Method for regulating and controlling temperature field and structure evolution of casting blank

Abstract

The invention relates to the technical field of metal material hot working technologies, in particular to a casting blank temperature field and structure evolution regulation and control method which comprises the steps that firstly, a three-dimensional finite element model is established based on the casting blank size and material parameters, temperature field simulation is conducted by setting different surface comprehensive heat exchange coefficients, and section temperature difference and heat transfer efficiency data are obtained; determining an optimized heat exchange condition; secondly, selecting a key temperature point based on temperature field characteristics disclosed by simulation to carry out a heat treatment experiment, establishing a quantitative relation among the heating temperature, the heat preservation time and the grain size, and determining a critical temperature and a critical heat preservation time for remarkable coarsening of the grains; and finally, in the actual heating process, the surface heat exchange boundary is controlled according to the optimized heat exchange conditions, and a heating curve and heat preservation time are set according to the quantitative relation and the critical parameters, so that the casting blank with the uniform section temperature and controlled grain coarsening is obtained. According to the method, precise cooperative regulation and control in the large casting blank heating process are achieved.

Description

Technical Field

[0001] This invention relates to the field of hot working technology for metallic materials, and in particular to a method for controlling the temperature field and microstructure evolution of a cast billet. Background Technology

[0002] GH4169 nickel-based superalloy is widely used in critical load-bearing components such as turbine disks in aero-engines due to its excellent high-temperature strength, creep resistance, and corrosion resistance. These components are typically manufactured from large cast slabs through hot working processes such as forging. During the pre-forging heating process, due to the low thermal conductivity of GH4169 alloy and the large size of the cast slab, heat transfer from the surface to the core is slow and uneven, resulting in a significant temperature gradient across the slab cross-section. This uneven temperature field not only affects heating efficiency but also leads to inconsistencies in subsequent microstructure evolution: the surface region, due to higher temperatures and relatively longer holding times, is prone to excessive grain coarsening, while the core region may experience insufficient recrystallization or inadequate microstructure refinement due to lower temperatures during subsequent forging. This microstructure inhomogeneity caused by the uneven temperature field directly impairs the uniformity of the mechanical properties, fatigue life, and reliability of the final forging.

[0003] Current research on the heating process of GH4169 large billets mainly focuses on single temperature field simulations or isolated microstructure and property experiments, lacking an integrated method that systematically links the two and uses them to directly guide process control. In particular, how to accurately and efficiently coordinate and control the heat transfer boundary conditions and heating regime during the heating process, so as to obtain large billets with uniform cross-sectional temperature and controlled grain refinement while ensuring production efficiency, has become a core technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] To overcome the above deficiencies, this invention provides a method for controlling the temperature field and microstructure evolution of a billet, aiming to improve the problem in the prior art where large high-temperature alloy billets suffer from large cross-sectional temperature gradients due to uneven heat transfer during pre-forging heating, resulting in uneven grain microstructure evolution and excessive grain coarsening, which affects the consistency of forging performance.

[0005] This invention provides the following technical solution: a method for controlling the temperature field and microstructure evolution of a cast billet, the method comprising the following steps: Based on the actual size and material thermophysical parameters of the large billet to be processed, a three-dimensional finite element model is established to analyze the heat transfer process from its surface to the core, and the initial temperature field is set to be uniform. In the three-dimensional finite element model, the combined radiation and convection heat transfer process on the outer surface of the billet is characterized as the surface comprehensive heat transfer coefficient, which is used as the core control parameter. The surface comprehensive heat transfer coefficient is set to multiple different fixed values ​​and / or function values ​​that vary with heating temperature to simulate the evolution of the temperature field inside the billet during the heating process and obtain simulation data of the temperature difference and heat transfer efficiency of the billet cross section under different settings. Based on the simulation data, the setting method and numerical range of the surface comprehensive heat transfer coefficient that minimizes the cross-sectional temperature difference and enables the billet to reach the target temperature within the process cycle are selected as the optimized heat transfer conditions. Based on the temperature field characteristics revealed by the simulation, key temperature points were selected, and samples were prepared using the billet material for heat treatment experiments. The experiments included heating at the key temperature points for different holding times, followed by detection of the grain size and microstructure of the samples. Based on the experimental results, a quantitative correspondence between heating temperature, holding time and grain size was established, and the critical temperature and critical holding time for significant grain coarsening were determined. In the actual heating process, the surface heat transfer boundary of the billet is set according to the optimized heat transfer conditions, and the heating temperature curve and holding time are set according to the temperature-time-structure control relationship, critical temperature and critical holding time, so as to obtain a billet with uniform cross-sectional temperature and controlled grain coarsening.

[0006] Preferably, the process for establishing a three-dimensional finite element model for analyzing the surface-to-core heat transfer process includes: Measure the diameter and length of the large casting billet to be processed, and determine the geometric dimensions of the three-dimensional finite element model based on the diameter and length; The density, specific heat capacity, and thermal conductivity parameters of the material used in the large casting billet are determined or referenced, and the density, specific heat capacity, and thermal conductivity parameters are input as material properties into the three-dimensional finite element model; Based on the geometric dimensions, a three-dimensional geometric entity with the shape of the large casting billet is constructed in the finite element preprocessing software, and the three-dimensional geometric entity is divided into tetrahedral meshes to complete the establishment of the three-dimensional finite element model. In the three-dimensional finite element model, the initial temperature of all nodes is set to a uniform room temperature to complete the setting of the initial temperature field uniformity.

[0007] Preferably, the process for obtaining simulation data on the temperature difference and heat transfer efficiency of the billet cross section under different settings includes: In the three-dimensional finite element model, all outer surfaces of the billet are set as heat exchange boundaries, and a unified surface comprehensive heat transfer coefficient parameter is defined for the heat exchange boundaries. To perform the simulation, the surface comprehensive heat transfer coefficient parameter is set to a first type of value and a second type of value, respectively. The first type of value consists of multiple independent fixed constants, while the second type of value is a continuous function based on the change of heating furnace gas temperature or billet surface temperature. Based on the preset heating process curve, transient thermal analysis simulation of the heating process is performed on the three-dimensional finite element model with the first type of value and / or the second type of value, respectively, and the temperature field data of the billet inside the casting as a function of time in each group of simulations are calculated. From the temperature field data simulated in each group, the temperature values ​​of the surface and core of the billet at the same process time are extracted, and the difference is calculated as the cross-sectional temperature difference data. At the same time, based on the temperature field data, the time required for the overall average temperature of the billet to reach the preset stage target value is calculated, and its reciprocal or related measure is used as the heat transfer efficiency data.

[0008] Preferably, the process of performing transient thermal analysis simulations of the heating process to calculate the temperature field data of the billet interior evolving over time in each simulation includes: The preset heating process curve is input into the three-dimensional finite element model. The heating process curve defines multiple heating and holding stages of the furnace gas temperature change over time. For the three-dimensional finite element model, the fixed surface comprehensive heat transfer coefficient boundary condition defined by the first type of numerical method and / or the temperature-varying surface comprehensive heat transfer coefficient boundary condition defined by the second type of numerical method are applied respectively. In the solver of the three-dimensional finite element model, the transient heat conduction equation, time step and convergence criterion are set, and multiple independent heating process simulation calculation tasks are submitted based on the heating process curve, the fixed surface comprehensive heat transfer coefficient boundary condition or the surface comprehensive heat transfer coefficient boundary condition that varies with temperature. After multiple sets of simulation calculation tasks are completed, the temperature values ​​of all internal nodes or selected characteristic location nodes of the billet at different process times are extracted from the solution results as the temperature field data that evolves over time.

[0009] Preferably, the process for obtaining the optimized heat exchange conditions includes: For the data sets in the simulation data corresponding to different surface comprehensive heat transfer coefficient setting methods and specific values, the cross-sectional temperature difference data at each key process moment is extracted and compared. For each set of data in the simulation data corresponding to different surface comprehensive heat transfer coefficient setting methods and specific values, the time required for the overall average temperature of the billet to reach the target temperature is calculated, and it is evaluated whether the time is shorter than or equal to the process cycle. Based on the analysis and evaluation results, parameters that simultaneously meet the conditions for temperature difference optimization and efficiency qualification were selected from different methods and specific values ​​for setting the comprehensive heat transfer coefficient of the surface. The range covered by the selected surface heat transfer coefficient setting method and specific values ​​is recorded and defined as the optimized heat transfer conditions.

[0010] Preferably, the temperature difference optimization condition refers to the cross-sectional temperature difference data being the relative minimum value among all compared process moments; The efficiency qualification condition means that the time required for the overall average temperature of the billet to reach the target temperature is shorter than or equal to the process cycle.

[0011] Preferably, the process of selecting key temperature points based on the temperature field characteristics revealed by the simulation and preparing samples from the cast billet material for heat treatment experiments includes: Analyze the simulation results of the three-dimensional finite element model to identify the stages and corresponding temperature ranges where the temperature difference between the core and surface of the billet is significant during the heating process. Based on the significant temperature difference stage and temperature range, a specific temperature value within the temperature range is selected as the key temperature point, and the key temperature point includes at least the critical temperature at which the billet material undergoes a significant microstructure transformation. Cylindrical or cubic standard specimens for heat treatment experiments are prepared from materials of the same batch or composition as the large cast billet. The standard sample is placed in a heating furnace and heated to each of the key temperature points. At each key temperature point, it is held for at least two different holding times. Then, it is cooled according to a preset cooling regime to complete the heat treatment experiment. The standard sample that has undergone heat treatment is cut, ground, polished and etched to prepare a metallographic sample. The grain size and microstructure of the metallographic sample are observed using an optical microscope or a scanning electron microscope.

[0012] Preferably, the process for determining the critical temperature and critical holding time for significant grain coarsening includes: The grain size measurements and microstructure observations of metallographic samples at different key temperature points and different holding times in the heat treatment experiments are summarized. Using heating temperature and holding time as independent variables and the measured grain size as the dependent variable, a quantitative mathematical relationship or data correspondence table reflecting the change of grain size with heating temperature and holding time is established through data fitting or interpolation methods. Based on the temperature-time-size quantification relationship and the microstructure observation results, the regions where the grain size changes abruptly with increasing heating temperature or prolonged holding time are analyzed. The initial heating temperature at which the grain size undergoes a sudden change is defined as the critical temperature at which the grains significantly coarsen, and the holding time at which the grain size undergoes a sudden change at this critical temperature is defined as the critical holding time.

[0013] Preferably, the process for obtaining a cast billet with uniform cross-sectional temperature and controlled grain coarsening includes: Based on the setting method and numerical range of the surface comprehensive heat transfer coefficient limited by the optimized heat transfer conditions, in the actual heating furnace of large billets, the surface comprehensive heat transfer coefficient of the billet is controlled within this range by adjusting the protective atmosphere, covering with heat insulation materials, or setting up a cooling device. Based on the temperature-time-organic regulation relationship, a heating path from room temperature to the termination temperature is planned, thereby generating the final heating temperature curve and holding time regime. The large billet is placed into a heating furnace, and the heating process is carried out according to the set surface heat transfer boundary, the heating temperature curve and the holding time system, while the furnace temperature and the temperature of the key points of the billet are monitored in real time. Once the heating process is complete, a cast billet is obtained with a cross-sectional temperature difference within the allowable range and an actual grain size that meets the preset requirements.

[0014] Preferably, the planned heating path from room temperature to the final temperature specifically includes: During the heating and holding stages below the critical temperature, parameters are set with the primary goal of improving temperature uniformity. During the stage of reaching or exceeding the critical temperature, the parameter is set to ensure that the heat preservation time does not exceed the critical heat preservation time.

[0015] The present invention has the following beneficial effects: 1. In this invention, a three-dimensional finite element model is established to systematically simulate the temperature field evolution of large billets under different surface heat transfer coefficients. Based on this, a guiding heat treatment experiment is conducted. For the first time, the key boundary condition of surface heat transfer coefficient is quantitatively correlated with the temperature-time-microstructure evolution relationship, which overcomes the shortcomings of traditional heating processes that rely on experience and have extensive control. This provides a scientific quantitative control basis for the heating process of large billets.

[0016] 2. In this invention, through simulation analysis, it is determined that the overall surface heat transfer coefficient is controlled within the optimized range. Based on this, the heat transfer boundary is actively controlled through engineering measures during actual heating, which can effectively reduce the temperature gradient between the surface and core of the billet at low temperature and during the heating stage, thereby significantly improving the uniformity of the cross-sectional temperature throughout the heating process.

[0017] 3. In this invention, a clear quantitative relationship between heating temperature, holding time, and grain size was established through experiments, and the critical temperature and critical holding time for significant grain coarsening were accurately determined. Based on this, when formulating the heating process, the constraint of not exceeding the critical holding time can be strictly enforced at the high temperature stage, thereby fundamentally suppressing abnormal grain growth caused by overheating or excessive holding time, ensuring the acquisition of a cast billet with fine grains and uniform structure, and laying a key foundation for the stability of subsequent forging and final product performance. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a large billet, illustrating a method for controlling the temperature field and microstructure evolution of a billet proposed in this invention. Figure 2 This is a schematic diagram of a GH4169 sample used to determine the thermal diffusivity and specific heat capacity of a billet temperature field and microstructure evolution control method proposed in this invention. Figure 3 This is a schematic diagram of a finite element model of a method for controlling the temperature field and microstructure evolution of a billet proposed in this invention. Figure 4 This is a schematic diagram of the furnace gas temperature change during the actual furnace heating process of the billet temperature field and microstructure evolution control method proposed in this invention. Figure 5 This is a schematic diagram of the surface comprehensive heat transfer coefficient as a function of temperature during actual furnace heating, which is a method for controlling the temperature field and microstructure evolution of a billet proposed in this invention. Figure 6 The simulation results (a)(b)(c)(d)(e)(f) of the method for controlling the temperature field and microstructure evolution of a billet proposed in this invention are shown in the schematic diagram of their positions in the heating process curve. Figure 7 This is a schematic diagram of the positions of four points P1, P2, P3, and P4 in the simulation results of a method for controlling the temperature field and microstructure evolution of a billet proposed in this invention. Figure 8 A schematic diagram of a GH4169 alloy sample for a method of controlling the temperature field and microstructure evolution of a billet proposed in this invention. Figure 9 This is a schematic diagram of the metallographic surface microstructure of a billet under heat treatment according to the actual furnace heating process proposed in this invention, including air cooling (a), water quenching (b), and metallographic surface microstructure under heat treatment at different temperatures and holding times, including water quenching at 1000℃ for 1h, water quenching at 1000℃ for 2h, water quenching at 1100℃ for 1h, and water quenching at 1100℃ for 2h (f). Figure 10 This is a schematic diagram of the initial metallographic surface structure of a method for controlling the temperature field and microstructure evolution of a cast billet proposed in this invention. Figure 11 The following are schematic diagrams of grain distribution under heat treatment at different temperatures and holding times for a billet temperature field and microstructure evolution method proposed in this invention: water quenching at 1000℃ for 1h (A), water quenching at 1000℃ for 2h (B), water quenching at 1100℃ for 1h (C), and water quenching at 1100℃ for 2h (D). Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In a first embodiment of the present invention, the present invention provides a method for controlling the temperature field and microstructure evolution of a cast billet, such as... Figures 1-11 As shown, it includes the following steps: Based on the actual size and material thermophysical parameters of the large billet to be processed, a three-dimensional finite element model is established to analyze the heat transfer process from its surface to the core, and the initial temperature field is set to be uniform.

[0021] Furthermore, the process for establishing a three-dimensional finite element model for analyzing the surface-to-core heat transfer process includes: Measure the diameter and length of the large casting billet to be processed, and determine the geometric dimensions of the three-dimensional finite element model based on the diameter and length; The density, specific heat capacity, and thermal conductivity parameters of the materials used in large castings are determined or referenced, and these parameters are input as material properties into the three-dimensional finite element model. Based on the geometric dimensions, a three-dimensional geometric entity with the shape of a large casting billet is constructed in the finite element preprocessing software, and tetrahedral meshing is performed on the three-dimensional geometric entity to complete the establishment of the three-dimensional finite element model. In the three-dimensional finite element model, the initial temperature of all nodes is set to a uniform room temperature to achieve a uniform initial temperature field.

[0022] Specifically, first, the geometric dimensions of the model are determined, taking a large cylindrical casting with dimensions of Φ508mm × 1640mm as the example, such as Figure 1 As shown, based on this actual size, the geometric dimensions corresponding to the three-dimensional finite element model are determined. Next, the thermal properties of the model material are defined. The material used is GH4169 alloy. The thermal diffusivity α and specific heat capacity c of this alloy at different temperatures are measured experimentally. The samples used are as follows... Figure 2As shown, the density ρ of the alloy is 8240 kg / m³. The corresponding thermal conductivity λ is calculated according to the formula λ=α·c·ρ, where λ is the thermal conductivity in watts per meter degree Celsius, α is the thermal diffusivity in square meters per second, c is the specific heat capacity in joules per kilogram degree Celsius, and ρ is the density in kilograms per cubic meter. The above measurement and calculation results are in accordance with relevant technical standards. Finally, the thermal properties of GH4169 alloy from 100℃ to 1200℃ are obtained as shown in Table 1, specifically including thermal diffusivity, specific heat capacity, and thermal conductivity. When building the model, the density, specific heat capacity, and thermal conductivity parameters listed in Table 1 need to be completely input into the material library of the finite element software as temperature-related material properties and assigned to the geometric entities subsequently built. Table 1: Thermophysical properties of GH4169 alloy samples

[0023] Next, geometric modeling and mesh generation are performed. In DEFORM-3D or other finite element preprocessing software with thermal analysis capabilities, a three-dimensional cylindrical geometric entity with a diameter of 508mm and a height of 1640mm is created based on the above geometric dimensions to correspond to the actual casting billet. Subsequently, automatic tetrahedral mesh generation is performed on this geometric entity to generate the following: Figure 3 The finite element mesh model shown has a total number of mesh elements controlled to approximately 200,000 to ensure a balance between computational accuracy and efficiency. Finally, the initial conditions of the model are set. In the meshed finite element model, the initial temperature of all nodes is uniformly set to 20℃, i.e., room temperature, to represent the uniform temperature state before the billet is loaded into the furnace, thus completing the uniform setting of the initial temperature field.

[0024] In the three-dimensional finite element model, the combined radiation and convection heat transfer process on the outer surface of the billet is characterized as the surface comprehensive heat transfer coefficient, which is used as the core control parameter. The surface comprehensive heat transfer coefficient is set to multiple different fixed values ​​and / or function values ​​that vary with heating temperature to simulate the evolution of the temperature field inside the billet during the heating process and obtain simulation data of the temperature difference and heat transfer efficiency of the billet cross section under different settings.

[0025] Furthermore, the process for obtaining simulation data on the temperature difference and heat transfer efficiency of the billet cross-section under different settings includes: In the three-dimensional finite element model, all outer surfaces of the billet are set as heat exchange boundaries, and a unified surface comprehensive heat transfer coefficient parameter is defined for the heat exchange boundaries; To perform the simulation, the surface heat transfer coefficient parameter was set to a first type of value and a second type of value, respectively. The first type of value consists of multiple independent fixed constants, while the second type of value is a continuous function based on the change of heating furnace gas temperature or billet surface temperature. Based on the preset heating process curve, transient thermal analysis simulation of the heating process is performed on the three-dimensional finite element model with the first type of value and / or the second type of value, and the temperature field data of the billet inside the casting as a function of time in each group of simulations are calculated. From the temperature field data of each group of simulations, the temperature values ​​of the surface and core of the billet at the same process time are extracted, and the difference is calculated as the cross-sectional temperature difference data. At the same time, based on the temperature field data, the time required for the overall average temperature of the billet to reach the preset stage target value is calculated, and its reciprocal or related measure is used as the heat transfer efficiency data.

[0026] Furthermore, the process of performing transient thermal analysis simulations of the heating process to calculate the temperature field data of the billet interior evolving over time in each simulation includes: The preset heating process curve is input into the three-dimensional finite element model. The heating process curve defines multiple heating and holding stages of the furnace gas temperature change over time. For the three-dimensional finite element model, apply the fixed surface heat transfer coefficient boundary condition defined by the first type of numerical method and / or apply the temperature-varying surface heat transfer coefficient boundary condition defined by the second type of numerical method. In the solver of the three-dimensional finite element model, the transient heat conduction equation, time step and convergence criterion are set, and multiple independent heating process simulation calculation tasks are submitted based on the heating process curve, fixed surface comprehensive heat transfer coefficient boundary conditions or surface comprehensive heat transfer coefficient boundary conditions that vary with temperature. After multiple sets of simulation calculation tasks are completed, the temperature values ​​of all internal nodes or selected characteristic nodes of the billet at different process times are extracted from the solution results as temperature field data that evolves over time.

[0027] Specifically, firstly, the heating process curve is loaded and simulated operating conditions are set. Figure 4 The actual furnace heating process curve shown is input into the finite element software. This curve represents a typical five-stage heating process, including three holding stages and two heating stages, defining the change in furnace gas temperature over time. Based on this curve, multiple sets of different surface heat transfer boundary conditions are set for simulation. For specific setting methods, please refer to [reference needed]. Figure 5 The system is divided into two categories. The first category uses a fixed surface heat transfer coefficient, set at 50, 100, 200, 300, and 400 W / (m²·℃), for five different operating conditions. The second category uses a surface heat transfer coefficient that varies with temperature. This coefficient is determined based on the combined radiation and convection heat transfer characteristics under actual furnace conditions without protective measures; its value increases with increasing temperature. Figure 5 As shown; Secondly, the solver was configured and transient thermal analysis calculations were performed. In the finite element software's solver settings, the transient heat conduction equation was selected as the governing equation, and the time step was set according to the total heating time and temperature change rate to ensure calculation stability and accuracy. The convergence criterion was set to energy residual less than the default or specified tolerance. Based on the loaded heating process curves and the boundary conditions of the above-mentioned comprehensive surface heat transfer coefficients, independent calculation tasks were submitted to simulate the transient evolution of the internal temperature field of the billet during approximately 20 hours of heating. Finally, the required data is extracted and calculated from the calculation results. After each set of simulations is completed, the temperature field data is exported from the software's post-processing module. The method for extracting the cross-sectional temperature difference data is as follows: for each set of simulations, at the same, representative process time, for example... Figure 6 At the end time of each stage marked (a) to (f), specific points on the surface of the cast billet are read, for example... Figure 7 Point P1 and specific points in the core, for example Figure 7 The temperature value at point P4 in the simulation is used to calculate the difference between the two values, thus obtaining the cross-sectional temperature difference data at that moment. The method for extracting heat transfer efficiency data is as follows: For each simulation, the change of the overall or volume-weighted average temperature of the billet over time is tracked from the temperature field data. The actual time required for this average temperature to reach the preset target temperature of the key stage is recorded. The reciprocal of this time is used as a direct measure of the heat transfer efficiency at that stage; the shorter the time required, the higher the heat transfer efficiency. Through the above processing, a series of simulation data on cross-sectional temperature difference and heat transfer efficiency corresponding to different surface comprehensive heat transfer coefficient settings are finally obtained.

[0028] Based on simulation data, the setting method and numerical range of the surface comprehensive heat transfer coefficient that minimizes the cross-sectional temperature difference and enables the billet to reach the target temperature within the process cycle are selected as the optimized heat transfer conditions.

[0029] Furthermore, the process for optimizing heat exchange conditions includes: For the data sets in the simulation data corresponding to different settings and specific values ​​of the comprehensive heat transfer coefficient of the surface, the cross-sectional temperature difference data at each key process moment were extracted and compared. For each set of data in the simulation data corresponding to different surface comprehensive heat transfer coefficient settings and specific values, the time required for the overall average temperature of the billet to reach the target temperature is calculated, and it is evaluated whether the time is shorter than or equal to the process cycle. Based on the analysis and evaluation results, parameters that simultaneously meet the conditions for temperature difference optimization and efficiency qualification were selected from different methods and specific values ​​for setting the comprehensive heat transfer coefficient of the surface. The method for setting the surface heat transfer coefficient and the range covered by the specific values ​​selected through comprehensive screening are recorded and defined as the optimized heat transfer conditions.

[0030] Furthermore, the temperature difference optimization condition refers to the cross-sectional temperature difference data being the relative minimum value among all compared process moments; The efficiency qualification condition refers to the time required for the overall average temperature of the billet to reach the target temperature being shorter than or equal to the process cycle.

[0031] Specifically, firstly, the cross-sectional temperature difference data under different settings were compared and analyzed. Five sets of fixed heat transfer coefficients, such as 50, 100, 200, 300, and 400 W / (m²·℃), and one set of variable heat transfer coefficients were compiled and compared at various critical process moments. These critical process moments included… Figure 6 The six stages shown are: initial state (a), end of the first stage of heat preservation (b), end of the second stage of heating (c), end of the second stage of heat preservation (d), end of the third stage of heating (e), and end of the final heat preservation (f). Through comparison, it was found that for a fixed heat transfer coefficient, in the low-temperature stage, such as at the end of the first stage of heat preservation, the cross-sectional temperature difference decreases significantly with the increase of the heat transfer coefficient. For example, when the heat transfer coefficient is 50 W / (m²·℃), the temperature difference can reach about 100℃, while when the heat transfer coefficient is 300 W / (m²·℃) and 400 W / (m²·℃), the temperature difference decreases to about 35℃. In the high-temperature stage, the cross-sectional temperature difference under different heat transfer coefficients becomes smaller. For the variable heat transfer coefficient, although the cross-sectional temperature difference is greater than some fixed value conditions in the low-temperature stage, it is relatively uniform throughout the heating process. The temperature difference optimization condition refers to the relative minimum value of the cross-sectional temperature difference data at all the process moments compared. Secondly, evaluate whether the heat transfer efficiency under different settings meets the process requirements, calculate and compare the time required for the overall average temperature of the billet to reach the preset target temperature in each group of simulations, and the target temperature and process cycle are based on the actual heating process curve, as shown in the figure. Figure 4 For example, if the total heating cycle is approximately 20 hours, the billet needs to reach and stabilize at a final temperature of 1110℃ within this cycle. Analysis reveals that when the overall surface heat transfer coefficient is 50W / (m²·℃), the final overall temperature of the billet is difficult to reach the target temperature. As the heat transfer coefficient increases, the time required to reach the target temperature decreases, i.e., the heat transfer efficiency improves. When the heat transfer coefficient increases to 300W / (m²·℃) or higher, the improvement in heating efficiency tends to level off. The qualified efficiency condition means that the time required for the overall average temperature of the billet to reach the target temperature does not exceed the process cycle. Finally, the optimal heat transfer conditions were comprehensively screened and determined. Based on the above analysis of temperature difference and efficiency, the following selection was made: under the premise of meeting the efficiency qualification conditions, priority was given to setting the heat transfer coefficient with smaller cross-sectional temperature difference at critical process moments. According to the simulation results, the working conditions with a surface comprehensive heat transfer coefficient of 300 W / (m²·℃) and 400 W / (m²·℃) not only have a low cross-sectional temperature difference at low temperature stage and the difference between the two is not significant, but also can ensure that the billet reaches the target temperature within the process cycle, showing excellent comprehensive performance. In addition, although the heat transfer efficiency of the variable value heat transfer coefficient scheme is relatively slightly lower, its temperature difference distribution is more uniform. Therefore, the optimization range of the surface comprehensive heat transfer coefficient was determined to be 300~400 W / (m²·℃), and this value range and its corresponding setting method (fixed value) were recorded as one of the optimized heat transfer conditions. At the same time, the function setting method that varies with temperature was also used as another feasible optimized heat transfer condition for selection and application in actual production to balance the heat transfer requirements at different stages.

[0032] Based on the temperature field characteristics revealed by simulation, key temperature points were selected, and samples were prepared using cast billet material for heat treatment experiments. The experiments included heating at key temperature points for different holding times, followed by detection of the grain size and microstructure of the samples.

[0033] Furthermore, based on the temperature field characteristics revealed by simulation, the process of selecting key temperature points and preparing samples from cast billet material for heat treatment experiments includes: Analyze the simulation results of the three-dimensional finite element model to identify the stage and corresponding temperature range where the temperature difference between the core and surface of the billet is significant during the heating process. Based on the stage and temperature range with significant temperature difference, a specific temperature value within the temperature range is selected as the key temperature point. The key temperature point includes at least the critical temperature at which the billet material undergoes a significant microstructure transformation. Standard cylindrical or cubic specimens for heat treatment experiments are prepared from materials of the same batch or composition as the large cast billet. The standard sample was placed in a heating furnace and heated to each critical temperature point. At each critical temperature point, it was held for at least two different holding times. Then, it was cooled according to the preset cooling regime to complete the heat treatment experiment. The standard samples that have undergone heat treatment experiments are cut, ground, polished and etched to prepare metallographic samples. The grain size and microstructure of the metallographic samples are observed using an optical microscope or a scanning electron microscope.

[0034] Specifically, firstly, the simulation results were analyzed and key temperature points were selected. That is, the simulation results of the above steps were analyzed, focusing on the stage where the core and surface of the billet had a significant temperature difference during the heating process. The simulation results showed that the cross-sectional temperature difference was most obvious in the low-temperature range, such as the first holding stage below 700℃ and the main heating stage, such as the stage from 700℃ to 1000℃. Based on this temperature field characteristic and combined with the phase transformation and recrystallization characteristics of GH4169 alloy, representative points in two key temperature ranges were selected as experimental temperatures: First, 1000℃ was selected as the representative point of the low-temperature range. This temperature is lower than the typical critical temperature for the severe coarsening of the alloy grains and is in the heating stage where the simulation showed a certain temperature difference. Second, 1100℃ was selected as the representative point of the high-temperature range. This temperature has exceeded the critical temperature for significant grain growth of the alloy and the recrystallization temperature of subsequent forging, and is an extreme key point for controlling the evolution of the microstructure. Secondly, standard specimens were prepared. Cylindrical standard specimens were machined from GH4169 alloy material of the same batch as the aforementioned large cast billet, with a chemical composition conforming to the requirements of Table 2, using wire electrical discharge machining. The specimen dimensions were Φ8mm × 12mm. Figure 8 As shown; Table 2: Chemical composition of GH4169 alloy (unit: mass fraction %)

[0035] Next, multiple heat treatment experiments were performed. The prepared standard samples were placed in a box-type resistance furnace for heat treatment. All heating processes were carried out by raising the temperature along with the furnace to control the rate of temperature change. The experimental groups are as follows: Group 1, according to Figure 4 The actual furnace heating process curve shown is used for complete heat treatment, with a total duration of about 20 hours. After heat treatment, air cooling and water quenching are performed respectively. The second group is heated from room temperature to 1000℃ in the furnace, held for 1 hour and 2 hours respectively, and then water quenched. The third group is heated from room temperature to 1100℃ in the furnace, held for 1 hour and 2 hours respectively, and then water quenched. During the heating process, the furnace temperature fluctuation is controlled within ±10℃ of the set value. Finally, metallographic samples were prepared and observed. All heat-treated samples underwent standard metallographic preparation, the specific procedure being as follows: the observation surface of the sample was polished step-by-step using sandpaper of different grits, from coarse to fine, until no obvious scratches were visible; then, a 0.5μm diamond gypsum suspension was used for final polishing on a cloth polishing disc to obtain a mirror finish; finally, aqua regia was used as the etchant, prepared at a volume ratio of concentrated hydrochloric acid to concentrated nitric acid of 3:1, and etched onto the polished surface for 3 to 5 minutes to clearly display the grain boundaries. The prepared metallographic samples were then observed under an optical microscope, and microstructure photographs were taken at 100x and 200x magnification to analyze grain size, morphology, and distribution. Typical observation results are shown below. Figure 9 As shown.

[0036] Based on the experimental results, a quantitative correspondence between heating temperature, holding time and grain size was established, and the critical temperature and critical holding time for significant grain coarsening were determined.

[0037] Furthermore, the process for determining the critical temperature and critical holding time for significant grain coarsening includes: The grain size measurements and microstructure observations of metallographic samples at different key temperature points and different holding times during the heat treatment experiments are summarized. Using heating temperature and holding time as independent variables and grain size measurement as dependent variable, a quantitative mathematical relationship or data correspondence table reflecting the change of grain size with heating temperature and holding time is established through data fitting or interpolation methods. Based on the temperature-time-size quantification relationship and microstructure observation results, we analyzed the regions where the grain size changed abruptly with increasing heating temperature or prolonged holding time. The initial heating temperature at which the grain size undergoes a sudden change is defined as the critical temperature at which the grains coarsen significantly, and the holding time at which the grain size undergoes a sudden change at this critical temperature is defined as the critical holding time.

[0038] Specifically, firstly, the experimental data were summarized and organized. Metallographic observation results under different heat treatment processes were compiled, including: the initial grain size of the original untreated sample, such as... Figure 10 As shown, the microstructure of the samples after air cooling and water quenching following the actual heating process is as follows. Figure 9 As shown in a and b, the microstructure and corresponding grain size of the water-quenched samples after being held at 1000℃ for 1 hour and 2 hours, respectively, are as follows: Figure 9 c, d and Figure 11 As shown in Figures A and B, the microstructure and corresponding grain size of the water-quenched samples after being held at 1100℃ for 1 hour and 2 hours, respectively, are as follows: Figure 9 e, f and Figure 11 As shown in C and D, the grain size in the metallographic images was statistically measured using image analysis software. Secondly, a temperature-time-size quantification relationship was established, with heating temperature and holding time as the two independent variables and the measured average grain size as the dependent variable, and data graphs were plotted. Analysis of the experimental data points clearly showed the trend of grain size variation with process parameters: at 1000℃ heat treatment, grain growth was slow, and after 1 hour of holding, the grain size was approximately 3-8 μm. Figure 11 A), after heat preservation for 2 hours, the size increased to approximately 30-45μm ( Figure 11 B), while during heat treatment at 1100℃, the grains coarsened rapidly, with grain sizes reaching approximately 75 μm and 100 μm after 1 hour and 2 hours of holding, respectively. Figure 11 Based on these discrete data points, empirical formulas or data tables describing the changes in grain size with temperature and time can be established using linear or nonlinear fitting methods; Furthermore, by analyzing the grain coarsening pattern and determining critical parameters, based on the aforementioned quantitative relationships and metallographic observations, the region where grain size undergoes abrupt changes can be clearly identified: when the heating temperature increases from 1000℃ to 1100℃, even with the same holding time, such as 1 hour, the grain size experiences an order-of-magnitude jump, indicating significant grain coarsening. Therefore, 1100℃ is defined as the critical temperature for significant grain coarsening. Simultaneously, at this critical temperature of 1100℃, comparing the grain size data after 1 hour and 2 hours of holding reveals that grain coarsening is essentially complete after 1 hour of holding; extending the holding time to 2 hours further slows the rate of size increase. Therefore, approximately 1 hour can be defined as the critical holding time reference value at this critical temperature that leads to abrupt changes in grain size. This means that in actual heating processes, when the temperature reaches or exceeds 1100℃, the holding time must be controlled, especially not exceeding 1 hour, to effectively suppress excessive grain growth. Based on the above analysis, key criteria for grain evolution of GH4169 alloy during heating were established, providing direct experimental basis for subsequent formulation of precise heating regimes.

[0039] In the actual heating process, the surface heat transfer boundary of the billet is set according to the optimized heat transfer conditions, and the heating temperature curve and holding time are set according to the temperature-time-microstructure control relationship, critical temperature and critical holding time, so as to obtain a billet with uniform cross-sectional temperature and controlled grain coarsening.

[0040] Furthermore, the process for obtaining a cast billet with uniform cross-sectional temperature and controlled grain coarsening includes: Based on the setting method and numerical range of the surface comprehensive heat transfer coefficient limited by the optimized heat exchange conditions, the comprehensive heat transfer coefficient of the outer surface of the billet can be controlled within this range in the actual heating furnace of large billets by adjusting the protective atmosphere, covering with heat insulation materials, or setting up cooling devices. Based on the temperature-time-organic regulation relationship, a heating path from room temperature to the final temperature is planned, thereby generating the final heating temperature curve and holding time regime. Large billets are placed into a heating furnace, and the heating process is carried out according to the set surface heat transfer boundary, heating temperature curve and holding time system, while the furnace temperature and the temperature of key points of the billet are monitored in real time. Once the heating process is complete, a cast billet is obtained with a cross-sectional temperature difference within the allowable range and an actual grain size that meets the preset requirements.

[0041] Furthermore, the specific heating path planned from room temperature to the final temperature includes: During the heating and holding stages below the critical temperature, parameters are set with the primary goal of improving temperature uniformity. During the stage of reaching and exceeding the critical temperature, the parameter is set to ensure that the heat preservation time does not exceed the critical heat preservation time.

[0042] Specifically, firstly, a surface heat transfer boundary is established within the actual heating furnace. Based on the optimized heat transfer conditions determined above, the overall surface heat transfer coefficient should ideally be controlled within the range of 300–400 W / (m²·℃). To achieve precise control of this boundary condition, one or more of the following engineering measures can be adopted in actual production: When it is necessary to improve heat transfer efficiency and reduce temperature difference in the low-temperature stage, forced cooling with water-cooled jackets can be used. Spiral water-cooled jackets are installed at the edges and corners of the billet, where they are prone to overheating. Forced circulation of cooling water enhances convective heat transfer, thereby achieving an effective heat transfer coefficient in this area ranging from 200 to 400 W / (m²·℃). The cooling water temperature should generally be controlled to not exceed 30℃ to avoid localized overcooling. When it is necessary to suppress the risk of overheating during high-temperature stages or balance the overall temperature difference, aluminum foil reflective insulation layers or ceramic fiber insulation blankets can be used for covering. A 0.1-0.3 mm thick aluminum foil composite material can be sprayed or pasted onto the surface of the blank to reduce radiative heat transfer by utilizing its high reflectivity, which can reduce the overall surface heat transfer coefficient to 50-100 W / (m²·℃). Alternatively, a 50-100 mm thick ceramic fiber blanket can be used to wrap the non-processed surface of the blank, which can control the overall heat transfer coefficient to 80-150 W / (m²·℃). Adding an aluminum foil layer on the surface of the fiber blanket can further improve the insulation effect. An inert gas protective cover is used to form a nitrogen protective layer around the billet (flow rate 0.5-1 m³ / h). By diluting the air, the convective heat transfer intensity is stabilized, and the overall heat transfer coefficient can be maintained at a low level of 50-100 W / (m²·℃). Secondly, the final heating temperature profile and holding time regime were established. Based on the established temperature-time-structure relationship and the determined critical parameters, namely a critical temperature of 1100℃ and a critical holding time of approximately 1 hour, and referring to... Figure 4 Based on the shown basic heating curve, the final heating process is formulated. This process planning follows a temperature zone control strategy, specifically: During the heating and holding stages below the critical temperature (1100℃), the main goal is to improve the temperature uniformity of the billet cross section. In this stage, a higher surface heat transfer coefficient can be set appropriately, such as using or partially using the water-cooled jacket, to accelerate the transfer of heat from the surface to the inside, reduce the core-surface temperature difference, and ensure that the heating rate and holding time are sufficient and uniformly heated as a whole. In the stage of reaching and exceeding the critical temperature (1100℃), the main goal is to suppress excessive grain coarsening. In this stage, the holding time must be strictly controlled to ensure that it does not exceed 1 hour. At the same time, heat insulation measures can be taken, such as covering with ceramic fiber blankets, to appropriately reduce the surface heat transfer coefficient, so as to slow down the surface heating rate and avoid abnormal grain growth caused by overheating in the surface area, so that the core temperature can be stably caught up. Next, the heating process is executed and monitored. A large GH4169 billet with a specification of Φ508mm×1640mm is placed into the heating furnace. The furnace environment is set according to the surface heat exchange engineering plan formulated above, and the heating is carried out according to the established heating temperature curve and holding time system. During the heating process, the temperature of multiple points in the furnace and the temperature of the billet surface and core need to be monitored in real time to ensure that the actual temperature field matches the process setting. Once the complete heating process is finished, the billet is removed from the furnace. Through the aforementioned process control, the final billet should meet the following requirements: during each heating stage, the temperature difference of its cross section is controlled within a small allowable range; and through subsequent sampling inspection, the actual grain size of its surface and core should be uniform and fine, meeting the product's preset grain size level requirements, thereby achieving effective control of grain coarsening. This billet can then be used for subsequent forging processes.

[0043] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the temperature field and microstructure evolution of a cast strand, characterized in that, The method comprises the following steps: Based on the actual size and material thermal physical parameters of the large-sized casting blank to be processed, a three-dimensional finite element model for analyzing the heat transfer process from the surface to the core thereof is established, and the initial temperature field is set to be uniform; In the three-dimensional finite element model, the radiation and the comprehensive convection heat exchange process of the outer surface of the casting blank are characterized as a surface comprehensive heat exchange coefficient, which is taken as a core control parameter, and the surface comprehensive heat exchange coefficient is set to be a plurality of different fixed values and / or a function value varying with the heating temperature, so as to simulate the temperature field evolution in the casting blank during the heating process and obtain simulation data of the cross-section temperature difference and the heat transfer efficiency of the casting blank under different settings; According to the simulation data, a setting mode and a numerical range of the surface comprehensive heat exchange coefficient, which minimize the cross-section temperature difference and enable the heat transfer efficiency to make the casting blank reach a target temperature within a process cycle, are selected as an optimized heat exchange condition; Based on the temperature field characteristics revealed by the simulation, a key temperature point is selected, a sample of the casting blank material is prepared for a heat treatment experiment, the experiment comprises heating at the key temperature point for different holding times, and then the grain size and the microstructure of the sample are detected; According to the experimental results, a quantitative correspondence relationship among the heating temperature, the holding time and the grain size is established, and a critical temperature and a critical holding time at which the grain significantly coarsens are determined; During the actual heating process, the surface heat exchange boundary of the casting blank is set according to the optimized heat exchange condition, and the heating temperature curve and the holding time are set according to the temperature-time-microstructure control relationship, the critical temperature and the critical holding time, so as to obtain a casting blank with uniform cross-section temperature and controlled grain coarsening.

2. The method according to claim 1, wherein the method is characterized by, The process of establishing the three-dimensional finite element model for analyzing the heat transfer process from the surface to the core thereof comprises: The diameter and the length of the large-sized casting blank to be processed are measured, and the geometric size of the three-dimensional finite element model is determined according to the diameter and the length; The density, the specific heat capacity and the thermal conductivity parameters of the material used for the large-sized casting blank are measured or referenced, and the density, the specific heat capacity and the thermal conductivity parameters are input into the three-dimensional finite element model as material properties; According to the geometric size, a three-dimensional geometric entity consistent with the shape of the large-sized casting blank is constructed in a finite element pre-processing software, and tetrahedral mesh division is performed on the three-dimensional geometric entity, so as to complete the establishment of the three-dimensional finite element model; In the three-dimensional finite element model, the initial temperature of all nodes is set to be uniform room temperature, and the setting of the uniform initial temperature field is completed.

3. The method according to claim 1, wherein the method is characterized by, The process of obtaining simulation data of the cross-section temperature difference and the heat transfer efficiency of the casting blank under different settings comprises: In the three-dimensional finite element model, all the outer surfaces of the casting blank are set as heat exchange boundaries, and a uniform surface comprehensive heat exchange coefficient parameter is defined for the heat exchange boundaries; For performing simulation, the surface comprehensive heat exchange coefficient parameter is set to be a first type of value and a second type of value, wherein the first type of value is a plurality of independent fixed constants, and the second type of value is a continuous function based on the variation of the heating furnace gas temperature or the casting blank surface temperature; Based on the preset heating process curve, the three-dimensional finite element model set with the first type of numerical value and / or the second type of numerical value is respectively executed to perform heating process transient thermal analysis simulation, and the temperature field data of the internal evolution of the casting blank over time in each simulation group is calculated; From the temperature field data of each simulation, the temperature values of the casting blank surface and the core at the same process time are extracted, and the difference value is calculated as the cross-section temperature difference data. At the same time, the time required for the overall average temperature of the casting blank to reach the preset stage target value is calculated according to the temperature field data, and its reciprocal or related measure is taken as the heat transfer efficiency data.

4. The method according to claim 3, wherein the method is characterized by, The process of respectively executing heating process transient thermal analysis simulation to calculate the temperature field data of the internal evolution of the casting blank over time in each simulation group includes: The preset heating process curve is input into the three-dimensional finite element model, and the heating process curve defines multiple heating stages and holding stages of the furnace gas temperature change over time; The three-dimensional finite element model is respectively applied to the fixed surface comprehensive heat transfer coefficient boundary condition defined by the first type of numerical value and / or the surface comprehensive heat transfer coefficient boundary condition varying with temperature defined by the second type of numerical value; In the solver of the three-dimensional finite element model, the transient heat conduction equation, the time step and the convergence criterion are set, and based on the heating process curve, the fixed surface comprehensive heat transfer coefficient boundary condition or the surface comprehensive heat transfer coefficient boundary condition varying with temperature, a plurality of independent heating process simulation calculation tasks are submitted; After the completion of the plurality of simulation calculation tasks, the temperature values of all nodes or selected feature position nodes inside the casting blank at different process times are respectively extracted from the solution results as the temperature field data evolving over time.

5. The method of claim 1, wherein the method further comprises: determining a temperature of the cast slab; and determining a temperature of the cast slab at a location of the cast slab where the cast slab is to be cut into the slab. The process of obtaining the optimized heat transfer condition includes: For the data groups in the simulation data corresponding to different surface comprehensive heat transfer coefficient setting methods and specific numerical values, the cross-section temperature difference data at each key process time is respectively extracted and compared; For the data groups in the simulation data corresponding to different surface comprehensive heat transfer coefficient setting methods and specific numerical values, the time required for the overall average temperature of the casting blank to reach the target temperature is calculated, and whether the time is shorter than or equal to the process cycle is evaluated; According to the analysis and evaluation results, the parameters that meet the temperature difference optimization condition and the efficiency qualified condition at the same time are selected from different surface comprehensive heat transfer coefficient setting methods and specific numerical values; The range covered by the surface comprehensive heat transfer coefficient setting method and the specific numerical value selected by comprehensive screening is recorded and defined as the optimized heat transfer condition.

6. The method according to claim 5, wherein: The temperature difference optimization condition refers to that the corresponding cross-section temperature difference data is the relative minimum value in all compared process times; The efficiency qualified condition refers to that the time required for the overall average temperature of the casting blank to reach the target temperature is shorter than or equal to the process cycle.

7. The method of claim 1, wherein the method further comprises: determining a temperature of the cast slab; and determining a temperature of the cast slab at a location of the cast slab where the cast slab is to be cut into the slab. Based on the temperature field characteristics revealed by the simulation, the key temperature points are selected, and the process of preparing a sample of the casting blank material for heat treatment experiment includes: Analyzing simulation results of the three-dimensional finite element model, identifying stages and corresponding temperature intervals in which temperature difference between core and surface of the casting blank is significant during heating process; Based on the stages and temperature intervals in which temperature difference is significant, selecting a specific temperature value within the temperature interval as the key temperature point, the key temperature point at least including a critical temperature at which significant microstructure transformation of the casting blank material occurs; Processing and preparing cylindrical or cubic standard samples for heat treatment experiment from materials of the same batch or same composition as the large casting blank; Placing the standard samples in a heating furnace, heating to each key temperature point respectively, and maintaining at each key temperature point for at least two different holding times respectively, then cooling according to a predetermined cooling schedule to complete the heat treatment experiment; Cutting, grinding, polishing and etching the standard samples after heat treatment experiment to prepare metallographic samples, and observing grain size and microstructure morphology of the metallographic samples using an optical microscope or a scanning electron microscope.

8. The method of claim 1, wherein the method further comprises: determining a temperature of the cast slab; and determining a temperature of the cast slab at a location of the cast slab where the cast slab is to be cut into the slab. The process of determining the critical temperature and critical holding time at which grain significantly coarsens includes: Summarizing grain size measurement values and microstructure observation results of metallographic samples corresponding to different key temperature points and different holding times in the heat treatment experiment; Establishing a quantitative mathematical relationship or data correspondence table reflecting the change of grain size with heating temperature and holding time by data fitting or interpolation method, taking heating temperature and holding time as independent variables and the grain size measurement values as dependent variables; Based on the temperature-time-size quantitative relationship and the microstructure observation results, analyzing the region where grain size suddenly changes with the increase of heating temperature or the extension of holding time; Defining the starting heating temperature value at which grain size suddenly changes as the critical temperature at which grain significantly coarsens, and defining the holding time value that leads to the sudden change of grain size at this critical temperature as the critical holding time.

9. The method of claim 1, wherein the method further comprises: determining a temperature of the cast slab; and determining a temperature of the cast slab at a location of the cast slab where the cast slab is to be cut into the slab. The process of obtaining a casting blank with uniform cross-sectional temperature and controlled grain coarsening includes: According to the surface comprehensive heat transfer coefficient setting mode and numerical range defined by the optimized heat exchange condition, controlling the comprehensive heat transfer coefficient of the outer surface of the large casting blank in the actual heating furnace by adjusting the protective atmosphere, covering the heat insulation material or setting the cooling device; According to the temperature-time-microstructure regulation relationship, planning the heating path from room temperature to the final temperature, thereby generating the final heating temperature curve and holding time schedule; Placing the large casting blank in the heating furnace, executing the heating process according to the set surface heat exchange boundary, the heating temperature curve and the holding time schedule, and monitoring the furnace temperature and the key point temperature of the casting blank in real time; After the heating process is completed, obtaining a casting blank with cross-sectional temperature difference within the allowable range and actual grain size meeting the preset requirements.

10. The method of claim 9, wherein the method further comprises: determining a temperature of the cast slab; and determining a temperature of the cast slab at a location of the cast slab where the cast slab is to be cut into the slab. Planning the heating path from room temperature to the final temperature specifically includes: In the temperature rising and holding stage below the critical temperature, setting parameters mainly aiming to improve temperature uniformity; In the stage reaching and exceeding the critical temperature, setting parameters with the constraint of ensuring that the holding time does not exceed the critical holding time.

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