Low-stress gradient ingot casting method for large-size titanium alloy bar

Abstract

The invention relates to the technical field of titanium alloy bar ingot casting, in particular to a low-stress gradient ingot casting method for a large-size titanium alloy bar. The method comprises the steps that the temperature and the pouring speed of an ingot casting material of a large-size titanium alloy bar in each ingot casting experiment process are obtained, and the high-gradient stress probability generated at each moment is obtained according to temperature distribution of the ingot casting material in each ingot casting experiment process and the weight of a poured titanium alloy material; the stress concentration trend of each position of the edge area of the titanium alloy material is obtained according to the temperature difference of the inner area and the outer area of the titanium alloy material at each moment in the cooling stage and the coupling property between formation of thermal stress in each cooling stage and flowing of molten alloy liquid; and correcting the high-gradient stress probability by using the stress concentration trend of every two positions of the marginal region and the temperature attenuation difference between the inner region and the outer region so as to screen the optimal scheme. According to the method, the accuracy of process parameter setting is improved, and the ingot casting quality of the large-size titanium alloy bar is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of titanium alloy bar ingot casting, and particularly relates to a low stress gradient ingot casting method for large-size titanium alloy bar. BACKGROUND

[0002] Titanium alloy plays a vital role in the fields of aerospace, national defense industry, ocean engineering and high-end manufacturing due to its high specific strength, corrosion resistance and excellent high performance. In these fields, large-size titanium alloy bar as a basic material for structural parts and functional components undertakes important tasks of bearing and connecting. Therefore, it is a key technical problem for modern advanced manufacturing industry to prepare large-size titanium alloy bar with low stress gradient, excellent microstructure uniformity and high performance.

[0003] At present, the ingot casting preparation methods for large-size titanium alloy bar mainly include vacuum self-consumption arc melting method and electron beam cold bed melting method. These two methods dominate the preparation of titanium alloy bar, but in the ingot casting process, for large-size bar, the existing method sets the optimal process parameters according to experience, which is difficult to adapt to complex thermodynamic behavior, resulting in too large stress gradient, difficult to control residual stress, and even cracks may occur. For large-size titanium alloy bar, although local temperature and stress change law can be obtained through experimental means, single experimental data is difficult to describe the stress field distribution in the whole ingot casting process, and there is a lack of method to integrate experimental data with numerical simulation, which makes it impossible to determine the optimal process parameters in the ingot casting process of large-size titanium alloy bar, and the ingot casting quality of large-size titanium alloy bar is difficult to control. SUMMARY

[0004] In order to solve the problem that the existing method cannot determine the optimal process parameters in the ingot casting process of large-size titanium alloy bar, the purpose of the present application is to provide a low stress gradient ingot casting method for large-size titanium alloy bar, and the technical scheme adopted is as follows: The present application provides a low stress gradient ingot casting method for large-size titanium alloy bar, which comprises the following steps: Obtaining the temperature of the ingot casting material and the pouring speed in each ingot casting experiment process of the large-size titanium alloy bar, and the ingot casting process includes a cooling stage; According to the temperature distribution of the ingot casting material and the weight of the poured titanium alloy material in each ingot casting experiment process, the high gradient stress probability of the temperature field at each time is obtained. The difference between the change trend of the high gradient stress probability of the temperature field and the pouring speed in each cooling stage is evaluated to evaluate the coupling between the formation of thermal stress and the flow of molten alloy liquid in each cooling stage; According to the temperature difference between the inner and outer regions of the titanium alloy material at each time in the cooling stage and the coupling, a stress concentration trend of each position of the edge region of the titanium alloy material is obtained; a high gradient stress probability is corrected by using the fluctuation difference between the stress concentration trends of each two positions of the edge region in the cooling stage and the temperature attenuation difference between the edge region and the center region; According to the distribution of the corrected high gradient stress probability in each ingot experiment process, an optimal scheme of the ingot is determined.

[0005] Preferably, the high gradient stress probability generated by the temperature field at each time in each ingot experiment process is obtained according to the temperature distribution of the ingot material in each ingot experiment process and the weight of the poured titanium alloy material, and includes: The information entropy of the temperature values of all positions of the ingot material at the time to be analyzed and the range of the temperature values of all positions of the ingot material at the time to be analyzed are integrated to obtain the confusion degree of the microstructure of the titanium alloy material at the time to be analyzed; The high gradient stress probability generated by the temperature field at the time to be analyzed is determined by integrating the confusion degree of the microstructure of the titanium alloy material at the time to be analyzed and the weight change amount of the poured titanium alloy material at the time to be analyzed, and the confusion degree and the weight change amount are positively correlated with the high gradient stress probability; The weight change amount of the poured titanium alloy material at the time to be analyzed is determined according to the weight of the poured titanium alloy material at the time to be analyzed and the time immediately before the time to be analyzed; The candidate ingot process is any ingot experiment process, and the time to be analyzed is any time in the candidate ingot process.

[0006] Preferably, the high gradient stress probability generated by the temperature field at the time to be analyzed is determined by integrating the confusion degree of the microstructure of the titanium alloy material at the time to be analyzed and the weight change amount of the poured titanium alloy material at the time to be analyzed, and the confusion degree and the weight change amount are positively correlated with the high gradient stress probability; The product of the confusion degree of the microstructure of the titanium alloy material at the time to be analyzed and the weight change amount of the poured titanium alloy material at the time to be analyzed is normalized to obtain the high gradient stress probability generated by the temperature field at the time to be analyzed.

[0007] Preferably, the coupling between the formation of thermal stress and the flow of molten alloy liquid in each cooling stage is evaluated by integrating the difference between the change trend of the high gradient stress probability of the temperature field and the pouring speed in each cooling stage, and includes: For any cooling stage: The mean square error between the high gradient stress probability of the temperature field and the pouring speed in the any cooling stage is calculated; The coupling between the thermal stress formation and the flow of the molten alloy liquid in any cooling stage is obtained according to the mean square error, and the mean square error is negatively correlated with the coupling.

[0008] Preferably, the stress concentration tendency of each position of the edge region of the titanium alloy material is obtained according to the temperature difference between the inner region and the outer region of the titanium alloy material at each time point in the cooling stage and the coupling, and the stress concentration tendency of each position of the edge region of the titanium alloy material comprises: For any time point in any cooling stage: The difference between the temperature of each position of the edge region of the titanium alloy material and the temperature of the center region at the time point is taken as a first difference value of each position of the edge region of the titanium alloy material at the time point. The product between the first difference value of each position of the edge region of the titanium alloy material at the time point and the coupling is determined as a stress concentration tendency value of the corresponding position at the corresponding time point.

[0009] Preferably, the high gradient stress probability is corrected by using the fluctuation difference between the stress concentration tendencies of each two positions of the edge region in the cooling stage, and the temperature decay difference between the edge region and the center region, and the correction comprises: For the cooling stage in the candidate ingot process: The stress concentration tendency values of each position of the edge region at all time points in the cooling stage are curve-fitted to obtain a fitting curve corresponding to each position; The stress synchronization factor of the edge region is obtained according to the fluctuation difference between the fitting curves corresponding to each two positions of the edge region. The correction coefficient is obtained according to the difference between the average temperature decay rates of all positions of the edge region and the average temperature decay rate of the center position in the cooling stage in the candidate ingot process, and the stress synchronization factor, and the difference between the average temperature decay rates is positively correlated with the correction coefficient. The high gradient stress probability generated at each time point in the candidate ingot process is corrected by using the correction coefficient.

[0010] Preferably, the stress synchronization factor of the edge region is obtained according to the fluctuation difference between the fitting curves corresponding to each two positions of the edge region, and the correction comprises: The maximum peak point of each fitting curve is obtained, and the average slope value of the curve corresponding to the maximum peak point on each curve is taken as a measurement value of the stress change speed of the corresponding position of the edge region. The stress synchronization factor of the edge region is obtained according to the difference between the measurement values of the stress change speeds of each two positions of the edge region and the difference between the data values of the corresponding maximum peak points, and the difference between the measurement values of the stress change speeds and the difference between the data values are positively correlated with the stress synchronization factor.

[0011] Preferably, the high gradient stress probability generated at each time point in the candidate ingot process is modified by using the correction coefficient, comprising: The product of the correction coefficient and the high gradient stress probability generated at each time point in the candidate ingot process is taken as the corresponding modified high gradient stress probability at each time point in the candidate ingot process.

[0012] Preferably, the optimal scheme of the ingot is determined according to the distribution of the modified high gradient stress probability in each ingot experiment process, comprising: According to the smoothness of the high gradient stress probability curve corresponding to each ingot experiment process, the optimal scheme of the ingot is screened from all ingot experiment processes. The high gradient stress probability curve is obtained according to the modified high gradient stress probability corresponding to each time point in each ingot experiment process.

[0013] Preferably, the difference between the temperature of each position of the edge region of the titanium alloy material at any time and the temperature of the central region is obtained by taking the absolute value of the difference between the temperature of each position of the edge region of the titanium alloy material at any time and the temperature of the central region as the difference between the temperature of each position of the edge region of the titanium alloy material at any time and the temperature of the central region.

[0014] The present application has at least the following beneficial effects: The present application changes the experimental conditions to perform multiple simulation experiments on the temperature field in the large-size titanium alloy bar ingot process, and the distribution of the temperature field can reflect the microstructure distribution state of the titanium alloy material in the ingot process, so as to determine the high gradient stress probability generated in the ingot process. The dynamic nature of the stress change of the temperature field in each cooling stage and the dynamic change of the pouring speed are combined to analyze the thermal stress evolution law in the ingot process, evaluate the coupling between the formation of thermal stress and the flow of molten alloy liquid, and then reflect the residual stress in the ingot cooling process through the synchronous change of the thermal stress at different positions in the edge region of the cooling stage and the difference in the temperature decay rate of the inner and outer regions. The high gradient stress probability in the ingot experiment process is modified, and finally the optimal scheme of the ingot is screened according to the distribution of the modified high gradient stress probability in each ingot experiment process. The present application compares the change results of the thermal stress by changing the experimental conditions to screen the optimal scheme, and thus provides optimization support for the large-size titanium alloy bar ingot process, so as to more scientifically and efficiently realize the subsequent large-size titanium alloy bar ingot process, and improve the production quality of the large-size titanium alloy bar. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, and the advantages thereof, below will briefly introduce the drawings required by the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A flow chart of a large-size titanium alloy bar low-stress gradient ingot casting method provided by the embodiments of the present application; Figure 2 A structural block diagram of a large-size titanium alloy bar low-stress gradient ingot casting system provided by the embodiments of the present application; Figure 3 A schematic diagram of the change trend of a high gradient stress probability curve and a pouring speed curve provided by the embodiments of the present application. DETAILED DESCRIPTION

[0017] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined purposes, below will combine the drawings and preferred embodiments to specifically describe a large-size titanium alloy bar low-stress gradient ingot casting method according to the present application as follows.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0019] Below will combine the drawings to specifically describe the specific scheme of the large-size titanium alloy bar low-stress gradient ingot casting method provided by the present application.

[0020] A large-size titanium alloy bar low-stress gradient ingot casting method embodiment: The specific scenario to which the present embodiment is directed is that, in the process of casting an ingot of a large-size titanium alloy bar, due to different cooling and solidification speeds of liquid metal, the heat transfer, phase change and shrinkage process inside the material will cause accumulation of residual stress, and then possibly cause mechanical stress, reduce the ingot casting effect of the large-size titanium alloy bar, and affect the product quality. In order to ensure the quality, it is necessary to set appropriate process parameters, that is, to select the best scheme for casting, and the present embodiment will evaluate the ingot casting process of the large-size titanium alloy bar under different process parameters, select the best scheme, and use the process parameters under the best scheme for ingot casting in the subsequent large-size titanium alloy bar ingot casting process.

[0021] The present embodiment proposes a large-size titanium alloy bar low-stress gradient ingot casting method, as shown in Figure 1 The large-size titanium alloy bar low-stress gradient ingot casting method provided by the present embodiment includes the following steps: Step S1, obtain the temperature of the ingot material, the pouring speed during each ingot experiment of the large-size titanium alloy bar, and the ingot process including the cooling stage.

[0022] The large-size titanium alloy bar generally needs to be processed by ingot casting, and needs to be forged and rolled multiple times to improve the microstructure performance, and the larger the size, the higher the deformation resistance in the process of hot working, and the more difficult the workmanship; the weight of the large-size ingot is not less than 14000kg, and the length is not less than 15000mm.

[0023] The stress gradient refers to the rate of change of the internal residual stress of the material in space, and the purpose of pursuing low stress gradient in the ingot casting process of the large-size alloy bar is to reduce stress concentration and improve the performance consistency and safety of the material; in the case of high stress gradient, the thermal expansion and contraction of different regions of the ingot are inconsistent, which is easy to produce cracks at the solid-liquid coexistence zone or the grain boundary.

[0024] This embodiment will conduct multiple ingot casting experiments of large-size titanium alloy bars, the process parameters of each experiment are different, and the best scheme is selected from the results of each experiment, and the subsequent ingot casting process will be carried out by using the best scheme.

[0025] The ingot casting experiment specifically includes: (1) According to the casting characteristics of titanium alloy, select appropriate ingot casting equipment, such as vacuum consumable arc melting furnace, which is suitable for high-purity titanium alloy ingot casting, and control the impurity content and microstructure uniformity; (2) Select the required large-size titanium alloy bar raw materials for the experiment, such as Ti-6Al-4V, Ti-5Al-2.5Sn, etc., ensure that the purity of the raw materials meets the experimental requirements, and avoid the interference of impurities (such as oxygen, nitrogen, etc.) on the experimental results; (3) According to the structure of the melting equipment, install thermocouples, weight monitoring and other equipment to ensure that the molten pool, ingot surface and cooling area are covered; (4) Preheat the equipment before the experiment to ensure stable melting conditions, load the titanium alloy raw materials, start the melting equipment, and gradually raise the temperature to the predetermined range (such as 1750℃); (5) The sensor collects the temperature, environmental temperature, weight data and other data of the ingot material in the molten pool, and transmits and stores them in the database; (6) Perform multiple ingot casting experiments within a period of time, and require the equipment lifting angle of the melting equipment to change constantly during the casting process, that is, to ensure the constant casting speed as much as possible, and collect all the experimental data.

[0026] In this embodiment, multiple ingot casting experiments of large-size titanium alloy bars are carried out, only one process parameter is changed each time, for example, the heating rate is gradually reduced, such as from 5℃ / s to 4℃ / s, 3℃ / s, etc., or multiple process parameters are adjusted, and each ingot casting process mainly includes a melting stage, a pouring stage, a cooling stage and a solidification stage. The experimental data in each ingot casting experiment of the large-size titanium alloy bar is collected by a sensor, transmitted and stored in a database, and the experimental data includes the temperature of the ingot casting material in the molten pool, the pouring speed, the weight of the poured titanium alloy material; the types and adjustment sizes of the process parameters are set according to specific conditions, which will not be described in detail here; in this embodiment, the collection frequency of temperature and pouring speed is set to one second each time, and in specific applications, the implementer can set the data collection frequency according to specific conditions.

[0027] Up to now, the temperature and pouring speed of the ingot casting material at each time in the multiple ingot casting experiments of the large-size titanium alloy bar have been collected in this embodiment.

[0028] Step S2, according to the temperature distribution of the ingot casting material and the weight of the poured titanium alloy material in each ingot casting experiment, the high gradient stress probability of the temperature field at each time in each ingot casting experiment is obtained; the difference between the change trend of the high gradient stress probability of the temperature field and the pouring speed in each cooling stage is comprehensively evaluated to evaluate the coupling between the formation of thermal stress and the flow of molten alloy liquid in each cooling stage.

[0029] The main purpose of this embodiment is to observe the temperature field in the ingot casting process according to the temperature data at different positions in the ingot casting experiment of the large-size titanium alloy bar, to provide support data for subsequent thermal stress change analysis.

[0030] The gradient of the temperature field is the main driving force of the stress field. In the process of ingot casting, the non-uniform temperature field will cause uneven thermal expansion and contraction, thereby causing the formation of thermal stress; if the temperature field appears sharp change locally, for example, uneven cooling or faster cooling speed at the corners of the mold, stress concentration areas are easily formed inside or at the edge of the ingot.

[0031] Under the non-uniform distribution of the temperature field, the cooling rate of different regions is different, which causes the deviation of the grain growth direction, forming preferred orientation or asymmetric microstructure; usually in the ingot casting process, columnar crystals expand from the edge to the inside of the ingot, and equiaxed crystals form in the center region. If the temperature field is uneven, the distribution of columnar crystals and equiaxed crystals will be unbalanced, which may produce dendritic segregation or microstructure layering.

[0032] The change of the angle of the smelting equipment is constant, but in the actual pouring process, the flow of the molten metal cannot be accurately controlled, and thus the instantaneous speed in the pouring process can not maintain a constant rate of change. In the ingot casting process, by measuring the actual weight of the mold, the weight of the mold during pouring of the titanium alloy material is obtained at each time, and the change of the weight of the mold can be used to reflect the instantaneous speed of the pouring process.

[0033] Based on the above features, first, according to the temperature distribution of the ingot material in each ingot casting experiment process, the unevenness of the microstructure of the titanium alloy material at a single time in the ingot casting process is evaluated, and the degree of confusion of the microstructure of the titanium alloy material at each time in the ingot casting process is obtained. Then, according to the degree of confusion of the microstructure of the titanium alloy material and the weight of the poured titanium alloy material, the probability of high gradient stress generated by the temperature field at each time is evaluated.

[0034] Next, this embodiment will be described by taking any ingot casting experiment process as an example. The method provided in this embodiment can be used to process other ingot casting experiment processes.

[0035] Specifically, any ingot casting experiment process is denoted as a candidate ingot casting process, and any time in the candidate ingot casting process is denoted as an analysis time. The information entropy of the temperature values of all positions on the ingot material at the analysis time and the range of the temperature values of all positions on the ingot material at the analysis time are combined to obtain the degree of confusion of the microstructure of the titanium alloy material at the analysis time. The degree of confusion of the microstructure of the titanium alloy material at the analysis time can be expressed as: wherein, represents the degree of confusion of the microstructure of the titanium alloy material at the analysis time, represents the information entropy of the temperature values of all positions on the ingot material at the analysis time, represents the maximum value of the temperature of all positions on the ingot material at the analysis time, represents the minimum value of the temperature of all positions on the ingot material at the analysis time.

[0036] The range of temperature values of all positions on the ingot material at the time to be analyzed, the greater the range, the greater the temperature span in the casting process. The information entropy of the temperature values of all positions on the ingot material at the time to be analyzed is used to reflect the uniformity of the temperature distribution on the ingot material at the time to be analyzed, the greater the information entropy, the more uneven the temperature distribution of the ingot material. The calculation method of the information entropy is the prior art, and will not be described in detail here. When the range of the temperature values of all positions on the ingot material at the time to be analyzed is greater, and the information entropy of the temperature values of all positions on the ingot material at the time to be analyzed is also greater, it indicates that the surface of the titanium alloy material at the time to be analyzed is more uneven, that is, the degree of confusion of the microstructure of the titanium alloy material at the time to be analyzed is greater.

[0037] After determining the degree of confusion of the microstructure of the titanium alloy material at the time to be analyzed, the degree of confusion of the microstructure of the titanium alloy material at the time to be analyzed and the weight change amount of the cast titanium alloy material at the time to be analyzed are comprehensively determined to determine the high gradient stress probability generated by the temperature field at the time to be analyzed, and the degree of confusion and the weight change amount are positively correlated with the high gradient stress probability.

[0038] Wherein, the positive correlation means that the dependent variable will increase with the increase of the independent variable, and will decrease with the decrease of the independent variable, which can be an additive relationship, a multiplication relationship, etc., and is determined by actual application. In this embodiment, the product of the degree of confusion of the microstructure of the titanium alloy material at the time to be analyzed and the weight change amount of the cast titanium alloy material at the time to be analyzed is normalized to obtain the high gradient stress probability generated by the temperature field at the time to be analyzed.

[0039] The weight change amount of the cast titanium alloy material at the time to be analyzed is determined according to the weight of the cast titanium alloy material at the time to be analyzed and the time before the time to be analyzed, that is, the difference between the weight of the cast titanium alloy material at the time to be analyzed and the weight of the cast titanium alloy material at the time before the time to be analyzed is taken as the weight change amount of the cast titanium alloy material at the time to be analyzed. It should be noted that if there is no time before the time to be analyzed, the weight of the cast titanium alloy material at the time before the time to be analyzed is 0.

[0040] In this embodiment, a specific calculation formula of the high gradient stress probability is given, and the high gradient stress probability generated by the temperature field at the time to be analyzed can be represented as: Wherein, represents the high gradient stress probability generated by the temperature field at the time to be analyzed, represents the degree of confusion of the microstructure of the titanium alloy material at the time to be analyzed, represents the weight change amount of the cast titanium alloy material at the time to be analyzed, represents the hyperbolic tangent function.

[0041] It should be noted that the weight change amount of the cast titanium alloy material at the moment to be analyzed is obtained by subtracting the weight of the cast titanium alloy material at the moment before the moment to be analyzed from the weight of the cast titanium alloy material at the moment to be analyzed. The hyperbolic tangent function is introduced in the high gradient stress probability in order to normalize the product. As other embodiments, other normalization methods can also be used for processing, which will not be described in detail here.

[0042] The degree of chaos is used to reflect the non-uniformity of the microstructure of the titanium alloy material, and the weight change amount of the cast titanium alloy material at the moment to be analyzed is used to reflect the flow speed of the molten titanium alloy material at the moment to be analyzed; when the degree of chaos of the microstructure of the titanium alloy material at the moment to be analyzed is greater, and the weight change amount of the cast titanium alloy material is also greater, it indicates that the high gradient stress probability generated at the moment to be analyzed is higher.

[0043] A large local thermal expansion difference between the high temperature zone and the low temperature zone will cause thermal stress concentration, which increases the possibility of local stress mismatch in the ingot; however, the expansion behavior of the material is not completely free, but is limited by internal and external constraint effects, which causes stress concentration in the local area of the material and further affects the distribution and evolution of stress through the dynamic change of the temperature field.

[0044] The temperature field of the ingot is dynamically changing, and with the change of time, the cooling and solidification are continuously carried out, and the stress field is also continuously evolving. By using the above method, the high gradient stress probability generated by the temperature field at each moment during each ingot experiment can be obtained. Next, the difference between the change trend of the high gradient stress probability of the temperature field and the pouring speed in the cooling stage is combined to evaluate the coupling between the formation of thermal stress and the flow of molten alloy liquid.

[0045] This embodiment still takes any cooling stage as an example for description, and the method provided in this embodiment can be used for processing for other cooling stages.

[0046] For any cooling stage: calculate the mean square error between the high gradient stress probability of the temperature field and the pouring speed in the cooling stage, and obtain the coupling between the formation of thermal stress and the flow of molten alloy liquid in the any cooling stage according to the mean square error. The mean square error and the coupling are in a negative correlation.

[0047] Wherein, the negative correlation means that the dependent variable will decrease with the increase of the independent variable, and the dependent variable will increase with the decrease of the independent variable, which can be a subtraction relationship, a division relationship, etc., which is determined by actual application.

[0048] In this embodiment, the specific calculation formula of the coupling between the formation of thermal stress and the flow of molten alloy liquid is given, which is as follows: wherein, represents the coupling between the formation of thermal stresses and the flow of the molten alloy liquid in the cooling stage of the i-th ingot casting experiment, represents a sequence of high gradient stress probability constitutions of the temperature field at all times in the cooling stage of the i-th ingot casting experiment, represents a sequence of normalized values of pouring speed at all times in the i-th ingot casting experiment, represents a function for calculating the mean square error, represents the mean square error between the sequence of high gradient stress probability constitutions of the temperature field at all times in the cooling stage of the i-th ingot casting experiment and the sequence of normalized values of pouring speed at all times in the i-th ingot casting experiment, represents a preset first adjustment parameter.

[0049] The preset first adjustment parameter is introduced into the calculation formula of the coupling to prevent the denominator from being 0. In the present embodiment, the preset first adjustment parameter is 0.01, which can be set according to specific circumstances in specific applications. It should be noted that the sequence of high gradient stress probability constitutions and the sequence of normalized values of pouring speed are calculated by using the existing mean square error calculation formula, that is, the elements in one of the two sequences are regarded as true values, and the elements in the other sequence are regarded as predicted values, and the mean square error is calculated by using the existing mean square error calculation formula. The specific calculation process is a prior art, which will not be described in detail here.

[0050] for representing the mean square error between the high gradient stress probability of the temperature field and the pouring speed in the cooling stage of the i-th ingot casting experiment. The smaller the mean square error, the more similar the change relationship between the high gradient stress probability of the temperature field and the pouring speed in the cooling stage of the i-th ingot casting experiment, that is, the higher the coupling between the formation of thermal stresses and the flow of the molten alloy liquid. As shown in FIG. 6, the change trend of the high gradient stress probability curve and the pouring speed curve is shown. Figure 3

[0051] When the pouring speed is high, the liquid flow homogenizes the temperature field, the thermal expansion of the material is more uniform, the thermal stress distribution is more stable, and high-speed pouring can delay the contact cooling between the material and the mold, weakening the external constraint effect of the mold; the temperature gradient is large, the non-uniformity of expansion is significant, and the internal stress is more likely to concentrate; the cooling time is longer, the constraint effect of the material and the mold is stronger, and the thermal stress is more difficult to release.

[0052] ​By using the above method, the coupling between the formation of thermal stress and the flow of molten alloy liquid in the cooling stage of each ingot casting experiment can be evaluated.

[0053] In step S3, the stress concentration tendency of each position of the edge region of the titanium alloy material is obtained according to the temperature difference between the inner and outer regions of the titanium alloy material at each time in the cooling stage and the coupling, and the high gradient stress probability is corrected by using the fluctuation difference between the stress concentration tendencies of each two positions of the edge region in the cooling stage and the temperature attenuation difference between the edge region and the center region.

[0054] In the casting process, the cooling of the molten metal liquid causes the temperature of the outer layer to rapidly decrease, while the temperature of the inner layer is relatively high, forming a significant temperature gradient. The cooling surface layer is subjected to the expansion pressure of the high-temperature region inside, forming a tensile stress, while the inner region is subjected to a compressive stress, which further causes the stress concentration tendency at the edge position to be more obvious. Therefore, the stress concentration tendency of the edge position of the titanium alloy material is evaluated according to the temperature difference between the inner and outer regions of the titanium alloy material at each time in the cooling stage and the coupling between the formation of thermal stress and the flow of molten alloy liquid in the cooling stage.

[0055] Specifically, for any time in any cooling stage: the absolute value of the difference between the temperature of each position of the edge region of the titanium alloy material at that time and the temperature of the center region is taken as the first difference value of each position of the edge region of the titanium alloy material at that time, and there is one first difference value for each position of the edge region at that time. The first difference value represents the temperature difference between the corresponding position of the edge region and the center position, that is, it reflects the temperature difference between the inside and outside. The larger the value, the greater the temperature gradient, that is, the more likely it is to form thermal stress. The product of the first difference value of each position of the edge region of the titanium alloy material at that time and the coupling between the formation of thermal stress and the flow of molten alloy liquid at that time is determined as the stress concentration tendency value of each position at that time. There is one stress concentration tendency value for each position of the edge region of the titanium alloy material at that time. By using the above method, the stress concentration tendency value of each position of the edge region of the titanium alloy material at each time in each cooling stage can be obtained.

[0056] The thermal stress evolution law at a certain position can be obtained by using the stress concentration tendency value obtained above, and then it can be evaluated whether the stress changes at different positions and different time points of the ingot have a certain synchronicity. The synchronization of thermal stress changes at different positions can help to reduce the stress concentration and crack risk.

[0057] Next, the present embodiment will still be described by taking the candidate ingot process as an example. The method provided by the present embodiment can be used for processing other ingot processes.

[0058] Specifically, for the cooling stage in the candidate ingot casting process: the stress concentration trend values of each position of the edge region at all times in the cooling stage are curve fitted to obtain a fitting curve corresponding to each position; each position of the edge region of the titanium alloy material corresponds to a fitting curve. The abscissa of the fitting curve is time, and the ordinate is the stress concentration trend value. Curve fitting is prior art, which will not be described in detail here. The maximum peak point of each fitting curve, i.e., the maximum value point, is obtained; the average slope value of the curve corresponding to the maximum peak point before each curve is taken as the measurement value of the stress change speed of the corresponding position of the edge region; it should be noted that there is a measurement value of the stress change speed for each position of the edge region. The process of obtaining the maximum peak point on the curve and calculating the average slope value of the curve both belong to prior art, which will not be described in detail here.

[0059] Further, according to the difference between the measurement values of the stress change speed of the two positions of the edge region and the difference between the data values of the corresponding maximum peak points, a stress synchronization factor of the edge region is obtained, and the difference between the measurement values of the stress change speed and the difference between the data values are positively correlated with the stress synchronization factor.

[0060] Wherein, the positive correlation means that the dependent variable will increase with the increase of the independent variable, and will decrease with the decrease of the independent variable, which can be an additive relationship, a multiplication relationship, etc., determined by actual application.

[0061] In this embodiment, a specific calculation formula of the stress synchronization factor is given, and the stress synchronization factor of the edge region in the cooling stage of the i-th ingot casting experiment can be expressed as: Wherein, represents the stress synchronization factor of the edge region in the cooling stage of the i-th ingot casting experiment, X represents the number of combinations of the two positions of the edge region, represents the difference between the data values of the two maximum peak points in the fitting curve corresponding to the xth group of positions of the edge region, represents the difference between the measurement values of the stress change speed of the two positions in the xth group of positions of the edge region.

[0062] It should be noted that any group of positions is composed of any two positions in all positions of the edge region. In this embodiment, the specific calculation method of the difference between the data values of the two maximum peak points is that the absolute value of the difference between the data values of the two maximum peak points is taken as the difference between the data values of the two maximum peak points. The specific calculation method of the difference between the measurement values of the stress change speed of the two positions is that the absolute value of the difference between the measurement values of the stress change speed of the two positions is taken as the difference between the measurement values of the stress change speed of the two positions.

[0063] The greater the difference between the data values of the maximum peak points in the fitting curves corresponding to different positions of the edge region, the greater the difference between the stress change rate measurement values, the worse the stress synchronization of the edge region of the titanium alloy during the solidification process, that is, the greater the stress synchronization factor of the edge region in the cooling stage.

[0064] The stress change synchronization performance of the edge region reflects the continuity of the transmission of external force or heat in the material. If the stress response synchronization of the edge region is poor, it will lead to insufficient release of thermal stress, thereby easily forming larger residual stress. The edge region may form coarse columnar crystals, while the center region may form fine equiaxed crystals, which in turn may cause the thermal expansion / contraction behavior of the edge region to be out of sync with the center region, causing the edge region of the ingot to bear additional bending or tensile stress.

[0065] Next, the fluctuation difference between the stress concentration trends of every two positions of the edge region in the cooling stage, and the temperature decay difference between the edge region and the center region, are used to measure the residual stress in the ingot process; if the residual stress in the ingot process is too large, it will cause micro-cracks in the local material, and there may be stress bursts in the stress concentration area, ultimately causing the material to break.

[0066] Based on the above characteristics, the embodiment next obtains a correction coefficient according to the difference between the average temperature decay rates of all positions of the edge region in the cooling stage of the candidate ingot process and the average temperature decay rate of the center position, and the stress synchronization factor, and the difference between the average temperature decay rates is positively correlated with the correction coefficient.

[0067] The positive correlation means that the dependent variable will increase as the independent variable increases, and the dependent variable will decrease as the independent variable decreases, which can be an additive relationship, a multiplicative relationship, etc., and is determined by actual application.

[0068] In the embodiment, a specific calculation formula of the correction coefficient is given, and the correction coefficient corresponding to the i th ingot experiment process can be represented as: wherein, represents the correction coefficient corresponding to the i th ingot experiment process, represents the stress synchronization factor of the edge region in the cooling stage of the i th ingot experiment process, represents the average temperature decay rate of all positions of the edge region in the cooling stage of the i th ingot experiment process, represents the average temperature decay rate of the center position in the i th ingot experiment process, represents a normalization function.

[0069] It should be noted that the average temperature decay rate is calculated according to the temperature decay rate, and the temperature decay rate is calculated according to the temperature value. The calculation of the temperature decay rate and the average value is a prior art, which will not be described in detail here.

[0070] The difference between the average temperature decay rate of all positions in the edge region of the cooling stage in the i-th ingot casting experiment and the average temperature decay rate of the center position is characterized, and the modification coefficient of the high gradient stress probability is determined in combination with the difference and the stress synchronization factor. When the difference is larger and the stress synchronization factor is larger, it indicates that the probability of residual stress generated in the cooling process is higher.

[0071] The formation of residual stress is accompanied by volume change of phase transition. For example, when the beta phase is converted into the alpha phase, the local volume expansion of the material can cause stress concentration and form residual stress. The residual stress and the newly introduced thermal stress can be superimposed, thereby strengthening or weakening the total stress state of the material. Residual stress is the result of incomplete release or rebalancing of thermal stress, and the probability value of residual stress occurrence can be regarded as a statistical description of the change rule of thermal stress, representing the degree to which thermal stress can evolve into residual stress under certain material or process conditions. The probability value is used to adjust the dynamic change of thermal stress, so as to make it more consistent with the characteristics of residual stress accumulation in the actual cooling process, thereby improving the physical accuracy of the subsequent simulation results of thermal stress field in the ingot casting process.

[0072] The high gradient stress probability generated at each time in the candidate ingot casting process is modified by using the modification coefficient corresponding to the candidate ingot casting process. Specifically, the product of the modification coefficient corresponding to the candidate ingot casting process and the high gradient stress probability generated at each time in the candidate ingot casting process is taken as the modified high gradient stress probability corresponding to each time in the candidate ingot casting process.

[0073] The high gradient stress probability generated at each time in each ingot casting experiment is modified by using the above method, and the modified high gradient stress probability at each time in each ingot casting experiment is obtained.

[0074] In step S4, the optimal scheme of the ingot is determined according to the distribution of the modified high gradient stress probability in each ingot casting experiment.

[0075] In this embodiment, the high gradient stress probability at each time in all ingot casting experiments is modified in step S3, and the modified high gradient stress probability is obtained. Next, the optimal scheme is screened based on the modified high gradient stress probability.

[0076] Specifically, for any once ingot casting experiment process: sort the high gradient stress probability of all time in the experiment process in chronological order, and record the sequence obtained at this time as the probability sequence corresponding to the ingot casting experiment process; the data in the sequence are fitted to obtain the high gradient stress probability curve corresponding to the ingot casting experiment process, the abscissa of the high gradient stress probability curve is time, and the ordinate is the corrected high gradient stress probability. Curve fitting is prior art, which will not be described in detail here.

[0077] The smoothness of the high gradient stress probability curve corresponding to each ingot casting experiment process is calculated, and each ingot casting experiment process has a smoothness, and the ingot casting experiment process corresponding to the minimum smoothness is selected from all ingot casting experiment processes to determine the optimal scheme of the ingot. The smoothness of the curve can be represented by indicators such as variance, standard deviation, curvature, etc., and in specific applications, the implementer can select according to the specific situation, which will not be described in detail here.

[0078] The process parameters of the above-mentioned selected optimal scheme of the ingot are used as the process parameters in the subsequent large-size titanium alloy bar ingot casting process.

[0079] In this embodiment, the temperature field in the large-size titanium alloy bar ingot casting process is simulated multiple times by changing the experimental conditions, the distribution of the temperature field can reflect the microstructure distribution state of the titanium alloy material in the ingot casting process, so as to determine the probability of high gradient stress in the ingot casting process; the thermal stress evolution law in the ingot casting process is analyzed in combination with the dynamic nature of the stress change of the temperature field in each cooling stage and the dynamic change of the pouring speed, and the coupling between the formation of thermal stress and the flow of molten alloy liquid is evaluated; then the residual stress in the ingot cooling process is reflected by the synchronous situation of the thermal stress change at different positions in the edge region of the cooling stage and the difference of the temperature decay rate between the inner and outer regions, so as to correct the high gradient stress probability in the ingot experiment process, and finally the optimal scheme of the ingot is selected according to the distribution of the corrected high gradient stress probability in each ingot experiment process. In this embodiment, the change results of thermal stress are compared by changing the experimental conditions, the optimal scheme is selected, and then optimization support is provided for the large-size titanium alloy bar ingot casting process, so that the subsequent large-size titanium alloy bar ingot casting process is more scientific and efficient, and the production quality of the large-size titanium alloy bar is improved.

[0080] An embodiment of a large-size titanium alloy bar low-stress gradient ingot casting system: Refer to Figure 2 which shows the structure block diagram of a large-size titanium alloy bar low-stress gradient ingot casting system provided by an embodiment of the present application, the system can include a data acquisition module, an evaluation module, a correction module and a screening module.

[0081] The data acquisition module is configured to acquire the temperature of the cast ingot material and the pouring speed during each casting experiment of the large-size titanium alloy bar, and the casting process includes a cooling stage. The evaluation module is configured to obtain the high-gradient stress probability of the temperature field at each time during each casting experiment according to the temperature distribution of the cast ingot material and the weight of the poured titanium alloy material, and evaluate the coupling between the formation of thermal stress and the flow of the molten alloy liquid in each cooling stage according to the difference between the change trends of the high-gradient stress probability and the pouring speed of the temperature field in the cooling stage. The correction module is configured to obtain the stress concentration trend of each position of the edge region of the titanium alloy material according to the temperature difference between the inner region and the outer region of the titanium alloy material at each time in the cooling stage and the coupling, and correct the high-gradient stress probability according to the fluctuation difference between the stress concentration trends of each two positions of the edge region in the cooling stage and the temperature attenuation difference between the edge region and the center region. The screening module is configured to determine the optimal scheme of the cast ingot according to the distribution of the corrected high-gradient stress probability during each casting experiment.

[0082] It should be understood that Figure 2 The structure diagram of the low-stress gradient casting system for the large-size titanium alloy bar and the modules thereof shown can be implemented in various ways. For example, in some embodiments, the system and the modules thereof can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented by using special logic; the software part can be stored in a memory and executed by a suitable instruction execution system, such as a microprocessor or a specially designed hardware. Those skilled in the art can understand that the above-mentioned method and system can be implemented by using computer executable instructions and / or included in processor control code, such as provided on a carrier medium, such as a magnetic disk, CD or DVD-ROM, a programmable memory, such as a read-only memory (firmware), or a data carrier, such as an optical or electronic signal carrier. The system and the modules thereof of the present specification can not only be implemented by hardware circuits, such as very large scale integrated circuits or gate arrays, semiconductors, such as logic chips, transistors, or programmable hardware devices, such as field programmable gate arrays, programmable logic devices, etc., but also by software, for example, executed by various types of processors, and also by a combination of the above-mentioned hardware circuits and software (for example, firmware).

[0083] More details about each of the above modules can be referred to other places in the present specification, and will not be described here.

[0084] In other embodiments, a low stress gradient ingot equipment for large-size titanium alloy bar is also provided, comprising a memory and a processor. The memory is configured to store executable program code, and the processor is configured to call and run the executable program code from the memory, so that the device performs the above-mentioned low stress gradient ingot method for large-size titanium alloy bar. The equipment can be a chip, an assembly or a module, the chip can include a connected processor and memory; wherein the memory is configured to store instructions, and when the processor calls and executes the instructions, the chip can perform the low stress gradient ingot method for large-size titanium alloy bar provided by the above-mentioned embodiments.

[0085] In other embodiments, a computer program product is also provided, which, when running on a computer, causes the computer to perform the above-mentioned related steps to realize the low stress gradient ingot method for large-size titanium alloy bar provided by the above-mentioned embodiments.

[0086] In other embodiments, a computer readable storage medium is also provided, which stores computer program code, and when the computer program code runs on a computer, the computer performs the above-mentioned related method steps to realize the low stress gradient ingot method for large-size titanium alloy bar provided by the above-mentioned embodiments.

[0087] Among them, the system, electronic equipment, computer program product and computer readable storage medium provided are used to execute the corresponding method provided above, so the beneficial effects they can achieve can refer to the beneficial effects in the corresponding method provided above, which will not be repeated here.

[0088] It should be noted that: the above only describes the preferred embodiments of the present application, and does not limit the present application, any modification, equivalent replacement, improvement, etc. within the principles of the present application, should be included in the protection scope of the present application.

Claims

1. A low stress gradient ingot casting method for large-size titanium alloy bars, characterized in that: The method comprises the following steps: Obtain the temperature and pouring rate of the ingot material during each ingot casting experiment of large-sized titanium alloy bars, including the cooling stage; Based on the temperature distribution of the ingot material and the weight of the cast titanium alloy material during each ingot casting experiment, the probability of high gradient stress generated by the temperature field at each moment during each ingot casting experiment was obtained; the difference in the changing trend between the high gradient stress probability of the temperature field and the casting speed during each cooling stage was combined to evaluate the coupling between the formation of thermal stress and the flow of the molten alloy liquid during each cooling stage; The stress concentration trend at each position in the edge region of the titanium alloy material is obtained based on the temperature difference between the inner and outer regions of the titanium alloy material at each moment in the cooling stage and the coupling property; the high gradient stress probability is corrected by utilizing the fluctuation difference between the stress concentration trends of every two positions in the edge region and the temperature attenuation difference between the edge region and the central region during the cooling stage; The optimal casting scheme is determined based on the distribution of the corrected high gradient stress probability during each casting experiment.

2. The low stress gradient ingot casting method for large-size titanium alloy bars according to claim 1, characterized in that: The method of obtaining the probability of high gradient stress generated by the temperature field at each moment during each ingot casting experiment based on the temperature distribution of the ingot material and the weight of the cast titanium alloy material during each ingot casting experiment comprises: The degree of disorder of the microstructure of the titanium alloy material at the time to be analyzed is obtained by combining the information entropy of the temperature values ​​of all positions on the ingot material at the time to be analyzed and the range of the temperature values ​​of all positions on the ingot material at the time to be analyzed; The probability of high gradient stress generated by the temperature field at the time to be analyzed is determined by comprehensively considering the degree of disorder of the microstructure of the titanium alloy material at the time to be analyzed and the weight change of the cast titanium alloy material at the time to be analyzed, wherein the degree of disorder and the weight change are both positively correlated with the probability of high gradient stress; The weight change of the cast titanium alloy material at the time to be analyzed is determined based on the weight of the cast titanium alloy material at the time to be analyzed and the time immediately before the time to be analyzed; The candidate ingot casting process is any ingot casting experimental process, and the time to be analyzed is any time in the candidate ingot casting process.

3. The low stress gradient ingot casting method for large-size titanium alloy bars according to claim 2, characterized in that: The method of comprehensively considering the degree of disorder of the microstructure of the titanium alloy material at the time to be analyzed and the weight change of the cast titanium alloy material at the time to be analyzed to determine the probability of high gradient stress generated by the temperature field at the time to be analyzed includes: The product of the disorder degree of the titanium alloy material microstructure at the time to be analyzed and the weight change of the cast titanium alloy material at the time to be analyzed is normalized to obtain the probability of high gradient stress generated by the temperature field at the time to be analyzed.

4. The low stress gradient ingot casting method for large-size titanium alloy bars according to claim 2, characterized in that: The differences in the changing trends between the high gradient stress probability of the temperature field and the pouring speed in each cooling stage are comprehensively analyzed to evaluate the coupling between the formation of thermal stress and the flow of the molten alloy liquid in each cooling stage, including: For any cooling phase: Calculating the mean square error between the high gradient stress probability of the temperature field and the pouring speed in any cooling stage; The coupling between the formation of thermal stress and the flow of the molten alloy liquid in any cooling stage is obtained according to the mean square error, and the mean square error is negatively correlated with the coupling.

5. The low stress gradient ingot casting method for large-size titanium alloy bars according to claim 2, characterized in that: The step of obtaining the stress concentration trend at each position of the edge region of the titanium alloy material based on the temperature difference between the inner and outer regions of the titanium alloy material at each moment in the cooling stage and the coupling property comprises: At any moment in any cooling phase: The difference between the temperature of each position in the edge region of the titanium alloy material at any moment and the temperature of the central region is used as the first difference value of each position in the edge region of the titanium alloy material at any moment; The product of the first difference value at each position in the edge region of the titanium alloy material at any moment and the coupling property is determined as the stress concentration trend value at the corresponding position at the corresponding moment.

6. The low stress gradient ingot casting method for large-size titanium alloy bars according to claim 5, characterized in that: The method of correcting the high gradient stress probability by utilizing the fluctuation difference between the stress concentration trends of every two positions in the edge region and the temperature attenuation difference between the edge region and the central region during the cooling stage includes: For the cooling stage during the candidate ingot casting process: Perform curve fitting on the stress concentration trend value at each position in the edge area at all times during the cooling stage to obtain the fitting curve corresponding to each position; The stress synchronization factor of the edge region is obtained based on the fluctuation difference between the fitting curves corresponding to each two positions in the edge region. Obtaining a correction coefficient based on the difference between the average temperature decay rate at all locations in the edge region and the average temperature decay rate at the center during the cooling stage of the candidate ingot casting process, and the stress synchronization factor, wherein the difference between the average temperature decay rates is positively correlated with the correction coefficient; The correction coefficient is used to correct the probability of high gradient stress generated at each moment in the candidate ingot casting process.

7. The low stress gradient ingot casting method for large-size titanium alloy bars according to claim 6, characterized in that: The stress synchronization factor of the edge region is obtained based on the fluctuation difference between the fitting curves corresponding to each position in the edge region, including: Obtain the maximum peak point of each fitting curve; use the average slope value of the curve corresponding to the maximum peak point on each curve as a measure of the stress change rate at the corresponding position of the edge area; The stress synchronization factor of the edge area is obtained based on the difference between the measured values ​​of the stress change rate at two positions in the edge area and the difference between the data values ​​of the corresponding maximum peak points. The difference between the measured values ​​of the stress change rate and the difference in the data values ​​are both positively correlated with the stress synchronization factor.

8. The low stress gradient ingot casting method for large-size titanium alloy bars according to claim 6, characterized in that: The method of using the correction coefficient to correct the probability of high gradient stress generated at each moment in the candidate ingot casting process includes: The product of the correction coefficient and the probability of high gradient stress generated at each moment in the candidate ingot casting process is used as the corrected high gradient stress probability corresponding to each moment in the candidate ingot casting process.

9. The low stress gradient ingot casting method for large-size titanium alloy bars according to claim 1, characterized in that: The method of determining the optimal ingot casting scheme according to the distribution of the corrected high gradient stress probability during each ingot casting experiment comprises: According to the smoothness of the high gradient stress probability curve corresponding to each ingot casting experiment process, the optimal ingot casting scheme is selected from all ingot casting experiments; The high gradient stress probability curve is obtained based on the corrected high gradient stress probability corresponding to all moments in each ingot casting experiment.

10. The low stress gradient ingot casting method for large-size titanium alloy bars according to claim 5, characterized in that: The acquisition of the difference between the temperature of each position in the edge area of ​​the titanium alloy material at any moment and the temperature of the central area includes: determining the absolute value of the difference between the temperature of each position in the edge area of ​​the titanium alloy material at any moment and the temperature of the central area as the difference between the temperature of each position in the edge area of ​​the titanium alloy material at any moment and the temperature of the central area.

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