Method and device for quantifying quench cracking criteria

Abstract

Identify the quench cracking criteria for heterogeneous steel materials. [Solution] A method for quantifying quenching cracking criteria includes acquiring quenching experiment results, performing quenching analysis that takes heterogeneity into account to acquire a maximum stress for evaluation, and identifying stress criteria for quenching cracking by correlating the quenching experiment results with the maximum stress for evaluation. The analysis includes creating a global finite element model (2) assuming that each of a plurality of test pieces is made of a homogeneous material, performing a global analysis simulating quenching using the model (2) to acquire strain and temperature histories, extracting a plurality of evaluation elements (2a), creating a local finite element model (3) in which a heterogeneous component distribution is set for each of the elements (2a), inputting the history into the model (3) to perform a local analysis to acquire a local maximum stress from each of the plurality of evaluation elements (2a), and acquiring the largest value of the local maximum stresses as the maximum stress for evaluation.

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for quantifying quenching crack criteria. [Background technology]

[0002] Although the strength of steel forgings is ensured by quenching, quench cracks can occur due to the influence of temperature distribution during heat treatment. To prevent quench cracks, it is necessary to optimize the manufacturing conditions. To optimize the manufacturing conditions, it is necessary to confirm the stress behavior within the steel forging during quenching. However, since it is difficult to grasp this stress behavior experimentally, numerical analysis is generally used (see Non-Patent Document 1).

[0003] In the ingot-making process, segregation inevitably occurs when molten steel solidifies, resulting in a non-uniform distribution of elements in steel forgings. There are several types of segregation in steel forgings, such as V-segregation and inverted V-segregation. Non-Patent Document 2 experimentally clarified that inverted V-segregation, which occurs when manufacturing large steel ingots, increases the risk of cracking during heat treatment. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] "Relationship between Transient Stress and Quenching Crack Occurrence during Cylinder Quenching," by Fukutani, M. et al., Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol. 6 (2007) [Non-patent document 2] "Relationship between Segregation Zones and Quench Cracks in Large Steel Forgings," Transactions of the Japan Society of Mechanical Engineers, Vol. 83, No. 845 (2017) Summary of the Invention [Problem to be solved by the invention]

[0005] Non-Patent Document 1 proposes a method for identifying quench cracking criteria, but the study is limited to homogeneous materials. Non-Patent Document 2 also clarifies through an experimental approach that the risk of cracking increases in heterogeneous steel materials containing inverted V segregation, but does not quantitatively and in detail consider the stresses that occur and the crack initiation limits. Therefore, there is room for improvement in identifying quench cracking criteria for heterogeneous steel materials.

[0006] An object of the present invention is to identify quench cracking criteria for heterogeneous steel materials. [Means for solving the problem]

[0007] The present invention provides Obtaining the results of quenching experiments to confirm the presence or absence of quench cracks on multiple test pieces made of heterogeneous steel materials and having different shapes, performing a hardening analysis that takes into account heterogeneity on each of the plurality of test pieces to obtain a maximum stress for evaluation; The stress criteria for the occurrence of quench cracks are identified by correlating the quenching experiment results with the maximum stress for evaluation. This includes: The quenching analysis is creating an overall finite element model assuming that each of the plurality of test pieces is a homogeneous material; performing a global analysis simulating hardening using the global finite element model to obtain strain and temperature histories of each element of the global finite element model; extracting a plurality of evaluation elements to be evaluated from all elements constituting the entire finite element model; creating a local finite element model in which a non-uniform component distribution is set for each of the plurality of evaluation elements; acquiring a local maximum stress from each of the plurality of evaluation elements by inputting the corresponding history into the local finite element model and performing a local analysis; The largest value among the local maximum stresses is obtained as the maximum stress for evaluation. The present invention provides a method for quantifying quench cracking criteria, including:

[0008] This method allows for the identification of quench cracking criteria by correlating the occurrence or nonoccurrence of quench cracking in quenching experiments with the maximum evaluation stress in quenching analysis. The maximum evaluation stress is calculated in two stages: global analysis and local analysis. Based on the strain and temperature change history calculated by global analysis (e.g., heat transfer, phase transformation, and thermo-elastic-plastic analysis), the local maximum stress is calculated for each evaluation element with a heterogeneous component distribution by local analysis (e.g., thermo-elastic-plastic analysis). The maximum value of the obtained local maximum stresses for each evaluation element is used as the maximum evaluation stress. Then, by checking the maximum evaluation stress in quenching analysis for test pieces in which quench cracking occurred and test pieces in which it did not occur in the quenching experiment, the stress range in which quench cracking and the stress range in which it does not occur (quench cracking criteria) can be identified with high accuracy.

[0009] The local maximum stress may be acquired only when the martensite fraction is equal to or greater than a predetermined value.

[0010] This method allows the local maximum stress to be confirmed only when the martensite fraction is higher than a certain level and the risk of quenching cracking is high, thereby efficiently identifying the quenching cracking criteria. Furthermore, since the risk of quenching cracking is low when the martensite fraction is less than a certain level, it is possible to prevent erroneous detection of high stress occurring when the risk of quenching cracking is low. Here, the predetermined martensite fraction or higher may be 80% or higher.

[0011] The non-uniform component distribution may include a segregation distribution.

[0012] This method allows for the identification of quench cracking criteria by taking into account the heterogeneous distribution of elements due to segregation. In particular, the heterogeneous distribution of elements due to segregation has a large effect on quench cracking, and identifying quench cracking criteria by taking segregation into account ensures high identification accuracy.

[0013] The segregation distribution may include inverted V segregation.

[0014] This method allows identification of quench cracking criteria for inverted V segregation, which has a high risk of quench cracking among segregations.

[0015] an experiment result acquisition unit that acquires quenching experiment results that confirm the presence or absence of quench cracks on a plurality of test pieces made of heterogeneous steel materials and having different shapes; an analysis result acquisition unit that acquires a maximum stress for evaluation by performing a quenching analysis that takes into account heterogeneity on each of the plurality of test pieces; an identification unit that identifies stress criteria for quench crack occurrence by correlating the quenching experiment results with the maximum stress for evaluation; Equipped with The analysis result acquisition unit an overall analytical model creation unit that creates an overall finite element model by assuming that each of the plurality of test pieces is made of a homogeneous material; an overall analysis calculation unit that acquires strain and temperature histories of each element of the test piece by performing an overall analysis that simulates quenching using the overall finite element model; an evaluation element extraction unit that extracts a plurality of evaluation elements to be evaluated from all elements that constitute the entire finite element model; a local analysis model creation unit that creates a local finite element model in which a non-uniform component distribution is set for each of the plurality of evaluation elements; a local analysis calculation unit that inputs the corresponding history into the local finite element model and performs a local analysis to acquire a local maximum stress from each of the plurality of evaluation elements; a maximum stress for evaluation acquisition unit that acquires the largest value of the local maximum stresses as the maximum stress for evaluation; The present invention provides a quantification device for quench cracking criteria, which has the following characteristics: [Effects of the Invention]

[0016] According to the present invention, the quench cracking criteria of a heterogeneous steel material can be identified. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic configuration diagram of a quench crack criteria quantification device according to an embodiment of the present invention. [Figure 2] FIG. 1 is a perspective view showing an overall finite element model of a test specimen. [Figure 3] FIG. [Figure 4] Schematic cross-section of a steel ingot showing various segregations. [Figure 5] Local finite element model considering inverse V segregation. [Figure 6] 3 is a flowchart of a method for quantifying quench crack criteria according to an embodiment of the present invention. [Figure 7] 7 is a flowchart for obtaining the hardening analysis results of FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0019] FIG. 1 shows a schematic configuration diagram of a quench crack criteria quantification device 1 according to one embodiment of the present invention.

[0020] The quench crack criterion quantification device 1 of this embodiment includes a control unit (processor) 10, an input unit 20, an output unit 30, and a memory unit 40. The control unit 10 performs calculation processing and controls the entire device. The input unit 20 generates or receives input data for the device and is composed of, for example, a keyboard, a mouse, a touch panel, etc. The output unit 30 displays processing results by the control unit 10 and is composed of, for example, a liquid crystal display, an organic electroluminescence (EL) display, a plasma display, etc. The memory unit 40 stores programs running on the control unit 10 and parameter data required for the finite element analysis described below. The control unit 10, the input unit 20, and the output unit 30 are interconnected by an appropriate bus. Specifically, the quench crack criterion quantification device 1 can be composed of, for example, an information processing device such as a desktop computer, a laptop computer, a workstation, or a tablet terminal, or a printed circuit board with equivalent functions.

[0021] The quench crack criteria quantification device 1 realizes predetermined functions by reading data and programs stored in the memory unit 40 and performing various calculation processes. The programs executed by the quench crack criteria quantification device 1 and necessary data may be provided from an external device using a communication unit that communicates according to a predetermined communication standard, or may be stored on a portable recording medium.

[0022] The control unit 10 includes, as its functional components, an experiment result acquisition unit 11, an analysis result acquisition unit 12, and an identification unit 13. These are realized by the cooperation of hardware and software. These may also be interpreted as corresponding circuits.

[0023] The experimental result acquisition unit 11 acquires the results of a quenching experiment in which the presence or absence of quench cracks is confirmed for a plurality of test pieces made of heterogeneous steel materials and having different shapes. For example, the plurality of test pieces may be made of the same steel material and may have cylindrical shapes with various diameters. Due to the differences in shape, some test pieces will develop quench cracks during quenching and some will not. The quenching experiment results may be stored as data in the memory unit 40 or input from the input unit 20.

[0024] The analysis result acquisition unit 12 acquires the maximum stress for evaluation, which will be described later, for each of the plurality of test pieces by performing a hardening analysis that takes into account heterogeneity. In the hardening analysis, hardening is simulated in two stages, a global analysis and a local analysis, and the maximum stress for evaluation is calculated.

[0025] The analysis result acquisition unit 12 includes an overall analysis model creation unit 12a, an overall analysis calculation unit 12b, an evaluation element extraction unit 12c, a local analysis model creation unit 12d, a local analysis calculation unit 12e, and an evaluation maximum stress acquisition unit 12f.

[0026] The overall analytical model creation unit 12a creates an overall finite element model 2 on the assumption that the test piece is made of a homogeneous material.

[0027] Fig. 2 is a perspective view showing the entire finite element model 2 of the test piece. In Fig. 2, the horizontal direction is indicated by the XY direction, and the height direction (upward) is indicated by the Z direction.

[0028] In this embodiment, the test piece is assumed to be cylindrical, and in order to reduce analysis time, a one-eighth model of the cylindrical test piece is divided into finite elements, taking symmetry into consideration, to create the overall finite element model 2.

[0029] In the global finite element model 2, the analysis conditions set include physical properties such as the density, specific heat, and thermal conductivity of the steel, the TTT (Time Temperature Transformation) diagram, the heat transfer coefficient, the SS (Stress Strain) curve, the linear expansion coefficient, and the transformation expansion amount, as well as quenching conditions such as the quenching temperature.

[0030] The global analysis calculation unit 12b acquires the strain and temperature history of each element by performing a global analysis (analysis of heat transfer, phase transformation, and thermo-elastic-plasticity) that simulates quenching of the test piece using the global finite element model 2. For example, the global analysis may be an analysis of phase transformation, heat transfer, and thermo-elastic-plasticity, such as simulating quenching of a 900°C test piece in water at room temperature. In this way, the global analysis is performed by the global analysis model creation unit 12a and the global analysis calculation unit 12b before the local analysis.

[0031] The evaluation element extraction unit 12c extracts multiple evaluation elements to be evaluated from all elements constituting the entire finite element model 2. The multiple evaluation elements are elements to be subjected to subsequent local analysis. The number of multiple evaluation elements can be set arbitrarily.

[0032] FIG. 3 is a front view showing a plurality of evaluation elements 2a (see the shaded areas).

[0033] The multiple evaluation elements 2a are extracted evenly from various locations in the upper half of the model on the front (XZ plane) of the overall finite element model 2. The reason for extracting from the upper half of the model is that the analysis results are symmetrical from top to bottom under these analysis conditions, and therefore extraction from the lower half is omitted.

[0034] FIG. 4 is a schematic cross-sectional view of a steel ingot 4 showing various types of segregation. This shows a typical distribution of elemental segregation that occurs during the casting of a steel ingot 4 for large forging. Note that hatching indicating a cross-sectional view has been omitted to ensure clarity of the illustration.

[0035] No elemental segregation zones are present in the surface layer of the steel ingot 4, but a segregation zone called an inverted V-shaped segregation zone 4a, where various elements such as carbon are significantly concentrated, is present between the surface layer and the center of the steel ingot 4. Furthermore, in the center of the steel ingot 4, a V-shaped segregation zone 4b, where various elements are concentrated similarly to the inverted V-shaped segregation zone 4a, is present in the upper layer, while a negative segregation zone 4c, where the values ​​of various elements are lower than in other regions, is present in the lower layer. Thus, the steel ingot 4 becomes a heterogeneous material with a heterogeneous elemental distribution due to segregation. Such heterogeneity must be taken into consideration because it affects quench cracking.

[0036] The local analytical model creation unit 12d creates a local finite element model in which a non-uniform component distribution is set for each of the multiple evaluation elements 2a. Here, the local analytical model creation unit 12d creates a local finite element model that takes inverse V segregation into consideration.

[0037] Figure 5 shows the local finite element model 3 that takes into account the inverse V segregation.

[0038] The local finite element model 3 is formed by further dividing one of the multiple evaluation elements 2a into multiple elements. Figure 5 shows the top surface of the local finite element model 3, with the same cross section continuing in the height direction (Z direction). In the local finite element model 3, a carbon component concentration is set for each element. In Figure 5, the carbon component concentration is shown in shades of gray, with white areas having a high carbon component concentration and black areas having a low carbon component concentration. Note that in Figure 5, the shaded display makes it difficult to see each element.

[0039] In the illustrated example, the local finite element model 3 has an elliptical inverted-V segregation region 3a with a high carbon concentration in the center, and a normal region 3b with a low carbon concentration and no segregation outside the inverted-V segregation region 3a. The inverted-V segregation region 3a can be seen as a stripe in the cross section shown in FIG. 4 (see inverted-V segregation zone 4a), but when viewed from above, it appears as a dot, and when further enlarged, the dot becomes elliptical, as shown in FIG. 5. Note that when creating the local finite element model 3 for segregation other than inverted-V segregation, such as V segregation or microsegregation, or other heterogeneous component distributions, the elliptical shape may be different.

[0040] Furthermore, physical property values ​​such as a time-temperature transformation (TTT) diagram, a stress-strain (SS) curve, a linear expansion coefficient, a transformation expansion amount, and an Ms point (martensitic transformation start point) are set as analysis conditions in the local finite element model 3. The Ms point is set according to the carbon concentration.

[0041] The local analysis calculation unit 12e inputs the strain and temperature change history of the corresponding evaluation element 2a obtained in the global analysis into the local finite element model 3 and performs a local analysis to obtain the local maximum stress from each of the multiple evaluation elements 2a. Specifically, in the local analysis, the strain increments and temperature increments of each of the multiple evaluation elements 2a output in the global analysis are applied to all integration points of the local finite element model 3, and a thermo-elastic-plastic analysis based on the homogenization method is performed. Here, thermal strain is calculated based on the temperature increment, and transformation strain according to the temperature history and component values ​​is calculated and taken into account. Data calculated by physical property calculation software is used for the TTT diagram, and martensitic transformation is expressed using the Koistinen-Marburger equation, etc. This allows the martensite fraction to be obtained. Because quench cracking is a brittle fracture and is thought to occur after the end of martensitic transformation, it is preferable to evaluate it only when the martensite fraction is above a certain level (e.g., 80% or higher). The local maximum stress indicates the maximum stress in the local finite element model 3. Therefore, one local maximum stress is obtained from each of the multiple evaluation elements 2a.

[0042] The maximum stress for evaluation acquisition unit 12f acquires the largest value of the local maximum stresses of each of the plurality of evaluation elements 2a as the maximum stress for evaluation. This acquisition of the maximum stress for evaluation is performed for each of the plurality of test pieces on which the hardening experiment was performed, and the maximum stress for evaluation corresponding to each of the plurality of test pieces is acquired.

[0043] The identification unit 13 identifies the stress criteria for quenching crack occurrence by associating the quenching experiment results acquired by the experiment result acquisition unit 11 with the maximum evaluation stress acquired by the analysis result acquisition unit 12. For example, suppose that a quenching experiment was conducted on cylindrical test pieces whose diameters were changed in 4 mm increments, and the results showed that no quenching cracks occurred in the test pieces with a diameter of 4 mm, but quenching cracks occurred in the test pieces with a diameter of 8 mm or more. If the maximum evaluation stress for the 4 mm diameter test piece is 100 MPa and the maximum evaluation stress for the 8 mm diameter test piece is 200 MPa, the stress criteria for quenching crack occurrence can be identified as being in the range of 100 MPa to 200 MPa.

[0044] The method for quantifying quench crack criteria in this embodiment will be described with reference to FIGS.

[0045] Fig. 6 shows a flowchart of a method for quantifying quench crack criteria according to one embodiment of the present invention, and Fig. 7 shows a flowchart related to the acquisition of quench analysis results (step S6-2) in Fig. 6.

[0046] Referring to FIG. 6, first, the results of the quenching experiment are acquired (step S6-1). In this quenching experiment, cylindrical steel test pieces measuring φ20×60 mm, φ12×36 mm, φ8×24 mm, and φ4×12 mm were each held at 900°C for 30 minutes and then quenched by water cooling. As a result, quenching cracks occurred only in the φ4 test piece, and substantially no quenching cracks occurred in the other test pieces (φ20, φ12, and φ8). Therefore, it was confirmed that the transition point between the occurrence of quenching cracks and the non-occurrence of quenching cracks was between the φ4 and φ8 test pieces. The experimental results can be acquired by the experimental result acquisition unit 11.

[0047] Next, the maximum stress for evaluation is acquired as the hardening analysis result (step S6-2). The analysis result can be acquired by the analysis result acquisition unit 12.

[0048] Referring to FIG. 7, when obtaining the maximum stress for evaluation as the quenching analysis result (step S6-2), a global finite element model 2 (see FIG. 2) is created (step S7-1), and a global analysis calculation is performed (step S7-2). The global finite element model 2 can be created by the global analysis model creation unit 12a. The global analysis calculation can be performed by the global analysis calculation unit 12b. Here, as the quenching analysis, a global analysis simulating water quenching from 900°C was performed using the global finite element models 2 of test pieces with dimensions of φ4×12 mm and φ8×24 mm, and the strain and temperature history of each element during the heat treatment was obtained.

[0049] Next, a plurality of evaluation elements 2a are extracted from the overall finite element model 2 (step S7-3). The plurality of evaluation elements 2a can be extracted by the evaluation element extraction unit 12c. Here, 78 elements were extracted as the plurality of evaluation elements 2a (see FIG. 3). In particular, the plurality of evaluation elements 2a were not extracted only from specific locations of the overall finite element model 2, but were extracted evenly from the entirety of a predetermined cross section. Specifically, the plurality of evaluation elements 2a were extracted every 3 to 4 elements in the radial direction (X direction) and every 3 to 4 elements in the height direction (Z direction).

[0050] Next, a local finite element model 3 is created (step S7-4), and a local analysis calculation is performed (step S7-5). The local finite element model 3 may be created by the local analysis model creation unit 12d. The local analysis calculation may be performed by the local analysis calculation unit 12e. Then, the largest value of the local maximum stresses obtained by the local analysis is acquired as the maximum evaluation stress (step S7-6). The maximum evaluation stress may be acquired by the maximum evaluation stress acquisition unit 12f. Here, a local finite element model 3 (see FIG. 5) for a case where inverse V segregation is present for multiple (78 here) evaluation elements 2a is created, and a local analysis to obtain the local maximum stress is performed using the local finite element model 3. Then, the maximum value from the multiple (78 here) obtained local maximum stresses is acquired as the maximum evaluation stress. As a result, the maximum evaluation stress for a φ4×12 mm diameter was 448 MPa, and the maximum evaluation stress for a φ8×24 mm diameter was 536 MPa.

[0051] The local maximum stress was measured only when the martensite fraction was equal to or greater than a predetermined value (e.g., 80% or greater). Elements with a martensite fraction of less than 80% were excluded from the detection because they were less likely to develop quench cracks.

[0052] Referring again to Figure 6, finally, the quenching cracking criteria are identified by matching the experiment and analysis (step S6-3). The quenching cracking criteria can be identified by the identification unit 13. Here, since the maximum evaluation stresses of φ4 × 12 mm and φ8 × 24 mm, which were the transition points of quenching cracking, were 448 MPa and 536 MPa, respectively, it was identified that the stress criteria at which quenching cracking occurs is between 448 MPa and 536 MPa.

[0053] As a follow-up test to confirm the accuracy of the quench cracking criteria, a similar quenching experiment and analysis was conducted using a φ12 mm homogeneous material test piece. A maximum stress of 270 MPa was recorded, and no quench cracking occurred. This is thought to be because the maximum stress of 270 MPa is lower than the quench cracking criteria of 448 MPa to 536 MPa, so no quench cracking occurred. Therefore, it was confirmed that the quench cracking criteria obtained as described above have a certain degree of accuracy.

[0054] According to this embodiment, the following advantageous effects are achieved.

[0055] The quenching cracking criteria can be identified by correlating the occurrence or non-occurrence of quenching cracks in the quenching experiment with the maximum evaluation stress in the quenching analysis. The maximum evaluation stress is calculated in two stages: global analysis and local analysis. Based on the strain and temperature change history calculated by the global analysis (e.g., heat transfer, phase transformation, and thermo-elastic-plastic analysis), the local maximum stress is calculated for each evaluation element 2a when it has a heterogeneous component distribution by local analysis (e.g., thermo-elastic-plastic analysis). The maximum value of the obtained local maximum stresses for each evaluation element 2a is used as the maximum evaluation stress. Then, by checking the maximum evaluation stress in the quenching analysis for test pieces in which quenching cracks occurred and test pieces in which they did not occur in the quenching experiment, the stress range in which quenching cracks occur and the stress range in which they do not occur (quenching cracking criteria) can be identified with high accuracy.

[0056] Furthermore, since the local maximum stress is confirmed only when the martensite fraction is above a certain level and the risk of quench cracking is high, the quench cracking criteria can be efficiently identified. Furthermore, since the risk of quench cracking is low when the martensite fraction is below a certain level, it is possible to prevent false detection of high stress occurring when the risk of quench cracking is low.

[0057] Furthermore, the quench cracking criteria can be identified taking into account the inhomogeneous distribution of elements due to segregation. In particular, the inhomogeneous distribution of elements due to segregation has a large effect on quench cracking, and identifying the quench cracking criteria while taking segregation into account ensures high identification accuracy.

[0058] Furthermore, it is possible to identify quench cracking criteria for inverted V segregation, which has a high risk of quench cracking among segregations.

[0059] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be practiced with various modifications within the scope of the present invention.

[0060] The present disclosure may include the following aspects. (Aspect 1) Obtaining the results of quenching experiments to confirm the presence or absence of quench cracks on multiple test pieces made of heterogeneous steel materials and having different shapes, performing a hardening analysis that takes into account heterogeneity on each of the plurality of test pieces to obtain a maximum stress for evaluation; The stress criteria for the occurrence of quench cracks are identified by correlating the quenching experiment results with the maximum stress for evaluation. This includes: The quenching analysis is creating an overall finite element model assuming that each of the plurality of test pieces is made of a homogeneous material; performing a global analysis simulating hardening using the global finite element model to obtain strain and temperature histories of each element of the global finite element model; extracting a plurality of evaluation elements to be evaluated from all elements constituting the entire finite element model; creating a local finite element model in which a non-uniform component distribution is set for each of the plurality of evaluation elements; acquiring a local maximum stress from each of the plurality of evaluation elements by inputting the corresponding history into the local finite element model and performing a local analysis; The largest value among the local maximum stresses is obtained as the maximum stress for evaluation. A method for quantifying quench cracking criteria, including: (Aspect 2) The method for quantifying quench cracking criteria according to aspect 1, wherein the local maximum stress is acquired only when the martensite fraction is equal to or greater than a predetermined value. (Aspect 3) 3. The method for quantifying quench cracking criteria according to claim 1 or 2, wherein the non-uniform component distribution includes a segregation distribution. (Aspect 4) 4. The method for quantifying quench cracking criteria according to aspect 3, wherein the segregation distribution includes inverted V segregation. (Aspect 5) an experiment result acquisition unit that acquires quenching experiment results that confirm the presence or absence of quench cracks on a plurality of test pieces made of heterogeneous steel materials and having different shapes; an analysis result acquisition unit that acquires a maximum stress for evaluation by performing a quenching analysis that takes into account heterogeneity on each of the plurality of test pieces; an identification unit that identifies stress criteria for quench crack occurrence by correlating the quenching experiment results with the maximum stress for evaluation; Equipped with The analysis result acquisition unit an overall analytical model creation unit that creates an overall finite element model by assuming that each of the plurality of test pieces is made of a homogeneous material; an overall analysis calculation unit that acquires strain and temperature histories of each element of the test piece by performing an overall analysis that simulates quenching using the overall finite element model; an evaluation element extraction unit that extracts a plurality of evaluation elements to be evaluated from all elements that constitute the entire finite element model; a local analysis model creation unit that creates a local finite element model in which a non-uniform component distribution is set for each of the plurality of evaluation elements; a local analysis calculation unit that inputs the corresponding history into the local finite element model and performs a local analysis to acquire a local maximum stress from each of the plurality of evaluation elements; a maximum stress for evaluation acquisition unit that acquires the largest value of the local maximum stresses as the maximum stress for evaluation; A quantification device for quench cracking criteria. [Explanation of symbols]

[0061] 1. Quench cracking criteria quantification device 2. Overall finite element model 2a Evaluation Elements 3 Local finite element model 3a Inverted V segregation section 3b Normal part 4 Steel ingot 4a Inverted V segregation zone 4b V segregation zone 4c Negative segregation zone 10 Control Unit 11 Experimental results acquisition section 12 Analysis result acquisition section 12a Overall analysis model creation section 12b Overall analysis calculation section 12c Evaluation element extraction part 12d Local analysis model creation section 12e Local analysis calculation section 12f Maximum stress acquisition section for evaluation 13 Identification section 20 Input section 30 Output section 40 Storage section

Claims

1. Obtaining the results of quenching experiments to confirm the presence or absence of quench cracks on multiple test pieces made of heterogeneous steel materials and having different shapes, performing a hardening analysis that takes into account heterogeneity on each of the plurality of test pieces to obtain a maximum stress for evaluation; The stress criteria for the occurrence of quench cracks are identified by correlating the quenching experiment results with the maximum stress for evaluation. This includes: The quenching analysis is creating an overall finite element model assuming that each of the plurality of test pieces is made of a homogeneous material; performing a global analysis simulating hardening using the global finite element model to obtain strain and temperature histories of each element of the global finite element model; extracting a plurality of evaluation elements to be evaluated from all elements constituting the entire finite element model; creating a local finite element model in which a non-uniform component distribution is set for each of the plurality of evaluation elements; acquiring a local maximum stress from each of the plurality of evaluation elements by inputting the corresponding history into the local finite element model and performing a local analysis; The largest value among the local maximum stresses is obtained as the maximum stress for evaluation. A method for quantifying quench cracking criteria, including:

2. The method for quantifying quench cracking criteria according to claim 1 , wherein the local maximum stress is acquired only when the martensite fraction is equal to or greater than a predetermined value.

3. The method for quantifying quench cracking criteria according to claim 1 or 2, wherein the non-uniform component distribution includes a distribution of segregation.

4. The method for quantifying quench crack criteria according to claim 3 , wherein the distribution of segregation includes inverted V segregation.

5. an experiment result acquisition unit that acquires quenching experiment results that confirm the presence or absence of quench cracks on a plurality of test pieces made of heterogeneous steel materials and having different shapes; an analysis result acquisition unit that acquires a maximum stress for evaluation by performing a quenching analysis that takes into account heterogeneity on each of the plurality of test pieces; an identification unit that identifies stress criteria for quench crack occurrence by correlating the quenching experiment results with the maximum stress for evaluation; Equipped with The analysis result acquisition unit an overall analytical model creation unit that creates an overall finite element model by assuming that each of the plurality of test pieces is made of a homogeneous material; an overall analysis calculation unit that acquires strain and temperature histories of each element of the test piece by performing an overall analysis that simulates quenching using the overall finite element model; an evaluation element extraction unit that extracts a plurality of evaluation elements to be evaluated from all elements that constitute the entire finite element model; a local analysis model creation unit that creates a local finite element model in which a non-uniform component distribution is set for each of the plurality of evaluation elements; a local analysis calculation unit that inputs the corresponding history into the local finite element model and performs a local analysis to acquire a local maximum stress from each of the plurality of evaluation elements; a maximum stress for evaluation acquisition unit that acquires the largest value of the local maximum stresses as the maximum stress for evaluation; A quantification device for quench cracking criteria.

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