Method and device for predicting crystal grain structure

Abstract

To improve prediction accuracy of a grain structure of a plastically processed metal material, in a prediction method of a grain structure.SOLUTION: A method of predicting a crystal grain structure of a plastically processed metal material comprises: an initial crystal grain shape setting step that sets the shape of initial crystal grains before plasticity processing; a first cross-sectional area calculation step of calculating a first cross-section area, which is the cross-section area of initial crystal grains; a second cross-section area calculation step for calculating a second cross-section area that is a cross-section of the initial crystal grains after deformation after recrystallized grain corrosion, by eliminating an area by which the initial crystal grains after deformation are corroded after deformation from the first cross-section area; a second crystal grain calculation step for calculating crystal grain diameters of the initial crystal grains after deformation after the recrystallized grain corrosion by converting a second cross-section area into a circle; and an average crystal grain diameter calculation step for averaging a crystal grain diameter of the initial crystal grains after deformation after recrystallized grain corrosion, and a crystal grain diameter of the recrystallized grain to calculate an average crystal grain diameter of the crystal grain structure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method and an apparatus for predicting a grain structure, and more particularly to a method and an apparatus for predicting a grain structure in a plastically processed metal material. [Background technology]

[0002] The mechanical properties of metal materials made of Ni alloys and the like depend on the crystal grain structure inside the metal material. For this reason, standard values ​​are often set for the crystal grain size of the crystal grain structure in metal materials such as engine parts. In plastic processing such as forging, the crystal grain size changes depending on the processing conditions, so processes are designed so that the crystal grain size meets the standard value. The quality of the designed process is judged by conducting prototypes. However, because prototypes are time-consuming and costly, the crystal grain size of the crystal grain structure is predicted in advance by simulation (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6032105 Summary of the Invention [Problem to be solved by the invention]

[0004] In a method for predicting the grain structure of a metal material that has been plastically processed, the average grain size of the grain structure is predicted based on the grain size of the initial grains and the grain size of the recrystallized grains that are formed during the plastic processing. Previous methods for predicting the grain structure have assumed that the grain size of the initial grains remains constant before and after the plastic processing, and that the initial grains are not eroded by the recrystallized grains. However, in reality, the initial grains are deformed by the plastic processing and are eroded by the recrystallized grains. Therefore, previous methods for predicting the grain structure may result in a decrease in the accuracy of the grain structure prediction.

[0005] Therefore, an object of the present disclosure is to provide a method and device for predicting a grain structure that can improve the accuracy of predicting a grain structure in a plastically processed metal material. [Means for solving the problem]

[0006] The method for predicting a crystal grain structure according to the present disclosure is a method for predicting a crystal grain structure in a metal material that has been subjected to plastic processing, and includes an initial crystal grain shape setting step for setting the shape of an initial crystal grain before plastic processing; and a first cross-sectional area calculation step for calculating a first cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation when the initial crystal grain is deformed by plastic processing. a first cross-sectional area calculation step of calculating strain generated in the initial crystal grain after deformation by finite element analysis, and calculating the lengths of the long and short sides of the rectangular cross section when the cross-sectional shape of the initial crystal grain after deformation is rectangular, and calculating the long and short axes of the elliptical cross section when the cross-sectional shape of the initial crystal grain after deformation is elliptical, from the calculated strain, to calculate the first cross-sectional area. and, Based on the recrystallization rate calculated using the JMAK model or obtained by observing the structure of recrystallized grains using an optical microscope a second cross-sectional area calculation step of calculating a second cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation after recrystallization by subtracting an area of ​​the initial crystal grain after deformation eroded by the recrystallized grain from the first cross-sectional area; By assuming that the shape of the initial grain after deformation after recrystallization is a circle, an initial crystal grain size calculation step of converting the second cross-sectional area into a circle and calculating the crystal grain size of the initial crystal grain after deformation after the recrystallized grain erosion; and Proportional distribution based on the unrecrystallized and recrystallized fractions calculated using the JMAK model and an average grain size calculation step of averaging the grains to calculate the average grain size of the grain structure.

[0008] In the method for predicting the crystal grain structure according to the present disclosure, the strain occurring in the initial crystal grains after deformation may be the maximum principal strain, the minimum principal strain, the intermediate principal strain, the thickness direction strain, or the width direction strain.

[0010] The crystal grain structure prediction device according to the present disclosure is a crystal grain structure prediction device that predicts the crystal grain structure in a metal material that has been subjected to plastic processing, and includes an initial crystal grain shape setting unit that sets the shape of an initial crystal grain before plastic processing, and a first cross-sectional area calculation unit that calculates a first cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation when the initial crystal grain is deformed by plastic processing. a first cross-sectional area calculation unit that calculates strain generated in the initial crystal grain after deformation by finite element analysis, and calculates the lengths of the long and short sides of the rectangular cross section when the cross-sectional shape of the initial crystal grain after deformation is rectangular, and calculates the long and short axes of the elliptical cross section when the cross-sectional shape of the initial crystal grain after deformation is elliptical, from the calculated strain, to calculate the first cross-sectional area. and, Based on the recrystallization rate calculated using the JMAK model or obtained by observing the structure of recrystallized grains using an optical microscopea second cross-sectional area calculation unit that calculates a second cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation after recrystallization by subtracting an area of ​​the initial crystal grain after deformation eroded by the recrystallized grain from the first cross-sectional area; By assuming that the shape of the initial grain after deformation after recrystallization is a circle, An initial crystal grain size calculation unit that converts the second cross-sectional area into a circle and calculates the crystal grain size of the initial crystal grain after deformation after the recrystallized grain erosion, and the crystal grain size of the initial crystal grain after deformation after the recrystallized grain erosion and the crystal grain size of the recrystallized grain. Proportional distribution based on the unrecrystallized and recrystallized fractions calculated using the JMAK model The apparatus includes an average grain size calculation unit that calculates the average grain size of the grain structure by averaging, and a control unit that controls the initial grain shape setting unit, the first cross-sectional area calculation unit, the second cross-sectional area calculation unit, the initial grain size calculation unit, and the average grain size calculation unit. [Effects of the Invention]

[0011] According to the above configuration, the accuracy of predicting the crystal grain structure in a plastically worked metal material is improved. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a flowchart illustrating a configuration of a method for predicting grain structure in an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram for explaining the crystal grain structure of a plastically worked metal material in an embodiment of the present disclosure. [Figure 3] FIG. 1 is a schematic diagram illustrating a method for predicting the grain structure of a uniaxially compressed metal cylinder according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a diagram illustrating a configuration of a grain structure prediction device in an embodiment of the present disclosure. [Figure 5] 1A and 1B are diagrams showing the grain distribution of a cylindrical specimen before and after hot uniaxial compression processing in an embodiment of the present disclosure. [Figure 6] 1 is a graph showing a comparison between experimental results and predicted results of average crystal grain size under various processing conditions in an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Fig. 1 is a flowchart showing the configuration of a method for predicting a crystal grain structure. The method for predicting a crystal grain structure includes an initial crystal grain shape setting step (S10), a first cross-sectional area calculation step (S12), a second cross-sectional area calculation step (S14), an initial crystal grain size calculation step (S16), and an average crystal grain size calculation step (S18).

[0014] The method for predicting the grain structure is a method for predicting the average grain size of the grain structure in a plastically processed metal material. The metal material is formed of a metal material that undergoes recrystallization, such as a Ni alloy, an Al alloy, a Cu alloy, or an Fe alloy. The metal material includes metal members and metal parts. The metal parts include aircraft engine parts such as compressor blades and disks. The plastic processing includes, for example, forging, rolling, extrusion, and drawing. The plastic processing may be hot processing or cold processing. The plastic processing may be processing alone, or may include heat treatment after processing.

[0015] Next, the grain structure of a plastically processed metal material will be described. Figure 2 is a schematic diagram for explaining the grain structure of a plastically processed metal material. More specifically, Figure 2(a) is a schematic diagram showing the grain structure in the initial state before plastic processing, Figure 2(b) is a schematic diagram showing the grain structure after processing, and Figure 2(c) is a schematic diagram showing the grain structure after heat treatment.

[0016] As shown in Figure 2(a), the initial grain structure before plastic processing consists of the initial grains before deformation and does not contain recrystallized grains. Recrystallized grains are newly formed grains due to the recrystallization of metals. During plastic processing or heat treatment, recrystallization nuclei are generated or grow according to the temperature and strain distribution inside the metal, eroding the initial grain structure. Depending on the cause and timing of recrystallization, recrystallization is classified as dynamic recrystallization (DRX), meta-dynamic recrystallization (MRX), and static recrystallization (SRX). For this reason, recrystallized grains are classified as dynamically recrystallized grains, meta-dynamically recrystallized grains, and statically recrystallized grains.

[0017] As shown in Figure 2(b), the crystal grain structure after processing is composed of, for example, initial crystal grains after deformation that have been eroded by recrystallized grains, and dynamically recrystallized grains. As shown in Figure 2(c), the crystal grain structure after heat treatment is composed of, for example, initial crystal grains after deformation that have been eroded by recrystallized grains, dynamically recrystallized grains, quasi-dynamically recrystallized grains, and statically recrystallized grains. The crystal grain structure of a metal material that has been plastically processed in this way is a mixed structure composed of initial crystal grains after deformation that have been eroded by recrystallized grains, and recrystallized grains.

[0018] The initial crystal grain shape setting step (S10) is a step of setting the shape of the initial crystal grains before plastic working. First, the shape of the initial crystal grains before plastic working is set. The initial crystal grains before plastic working are crystal grains in their initial state before being deformed by plastic working. The shape of the initial crystal grains before plastic working is not particularly limited, and can be set to, for example, a spherical shape, a rectangular parallelepiped shape, a polyhedron shape, etc. If the shape of the initial crystal grains before plastic working is set to a spherical shape or a rectangular parallelepiped shape, the shape of the initial crystal grains before plastic working becomes a simple shape, making it easier to calculate the average crystal grain size of the crystal grain structure. The shape of the initial crystal grains before plastic working may be set to a shape similar to the shape of crystal grains observed in the metal structure using an optical microscope, etc. For example, if the material before plastic working is an ingot, the shape of the initial crystal grains before plastic working may be spherical. If the material before plastic working is a plate, the shape of the initial crystal grains before plastic working may be rectangular. The grain size of the initial grains before the plastic working can be determined, for example, by observing the metal structure using an optical microscope or the like.

[0019] The first cross-sectional area calculation step (S12) is a step of calculating the first cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation when the initial crystal grain before plastic processing is deformed by the plastic processing. When a load is applied to the initial crystal grain before plastic processing, the initial crystal grain is deformed. This causes strain in the initial crystal grain, and for example, the aspect ratio of the initial crystal grain changes before and after processing. The shape change of the initial crystal grain due to this processing is evaluated based on the change in the cross-sectional shape of the initial crystal grain. The reason for evaluating the shape change of the initial crystal grain based on the change in cross-sectional shape is that observation and evaluation of the crystal grain structure is generally performed on a two-dimensional cross section. The cross section for evaluating the shape change of the initial crystal grain due to processing is not particularly limited, but it is preferable to use, for example, a cross section of the center of the initial crystal grain.

[0020] To evaluate the change in the cross-sectional shape of the initial crystal grain, a first cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation, is calculated. The first cross-sectional area can be calculated based on the cross-sectional shape of the initial crystal grain after deformation and the strain generated in the initial crystal grain after deformation. The cross-sectional shape of the initial crystal grain after deformation can be determined, for example, using a plastic processing simulation. The strain generated in the initial crystal grain after deformation can be calculated, for example, by finite element analysis or desk calculation using a plastic processing simulation. The strain generated in the initial crystal grain after deformation can be expressed as the maximum principal strain, minimum principal strain, intermediate principal strain, thickness direction strain, width direction strain, etc. Note that the plastic processing simulation can be performed using commonly available forming simulation software. For example, when performing a plastic processing simulation using a model in which one element corresponds to one crystal grain, the crystal grain shape after processing can be estimated from the element shape after processing such as compression processing. As such commonly used forming simulation software, for example, commercially available software such as "DEFORM" or "FORGE" can be used.

[0021] Next, parameters for determining the first cross-sectional area from the cross-sectional shape of the initial crystal grain after deformation are set. The parameters for determining the first cross-sectional area are calculated from the strain occurring in the initial crystal grain after deformation. For example, if the cross-sectional shape of the initial crystal grain after deformation is rectangular, the parameters for determining the first cross-sectional area are the long and short sides of the rectangular cross-section. The first cross-sectional area can be calculated by calculating the lengths of the long and short sides of the rectangular cross-section from the strain occurring in the initial crystal grain after deformation. Furthermore, if the cross-sectional shape of the initial crystal grain after deformation is elliptical, the parameters for determining the first cross-sectional area are the long and short sides of the elliptical cross-section. The first cross-sectional area can be calculated by calculating the lengths of the long and short sides of the elliptical cross-section from the strain occurring in the initial crystal grain after deformation. The length L in a predetermined direction of the initial crystal grain after deformation can be calculated, for example, from equation (1) where d0 is the crystal grain size of the initial crystal grain before deformation and ε is the strain in the predetermined direction of the initial crystal grain after deformation.

[0022]

number

[0023] The second cross-sectional area calculation step (S14) is a step of calculating the second cross-sectional area, which is the cross-sectional area of ​​the deformed initial crystal grain after recrystallization by subtracting the area of ​​the deformed initial crystal grain eroded by the recrystallized grain from the first cross-sectional area. After determining the area of ​​the deformed initial crystal grain eroded by the recrystallized grain, the second cross-sectional area is calculated by subtracting the area eroded by the recrystallized grain from the first cross-sectional area. As explained above with reference to Figures 2(a) to 2(c) , recrystallization occurs in plastically processed metal materials, so the initial crystal grains are not only deformed but also eroded by the recrystallized grains. Therefore, the second cross-sectional area is calculated by subtracting the area eroded by the recrystallized grains from the first cross-sectional area, which is the cross-sectional area of ​​the deformed initial crystal grain.

[0024] The area eroded by recrystallized grains can be determined based on the recrystallization ratio. The recrystallization ratio is the ratio of recrystallized grains to all crystal grains contained in the crystal grain structure. The recrystallization ratio is calculated as the sum of the dynamic recrystallization ratio, quasi-dynamic recrystallization ratio, and static recrystallization ratio. The dynamic recrystallization ratio is the ratio of dynamically recrystallized grains to all crystal grains contained in the crystal grain structure. The quasi-dynamic recrystallization ratio is the ratio of quasi-dynamic recrystallized grains to all crystal grains contained in the crystal grain structure. The static recrystallization ratio is the ratio of statically recrystallized grains to all crystal grains contained in the crystal grain structure. Note that, for example, if plastic processing is performed only by processing without heat treatment, quasi-dynamic recrystallization and static recrystallization do not occur, so the recrystallization ratio is the dynamic recrystallization ratio. The recrystallization ratio can be determined, for example, using the JMAK (Johnson-Mehl, Avrami, Kolmogorov) model. The recrystallization ratio may also be determined by observing the structure of recrystallized grains such as dynamically recrystallized grains using an optical microscope or the like and measuring the cross-sectional area ratio of the recrystallized grains.

[0025] The second cross-sectional area A' is the dynamic recrystallization rate X drx , the quasi-dynamic recrystallization rate X mrx , the static recrystallization rate X srxWhen the first cross-sectional area is A, it can be calculated using equation (2).

[0026]

number

[0027] The initial grain size calculation step (S16) is a step of converting the second cross-sectional area into a circle to calculate the grain size of the initial grain after deformation after recrystallization grain erosion. The grain size of a grain is usually expressed as the diameter of the grain when converted into a circle, regardless of the shape of the grain. Therefore, the second cross-sectional area is converted into a circle to calculate the grain size of the initial grain after deformation after recrystallization grain erosion. The grain size d'0 of the initial grain after deformation after recrystallization grain erosion can be calculated using equation (3) when the second cross-sectional area is A'.

[0028]

number

[0029] The average grain size calculation step (S18) is a step of calculating the average grain size of the grain structure by averaging the grain sizes of the initial grains after deformation after recrystallization erosion and the recrystallized grains. The grain structure of a plastically processed metal material is composed of a mixed structure of the initial grains after deformation after recrystallization erosion and the recrystallized grains. Therefore, the average grain size of the grain structure can be calculated by averaging the grain sizes of the initial grains after deformation after recrystallization erosion and the recrystallized grains.

[0030] The grain size of the initial crystal grains after deformation after recrystallization and the grain size of the recrystallized grains can be averaged, for example, based on the unrecrystallized fraction and the recrystallized fraction. The unrecrystallized fraction is the ratio of the initial crystal grains after deformation after recrystallization to all crystal grains contained in the crystal grain structure. The unrecrystallized fraction can be calculated by (1 - recrystallized fraction). The average grain size of the crystal grain structure can be calculated by proportionally allocating and averaging the grain sizes of the initial crystal grains after deformation after recrystallization and the recrystallized grains based on the unrecrystallized fraction and the recrystallized fraction.

[0031] When recrystallized grains are composed of dynamically recrystallized grains, quasi-dynamically recrystallized grains, and statically recrystallized grains, the average grain size of the recrystallized grains can be calculated by the sum of the dynamically recrystallized grain size x the dynamic recrystallization rate, the quasi-dynamically recrystallized grain size x the quasi-dynamic recrystallization rate, and the statically recrystallized grain size x the static recrystallization rate. When recrystallized grains are composed only of dynamically recrystallized grains, the average grain size of the recrystallized grains can be calculated by the dynamic recrystallized grain size x the dynamic recrystallization rate. The recrystallization rate and the recrystallized grain size can be calculated, for example, using the JMAK (Johnson-Mehl, Avrami, Kolmogorov) model.

[0032] Average grain size of the grain structure d ave is the grain size of the initial grain after deformation after recrystallization, d'0 is the dynamic recrystallization rate, and X is the drx , the quasi-dynamic recrystallization rate X mrx , the static recrystallization rate X srx , the dynamically recrystallized grain size is d drx , quasi-dynamic recrystallized grain size d mrx , static recrystallized grain d srx When this is the case, it can be calculated using equation (4). In this way, the average grain size of the grain structure of a metal material that has been plastically processed can be predicted.

[0033]

number

[0034] As described above, the method for predicting a grain structure in the above configuration predicts the average grain size of the grain structure by taking into account the deformation of the initial grains during plastic processing and the erosion of the initial grains by recrystallized grains, thereby improving the accuracy of prediction of the grain structure in a metal material that has been plastically processed.

[0035] Next, as a specific example, a method for predicting the crystal grain structure of a uniaxially compressed metal cylinder will be described. FIG. 3 is a schematic diagram for explaining the method for predicting the crystal grain structure of a uniaxially compressed metal cylinder. More specifically, FIG. 3(a) is a schematic diagram for explaining the initial crystal grain shape setting step (S10), FIG. 3(b) is a schematic diagram for explaining the first cross-sectional area calculation step (S12), FIG. 3(c) is a schematic diagram for explaining the second cross-sectional area calculation step (S14), and FIG. 3(d) is a schematic diagram for explaining the initial crystal grain size calculation step (S16). Of course, the plastic processing is not limited to uniaxial compression processing, and the metal material is not limited to a metal cylinder.

[0036] In the initial crystal grain shape setting step (S10), the shape of the initial crystal grains at the center of the metal cylinder before the uniaxial compression is set to a spherical shape. As shown in Fig. 3(a), the grain size of the initial crystal grains before the uniaxial compression is set to a diameter d0.

[0037] In the first cross-sectional area calculation step (S12), when the initial crystal grain before the uniaxial compression processing is deformed by the uniaxial compression processing, the first cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation, is calculated. If the shape of the initial crystal grain before the uniaxial compression processing is set to a spherical shape, the shape of the initial crystal grain is deformed into an ellipsoidal shape by the uniaxial compression processing. Therefore, as shown in FIG. 3(b), the cross-sectional shape of the center of the initial crystal grain after the uniaxial compression processing is deformed from the circular cross-section before the uniaxial compression processing to an elliptical cross-section. The strain generated in the initial crystal grain after deformation can be calculated by, for example, finite element analysis using a forming simulation of plastic processing, etc., to obtain the maximum principal strain ε 1st , minimum principal strain ε 3rd can be obtained.

[0038] Next, the major axis d1 and minor axis d3, which are parameters for calculating the cross-sectional area of ​​the elliptical cross section, are calculated based on the strain generated in the initial crystal grain after deformation. The major axis d1 of the elliptical cross section is calculated by the diameter d0 of the initial crystal grain before uniaxial compression and the maximum principal strain ε 1st The minor axis d3 of the elliptical cross section can be calculated using equation (5). The minor axis d3 is the diameter d0 of the initial grain before uniaxial compression and the minimum principal strain ε 3rd Therefore, it can be calculated using formula (6). The first cross-sectional area A, which is the cross-sectional area of ​​the initial crystal grain after deformation, can be calculated using formula (7).

[0039]

number

[0040]

number

[0041]

number

[0042] In the second cross-sectional area calculation step (S14), the area of ​​the initial crystal grain after deformation eroded by the recrystallized grains is subtracted from the first cross-sectional area to calculate the second cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation eroded by the recrystallized grains. As shown in FIG. 3(c), the initial crystal grain after deformation is eroded by the recrystallized grains. FIG. 3(c) shows an example in which the initial crystal grain after deformation is eroded by dynamically recrystallized grains, quasi-dynamically recrystallized grains, and statically recrystallized grains. The second cross-sectional area A' is calculated by subtracting the first cross-sectional area A and the dynamic recrystallization rate X. drx , the quasi-dynamic recrystallization rate X mrx , the static recrystallization rate X srx Then, it can be calculated using equation (8).

[0043]

number

[0044] In the initial crystal grain size calculation step (S16), the second cross-sectional area A' is converted into a circle to calculate the crystal grain size d'0 of the initial crystal grain after deformation after recrystallized grain erosion. The crystal grain size d'0 of the initial crystal grain after deformation after recrystallized grain erosion can be calculated using equation (9).

[0045]

number

[0046] In the average grain size calculation step (S18), the grain size d'0 of the initial grains after deformation after recrystallization and the grain size of the recrystallized grains are averaged based on the unrecrystallized rate and the recrystallized rate to calculate the average grain size d ave Calculate the dynamic recrystallization rate X drx , the quasi-dynamic recrystallization rate X mrx , the static recrystallization rate X srx , the dynamically recrystallized grain size is d drx , quasi-dynamically recrystallized grain size is d mrx , statically recrystallized grains d srx Then, the average grain size of the grain structure is d ave is calculated using equation (10). Equation (10) is obtained by substituting d'0 in equation (9) for d'0 in equation (4). Note that the second cross-sectional area A' obtained using equation (8) is substituted for the second cross-sectional area A' in equation (9), and the first cross-sectional area A obtained using equation (7) is substituted for the first cross-sectional area A in equation (8).

[0047]

number

[0048] Next, a grain structure prediction device for predicting the grain structure of a plastically processed metal material will be described. Fig. 4 is a diagram showing the configuration of a grain structure prediction device 10. The grain structure prediction device 10 includes an initial grain shape setting unit 12, a first cross-sectional area calculation unit 14, a second cross-sectional area calculation unit 16, an initial grain size calculation unit 18, an average grain size calculation unit 20, and a control unit 22.

[0049] The initial crystal grain shape setting unit 12 has a function of setting the shape of the initial crystal grain before plastic deformation. The first cross-sectional area calculation unit 14 has a function of calculating a first cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation when the initial crystal grain is deformed by plastic processing. The second cross-sectional area calculation unit 16 has a function of calculating a second cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation after recrystallization grain erosion, by subtracting the area of ​​the deformed initial crystal grain eroded by the recrystallized grains from the first cross-sectional area. The initial crystal grain size calculation unit 18 has a function of converting the second cross-sectional area into a circle to calculate the crystal grain size of the initial crystal grain after deformation after recrystallization grain erosion. The average crystal grain size calculation unit 20 has a function of calculating the average crystal grain size of the crystal grain structure by averaging the crystal grain size of the initial crystal grain after deformation after recrystallization grain erosion and the crystal grain size of the recrystallized grain.

[0050] The control unit 22 has a function of controlling the initial grain shape setting unit 12, the first cross-sectional area calculation unit 14, the second cross-sectional area calculation unit 16, the initial grain size calculation unit 18, and the average grain size calculation unit 20. The initial grain shape setting unit 12, the first cross-sectional area calculation unit 14, the second cross-sectional area calculation unit 16, the initial grain size calculation unit 18, the average grain size calculation unit 20, and the control unit 22 can be configured, for example, by a general computer system or the like.

[0051] The grain structure prediction device 10 may include a memory unit (not shown) and an output unit (not shown). The memory unit has a function of storing the shape of the initial grain, the first cross-sectional area, the second cross-sectional area, the grain size of the initial grain after deformation after recrystallization erosion, the average grain size of the grain structure, etc. The memory unit can be configured with a general memory, etc. The output unit has a function of outputting the average grain size of the grain structure, etc. The output unit can be configured with a general display, printer, etc.

[0052] As described above, the above-described configuration predicts the average grain size of the grain structure by taking into account the deformation of the initial grains during plastic processing and the erosion of the initial grains by recrystallized grains, thereby improving the prediction accuracy of the grain structure in a plastically processed metal material. Furthermore, the above-described configuration can take into account the deformation of the initial grains and the erosion of the initial grains by recrystallized grains, thereby improving the prediction accuracy of the grain structure in accordance with the plastic processing conditions even when the plastic processing conditions are different.

[0053] More specifically, the shape of the initial crystal grains after deformation changes depending on the plastic processing conditions. For example, when a metal material is rolled in one direction, the thickness of the crystal grains decreases as the strain in the rolling direction increases. However, as the plastic processing conditions become more complex, it becomes difficult to express the shape change of the initial crystal grains mathematically. Furthermore, because the initial crystal grains are eroded by recrystallized grains that are generated unevenly, the apparent crystal grain size of the initial crystal grains also becomes uneven. For this reason, the crystal grain size of the initial crystal grains has traditionally been assumed to be constant without considering the deformation of the initial crystal grains or the erosion by recrystallized grains. However, the above configuration makes it possible to consider the deformation of the initial crystal grains and the erosion of the initial crystal grains by recrystallized grains depending on the plastic processing conditions, thereby improving the accuracy of predicting the crystal grain structure.

[0054] Furthermore, with the above configuration, the prediction accuracy of the average grain size of the grain structure in the plastically worked metal material is improved, so that it is possible to reduce reworking and the number of prototypes required in the process design.

[0055] According to the above configuration, the first cross-sectional area calculation step can calculate the first cross-sectional area based on the cross-sectional shape of the initial crystal grain after deformation and the strain generated in the initial crystal grain after deformation. The cross-sectional shape of the initial crystal grain after deformation and the strain generated in the initial crystal grain after deformation can be easily determined using commonly available plastic processing forming simulation software, so calculations can be performed using existing programs without creating a new program. Thus, according to the above configuration, it is possible to predict the crystal grain structure in a plastic processed metal material in a shorter time and at lower cost than by prototyping.

[0056] According to the above configuration, the strain generated in the initial crystal grains after deformation can be the maximum principal strain, the minimum principal strain, the intermediate principal strain, the thickness direction strain, or the width direction strain. By selecting the type of strain generated in the initial crystal grains after deformation according to the processing conditions, it is possible to more accurately predict the crystal grain structure in a plastically processed metal material. Furthermore, by selecting the type of strain generated in the initial crystal grains after deformation, it is possible to balance the calculation load and the estimation accuracy and predict the crystal grain structure in a plastically processed metal material. [Example]

[0057] A cylindrical specimen made of a Ni-based superalloy was subjected to hot uniaxial compression, and a prediction test of the grain structure of the hot uniaxially compressed cylindrical specimen was conducted. No post-processing heat treatment was performed during the hot uniaxial compression. First, the metallographic structure of the cylindrical specimen was observed before and after the hot uniaxial compression by electron backscatter diffraction (EBSD) measurement. Figure 5 shows the grain distribution of the cylindrical specimen before and after the hot uniaxial compression. More specifically, Figure 5(a) shows the grain distribution before the hot uniaxial compression, and Figure 5(b) shows the grain distribution after the hot uniaxial compression.

[0058] The grain structure before the hot uniaxial compression process had an initial grain size d0 of 12 μm. The grain structure after the hot uniaxial compression process had an average grain size d ave The dynamic recrystallization rate was calculated using the JMAK (Johnson-Mehl, Avrami, Kolmogorov) model. drx is 0.49, and the dynamically recrystallized grain size d drx The thickness was 0.84 μm. Note that under these processing conditions, neither quasi-dynamic recrystallization nor static recrystallization occurred.

[0059] Next, a method for predicting the crystal grain structure in the example will be described. The shape of the initial crystal grains at the center of the cylindrical specimen before hot uniaxial compression was set to a spherical shape. The crystal grain size d0 of the initial crystal grains was set to 12 μm. When the initial crystal grains were deformed by hot uniaxial compression, the cross-sectional area of ​​the initial crystal grains after deformation was determined. The cross-sectional shape of the initial crystal grains after deformation was set to an elliptical shape. The maximum principal strain and minimum principal strain were used as the strain occurring in the initial crystal grains after deformation. The cross-sectional area of ​​the initial crystal grains after deformation after recrystallization grain erosion was determined by subtracting the area eroded by the recrystallized grains from the cross-sectional area of ​​the initial crystal grains after deformation. The recrystallization rate was calculated as the dynamic recrystallization rate X drx is 0.49, and the quasi-dynamic recrystallization rate X mrx 0, static recrystallization rate X srx was set to 0.

[0060] The cross-sectional area of ​​the initial crystal grains after deformation after recrystallization was converted into a circle, and the grain size of the initial crystal grains after deformation after recrystallization was calculated. The grain size of the initial crystal grains after deformation after recrystallization and the grain size of the recrystallized grains were then proportionally distributed and averaged based on the unrecrystallized rate and the recrystallized rate, and the average grain size of the crystal grain structure was calculated using equation (10). Dynamic recrystallization rate X drx is set to 0.49, and the dynamically recrystallized grain size d drx Since neither quasi-dynamic recrystallization nor static recrystallization occurred, the quasi-dynamic recrystallization rate X mrx and static recrystallization rate X srx was set to 0. As a result, the average grain size of the grain structure in the cylindrical specimens processed by hot uniaxial compression was 3.48 μm.

[0061] Next, a method for predicting the grain structure of a reference example will be described. The method for predicting the grain structure of a reference example differs from the method for predicting the grain structure of the examples in the following two points. In the method for predicting the grain structure of the reference example, predictions were made assuming that the shape of the initial grains remains constant before and after the hot uniaxial compression working. Furthermore, in the method for predicting the grain structure of the reference example, predictions were made assuming that the initial grains are not eroded by recrystallized grains. Other aspects were the same as in the method for predicting the grain structure of the examples.

[0062] More specifically, in the method for predicting the grain structure of the reference example, the shape of the initial grains was set to a spherical shape, and the grain sizes of the initial grains and the recrystallized grains were proportionally distributed and averaged based on the unrecrystallized rate and the recrystallized rate, and the average grain size of the grain structure was calculated using equation (11). The grain size d0 of the initial grains was set to 12 μm. The dynamic recrystallization rate X drx is set to 0.49, and the dynamically recrystallized grain size d drx Since neither quasi-dynamic recrystallization nor static recrystallization occurred, the quasi-dynamic recrystallization rate X mrx and static recrystallization rate X srx was set to 0. As a result, the average grain size of the grain structure of the cylindrical specimen processed by hot uniaxial compression was 6.53 μm.

[0063]

number

[0064] In the grain structure prediction method of the Reference Example, the difference between the predicted average grain size of 6.53 μm and the experimental average grain size of 2.94 μm was 3.59 μm. On the other hand, in the grain structure prediction method of the Example, the difference between the predicted average grain size of 3.48 μm and the experimental average grain size of 2.94 μm was 0.54 μm. Thus, the difference between the predicted and experimental average grain size was reduced from 3.59 μm to 0.54 μm. This result demonstrates that the grain structure prediction method of the Example has improved prediction accuracy for the average grain size of the grain structure compared to the grain structure prediction method of the Reference Example.

[0065] Next, the reason for the improved prediction accuracy of the grain structure in the examples will be explained. Figures 5(a) and 5(b) show that the shape of the initial grains changes due to compressive deformation caused by hot uniaxial compression. However, the grain structure prediction method of the reference example does not consider the change in shape of the initial grains before and after hot uniaxial compression, which is thought to have reduced the prediction accuracy of the average grain size of the grain structure. On the other hand, the grain structure prediction method of the examples considers the change in shape of the initial grains before and after hot uniaxial compression, which is thought to have improved the prediction accuracy of the average grain size of the grain structure. Furthermore, the grain structure prediction method of the reference example predicted that the initial grains would not be eroded by recrystallized grains, while the grain structure prediction method of the examples predicted that the initial grains would be eroded by recrystallized grains. The grain structure prediction method of the examples considers the erosion of recrystallized grains in the initial grains, which is thought to have further improved the prediction accuracy of the average grain size of the grain structure.

[0066] Next, the grain structure of the cylindrical specimen was predicted by changing the processing conditions of the hot uniaxial compression processing. The processing conditions were nine in total, with three conditions for the processing temperature and three conditions for the strain generated in the cylindrical specimen. The processing temperature was T A , T B , T C The relationship between these processing temperatures is T A <T B <T C The strain generated in the cylindrical specimen is ε a , ε b , ε c The relationship between the magnitude of these strains is ε a <ε b <ε c For each processing condition, the average crystal grain size was measured by observing the metal structure with an optical microscope, and the average crystal grain size was predicted by the method for predicting the crystal grain structure of the above-mentioned Example and the method for predicting the crystal grain structure of the above-mentioned Reference Example.

[0067] Figure 6 is a graph showing a comparison of the experimental results and predicted results for the average grain size under each processing condition. In the graph of Figure 6, the horizontal axis represents each processing condition, the vertical axis represents the average grain size, and the experimental and predicted values ​​for the average grain size are shown in a bar graph. Under all processing conditions, the difference between the experimental and predicted values ​​for the average grain size was smaller with the grain structure prediction method of the Example than with the grain structure prediction method of the Reference Example. This result demonstrates that even when the processing conditions of the hot uniaxial compression processing are changed, the grain structure prediction method of the Example improves the prediction accuracy of the average grain size in the grain structure. [Explanation of symbols]

[0068] 10. Grain structure prediction device 12 Initial grain shape setting section 14 First cross-sectional area calculation section 16 Second cross-sectional area calculation section 18 Initial grain size calculation section 20 Average grain size calculation section 22 Control Unit

Claims

1. A method for predicting grain structure in a plastically worked metal material, comprising: an initial crystal grain shape setting step of setting the shape of the initial crystal grains before plastic working; a first cross-sectional area calculation step of calculating a first cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation when the initial crystal grain is deformed by plastic processing, in which strain occurring in the initial crystal grain after deformation is calculated by finite element method analysis, and calculating the lengths of the long and short sides of the rectangular cross section when the cross-sectional shape of the initial crystal grain after deformation is rectangular, or the long and short axes of the elliptical cross section when the cross-sectional shape of the initial crystal grain after deformation is elliptical, from the calculated strain to calculate the first cross-sectional area; a second cross-sectional area calculation step of calculating a second cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation after recrystallization by subtracting an area of ​​the initial crystal grain after deformation eroded by the recrystallized grain from the first cross-sectional area based on a recrystallization rate calculated by a JMAK model or obtained by observing the structure of the recrystallized grain with an optical microscope; an initial crystal grain size calculation step of calculating the crystal grain size of the initial crystal grain after deformation after recrystallization grain erosion by converting the second cross-sectional area into a circle by assuming that the shape of the initial crystal grain after deformation after recrystallization grain erosion is a circle; an average grain size calculation step of calculating an average grain size of the crystal grain structure by proportionally allocating and averaging the grain sizes of the initial crystal grains after deformation following the recrystallization and the recrystallization based on the unrecrystallized rate and the recrystallized rate calculated using the JMAK model; A method for predicting grain structure comprising:

2. 2. The method for predicting grain structure according to claim 1, The method for predicting a crystal grain structure uses the maximum principal strain, minimum principal strain, intermediate principal strain, thickness direction strain, or width direction strain as the strain occurring in the initial crystal grains after the deformation.

3. A grain structure prediction device for predicting a grain structure in a plastically processed metal material, comprising: an initial crystal grain shape setting unit that sets the shape of the initial crystal grains before plastic working; a first cross-sectional area calculation unit that calculates a first cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation when the initial crystal grain is deformed by plastic processing, by calculating strain generated in the initial crystal grain after deformation by finite element method analysis, and calculating the lengths of the long and short sides of the rectangular cross section when the cross-sectional shape of the initial crystal grain after deformation is rectangular, or the long and short axes of the elliptical cross section when the cross-sectional shape of the initial crystal grain after deformation is elliptical, from the calculated strain to calculate the first cross-sectional area; a second cross-sectional area calculation unit that calculates a second cross-sectional area, which is the cross-sectional area of ​​the initial crystal grain after deformation after recrystallization by subtracting an area of ​​the initial crystal grain after deformation eroded by the recrystallized grain from the first cross-sectional area based on a recrystallization rate calculated using a JMAK model or obtained by observing the structure of the recrystallized grains using an optical microscope; an initial crystal grain size calculation unit that calculates the crystal grain size of the initial crystal grain after deformation after recrystallization grain erosion by converting the second cross-sectional area into a circle by assuming that the shape of the initial crystal grain after deformation after recrystallization grain erosion is a circle; an average grain size calculation unit that calculates an average grain size of the crystal grain structure by proportionally allocating and averaging the grain sizes of the initial crystal grains after deformation after the recrystallization and the recrystallization based on the unrecrystallized rate and the recrystallized rate calculated by the JMAK model; a control unit that controls the initial crystal grain shape setting unit, the first cross-sectional area calculation unit, the second cross-sectional area calculation unit, the initial crystal grain size calculation unit, and the average crystal grain size calculation unit; A grain structure prediction device comprising:

Images