Method for predicting mechanical properties of dual-phase steel

Abstract

The application discloses a kind of prediction methods of the mechanical properties of dual-phase steel, comprising: based on the content of each phase in dual-phase steel, the three-dimensional representative volume element of the dual-phase steel is established;Based on dislocation strengthening theory, the stress-strain relationship of two single phases in the three-dimensional representative volume element is established;Based on the three-dimensional representative volume element and the stress-strain relationship, a finite element model is established, and a mechanical simulation test is carried out to obtain the macro mechanical properties of the dual-phase steel;Wherein in the finite element model, the stress-strain relationship of two single phases is respectively assigned to the corresponding area of two single phases respectively.By the technical scheme of the application, the prediction accuracy of mechanical properties can be improved.

Description

Technical Field

[0001] This invention relates to the field of material mechanical property prediction technology, specifically to a method for predicting the mechanical properties of dual-phase steel. Background Technology

[0002] Advanced high-strength steel (AHSS) is a material with a multiphase microstructure. Through controlled rolling and cooling processes, the required microstructure and mechanical properties can be achieved, and various strengthening mechanisms can be employed to realize different strengths, toughness, ductility, and fatigue properties. Dual-phase steel is a typical representative of AHSS. Its microstructure consists of a relatively soft ferrite phase as the matrix, supplemented by a certain proportion of hard martensite phase, thus giving the material a good balance of strength and toughness. The microstructure of dual-phase steel is relatively complex, and the mechanical properties of the material are closely related to its microstructure morphology. Therefore, it is necessary to study the mechanical properties of dual-phase steels with different microstructure proportions.

[0003] Currently, finite element simulation based on representative volume elements is an effective method for predicting material properties. A representative volume element is a finite element model used for statistical analysis based on two-phase or multi-phase microstructure. Although the area or volume of the element is finite, it contains enough microstructural information to statistically represent the basic characteristics of the material's microstructure.

[0004] However, existing technologies typically predict steel properties based on two-dimensional representative volume units, which results in limited accuracy in the predictions. Summary of the Invention

[0005] The main objective of this invention is to provide a method for predicting the mechanical properties of dual-phase steel, so as to solve the problem of limited prediction accuracy when predicting properties based on two-dimensional representative volume units in the prior art.

[0006] According to one aspect of the present invention, a method for predicting the mechanical properties of dual-phase steel is proposed, comprising:

[0007] Based on the content of each phase in the dual-phase steel, a three-dimensional representative volume unit for the dual-phase steel is established.

[0008] Based on the dislocation strengthening theory, the stress-strain relationship of the two single phases in the three-dimensional representative volume element is established.

[0009] Based on the three-dimensional representative volume element and the stress-strain relationship, a finite element model is established, and mechanical simulation experiments are carried out to obtain the macroscopic mechanical properties of the dual-phase steel; wherein, in the finite element model, the stress-strain relationship of each of the two single phases is assigned to the corresponding region of each of the two single phases.

[0010] According to one embodiment of the present invention, the method further includes: grinding and polishing the cross-section of the duplex steel sample, etching it with an etchant, and then observing and statistically determining the content of each phase in the duplex steel using a metallographic microscope.

[0011] According to an embodiment of the present invention, the phases in the dual-phase steel include martensite and ferrite. The step of establishing the stress-strain relationship between the two single phases in the three-dimensional representative volume element based on dislocation strengthening theory includes:

[0012] The stress-strain relationship is defined by the following formula:

[0013]

[0014] Where σ is the equivalent plastic stress;

[0015] σ0 is the internal frictional stress of the material, which depends on the chemical composition, and is calculated using the following formula:

[0016] σ0=77+80(%Mn)+750(%P)+60(%Si)+80(%Cu)+45(%Ni)

[0017] +60(%Cr)+11(%Mo)+5000(%N)

[0018] Δσ is the carbon atom solid solution strengthening stress, where:

[0019] For martensite, the carbon atom solid solution strengthening stress Δσ m =3065 (%C) m )-161

[0020] For ferrite, the carbon atom solid solution strengthening stress Δσ f =5000(%C) f )

[0021] Among them, C m and C f These are the carbon contents in martensite and ferrite, respectively;

[0022] This indicates hardening caused by dislocation proliferation during plastic deformation.

[0023] Where α is the material constant; M is the Taylor factor; u is the shear modulus; b is the Burgers vector of the dislocation; and L is the mean free path of the dislocation, which is substituted into the mean free path L of the martensitic dislocation during the calculation. m and the mean free path L of ferrite dislocations f k is the dislocation recovery rate, which is substituted into the martensitic dislocation recovery rate k during calculation. m and ferrite dislocation recovery rate k f ε represents the equivalent plastic strain.

[0024] According to an embodiment of the present invention, establishing a finite element model based on the three-dimensional representative volume element and the stress-strain relationship includes:

[0025] Homogenized boundary conditions are set using multi-point constraint equations;

[0026] Select a vertex of the three-dimensional representative volume element as the initial displacement point, set the initial displacement, and set the mesh element type to linear hexahedral element.

[0027] According to one embodiment of the present invention, conducting mechanical simulation tests to obtain the macroscopic mechanical properties of the duplex steel includes:

[0028] Based on the aforementioned mechanical simulation experiment, the micro-stress and micro-strain during plastic deformation were obtained;

[0029] Based on the micro-stress and micro-strain, as well as the homogenization method, the macro-stress and macro-strain of the dual-phase steel are determined.

[0030] According to one embodiment of the present invention, the duplex steel comprises multiple samples with different phase contents, and the method further includes:

[0031] Based on the phase content and macroscopic mechanical properties of multiple samples, the relationship between the macroscopic mechanical properties and phase content of dual-phase steel is analyzed.

[0032] According to one embodiment of the present invention, the method further includes: heating the initial sample to different annealing temperatures at a heating rate of 5°C / s and holding it at that temperature for 60s, and then cooling it at a cooling rate of 230°C / s to obtain multiple samples with different phase contents.

[0033] According to one embodiment of the present invention, the duplex steel comprises, by mass percentage: 0.08% C, 1.35% Mn, 0.23% Si, 0.47% Cr, 0.03% Al, 0.013% P, and 0.002% S.

[0034] According to one embodiment of the present invention, the three-dimensional representative volume unit is cubic in shape and has a side length of 25 μm.

[0035] According to one embodiment of the present invention, establishing a three-dimensional representative volume unit of the dual-phase steel based on the content of each phase in the dual-phase steel includes:

[0036] A cube is set as a representative volume unit region, and multiple seed points are distributed at equal intervals along the side lengths of the cube in three directions.

[0037] Using the seed point as the vertex, multiple cubic units are generated, each of which represents a voxel of the phase;

[0038] The cubic units are randomly divided into two categories, each category representing a phase, and the content of each category of cubic units corresponds to the content of each phase in the dual-phase steel.

[0039] The location information of each type of cubic cell is created into a separate set and written to a readable file;

[0040] The step of establishing a finite element model based on the three-dimensional representative volume element includes: importing the readable file into the finite element software.

[0041] In the method for predicting the mechanical properties of dual-phase steel according to an embodiment of the present invention, by establishing a three-dimensional representative volume element, the microstructure information of the actual material can be simulated more accurately and the local stress-strain distribution during material deformation can be described more effectively, thereby improving the prediction accuracy of mechanical properties. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 A flowchart illustrating a method for predicting the mechanical properties of duplex steel according to an embodiment of the present invention is provided.

[0044] Figure 2 A schematic diagram of a three-dimensional representative volume unit according to an embodiment of the present invention is shown;

[0045] Figure 3 Stress-strain curves of ferrite single-phase and martensitic single-phase are shown according to embodiments of the present invention.

[0046] Figure 4 A three-dimensional representative volume element plastic stress distribution cloud map is shown according to an embodiment of the present invention;

[0047] Figure 5 A three-dimensional representative volume element plastic strain distribution cloud map is shown according to an embodiment of the present invention;

[0048] Figure 6 A schematic diagram showing the variation of macroscopic mechanical properties of duplex steel with different martensite contents according to an embodiment of the present invention is provided.

[0049] Figure 7 The stress-strain curves obtained by two-dimensional simulation, three-dimensional simulation and actual experimental methods are shown. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0051] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0052] Figure 1 A flowchart illustrating a method for predicting the mechanical properties of duplex steel according to an embodiment of the present invention is shown, as follows: Figure 1 As shown, the method for predicting the mechanical properties of duplex steel includes the following steps:

[0053] S1. Based on the content of each phase in the dual-phase steel, a three-dimensional representative volume unit of the dual-phase steel is established.

[0054] S2, Based on the dislocation strengthening theory, establish the stress-strain relationship between the two single phases in the three-dimensional representative volume element;

[0055] S3. Based on the three-dimensional representative volume element and the stress-strain relationship, a finite element model is established, and a mechanical simulation test is carried out to obtain the macroscopic mechanical properties of the dual-phase steel; wherein in the finite element model, the stress-strain relationship of each of the two single phases is assigned to the corresponding region of each of the two single phases.

[0056] In the method for predicting the mechanical properties of dual-phase steel according to an embodiment of the present invention, by establishing a three-dimensional representative volume element, the microstructure information of the actual material can be simulated more accurately and the local stress-strain distribution during material deformation can be described more effectively, thereby improving the prediction accuracy of mechanical properties.

[0057] In some embodiments, the three-dimensional representative volume units can be constructed using Python code. The phase content in each three-dimensional representative volume unit is consistent with the actual microstructure, and both single phases (e.g., martensite and ferrite phases) are randomly distributed. In some embodiments, the three-dimensional representative volume units are cubic in shape and have a side length of, for example, 25 μm.

[0058] In some embodiments, establishing a three-dimensional representative volume unit for the dual-phase steel based on the content of each phase in the dual-phase steel includes:

[0059] A cube is set as a representative volume unit region, and multiple seed points are distributed at equal intervals along the side lengths of the cube in three directions.

[0060] Using the seed point as the vertex, multiple cubic units are generated, each of which represents a voxel of the phase;

[0061] The cubic units are randomly divided into two categories, each category representing a phase, and the content of each category of cubic units corresponds to the content of each phase in the dual-phase steel.

[0062] Create a set of location information for each type of cubic cell (e.g., location information of multiple cubic cells in each type of cubic cell, where location information is, for example, coordinate information) and write it to a readable file.

[0063] Accordingly, establishing a finite element model based on the three-dimensional representative volume element includes: importing the readable file into the finite element software.

[0064] In some embodiments, the method further includes: grinding and polishing the cross-section of the duplex steel sample, etching it with an etchant, and then observing and statistically determining the content of each phase in the duplex steel using a metallographic microscope.

[0065] In some embodiments, the phases in the dual-phase steel include martensite and ferrite. Establishing the stress-strain relationship between the two single phases in the three-dimensional representative volume element based on dislocation strengthening theory includes:

[0066] The stress-strain relationship is defined by the following formula:

[0067]

[0068] Where σ is the equivalent plastic stress;

[0069] σ0 is the internal frictional stress of the material, which depends on the chemical composition, and is calculated using the following formula:

[0070] σ0=77+80(%Mn)+750(%P)+60(%Si)+80(%Cu)+45(%Ni)

[0071] +60(%Cr)+11(%Mo)+5000(%N)

[0072] Δσ is the carbon atom solid solution strengthening stress, where:

[0073] For martensite, the carbon atom solid solution strengthening stress Δσ m =3065 (%C) m )-161

[0074] For ferrite, the carbon atom solid solution strengthening stress Δσ f =5000(%C) f )

[0075] Among them, C mand C f These are the carbon contents in martensite and ferrite, respectively, which can be calculated using ThermalCalc software.

[0076] This indicates hardening caused by dislocation proliferation during plastic deformation.

[0077] Where α is the material constant; M is the Taylor factor; u is the shear modulus; b is the Burgers vector of the dislocation; and L is the mean free path of the dislocation, which is substituted into the mean free path L of the martensitic dislocation during the calculation. m and the mean free path L of ferrite dislocations f k is the dislocation recovery rate, which is substituted into the martensitic dislocation recovery rate k during calculation. m and ferrite dislocation recovery rate k f ε represents the equivalent plastic strain.

[0078] In the process of constructing the finite element model, constraints and initial displacements can also be set. In some embodiments, the establishment of the finite element model based on the three-dimensional representative volume element and the stress-strain relationship includes: setting homogenizing boundary conditions through multi-point constraint equations to keep the surfaces flat during the mechanical simulation test (close to the real mechanical test); selecting a vertex of the three-dimensional representative volume element as the initial displacement application point, setting the initial displacement, and setting the mesh element type to linear hexahedral element.

[0079] In some embodiments, conducting mechanical simulation tests to obtain the macroscopic mechanical properties of the duplex steel includes: obtaining the microscopic stress and microscopic strain during plastic deformation based on the mechanical simulation tests; and determining the macroscopic stress and macroscopic strain of the duplex steel based on the microscopic stress and the microscopic strain and a homogenization method.

[0080] In some embodiments, the duplex steel includes multiple samples with different phase contents, and the method further includes: analyzing the relationship between the macroscopic mechanical properties of the duplex steel and the phase content based on the phase contents and macroscopic mechanical properties of the multiple samples.

[0081] Duplex steel samples with different phase contents can be obtained through heat treatment. In some embodiments, the method further includes: heating the initial sample to different annealing temperatures at a heating rate of 5°C / s and holding it at that temperature for 60s, and then cooling it at a cooling rate of 230°C / s to promote the transformation of austenite to martensite, thereby obtaining multiple samples with different phase contents.

[0082] In some embodiments, the duplex steel comprises, by mass percentage: 0.08% C, 1.35% Mn, 0.23% Si, 0.47% Cr, 0.03% Al, 0.013% P, and 0.002% S.

[0083] In one specific embodiment, the mechanical properties of duplex steel are predicted according to the following steps:

[0084] (1) Establish a three-dimensional representative volume element for duplex steel.

[0085] 1.1 DP600 high-strength steel was used as the initial material, and its chemical composition is shown in Table 1. The sample was heated to 830℃ at a heating rate of 5℃ / s and held for 60s using a phase transformation apparatus, followed by cooling at a cooling rate of 230℃ / s. The cross-section of the sample was ground and polished, etched with nitric acid alcohol, and observed using a metallographic microscope. The martensite content was determined to be 50%. A three-dimensional representative volume element of the dual-phase steel was constructed using Python, in which martensite and ferrite each accounted for 50%, and both microstructures were randomly distributed. The side length of the representative volume element was 25×25×25μm. Figure 2 The diagram shows a three-dimensional representation of a volume element, where the black portion represents martensite and the white portion represents ferrite.

[0086] Table 1: Main Chemical Composition of Duplex Steel (mass percentage)

[0087] C Mn Si Cr Al P S 0.08 1.35 0.23 0.47 0.03 0.013 0.002

[0088] 1.2 Using DP600 as the initial material, its chemical composition is shown in Table 1. The sample was heated to 790℃ at a heating rate of 5℃ / s and held for 60s using a phase transformation apparatus, and then cooled at a cooling rate of 230℃ / s. The cross-section of the sample was ground and polished, etched with nitric acid alcohol, and observed and counted by metallographic microscope. The martensite content was found to be 30%. A three-dimensional representative volume element of the duplex steel was constructed using Python, in which martensite and ferrite accounted for 30% and 70% respectively, and both microstructures were randomly distributed. The side length of the representative volume element was 25×25×25μm.

[0089] 1.3 Using DP600 as the initial material, its chemical composition is shown in Table 1. The sample was heated to 770℃ at a heating rate of 5℃ / s and held for 60s using a phase transformation apparatus, and then cooled at a cooling rate of 230℃ / s. The cross-section of the sample was ground and polished, etched with nitric acid alcohol, and observed and counted by metallographic microscope. The martensite content was found to be 20%. A three-dimensional representative volume element of the dual-phase steel was constructed using Python, in which martensite and ferrite accounted for 20% and 80% respectively, and both microstructures were randomly distributed. The side length of the representative volume element was 25×25×25μm.

[0090] The details of constructing the three-dimensional representative volume element in sections 1.1-1.3 are as follows:

[0091] (a) Set a cube as the representative volume unit region with a side length of 25μm, and distribute 10 seed points (excluding the two vertices of the side length) at equal intervals along the side length in three directions.

[0092] (b) Generate multiple cubic units with the seed point as the vertex, each cubic unit representing a voxel of the phase;

[0093] (c) Based on the results of metallographic analysis, the multiple cubic units are randomly divided into two categories, each category of cubic units representing a phase, and the content of each category of cubic units corresponds to the content of each phase in the dual-phase steel.

[0094] (d) Create a set of coordinate information for each type of cubic cell and write it into a readable file.

[0095] (2) Establish the stress-strain relationship between the ferrite and martensite phases.

[0096] During plastic deformation, the relationship between the equivalent plastic stress σ and the equivalent plastic strain ε in ferrite and martensite is determined based on the dislocation strengthening theory:

[0097]

[0098] Where σ is the equivalent plastic stress, and the unit is MPa;

[0099] σ0 is the internal frictional stress of the material, which depends on the chemical composition, and is calculated using the following formula:

[0100] σ0=77+80(%Mn)+750(%P)+60(%Si)+80(%Cu)+45(%Ni)

[0101] +60(%Cr)+11(%Mo)+5000(%N)

[0102] Δσ is the carbon atom solid solution strengthening stress, where:

[0103] For martensite, the carbon atom solid solution strengthening stress Δσ m =3065 (%C) m )-161

[0104] For ferrite, the carbon atom solid solution strengthening stress Δσ f =5000(%C) f )

[0105] Among them, C m and C f These are the carbon contents in martensite and ferrite, respectively, calculated using ThermalCalc software. (C) m It is 0.4%, C f It is 0.05%;

[0106] This indicates hardening caused by dislocation proliferation during plastic deformation.

[0107] Where α is the material constant; M is the Taylor factor; u is the shear modulus; b is the Burgers vector of the dislocation; and L is the mean free path of the dislocation, which is substituted into the mean free path L of the martensitic dislocation during the calculation. m and the mean free path L of ferrite dislocations f k is the dislocation recovery rate, which is substituted into the martensitic dislocation recovery rate k during calculation. m and ferrite dislocation recovery rate k f ε represents the equivalent plastic strain. Relevant parameters are shown in Table 2. Figure 3 The stress-strain curves for ferrite and martensite are shown.

[0108] Table 2: Relevant Simulation Parameters for Duplex Steel

[0109] α M u b <![CDATA[k m ]]> <![CDATA[k f ]]> <![CDATA[L m ]]> <![CDATA[L f ]]> 0.33 3.06 80GPa 25nm 40 2.5 0.38nm 4μm

[0110] (3) Import the readable file containing the three-dimensional representative volume element information generated in step (1) into the finite element analysis software, and assign the stress-strain curves of the ferrite and martensite phases to the corresponding regions respectively; set homogenization boundary conditions through multi-point constraint equations to keep the surfaces flat during the stretching process; select a vertex as the initial displacement point (e.g., Figure 2 As shown in the figure, the displacement size is set to 10 micrometers; the element type is linear hexahedral element, and the mesh size is approximately 2.3 micrometers; the analysis mode is selected as static implicit, and the calculation time is 1 second; after the model is established, a uniaxial tensile simulation of dual-phase steel is carried out.

[0111] Figure 4 and Figure 5 The plastic stress and plastic strain distribution cloud maps of three-dimensional representative volume elements (50% martensite and 50% ferrite) are shown respectively. The martensitic structure exhibits obvious stress concentration, with the maximum stress exceeding 2500 MPa; while the plastic deformation capacity of ferrite is much stronger than that of martensite, with a maximum strain of 0.645. The three-dimensional model can effectively describe the local stress and strain distribution during the plastic deformation of the material.

[0112] (4) The relationship between macroscopic and microscopic mechanical properties is achieved through a homogenization method:

[0113]

[0114]

[0115] Among them, S ij and E ij They are respectively micro-stress σij and micro-strain ε ij The average values ​​after integration over the entire volume of the micromechanical model are the macroscopic stress and macroscopic strain.

[0116] Figure 6 The changes in macroscopic mechanical properties of duplex steel under different martensite contents are shown. As the martensite content increases, the tensile strength of the duplex steel also gradually increases. Material properties reflect the microstructure, which in turn reflects the processing technology. Combining the laws governing microstructure evolution allows for rapid performance prediction and process improvement, thereby accelerating product development and solving the problems of long development cycles and extensive trial production required in traditional R&D models.

[0117] Figure 7 The results show a comparison between simulation and experiment at a martensite content of 20%. The results indicate that the three-dimensional model and the experiment have a higher degree of matching and greater accuracy than the two-dimensional model.

[0118] In summary, the prediction method of this invention establishes a three-dimensional representative volume element of dual-phase steel, which contains ferrite and martensite phases. Based on the dislocation strengthening theory, stress-strain curves of the two phases are established, and finite element tensile simulation is carried out. This invention can effectively describe the stress and strain distribution of each phase in the local area during plastic deformation, predict the macroscopic mechanical properties of dual-phase steel, and has certain engineering reference value for the control of material microstructure and properties.

[0119] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for predicting the mechanical properties of dual-phase steel, characterized in that, include: Based on the content of each phase in the dual-phase steel, a three-dimensional representative volume unit for the dual-phase steel is established. Based on the dislocation strengthening theory, the stress-strain relationship of the two single phases in the three-dimensional representative volume element is established. Based on the three-dimensional representative volume element and the stress-strain relationship, a finite element model is established, and mechanical simulation experiments are carried out to obtain the macroscopic mechanical properties of the dual-phase steel; wherein, in the finite element model, the stress-strain relationship of each of the two single phases is assigned to the corresponding region of each of the two single phases respectively; The method of establishing a three-dimensional representative volume element for the dual-phase steel based on the content of each phase includes: A cube is set as a representative volume unit region, and multiple seed points are distributed at equal intervals along the side lengths of the cube in three directions. Multiple cubic units are generated using the seed point as the vertex, and each cubic unit represents a voxel of the phase; The cubic units are randomly divided into two categories, each category representing a phase, and the content of each category of cubic units corresponds to the content of each phase in the dual-phase steel. The location information of each type of cubic cell is created into a separate set and written to a readable file; The step of establishing a finite element model based on the three-dimensional representative volume element includes: importing the readable file into the finite element software; The phases in the dual-phase steel include martensite and ferrite. Based on dislocation strengthening theory, the stress-strain relationships of the two single phases in the three-dimensional representative volume element are established, including: The stress-strain relationship is defined by the following formula: wherein, is the equivalent plastic stress; For internal friction stress of the material, depending on the chemical composition, the formula is as follows: For carbon atom solid solution strengthening stress, where: For martensite, carbon atom solid solution strengthening stress For ferrite, carbon atom solid solution strengthening stress wherein, and Cm and Cf are the carbon content in martensite and ferrite, respectively; represents hardening due to dislocation multiplication during plastic deformation, in, These are material constants; Taylor factor; Shear modulus; The Burgers vector for dislocations; The mean free path of dislocations is substituted into the mean free path of martensitic dislocations during the calculation. Mean free path of ferrite dislocations ; For the dislocation recovery rate, substitute the martensitic dislocation recovery rate into the calculation. Ferrite dislocation recovery rate ; Equivalent plastic strain; The establishment of a finite element model based on the three-dimensional representative volume element and the stress-strain relationship includes: Homogenized boundary conditions are set using multi-point constraint equations; Select a vertex of the three-dimensional representative volume element as the initial displacement point, set the initial displacement, and set the mesh element type to linear hexahedral element.

2. The method of claim 1, wherein, Also includes: After grinding and polishing the cross-section of the duplex steel sample, it was etched with an etchant, and then the content of each phase in the duplex steel was obtained by observation and statistical analysis using a metallographic microscope.

3. The method of claim 1, wherein, The mechanical simulation test to obtain the macroscopic mechanical properties of the dual-phase steel includes: Based on the aforementioned mechanical simulation experiment, the micro-stress and micro-strain during plastic deformation were obtained; Based on the micro-stress and micro-strain, as well as the homogenization method, the macro-stress and macro-strain of the dual-phase steel are determined.

4. The method of claim 1, wherein, The dual-phase steel comprises multiple samples with different phase contents, and the method further includes: Based on the phase content and macroscopic mechanical properties of multiple samples, the relationship between the macroscopic mechanical properties and phase content of dual-phase steel is analyzed.

5. The method of claim 4, wherein, Also includes: The initial sample was heated to different annealing temperatures at a heating rate of 5℃ / s and held for 60s, and then cooled at a cooling rate of 230℃ / s to obtain multiple samples with different phase contents.

6. The method of claim 1, wherein, The dual-phase steel contains, by mass percentage: 0.08% C, 1.35% Mn, 0.23% Si, 0.47% Cr, 0.03% Al, 0.013% P, and 0.002% S.

7. The method according to claim 1, characterized in that, The three-dimensional representative volume unit is a cube with a side length of 25 μm.

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