Microstructure quantification method for effectively hindering brittle crack propagation in weld metal

Abstract

The present invention relates to the field of crack extension of metal materials, and provides a microstructure quantification method and system for effectively hindering the extension of brittle cracks in weld metal; the method comprises: S1 using EBSD to collect microstructure crystallographic data of weld metal samples; S2 extracting crystallographic data and experimental {100} pole figures; S3 calculating crystallographic data and reconstructing parent phase austenite grains to determine the type of microstructure variant; S4 obtaining microstructure crystallographic structure unit images, performing boundary processing, and obtaining Bain units; S5 completing the quantification of microstructures that effectively hinder the extension of brittle cracks in weld metal. The present invention avoids the problem of insufficient accuracy of quantifying weld tissue from the perspective of morphology in the past, and also avoids the generality problem of calculating only from the grain boundary misorientation angle obtained by EBSD; accurately realizing the microstructure characterization and unit size quantification that can effectively hinder the extension of brittle cracks in weld metal.

Description

Technical Field

[0001] The present invention relates to the technical field of crack expansion of metal materials, and in particular to a microstructure quantification method and system for effectively hindering the expansion of brittle cracks in weld metal. Background Art

[0002] The performance of steel material welded joints is the key to the safety of the entire engineering component, and the performance of welded joints must be guaranteed to meet the standards. In the welded joint area, the typical structure of the weld metal is acicular ferrite, which presents an interlocking structure and a grain size at the micron level. It has a good barrier and deflection effect on the propagation of brittle cracks caused by impact, fatigue and other processes, and can improve the fracture toughness of the weld metal. Therefore, it is very necessary to quantitatively characterize the weld metal structure.

[0003] At present, the traditional method of characterizing weld metal structure mainly relies on optical microscope, scanning electron microscope and transmission electron microscope, which can give the morphological characteristics, content and size of needle-shaped ferrite from different angles, but the brittle crack extension process is not only related to the grain size of the material microstructure, but more importantly, it is related to the orientation difference between adjacent grains. Researchers have generally recognized that the microstructure that can effectively hinder the extension of brittle cracks in steel materials is the effective unit of its crystallographic structure, namely Bain group or Block. This type of crystallographic structure can only be obtained by crystallographic analysis, and the traditional morphological method of identifying microstructure grains cannot be achieved. Based on this, the electron backscatter diffraction (EBSD) probe equipped in the scanning electron microscope can obtain various types of microstructure crystallographic orientation information, but there are still many material researchers who only count the grain size through the grain boundary density of different orientation differences, and it is also difficult to accurately quantify the grain size that affects the extension of brittle cracks. To address this problem, the present invention proposes a method for obtaining crystallographic data of weld metal microstructure based on EBSD. Through the reconstruction of high-temperature parent phase austenite of the phase transformation structure and the crystallographic transformation relationship between the parent phase austenite and the daughter phase ferrite during the phase transformation process, the crystallographic structural units in the weld structure that effectively hinder the propagation of brittle cracks can be quantified, including their equivalent circle diameters and major and minor axis sizes. Summary of the invention

[0004] In view of the problem that the prior art is not accurate in quantifying the microstructure that hinders the growth of brittle cracks in weld metals, the present invention provides a method and system for quantifying the microstructure that effectively hinders the growth of brittle cracks in weld metals. EBSD technology is applied to extract microstructure crystallographic data, and data processing is combined with a microstructure crystallographic effective unit visualization method to achieve the purpose of quantifying the microstructure that can effectively hinder the growth of brittle cracks in weld metals.

[0005] The present invention adopts the following technical solution:

[0006] In one aspect, the present invention provides a method for quantifying microstructure in weld metal that effectively hinders the propagation of brittle cracks, comprising:

[0007] S1. Select a weld metal sample and collect microstructure crystallographic data of the weld metal sample using EBSD equipped in a scanning electron microscope;

[0008] S2, extracting the crystallographic data of step S1 and the experimental {100} pole figures corresponding to the crystallographic data; the crystallographic data includes Euler angles (and coordinate data);

[0009] S3, according to the theoretical phase transformation relationship of austenite to ferrite, reverse calculation is performed on the crystallographic data of step S2 (ferrite to austenite), the parent austenite grain orientation is obtained and the parent austenite grain reconstruction is completed, and then the theoretical {100} pole figure of the phase transformation structure is calculated according to the parent austenite orientation, and the actual phase transformation relationship between the parent austenite and the daughter ferrite is determined by matching the theoretical {100} pole figure with the experimental {100} pole figure, and the microstructure variant type under the actual phase transformation relationship is determined;

[0010] S4, according to the theoretical {100} pole figure obtained in step S3 and the determined microstructure variant type, the crystallographic data in step S2 is subjected to a "data-to-image" conversion process to obtain three microstructure crystallographic structure unit images that can effectively hinder the propagation of brittle cracks, and a boundary process is performed to obtain a closed unit structure, namely, a Bain unit;

[0011] S5. Process the crystallographic structure unit image of the microstructure obtained in step S4 to obtain the area size, equivalent circle diameter size, and major and minor axis size of each closed unit structure, that is, to complete the quantification of the microstructure in the weld metal that effectively hinders the propagation of brittle cracks.

[0012] Any possible implementation as described above further provides an implementation, in step S1, when collecting microstructure crystallographic data using EBSD, the scanning step length does not exceed 0.15 μm, and the resolution rate of each phase of the microstructure is not less than 85%.

[0013] As any possible implementation described above, a further implementation is provided, in step S2, when extracting microstructure crystallographic data and corresponding {100} experimental pole figures, EBSD post-processing software HKL Channel5 is used.

[0014] Any possible implementation as described above further provides an implementation, in step S3, using MATLAB programming to calculate the microstructure crystallographic data and reconstruct the parent phase austenite grains.

[0015] As any possible implementation described above, a further implementation is provided, in step S4, the crystallographic data is processed using HKLChannel5 software to obtain a microstructure crystallographic structure unit image, and the image is subjected to boundary processing to obtain a closed unit structure.

[0016] Any possible implementation as described above, further provides an implementation, in step S5, using the image processing software Image-Pro to process the crystallographic structure unit image to obtain the area size, equivalent circle diameter size, major and minor axis size of each closed unit structure.

[0017] On the other hand, the present invention also provides a microstructure quantification system for effectively hindering the growth of brittle cracks in weld metal, and the system adopts the above-mentioned microstructure quantification method for effectively hindering the growth of brittle cracks in weld metal.

[0018] On the other hand, the present invention also provides a terminal, comprising: a processor and a memory; the memory is used to store a computer program; the processor is used to execute the computer program stored in the memory, so that the terminal executes the above-mentioned microstructure quantification method in the weld metal that effectively hinders the extension of brittle cracks.

[0019] The beneficial effects of the present invention are:

[0020] 1. From the perspective of microstructure crystallographic structure, the problem of insufficient accuracy in quantifying weld structure from the perspective of morphology is avoided. It is also different from the generality of calculating only from the grain boundary misorientation angle obtained from EBSD.

[0021] 2. The method proposed in the present invention uses EBSD data for calculation, and then combines software processing to accurately realize the microstructural characterization and unit size quantification in the weld metal that can effectively hinder the propagation of brittle cracks, which can further provide more accurate data support for the service safety of welding engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Shown is a schematic flow chart of a microstructure quantification method for effectively hindering the propagation of brittle cracks in weld metal according to an embodiment of the present invention.

[0023] Figure 2 Shown are metallographic images, quality images, 5° grain boundary images and corresponding grain size distribution images of three types of weld metal structures obtained by optical microscopy and EBSD, respectively, in Examples 1, 2 and 3 of the present invention.

[0024] Figure 3Shown are the microstructural crystallographic structural units (three colors represent three different Bain units) diagrams of the weld metal obtained after the processing of steps S3-S5 in Example 1, which can effectively hinder the propagation of brittle cracks, the corresponding grain boundary diagrams, the overlapping {100} theoretical and experimental pole figures, and the quantitative unit size distribution diagram.

[0025] Figure 4 Shown are the expansion diagram of brittle cracks in the actual weld metal structure, the microstructure crystallographic structure unit diagram that can effectively hinder the expansion of brittle cracks, and the corresponding grain boundary diagram. DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention will be described in detail below in conjunction with specific drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered isolated, and they can be combined with each other to achieve better technical effects. In the drawings of the following embodiments, the same reference numerals appearing in each drawing represent the same features or components, which can be applied to different embodiments.

[0027] like Figure 1 As shown, a microstructure quantification method for effectively hindering the propagation of brittle cracks in a weld metal according to an embodiment of the present invention comprises:

[0028] S1. Select a weld metal sample and collect microstructure crystallographic data of the weld metal sample using EBSD equipped in a scanning electron microscope;

[0029] S2, extracting the crystallographic data of step S1 and the corresponding experimental {100} pole figures; the crystallographic data includes Euler angles;

[0030] S3, according to the theoretical phase transformation relationship of austenite to ferrite, reverse calculation is performed on the crystallographic data of step S2 (ferrite to austenite), the parent austenite grain orientation is obtained and the parent austenite grain reconstruction is completed, and then the theoretical {100} pole figure of the phase transformation structure is calculated according to the parent austenite orientation, and the actual phase transformation relationship between the parent austenite and the daughter ferrite is determined by matching the theoretical {100} pole figure with the experimental {100} pole figure, and the microstructure variant type under the actual phase transformation relationship is determined;

[0031] S4, according to the theoretical {100} pole figure obtained in step S3 and the determined microstructure variant type, the crystallographic data in step S2 is subjected to a "data-to-image" conversion process to obtain three microstructure crystallographic structure unit images that can effectively hinder the propagation of brittle cracks, and a boundary process is performed to obtain a closed unit structure, namely, a Bain unit;

[0032] S5. Process the crystallographic structure unit image obtained in step S4 to obtain the area size, equivalent circle diameter size, and major and minor axis size of each closed unit structure, that is, to complete the quantitative determination of the microstructure in the weld metal that effectively hinders the propagation of brittle cracks.

[0033] In this paper, 550MPa grade marine engineering steel is used as the experimental material, and a flat plate butt welding experiment is carried out on it by submerged arc welding. The difference in the welding process is the interlayer temperature, which is designed to be 80℃, 130℃ and 250℃. In this way, three different weld metal structures are obtained, and the acicular ferrite characterization is used to demonstrate the quantitative method of microstructure in weld metal that effectively hinders the propagation of brittle cracks.

[0034] like Figure 2 The optical micrographs of the three weld metal structures and the quality map and grain boundary distribution map obtained by EBSD show that the metallographic structure is basically consistent with the weld structure in the EBSD quality image, that is, the morphology and size of the acicular ferrite, and is also consistent with the unit size of the grain boundary map with a 5° orientation difference as the interface. According to the EBSD quality map and the 5° orientation difference grain boundary map, the acicular ferrite grain sizes of the three embodiments are 0.91μm, 1.20μm and 1.70μm respectively, and the ferrite grain size increases with the increase of the interlayer temperature.

[0035] Based on the small-angle misorientation of the acicular ferrite interface, which cannot effectively hinder the propagation of brittle cracks, the present invention processes the acquired acicular ferrite EBSD data and visualizes the crystallographic structural units (Bian group) that can effectively hinder the propagation of brittle cracks, and obtains the following: Figure 3 The Bain unit diagram shown in FIG. 1 , in which three colors (light gray, light gray, and dark gray) represent three different Bain groups, can be further combined with HKL Channel5 software to perform interface calibration on the Bain unit. Finally, the Bain unit sizes in the three embodiments can be obtained by calculation using Image-Pro software, which are 1.33 μm, 1.56 μm, and 2.38 μm, respectively.

[0036] It should be pointed out that the effective unit size calculated by this method is different from that of the metallographic method or the EBSD orientation difference method. This method can accurately count the structural units in the weld metal structure that can effectively hinder the propagation of brittle cracks from the perspective of the relationship between crack propagation and crystallographic structure in the material fracture process, and realize the quantification of effective crystallographic structural units. It is an innovative method.

[0037] In order to more clearly present the relationship between the effective crystallographic structural unit and the brittle crack extension achieved by the method of the present invention, Figure 4The brittle crack propagation in a typical weld metal structure is given. As shown by the arrow, it can be significantly found that the brittle crack will pass through some ferrite grains without deflection or hindrance, but when the crack propagates to the interface of the effective crystallographic structure unit, it will be hindered or stopped, indicating that the effective unit quantified by this method can more accurately reflect the toughness of the weld metal.

[0038] The present invention proposes a method for obtaining crystallographic data of weld metal microstructure based on EBSD. Through the reconstruction of high-temperature parent phase austenite of phase transformation structure and the crystallographic transformation relationship between parent phase austenite and daughter phase ferrite during phase transformation process, the crystallographic structural unit that effectively hinders the propagation of brittle cracks in weld structure can be quantified, including its equivalent circle diameter and major and minor axis dimensions. The application of the method of the present invention can provide more accurate data support for the judgment of the quality of metal material welding toughness and provide scientific data guidance for the service safety of actual welding engineering.

[0039] Although several embodiments of the present invention have been given herein, those skilled in the art should understand that the embodiments of the present invention may be modified without departing from the spirit of the present invention. The above embodiments are merely exemplary and should not be used as a limitation on the scope of the present invention.

Claims

1. A microstructure quantitative method for effectively hindering the propagation of brittle cracks in weld metal, characterized in that: The method comprises: S1. Select a weld metal sample and collect microstructure crystallography data of the weld metal sample; S2, extracting the crystallographic data of step S1 and the experimental {100} pole figures corresponding to the crystallographic data; S3, performing reverse calculation on the crystallographic data of step S2, wherein the reverse calculation is the transformation of ferrite into austenite, obtaining the orientation of the parent austenite grains and completing the reconstruction of the parent austenite grains, and then calculating the theoretical {100} pole figure of the phase transformation structure according to the orientation of the parent austenite, and determining the actual phase transformation relationship between the parent austenite and the daughter ferrite by matching the theoretical {100} pole figure with the experimental {100} pole figure, and determining the type of microstructure variant under the actual phase transformation relationship; S4, according to the theoretical {100} pole figure obtained in step S3 and the determined microstructure variant type, the crystallographic data in step S2 is subjected to a "data-to-image" conversion process to obtain three microstructure crystallographic structure unit images that can effectively hinder the propagation of brittle cracks, and a boundary process is performed to obtain a closed unit structure, namely, a Bain unit; S5, processing the microstructure crystallographic structure unit image obtained in step S4 to obtain the area size, equivalent circle diameter size, and major and minor axis size of each closed unit structure, that is, completing the quantitative determination of the microstructure in the weld metal that effectively hinders the propagation of brittle cracks; In step S2, when extracting microstructure crystallographic data and corresponding experimental {100} pole figures, EBSD post-processing software HKL Channel5 is used; the crystallographic data includes Euler angles.

2. The microstructure quantification method for effectively inhibiting brittle crack propagation in weld metal according to claim 1, characterized in that: In step S1, The microstructure crystallographic data of the weld metal sample is collected by using EBSD equipped in a scanning electron microscope, the scanning step length does not exceed 0.15 μm, and the resolution rate of each phase of the microstructure is not less than 85%.

3. The microstructure quantification method for effectively inhibiting the propagation of brittle cracks in weld metal according to claim 1, characterized in that: In step S3, MATLAB programming is used to calculate the microstructure crystallographic data and reconstruct the parent phase austenite grains.

4. The microstructure quantification method for effectively inhibiting brittle crack propagation in weld metal according to claim 1, characterized in that: In step S4, the crystallographic data is processed using HKL Channel5 software to obtain a microstructure crystallographic structure unit image, and a boundary processing is performed to obtain a closed unit structure.

5. The microstructure quantification method for effectively inhibiting the propagation of brittle cracks in weld metal according to claim 1, characterized in that: In step S5, the crystallographic structure unit image is processed using the image processing software Image-Pro to obtain the area size, equivalent circle diameter size, and major and minor axis size of each closed unit structure.

6. A microstructure quantification system for effectively hindering the propagation of brittle cracks in weld metal, characterized in that: The system adopts the microstructure quantification method for effectively hindering the propagation of brittle cracks in weld metal as described in any one of claims 1-5.

7. A terminal, characterized in that: include: Processor and memory; The memory is used to store computer programs; The processor is used to execute the computer program stored in the memory so that the terminal executes the microstructure quantification method for effectively hindering the extension of brittle cracks in the weld metal according to any one of claims 1 to 5.

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