forging ratio for each time of forging is 9.0-11.8, the forging method is upsetting, rounding and octagonal turning, and the surface cracks of the material are polished after air cooling. The initial forging temperature for each time of forging is 100℃ above the phase transition point, and the final forging temperature is 50℃ below the phase transition point, so as to obtain the intermediate blank.

[0115] Stage two: intermediate forging.

[0116] In this embodiment, the intermediate blank after blooming forging is forged by 3 times of upsetting and drawing (i.e. upsetting and drawing forging), which includes 1 time of heating at 30℃ below the phase transition point, 1 time of heating at 120℃ above the phase transition point, and 1 time of heating at 50℃ below the phase transition point; the forging ratio for each time of forging is 3.1-4.9, the forging method is upsetting, square drawing, flat square drawing and octagonal turning, the cooling method after forging is air cooling, the surface cracks of the material are polished after air cooling, and the deformation of each part of the blank is ensured to be uniform. The initial forging temperature for each time of forging in the two-phase region is 110℃ below the phase transition point, and the final forging temperature is 200℃ below the phase transition point; the initial forging temperature for each time of forging in the single-phase region is 50℃ above the phase transition point, and the final forging temperature is 120℃ below the phase transition point, so as to obtain the intermediate bar blank.

[0117] Stage three: forming forging.

[0118] In this embodiment, the intermediate billet obtained by intermediate forging is heated to 45 DEG C below the phase transition point, and the holding time is 7.5 h; then 2 fire times of forging are performed, the forging ratio is 1.0-2.0, the forging mode is straight pulling, beveling and round rolling, the shape of the billet changes from square to round, and the forging process can appropriately use the reheat temperature of the furnace, and the surface cracks of the material are polished after air cooling; the initial forging temperature of each forming forging is 130 DEG C below the phase transition point, and the final forging temperature is 180 DEG C below the phase transition point; then machining is performed to obtain a Ti 55531 titanium alloy rod with a diameter of 40 mm.

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

[0120] Embodiment 3

[0121] Please refer to Figure 1 which shows a step flow chart of a titanium alloy rod forging process provided by Embodiment 3 of the present application, which comprises:

[0122] Stage one: blooming forging.

[0123] In this embodiment, the Ti-55531 titanium alloy ingot is forged (i.e. upsetting and drawing forging) at 330 DEG C above the phase transition point by a hydraulic machine, and 3 upsetting and drawing are completed for each fire time to obtain a beta structure with a grain size of 10 mm; the cumulative forging ratio of each fire time is 9.0-11.8, the forging mode is upsetting, round rolling and inverted octagonal, and the surface cracks of the material are polished after air cooling. The initial forging temperature of each fire time is 150 DEG C above the phase transition point, and the final forging temperature is 100 DEG C below the phase transition point, to obtain an intermediate billet.

[0124] Stage two: intermediate forging.

[0125] In this embodiment, the intermediate billet after blooming forging is heated at 40 DEG C above the phase transition point for 2 fire times (i.e. upsetting and drawing forging), which is divided into 1 fire time heating at 50 DEG C below the phase transition point and 1 fire time heating at 80 DEG C above the phase transition point; the forging ratio of each fire time is 3.1-4.9, the forging mode is upsetting, square drawing, flat square drawing and inverted octagonal, the cooling mode after forging is air cooling, the surface cracks of the material are polished after air cooling, and the deformation of each part of the billet is ensured to be uniform. The initial forging temperature of each fire time in the two-phase region is 150 DEG C below the phase transition point, and the final forging temperature is 250 DEG C below the phase transition point; the initial forging temperature of each fire time in the single-phase region is 80 DEG C above the phase transition point, and the final forging temperature is 150 DEG C below the phase transition point, to obtain an intermediate rod billet.

[0126] Stage three: forming forging.

[0127] The embodiment is aimed at the intermediate bar blank obtained by intermediate forging, which is heated to 50 DEG C below the phase transition point, and the holding time is 8h; then 1 fire forging is carried out, the forging ratio is 1.0-2.0, the forging mode is straight pulling, inverted angle and round, the blank shape changes from square blank to round bar blank, the forging process can be appropriately supplemented by reheat, and the surface cracks of the material are polished after air cooling; the initial forging temperature of each forming forging is 180 DEG C below the phase transition point, and the final forging temperature is 200 DEG C below the phase transition point; then machining is carried out, and finally the Ti 55531 titanium alloy bar with a diameter of 40mm is obtained.

[0128] The remaining steps are processed according to the same steps as in the embodiment 1 of the present application, and the titanium alloy wire is obtained.

[0129] Each embodiment in the present application is described in a progressive manner, and the same and similar parts between each embodiment can be referred to each other, and each embodiment mainly explains the difference from other embodiments.

[0130] It should be noted that unless otherwise specified and limited, terms such as "including", "containing" or any other variants thereof are intended to cover non-exclusive inclusion, so that the circuit structure, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such article or device. Without more limitation, the element limited by the statement "including a" does not exclude the existence of another same element 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] Other embodiments of the present application will be apparent to those skilled in the art upon consideration of the specification and practice of the present application. The present application is intended to cover any variations, uses or adaptive changes of the present application following the general principles of the present application and including common knowledge or conventional techniques in the art which are not invented by the present application.

[0132] It should be understood that the present application is not limited to the precise construction which has been described and shown in the accompanying drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the present application.

Claims

1. A forging process for titanium alloy bars to improve microstructure uniformity, characterized in that, The process includes the following steps: Forging: The titanium alloy ingot is forged 1 to 2 times at 280℃~330℃ above the phase transformation point and then cooled to obtain an intermediate billet. Intermediate forging: The intermediate billet is heated and held at that temperature, then forged 2-4 times before cooling to obtain an intermediate bar billet. Simultaneously, the temperature, stress, and strain distribution of the bar billet during each forging cycle is analyzed through simulation, and the local pressing speed of the hydraulic press in the current local area of ​​the bar billet is adjusted in real time. Specifically: The three-dimensional point cloud data of the billet after each forging is obtained, and then converted into STL format for finite element analysis to obtain several meshes. At the same time, the initial temperature of the billet is set to the temperature after heating in that forging. The initial reduction rate of the current pass is calculated based on the proportion 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 rate of the current pass is calculated based on the differences in stress and strain magnitudes 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 rate of the current pass. Based on the abnormal distribution of temperature, stress, and strain of all grid cells of the billet, calculate the adjustment limit of the current pass pressing speed; obtain the billet between the upper and lower anvils of the hydraulic press as the current local area of ​​the billet; calculate the local difference characteristic value based on the difference between the local area of ​​the billet and the mean values ​​of the three parameters of temperature, stress, and strain of the whole; calculate the local pressing speed of the current local area of ​​the billet based on the local difference characteristic value and the adjustment limit of the pressing speed. Forming and forging: The intermediate billet is heated and held at a certain temperature, then forged 1 to 2 times and cooled to obtain the final finished bar.

2. The forging process for titanium alloy bars to improve microstructure uniformity as described in claim 1, characterized in that, During the initial forging, 2 to 3 upsetting and drawing operations are completed per forging pass to obtain a β microstructure with a grain size of 10 mm to 20 mm; the cumulative forging ratio per forging pass is 9.0 to 11.

8.

3. The forging process for titanium alloy bars to improve microstructure uniformity as described in claim 1, characterized in that, During intermediate forging, the intermediate billet that has completed the initial forging is subjected to 2 to 4 forging cycles at a temperature ranging from 60°C below the phase transformation point to 140°C above the phase transformation point, with a forging ratio of 2.8 to 5.2 per cycle.

4. The forging process for titanium alloy bars to improve microstructure uniformity as described in claim 1, characterized in that, The method for calculating the initial pressing velocity of the current firing cycle is as follows: Where v1 represents the initial pressing speed of the current firing pass, which is the pressing speed of the first pass in this firing pass; v max T represents the maximum pressing speed; T represents the heating temperature of the current firing cycle; T max This indicates the highest heating temperature of all heats during the intermediate forging process.

5. The forging process for titanium alloy bars to improve microstructure uniformity as described in claim 1, characterized in that, The method for calculating the reduction rate of the current pass speed is as follows: Where, η i T represents the rate of decrease in the compression speed of the i-th pass; i-1 and T i These represent the average temperatures of all grid elements in the billet during the (i-1)th and i-th passes, respectively. The expression represents the average strain difference of all mesh elements in the bar billet during the i-th pass; norm[] represents the normalization function; Among them, the strain difference value D of the same mesh element in the i-th pass. i The calculation expression is: Among them, D i ε represents the strain difference value of the same mesh element in the i-th pass; i-1 and ε i σ represents the strain magnitude of the same mesh element in the (i-1)th and i-th passes, respectively; i-1 and σ i These represent the stress magnitudes of the same mesh element in the (i-1)th and i-th passes, respectively.

6. The forging process for titanium alloy bars to improve microstructure uniformity as described in claim 1, characterized in that, The method for adjusting the pressing speed of the current track is as follows: v i =v i-1 -η i ×(v i-1 -v min ) Among them, v i This represents the current pull-down speed, v. min η is the preset minimum compression speed. i This represents the rate of decrease in the compression speed of the i-th pass; v i-1 and v i These represent the pressing speeds of the (i-1)th and i-th passes, respectively.

7. The forging process for titanium alloy bars to improve microstructure uniformity as described in claim 1, characterized in that, The method for calculating the adjustment limit of the current pass pressing speed is as follows: Th = v × exp(-CV) Where Th represents the adjustment limit of the current pass pressing speed, v represents the current pass pressing speed, CV represents the average of the temperature variation coefficient, stress variation coefficient and strain variation coefficient of all grid elements of the billet before the current pass forging, and exp() represents the exponential function with the natural constant as the base.

8. The forging process for titanium alloy bars to improve microstructure uniformity as described in claim 1, characterized in that, The method for calculating the local difference feature value is as follows: λ = norm(ΔT) × (sim + δ) Where λ represents the local difference feature value of the local region of the current billet; ΔT represents the difference between the average temperature of the grid cells in the local region of the current billet and the average temperature of all grid cells in the entire billet; norm() represents the normalization function; sim represents the cosine similarity between the parameter feature vector of the local region of the billet and the entire billet; and δ is the preset adjustment parameter. Among them, the parameter feature vectors of the local region of the billet and the entire billet are respectively composed of the average temperature, average stress, and average strain of all grid elements within it.

9. The forging process for titanium alloy bars to improve microstructure uniformity as described in claim 1, characterized in that, The method for calculating the local reduction velocity of the current local region of the billet is as follows: va = v + λ × Th Where va represents the local reduction speed of the current billet region; v represents the reduction speed of the current pass; λ represents the local difference characteristic value of the current billet region; and Th represents the adjustment limit of the reduction speed of the current pass.

10. The forging process for titanium alloy bars to improve microstructure uniformity as described in claim 1, characterized in that, The forging methods for rough forging and intermediate forging are upsetting, drawing square, drawing flat square, and inverted octagon, while the forging methods for forming forging are straight drawing, chamfering, and rounding.

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