A method and system for formulating a forging process to improve the fatigue strength of titanium alloy

Abstract

The present invention discloses a method and system for formulating a forging process to improve the fatigue strength of titanium alloys, which relates to the technical field of forging processes. A strain rate compensation type forging process J-C constitutive model that comprehensively considers the coupled effects of deformation temperature, strain rate, and strain on the high-temperature rheological behavior of materials is established; according to the J-C constitutive model, the microstructure of each forging process is determined, and based on the relationship between fatigue performance and microstructure, a process method for improving the fatigue strength of titanium alloys is formulated. The strain rate compensation type forging process J-C model established by the present invention based on comprehensively considering the coupled effects of deformation temperature, strain rate, and strain on the high-temperature rheological behavior of materials can form an effective process method for improving the fatigue strength of titanium alloys.

Description

Technical Field

[0001] The present invention relates to the technical field of forging processes, and particularly to a method and system for formulating a forging process to improve the fatigue strength of titanium alloys. Background Art

[0002] With the increase in the speed of rail vehicles, the various complex loads acting on the train during service are becoming more intense. Coupled with the combined effects of wide-area complex climates such as high temperature and humidity, higher requirements are put forward for the static performance and fatigue performance of train forging components under dynamic loads. Titanium alloys are widely used in the manufacture of mounting seats such as the car body and bogie of rail vehicles due to their good specific strength, specific stiffness, corrosion resistance, joining performance, high-temperature mechanical properties, fatigue resistance, and creep resistance.

[0003] CN114818437A discloses an optimization method for the isothermal forging process of titanium alloy integral bladed disks, including establishing a constitutive model of the influence of different compositions of titanium alloy on the flow stress, designing the blank size, establishing the material constitutive characteristics, and a three-dimensional finite element numerical simulation system of plastic deformation - heat transfer, obtaining simulation diagrams of the filling, stress field, strain field, and temperature field distribution of pre-forged and final-forged parts under different blanks, and simulation diagrams of the influence of the stress field, strain field, and temperature field of pre-forged and final-forged parts under forging temperature, forging speed, reduction amount, and friction factor conditions, so as to obtain the optimal process parameters for isothermal forging. Although this scheme optimizes the forging process parameters of titanium alloy components, the titanium alloy components used in rail vehicles bear complex loads during service. In addition to requiring static strength, they also require high fatigue strength. Therefore, it is not applicable to the titanium alloy components of rail vehicles. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method and system for formulating a forging process to improve the fatigue strength of titanium alloys. Based on the strain rate compensation type forging process J-C model established by comprehensively considering the coupled effects of deformation temperature, strain rate, and strain on the high-temperature rheological behavior of materials, an effective process method for improving the fatigue strength of titanium alloys can be formed.

[0005] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0006] In the first aspect, the present invention provides a method for formulating a forging process to improve the fatigue strength of titanium alloys, establishing a strain rate compensation type forging process J-C constitutive model that comprehensively considers the coupled effects of deformation temperature, strain rate, and strain on the high-temperature rheological behavior of materials; determining the microstructure of each forging process according to the J-C constitutive model, and formulating a process method for improving the fatigue strength of titanium alloys according to the relationship between fatigue performance and microstructure.

[0007] As a further technical solution, the relationship between different strain rates and stresses of the titanium alloy is tested at different forging temperatures.

[0008] As a further technical solution, a strain rate compensation type J-C constitutive model for the forging temperature, deformation amount, and heat treatment strain rate of the forging process component is established based on different deformation temperatures, strain rates, stress curves, and corresponding microstructures.

[0009] As a further technical solution, the J-C constitutive model is as follows:

[0010]

[0011] Among them, σ0 is the yield stress at the reference temperature and reference strain rate; B is the strain hardening coefficient; is the strain rate, is the reference strain rate; n is the strain hardening index; T * is the normalized temperature, and P is the material parameter.

[0012] As a further technical solution, based on the J-C constitutive model and the microstructure, the corresponding relationship between the microstructure and fatigue performance is determined, and the numerical simulation technology is used to simulate the change of the microstructure during the forging process of the component.

[0013] As a further technical solution, the relationship between the microstructure and fatigue performance is established by analyzing the relationship between the microstructure and fatigue performance under the forging temperature-forging stress-strain relationship through fatigue test data analysis.

[0014] As a further technical solution, the microstructure of the titanium alloy at different temperatures and upsetting amounts is analyzed, including the grain size, volume fraction, size, and distribution of the primary α state, α lamellae, and β phase.

[0015] As a further technical solution, after forging according to the process method, surface shot peening process treatment is carried out.

[0016] In the second aspect, the present invention also provides a forging process formulation system for improving the fatigue strength of titanium alloy, including:

[0017] A model construction module, configured to: establish a strain rate compensation type forging process J-C constitutive model that comprehensively considers the coupling effect of deformation temperature, strain rate, and strain on the high-temperature rheological behavior of the material;

[0018] A process method formulation module, configured to: determine the microstructure of each forging process according to the J-C constitutive model, and formulate a process method for improving the fatigue strength of titanium alloy according to the relationship between fatigue performance and microstructure.

[0019] As a further technical solution, it further includes a microstructure identification module, which is configured to: observe the microstructure of the titanium alloy component and analyze the microstructure of the titanium alloy under different temperatures and upset amounts.

[0020] The beneficial effects of the present invention are as follows:

[0021] Based on the established stress-strain rate-working temperature strain rate compensated JC constitutive model, the present invention formulates the forging process of components. By means of fatigue tests and microstructure analysis tests, the relationship between microstructure and fatigue performance is established. The numerical simulation technology is used to simulate the microstructure changes during the forging process of components. Based on the microstructure changes, the fatigue performance of materials is predicted to optimize the welding process parameters. Then, shot peening treatment is adopted to generate surface compressive stress on the surface of the components, improve the fatigue strength of the titanium alloy components, reduce the process R & D tests, shorten the manufacturing cycle, and improve the economic benefits. Description of the Drawings

[0022] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0023] Figure 1 is a flowchart according to one or more embodiments of the present invention;

[0024] Figure 2 is a schematic diagram of the relationship between strain, strain rate and upset amount at 720 °C according to one or more embodiments of the present invention;

[0025] FIG. 3(a) and FIG. 3(b) are the microstructural morphologies of TC4 titanium alloy according to one or more embodiments of the present invention;

[0026] FIG. 4(a) and FIG. 4(b) are the microstructural morphologies of TA18 titanium alloy according to one or more embodiments of the present invention;

[0027] FIG. 5(a) is the fatigue performance of the forged titanium alloy component TC4 according to one or more embodiments of the present invention;

[0028] FIG. 5(b) is the fatigue performance of the forged titanium alloy component TA18 titanium alloy according to one or more embodiments of the present invention;

[0029] Figure 6 is the surface microstructure of the component after shot peening according to one or more embodiments of the present invention;

[0030] In the figures: the distances or sizes between each part are exaggerated for showing the positions of each part, and the schematic diagrams are only for illustration. Detailed Embodiments

[0031] Embodiment 1:

[0032] This embodiment provides a method for formulating a forging process to improve the fatigue strength of titanium alloy, as Figure 1 shown, including:

[0033] S101: Establish a strain rate compensation type forging process J-C constitutive model that comprehensively considers the coupling effects of deformation temperature, strain rate, and strain on the high-temperature rheological behavior of the material based on forging process tests;

[0034] S102: Determine the microstructure of each forging process according to the J-C constitutive model;

[0035] S103: Formulate a process method to improve the fatigue strength of titanium alloy according to the relationship between fatigue performance and microstructure.

[0036] The specific steps are as follows:

[0037] (1) Obtain the parameters of titanium alloy for rail vehicles through forging process tests, and test the relationship between different strain rates and stresses of titanium alloy at different forging temperatures.

[0038] (2) Based on different deformation temperatures, strain rates, stress curves, and corresponding microstructures, establish a forging temperature, deformation amount, and heat treatment strain rate compensation type J-C constitutive model for forging process components, that is:

[0039]

[0040] In the formula, σ0 is the yield stress at the reference temperature and reference strain rate; B is the strain hardening coefficient; is the strain rate; is the reference strain rate; n is the strain hardening index; T * is the normalized temperature, and P is the material parameter.

[0041] Among them, observe the microstructure of titanium alloy components through SEM (scanning electron microscope) and TEM (transmission electron microscope), and analyze the microstructure of titanium alloy at different temperatures and upsetting amounts, including grain size and the volume fraction, size, and distribution of primary α state, α lamellae, and β phase, etc.

[0042] (2) Analyze the relationship between the microstructure and fatigue performance under the relationship of forging temperature - forging stress - strain amount through fatigue test data analysis, and establish the relationship between the microstructure and fatigue performance.

[0043] (3) Use the forging process digital model and numerical simulation technology to optimize the forging steps, simulate the change of the microstructure of components during the forging process, and formulate processes such as forging parameters, and formulate a forging process to improve the fatigue strength of titanium alloy materials. The specific forging parameters include heat treatment temperature, forging pressure, strain rate, etc.

[0044] (4) The forged titanium alloy components are subjected to surface shot peening. In this embodiment, S110 cast steel shots are used, and the shot peening intensity is 0.15 mA. (Except for the shape mutation points), residual compressive stress is generated on the surface of the components to further improve the fatigue performance of the components.

[0045] In this embodiment, the forging process of the components is formulated based on the established stress-strain rate-work temperature strain rate compensated JC constitutive model. The relationship between the microstructure and the fatigue performance is established through fatigue tests and microstructure analysis tests. The numerical simulation technology is used to simulate the microstructure changes during the forging process of the components. Based on the microstructure changes, the fatigue performance of the material is predicted to optimize the welding process parameters. Then, shot peening treatment is used to generate surface compressive stress on the surface of the components, improve the fatigue strength of the titanium alloy components, reduce the process R & D tests, shorten the manufacturing cycle, and improve the economic benefits.

[0046] Example Two:

[0047] In this embodiment, the forging process formulation method described in Example One is adopted. Taking the mounting seat component of the titanium alloy car body for rail vehicles as an example, the specific steps are as follows:

[0048] (1) Through the forging process tests at 690 °C, 720 °C, 750 °C, 780 °C, and 810 °C, the relationship between the forging temperature, the reduction amount, and the forging stress is obtained, and the relationship among temperature-reduction amount-forging stress is plotted. The schematic diagram of the relationship between the reduction amount and the forging stress at 720 °C is as Figure 2 shown.

[0049] (2) SEM scanning is used to observe the microstructure of the components under different temperatures, reduction amounts, and forging stresses, mainly including the grain size, the volume fraction, size, morphology, and distribution of primary α, α lamellae, and β phase;

[0050] As shown in Figures 3(a) and 3(b), the microstructure morphology of TC4 titanium alloy is shown, and as shown in Figures 4(a) and 4(b), the microstructure morphology of TA18 titanium alloy is shown.

[0051] (3) Fatigue tests are used to measure the fatigue strength (107 cycles) under the above different temperatures, different downward pressures, and different reduction amounts. The fatigue performance of TC4 titanium alloy is shown in Figure 5(a), and the fatigue performance of TA18 titanium alloy is shown in Figure 5(b);

[0052] (4) The relationship among the above temperature-reduction amount-forging stress is imported into the preprocessing of numerical simulation. Combining the relationship between the fatigue strengths, the parameters such as heat treatment temperature, forging pressure, and strain rate are optimized to confirm the final forging process and improve the fatigue strength.

[0053] (5) Perform surface sandblasting treatment on the titanium alloy component. After shot peening, the surface of the component is as shown in Figure 6 , generating surface compressive stress on the surface to improve the fatigue strength of the component.

[0054] Example 3:

[0055] This example provides a forging process formulation system for improving the fatigue strength of titanium alloy, including:

[0056] A model construction module, configured to: establish a strain rate compensation type forging process J-C constitutive model that comprehensively considers the coupling effects of deformation temperature, strain rate, and strain on the high-temperature rheological behavior of the material;

[0057] A process method formulation module, configured to: determine the microstructure of each forging process according to the J-C constitutive model, and formulate a process method for improving the fatigue strength of titanium alloy according to the relationship between fatigue performance and microstructure.

[0058] This example also includes a microstructure identification module, configured to: observe the microstructure of the titanium alloy component and analyze the microstructure of the titanium alloy under different temperatures and upsetting amounts.

[0059] Further, the J-C constitutive model is:

[0060] In the formula, σ0 is the yield stress at the reference temperature and reference strain rate; B is the strain hardening coefficient; is the strain rate; is the reference strain rate; n is the strain hardening index; T * is the normalized temperature, and P is the material parameter.

[0061] In this example, the microstructure identification module can be SEM or TEM.

[0062] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for formulating a forging process to improve the fatigue strength of titanium alloy, characterized in that, Establish a strain rate compensated forging process J-C constitutive model that comprehensively considers the coupling effects of deformation temperature, strain rate, and strain on the high-temperature rheological behavior of materials; determine the microstructure of each forging process according to the J-C constitutive model, and formulate a process method to improve the fatigue strength of titanium alloys based on the relationship between fatigue performance and microstructure; The J-C constitutive model is: ； wherein, is the yield stress at the reference temperature and reference strain rate; is the strain hardening coefficient; is the strain rate, is the reference strain rate; is the strain hardening exponent; is the normalized temperature, is the material parameter; Based on the J-C constitutive model and microstructure, determine the corresponding relationship between microstructure and fatigue performance, and use numerical simulation technology to simulate the change of microstructure during the forging process of components; through fatigue test data analysis, analyze the relationship between microstructure and fatigue performance under the relationship of forging temperature-forging stress-strain, and establish the relationship between microstructure and fatigue performance.

2. The method for formulating a forging process to improve the fatigue strength of titanium alloy according to claim 1, characterized in that, Test the relationship between different strain rates and stresses of titanium alloys at different forging temperatures.

3. The method for formulating a forging process to improve the fatigue strength of titanium alloy according to claim 1 or 2, characterized in that, Based on different deformation temperatures, strain rates, stress curves, and corresponding microstructures, establish a forging temperature, deformation amount, and heat treatment strain rate compensated J-C constitutive model for forging process components.

4. The method for formulating a forging process to improve the fatigue strength of titanium alloy according to claim 1, characterized in that, Analyze the microstructure of titanium alloys at different temperatures and upsetting amounts, including grain size, volume fraction, size, and distribution of primary α state, α lamellae, and β phase.

5. The method for formulating a forging process to improve the fatigue strength of titanium alloy according to claim 1, characterized in that, After forging according to the said process method, perform surface shot peening process treatment.

6. A system for formulating a forging process to improve the fatigue strength of titanium alloy, characterized in that, Including: A model construction module, configured to: establish a strain rate compensated forging process J-C constitutive model that comprehensively considers the coupling effects of deformation temperature, strain rate, and strain on the high-temperature rheological behavior of materials; the J-C constitutive model is: ； wherein, is the yield stress at the reference temperature and reference strain rate; is the strain hardening coefficient; is the strain rate, is the reference strain rate; is the strain hardening exponent; is the normalized temperature, is the material parameter; A process method formulation module, configured to: determine the microstructure of each forging process according to the J-C constitutive model, and formulate a process method to improve the fatigue strength of titanium alloys based on the relationship between fatigue performance and microstructure; based on the J-C constitutive model and microstructure, determine the corresponding relationship between microstructure and fatigue performance, and use numerical simulation technology to simulate the change of microstructure during the forging process of components; through fatigue test data analysis, analyze the relationship between microstructure and fatigue performance under the relationship of forging temperature-forging stress-strain, and establish the relationship between microstructure and fatigue performance.

7. The system for formulating a forging process to improve the fatigue strength of titanium alloy according to claim 6, characterized in that, It also includes a microstructure identification module, configured to: observe the microstructure of titanium alloy components and analyze the microstructure of titanium alloys at different temperatures and upsetting amounts.

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