Method for optimizing parameters of high-pressure gas quenching process of thin-wall shell

Abstract

The invention relates to a thin-wall shell high-pressure gas quenching process parameter optimization method, and relates to the field of heat treatment. The optimization method comprises the following steps: inputting high-pressure gas quenching process parameters of the thin-wall shell; establishing geometric models and grids of an in-furnace gas flow channel, in-furnace components and a thin-wall shell of the vacuum high-pressure gas quenching furnace; parameters of flow in the vacuum high-pressure gas quenching furnace, components in the furnace and a thin-wall shell are obtained; constructing a convective heat transfer coupling model and a stress-strain model of in-furnace flow, in-furnace components and a thin-wall shell in the vacuum high-pressure gas quenching process; establishing a numerical model, and carrying out thin-wall part vacuum high-pressure gas quenching process finite element analysis to obtain simulation results of gas velocity and thin-wall shell temperature, structure and deformation; and gas quenching process parameters are adjusted until the deformation result of the thin-wall shell meets the process requirements, process parameter optimization is completed, and finally optimized process parameters are output. Compared with the prior art, the method has the advantages of reducing the cost caused by determining process parameters in a test, improving the working efficiency and the like.

Description

Technical Field

[0001] The invention relates to the field of heat treatment, and in particular to a method for optimizing process parameters of high-pressure gas quenching of a thin-walled shell. Background Art

[0002] Heat treatment technology can strengthen metal materials and enable them to fully exert their properties. It is usually the last link in product manufacturing and plays a vital role in the quality and performance of the product. The aerospace industry requires a large number of high-strength steel thin-walled parts. When high-strength steel is heated in the air medium, oxidation and decarburization will occur on the surface of the material, which will damage the surface quality of the parts, causing the surface hardness and material strength of the material to decrease after quenching, and the product performance is unqualified. Vacuum heat treatment can achieve no oxidation and no decarburization. The surface brightness of the workpiece after quenching is good. It also has the advantages of high efficiency, energy saving, and no pollution. At the same time, the vacuum heat treatment process itself is flexible and pollution-free. Therefore, vacuum heat treatment has been widely used in the heat treatment process of aerospace parts.

[0003] After thin-walled parts have undergone multiple heat treatment processes, the most prominent problem is large distortion and it is difficult to ensure the dimensional accuracy of the product. The deformation of the workpiece is mainly caused by thermal stress and structural stress during the heat treatment process. When the workpiece is heated or cooled, the temperature of the surface and core of the workpiece or different parts of the workpiece are different, resulting in uneven heating or cooling of the workpiece, generating thermal stress; high-strength steel materials will undergo structural transformation at the critical temperature points of heating and cooling, and the different organizational structures formed are different, and there are differences in volume, causing structural stress inside the workpiece; at the same time, the material itself will also undergo plastic deformation, so the deformation of the workpiece during heat treatment is the result of the coupling and evolution of multiple factors.

[0004] The changing law of deformation factors in heat treatment of thin-walled parts is complex and difficult to fully grasp through a limited number of process tests. Especially for vacuum heat treatment processes, the process parameters are relatively complex and the test cost is very high. In addition, due to the sealing of vacuum equipment, it is difficult to obtain measurement parameters. The test results are not very instructive for process optimization, and it is impossible to optimize process parameters only through experiments. The numerical simulation technology of heat treatment processes can predict the deformation of workpieces and has become an important auxiliary means in heat treatment process research. Ge Ping calculated the temperature and deformation of thin-walled parts during quenching in "Numerical Simulation of Quenching Process of Complex Thin-walled Shells" and obtained the deformation of thin-walled parts. However, the microstructure transformation during quenching was not considered in the calculation process, so its applicability and application range are relatively limited. In addition, during vacuum high-pressure gas quenching, the cooling gas is ejected from the nozzle, resulting in uneven surface temperature of thin-walled parts. Therefore, the uniformity of the gas flow has a great influence on the hardening effect, mass dispersion and deformation of thin-walled parts. Ignoring this factor has a huge impact on the prediction results of thin-walled parts deformation. Summary of the invention

[0005] To solve the above problems, the present invention provides a method for optimizing the process parameters of vacuum high-pressure gas quenching of thin-walled parts based on numerical simulation technology of convective heat transfer, which is characterized by using a fluid-solid coupling algorithm to accurately predict the flow field near the workpiece and the temperature field, structure field and stress / strain field inside the workpiece, and optimizing the vacuum high-pressure gas quenching process parameters in combination with the deformation results of the thin-walled parts.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A method for optimizing process parameters of a thin-walled shell high-pressure gas quenching process, the specific steps comprising:

[0008] Step 1: Input the thin-wall shell high-pressure gas quenching process parameters.

[0009] Step 2: Establish the geometric model and mesh of the gas flow channel, furnace internal components and thin-walled shell in the vacuum high-pressure gas quenching furnace. The gas flow channel includes a nozzle and an air outlet, and the furnace internal components of the vacuum high-pressure gas quenching furnace include fixtures and furnace internal components that affect gas flow. The thin-walled shell adopts a hexahedral mesh, and the mesh density of the furnace internal components of the vacuum high-pressure gas quenching furnace is less than the gas mesh density.

[0010] Step 3: Obtain parameters of the flow in the vacuum high-pressure gas quenching furnace, furnace components and thin-walled shell. The furnace flow parameters include gas pressure and velocity. The furnace components and thin-walled shell parameters include thermophysical performance parameters, phase change kinetic parameters, and mechanical parameters; the thermophysical performance parameters include density, specific heat capacity, and thermal conductivity; the phase change kinetic parameters are isothermal transformation kinetic parameters; the mechanical parameters include Poisson's ratio, elastic modulus, and plasticity curve.

[0011] Step 4: Construct a coupled model of heat transfer and stress-strain for the flow in the furnace, the components in the furnace and the thin-walled shell during vacuum high-pressure gas quenching. The coupled model of heat transfer and convection must ensure the continuity of temperature and heat flow at the fluid-solid interface. The strain in the stress-strain model includes mechanical elastic strain. Mechanical plastic strain Thermal strain Phase change strain Phase change shaping Right now The structural transformation in the stress-strain model adopts the Avrami equation and the KM equation, and the latent heat generated by the structural transformation is the internal heat source of the thin wall.

[0012] Step 5: According to steps 1 to 4, a numerical model is established to perform finite element analysis of the vacuum high-pressure gas quenching process of thin-walled parts to obtain simulation results of gas velocity, temperature and deformation of thin-walled shells. The boundary conditions of high-pressure gas quenching flow and the initial temperature of thin-walled parts need to be set during the finite element analysis process; the temperature change over time during the cooling process of thin-walled parts, the change of organizational transformation over time, and the change of stress and strain over time need to be saved during the finite element analysis process.

[0013] Step 6: Adjust the gas quenching process parameters and repeat steps 1 to 5 until the thin-walled shell deformation results meet the process requirements. The process requirements include that the straightness and roundness of the thin-walled parts after vacuum high-pressure gas quenching reach the specified range, and the microstructure distribution of the thin-walled parts reaches the specified range.

[0014] Step 7: Process parameter optimization is completed, and the final optimized process parameters are output.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention constructs a convection heat transfer coupling model and a structural stress model, and uses computer numerical simulation technology of fluid-solid coupling to accurately predict the flow field during high-pressure gas quenching of a thin-walled shell and the temperature field, structural field and stress / strain field inside the workpiece, and shows in detail the influence of gas flow on the temperature structure and deformation of thin-walled parts, optimizes the gas quenching parameters efficiently and economically, reduces the waste of materials and energy caused by determining the process through experiments, and reduces research and development costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 The present invention provides a schematic flow chart of the optimization method.

[0019] Figure 2 It is a geometric model of the gas flow channel, furnace internal components and thin-walled shell of the vacuum high-pressure gas quenching furnace in the embodiment.

[0020] Figure 3 : isothermal transformation curve of 30Cr3SiNiMoVA thin-walled shell material tested in the embodiment.

[0021] Figure 4 : is the temperature-time curve during the gas quenching process of the thin-walled shell in the embodiment.

[0022] Figure 5 This is the thin-walled shell structure transformation-time curve in the embodiment.

[0023] Figure 6 It is the straightness curve of the thin-walled shell in the embodiment. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0026] In order to optimize the gas quenching process parameters and solve the problem of large distortion of thin-walled shells after gas quenching, a method for optimizing the process parameters of vacuum high-pressure gas quenching of thin-walled shells based on numerical simulation technology of convective heat transfer was adopted. The flow field near the workpiece and the temperature field, structure field and stress / strain field inside the workpiece were accurately predicted using the fluid-solid coupling algorithm. Combined with the deformation results of thin-walled parts, the purpose of optimizing the process parameters of vacuum high-pressure gas quenching was achieved.

[0027] A method for optimizing process parameters of a thin-walled shell high-pressure gas quenching process, characterized in that the specific steps include:

[0028] Step 1: Input the thin-wall shell high-pressure gas quenching process parameters;

[0029] Step 2: Establish the geometric model and mesh of the gas flow channel, furnace components and thin-walled shell in the vacuum high-pressure gas quenching furnace;

[0030] Step 3: Obtain parameters of the flow in the vacuum high-pressure gas quenching furnace, the furnace internal components and the thin-walled shell;

[0031] Step 4: Construct a coupled model of the flow in the furnace, the convection heat transfer of the furnace components and the thin-walled shell, and a stress-strain model during vacuum high-pressure gas quenching;

[0032] Step 5: A numerical model is established according to steps 1 to 4, and a finite element analysis is performed on the vacuum high-pressure gas quenching process of the thin-walled part to obtain simulation results of the gas velocity and the temperature and deformation of the thin-walled shell;

[0033] Step 6: Adjust the gas quenching process parameters and repeat steps 1 to 5 until the deformation result of the thin-walled shell meets the process requirements;

[0034] Step 7: Process parameter optimization is completed, and the final optimized process parameters are output.

[0035] A specific embodiment of a method for optimizing process parameters of a thin-walled shell high-pressure gas quenching in this embodiment is as follows:

[0036] Step 1: Input the process parameters of high-pressure gas quenching of thin-walled shell, including gas pressure, gas velocity, outlet position, furnace loading quantity and furnace loading position of high-pressure gas quenching.

[0037] Step 2: Establish the geometric model and mesh of the gas flow channel, furnace components and thin-walled shell in the vacuum high-pressure gas quenching furnace, such as Figure 2 The geometric model of the embodiment of the present invention includes the geometric model of the gas flow channel in the vacuum furnace, the geometric model of 224 nozzles and air outlets in the circumferential direction of the furnace, the geometric model of the fixture and shell in the vacuum furnace, and the geometric model of 18 groups of radiation belts and columns in the furnace that affect the gas flow. The shell parts use hexahedral meshes, and other components and the gas flow channel in the furnace use tetrahedral meshes, with a total of 5.5 million meshes.

[0038] Step 3: Obtain the parameters of the flow in the vacuum high-pressure gas quenching furnace, the furnace components and the thin-walled shell. The gas pressure is 6 bar and the cooling gas is nitrogen through the pressure gauge and flow meter outside the vacuum high-pressure gas quenching furnace. The specific heat capacity and thermal conductivity of the 30Cr3SiNiMoVA shell with temperature are measured by thermal analyzer and laser thermal conductivity meter. The thermal expansion curve of the 30Cr3SiNiMoVA material at different isothermal temperatures is measured by DIL-805A / D quenching expansion instrument, and the isothermal transformation curve of the shell is obtained as follows: Figure 3 As shown; the stress-strain curve of 30Cr3SiNiMoVA material is measured by the tensile module of the dilatometer, and its mechanical properties parameters such as elastic modulus, yield strength and plastic modulus are obtained.

[0039] Step 4: Construct a coupled model of convection heat transfer and stress-strain model for the flow in the furnace, the components in the furnace, and the thin-walled shell during vacuum high-pressure gas quenching. First, ensure that the temperature and heat flow are continuous at the interface between the cooling gas and the shell; second, the strain in the stress-strain model includes mechanical elastic strain. Mechanical plastic strain Thermal strain Phase change strain Phase change shaping Right now Finally, the structural transformation includes pearlite and bainite transformation and martensite transformation. The pearlite and bainite transformation adopts Avrami equation, and the martensite transformation adopts KM equation. The latent heat generated by the structural transformation is used as the internal heat source of the shell.

[0040] Step 5: According to the established numerical model, finite element analysis of the vacuum high-pressure gas quenching process of 30Cr3SiNiMoVA shell is carried out to obtain the simulation results of gas velocity and thin-wall shell temperature, structure and deformation, such as Figure 4 As shown. Import the gas in the vacuum furnace and the geometric model and mesh of the furnace shell and components established in step 2; input the thermophysical parameters, isothermal transformation kinetic parameters and mechanical properties parameters of the 30Cr3SiNiMoVA material in step 2; set the boundary conditions and initial conditions of the high-pressure gas quenching flow, the gas velocity is 10m / s, and the initial temperature of the shell is 920℃; calculate the convective heat transfer between the high-pressure gas and the shell, and calculate the temperature, structure and deformation inside the shell according to the principle of consistent shell surface temperature, and save the change of shell cooling temperature over time, the change of structure transformation over time, and the change of stress and strain over time. Figure 4 is the cooling curve of the shell during gas quenching. Figure 5 is the shell tissue transformation curve, Figure 6 is the straightness curve of the shell.

[0041] Step 6: Adjust the gas quenching process parameters and repeat steps 1 to 5 until the deformation result of the thin-walled shell meets the process requirements.

[0042] Step 7: Process parameter optimization is completed, and the final optimized process parameters are output.

[0043] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention using the above disclosed contents without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the contents of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for optimizing process parameters of high pressure gas quenching of thin-walled shells, characterized in that: The specific steps include: Step 1: Input the thin-wall shell high-pressure gas quenching process parameters; Step 2: Establish the geometric model and mesh of the gas flow channel, furnace components and thin-walled shell in the vacuum high-pressure gas quenching furnace; Step 3: Obtain parameters of the flow in the vacuum high-pressure gas quenching furnace, the furnace internal components and the thin-walled shell; Step 4: Construct a coupled model of the flow in the furnace, the convection heat transfer of the furnace components and the thin-walled shell, and a stress-strain model during vacuum high-pressure gas quenching; Step 5: A numerical model is established according to steps 1 to 4, and a finite element analysis is performed on the vacuum high-pressure gas quenching process of the thin-walled part to obtain simulation results of the gas velocity and the temperature and deformation of the thin-walled shell; Step 6: Adjust the gas quenching process parameters and repeat steps 1 to 5 until the deformation result of the thin-walled shell meets the process requirements; Step 7: Process parameter optimization is completed, and the final optimized process parameters are output.

2. The method for optimizing process parameters of thin-walled shell high pressure gas quenching according to claim 1, characterized in that: In step 2, the gas flow channel includes a nozzle and an air outlet, and the thin-walled shell adopts a hexahedral grid.

3. The method for optimizing process parameters of thin-walled shell high pressure gas quenching according to claim 1, characterized in that: Step 2: The internal components of the vacuum high-pressure gas quenching furnace include fixtures and internal components that affect gas flow. The grid density of the internal components of the vacuum high-pressure gas quenching furnace is less than the gas grid density.

4. The method for optimizing process parameters of thin-walled shell high pressure gas quenching according to claim 1, characterized in that: The flow parameters in the vacuum high-pressure gas quenching furnace described in step 3 include gas pressure and velocity.

5. The method for optimizing process parameters of thin-walled shell high pressure gas quenching according to claim 1, characterized in that: The parameters of the furnace internal components and thin-walled shell in step 3 include thermophysical performance parameters, phase change kinetic parameters, and mechanical parameters, among which: The thermophysical performance parameters include density, specific heat capacity, and thermal conductivity; The phase change kinetic parameters are isothermal transformation kinetic parameters; The mechanical parameters include Poisson's ratio, elastic modulus and plasticity curve.

6. The method for optimizing process parameters of thin-walled shell high pressure gas quenching according to claim 1, characterized in that: The fourth step must ensure the continuity of temperature and heat flow at the fluid-solid interface of the convective heat transfer coupling model.

7. The method for optimizing process parameters of thin-walled shell high pressure gas quenching according to claim 1, characterized in that: The strain in the stress-strain model in step 4 includes mechanical elastic strain Mechanical plastic strain Thermal strain Phase change strain Phase change shaping Right now 8. The method for optimizing process parameters of thin-walled shell high pressure gas quenching according to claim 1, characterized in that: The structural transformation in the stress-strain model described in step 4 adopts the Avrami equation and the KM equation, and the latent heat generated by the structural transformation is the internal heat source of the thin wall.

9. The method for optimizing process parameters of thin-walled shell high pressure gas quenching according to claim 1, characterized in that: In the finite element analysis process described in step 5, the boundary conditions of high-pressure gas quenching flow and the initial temperature of the thin-walled part need to be set; During the finite element analysis process described in step five, it is necessary to save the temperature change over time during the cooling process of the thin-walled part, the change over time of the organizational transformation, and the change over time of the stress and strain.

10. The method for optimizing process parameters of thin-walled shell high pressure gas quenching according to claim 1, characterized in that: The process requirements described in step six include that the straightness and roundness of the thin-walled parts after vacuum high-pressure gas quenching reach the specified range, and the microstructure distribution of the thin-walled parts reaches the specified range.

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