Method for displaying isothermal softening structure of high-nitrogen martensitic steel through reconstruction variant and application

Abstract

The invention discloses a method for displaying a high-nitrogen martensitic steel isothermal softening structure by reconstructing variants and application, and relates to the technical field of material science. The method comprises the following steps: data acquisition: obtaining electron back scattering diffraction data after isothermal softening of the high-nitrogen martensitic steel; data processing: calculating and smoothing the electron back scattering diffraction data to obtain calculated and smoothed electron back scattering diffraction data; variant reconstruction: carrying out variant reconstruction on the calculated and smoothed electron back scattering diffraction data according to an orientation relationship; the variants are quantified, and image visualization analysis and statistics of the martensite variants are achieved. The isothermal softening structure of the high-nitrogen martensitic steel is displayed by reconstructing the variant, and the structure evolution of the martensitic variant in the isothermal softening process can be quantitatively displayed, so that the isothermal softening mechanism of the high-nitrogen martensitic steel is disclosed, a new thought is developed for research of the softening mechanism, and the method has important scientific significance and application value.

Description

Technical Field

[0001] The invention relates to the field of material science and technology, and in particular to a method and application of displaying isothermal softening structure of high nitrogen martensitic steel through reconstruction variants. Background Art

[0002] The rapid development of modern industrial technology has led to an increasing demand for the performance of metal materials. Especially in extreme working environments such as high temperature, high pressure and high stress, the thermal stability of metal materials has become a key factor restricting their application. Thermal stability is the ability of metal materials to maintain stable performance under high temperature environments. Under high-temperature working conditions, metal materials often experience problems such as organizational changes and performance degradation, leading to premature failure of the material. Therefore, in-depth research on the thermal stability mechanism of metal materials is expected to improve the performance stability of materials under high-temperature environments.

[0003] The research contents of traditional thermal stability mechanism mainly include carbide precipitation and coarsening and dislocation recovery. Among them, Ostwald ripening theory and Lifshitz-Slyozov-Wagner theory systematically reveal the evolution and coarsening mechanism of carbides. Dislocations will be annihilated and rearranged during isothermal softening, and subgrains will be formed. However, the evolution of martensitic substructures remains to be explored. Martensitic variants refer to martensitic substructures with different orientations formed during the martensitic phase transformation, and their distribution and morphology have a significant effect on the properties of the material. By studying martensitic variants, the martensitic formation mechanism, transformation conditions and performance characteristics can be revealed, the material composition design can be guided, the microstructure of the material can be optimized, and thus the thermal stability of the material can be improved. CN 106546458A discloses a method for observing martensitic variants of MnNiGe-based alloys, and the martensitic variants can be observed through traditional sample preparation, heat treatment, polishing and corrosion. CN 116622962 A discloses a method for preparing hot-rolled high-strength and tough engineering machinery steel by regulating martensitic variants, wherein the selection tendency of martensitic variants is regulated by adjusting the rolling temperature, thereby increasing the number of high-angle grain boundaries and improving toughness. However, in the above method, the martensitic variants are directly observed by a simple corrosion method, and the orientation relationship between the martensitic variants cannot be analyzed, nor can quantitative statistics be performed. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0005] To this end, a first aspect of the present invention provides a method for displaying an isothermal softening structure of a high nitrogen martensitic steel by reconstructing a variant, comprising:

[0006] Data acquisition, obtaining electron backscatter diffraction data of high nitrogen martensitic steel after isothermal softening;

[0007] Data processing, calculating and smoothing the electron backscatter diffraction data to obtain calculated and smoothed electron backscatter diffraction data;

[0008] variant reconstruction, reconstructing the calculated and smoothed electron backscatter diffraction data according to different orientation relationships;

[0009] Quantification and analysis, based on the variant reconstruction effects under different orientation relationships, determine the reasonable orientation relationship for displaying the isothermal softening structure of high nitrogen martensitic steel, and then realize quantitative display of the organizational evolution of martensitic variants during the isothermal softening process through variant reconstruction, revealing the variant evolution mechanism of the high nitrogen martensitic steel after isothermal softening.

[0010] Furthermore, the data acquisition includes:

[0011] The electron backscatter diffraction data of the high nitrogen martensitic steel after isothermal softening are obtained by using a scanning electron microscope with electron backscatter diffraction, the acquisition step length is 0.05 μm to 0.1 μm, and the resolution is 80% to 100%.

[0012] Preferably, the acquisition step is 0.05 μm to 0.08 μm, and the resolution is 90% to 100%.

[0013] Furthermore, before the data is acquired, the high nitrogen martensitic steel after isothermal softening is electrolytically polished; the electrolytic polishing: the electrolyte is a perchloric acid alcohol solution with a volume fraction of 8% to 15%, the voltage is 20V to 30V, the current is 0.5A to 1.0A, and the electrolysis time is 10s to 30s.

[0014] Preferably, the electrolyte is a perchloric acid alcohol solution with a volume fraction of 8% to 10%, the voltage is 25V to 30V, the current is 0.8A to 1.0A, and the electrolysis time is 20s to 25s.

[0015] Furthermore, the data processing includes:

[0016] The electron backscatter diffraction data is calculated with a threshold of 0° to 10°, and the grain smoothing range is 0° to 20°, to form calculated and smoothed electron backscatter diffraction data.

[0017] Preferably, the electron backscatter diffraction data is calculated with a threshold of 2° to 5°, and the grain smoothing range is 5° to 10°, to form calculated and smoothed electron backscatter diffraction data.

[0018] Furthermore, the variant reconstruction includes: reconstructing the calculated and smoothed electron backscatter diffraction data according to the Kurdjumov-Sachs orientation relationship, the Nishiyama-Wassermann orientation relationship, the Greninger-Troiano orientation relationship and the Pitsch orientation relationship.

[0019] Furthermore, the quantitative variants and analysis include:

[0020] Based on the reconstructed parent phase austenite grain structure, image visualization analysis and statistics of martensite variants are carried out, including calculation of variant frequency and variant boundary density of electron backscattered diffraction patterns, thereby revealing the isothermal softening mechanism of high nitrogen martensitic steel.

[0021] The second aspect of the present invention provides an application of a method for displaying the isothermal softening structure of high nitrogen martensitic steel through reconstructed variants, wherein the method for displaying the isothermal softening structure of high nitrogen martensitic steel through reconstructed variants is used to guide the composition design of metal materials and improve the thermal stability of metal materials.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] The method provided by the present invention for displaying the isothermal softening structure of high nitrogen martensitic steel by reconstructing variants can quantitatively display the organizational evolution of martensitic variants during the isothermal softening process, thereby revealing the isothermal softening mechanism of the material, and can provide strong theoretical support and technical guidance for improving the thermal stability of metal materials, open up new ideas for the study of softening mechanism, and has important scientific significance and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 a is a variant frequency distribution diagram corresponding to the Kurdjumov-Sachs orientation relationship provided in Example 1 of the present invention;

[0025] Figure 1 b is a variant pair boundary density map corresponding to the Kurdjumov-Sachs orientation relationship provided in Example 1 of the present invention;

[0026] Figure 2 a is a variant frequency distribution diagram corresponding to the Nishiyama-Wassermann orientation relationship provided in Example 2 of the present invention;

[0027] Figure 2 b is a variant pair boundary density map corresponding to the Nishiyama-Wassermann orientation relationship provided in Example 2 of the present invention;

[0028] Figure 3a is a variant frequency distribution diagram corresponding to the Greninger-Troiano orientation relationship provided in Example 3 of the present invention;

[0029] Figure 3 b is a variant pair boundary density map corresponding to the Greninger-Troiano orientation relationship provided in Example 3 of the present invention;

[0030] Figure 4 a is a variant frequency distribution diagram corresponding to the Pitsch orientation relationship provided in Example 4 of the present invention;

[0031] Figure 4 b is a variant pair boundary density map corresponding to the Pitsch orientation relationship provided in Example 4 of the present invention;

[0032] Figure 5 a is an isothermal softening structure diagram without reconstruction provided in Comparative Example 1 of the present invention;

[0033] Figure 5 b is an isothermal softening structure diagram of variant reconstruction through Kurdjumov-Sachs orientation relationship provided in Example 1 of the present invention;

[0034] Figure 5 c is an isothermal softening structure diagram of variant reconstruction through Nishiyama-Wassermann orientation relationship provided in Example 2 of the present invention;

[0035] Figure 5 d is an isothermal softening structure diagram of variant reconstruction through Greninger-Troiano orientation relationship provided in Example 3 of the present invention;

[0036] Figure 5 e is an isothermal softening structure diagram of variant reconstruction through Pitsch orientation relationship provided in Example 4 of the present invention.

[0037] Figure 6 a is a variant frequency distribution diagram corresponding to the Kurdjumov-Sachs orientation relationship provided in Example 5 of the present invention;

[0038] Figure 6 b is a variant pair boundary density map corresponding to the Kurdjumov-Sachs orientation relationship provided in Example 5 of the present invention;

[0039] Figure 7 a is a variant frequency distribution diagram corresponding to the Nishiyama-Wassermann orientation relationship provided in Example 6 of the present invention;

[0040] Figure 7b is a variant pair boundary density map corresponding to the Nishiyama-Wassermann orientation relationship provided in Example 6 of the present invention;

[0041] Figure 8 a is a variant frequency distribution diagram corresponding to the Greninger-Troiano orientation relationship provided in Example 7 of the present invention;

[0042] Figure 8 b is a variant pair boundary density map corresponding to the Greninger-Troiano orientation relationship provided in Example 7 of the present invention;

[0043] Fig. 9 a is a variant frequency distribution diagram corresponding to the Pitsch orientation relationship provided in Example 8 of the present invention;

[0044] Fig. 9 b is a variant pair boundary density map corresponding to the Pitsch orientation relationship provided in Example 8 of the present invention;

[0045] Fig.10 a is an isothermal softening structure diagram without reconstruction provided in Comparative Example 2 of the present invention;

[0046] Fig.10 b is an isothermal softening microstructure diagram of variant reconstruction through Kurdjumov-Sachs orientation relationship provided in Example 5 of the present invention;

[0047] Fig.10 c is an isothermal softening structure diagram of variant reconstruction through Nishiyama-Wassermann orientation relationship provided in Example 6 of the present invention;

[0048] Fig.10 d is an isothermal softening structure diagram of variant reconstruction through Greninger-Troiano orientation relationship provided in Example 7 of the present invention;

[0049] Fig.10 e is an isothermal softening structure diagram of variant reconstruction through Pitsch orientation relationship provided in Example 8 of the present invention.

[0050] Fig.11 a is a variant frequency distribution diagram corresponding to the Kurdjumov-Sachs orientation relationship provided in Example 9 of the present invention;

[0051] Fig.11 b is a variant pair boundary density map corresponding to the Kurdjumov-Sachs orientation relationship provided in Example 9 of the present invention;

[0052] Fig.12a is a variant frequency distribution diagram corresponding to the Nishiyama-Wassermann orientation relationship provided in Example 10 of the present invention;

[0053] Fig.12 b is a variant pair boundary density map corresponding to the Nishiyama-Wassermann orientation relationship provided in Example 10 of the present invention;

[0054] Fig.13 a is a variant frequency distribution diagram corresponding to the Greninger-Troiano orientation relationship provided in Example 11 of the present invention;

[0055] Fig.13 b is a variant pair boundary density map corresponding to the Greninger-Troiano orientation relationship provided in Example 11 of the present invention;

[0056] Fig.14 a is a variant frequency distribution diagram corresponding to the Pitsch orientation relationship provided in Example 12 of the present invention;

[0057] Fig.14 b is a variant pair boundary density map corresponding to the Pitsch orientation relationship provided in Example 12 of the present invention;

[0058] Fig.15 a is an isothermal softening structure diagram without reconstruction provided in Comparative Example 3 of the present invention;

[0059] Fig.15 b is an isothermal softening microstructure diagram of variant reconstruction through Kurdjumov-Sachs orientation relationship provided in Example 9 of the present invention;

[0060] Fig.15 c is an isothermal softening structure diagram of variant reconstruction through Nishiyama-Wassermann orientation relationship provided in Example 10 of the present invention;

[0061] Fig.15 d is an isothermal softening microstructure diagram of variant reconstruction through Greninger-Troiano orientation relationship provided in Example 11 of the present invention;

[0062] Fig.15 e is the isothermal softening structure diagram of the variant reconstruction through the Pitsch orientation relationship provided in Example 12 of the present invention. DETAILED DESCRIPTION

[0063] In order to better understand the above-mentioned technical scheme, the technical scheme of the embodiments of the present application is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical scheme of the embodiments of the present application, rather than limitations on the technical scheme of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments may be combined with each other.

[0064] A first aspect of an embodiment of the present invention provides a method for displaying an isothermal softening structure of a high nitrogen martensitic steel by reconstructing a variant, comprising:

[0065] Data acquisition, obtaining electron backscatter diffraction data of high nitrogen martensitic steel after isothermal softening;

[0066] Data processing, calculating and smoothing the electron backscatter diffraction data to obtain calculated and smoothed electron backscatter diffraction data;

[0067] variant reconstruction, reconstructing the calculated and smoothed electron backscatter diffraction data according to different orientation relationships;

[0068] Quantification and analysis, based on the variant reconstruction effects under different orientation relationships, determine the reasonable orientation relationship for displaying the isothermal softening structure of high nitrogen martensitic steel, and then realize quantitative display of the organizational evolution of martensitic variants during the isothermal softening process through variant reconstruction, revealing the variant evolution mechanism of the high nitrogen martensitic steel after isothermal softening.

[0069] The method for displaying the isothermal softening structure of high nitrogen martensitic steel by reconstructing variants provided in an embodiment of the present invention can quantitatively display the organizational evolution of martensitic variants during the isothermal softening process, thereby revealing the isothermal softening mechanism of the material, and can provide strong theoretical support and technical guidance for improving the thermal stability of metal materials, open up new ideas for the study of softening mechanism, and has important scientific significance and application value.

[0070] It can be understood that the method for displaying the isothermal softening structure of high nitrogen martensitic steel by reconstructing variants provided in the embodiment of the present invention is applicable to all types of high nitrogen martensitic steels, for example: the chemical composition weight percentage of high nitrogen martensitic steel is C 0.2%~0.5%, Si 0.2%~1.5%, Mn 0.1%~2%, Cr 2%~10%, Mo 0.2%~3%, V0.2%~2%, N 0.08%~0.2%, and the balance is Fe and other inevitable impurity elements; or, the chemical composition weight percentage of high nitrogen martensitic steel is C 0.2%~0.6%, Si≤1.0%, Mn≤1.0%, Cr 10%~18%, Mo 0.2%~2%, Ni≤2%, N 0.2%~0.6%, and the balance is Fe and other inevitable impurity elements; or, the chemical composition weight percentage of high nitrogen martensitic steel is C 0.5%~2%, Si 0.05%~2%, Mn 0.1%~2%, Cr 2%~6%, Mo3%~15%, Co 5%~10%, N0.1%~0.4%, W 1%~3%, V 1%~3%, the balance is Fe and other inevitable impurity elements; etc. The method provided in the embodiment of the present invention for displaying the isothermal softening structure of high nitrogen martensitic steel by reconstructing variants first obtains the electron backscatter diffraction data after isothermal softening by a scanning electron microscope with electron backscatter diffraction, and then reconstructs the data collected by the electron backscatter diffraction into martensitic variants to display the isothermal softening structure of high nitrogen martensitic steel, thereby revealing the isothermal softening law. Specifically, it includes the following: (1) before data acquisition, prepare an isothermal softening sample and conduct a thermal stability experiment. Optionally, the experimental method of thermal stability is as follows: the high nitrogen martensitic steel after quenching and tempering is isothermally treated at a temperature of 500℃~700℃ and an isothermal time of 2h~96h; with the increase of the isothermal softening temperature and the extension of the isothermal softening time, the structure will undergo obvious recovery. Under the premise of maintaining the lath martensite morphology, the isothermal softening temperature is preferably 550℃~650℃, and the isothermal time is preferably 2h~72h. (2) Collect electron backscatter diffraction data using a scanning electron microscope with electron backscatter diffraction; (3) Import the electron backscatter diffraction data into MATLAB for calculation and smoothing to obtain the calculated and smoothed electron backscatter diffraction data; (4) Reconstruct the calculated and smoothed electron backscatter diffraction data according to the orientation relationship; (5) Quantify the variants and analyze the evolution mechanism of the variants after isothermal softening.

[0071] In a feasible implementation manner, the data acquisition includes:

[0072] The electron backscatter diffraction data of the high nitrogen martensitic steel after isothermal softening is obtained by using a scanning electron microscope with electron backscatter diffraction, and the acquisition step length is set to 0.05 μm to 0.1 μm, and the resolution rate is 80% to 100%. Preferably, the acquisition step length is 0.05 μm to 0.08 μm, and the resolution rate is 90% to 100%.

[0073] It is understood that electron backscatter diffraction (EBSD) is used to obtain crystallographic information such as crystal orientation and grain boundary misorientation. Taking into account the resolution and accuracy of data acquisition, as well as the data acquisition time, the acquisition step is set to 0.05μm to 0.1μm, preferably 0.05μm to 0.08μm; to ensure the accuracy and reliability of the data, the resolution is set to 80% to 100%, preferably 90% to 100%.

[0074] In a feasible implementation, before the data acquisition, the high nitrogen martensitic steel after isothermal softening is electropolished; the electropolishing: the electrolyte is a perchloric acid alcohol solution with a volume fraction of 8% to 15%, the voltage is 20V to 30V, the current is 0.5A to 1.0A, and the electrolysis time is 10s to 30s. The electropolishing is preferably an electrolyte with a volume fraction of 8% to 10% perchloric acid alcohol solution, a voltage of 25V to 30V, a current of 0.8A to 1.0A, and an electrolysis time of 20s to 25s.

[0075] Specifically, the surface stress layer generated by mechanical grinding of the isothermally softened high nitrogen martensitic steel is eliminated by electrolytic polishing.

[0076] In a feasible implementation manner, the data processing includes:

[0077] The electron backscatter diffraction data is calculated with a threshold value of 0° to 10°, and the grain smoothing range is 0° to 20°, to form the calculated and smoothed electron backscatter diffraction data. Preferably, the electron backscatter diffraction data is calculated with a threshold value of 2° to 5°, and the grain smoothing range is 5° to 10°, to form the calculated and smoothed electron backscatter diffraction data.

[0078] Optionally, the electron backscatter diffraction data is imported into MATLAB software for data calculation and smoothing. The electron backscatter diffraction data is calculated with a threshold of 0° to 10°, preferably the electron backscatter diffraction data is calculated with a threshold of 2° to 5° to form grain data, and the grain smoothing range is 0° to 20°, preferably the grain smoothing range is 5° to 10°.

[0079] In a feasible implementation, the variant reconstruction includes: reconstructing the calculated and smoothed electron backscatter diffraction data according to the Kurdjumov-Sachs orientation relationship, the Nishiyama-Wassermann orientation relationship, the Greninger-Troiano orientation relationship and the Pitsch orientation relationship.

[0080] Specifically, we relied on the Kurdjumov-Sachs orientation relationship, Nishiyama-Wassermann orientation relationship, Greninger-Troiano orientation relationship and Pitsch orientation relationship to perform variant reconstruction of the isothermal softening structure of high nitrogen martensitic steels with various different compositions. We found that the reconstruction effects of the Kurdjumov-Sachs, Nishiyama-Wassermann and Greninger-Troiano orientation relationships were better, and the variant structures were completely reconstructed, while the reconstruction effect of the Pitsch orientation relationship was poor, and the variant structure was not fully displayed.

[0081] In a feasible implementation, the quantitative variant and analysis include:

[0082] Based on the reconstructed parent phase austenite grain structure, image visualization analysis and statistics of martensite variants are carried out, including calculation of variant frequency and variant boundary density of electron backscattered diffraction patterns, thereby revealing the isothermal softening mechanism of high nitrogen martensitic steel.

[0083] A second aspect of an embodiment of the present invention provides an application of a method for displaying the isothermal softening structure of high nitrogen martensitic steel by reconstructing variants. The method for displaying the isothermal softening structure of high nitrogen martensitic steel by reconstructing variants is used to guide the design of metal material composition, optimize the microstructure of metal materials, and improve the thermal stability of metal materials.

[0084] It is understandable that, in view of the increasing demand for high-performance metal materials in modern industry, showing the isothermal softening structure of high-nitrogen martensitic steel by reconstructing variants and revealing the softening mechanism of the material can provide strong theoretical support and technical guidance for improving the thermal stability of metal materials.

[0085] The microstructure in the embodiment of the present invention is observed using a Zeiss Crossbeam 550 scanning electron microscope with electron backscatter diffraction, and the electron backscatter diffraction probe model is: Oxford Instruments Symmetry S2.

[0086] The present invention is described below in conjunction with specific embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0087] Example 1

[0088] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0089] (1) Preparation of isothermal softening samples and thermal stability test: The chemical composition weight percentage of the high nitrogen martensitic steel used in the experiment is C 0.38%, Si 1.00%, Mn 0.40%, Cr 5.10%, Mo 1.40%, V 1.00%, N 0.10%, and the balance is Fe and other inevitable impurity elements. The high nitrogen martensitic steel after quenching and tempering is isothermally treated at a temperature of 600°C and an isothermal time of 48h.

[0090] (2) The samples after isothermal softening treatment were electropolished and electron backscatter diffraction data were collected. The observation surface of the sample was electropolished using a perchloric acid alcohol solution with a volume fraction of 8% to eliminate the surface stress layer generated by the sample after mechanical grinding. The electropolishing parameters were a voltage of 28V and a current of 0.9A. Subsequently, electron backscatter diffraction data with a step size of 0.07μm and a resolution of 95% were collected.

[0091] (3) The electron backscatter diffraction data were imported into MATLAB software for data calculation and smoothing. The electron backscatter diffraction data were calculated with a threshold of 3° to form calculated and smoothed electron backscatter diffraction data, and the grain smoothing angle was 5°.

[0092] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Kurdjumov-Sachs orientation relationship, see Table 1.

[0093] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Figure 1 (a) As shown. It can be seen that the variants are selectively distributed after softening, with high-frequency V7, V19, V21, V22, and V24 variants being the main ones, accounting for 0.070, 0.075, 0.087, 0.081, and 0.078, respectively. The variant pair groups V1 to V24 are classified, and the variant pair groups V1 to V6 are integrated to calculate the variant pair boundary density score of the entire electron backscatter diffraction image, as shown in Figure 1 (b) It can be seen that the density of the highly selective V1-V2 boundary in the isothermal softening structure is the highest, which is 1.16 μm -1 .

[0094] Example 2

[0095] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0096] (1) Preparation of isothermal softening samples and thermal stability test: the same as in Example 1.

[0097] (2) The sample after isothermal softening treatment is electropolished and electron backscatter diffraction data is collected: the same as Example 1.

[0098] (3) Importing the electron backscatter diffraction data into MATLAB software for data calculation and smoothing: the same as in Example 1.

[0099] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Nishiyama-Wassermann orientation relationship, see Table 1.

[0100] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Figure 2 (a) As shown. It can be seen that the variants are selectively distributed after softening, with the high-frequency V10 and V12 variants being the main ones, accounting for 0.156 and 0.155 respectively. The variant pair groups V1 to V12 are classified, and the variant pair groups V1 to V6 are integrated to calculate the variant pair boundary density score of the entire electron backscatter diffraction image, as shown in Figure 2 (b) It can be seen that the density of the strongly selective V1-V6 boundary in the isothermal softening structure is the highest, which is 0.09 μm. -1 .

[0101] Example 3

[0102] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0103] (1) Preparation of isothermal softening samples and thermal stability test: the same as in Example 1.

[0104] (2) The sample after isothermal softening treatment is electropolished and electron backscatter diffraction data is collected: the same as Example 1.

[0105] (3) Importing the electron backscatter diffraction data into MATLAB software for data calculation and smoothing: the same as in Example 1.

[0106] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Greninger-Troiano orientation relationship, see Table 1.

[0107] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Figure 3 (a) As shown. It can be seen that the variants are selectively distributed after softening, with high-frequency V10, V19, V21, V22, and V24 variants as the main ones, accounting for 0.064, 0.081, 0.077, 0.076, and 0.088, respectively. The variant pair groups V1 to V24 are classified and the V1 to V6 variant pair groups are integrated. The variant pair boundary density distribution is shown in Figure 3 (b) It can be seen that the density of the highly selective V1-V6 boundary in the isothermal softening structure is the highest, which is 1.17 μm -1 .

[0108] Example 4

[0109] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0110] (1) Preparation of isothermal softening samples and thermal stability test: the same as in Example 1.

[0111] (2) The sample after isothermal softening treatment is electropolished and electron backscatter diffraction data is collected: the same as Example 1.

[0112] (3) Importing the electron backscatter diffraction data into MATLAB software for data calculation and smoothing: the same as in Example 1.

[0113] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Pitsch orientation relationship, see Table 1.

[0114] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Figure 4 (a) As shown. It can be seen that the variants are selectively distributed after softening, with high-frequency V9, V10, and V11 variants as the main ones, accounting for 0.125, 0.120, and 0.114, respectively. The variant pair groups V1 to V12 are classified, and the variant pair groups V1 to V6 are integrated. The density distribution of the variant pair boundaries is shown in Figure 4 (b) It can be seen that the density of the highly selective V1-V2 boundary in the isothermal softening structure is the highest, which is 0.36 μm -1 .

[0115] Comparative Example 1

[0116] In this comparative example, an isothermal softening sample was prepared and a thermal stability test was performed: the same as in Example 1, the isothermal softening tissue of Comparative Example 1 was not reconstructed. Figure 5 (a) shown.

[0117] Example 5

[0118] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0119] (1) Preparation of isothermal softening samples and thermal stability test: The chemical composition weight percentage of the high nitrogen martensitic steel used in the experiment is C 0.31%, Si 0.17%, Mn 0.39%, Cr 15.11%, Mo 0.98%, Ni 0.11%, N0.39%, and the balance is Fe and other inevitable impurity elements. The high nitrogen martensitic steel after quenching and tempering is isothermally treated at a temperature of 600°C and an isothermal time of 4h.

[0120] (2) The samples after isothermal softening treatment were electropolished and electron backscatter diffraction data were collected. The observation surface of the sample was electropolished using a perchloric acid alcohol solution with a volume fraction of 8% to eliminate the surface stress layer generated by the sample after mechanical grinding. The electropolishing parameters were a voltage of 28V and a current of 0.9A. Subsequently, electron backscatter diffraction data with a step size of 0.07μm and a resolution of 96% were collected.

[0121] (3) The electron backscatter diffraction data were imported into MATLAB software for data calculation and smoothing. The electron backscatter diffraction data were calculated with a threshold of 3° to form calculated and smoothed electron backscatter diffraction data, and the grain smoothing angle was 5°.

[0122] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Kurdjumov-Sachs orientation relationship, see Table 1.

[0123] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Figure 6 (a) As shown. It can be seen that the variants are selectively distributed after softening, with the high-frequency V9 and V10 variants being the main ones, accounting for 0.065 and 0.055 respectively. The variant pair groups V1 to V24 are classified, and the variant pair groups V1 to V6 are integrated to calculate the variant pair boundary density score of the entire electron backscatter diffraction image, as shown in Figure 6 (b) It can be seen that the density of the strongly selective V1-V3 (V5) boundary in the isothermal softening structure is the highest, which is 1.03 μm -1 .

[0124] Example 6

[0125] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0126] (1) Preparation of isothermal softening samples and thermal stability test: the same as in Example 5.

[0127] (2) The sample after isothermal softening treatment is electropolished and electron backscatter diffraction data is collected: the same as Example 5.

[0128] (3) Importing the electron backscatter diffraction data into MATLAB software for data calculation and smoothing: the same as in Example 5.

[0129] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Nishiyama-Wassermann orientation relationship, see Table 1.

[0130] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Figure 7 (a) As shown. It can be seen that the variants are selectively distributed after softening, with the high-frequency V7 variant being the main one, accounting for 0.20. The variant pair groups V1 to V12 are classified, and the variant pair groups V1 to V6 are integrated to calculate the variant pair boundary density score of the entire electron backscatter diffraction image, as shown in Figure 7 (b) It can be seen that the density of the highly selective V1-V2 boundary in the isothermal softening structure is the highest, which is 0.13 μm -1 .

[0131] Example 7

[0132] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0133] (1) Preparation of isothermal softening samples and thermal stability test: the same as in Example 5.

[0134] (2) The sample after isothermal softening treatment is electropolished and electron backscatter diffraction data is collected: the same as Example 5.

[0135] (3) Importing the electron backscatter diffraction data into MATLAB software for data calculation and smoothing: the same as in Example 5.

[0136] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Greninger-Troiano orientation relationship, see Table 1.

[0137] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Figure 8 (a) As shown. It can be seen that the variants are selectively distributed after softening, with the high-frequency V12 variant being the main one, accounting for 0.054. The variant pair groups V1 to V24 are classified, and the V1 to V6 variant pair groups are integrated. The density distribution of the variant pair boundaries is shown in Figure 8 (b) It can be seen that the V1-V3 (V5) boundary density of strong selectivity in the isothermal softening structure is the highest, which is 0.96 μm -1 .

[0138] Example 8

[0139] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0140] (1) Preparation of isothermal softening samples and thermal stability test: the same as in Example 5.

[0141] (2) The sample after isothermal softening treatment is electropolished and electron backscatter diffraction data is collected: the same as Example 5.

[0142] (3) Importing the electron backscatter diffraction data into MATLAB software for data calculation and smoothing: the same as in Example 5.

[0143] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Pitsch orientation relationship, see Table 1.

[0144] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Fig. 9 (a) As shown. It can be seen that the variants are selectively distributed after softening, with high-frequency V2, V5, and V12 variants as the main ones, accounting for 0.225, 0.276, and 0.248, respectively. The variant pair groups V1 to V12 are classified, and the variant pair groups V1 to V6 are integrated. The density distribution of the variant pair boundaries is shown in Fig. 9 (b) It can be seen that the density of the highly selective V1-V2 boundary in the isothermal softening structure is the highest, which is 0.11 μm -1 .

[0145] Comparative Example 2

[0146] In this comparative example, an isothermal softening sample was prepared and a thermal stability test was performed: the same as in Example 5, the isothermal softening structure of Comparative Example 1 was not reconstructed. Fig.10 (a) shown.

[0147] Example 9

[0148] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0149] (1) Preparation of isothermal softening samples and thermal stability test: The chemical composition weight percentage of the high nitrogen martensitic steel used in the experiment is C1.15%, Si 0.28%, Mn 0.29%, Cr 3.75%, Mo 9.47%, Co 8.01%, N 0.18%, W 1.49%, V 1.14%, and the balance is Fe and other inevitable impurity elements. The high nitrogen martensitic steel after quenching is isothermally treated at a temperature of 540°C and an isothermal time of 4h.

[0150] (2) The samples after isothermal softening treatment were electropolished and electron backscatter diffraction data were collected. The observation surface of the sample was electropolished using a perchloric acid alcohol solution with a volume fraction of 8% to eliminate the surface stress layer generated by the sample after mechanical grinding. The electropolishing parameters were a voltage of 28V and a current of 0.9A. Subsequently, electron backscatter diffraction data with a step size of 0.07μm and a resolution of 95% were collected.

[0151] (3) The electron backscatter diffraction data were imported into MATLAB software for data calculation and smoothing. The electron backscatter diffraction data were calculated with a threshold of 3° to form calculated and smoothed electron backscatter diffraction data, and the grain smoothing angle was 5°.

[0152] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Kurdjumov-Sachs orientation relationship, see Table 1.

[0153] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Fig.11 (a) As shown. It can be seen that the variants are selectively distributed after softening, with the high-frequency V5 and V9 variants being the main ones, accounting for 0.064 and 0.060 respectively. The variant pair groups V1 to V24 are classified, and the variant pair groups V1 to V6 are integrated to calculate the variant pair boundary density score of the entire electron backscatter diffraction image, as shown in Fig.11 (b) It can be seen that the V1-V3 (V5) boundary density with strong selectivity in the isothermal softening structure is the highest, which is 1.23 μm -1 .

[0154] Example 10

[0155] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0156] (1) Preparation of isothermal softening samples and thermal stability test: the same as in Example 9.

[0157] (2) The sample after isothermal softening treatment is electropolished and electron backscatter diffraction data is collected: the same as Example 9.

[0158] (3) Importing the electron backscatter diffraction data into MATLAB software for data calculation and smoothing: the same as in Example 9.

[0159] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Nishiyama-Wassermann orientation relationship, see Table 1.

[0160] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Fig.12(a) As shown. It can be seen that the variants are selectively distributed after softening, with the high-frequency V10 and V11 variants being the main ones, accounting for 0.238 and 0.208 respectively. The variant pair groups V1 to V12 are classified, and the variant pair groups V1 to V6 are integrated to calculate the variant pair boundary density score of the entire electron backscatter diffraction image, as shown in Fig.12 (b) It can be seen that the density of the strongly selective V1-V2 boundary in the isothermal softening structure is the highest, which is 0.104 μm -1 .

[0161] Embodiment 11

[0162] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0163] (1) Preparation of isothermal softening samples and thermal stability test: the same as in Example 9.

[0164] (2) The sample after isothermal softening treatment is electropolished and electron backscatter diffraction data is collected: the same as Example 9.

[0165] (3) Importing the electron backscatter diffraction data into MATLAB software for data calculation and smoothing: the same as in Example 9.

[0166] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Greninger-Troiano orientation relationship, see Table 1.

[0167] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Fig.13 (a) As shown. It can be seen that the variants are selectively distributed after softening, with the high-frequency V11, V17, and V22 variants being the main ones, accounting for 0.053, 0.053, and 0.052, respectively. The variant pair groups V1 to V24 are classified, and the V1 to V6 variant pair groups are integrated. The density distribution of the variant pair boundaries is shown in Fig.13 (b) It can be seen that the V1-V3 (V5) boundary density of strong selectivity in the isothermal softening structure is the highest, which is 1.25 μm -1 .

[0168] Example 12

[0169] A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, comprising the following steps:

[0170] (1) Preparation of isothermal softening samples and thermal stability test: the same as in Example 9.

[0171] (2) The sample after isothermal softening treatment is electropolished and electron backscatter diffraction data is collected: the same as Example 9.

[0172] (3) Importing the electron backscatter diffraction data into MATLAB software for data calculation and smoothing: the same as in Example 5.

[0173] (4) The calculated and smoothed electron backscatter diffraction data were reconstructed using the Pitsch orientation relationship, see Table 1.

[0174] (5) Calculate the variant frequency of the entire electron backscatter diffraction pattern, such as Fig.14 (a) As shown. It can be seen that the variants are selectively distributed after softening, with the high-frequency V3 variant being the main one, accounting for 0.355. The variant pair groups V1 to V12 are classified, and the V1 to V6 variant pair groups are integrated. The density distribution of the variant pair boundaries is shown in Fig.14 (b) It can be seen that the density of the highly selective V1-V2 boundary in the isothermal softening structure is the highest, which is 0.19 μm -1 .

[0175] Comparative Example 3

[0176] In this comparative example, an isothermal softening sample was prepared and a thermal stability test was performed: the same as in Example 9, the isothermal softening tissue of Comparative Example 1 was not reconstructed. Fig.14 (a) shown.

[0177] Examples 1 to 12 perform variant reconstruction according to the different orientation relationships in Table 1.

[0178] Table 1 Orientation relationship information between variants

[0179]

[0180] Results Analysis

[0181] Since variant analysis could not be performed for comparative examples 1, 2 and 3, quantitative statistics of the martensite structure after isothermal softening could not be performed. Figure 5 b~ Figure 5 As shown in Figure 5, they correspond to Kurdjumov-Sachs, Nishiyama-Wassermann, Greninger-Troiano and Pitsch relationships respectively. It can be seen that the variant organizations after reconstruction of different orientation relationships are divided into colors, representing the division of different martensite orientation relationships. Figure 5 b. Figure 5 c and Figure 5 d corresponds to Kurdjumov-Sachs, Nishiyama-Wassermann, and Greninger-Troiano orientation relationships, respectively, showing that the isothermal softening effect of high nitrogen martensitic steel is good, and the variant structure is completely reconstructed. Figure 5 e The corresponding Pitsch orientation relationship shows that the isothermal softening effect of high nitrogen martensitic steel is poor, and the variant organization is not fully displayed. Through quantitative statistics, the variant frequency distribution diagram and the variant boundary density diagram can be drawn.

[0182] Examples 5 to 8 Variant tissues reconstructed according to different orientation relationships are as follows Fig.10 b~ Fig.10 As shown in Figure 5, they correspond to Kurdjumov-Sachs, Nishiyama-Wassermann, Greninger-Troiano and Pitsch relationships respectively. It can be seen that the variant organizations after reconstruction of different orientation relationships are divided into colors, representing the division of different martensite orientation relationships. Fig.10 b. Fig.10 c and Fig.10 d corresponds to Kurdjumov-Sachs, Nishiyama-Wassermann, and Greninger-Troiano orientation relationships, respectively, showing that the isothermal softening effect of high nitrogen martensitic steel is good, and the variant structure is completely reconstructed. Fig.10 e The corresponding Pitsch orientation relationship shows that the isothermal softening effect of high nitrogen martensitic steel is poor, and the variant organization is not fully displayed. Through quantitative statistics, the variant frequency distribution diagram and the variant boundary density diagram can be drawn.

[0183] Examples 9 to 12 Variant tissues reconstructed according to different orientation relationships are as follows Fig.15 b~ Fig.15 As shown in Figure 5, they correspond to Kurdjumov-Sachs, Nishiyama-Wassermann, Greninger-Troiano and Pitsch relationships respectively. It can be seen that the variant organizations after reconstruction of different orientation relationships are divided into colors, representing the division of different martensite orientation relationships. Fig.15 b. Fig.15 c and Fig.15 d corresponds to Kurdjumov-Sachs, Nishiyama-Wassermann, and Greninger-Troiano orientation relationships, respectively, showing that the isothermal softening effect of high nitrogen martensitic steel is good, and the variant structure is completely reconstructed. Fig.15 e The corresponding Pitsch orientation relationship shows that the isothermal softening effect of high nitrogen martensitic steel is poor, and the variant organization is not fully displayed. Through quantitative statistics, the variant frequency distribution diagram and the variant boundary density diagram can be drawn.

[0184] In summary, in all embodiments, the reconstruction variants according to Kurdjumov-Sachs, Nishiyama-Wassermann, and Greninger-Troiano have better effects, while the Pitsch relationship shows that the variants are incomplete and the reconstruction effect is poor.

[0185] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0186] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, characterized in that: include: Data acquisition, obtaining electron backscatter diffraction data of high nitrogen martensitic steel after isothermal softening; Data processing, calculating and smoothing the electron backscatter diffraction data to obtain calculated and smoothed electron backscatter diffraction data; variant reconstruction, reconstructing the calculated and smoothed electron backscatter diffraction data according to different orientation relationships; Quantify the variants and determine the reasonable orientation relationship for displaying the isothermal softening structure of the high nitrogen martensitic steel based on the variant reconstruction effects under different orientation relationships, thereby achieving quantitative display of the organizational evolution of the martensitic variants during the isothermal softening process through variant reconstruction, and revealing the variant evolution mechanism of the high nitrogen martensitic steel after isothermal softening.

2. The method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants according to claim 1, characterized in that: The data acquisition includes: The electron backscatter diffraction data of the high nitrogen martensitic steel after isothermal softening are obtained by using a scanning electron microscope with electron backscatter diffraction, the acquisition step length is 0.05 μm to 0.1 μm, and the resolution is 80% to 100%.

3. The method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants according to claim 2, characterized in that: The acquisition step length is 0.05 μm to 0.08 μm, and the resolution rate is 90% to 100%.

4. The method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants according to claim 2 or 3, characterized in that: Before the data acquisition, the high nitrogen martensitic steel after isothermal softening is electrolytically polished; the electrolytic polishing: the electrolyte is a perchloric acid alcohol solution with a volume fraction of 8% to 15%, the voltage is 20V to 30V, the current is 0.5A to 1.0A, and the electrolysis time is 10s to 30s.

5. The method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants according to claim 4, characterized in that: The electrolyte is a perchloric acid alcohol solution with a volume fraction of 8% to 10%, the voltage is 25V to 30V, the current is 0.8A to 1.0A, and the electrolysis time is 20s to 25s.

6. The method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants according to claim 1, characterized in that: The data processing includes: The electron backscatter diffraction data is calculated with a threshold of 0° to 10°, and the grain smoothing range is 0° to 20°, to form calculated and smoothed electron backscatter diffraction data.

7. The method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants according to claim 6, characterized in that: The electron backscatter diffraction data is calculated with a threshold of 2° to 5°, and the grain smoothing range is 5° to 10°, to form calculated and smoothed electron backscatter diffraction data.

8. The method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants according to claim 1, characterized in that: The variant reconstruction includes: reconstructing the calculated and smoothed electron backscatter diffraction data according to the Kurdjumov-Sachs orientation relationship, the Nishiyama-Wassermann orientation relationship, the Greninger-Troiano orientation relationship and the Pitsch orientation relationship.

9. The method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants according to claim 1, characterized in that: The quantitative variants and analysis include: Based on the reconstructed parent phase austenite grain structure, image visualization analysis and statistics of martensite variants are carried out, including calculation of variant frequency and variant boundary density of electron backscattered diffraction patterns, thereby revealing the isothermal softening mechanism of high nitrogen martensitic steel.

10. Application of a method for displaying isothermal softening structure of high nitrogen martensitic steel by reconstructing variants, characterized in that: The method for displaying the isothermal softening structure of high nitrogen martensitic steel by reconstructing variants as described in any one of claims 1 to 9 is used to guide the composition design of metal materials and improve the thermal stability of metal materials.

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