Casting process optimization method for heat-resistant steel cylinder body based on finite element model

Abstract

The invention discloses a casting process optimization method for a heat-resistant steel cylinder body based on a finite element model, and belongs to the technical field of computer aided design casting process optimization. The method comprises the following steps: S1, determining thermophysical parameters of a cylinder body material according to chemical components and a solid-liquid phase line of the cylinder body material; s2, establishing a three-dimensional model of the cylinder body; wherein the cylinder body is provided with a pipeline, and at least one side of the pipeline is not provided with a patch; s3, performing grid division on the three-dimensional model to obtain a grid model of the cylinder body; s4, performing parameter setting on the grid model; wherein the set parameters comprise the thermophysical parameters, determined in the step S1, of the cylinder body material; s5, carrying out simulation calculation on a flow field and a temperature field in the casting process on the grid model to obtain a shrinkage cavity shrinkage porosity prediction result of the pipeline wall; and step S6, according to the prediction result, determining whether the pipeline of the cylinder needs to be provided with subsidy and / or whether the current subsidy is reasonable.

Description

Technical Field

[0001] The invention relates to the technical field of computer-aided design optimization of casting processes, and in particular to a casting process optimization method for a heat-resistant steel cylinder body based on a finite element model. Background Art

[0002] Ultra-supercritical thermal power units have a broad market space due to their advantages of high parameters, large capacity and low emissions. In order to ensure the high reliability and high stability of the operation of ultra-supercritical thermal power units, higher requirements are placed on the quality of turbine cylinder casting products.

[0003] The new high-alloy heat-resistant steel used in the intermediate-pressure inner cylinder of ultra-supercritical steam turbine has a wide crystallization temperature range and tends to solidify in a paste state, which easily produces shrinkage defects during the casting process. At the same time, the shape and structure of this type of cylinder are complex, and the wall thickness varies greatly, especially in special parts such as airways and pipes, which increases the difficulty of process design. Designers refer to general casting process design specifications and combine their own experience to carry out process design and development. The R&D cycle is long, and the effectiveness and accuracy of the design are difficult to fully guarantee.

[0004] In addition, for ultra-supercritical steam turbine cylinders with special structures such as airways and pipes, subsidies are set at the airways, pipes and other pipelines to increase shrinkage compensation and avoid shrinkage defects in the pipeline parts. However, after the cylinder is boxed, the subsidies need to be removed through processes such as hot cutting, carbon planing, and grinding. The process is complicated, which will not only cause possible adverse effects on the original parts where the subsidies are set, but also increase energy consumption and costs. In addition, the gas pollution and noise pollution generated during the whole process will cause immeasurable harm to the human body and the environment. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a casting process optimization method for a heat-resistant steel cylinder body based on a finite element model, so as to solve at least one of the problems of the existing heat-resistant steel cylinder body, such as the difficulty in casting process design, long research and development cycle, and the installation of subsidies at the pipelines, which leads to complex casting process, high cost, and environmental pollution.

[0006] An embodiment of the present invention provides a casting process optimization method for a heat-resistant steel cylinder body based on a finite element model, comprising: step S1, determining the thermophysical parameters of the cylinder body material according to the chemical composition and solid-liquid phase line of the cylinder body material; step S2, establishing a three-dimensional model of the cylinder body; wherein the cylinder body has a pipeline, and there is no subsidy on at least one side of the pipeline; step S3, meshing the three-dimensional model to obtain a mesh model of the cylinder body; step S4, setting parameters for the mesh model; wherein the set parameters include the thermophysical parameters of the cylinder body material determined in step S1; step S5, simulating and calculating the flow field and temperature field during the casting process on the mesh model to obtain the shrinkage porosity and shrinkage prediction results of the pipeline wall; step S6, determining whether the pipeline of the cylinder body needs to be subsidized and / or whether the current subsidy is reasonable based on the prediction results.

[0007] Furthermore, in step S2, when the pipeline of the cylinder body is an asymmetric structure, no subsidy is set on the pipeline; when the pipeline of the cylinder body is a symmetric structure, a subsidy is set on one side of the pipeline, and no subsidy is set on the other side of the pipeline.

[0008] Furthermore, when the prediction results show that there are no shrinkage cavities or shrinkage in the unsubsidized area of ​​the pipeline, it is determined that the pipeline does not need to be subsidized; when the prediction results show that there are shrinkage cavities or shrinkage in the unsubsidized area of ​​the pipeline, it is determined that the pipeline needs to be subsidized.

[0009] Further, if no subsidy is set on the pipeline in the three-dimensional model, when it is determined in step S6 that the pipeline needs to be compensated, the three-dimensional model of the cylinder is adjusted, the subsidy is set on the pipeline, and steps S2 to S6 are repeated.

[0010] Furthermore, when the prediction results show that there are no shrinkage cavities or shrinkage in the subsidized area of ​​the pipeline, it is determined that the current subsidy setting is reasonable; when the prediction results show that there are shrinkage cavities or shrinkage in the subsidized area of ​​the pipeline, it is determined that the current subsidy setting is unreasonable, and the subsidy in the three-dimensional model is optimized, and steps S2 to S6 are repeated until there are no shrinkage cavities or shrinkage in the subsidized area of ​​the pipeline.

[0011] Further, adjusting the subsidy in the three-dimensional model includes: adjusting the size of the subsidy.

[0012] Furthermore, the size of the patch is determined using the spheronization method, with the initial spheronization diameter being the wall thickness of the pipe.

[0013] Furthermore, the size of the patch can be adjusted by adjusting the rolling diameter.

[0014] Furthermore, in step S2, the three-dimensional model of the cylinder body includes: a cylinder body casting, a sand box, a riser, and a chiller.

[0015] Furthermore, the thermophysical property parameters include: solid phase ratio curve, thermal conductivity, density, thermal enthalpy and viscosity.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0017] 1. The casting process optimization method of the present invention breaks the inherent ideas and technical prejudices of the conventional cylinder casting process, and verifies whether shrinkage cavities and shrinkage will occur in the cylinder pipeline part without setting subsidies. If it is verified that subsidies are not needed, it can not only simplify the casting process and save design costs, but also save production costs and shorten production time. At the same time, it can reduce the environmental pollution caused by the subsidy removal process and the impact on workers' health.

[0018] 2. The present invention predicts shrinkage cavities and shrinkage porosity in pipeline parts through ProCAST software. When subsidies are required, it can help designers to improve and optimize the subsidy process, thereby improving the quality of cylinder products.

[0019] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the embodiments of the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0021] Figure 1 Schematic diagram of the process of a casting process optimization method according to an embodiment of the present invention.

[0022] Figure 2 1 is a graph of the interface heat transfer coefficient between a casting and a sand box according to an embodiment of the present invention.

[0023] Figure 3 The figure is a schematic diagram of a process for determining the thermophysical property parameters of a cylinder material according to an embodiment of the present invention.

[0024] Figure 4 This is a temperature variation curve diagram of the sample in Example 1 of the present invention during the temperature increase and decrease heat treatment process.

[0025] Figure 5 This is the heat absorption and release curve of the material sample of Example 1 of the present invention.

[0026] Figure 6 This is an exothermic peak curve diagram of the cooling process of Example 1 of the present invention.

[0027] Figure 7This is a solid phase ratio curve diagram of Example 1 of the present invention.

[0028] Figure 8 This is a schematic diagram of a three-dimensional model of the upper half of the cylinder test piece of Example 1 of the present invention.

[0029] Fig. 9 Schematic diagram of the shrinkage porosity simulation prediction results of the test piece of Example 1 of the present invention.

[0030] Fig.10 This is an experimental photograph of a low-magnification experiment on an airway wall slice in the test piece of Example 1 of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention clearer, exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. For the sake of clarity and conciseness, not all features of the actual implementation are described in the specification.

[0032] It is also necessary to explain here that, in order to avoid obscuring the present invention due to unnecessary details, only the device structure and / or processing steps closely related to the solution according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0033] The embodiment of the present invention provides a casting process optimization method for a heat-resistant steel cylinder body based on a finite element model, such as Figure 1 As shown, the method comprises the following steps:

[0034] Step S1, determining the thermophysical property parameters of the cylinder material according to the chemical composition and solid-liquid phase line of the cylinder material;

[0035] Step S2, establishing a three-dimensional model of the cylinder body; wherein the cylinder body has a pipeline, and at least one side of the pipeline is unsubstantiated;

[0036] Step S3, meshing the three-dimensional model to obtain a mesh model of the cylinder body;

[0037] Step S4, setting parameters for the grid model; wherein the set parameters include the thermophysical property parameters of the cylinder material determined in step S1;

[0038] Step S5, simulating and calculating the flow field and temperature field during the casting process on the grid model to obtain the prediction results of shrinkage cavities and porosity of the pipe wall;

[0039] Step S6, based on the prediction result, determine whether the pipeline of the cylinder body needs to be subsidized and / or whether the current subsidy of the pipeline is reasonable.

[0040] In this embodiment, ProCAST software is used to simulate and calculate the flow field and temperature field in the cylinder casting process, which can perform a visual analysis of the entire filling and solidification process of the cylinder, thereby being able to more accurately predict the generation and location of shrinkage cavities and shrinkage in the cylinder's air ducts, pipes and other pipelines, reducing the difficulty of process design, and helping designers to improve and optimize the casting process, thereby shortening the design cycle, improving product quality and reducing production costs.

[0041] In the traditional casting process design, for the ultra-supercritical steam turbine cylinder with special structures such as air ducts and pipes, subsidies are set at the air ducts, pipes and other pipelines to increase shrinkage compensation and avoid shrinkage defects in the pipeline area. However, whether shrinkage defects will definitely occur in the pipeline area without subsidies has not been verified yet.

[0042] The casting process optimization method of the present invention breaks the inherent ideas and technical prejudices of the conventional cylinder casting process, and verifies whether shrinkage cavities and porosity will occur in the cylinder pipeline part without setting subsidies. If it is verified that subsidies are not needed, it can not only save design costs, but also save production costs and shorten production time. At the same time, it can reduce the environmental pollution caused by the subsidy removal process and the impact on workers' health.

[0043] When subsidies are required, the prediction of shrinkage and porosity in the pipeline area through ProCAST software can help designers improve and optimize the subsidy process, thereby improving the quality of cylinder products.

[0044] In some embodiments of the present invention, in step S2, when the pipeline of the cylinder body is an asymmetric structure, no subsidy is set on the pipeline; when the pipeline of the cylinder body is a symmetric structure, a subsidy is set on one side of the pipeline, and no subsidy is set on the other side of the pipeline.

[0045] In the embodiment of the present invention, when the pipeline of the cylinder body is an asymmetric structure, a simulation prediction is performed on whether shrinkage cavities and shrinkage occur at the pipeline position without setting subsidies, so as to verify whether subsidies are required for the pipeline. When the pipeline is a symmetrical structure, subsidies are set on one side of the pipeline, and subsidies are not set on the other symmetrical side, so as to verify whether subsidies are required for the pipeline and determine whether the set subsidies are reasonable, so that when subsidies are required, the link of re-establishing a three-dimensional model to add subsidies can be saved, thereby shortening the design time.

[0046] In step S2, a three-dimensional model of the cylinder casting process is established using three-dimensional modeling software. The established three-dimensional model includes structures such as the cylinder casting, sand box, riser, and chiller. Designers can design these structures according to general methods and experience.

[0047] In step S3 to step S5, the casting process is simulated using ProCAST software. In step S3, the established three-dimensional model is imported into ProCAST software and meshed. When meshing, it can be divided according to tetrahedral meshes to obtain a tetrahedral mesh model.

[0048] In step S4, when setting parameters for the grid model, the set parameters also include thermophysical parameters of materials of other components such as the sand box and chiller, initial temperature, interface heat transfer coefficient between the cylinder casting and other components, calculation operation parameters and storage parameters.

[0049] The thermophysical parameters of other components can adopt the thermophysical parameters of the materials in the software database. For example, the sand box can choose chromite sand, and the chiller can choose low-carbon steel.

[0050] The interface heat transfer coefficient between the casting and the sand box can be obtained by using the data in the software database, such as Figure 2 The interface heat transfer coefficients between other components can be set as constants based on conventional experience. For example, the interface heat transfer coefficient between the chiller and the casting is set to 2000 W / m 2 / K, the interface heat transfer coefficient between the chiller and the flask is set to 500W / m 2 / K.

[0051] The initial temperature includes the initial temperature of all components, which can be set according to on-site production experience. The initial temperature of the casting (i.e., the pouring temperature) is set to increase 50-60°C on the basis of the liquidus temperature. Since the sand box needs to be dried with hot air before pouring, the initial temperature of the sand box and the cold iron is predicted to be 30-50°C.

[0052] The calculation operation parameters include the calculation stop condition, calculation time step, etc. The storage parameters refer to the saving frequency of the calculation results.

[0053] like Figure 1 As shown, in some embodiments, when the prediction result in step S5 shows that there are no shrinkage cavities and shrinkage in the unsubsidized area of ​​the pipeline, it is determined that the pipeline does not need to be subsidized; when the prediction result shows that there are shrinkage cavities and shrinkage in the unsubsidized area of ​​the pipeline, it is determined that the pipeline needs to be subsidized.

[0054] If no subsidy is set on the pipeline in the three-dimensional model, when it is determined in step S6 that the pipeline needs to be compensated, the three-dimensional model of the cylinder body is adjusted, the subsidy is set on the pipeline, and steps S2 to S6 are repeated.

[0055] like Figure 1As shown, in some embodiments, when the prediction result in step S5 shows that there are no shrinkage cavities or shrinkage in the subsidized area of ​​the pipeline, it is determined that the subsidy setting is reasonable; when the prediction result shows that there are shrinkage cavities or shrinkage in the subsidized area of ​​the pipeline, it is determined that the subsidy setting is unreasonable, and the subsidy in the three-dimensional model is optimized, and steps S2 to S6 are repeated until there are no shrinkage cavities or shrinkage in the subsidized area of ​​the pipeline.

[0056] Specifically, when optimizing subsidies in a three-dimensional model, the size of the subsidies may be adjusted.

[0057] Based on the casting process design specifications, the size of the subsidy can be determined by the rolling method. Among them, the starting circle d is located at the end of the compensation of the pipe, and the diameter is the thickness of the pipe wall, that is, the starting circle d is inscribed in the pipe wall. The diameters of the subsequent circles in the rolling process are d1 = (1.05 ~ 1.1) d, d2 = (1.05 ~ 1.1) d1, and the centers of circles d1 and d2 are respectively on the circumference of the starting circle d and circle d1, and are tangent to the inside of the pipe wall, and so on; then, a curve is drawn with the tangent point between the starting circle d and the outside of the pipe wall as the starting point, and the curve is tangent to circles d1, d2, ..., etc., until it reaches a certain structure in the compensation direction (such as a flange or riser), thereby obtaining the subsidy of the pipe wall.

[0058] In some embodiments, the size of the patch can be adjusted by adjusting the diameter of the rounding. Specifically, the increase multiple of the rounding diameter during the rounding process can be adjusted within a range of 1.05 to 1.1 times.

[0059] The embodiments of the present invention optimize the subsidy structure to ensure that the subsidy structure is reasonably set and avoid shrinkage defects in the pipeline.

[0060] Specifically, when the pipeline of the cylinder body is an asymmetric structure, no compensation is provided on the pipeline in step S2. Figure 1 As shown, if the prediction result in step S5 shows that there is no shrinkage porosity in the pipe wall, it is determined that the pipe does not need to be subsidized; if the prediction result in step S5 shows that there is shrinkage porosity in the pipe wall, it is determined that the pipe needs to be subsidized, and additional subsidies are set on the pipe, and steps S2 to S6 are repeated. Then, according to the prediction results, it is analyzed whether there is shrinkage porosity in the subsidized area of ​​the pipe when the subsidy is set. If there is no shrinkage porosity, it is determined that the current subsidy setting is reasonable and a reasonable casting process is obtained; if there is shrinkage porosity, it is necessary to optimize the subsidy, and steps S2 to S6 are repeated until there is no shrinkage porosity in the subsidized area.

[0061] When the pipeline of the cylinder body is a symmetrical structure, a subsidy is set on one side of the pipeline in step S2, and no subsidy is set on the other symmetrical side. Figure 1As shown, if the prediction result in step S5 shows that there are no shrinkage cavities and shrinkage on both symmetrical sides of the pipeline (the non-subsidized area and the subsidized area), it is determined that the pipeline does not need to be subsidized; if there are shrinkage cavities and shrinkage in the non-subsidized area of ​​the pipeline, and there are no shrinkage cavities and shrinkage in the subsidized area, it is determined that the current subsidy setting is reasonable and a reasonable casting process is obtained; if there are shrinkage cavities and shrinkage on both symmetrical sides of the pipeline, it means that the current subsidy setting is unreasonable and the subsidy needs to be optimized, and steps S2 to S6 are repeated until there are no shrinkage cavities and shrinkage in the subsidized area, thereby continuously optimizing the casting process, and finally obtaining suitable subsidies for casting, thereby improving the quality of the cylinder body.

[0062] Cleaning an airway subsidy of the cylinder body is expensive and time-consuming, and the gas pollution and noise pollution generated in the whole process are incalculable harm to the human body and the environment. The method of the present invention, if it is verified that there is no need to set the subsidy, can not only save design costs, but also save production costs, shorten production time, and have considerable economic benefits. At the same time, it can reduce environmental pollution and the impact on the health of workers, and has good social benefits.

[0063] In some embodiments, the thermophysical parameters include solid phase ratio curve, thermal conductivity, density, thermal enthalpy and viscosity. The thermophysical parameters of the cylinder material can be calculated by the thermodynamic calculation module in the ProCAST software. The thermodynamic calculation module that comes with the ProCAST software includes three models: Lever, Scheil and Back Diffusion models. Among them, the Lever and Scheil models correspond to two different microsegregation models respectively. Both models assume that the solute is fully diffused in the liquid phase. The Lever model applies the lever law, that is, the solute can diffuse well in the solid phase; the Scheil model assumes that the solute is not diffused at all in the solid phase; the Back Diffusion model assumes that the solute can partially diffuse in the solid phase, which is a model between Lever and Scheil. The main difference between these three models is that the solid phase ratio curve shape is different at the end of solidification of the cylinder material, and the solidus temperature is different.

[0064] Therefore, for the same cylinder material, different thermodynamic calculation models are used for calculation, and different thermophysical parameters are obtained. Using these thermophysical parameters for casting simulation will result in different simulation results. It can be seen that the rationality and reliability of thermophysical parameters will directly affect the accuracy of casting simulation results. However, the thermophysical parameters used in the prior art usually only select one model for calculation at random or set according to experience, resulting in the inability to guarantee the rationality and accuracy of the simulation calculation results.

[0065] In order to improve the accuracy and reliability of the setting of the thermophysical property parameters, in step S1, the present invention combines the simulation calculation of the thermodynamic calculation module in the ProCAST software with the experimental measurement of the solid-liquid phase line to determine the thermophysical property parameters of the cylinder material. Specifically, in some embodiments of the present invention, step S1 includes:

[0066] Step S11, using various thermodynamic calculation models in the ProCAST software to calculate the thermophysical property parameters of the cylinder material according to the chemical composition of the cylinder material, and obtaining multiple sets of solid-liquid phase line calculation values;

[0067] Step S12, measuring the material sample of the cylinder body to obtain the solid-liquid phase line measured value;

[0068] Step S13, selecting a thermodynamic calculation model suitable for the cylinder body according to multiple sets of solid-liquid phase line calculation values;

[0069] Step S14, comparing the measured value of the solid-liquid phase line with the calculated value of the solid-liquid phase line calculated by the thermodynamic calculation model selected in step S13, and determining whether the current calculated value of the solid-liquid phase line meets the preset requirements;

[0070] Step S15, when the solid-liquid phase line calculation value meets the preset requirements, the thermophysical property parameters of the cylinder body are determined to be the thermophysical property parameters calculated by the thermodynamic calculation model selected in step S13;

[0071] Step S16, when the solid-liquid phase line calculation value does not meet the preset requirements, remove the elements with smaller content in the chemical composition of the material, and recalculate the thermophysical parameters using the thermodynamic calculation model selected in step S13 until the solid-liquid phase line calculation value meets the preset requirements, and select all the thermophysical parameters calculated by the thermodynamic calculation model when the preset requirements are met as the parameters used in the final casting simulation process. The preset requirement may be that the difference between the solid-liquid phase line calculation value and the measured value does not exceed 20°C.

[0072] The present invention obtains the thermophysical property parameters of the cylinder material through a comprehensive method combining simulation calculation and experimental measurement, which improves the rationality and reliability of the thermophysical property parameters, helps to improve the accuracy of the casting process simulation results, and thus can carry out an efficient and accurate process optimization process. Using the method of the present invention to determine the thermophysical property parameters can reduce the trial and error cost, improve research and development efficiency and product quality.

[0073] In some embodiments, when selecting a suitable thermodynamic calculation model in step S13, a plurality of sets of solid-liquid phase line calculated values ​​and solid-liquid phase line measured values ​​obtained by using a plurality of thermodynamic calculation models can be compared and analyzed, and the thermodynamic calculation model corresponding to the solid-liquid phase line calculated value closest to the solid-liquid phase line measured value can be selected.

[0074] In addition, in some embodiments, in step S13, a suitable thermodynamic calculation model can also be selected according to the solid-liquid phase empirical value of the cylinder material. For example, the solid phase of steel is generally around 1400°C, and the thermodynamic calculation model corresponding to the solid phase calculated value closest to the empirical value is selected as the most suitable model.

[0075] In some embodiments, in step S16, when removing elements with a smaller content in the chemical composition, at least one element with a content less than 1 wt.% may be removed.

[0076] Specifically, one element with a content of less than 1wt.% can be removed one by one to study the influence of different small content elements on the calculation results of thermophysical property parameters. In this process, if the calculated solid-liquid phase line value meets the preset requirements, the calculation is stopped.

[0077] If the calculated solid-liquid phase line values ​​after removing one element alone do not meet the preset requirements, then remove two elements with contents less than 1wt.% at the same time for calculation. Remove different element combinations in turn for calculation. In this process, if the calculated solid-liquid phase line values ​​meet the preset requirements, the calculation is stopped.

[0078] If the solid-liquid phase line calculated values ​​obtained after removing two elements in sequence do not meet the preset requirements, then three elements with a content less than 1wt.% are removed at the same time for calculation, and so on, finally obtaining the solid-liquid phase line calculated values ​​that meet the preset requirements.

[0079] In some embodiments of the present invention, in step S12, measuring the material sample of the cylinder to obtain the solid-liquid phase line measured value includes:

[0080] Prepare material samples of the cylinder body;

[0081] Conduct differential thermal analysis test on the material sample to obtain the heat absorption and release curve of the material sample;

[0082] Intercept the exothermic peak curve contained in the cooling process of the endothermic and exothermic curves;

[0083] Integrate the exothermic peak curve to obtain the solid phase ratio curve of the material sample;

[0084] According to the solid phase ratio curve, the actual measured value of the solid-liquid phase line is determined.

[0085] It should be noted that the embodiments of the present invention use the measured solid phase ratio curve to determine whether the solid-liquid phase line calculated by the thermodynamic calculation model is accurate. During the simulation calculation process, a complete set of thermophysical property parameters calculated by the thermodynamic calculation model is used to ensure that the various parameters match each other.

[0086] The embodiment of the present invention can obtain a true and reliable solid-liquid phase line measured value by performing a differential thermal analysis test on a cylinder sample, and the test method is simple. In addition, the present invention determines the solid-liquid phase line by integrating the exothermic peak curve. Compared with the traditional method of measuring the solid-liquid phase line (for example, determining the solid-liquid phase line by peak extrapolation starting temperature or reading the solid-liquid phase line by the peak of the DSC curve), the solid-liquid phase line obtained by the method of the embodiment of the present invention is more accurate and has a smaller deviation from the actual value.

[0087] In addition, in the embodiment of the present invention, since it is necessary to focus on the solidification process of the cylinder material, the partial curve of the exothermic peak included in the cooling process of the sample endothermic curve is intercepted, and the baseline of the exothermic peak curve is reset to zero to ensure the accuracy of the integral calculation. By integrating the exothermic peak curve, the solid phase rate curve of the material sample changing with temperature can be obtained. The solid phase line and liquid phase line of the cylinder material can be directly read in the solid phase rate curve, that is, the solid-liquid phase line measured value is obtained.

[0088] In some embodiments, in order to eliminate the influence of the precipitated phase in the sample on the subsequent test and ensure the uniformity of the sample, when preparing the material sample of the cylinder body, the sample is heated to 1150-1250°C and kept warm for 10-20 hours. For example, the holding temperature is 1150°C, 1170°C, 1190°C, 1210°C, 1230°C, 1250°C, etc., and the holding time is 10h, 12h, 14h, 16h, 20h, so as to homogenize the sample. If the holding temperature is too low or the holding time is too short, it will be unfavorable for the uniform diffusion of the alloy elements and the elimination of the precipitated phase in the cast material; if the holding temperature is too high or the holding time is too long, high-temperature ferrite will be formed in the cylinder body material or overburning will occur.

[0089] Furthermore, after the sample is homogenized, the surface of the sample is polished to avoid contamination. The sample can be processed into φ2*2mm to facilitate the subsequent differential thermal analysis test.

[0090] In some embodiments, when performing a differential thermal analysis test on a material sample, the material sample is heated to a first critical temperature at a constant heating rate, then cooled to a second critical temperature at a first cooling rate, and then cooled to room temperature at a second cooling rate. The first critical temperature and the second critical temperature refer to the starting temperature and the ending temperature of the cooling at the first cooling rate, respectively, wherein the first critical temperature can be set to increase 50°C to 100°C based on the liquidus calculated value, and the second critical temperature can be set to decrease 50°C to 100°C based on the solidus calculated value.

[0091] This embodiment uses the solid-liquid phase line calculated value as a reference, and expands the temperature range of the solid-liquid phase line by increasing and decreasing 50-100°C at both ends to cover the calculation error of the solid-liquid phase line calculated value, thereby ensuring that the sample material solidifies at a slower first cooling rate between the actual solid phase line temperature and the liquid phase line temperature during the test, making it close to the actual solidification process, thereby improving the accuracy of the measured value. Among them, the liquid phase line calculated value and the solid phase line calculated value used can be selected from the multiple groups of solid-liquid phase line calculated values ​​obtained in step S11 based on experience.

[0092] In some embodiments, the heating rate can be any value in the range of 10 to 20 k / s, such as 10 k / s, 11 k / s, 12 k / s, 13 k / s, 14 k / s, 15 k / s, 16 k / s, 17 k / s, 18 k / s, 19 k / s, and 20 k / s. The first cooling rate is determined according to the actual cooling rate of the cylinder material; the second cooling rate is greater than the first cooling rate. Specifically, the second cooling rate can be any value in the range of 10 to 20 k / s, such as 10 k / s, 11 k / s, 12 k / s, 13 k / s, 14 k / s, 15 k / s, 16 k / s, 17 k / s, 18 k / s, 19 k / s, and 20 k / s.

[0093] The embodiment of the present invention adopts a segmented cooling heat treatment method so that the sample melt in the first cooling stage is as close as possible to the actual cooling process during cylinder casting, so as to improve the authenticity and reliability of the test results; at the same time, rapid cooling in the second cooling stage can shorten the test time, improve the test efficiency, and reduce the loss of the test equipment.

[0094] In step S11, when using ProCAST software to calculate the thermophysical parameters of the cylinder, in the material parameter calculation module, select the iron-based alloy, input the chemical composition of the cylinder material, select three thermodynamic calculation models in turn for calculation, and obtain three different sets of solid-liquid phase line calculation values.

[0095] When the Back Diffusion model is selected for calculation, the average cooling rate is set to 0.01-1 K / s. The average cooling rate set within this range has little effect on the calculation results of the thermophysical parameters. Preferably, the average cooling rate is set to 0.01 K / s.

[0096] The method of the present invention can better use ProCAST software to reasonably select thermophysical property parameters and improve the accuracy of simulation calculation results; at the same time, the patching process is reasonably optimized, the product quality of the cylinder body is improved, and the design and research and development efficiency is improved.

[0097] The cylinder casting process optimization method of the present invention is further illustrated by specific embodiments below.

[0098] Example 1

[0099] The casting process simulation was carried out on the upper half test piece of the inner cylinder of an ultra-supercritical steam turbine.

[0100] Step S1, determining the thermophysical parameters of the cylinder material.

[0101] (1) Calculate the thermal physical parameters of the cylinder material:

[0102] In the material parameter calculation module, select the iron-based alloy and enter the chemical composition of the heat-resistant steel material used in the cylinder body. The content range of each chemical component of the heat-resistant steel material is shown in Table 1, and the remaining components are iron and unavoidable impurities. In the calculation module, the chemical composition of the heat-resistant steel material is set to the middle value of the content range of each component to calculate the thermophysical parameters; for elements such as P and S that only set the upper limit of the content range, the element content is set to the upper limit of the element content range in the calculation module.

[0103] Table 1 Chemical composition of heat-resistant steel materials

[0104]

[0105] The Scheil, Lever, and Back Diffusion models (specifying the average cooling rate to be 0.01 K / s) were used in turn to calculate, and three sets of solid-liquid phase line calculated values ​​were obtained, which were 1131-1493°C, 1355-1493°C, and 1298-1493°C, respectively.

[0106] According to experience, the solidus of steel is generally around 1400℃, of which 1131-1493℃ is obviously unreasonable. The first critical temperature and the second critical temperature in the subsequent differential thermal analysis test can be determined according to any of the other two groups.

[0107] (2) Sample preparation: The sample was heated to 1250°C and kept at this temperature for 20 h before being water-cooled to homogenize the sample. The sample was then processed into small samples of φ2*2 mm and the surface was polished to avoid contamination.

[0108] (3) Differential thermal analysis test:

[0109] According to Figure 4 The heat treatment process shown is to heat and cool the sample. Specifically, the sample is heated to 1550°C at a heating rate of 10°C / min, then cooled to 1300°C at a first cooling rate of 1°C / min, and then cooled to room temperature at a second cooling rate of 20°C / min.

[0110] Among them, the solid-liquid phase line calculated value 1355-1493°C obtained by Lever model calculation is selected to determine the first key temperature and the second key temperature, wherein the first key temperature is 1493°C+57°C=1550°C, and the second key temperature is 1355°C-55°C=1300°C. According to experience, the actual average cooling rate of large castings in the temperature range of 1550-1300°C is about 1°C / min.

[0111] The endothermic and exothermic curves obtained in the final test are as follows: Figure 5 shown.

[0112] (4) Determine the measured value of the solid-liquid phase line: Figure 5 The exothermic peak curve included in the cooling process of the endothermic and exothermic curve shown in the figure is cut out, and its baseline is reset to zero, and the following is obtained: Figure 6 The exothermic peak curve shown; Figure 6 By integrating the exothermic peak curve shown in the figure, we can get the solid phase ratio curve of the cylinder material changing with temperature, as shown in Figure 7 As shown; from the solid phase ratio curve, it can be directly read that the liquidus measured value is 1502℃, and the solidus measured value is 1433℃.

[0113] (5) Determine the appropriate thermodynamic calculation model: Compare the three sets of solid-liquid phase line calculated values ​​with the solid-liquid phase line measured values. The 1355-1493℃ calculated by the Lever model is closest to the solid-liquid phase line measured value of 1433-1502℃. Therefore, it is more appropriate to choose the Lever model to calculate the thermophysical property parameters.

[0114] (6) Comparing the calculated solid-liquid phase value of 1355-1493℃ with the measured solid-liquid phase value of 1433-1502℃, there is a big difference between the two. Therefore, the elements P and S with a content of less than 1wt.% in the chemical composition are removed, and the thermophysical parameters are recalculated to obtain a new solid-liquid phase calculated value of 1420-1494℃. The calculated solid-liquid phase value is close to the measured value. Therefore, it is believed that all the thermophysical parameters recalculated by the Lever model are reasonable and reliable, and can be used for subsequent casting process simulation.

[0115] Step S2, establishing a three-dimensional model of the casting process of the upper half test piece of the cylinder body:

[0116] Establish a three-dimensional model of the casting process of the test piece, such as Figure 8 As shown, the three-dimensional model is a symmetrical structure, including the upper half of the cylinder body, the sand box, the riser, the chiller, and the pouring system. A subsidy is set on one side of the airway wall, and no subsidy is set on the other symmetrical side.

[0117] Step S3, meshing of the three-dimensional model:

[0118] The three-dimensional model was imported into ProCAST software for meshing to obtain a tetrahedral mesh model.

[0119] Step S4, setting parameters for the grid model:

[0120] The parameters of the grid model in step 3 are set. The main parameters include: (a) the thermal properties of the materials such as the cylinder body, the sand box, and the chiller. The thermal properties of the cylinder body material are obtained by step S1; (b) the initial temperature: the initial temperature of the casting is 1494℃+60℃≈1555℃, and the initial temperature of the sand box and the chiller is 50℃; (c) the interface heat transfer coefficient: the interface heat transfer coefficient between the casting and the sand box is as follows: Figure 2 As shown, the interface heat transfer coefficient between the chiller and the casting is set to 2000 W / m 2 / K, the interface heat transfer coefficient between the chiller and the flask is set to 500W / m 2 / K; (d) Calculation operation parameters and storage parameters: calculation stop temperature is 1410℃, time step is 20s; storage frequency is 100.

[0121] Step S5, simulate and calculate the flow field and temperature field of the grid model after the parameters are set in step S4, and obtain the prediction results of shrinkage and porosity of the airway wall, such as Fig. 9 shown.

[0122] Step S6, according to Fig. 9 From the prediction results shown, it can be seen that there are no shrinkage cavities or shrinkage on both sides of the airway wall, which means that no subsidy is required at the airway position of the cylinder body.

[0123] The upper half of the cylinder block was actually cast, and ultrasonic testing was performed after boxing and sand removal. The test results showed that no shrinkage defects were found in the airway wall on the side without the subsidy. The airway wall on the side without the subsidy was cut off from the test piece and sliced. Each slice was about 15mm thick. Low-magnification tests were performed on all the slices, and it was found that there were no shrinkage defects on each slice. The low-magnification test photo of one of the slices is shown below. Fig.10 shown.

[0124] Therefore, the accuracy of the simulation results was verified through nondestructive testing and experimental testing, further proving that no subsidy was needed for the airway wall of the test piece.

[0125] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A casting process optimization method for a heat-resistant steel cylinder body based on a finite element model, characterized in that: include: Step S1, determining the thermophysical property parameters of the cylinder according to the chemical composition and solid-liquid phase line of the cylinder material; Step S2, establishing a three-dimensional model of the cylinder; wherein the cylinder has a pipeline, and there is no subsidy on at least one side of the pipeline; Step S3, meshing the three-dimensional model to obtain a mesh model of the cylinder body; Step S4, setting parameters for the grid model; wherein the set parameters include the thermophysical property parameters of the cylinder material determined in step S1; Step S5, performing simulation calculations on the flow field and temperature field during the casting process on the grid model to obtain prediction results of shrinkage cavities and porosity of the pipe wall; Step S6, determining whether a subsidy is required for the pipeline of the cylinder body and / or whether the current subsidy is reasonable based on the prediction result.

2. The method according to claim 1, characterized in that In step S2, When the pipeline of the cylinder body is of an asymmetric structure, no subsidy is provided on the pipeline; When the pipeline of the cylinder body is a symmetrical structure, a subsidy is provided on one side of the pipeline, and no subsidy is provided on the other side opposite to the pipeline.

3. The method according to claim 2, characterized in that When the prediction result shows that there is no shrinkage cavity or shrinkage porosity in the non-subsidized area of ​​the pipeline, it is determined that the pipeline does not need to be subsidized; When the prediction result shows that shrinkage cavities and porosity exist in the unsubsidized area of ​​the pipeline, it is determined that the pipeline needs to be subsidized.

4. The method according to claim 3, characterized in that: If no subsidy is provided on the pipeline in the three-dimensional model, when it is determined in step S6 that the pipeline needs to be provided with a subsidy, the three-dimensional model of the cylinder body is adjusted, the subsidy is provided on the pipeline, and steps S2 to S6 are repeated.

5. The method according to claim 2 or 4, characterized in that: When the prediction result shows that there is no shrinkage cavity or shrinkage porosity in the subsidized area of ​​the pipeline, it is determined that the current subsidy setting is reasonable; When the prediction result shows that shrinkage cavities and shrinkage exist in the subsidized area of ​​the pipeline, it is determined that the current subsidy setting is unreasonable, and the subsidy in the three-dimensional model is optimized, and steps S2 to S6 are repeated until there are no shrinkage cavities and shrinkage in the subsidized area of ​​the pipeline.

6. The method according to claim 5, characterized in that The adjusting the subsidy in the three-dimensional model includes: adjusting the size of the subsidy.

7. The method according to claim 6, characterized in that The size of the patch is determined using the spheronization method, with the initial spheronization diameter being the wall thickness of the pipe.

8. The method according to claim 7, characterized in that The size of the patch is adjusted by adjusting the rolling diameter.

9. The method according to claim 1, characterized in that: In step S2, the three-dimensional model of the cylinder body includes: a cylinder body casting, a sand box, a riser, and a chiller.

10. The method according to claim 1, characterized in that The thermophysical property parameters include: solid phase ratio curve, thermal conductivity, density, thermal enthalpy and viscosity.

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