Method for determining thermophysical parameters of casting steel and application thereof

Abstract

The invention discloses a method for determining thermophysical parameters of casting steel and application of the method, and belongs to the technical field of computer aided design optimization. The determination method comprises the following steps: step S11, calculating thermophysical parameters of the casting steel according to chemical components of the casting steel by adopting a plurality of thermodynamic calculation models to obtain a plurality of groups of thermophysical parameters; step S12, measuring a sample of the casting steel to obtain a solid-liquid phase line measured value of the casting steel; step S13, comparing and analyzing the plurality of groups of solid-liquid phase line calculated values and solid-liquid phase line measured values, and judging whether the solid-liquid phase line calculated values meet preset requirements or not; s14, when the solid-liquid phase line calculation value meets the preset requirement, all the thermophysical parameters corresponding to the solid-liquid phase line calculation value are selected as the thermophysical parameters of the casting steel; and S15, when the solid-liquid phase line calculation value does not meet the preset requirement, removing at least one element with the content smaller than a preset threshold value in the chemical components, and recalculating the thermophysical property parameters until the solid-liquid phase line calculation value meets the preset requirement.

Description

Technical Field

[0001] The invention relates to the technical field of computer-aided design optimization, and in particular to a method for determining thermophysical property parameters of steel for casting and an application thereof. Background Art

[0002] Casting simulation software ProCAST can visualize the entire process of filling and solidification, accurately predict the location and causes of casting defects, and help designers improve and optimize the process. When using ProCAST software for casting simulation, the thermophysical parameters of the casting are required. Usually, the thermodynamic calculation module that comes with ProCAST software can be used to calculate the thermophysical parameters.

[0003] However, the thermodynamic calculation module includes three models: Lever, Scheil and Back Diffusion models. Using different models for calculation will result in different thermophysical parameters, and using these parameters for casting simulation will result in different simulation results. It can be seen that the rationality and reliability of the thermophysical parameters will directly affect the accuracy of the casting simulation results. However, there is currently no research on the applicability of the three models, and the thermophysical parameters used in the prior art usually only select one of the models for calculation, and the rationality and accuracy of the calculation results cannot be guaranteed. Summary of the invention

[0004] In view of the above analysis, the present invention aims to provide a method for determining the thermophysical property parameters of steel for casting and its application, so as to solve the above problems in the prior art.

[0005] An embodiment of the present invention provides a method for determining thermophysical property parameters of steel for casting, which comprises: step S11, respectively using a plurality of thermodynamic calculation models in ProCAST software, according to the chemical composition of the steel for casting, calculating the thermophysical property parameters of the steel for casting, and obtaining a plurality of groups of thermophysical property parameters, each group of thermophysical property parameters including a solid-liquid phase line calculated value; step S12, measuring a sample of the steel for casting, and obtaining a solid-liquid phase line measured value of the steel for casting; step S13, comparing and analyzing a plurality of groups of solid-liquid phase line calculated values ​​and solid-liquid phase line measured values ​​obtained by using a plurality of thermodynamic calculation models, and judging whether the solid-liquid phase line calculated value meets a preset requirement; step S14, when the solid-liquid phase line calculated value meets the preset requirement, selecting all thermophysical property parameters corresponding to the solid-liquid phase line calculated value as the thermophysical property parameters of the steel for casting; step S15, when the solid-liquid phase line calculated value does not meet the preset requirement, removing at least one element whose content in the chemical composition is less than a predetermined threshold value, and recalculating the thermophysical property parameters until the solid-liquid phase line calculated value meets the preset requirement.

[0006] Further, in step S13, a thermodynamic calculation model corresponding to the solid-liquid phase line calculated value closest to the solid-liquid phase line measured value is selected; and it is determined whether the closest solid-liquid phase line calculated value meets the preset requirements; in step S14, when the solid-liquid phase line calculated value meets the preset requirements, all the thermophysical property parameters corresponding to the solid-liquid phase line calculated value are determined to be the thermophysical property parameters of the casting steel; in step S15, when the solid-liquid phase line calculated value does not meet the preset requirements, at least one element whose content is less than a predetermined threshold value in the chemical composition is removed, and the thermodynamic calculation model selected in step S13 is used to recalculate the thermophysical property parameters until the solid-liquid phase line calculated value meets the preset requirements.

[0007] Furthermore, when the casting steel is a large ingot, in step S13, it is determined whether multiple sets of solid-liquid phase line calculated values ​​meet the preset requirements; in step S14, when the solid-liquid phase line calculated values ​​meet the preset requirements, all the thermophysical property parameters corresponding to the solid-liquid phase line calculated values ​​are selected as backup parameters; in step S15, when multiple sets of solid-liquid phase line calculated values ​​do not meet the preset requirements, remove at least one element in the chemical composition whose content is less than a predetermined threshold, and recalculate the thermophysical property parameters until the solid-liquid phase line calculated values ​​meet the preset requirements.

[0008] Furthermore, if the backup parameters include multiple sets of thermophysical property parameters, the determination method also includes: establishing a three-dimensional casting model of the steel ingot; simulating and calculating the temperature field of the casting process on the three-dimensional casting model based on the multiple sets of thermophysical property parameters to obtain multiple corresponding complete solidification times of the steel ingots; and selecting a set of thermophysical property parameters based on each complete solidification time.

[0009] Furthermore, when screening the thermophysical property parameters, the complete solidification times and the actual demoulding time of the steel ingot are compared to screen out a set of thermophysical property parameters that are closest to the actual demoulding time.

[0010] Furthermore, in step S12, a sample of casting steel is measured to obtain the actual measured value of the solid-liquid phase line of the casting steel, including: preparing a sample of casting steel; performing a differential thermal analysis test on the sample to obtain an endothermic and exothermic curve of the sample; and determining the actual measured value of the solid-liquid phase line of the casting steel according to the endothermic and exothermic curve.

[0011] Furthermore, according to the endothermic and exothermic curves, the actual measured value of the solid-liquid phase line of the casting steel is determined, including: intercepting the exothermic peak curve included in the cooling process of the endothermic and exothermic curves; integrating the exothermic peak curve to obtain the solid phase ratio curve of the sample; and determining the actual measured value of the solid-liquid phase line according to the solid phase ratio curve.

[0012] Furthermore, when the sample is subjected to a differential thermal analysis test, the sample is heated to a first critical temperature, then cooled to a second critical temperature at a first cooling rate, and then cooled to room temperature at a second cooling rate; wherein the first cooling rate is determined based on an actual cooling rate of the casting steel; and the second cooling rate is greater than the first cooling rate.

[0013] On the other hand, an embodiment of the present invention also provides an application of a method for determining thermophysical property parameters in a casting process optimization method for a heat-resistant steel cylinder body, which includes: using the determination method of the above embodiment to determine the thermophysical property parameters of the cylinder body material according to the chemical composition of the heat-resistant steel cylinder body material; simulating the casting process of the cylinder body according to the thermophysical property parameters; and determining whether the cylinder body pipes need to be subsidized according to the simulation results.

[0014] On the other hand, an embodiment of the present invention also provides an application of a method for determining thermophysical property parameters in a method for optimizing the casting process of large steel ingots, which includes: using the determination method of the above embodiment to determine the thermophysical property parameters of the steel ingot material according to the chemical composition of the steel ingot material; simulating the casting process of the steel ingot according to the thermophysical property parameters; and optimizing the casting process of the steel ingot according to the simulation results to reduce the surface stress of the steel ingot.

[0015] Compared with the prior art, the method of the present invention can achieve at least one of the following beneficial effects:

[0016] 1. The present invention determines the thermophysical parameters of casting steel by combining simulation calculation and experimental measurement, thereby improving the rationality and reliability of the thermophysical parameters. When applied to casting simulation of casting steel, it helps to improve the accuracy of casting process simulation results, thereby enabling efficient and accurate process optimization, reducing trial and error costs, and improving R&D efficiency and product quality.

[0017] 2. For large steel ingots, when multiple sets of thermophysical property parameter backup data are selected, the multiple sets of thermophysical property parameters are screened in combination with the simulation calculation results of the temperature field during the steel ingot casting process to further improve the rationality and reliability of the thermophysical property parameters.

[0018] 3. The present invention tests the solid-liquid phase line measured value of casting steel by differential thermal analysis, and can obtain a true and reliable solid-liquid phase line measured value, and the testing method is simple. Before the test, the test sample is homogenized to ensure the uniformity of the sample, eliminate the precipitated phase in the sample, and reduce the impact on the test.

[0019] 4. When the present invention performs differential thermal analysis testing on casting steel, a segmented cooling heat treatment method is adopted, so that the sample melt in the first cooling stage is as close as possible to the actual cooling process of the casting steel during 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 avoid equipment loss.

[0020] 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

[0021] 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.

[0022] Figure 1 Schematic diagram of a process for determining thermophysical property parameters according to some embodiments of the present invention.

[0023] Figure 2 Schematic diagram of a process for determining thermophysical property parameters of materials for large steel ingots according to some embodiments of the present invention.

[0024] Figure 3 The temperature variation curves of the samples of Example 1 and Example 3 of the present invention during the heat treatment process during the differential thermal analysis test are shown in FIG.

[0025] Figure 4 This is the endothermic and exothermic curve of the sample of Example 1 of the present invention.

[0026] Figure 5 This is a graph showing the exothermic peak of the sample in Example 1 of the present invention during the cooling process.

[0027] Figure 6 This is a solid phase ratio curve diagram of the sample of Example 1 of the present invention.

[0028] Figure 7 This is a schematic diagram of the casting three-dimensional model of Example 2 of the present invention.

[0029] Figure 8 This is a graph of the interface heat transfer coefficient between the casting and the sand box in Example 2 of the present invention.

[0030] Fig. 9 Schematic diagram of shrinkage prediction results of the upper half test piece of the cylinder body of Example 2 of the present invention.

[0031] Fig.10 This is an experimental photograph of a low-magnification experiment on airway wall slices according to Example 2 of the present invention.

[0032] Fig.11 This is the endothermic and exothermic curve of the sample of Example 3 of the present invention.

[0033] Fig.12 This is the exothermic peak curve diagram of the sample of Example 3 of the present invention.

[0034] Fig.13 This is a solid phase ratio curve diagram of the sample of Example 3 of the present invention.

[0035] Fig.14 Graph showing the interface heat transfer coefficient between the steel ingot and the steel ingot mold according to Example 3 of the present invention.

[0036] Fig.15 Schematic diagram of the three-dimensional model of a large steel ingot according to Example 4 of the present invention; wherein (a) is the initial three-dimensional model, (b) and (c) are three-dimensional models after different edge shape optimizations, respectively.

[0037] Fig.16 Schematic diagram of the stress analysis results of a large steel ingot according to Example 4 of the present invention; wherein (a) is the initial three-dimensional model, and (b) and (c) are three-dimensional models after different edge-type optimizations, respectively.

[0038] Fig.17 It is a partial schematic diagram of the three-dimensional model of a large steel ingot of Example 4 of the present invention; wherein (a) is the initial three-dimensional model, (b) and (c) are three-dimensional models for optimizing different steel ingot mold thicknesses, respectively.

[0039] Fig.18 Schematic diagram of the stress analysis results of the large steel ingot of Example 4 of the present invention; wherein (a) is a three-dimensional model of the original steel ingot mold thickness, (b) and (c) are three-dimensional models for optimizing different steel ingot mold thicknesses, respectively. DETAILED DESCRIPTION

[0040] 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.

[0041] 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.

[0042] In order to improve the rationality and reliability of the thermophysical property parameters of casting materials used in the casting process simulation, an embodiment of the present invention provides a method for determining the thermophysical property parameters of steel for casting, such as Figure 1 As shown, the method comprises the following steps:

[0043] Step S11, using a variety of thermodynamic calculation models in the ProCAST software, respectively, according to the chemical composition of the casting steel, calculate the thermophysical property parameters of the casting steel, and obtain multiple groups of thermophysical property parameters, each group of thermophysical property parameters includes a solid-liquid phase line calculation value;

[0044] Step S12, measuring the sample of the casting steel to obtain the solidus-liquidus phase measured value of the casting steel;

[0045] Step S13, comparing and analyzing multiple groups of solid-liquid phase line calculated values ​​and solid-liquid phase line measured values ​​obtained by using multiple thermodynamic calculation models, and determining whether the solid-liquid phase line calculated values ​​meet preset requirements;

[0046] Step S14, when the solid-liquid phase line calculation value meets the preset requirements, the thermophysical property parameters corresponding to the solid-liquid phase line calculation value are selected as the thermophysical property parameters of the casting steel;

[0047] Step S15, when the calculated value of the solid-liquid phase line does not meet the preset requirements, at least one element whose content is less than a predetermined threshold value in the chemical composition is removed, and the thermophysical property parameters are recalculated until the calculated value of the solid-liquid phase line meets the preset requirements.

[0048] The embodiments of the present invention combine simulation calculation and experimental measurement to determine the thermophysical parameters of steel for casting, which improves the rationality and reliability of the thermophysical parameters, helps to improve the accuracy of the simulation results of the casting process of castings, and then can carry out an efficient and accurate process optimization process, which can reduce the trial and error cost of the casting process design of castings, and improve research and development efficiency and product quality.

[0049] In step S11, the thermodynamic calculation module of ProCAST software includes three models: Lever, Scheil and Back Diffusion models. Among them, the Lever and Scheil models correspond to two different microsegregation models, and 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 has no diffusion 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. When these three models are used to calculate the thermophysical parameters, the shape of the solid phase ratio curve and the solidus temperature of the casting steel at the end of solidification are different.

[0050] When using ProCAST software to calculate the thermophysical properties of casting steel, select the iron-based alloy in the material parameter calculation module, input the chemical composition of the casting steel, and select three thermodynamic calculation models in turn to obtain three different sets of solid-liquid phase line calculation values.

[0051] 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.

[0052] In some embodiments, the thermophysical parameters include parameters required for temperature field calculation, parameters required for flow field calculation, and parameters required for stress field calculation. The parameters required for temperature field calculation include solid phase ratio curve, thermal conductivity, density, and thermal enthalpy; based on the temperature field calculation, the parameters required for flow field calculation also include viscosity; the parameters required for stress field calculation also include: thermal expansion coefficient, Young's modulus, Poisson's ratio, yield strength, and plastic modulus.

[0053] In some embodiments, in step S13, the preset requirement may be that the difference between the calculated solid-liquid phase line value and the measured solid-liquid phase line value does not exceed 20°C, that is, the difference between the calculated solid-liquid phase line value and the measured solid-liquid phase line value does not exceed 20°C, and the difference between the calculated liquid phase line value and the measured liquid phase line value does not exceed 20°C. By adopting the method of the present invention, the difference between the calculated solid-liquid phase line value and the measured solid-liquid phase line value does not exceed 20°C, which can improve the accuracy of the determined thermophysical parameters including the solid-liquid phase line, while avoiding excessive calculation time and ensuring calculation efficiency.

[0054] In some embodiments, in step S15, when at least one element in the chemical composition having a content less than a predetermined threshold is removed, the predetermined threshold may be 1 wt.%, that is, at least one element having a content less than 1 wt.% may be removed.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] In some embodiments, for conventional casting steel, after multiple sets of thermophysical property parameters are calculated using multiple thermodynamic calculation models, a suitable thermodynamic calculation model can be selected based on the multiple sets of solid-liquid phase line calculation values ​​obtained by the calculation, and then it can be determined whether the solid-liquid phase line calculation values ​​calculated by the thermodynamic calculation model meet the preset requirements.

[0059] Optionally, a thermodynamic calculation model corresponding to a calculated solid-liquid phase line value closest to the measured solid-liquid phase line value may be selected, and it may be determined whether the above-mentioned closest calculated solid-liquid phase line value meets preset requirements.

[0060] Alternatively, a thermodynamic calculation model corresponding to the calculated solid-liquid phase value closest to the empirical value of the solid-liquid phase can be selected, and it can be determined whether the closest calculated solid-liquid phase value meets the preset requirements. For example, the solid phase of steel is generally around 1400°C, and the thermodynamic calculation model corresponding to the calculated solid phase value closest to the empirical value is selected as the most suitable model.

[0061] Further, in step S14, when the solid-liquid phase line calculated value obtained by the above-selected thermodynamic calculation model meets the preset requirements, all the thermophysical property parameters corresponding to the solid-liquid phase line calculated value are determined as the thermophysical property parameters of the casting steel; in step S15, when the solid-liquid phase line calculated value does not meet the preset requirements, at least one element in the chemical composition whose content is less than a predetermined threshold is removed, and the thermophysical property parameters are recalculated using the thermodynamic calculation model selected in step S13 until the solid-liquid phase line calculated value meets the preset requirements.

[0062] In some embodiments, when the steel for casting is a large ingot, for example, a large ingot used for a nuclear reactor pressure vessel, a motor rotor of a large power station, a support roller in a large mechanical equipment, etc., Figure 2 As shown, in step S13, it is determined whether the multiple groups of solid-liquid phase line calculation values ​​calculated by multiple thermodynamic calculation models meet the preset requirements; in step S14, when the solid-liquid phase line calculation values ​​meet the preset requirements, all the thermophysical parameters corresponding to the solid-liquid phase line calculation values ​​are selected as standby parameters; in step S15, when the multiple groups of solid-liquid phase line calculation values ​​do not meet the preset requirements, at least one element whose content is less than a predetermined threshold value in the chemical composition of the casting steel is removed, and the thermophysical parameters are recalculated until at least one group of solid-liquid phase line calculation values ​​meets the preset requirements. Among them, the standby parameters may include one group of thermophysical parameters, and may also include multiple groups of thermophysical parameters.

[0063] In some embodiments, if the backup parameters include only one set of thermophysical property parameters, then the set of thermophysical property parameters is the finally determined thermophysical property parameters.

[0064] In some embodiments, Figure 2 As shown, if the backup parameters include multiple groups of thermophysical property parameters, the determination method also includes:

[0065] Step S16, establishing a three-dimensional casting model of the steel ingot;

[0066] Step S17, performing simulation calculation of the temperature field of the casting process on the casting three-dimensional model according to the multiple sets of thermophysical property parameters, and obtaining multiple complete solidification times of the steel ingots corresponding to the thermophysical property parameters;

[0067] Step S18, screening a group of thermophysical property parameters according to each complete solidification time.

[0068] When a plurality of sets of thermophysical property parameters are obtained for use, the embodiment of the present invention obtains different complete solidification times of the steel ingot by simulating and calculating the temperature field of the casting three-dimensional model with different thermophysical property parameters, and then selects a set of most suitable thermophysical property parameters according to the complete solidification time, thereby improving the accuracy and reliability of the determination of the thermophysical property parameters and providing reliable data for the casting simulation of large steel ingots.

[0069] In some embodiments, in step S16, a three-dimensional modeling software is used to establish a casting three-dimensional model of a large steel ingot, and the established casting three-dimensional model includes a steel ingot, an insulation cap, an ingot mold, a chassis, refractory bricks, and a covering agent.

[0070] In some embodiments, in step S17, the casting simulation is performed using ProCAST software. First, the established casting three-dimensional model is imported into the ProCAST software and meshed. When meshing, it can be divided according to the tetrahedral mesh to obtain a tetrahedral mesh model. Then, the mesh model is parameterized. Finally, the mesh model is simulated and calculated for the temperature field of the casting process to obtain a plurality of ingot complete solidification times corresponding to the thermophysical property parameters.

[0071] When setting parameters, the set parameters include the thermophysical parameters of the materials of each component, the initial temperature, the interface heat transfer coefficient between the components, the calculation operation parameters and the storage parameters. The thermophysical parameters of the steel ingot adopt the spare parameters obtained in step S14, and the thermophysical parameters of other components can adopt the thermophysical parameters of the materials in the software database.

[0072] The initial temperature includes the initial temperature of all components, which can be set according to on-site production experience. In some embodiments, the initial temperature of the ingot (i.e., the pouring temperature) is set to increase 60 to 80°C on the basis of the liquidus temperature. Since the ingot mold needs to be hot-air baked before pouring, it is predicted that the initial temperature of the ingot mold is 30 to 50°C.

[0073] The interface heat transfer coefficient between the ingot and the ingot mold can be obtained by using the data in the software database, for example, Fig.14The interface heat transfer coefficient curve between the steel ingot and the steel ingot mold is shown. The interface heat transfer coefficient between other components can be set as a constant according to conventional experience. For example, the interface heat transfer coefficient between refractory bricks, covering agents and other components can be set to 200W / m 2 / K.

[0074] The calculation operation parameters include the calculation stop condition (for example, the temperature at which the calculation stops), the calculation time step, etc. The storage parameter refers to the saving frequency of the calculation results.

[0075] In some embodiments, in step S18, when screening the thermophysical property parameters, the calculated complete solidification times are compared with the actual demolding time of the steel ingot, and a set of thermophysical property parameters closest to the actual demolding time is screened out as the most reasonable set of thermophysical property parameters for use in the casting simulation of large steel ingots to ensure the accuracy and reliability of the simulation calculation results.

[0076] In some embodiments of the present invention, in step S12, measuring a sample of the casting steel to obtain a measured value of the solidus-liquidus phase of the casting steel includes:

[0077] Preparation of steel specimens for casting;

[0078] Perform differential thermal analysis on the sample to obtain the heat absorption and release curve of the sample;

[0079] According to the endothermic and exothermic curves, the actual measured values ​​of the solidus and liquidus phases of the casting steel are determined.

[0080] The embodiment of the present invention can obtain a true and reliable solidus-liquidus phase line measured value by performing a differential thermal analysis test on a sample of casting steel, and the test method is simple.

[0081] In some embodiments, when preparing a sample of steel for casting, the sample may be subjected to a homogenization treatment to ensure the uniformity of the sample, eliminate the precipitated phase in the sample, and reduce the impact on subsequent tests.

[0082] During the homogenization treatment, the sample can be heated to 1150-1250℃ and kept warm for 10-30h 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 alloy elements and the elimination of precipitation phases in the cast steel for casting; if the holding temperature is too high or the holding time is too long, high-temperature ferrite will be formed in the sample or over-burning will occur, affecting the accuracy of the test results. For example, the holding temperature is 1150℃, 1170℃, 1190℃, 1210℃, 1230℃, 1250℃, etc., and the holding time is 10h, 12h, 14h, 16h, 20h, 22h, 24h, 26h, 28h, 30h.

[0083] 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 subsequent differential thermal analysis testing.

[0084] In some embodiments, when a differential thermal analysis test is performed on a sample, the 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; wherein the first cooling rate is determined based on the actual cooling rate of the casting steel, and the second cooling rate is greater than the first cooling rate.

[0085] It should be noted that the first critical temperature and the second critical temperature respectively refer to the starting temperature and the ending temperature of the cooling process using the first cooling rate, 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.

[0086] The embodiment of the present invention uses the solid-liquid phase line calculated value as a reference, and expands the temperature range of the solid-liquid phase by increasing and decreasing 50 to 100°C at both ends, respectively, to cover the calculation error of the solid-liquid phase line calculated value, thereby ensuring that the sample is solidified at a slower first cooling rate between the actual solidus temperature and the liquidus temperature during the test, thereby improving the accuracy of the measured value. At the same time, it avoids the temperature range being too wide, resulting in reduced test efficiency and equipment loss. Among them, the liquidus calculated value and the solidus calculated value used can be selected based on experience from a more reasonable set of multiple sets of solid-liquid phase line calculated values ​​obtained in step S11.

[0087] 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 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.

[0088] 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 of casting steel, 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 avoid equipment loss.

[0089] In some embodiments, determining the measured value of the solid-liquid phase line of the material according to the endothermic and exothermic curves includes:

[0090] Intercept the exothermic peak curve contained in the cooling process of the endothermic and exothermic curves;

[0091] Integrate the exothermic peak curve to obtain the solid phase ratio curve of the sample;

[0092] According to the solid phase ratio curve, the actual measured value of the solid-liquid phase line is determined.

[0093] The solid-liquid phase line is determined by integrating the exothermic peak curve. Compared with the traditional method of measuring the solid-liquid phase line (for example, reading the solid-liquid phase line by drawing a tangent at the peak), 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 solid-liquid phase line.

[0094] Specifically, since it is necessary to focus on the solidification process of casting steel, the partial curve of the exothermic peak contained in the cooling process of the sample's endothermic and exothermic 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 sample changing with temperature can be obtained. The solid phase line and liquid phase line of the casting steel can be directly read in the solid phase rate curve, that is, the solid-liquid phase line measured value is obtained.

[0095] The method of the present invention can use ProCAST software to more accurately determine the thermophysical property parameters, improve the accuracy of the thermophysical property parameter calculation results, and provide a reliable basis for the casting simulation of casting steel.

[0096] An embodiment of the present invention further provides an application of a method for determining thermophysical property parameters in a casting process optimization method for a heat-resistant steel cylinder body, which comprises the following steps:

[0097] Using the determination method in the above embodiment, the thermophysical property parameters of the cylinder material are determined according to the chemical composition of the heat-resistant steel cylinder material;

[0098] According to the thermophysical parameters, the casting process of the cylinder body is simulated; according to the simulation results, it is determined whether the pipes of the cylinder body need to be compensated.

[0099] In the embodiment of the present invention, reasonable and reliable thermophysical property parameters can be obtained by combining the above-mentioned simulation calculation with experimental measurement, and the method is applied to the casting simulation of the heat-resistant steel cylinder body, thereby improving the accuracy of the simulation results.

[0100] Specifically, when performing casting simulation on a heat-resistant steel cylinder body, the following steps are included:

[0101] (1) Establish a three-dimensional casting model of a heat-resistant steel cylinder body, on which a pipeline is arranged;

[0102] (2) meshing and parameter setting of the casting three-dimensional model, wherein the set parameters include the thermophysical property parameters of the cylinder material determined by the determination method in the above embodiment;

[0103] (3) The mesh model is used to simulate the flow field and temperature field of the casting process to obtain the prediction results of shrinkage and porosity of the pipe wall;

[0104] (4) Based on the prediction results, determine whether the cylinder pipes need to be subsidized.

[0105] The embodiment of the present invention applies the thermophysical property parameters determined by the above method to the casting simulation of the heat-resistant steel cylinder body, thereby improving the reliability of the prediction results of shrinkage and porosity of the cylinder body and providing a reliable basis for the casting process design of the cylinder body.

[0106] It should be noted that when the present invention adopts the method of the above embodiment to determine the thermophysical properties of the cylinder material, the measured solid phase ratio curve is used to determine whether the solid-liquid phase line calculation value obtained by the thermodynamic calculation model is accurate; and in the casting simulation process of the cylinder, a complete set of thermophysical property parameters calculated by the thermodynamic calculation model is used instead of the measured solid phase ratio curve to ensure the mutual matching between the various parameters.

[0107] In addition, the embodiment of the present invention 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, not only the design cost can be saved, but also the production cost can be saved and the production time can be shortened. At the same time, the environmental pollution generated by the subsidy removal process and the impact on workers' health can be reduced.

[0108] 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.

[0109] In some embodiments of the present invention, in step (1), 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 of a symmetric structure, a subsidy is provided on one side of the pipeline, and no subsidy is provided on the other side of the pipeline.

[0110] 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.

[0111] In step (1), 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.

[0112] In step (2), the casting process is simulated using ProCAST software. Specifically, the established casting three-dimensional model is imported into the ProCAST software and meshed. When meshing, it can be divided according to tetrahedral meshes to obtain a tetrahedral mesh model. When setting parameters for the mesh model, in addition to the thermophysical parameters of the cylinder material, the set parameters also include the thermophysical parameters of the materials of other components such as the sand box and the chiller, the initial temperature, the interface heat transfer coefficient between the cylinder casting and other components, the calculation operation parameters and the storage parameters.

[0113] 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.

[0114] The interface heat transfer coefficient between the casting and the sand box can use the data in the software database. The interface heat transfer coefficient between other components can be set as a constant based on conventional experience. For example, the interface heat transfer coefficient between the chiller and the casting is set to 2000W / m 2 / K, the interface heat transfer coefficient between the chiller and the flask is set to 500W / m 2 / K.

[0115] 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.

[0116] 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.

[0117] In some embodiments, when the prediction results in step (3) 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.

[0118] If no subsidy is set on the pipeline in the casting three-dimensional model, when it is determined in step (4) that the pipeline needs to be compensated, the casting three-dimensional model of the cylinder body is adjusted, the subsidy is set on the pipeline, and steps (1) to (3) are repeated.

[0119] In some embodiments, after setting the subsidy, if the prediction result shows that there are no shrinkage cavities or shrinkage in the subsidized area of ​​the pipeline, the subsidy setting is determined to be reasonable; if the prediction result shows that there are shrinkage cavities or shrinkage in the subsidized area of ​​the pipeline, the subsidy setting is determined to be unreasonable, and the subsidy in the three-dimensional model is optimized, and steps (1) to (3) are repeated until there are no shrinkage cavities or shrinkage in the subsidized area of ​​the pipeline.

[0120] Specifically, when the pipeline of the cylinder body is an asymmetric structure, no subsidy is set on the pipeline in step (1). If the prediction result in step (3) shows that there is no shrinkage cavity or shrinkage in the pipeline wall, it is determined that the pipeline does not need to be subsidized; if the prediction result in step (3) shows that there is shrinkage cavity or shrinkage in the pipeline wall, it is determined that the pipeline needs to be subsidized, and additional subsidies are set on the pipeline, and steps (1) to (3) are repeated. Then, according to the prediction results, when the pipeline is subsidized, whether there is shrinkage cavity or shrinkage in the subsidized area is analyzed. If there is no shrinkage cavity or shrinkage, it is determined that the current subsidy setting is reasonable and a reasonable casting process is obtained; if there is shrinkage cavity or shrinkage, it is necessary to optimize the subsidy, and steps (1) to (3) are repeated until there is no shrinkage cavity or shrinkage in the subsidized area.

[0121] When the pipeline of the cylinder body is a symmetrical structure, in step (1), one side of the pipeline is provided with a subsidy, and the other symmetrical side is not provided with a subsidy. If the prediction result in step (1) shows that there are no shrinkage cavities or shrinkage porosity 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 provided with a subsidy; if there are shrinkage cavities or shrinkage porosity in the non-subsidized area of ​​the pipeline, and there are no shrinkage cavities or shrinkage porosity 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 or shrinkage porosity on both symmetrical sides of the pipeline, it is determined that the current subsidy setting is unreasonable and the subsidy needs to be optimized, and steps (1) to (3) are repeated until there are no shrinkage cavities or shrinkage porosity in the subsidized area, thereby continuously optimizing the casting process, and finally obtaining a suitable subsidy for casting, thereby improving the quality of the cylinder body.

[0122] In some embodiments, when optimizing subsidies in a three-dimensional model, the size of the subsidies may be adjusted.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] The embodiment of the present invention also provides an application of a method for determining thermophysical property parameters in a large ingot casting process optimization method, which comprises the following steps:

[0127] Using the determination method in the above embodiment, the thermophysical property parameters of the steel ingot material are determined according to the chemical composition of the steel ingot material;

[0128] According to the thermophysical property parameters, the casting process of the steel ingot is simulated; according to the simulation results, the casting process of the steel ingot is optimized to reduce the surface stress of the steel ingot.

[0129] In the embodiment of the present invention, reasonable and reliable thermophysical property parameters can be obtained by combining the above-mentioned simulation calculation with experimental measurement, which is applied to the casting simulation of large ingots to improve the accuracy of the simulation results.

[0130] It should be noted that when the present invention adopts the method of the above embodiment to determine the thermophysical properties of the steel ingot material, the measured solid phase ratio curve is used to judge whether the solid-liquid phase line calculation value obtained by the thermodynamic calculation model is accurate; and in the casting simulation process of the steel ingot, a complete set of thermophysical property parameters calculated by the thermodynamic calculation model is used instead of the measured solid phase ratio curve to ensure the mutual matching between the various parameters.

[0131] Specifically, when performing casting simulation on a large steel ingot, the following steps are included:

[0132] (1) Establish a three-dimensional casting model of large steel ingots;

[0133] (2) meshing and parameter setting of the casting three-dimensional model, wherein the set parameters include the thermophysical property parameters of the steel ingot material determined by the determination method in the above embodiment;

[0134] (3) simulating the temperature field and stress field of the casting process on the grid model to obtain the surface stress at the end of the solidification of the ingot;

[0135] (4) Optimizing the structure of the casting three-dimensional model of the steel ingot, and repeating steps (2) to (3) to reduce the surface stress of the steel ingot until the optimization stop condition is reached.

[0136] The embodiment of the present invention applies the thermophysical property parameters determined by the above method to the casting simulation of large steel ingots, improves the accuracy of the calculation results of the surface stress of large steel ingots, and provides a reliable basis for the optimization of the casting process of large steel ingots.

[0137] In some embodiments, step (1) and step (2) are the same as step S16 and step S17 in the above-mentioned process of determining the thermophysical property parameters, and are not repeated here.

[0138] In step (4), optimizing the casting three-dimensional model structure of the steel ingot includes: optimizing the rib shape of the steel ingot, and / or optimizing the thickness of the steel ingot mold. The present invention can reduce the surface stress of the steel ingot rib at the end of solidification by optimizing and adjusting the rib shape of the steel ingot or the thickness of the steel ingot mold, thereby reducing the longitudinal cracking of the surface of the steel ingot rib.

[0139] In addition, optimizing the ingot mold thickness on the basis of optimizing the ingot edge shape can significantly reduce the stress on the surface of the ingot edge, thereby greatly alleviating the longitudinal cracking of the ingot edge.

[0140] In some embodiments, when optimizing the edge shape of the steel ingot, the size of the edge of the steel ingot may be optimized, for example, by increasing the diameter of the fillet of the edge of the steel ingot.

[0141] In some embodiments, when optimizing the prism shape of the steel ingot in step (4), the optimization termination conditions include: the maximum principal stress value on the surface of the prism of the steel ingot after optimization is reduced by less than or equal to 5%, that is, the ratio of the difference between the maximum principal stress value after optimization and before the optimization to the maximum principal stress value before the optimization is less than or equal to 5%. As the diameter of the fillet of the prism increases, the heat dissipation surface area of ​​the steel ingot decreases, which is not conducive to heat dissipation. In addition, if the fillet diameter of the prism is infinitely increased, the surface of the steel ingot approaches the circumferential surface. From the actual production experience, the cracking tendency of the cylindrical billet is more serious. This embodiment limits the reduction of the maximum principal stress value to avoid the reduction of the heat dissipation effect and the increase of the cracking tendency due to the excessive diameter of the fillet of the prism.

[0142] In some embodiments, when optimizing the thickness of the steel ingot mold, the thickness of the steel ingot mold is gradually increased to continuously reduce the surface stress of the steel ingot edge.

[0143] In some embodiments, when optimizing the thickness of the ingot mold, the optimization termination condition also includes: compared with the original thickness, the increased thickness of the ingot mold is greater than or equal to 100 mm. After the molten steel is poured into the ingot mold, the surface of the ingot solidifies rapidly to form a shell. As the shell shrinks, an air gap is formed between the ingot and the ingot mold wall. At this time, the cooling effect of the ingot mold is reduced, and the cooling effect brought by increasing the thickness of the ingot mold will not be obvious; at the same time, increasing the thickness will also increase the production cost of the ingot mold. Therefore, this embodiment avoids the cooling effect of the ingot mold on the ingot and the excessively high production cost by limiting the increased size of the ingot mold.

[0144] The present invention simulates and calculates the temperature field and stress field of the large steel ingot casting process to obtain the stress distribution during the solidification process of the large steel ingot, so that the casting process of the steel ingot can be continuously optimized according to the surface stress of the steel ingot to reduce the surface stress of the steel ingot and alleviate the longitudinal cracks on the surface of the edge of the steel ingot, which can not only save production costs and shorten the cleaning time, but also reduce the environmental pollution caused by the crack cleaning process and the impact on the health of workers.

[0145] The following is a specific example to further illustrate the method for determining the thermal physical property parameters and its application method of the present invention.

[0146] Example 1

[0147] Determine the thermophysical parameters of a heat-resistant steel cylinder material.

[0148] Step S11, using three thermodynamic calculation models (Scheil, Lever, BackDiffusion models) in ProCAST software to calculate the thermophysical parameters of the cylinder material. When the BackDiffusion model is used for calculation, the average cooling rate is specified to be 0.01K / s.

[0149] Specifically, in the material parameter calculation module, select the iron-based alloy and input the chemical composition of the cylinder material. 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 cylinder material takes the middle value of the content range of each component; for elements such as P and S that only have the upper limit of the content range set, take the upper limit of the element content range.

[0150] Table 1 Chemical composition of heat-resistant steel materials

[0151]

[0152] The three sets of solid-liquid phase line calculated by Scheil, Lever and Back Diffusion models are 1131-1493℃, 1355-1493℃ and 1298-1493℃ respectively.

[0153] Step S12, measuring the sample of the cylinder material to obtain the actual measured value of the solid-liquid phase line:

[0154] The sample was heated to 1250℃ and kept warm for 20h before being water-cooled to homogenize the sample; the sample was then processed into small samples of φ2*2mm and the surface was polished to avoid contamination.

[0155] The samples were subjected to differential thermal analysis test as follows: Figure 3 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.

[0156] Among them, according to experience, the solidus of steel is generally around 1400°C, of ​​which 1131-1493°C is obviously unreasonable. Therefore, the first key temperature and the second key temperature can be determined according to any of the other two groups. In this embodiment, the solidus calculated value of 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.

[0157] The endothermic and exothermic curves obtained in the final test are as follows: Figure 4 As shown. Figure 4 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 5 The exothermic peak curve shown; Figure 5 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 6 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℃.

[0158] Step S13, judging whether the calculated value of the solid-liquid phase line meets the preset requirements:

[0159] First, select a suitable thermodynamic calculation model. Comparing the three groups of solid-liquid phase line calculation 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℃, so it is more appropriate to choose the Lever model to calculate the thermophysical parameters.

[0160] Secondly, determine whether the solid-liquid phase line calculated by the Lever model meets the preset requirements. Comparing the solid-liquid phase line calculated value of 1355-1493℃ with the solid-liquid phase line measured value of 1433-1502℃, the solid phase lines of the two are quite different and do not meet the preset requirements.

[0161] Step S15, removing the elements P and S with a content of less than 1wt.% in the chemical composition, recalculating the thermophysical property parameters, and obtaining a new solid-liquid phase line calculated value of 1420-1494° C. The difference between the solid-liquid phase line calculated value and the measured value is less than 20° C.

[0162] Therefore, it is believed that all the thermophysical parameters recalculated using the Lever model are more reasonable and reliable.

[0163] Example 2

[0164] The thermophysical property parameters determined in Example 1 were used to perform casting simulation on the upper half test piece of the heat-resistant steel cylinder block.

[0165] (1) Establish a three-dimensional model of the casting process of the upper half of the cylinder test piece:

[0166] Establish a casting 3D model of the test piece, such as Figure 7 As shown, the casting three-dimensional model is a symmetrical structure, which includes 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.

[0167] (2) Meshing and parameter setting of the casting 3D model:

[0168] The casting three-dimensional model was imported into ProCAST software for meshing to obtain a tetrahedral mesh model.

[0169] The parameters of the grid model are set, including: (a) the thermal properties of the cylinder, flask, chiller and other materials. The thermal properties of the cylinder are the thermal properties of the materials obtained in Example 1, and the thermal properties of the other components are the thermal properties of the materials in the software database. The flask is chromite sand, and the chiller is low carbon steel; (b) initial temperature: the initial temperature of the casting is 1494°C + 60°C ≈ 1555°C, and the initial temperature of the flask and chiller is 50°C; (c) interface heat transfer coefficient: the interface heat transfer coefficient between the casting and the flask is as follows: Figure 8 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.

[0170] (3) The flow field and temperature field of the grid model are simulated and calculated to obtain the prediction results of shrinkage and porosity of the airway wall, such as Fig. 9 shown.

[0171] (4) Based on Fig. 9 The shrinkage porosity prediction results shown in the figure show that there are no shrinkage porosity on both sides of the airway wall, which means that no subsidy is required at the airway position of the cylinder body.

[0172] 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.

[0173] 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.

[0174] Example 3

[0175] Determine the thermophysical parameters of large steel ingots of 83t-45Cr5NiMoV.

[0176] Step S11, using three thermodynamic calculation models (Scheil, Lever, BackDiffusion models) in ProCAST software to calculate the thermophysical parameters of the ingot material; wherein, when the Back Diffusion model is used for calculation, the average cooling rate is specified to be 0.01 K / s.

[0177] Specifically, in the material parameter calculation module, select the iron-based alloy and input the chemical composition of the steel ingot material 45Cr5NiMoV. The chemical composition range of 45Cr5NiMoV is shown in Table 2, and the remaining components are iron and unavoidable impurities. In the calculation module, the chemical composition of the steel ingot material takes the middle value of the content range of each component; for elements such as P and S that only have the upper limit of the content range set, take the upper limit of the element content range.

[0178] Table 2 Chemical composition of 45Cr5NiMoV material

[0179]

[0180] The three sets of solid-liquid phase line calculated by Scheil, Lever and Back Diffusion models are 1169-1468℃, 1391-1467℃ and 1384-1468℃ respectively.

[0181] Step S12, measuring the sample of the steel ingot to obtain the solid-liquid phase line measured value:

[0182] The sample was heated to 1250℃ and kept warm for 20h before being water-cooled to homogenize the sample; the sample was then processed into small samples of φ2*2mm and the surface was polished to avoid contamination.

[0183] According to Figure 3 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.

[0184] Among them, according to experience, the solidus of steel is generally around 1400℃, of which 1169-1468℃ is obviously unreasonable, so the solidus and liquidus calculated value 1391-1467℃ calculated by the Lever model is selected to determine the first key temperature and the second key temperature, of which the first key temperature is 1467℃+83℃=1550℃, and the second key temperature is 1391℃-91℃=1300℃. The actual average cooling rate of large ingots in this temperature range is about 1℃ / min.

[0185] The endothermic and exothermic curves obtained in the final test are as follows: Fig.11 shown.

[0186] Will Fig.11 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: Fig.12 The exothermic peak curve shown; Fig.12 The exothermic peak curve shown is integrated to obtain the solid phase ratio curve of the steel ingot changing with temperature, as shown in Fig.13 As shown; from the solid phase ratio curve, it can be directly read that the liquidus measured value is 1472℃, and the solidus measured value is 1378℃.

[0187] Step S13, judging whether the three sets of solid-liquid phase line calculation values ​​meet the preset requirements:

[0188] Compare the three sets of calculated solid-liquid phase line values ​​with the measured solid-liquid phase line values, and determine whether the difference between the three sets of calculated solid-liquid phase line values ​​and the measured solid-liquid phase line values ​​is less than 20°C.

[0189] Step S14, selecting 1391-1467°C and 1384-1468°C, both of which have a difference less than 20°C, as backup data.

[0190] Step S16, establishing a three-dimensional casting model of a large steel ingot, wherein the three-dimensional casting model includes: an insulation cap, a steel ingot mold, a chassis, a steel ingot, refractory bricks, a covering agent, and the like.

[0191] Step S17, calculating the complete solidification time of the steel ingot:

[0192] The above casting three-dimensional model was imported into ProCAST software for meshing to obtain a tetrahedral mesh model.

[0193] The parameters of the above grid model are set, including: (a) the thermal property parameters of each component material, wherein the thermal property parameters of the steel ingot material are the thermal property parameter backup data obtained in step S14; (b) initial temperature: the initial temperature of the steel ingot is 1540°C, and the initial temperature of the steel ingot mold is 50°C; (c) the interface heat transfer coefficient between each component: the interface heat transfer coefficient between the steel ingot and the steel ingot mold is as follows: Fig.14 As shown; the interface heat transfer coefficient between refractory bricks, covering agents and other components is set to 200W / m 2 / K; (d) Calculation operation parameters and storage parameters: calculation stop time is 1380℃, time step is 20s; storage frequency is 180.

[0194] The temperature field of the grid model is simulated and calculated. The thermophysical property parameters of the steel ingot use the two sets of backup data obtained in step S14, and the obtained complete solidification times are 23.58 h and 22.95 h respectively.

[0195] Step S18, screening thermophysical property parameters:

[0196] The two groups of complete solidification times obtained in step S17 are compared with the demolding time of 22h during the actual production of steel ingots, and the thermophysical parameters corresponding to the complete solidification time of 22.95h (the corresponding solidus calculated value is 1384°C, and the liquidus calculated value is 1468°C) are selected as the most reasonable thermophysical parameters.

[0197] Example 4

[0198] The thermophysical property parameters determined in Example 3 were used to perform casting simulation on the large steel ingot to optimize the casting process of the large steel ingot.

[0199] (1) Establishing a three-dimensional casting model of a large steel ingot; the structure of the three-dimensional casting model is the same as that in Example 3 and will not be repeated here.

[0200] (2) Meshing and parameter setting are performed on the casting three-dimensional model, and the set parameters include the thermophysical property parameters of the large steel ingot determined in Example 3; the meshing and the setting of the remaining parameters are the same as those in Example 3 and are not repeated here.

[0201] (3) The temperature and stress fields of the casting process are simulated and calculated on the grid model to analyze the maximum principal stress on the edge surface of the ingot at the end of solidification.

[0202] (4) Optimize the casting structure of steel ingots:

[0203] Firstly, based on the original casting 3D model, the edge shape of the ingot was optimized, and the stress field simulation calculation was performed again to analyze the maximum principal stress on the edge surface of the ingot at the end of solidification.

[0204] Fig.15 (a) shows a partial schematic diagram of the three-dimensional model of the original steel ingot prism. Fig.15 (b) and (c) respectively show the structural schematic diagrams of the casting three-dimensional model after the first and second edge shape optimizations based on the original three-dimensional model, wherein the diameter of the edge fillet of the original steel ingot is 48 mm, and after the first edge shape optimization, the diameter of the edge fillet increases to 1.4 times of the original edge shape, and after the second edge shape optimization, the diameter of the edge fillet increases to 2.4 times of the original edge shape.

[0205] The corresponding stress field simulation results are as follows: Fig.16 As shown in (a), (b), and (c). Analyze the maximum principal stress on the edge of the ingot at the end of solidification, as shown in Fig.16 As shown, compared with the basic scheme of the original three-dimensional model, the stress value of the second prism optimization is significantly reduced, and compared with the maximum stress value after the first prism optimization, the reduction is about 5%, reaching the optimization stop condition.

[0206] Secondly, based on the second prism optimization, the thickness of the ingot mold is optimized and the stress field simulation calculation is performed again. Fig.17 (a), (b), and (c) respectively show the structural schematic diagrams of the casting three-dimensional model of the original ingot mold, the first increase in the thickness of the ingot mold, and the second increase in the thickness of the ingot mold, wherein the thickness of the original ingot mold is 350 mm, the increase in the thickness of the ingot mold for the first time is 50 mm compared to the original thickness, and the increase in the thickness of the ingot mold for the second time is 100 mm compared to the original thickness, reaching the maximum increase and meeting the optimization stop condition.

[0207] The corresponding stress field simulation results are as follows: Fig.18 As shown in (a), (b), and (c). Analyze the maximum principal stress on the edge of the ingot at the end of solidification, as shown in Fig.18 As shown in the figure, compared with the basic scheme of the original ingot mold thickness, the maximum stress value on the surface of the ingot edge is significantly reduced after the second increase in the ingot mold thickness. Therefore, the scheme of the second edge shape optimization superimposed on the second increase in the ingot mold thickness is selected as the best casting process optimization scheme for 83t-45Cr5NiMoV ingot.

[0208] 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 method for determining thermophysical property parameters of steel for casting, characterized in that: include: Step S11, using a plurality of thermodynamic calculation models in the ProCAST software respectively, according to the chemical composition of the casting steel, calculating the thermophysical property parameters of the casting steel, and obtaining a plurality of groups of thermophysical property parameters, each group of the thermophysical property parameters including a solid-liquid phase line calculation value; Step S12, measuring the sample of the casting steel to obtain the solidus-liquidus phase measured value of the casting steel; Step S13, comparing and analyzing a plurality of groups of solid-liquid phase line calculated values ​​obtained by using a plurality of thermodynamic calculation models and the solid-liquid phase line measured values, and determining whether the solid-liquid phase line calculated values ​​meet preset requirements; Step S14, when the solid-liquid phase line calculated value meets the preset requirements, all the thermophysical property parameters corresponding to the solid-liquid phase line calculated value are selected as the thermophysical property parameters of the casting steel; Step S15, when the calculated value of the solid-liquid phase line does not meet the preset requirements, remove at least one element in the chemical composition whose content is less than a predetermined threshold, and recalculate the thermophysical property parameters until the calculated value of the solid-liquid phase line meets the preset requirements.

2. The method according to claim 1, characterized in that In the step S13, a thermodynamic calculation model corresponding to a solid-liquid phase line calculated value closest to the solid-liquid phase line measured value is selected; and it is determined whether the closest solid-liquid phase line calculated value meets the preset requirements; In the step S14, when the solid-liquid phase line calculated value meets the preset requirements, all the thermophysical property parameters corresponding to the solid-liquid phase line calculated value are determined as the thermophysical property parameters of the casting steel; In step S15, when the calculated value of the solid-liquid phase line does not meet the preset requirements, at least one element whose content in the chemical composition is less than a predetermined threshold is removed, and the thermophysical property parameters are recalculated using the thermodynamic calculation model selected in step S13 until the calculated value of the solid-liquid phase line meets the preset requirements.

3. The method according to claim 1, characterized in that When the casting steel is a large ingot, in step S13, it is determined whether the plurality of sets of solid-liquid phase line calculation values ​​meet the preset requirements; In the step S14, when the solid-liquid phase line calculated value meets the preset requirements, all the thermophysical property parameters corresponding to the solid-liquid phase line calculated value are selected as backup parameters; Step S15, when the plurality of groups of solid-liquid phase line calculated values ​​do not meet the preset requirements, at least one element whose content in the chemical composition is less than a predetermined threshold is removed, and the thermophysical property parameters are recalculated until the solid-liquid phase line calculated values ​​meet the preset requirements.

4. The method according to claim 3, characterized in that: If the backup parameters include multiple groups of thermophysical property parameters, the determination method further includes: Establishing a three-dimensional casting model of the steel ingot; According to the multiple groups of thermophysical property parameters, a simulation calculation of the temperature field of the casting process is performed on the casting three-dimensional model to obtain multiple corresponding complete solidification times of the steel ingots; According to each of the complete solidification times, a group of the thermophysical property parameters are screened.

5. The method according to claim 4, characterized in that When screening the thermophysical property parameters, the complete solidification times and the actual demoulding time of the steel ingot are compared to screen out a group of the thermophysical property parameters that are closest to the actual demoulding time.

6. The method according to any one of claims 1 to 5, wherein in step S12, measuring the sample of the casting steel to obtain the solidus-liquidus measured value of the casting steel comprises: preparing a sample of the casting steel; Performing a differential thermal analysis test on the sample to obtain an endothermic and exothermic curve of the sample; According to the endothermic and exothermic curves, the actual measured value of the solidus-liquidus phase line of the casting steel is determined.

7. The method according to claim 6, characterized in that Determining the measured value of the solidus-liquidus phase line of the casting steel according to the endothermic and exothermic curves comprises: intercepting the exothermic peak curve included in the cooling process of the endothermic and exothermic curves; Integrating the exothermic peak curve to obtain a solid phase ratio curve of the sample; According to the solid phase ratio curve, the solid-liquid phase line measured value is determined.

8. The method according to claim 6, characterized in that When performing a differential thermal analysis test on the sample, the sample is heated to a first critical temperature, then cooled to a second critical temperature at a first cooling rate, and then cooled to room temperature at a second cooling rate; Wherein, the first cooling rate is determined according to the actual cooling rate of the casting steel; The second cooling rate is greater than the first cooling rate.

9. Application of a method for determining thermophysical property parameters in a casting process optimization method for a heat-resistant steel cylinder body, characterized in that: include: Using the determination method according to any one of claims 1 to 8, the thermophysical property parameters of the cylinder material are determined according to the chemical composition of the heat-resistant steel cylinder material; According to the thermophysical property parameters, a casting process simulation is performed on the cylinder body; According to the simulation results, it is determined whether the pipeline of the cylinder body needs to be compensated.

10. Application of a method for determining thermophysical property parameters in a method for optimizing the casting process of a large steel ingot, characterized in that: include: Determine the thermophysical property parameters of the steel ingot material according to the determination method according to any one of claims 1 to 8 according to the chemical composition of the steel ingot material; According to the thermophysical property parameters, a casting process simulation is performed on the steel ingot; According to the simulation results, the casting process of the steel ingot is optimized to reduce the surface stress of the steel ingot.

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