Creep crack prediction method for heat-resistant steel welded joints based on spatial distribution of precipitated phase

Abstract

A method for predicting creep cracks of heat-resistant steel welded joints based on spatial distribution of precipitated phases includes sample preparation, cutting a cubic sample at the fusion line on both sides of the deposited metal of the heat-resistant steel welded joint, dividing the cubic sample into a plurality of sheet samples, marking the sheet samples one by one and keeping their original spatial order unchanged, performing XRD powder diffraction experiments on the sheet samples point by point and layer by layer, and recording the diffraction spectrum of each layer of the sheet samples, using the Rietveld full spectrum fitting method to analyze the diffraction spectrum of each layer of the sheet samples, constructing a three-dimensional spatial distribution map of the precipitated phase, and analyzing and predicting the initiation position and spatial extension direction of creep damage cracks near the weld of the heat-resistant steel welded joint. The present invention conducts research on creep damage fracture of heat-resistant steel, predicts the initiation position and extension direction of crack defects, and conducts targeted prediction and supervision in advance, which is crucial to ensuring the safe service of thermal power units and can avoid major safety accidents in power companies.

Description

Technical Field

[0001] The invention relates to the technical field of crack prediction of heat-resistant steel pipeline welded joints, in particular to a creep crack prediction method of heat-resistant steel welded joints based on spatial distribution of precipitation phases. Background Art

[0002] In order to alleviate the energy and environmental crisis, the thermal power industry has long been focusing on improving the efficiency of generator sets by increasing the boiler steam temperature. However, the increase in steam temperature makes the working environment of metal parts more severe, which makes the steel used in thermal power units face more stringent requirements. At present, high-grade martensitic heat-resistant steel has important applications in the thermal power industry due to its excellent high-temperature endurance strength and good high-temperature oxidation resistance and corrosion resistance. In the supercritical units that represent the most advanced level of the industry, supercritical units refer to generator sets with a main steam temperature of 600°C or more and a steam pressure of not less than 31MPa. High-grade heat-resistant martensitic steel has been widely used in the main steam pipeline. Judging from the theory of metallurgy and microstructure, its good performance is due to the meticulous chemical composition design and steelmaking technology, which has achieved a good combination of multiple strengthening mechanisms such as lath martensite strengthening, grain boundary strengthening, dislocation strengthening, precipitation phase dispersion precipitation strengthening and solid solution strengthening. However, many studies at home and abroad have shown that there is a region with significantly reduced creep strength near the fusion line of high-grade heat-resistant martensitic steel welded joints, which is prone to initiate type IV creep cracks, ultimately causing brittle cracking failure of the weld.

[0003] Synchrotron radiation high-energy X-rays have excellent properties such as high light intensity, strong penetration, good coherence and collimation. Based on synchrotron radiation light sources, a variety of non-destructive, high-resolution, dynamic, three-dimensional imaging, diffraction or scattering experimental studies can be carried out, and they have been applied in the basic research of metallurgy and materials engineering. Internationally, scholars have used synchrotron radiation light sources to study heat-resistant steel. For example, synchrotron X-ray micro-tomography was used to characterize the morphology and spatial distribution of creep holes in heat-resistant steel welded joints, analyze the influence of microscopic hole defects on their macroscopic creep properties, and improve the accuracy of material creep life assessment. However, this testing technology still has limitations. Its resolution is about 1mm, and it is difficult to image the distribution of nano-sized hole defects, which brings a certain degree of hysteresis to the analysis of creep crack initiation and propagation. How to predict and analyze the distribution law of smaller-scale defects is an urgent problem to be solved.

[0004] Therefore, in view of the defects of existing research on creep damage fracture, it is necessary to propose a method for predicting creep cracks in heat-resistant steel welded joints based on the spatial distribution of precipitated phases. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide an analysis method for predicting the distribution law of small-scale defects in heat-resistant steel pipeline welded joint cracks.

[0006] The present invention solves the technical problem by adopting the following technical solutions:

[0007] The creep crack prediction method of heat-resistant steel welded joint based on the spatial distribution of precipitated phase includes the following steps:

[0008] The first step is sample preparation, cutting a cubic sample at the fusion line on both sides of the deposited metal of the heat-resistant steel weld joint, and dividing the cubic sample into a plurality of sheet samples;

[0009] The second step is to mark the sheet samples in the first step one by one while keeping their original spatial order unchanged, and polish the surface of the sheet samples to meet the XRD (X-ray diffraction) diffraction requirements;

[0010] The third step is to perform XRD powder diffraction experiments on a plurality of the sheet samples point by point and layer by layer, and record the diffraction spectrum of each layer of the sheet samples;

[0011] The fourth step is to analyze the diffraction pattern of each layer of the sheet sample obtained in the third step by using the Rietveld full spectrum fitting method;

[0012] The fifth step is to construct a three-dimensional spatial distribution map of the precipitated phase based on the analysis results of the diffraction spectrum of each layer of the flaky sample obtained in the fourth step;

[0013] The sixth step is to analyze and predict the initiation position and spatial propagation direction of the creep damage crack near the weld of the heat-resistant steel welded joint based on the three-dimensional spatial distribution diagram of the precipitated phase in the fifth step.

[0014] Preferably, in the first step, both sides of the deposited metal are high-grade heat-resistant martensitic steel.

[0015] Preferably, the area where the fusion line on both sides of the deposited metal in the first step is located includes the interface between multiple deposited weld layers, the deposited metal / base material interface, the base material heat affected zone and the base material.

[0016] Preferably, the method for performing the XRD powder diffraction experiment in the third step is: using a precise XY translation stage to control the displacement of the sheet sample, performing the XRD diffraction experiment point by point on the surface of the sheet sample, continuously recording the diffraction pattern and marking it so that the serial number of the diffraction pattern corresponds to the diffraction position, and after completing the diffraction experiment of the first sheet sample, repeating this step and analyzing the next layer of sheet samples until the diffraction experiments of all sheet samples are tested.

[0017] Preferably, the step of analyzing the diffraction pattern of each layer of the flaky sample in the fourth step is:

[0018] a. Use the Rietveld full spectrum fitting method built into the Maud (Material Analysis using Diffraction) software to analyze the two-dimensional diffraction pattern of each layer of the flake sample to obtain the type and size information of the precipitated phase;

[0019] b. Compare the quantitative analysis results of the XRD diffraction experiment with the experimental results of the transmission electron microscope, and continuously improve the Rietveld fitting parameters until the physical phase size obtained by fitting the diffraction peak shape is consistent with the result obtained by direct measurement of the morphology phase, and establish a high-precision XRD diffraction pattern analysis method;

[0020] c. Analyze the two-dimensional diffraction patterns of all flake samples to complete the qualitative and quantitative analysis of the physical phase in the selected three-dimensional spatial region.

[0021] Preferably, the step of constructing a three-dimensional spatial distribution diagram of the precipitated phase in the fifth step is: using the Matlabsimulink tool to establish a three-dimensional graphics module, and representing the isoconcentration surfaces of the physical volume fraction, particle size, parent phase dislocation density and residual stress of the main precipitated phases M23C6, MX phase and Laves phase in the spatial region analyzed by the diffraction spectrum in the fourth step in an interactive interface, and by adjusting the values ​​of relevant parameters, the display results in the graphical interface change accordingly.

[0022] Preferably, the sixth step determines the initiation position and propagation direction of the creep crack by analyzing the distribution of the parent phase dislocation density and residual stress of the diffraction pattern.

[0023] The advantages and positive effects of the present invention are:

[0024] 1. The present invention indirectly predicts the location and spatial expansion direction of creep holes and cracks by analyzing the type and volume of the precipitated phase, which can provide guidance for steam pipeline flaw detection during the overhaul of thermal power units and provide a basis for judgment for the qualitative characterization of suspected defects. The diffraction experiment based on synchrotron radiation light source can solve the contradictory problem that the microstructure information of the precipitated phase can be accurately reflected in the existing research, but the characterization of the macroscopic area of ​​the sample cannot be completed. By taking advantage of its high-speed acquisition of diffraction patterns, the measurement of the micrometer-scale area can be completed quickly. The subsequent continuous diffraction experiment can complete the analysis of samples in a larger scale (millimeter level) in a short time. Finally, the fitting analysis of the diffraction pattern can obtain the size of the nanoscale precipitated phase and other crystallographic information, which not only achieves the unity of macro and micro, but also ensures the analysis accuracy.

[0025] 2. The present invention conducts research on creep damage fracture of heat-resistant steel, predicts the initiation location and expansion direction of crack defects, and conducts targeted prediction and supervision in advance, which is crucial to ensuring the safe service of thermal power units and can avoid major safety accidents in power companies. It also has the environmental protection effects of improving energy conversion efficiency and saving energy, and has obvious social and economic benefits.

[0026] 3. The present invention focuses on analyzing the particle size and spatial distribution of carbon and nitrogen compound precipitation phases in the scale of hundreds of microns to several millimeters near the fusion line of heat-resistant steel welded joints, which can provide a basis for the prediction and accurate diagnosis of type IV creep cracks in high-grade heat-resistant steel welded joints, deepen the understanding of the high-temperature service performance of high-grade heat-resistant martensitic steel, and achieve high-throughput and multi-scale characterization of material organization structure and microscopic phase composition, providing technical support for comprehensive evaluation of material and component damage, which is of great significance to the life prediction and risk assessment of high-pressure steam pipelines of thermal power units. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of sampling at the fusion line of the heat-resistant steel pipeline welding joint of the present invention;

[0028] Figure 2 It is a schematic diagram of the XRD diffraction experiment of the present invention;

[0029] Figure 3 Schematic diagram of micro-area distribution of the heat-affected zone of the high-grade heat-resistant martensitic steel of the present invention;

[0030] Figure 4 Schematic diagram of the distribution of four creep cracks of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may also be a component centered. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may also be a component centered. When a component is considered to be "set on" another component, it may be directly set on the other component or there may also be a component centered. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0034] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings:

[0035] like Figure 1 and Figure 2 As shown, the method for predicting creep cracks of heat-resistant steel welded joints based on the spatial distribution of precipitated phases according to the present invention comprises the following steps:

[0036] The first step is sample preparation, cutting a cubic sample at the fusion line on both sides of the deposited metal of the heat-resistant steel weld joint, and dividing the cubic sample into a plurality of sheet samples;

[0037] The second step is, Figure 1 As shown in (b), the plurality of the sheet samples in the first step are marked one by one while keeping their original spatial order unchanged, and the surface of the sheet samples is polished to meet the XRD (X-ray diffraction) diffraction requirements;

[0038] The third step is to perform XRD powder diffraction experiments on a plurality of the sheet samples point by point and layer by layer, and record the diffraction spectrum of each layer of the sheet samples;

[0039] The fourth step is to analyze the diffraction pattern of each layer of the sheet sample obtained in the third step by using the Rietveld full spectrum fitting method;

[0040] The fifth step is to construct a three-dimensional spatial distribution map of the precipitated phase based on the analysis results of the diffraction spectrum of each layer of the flaky sample obtained in the fourth step;

[0041] The sixth step is to analyze and predict the initiation position and spatial propagation direction of the creep damage crack near the weld of the heat-resistant steel welded joint based on the three-dimensional spatial distribution diagram of the precipitated phase in the fifth step.

[0042] The use of XRD (diffraction experiment of synchrotron radiation light source) can solve the contradictory problem that although the microstructure information of the precipitated phase can be obtained, the characterization of the macroscopic area of ​​the flake sample cannot be completed. By taking advantage of its high-speed acquisition of diffraction patterns, the measurement of the micron-scale area can be quickly completed. Subsequently, continuous diffraction experiments can be performed to complete the analysis of samples within a larger scale (millimeter level) in a short time. Finally, the fitting analysis of the diffraction pattern can obtain the size of the nanoscale precipitated phase and other crystallographic information, which not only realizes the unity of the macro and micro, but also ensures the accuracy of the analysis.

[0043] Furthermore, in the first step, both sides of the deposited metal are high-grade heat-resistant martensitic steel, which has important applications in the thermal power industry due to its excellent high-temperature endurance strength and good high-temperature oxidation resistance and corrosion resistance.

[0044] The heat-resistant steel pipe welding joint of the present invention is welded by high-grade heat-resistant martensitic steel thick-walled steel pipe. After dozens of cladding welding passes, each welding pass will form a weak surface along the fusion line of the pass, and finally form a number of interconnected weak surface groups in three-dimensional space, which are prone to form creep holes and then creep cracking. By analyzing the weak surfaces, the crack development direction and crack initiation position of the creep holes can be obtained.

[0045] High-grade heat-resistant martensitic steel is a typical Cr-Mo series heat-resistant steel with high Cr content. For the welded joints of this type of steel, from the weld filler metal to the parent material, the heat-affected zone is usually divided into Figure 3 The four micro-zones shown are the coarse grain zone (CGHAZ, near the fusion line), the fine grain zone (FGHAZ, near the coarse grain zone), the critical zone (ICHAZ, near the base material, also known as the incomplete recrystallization zone) and the over-tempered zone. The formation of the microstructure in each zone is related to the peak temperature experienced during the welding process:

[0046] (1) The coarse grain zone is located near the fusion line, and the peak temperature experienced during welding is far higher than A. C 3. During the heating process of this thermal cycle, carbides that can hinder the growth of austenite grains are dissolved, resulting in the formation of coarse austenite grains, which transform into martensite during the cooling process after welding.

[0047] (2) The fine grain area is far away from the fusion line and experiences a lower peak temperature Tp during welding than the coarse grain area, but it also reaches A C 3 or above. During the heating process, the carbides in the material at this position are not completely dissolved, and the growth of austenite grains is restricted by these carbides, so fine austenite grains are generated. For 9-12Cr steel, it transforms into martensite during the subsequent cooling process.

[0048] (3) The peak temperature Tp experienced by the critical zone during the welding thermal cycle is between A C 1 and A C 3, resulting in only some austenite grains being refined during heating. The newly formed fine austenite grains nucleate at the previously coarse austenite grain boundaries and martensite lath grain boundaries. During cooling, the austenite in 9-12Cr steel transforms into untempered martensite.

[0049] (4) The peak temperature Tp experienced by the tempering zone during the welding thermal cycle is lower than AC 1, but at the same time reaches the area above the tempering temperature.

[0050] Creep fracture is possible in the weld filler metal and the above-mentioned areas. According to the location of creep cracks, they are classified into Figure 4 The four types shown are:

[0051] Type I cracking: Creep cracks appear in and are confined to the weld metal;

[0052] Type II cracking: Creep cracks appear in the weld metal and develop from the weld metal to the base metal;

[0053] Type III cracking: creep failure occurs in the coarse grain area;

[0054] Type IV cracking creep damage occurs in the fine grain zone or critical zone, namely zone IV.

[0055] Among them, at high temperatures, the position with the lowest creep strength is the IV zone of the weld heat-affected zone. This area has a very fast creep hole formation rate, and microcracks are very easy to initiate and expand, causing malignant creep damage. This type of failure is called type IV creep cracking. At present, it is generally believed in the industry that metallurgical factors are the internal cause of type IV creep rupture of joints, and mechanical factors are necessary external conditions. After post-weld heat treatment, Cr-Mo ferritic heat-resistant steel will have a typical hardness drop in the fine-grained area close to the heat-affected zone of the parent material due to changes in the microstructure. This is called a softening zone. Under the condition of longitudinal stress, it determines the creep rupture strength of the entire joint.

[0056] Further, if Figure 1 As shown in (a), the area where the fusion line on both sides of the deposited metal in the first step is located includes the interface between multiple deposited weld layers, the deposited metal / base material interface, the base material heat affected zone and the base material.

[0057] Furthermore, the method for performing the XRD powder diffraction experiment in the third step is: using a precise XY translation stage to control the displacement of the sheet sample, performing the XRD diffraction experiment point by point on the surface of the sheet sample, continuously recording the diffraction pattern and marking it so that the serial number of the diffraction pattern corresponds to the diffraction position, and after completing the diffraction experiment of the first sheet sample, repeating this step and analyzing the next layer of sheet samples until the diffraction experiments of all sheet samples are tested.

[0058] Furthermore, the step of analyzing the diffraction pattern of each layer of the flaky sample in the fourth step is:

[0059] a. Use the Rietveld full spectrum fitting method built into the Maud (Material Analysis using Diffraction) software to analyze the two-dimensional diffraction pattern of each layer of the flake sample to obtain the type and size information of the precipitated phase;

[0060] b. Compare the quantitative analysis results of the XRD diffraction experiment with the experimental results of the transmission electron microscope, and continuously improve the Rietveld fitting parameters until the physical phase size obtained by fitting the diffraction peak shape is consistent with the result obtained by direct measurement of the morphology phase, and establish a high-precision XRD diffraction pattern analysis method;

[0061] c. Analyze the two-dimensional diffraction patterns of all flake samples to complete the qualitative and quantitative analysis of the physical phase in the selected three-dimensional spatial region.

[0062] Further, the step of constructing the three-dimensional spatial distribution diagram of the precipitated phase in the fifth step is: using the Matlab simulink tool to establish a three-dimensional graphics module, and showing the isoconcentration surface of the physical volume fraction, particle size, parent phase dislocation density and residual stress of the main precipitated phases M23C6, MX phase, and Laves phase in the spatial region analyzed by the diffraction spectrum in the fourth step in the interactive interface, and by adjusting the relevant parameter values, the display results in the graphical interface change accordingly. The Matlab simulink is a tool for visual simulation and is widely used in linear systems, nonlinear systems, and digital control. The parent phase dislocation density refers to the total length of the dislocation lines contained in the unit volume of the parent phase crystal, and the unit is 1 / square centimeter. Another definition of dislocation density is: the number of dislocation lines passing through a unit cross-sectional area, and the unit is also 1 / square centimeter.

[0063] The formation of Laves phase consumes W (tungsten) and Mo (molybdenum) elements in the crystal matrix, resulting in a decrease in solid solution strengthening. Although in the early stage of Laves phase formation, the precipitation strengthening effect of the fine Laves phase will enhance the creep resistance of the material, but due to the rapid coarsening rate of the Laves phase, when the Laves phase grows, it will reduce the creep resistance of the material. Therefore, overall, the Laves phase reduces the creep strength of the material.

[0064] Furthermore, the sixth step determines the initiation position and propagation direction of the creep crack by analyzing the distribution of the parent phase misalignment density and residual stress of the diffraction pattern. There is a region with significantly reduced creep strength near the fusion line of the high-grade heat-resistant martensitic steel welded joint, which is prone to initiate IV type creep cracks, and ultimately causes brittle cracking failure of the weld. Since the nucleation of creep voids in heat-resistant steel is controlled by both metallurgical and mechanical factors, it is closely related to the carbide precipitation phase in the heat-affected zone of the weld fusion line. The welding process will over-age the heat-affected zone. In the subsequent service process, the diffusion of carbon elements and the coarsening of carbide precipitation phases in this region are faster than those in other regions. Under the action of residual stress, creep holes are preferentially generated at the interface between larger carbides and the martensite matrix, and cracks will form and develop along these creep holes. Therefore, when the residual stress is large, the creep holes will also increase accordingly. In this way, the propagation direction of the cracks in the heat-resistant steel pipeline welded joint can be inferred.

[0065] In the specific implementation, the above method is used to process the sheet samples of the welded joints of the high-grade heat-resistant martensitic steel pipes on both sides, and the diffraction spectrum of the sheet samples is analyzed layer by layer to construct a three-dimensional spatial distribution map of the precipitated phase. The development direction and specific location of the creep cracks are determined based on the parent phase misalignment density and residual stress obtained by the analysis, so as to detect and take remedial measures at an early stage.

[0066] The present invention focuses on analyzing the particle size and spatial distribution law of carbon and nitrogen compound precipitation phases in the scale of hundreds of microns to several millimeters near the fusion line of heat-resistant steel welded joints, which can provide a basis for the prediction and accurate diagnosis of type IV creep cracks in high-grade heat-resistant steel welded joints, deepen the understanding of the high-temperature service performance of high-grade heat-resistant martensitic steel, realize high-throughput and multi-scale characterization of material organization structure and microscopic phase composition, provide technical support for comprehensive evaluation of material and component damage, and have great significance for the life prediction and risk assessment of high-pressure steam pipelines of thermal power units.

[0067] It should be emphasized that the embodiments described in the present invention are illustrative rather than restrictive, and therefore the present invention is not limited to the embodiments described in the specific implementation manners. Any other implementation manners derived by those skilled in the art based on the technical solutions of the present invention also fall within the scope of protection of the present invention.

Claims

1. A creep crack prediction method for heat-resistant steel welded joints based on the spatial distribution of precipitated phases, characterized in that: The following steps are involved: The first step is sample preparation, cutting a cubic sample at the fusion line on both sides of the deposited metal of the heat-resistant steel weld joint, and dividing the cubic sample into a plurality of sheet samples; The second step is to mark the sheet samples in the first step one by one while keeping their original spatial order unchanged, and polish the surface of the sheet samples to meet the XRD diffraction requirements; The third step is to perform XRD powder diffraction experiments on a plurality of the sheet samples point by point and layer by layer, and record the diffraction spectrum of each layer of the sheet samples; The fourth step is to analyze the diffraction pattern of each layer of the sheet sample obtained in the third step by using the Rietveld full spectrum fitting method; The steps for analyzing the diffraction pattern of each layer of the flake sample are: a. Use the Rietveld full spectrum fitting method built into the Maud software to analyze the two-dimensional diffraction pattern of each layer of the flake sample to obtain the type and size information of the precipitated phase; b. Compare the quantitative analysis results of the XRD diffraction experiment with the experimental results of the transmission electron microscope, and continuously improve the Rietveld fitting parameters until the physical phase size obtained by fitting the diffraction peak shape is consistent with the result obtained by direct measurement of the morphology phase, and establish a high-precision XRD diffraction pattern analysis method; c. Analyze the two-dimensional diffraction patterns of all flake samples to complete the qualitative and quantitative analysis of the phases in the selected three-dimensional spatial region; The fifth step is to construct a three-dimensional spatial distribution map of the precipitated phase based on the analysis results of the diffraction spectrum of each layer of the flaky sample obtained in the fourth step; The steps of constructing the three-dimensional spatial distribution map of the precipitated phase are as follows: using Matlab simulink tool to establish a three-dimensional graphics module, and displaying the volume fraction, particle size, parent phase dislocation density and residual stress concentration surface of the precipitated phase M23C6, MX phase and Laves phase in the spatial region analyzed by the diffraction spectrum in the fourth step in an interactive interface; The sixth step is to analyze and predict the initiation position and spatial propagation direction of the creep damage crack near the weld of the heat-resistant steel welded joint based on the three-dimensional spatial distribution diagram of the precipitated phase in the fifth step.

2. The method for predicting creep cracks of heat-resistant steel welded joints based on spatial distribution of precipitated phases according to claim 1, characterized in that: In the first step, both sides of the deposited metal are high-grade heat-resistant martensitic steel.

3. The method for predicting creep cracks of heat-resistant steel welded joints based on spatial distribution of precipitated phases according to claim 1, characterized in that: The area where the fusion line on both sides of the deposited metal in the first step is located includes the interface between multiple deposited weld layers, the deposited metal / base material interface, the base material heat affected zone and the base material.

4. The method for predicting creep cracks of heat-resistant steel welded joints based on spatial distribution of precipitated phases according to claim 1, characterized in that: The method for performing the XRD powder diffraction experiment in the third step is: using a precise XY displacement stage to control the displacement of the sheet sample, performing the XRD diffraction experiment point by point on the surface of the sheet sample, continuously recording the diffraction pattern and marking it so that the serial number of the diffraction pattern corresponds to the diffraction position, and after completing the diffraction experiment of the first sheet sample, repeating this step and analyzing the next layer of sheet samples until the diffraction experiments of all sheet samples are tested.

5. The method for predicting creep cracks of heat-resistant steel welded joints based on spatial distribution of precipitated phase according to claim 1, characterized in that: The steps of analyzing the diffraction pattern of each layer of the flaky sample in the fourth step are: a. Use the Rietveld full spectrum fitting method built into the Maud software to analyze the two-dimensional diffraction pattern of each layer of the flake sample to obtain the type and size information of the precipitated phase; b. Compare the quantitative analysis results of the XRD diffraction experiment with the experimental results of the transmission electron microscope, and continuously improve the Rietveld fitting parameters until the physical phase size obtained by fitting the diffraction peak shape is consistent with the result obtained by direct measurement of the morphology phase, and establish a high-precision XRD diffraction pattern analysis method; c. Analyze the two-dimensional diffraction patterns of all flake samples to complete the qualitative and quantitative analysis of the physical phase in the selected three-dimensional spatial region.

6. The method for predicting creep cracks of heat-resistant steel welded joints based on spatial distribution of precipitated phases according to claim 1, characterized in that: The step of constructing the three-dimensional spatial distribution map of the precipitated phase in the fifth step is: using the Matlab simulink tool to establish a three-dimensional graphics module, and showing the isoconcentration surface of the volume fraction, particle size, parent phase dislocation density and residual stress of the precipitated phase M23C6, MX phase and Laves phase in the spatial area analyzed by the diffraction spectrum in the fourth step in the interactive interface, and by adjusting the relevant parameter values, the display results in the graphical interface change accordingly.

7. The method for predicting creep cracks of heat-resistant steel welded joints based on spatial distribution of precipitated phases according to claim 6, characterized in that: The sixth step is to determine the initiation position and propagation direction of the creep crack by analyzing the parent phase dislocation density and residual stress distribution of the diffraction spectrum.

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