Method for evaluating cracking tendency of valve sealing surface, evaluation model and its establishment method, and method for preparing valve sealing surface with low cracking tendency

Abstract

The application discloses a kind of valve sealing surface cracking tendency evaluation method, evaluation model and its establishment method and the preparation method of low cracking tendency valve sealing surface, evaluation method includes the following steps: based on phase equilibrium calculation and solidification path simulation, preliminary design of sealing surface composition is carried out;Based on the composition of preliminary design, the initial design of additive manufacturing process parameters and deposition path is carried out using finite element simulation, and sample preparation is completed;XRD residual stress test and three-point bending fracture toughness test are carried out on the sample, and based on the test results, the evaluation criterion of sealing surface cracking tendency is formed.The valve sealing surface cracking tendency evaluation method of the application proposes the results of XRD residual stress test and three-point bending fracture toughness test as the evaluation criterion of cracking tendency, which greatly reduces the preparation cost of valve sealing surface and significantly improves the research and development efficiency.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing and evaluation technology, specifically relating to an evaluation method for the cracking tendency of valve sealing surfaces, an evaluation model based on the evaluation method and its establishment method, and a method for preparing valve sealing surfaces with low cracking tendency, which is particularly suitable for high-stress components such as nuclear-grade valve sealing surfaces. Background Technology

[0002] Nuclear-grade valve sealing surfaces are critical components of nuclear power equipment, crucial for the safe and stable operation of nuclear power plants. However, they are prone to welding cracks and brittle fractures during manufacturing and operation, posing significant safety hazards. The sealing surface properties of nuclear-grade valves are mainly related to microstructure factors such as brittle precipitates and low-melting-point phases, as well as differences in physical properties such as thermal expansion coefficients and elastic moduli, or high levels of residual stress concentration caused by rapid heating and cooling during the cladding process. Therefore, preparing nuclear-grade valve sealing surfaces with low cracking tendency is currently one of the major technical bottlenecks in the nuclear power field.

[0003] Nuclear-grade valve sealing surfaces are primarily fabricated using methods such as manual arc welding, gas-shielded arc welding, and plasma arc welding. These methods utilize sealing surface metal welding wire, welding rods, and alloy powders as raw materials, depositing them onto the valve seat surface along specific paths. Compared to the aforementioned heat sources, lasers offer unique advantages, including smaller heat source size and heat-affected zone, higher energy density and control precision, and better forming quality. They are also more conducive to achieving micro-area composition and residual stress control. Laser-directed energy deposition technology, based on the discrete-stacking principle and combined with computer-aided 3D modeling, enables layer-by-layer melting and deposition, achieving rapid 3D forming of metal components. This technology holds great promise in the field of nuclear-grade valve sealing surface fabrication.

[0004] Regarding the cracking tendency of nuclear-grade valve sealing surfaces, according to standard GB / T 22652-2019, the evaluation standard for valve sealing surface welding process mainly includes conventional tests such as weld thickness, hardness, and chemical composition. Currently, only visual inspection or magnifying glass appearance inspection and penetrant testing are used to judge cracks. The detection accuracy and trial-and-error costs are high, and a mature technology for preparing valve sealing surfaces with low cracking tendency has not yet been formed. At the same time, due to the small thickness and poor plastic deformation capacity of valve sealing surfaces, conventional methods are difficult to be directly applied to analyze their cracking tendency. There is an urgent need to develop effective detection methods and evaluation criteria.

[0005] Although studies have shown that process optimization or post-weld heat treatment can help alleviate residual stress, there are numerous process parameters and complex mechanisms of interaction among multiple parameters. In addition, the formulation of additive manufacturing and post-processing processes is mainly based on experimental trial and error, lacking mature theoretical basis and technical support.

[0006] The above background information is provided only to aid in understanding the inventive concept and technical solution of this invention. It does not necessarily belong to the prior art of this invention. In the absence of clear evidence that the above information was disclosed before the filing date of this invention, the above background information should not be used to evaluate the novelty and inventiveness of this invention. Summary of the Invention

[0007] In view of this, the present invention provides a rapid assessment method for the cracking tendency of valve sealing surfaces, which effectively solves the existing technical problems. It achieves rapid assessment of the cracking tendency of valve sealing surfaces based on XRD residual stress test and three-point bending fracture toughness test.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for assessing the cracking tendency of a valve sealing surface includes the following steps:

[0010] Based on phase equilibrium calculations and solidification path simulations, the composition of the sealing surface is pre-designed.

[0011] Based on the pre-designed composition, the additive manufacturing process parameters and deposition path were initially designed using finite element simulation, and the sample preparation was completed.

[0012] XRD residual stress test and three-point bending fracture toughness test were performed on the sample. Based on the test results, an evaluation criterion for the tendency of the sealing surface to crack was formed.

[0013] According to some preferred embodiments of the present invention, the evaluation criterion for the cracking tendency of the sealing surface is: the average residual stress on the surface of the valve sealing surface ≤ 400 MPa, and the room temperature fracture toughness. K IC ≥25MPa·m 1 / 2 If so, it is judged as having a low tendency to crack.

[0014] According to some preferred embodiments of the present invention, the phase balance calculation includes the following steps:

[0015] Equilibrium thermodynamics calculations are performed based on the CALPHAD method. The material composition is input, the phase composition and equilibrium volume fraction of precipitated phases are calculated, and the types of low-melting-point phases and hard and brittle phases and their precipitation temperature ranges are identified.

[0016] According to some preferred embodiments of the present invention, the solidification path simulation includes the following steps:

[0017] The Scheil module of Thermo-Calc software was used to simulate the non-equilibrium solidification path and determine the non-equilibrium precipitation law of low-melting-point phase and hard and brittle phase in the additive manufacturing process. This information is used to guide the formulation of subsequent additive manufacturing process parameters and post-processing processes.

[0018] According to some preferred embodiments of the present invention, the process parameters include one or more of the following: heat source power, feeding speed, heat source moving speed, decoking amount, and protective gas flow rate.

[0019] In some embodiments, the laser powder feeding process parameters are: laser power 1800-2500W, defocusing amount -1 to -4mm, scanning speed 4-10mm / s, powder feeding speed 8-25g / min, and protective gas flow rate 12-30L / min;

[0020] In some embodiments, the laser wire feeding process parameters are: laser power 1400-2200W, defocusing amount -1 to -4mm, scanning speed 5-9mm / s, wire feeding speed 2-8mm / s, wire feeding diameter 1.2-1.6mm, and protective gas flow rate 10-20L / min.

[0021] According to some preferred embodiments of the invention, the deposition path includes radial deposition, circumferential deposition, and continuous reciprocating deposition. The deposition direction angle of each deposition layer can also be changed during the deposition process.

[0022] According to some preferred embodiments of the present invention, the finite element simulation is performed by using finite element software, importing material properties and heat source equations into the software, and using the birth and death element method to model the valve sealing surface workpiece as a whole and simulate the stress field distribution.

[0023] According to some preferred embodiments of the present invention, if the stress field distribution results of the finite element simulation show that the average residual stress on the surface is consistently higher than 400 MPa, then a post-processing process needs to be introduced during the finite element simulation; the post-processing process includes stepped slow cooling or multi-stage aging treatment. Whether or not to introduce a post-processing method may be selected depending on the stress field simulation results, with the main purpose of further mitigating the residual stress caused by rapid cooling during the preparation process.

[0024] According to some preferred embodiments of the present invention, during the XRD residual stress test and the three-point bending fracture toughness test of the specimen, the hardness test of the specimen is performed simultaneously according to the standard GB / T 22652-2019, and the specimen with an average surface hardness ≥38HRC is a qualified specimen.

[0025] According to standard GB / T 39520-2020, the XRD residual stress test includes the following steps: selecting a surface position far from the edge of the valve sealing surface, and calculating the residual stress based on the degree of XRD diffraction peak shift.

[0026] According to standard GB / T 21143-2014, the three-point bending fracture toughness test includes the following steps: based on a micro three-point bending fixture, a micron-sized notch is prepared on the surface of the sealing cladding layer, and the strain field at the tip of the notch is monitored in real time using digital image correlation (DIC) to calculate the fracture toughness value.

[0027] According to some preferred embodiments of the present invention, the machine learning model includes one of the following algorithms: decision tree, support vector machine, K-nearest neighbors, random forest, artificial neural network, adaptive boosting model, etc.

[0028] The present invention also provides a method for establishing an evaluation model for the cracking tendency of valve sealing surfaces, including the evaluation method described above.

[0029] According to some preferred embodiments of the present invention, the method further includes the step of:

[0030] Based on the composition of the sealing surface, additive manufacturing process parameters and deposition path, post-processing process, XRD residual stress test data and three-point bending fracture toughness test data, an evaluation model for the cracking tendency of the valve sealing surface is established based on machine learning methods to construct the mapping relationship between "composition-process-cracking tendency".

[0031] The present invention also provides an evaluation model for the cracking tendency of valve sealing surfaces, which is established using the method described above.

[0032] The present invention also provides a method for preparing a valve sealing surface, characterized in that the evaluation model described above is used to output the corresponding preparation process based on the composition of the sealing surface, thereby preparing a valve sealing surface with low cracking tendency.

[0033] The present invention also provides a method for manufacturing a low-cracking-prone nuclear-grade valve sealing surface, which includes the optimization method described above.

[0034] In some embodiments of the present invention, the method for preparing a valve sealing surface with low cracking tendency can solve the problem of brittle cracking caused by high-level residual stress in the sealing surface of nuclear-grade valves. It can achieve efficient synergistic optimization and proactive design of alloy composition, additive manufacturing process, and post-processing process, and specifically includes the following steps:

[0035] Step 1: Design of the sealing surface composition of nuclear-grade valves.

[0036] Composition pre-design was carried out for different sealing surface alloy systems and different alloy element additions, and phase balance calculations and solidification path simulations were performed to clarify the solidification and precipitation rules of low melting point phases and hard and brittle phases.

[0037] Step 2: Additive manufacturing process selection and path design.

[0038] Based on the pre-designed composition, and combined with the process parameters such as heat source power, feeding speed, and heat source moving speed simulated by finite element method, as well as the influence of additive manufacturing deposition path on the stress field, the additive manufacturing process parameters and deposition path are preliminarily designed. If the average residual stress of the surface layer is always higher than 400 MPa, post-processing methods such as stepped slow cooling and multi-stage aging treatment need to be introduced to determine the processing parameters of the sealing surface and complete the sample preparation.

[0039] Step 3: Testing and evaluation of the tendency of the sealing surface to crack.

[0040] By combining XRD residual stress testing and three-point bending fracture toughness testing, the results of composition optimization and process optimization of the sealing surface are verified, and a quantitative evaluation criterion for the cracking tendency of the sealing surface is formed. At the same time, the hardness of the sample is evaluated to meet the basic service requirements.

[0041] Step 4: Construct a multi-parameter machine learning model.

[0042] The system constructs a machine learning model of alloy composition, additive manufacturing process parameters and deposition path, post-processing process, residual stress and cracking tendency (XRD residual stress test and three-point bending fracture toughness test results), and establishes a mapping relationship of "composition-process-cracking tendency".

[0043] Step 5: Preparation of valve sealing surfaces with low cracking tendency.

[0044] Based on the predetermined valve sealing surface composition and the corresponding model analysis results, the corresponding preparation process is output to prepare the valve sealing surface.

[0045] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art: the method for evaluating the cracking tendency of the valve sealing surface of the present invention proposes the results of XRD residual stress test and three-point bending fracture toughness test as the evaluation criteria for cracking tendency, which greatly reduces the preparation cost of valve sealing surface and significantly improves R&D efficiency. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the logic flow of the method for preparing a valve sealing surface with low cracking tendency according to an embodiment of the present invention;

[0048] Figure 2 These are macroscopic images of the sealing surface of a nuclear-grade valve obtained by laser-directed energy deposition in Embodiment 2 of the present invention;

[0049] Figure 3 This is a microstructure image of the sealing surface of a nuclear-grade valve obtained by laser-directed energy deposition in Embodiment 2 of the present invention. Detailed Implementation

[0050] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0051] Currently, testing for cracking in nuclear-grade valve seals primarily relies on experimental trial-and-error methods. Samples are prepared after independent optimization of individual parameters, and crack inspection is conducted using traditional methods such as visual observation and penetrant testing. This approach has limited accuracy and development efficiency, resulting in high R&D costs. This invention addresses the critical engineering problem of brittle cracking in nuclear-grade valve seal surfaces. Addressing the limitations of theoretical support for cracking tendency in nuclear-grade valve seal surfaces and the constraints of preparation and evaluation methods, it considers multiple dimensions, including alloy composition, additive manufacturing process, and post-processing. It assesses the cracking tendency of valve seal surfaces based on residual stress and fracture toughness. Simultaneously, it utilizes machine learning models to construct a mapping relationship between multiple parameters (alloy composition, additive manufacturing process, post-processing) and cracking tendency, establishing a link between parameters and cracking tendency. Finally, it outputs an optimized preparation process based on the seal surface composition.

[0052] Valve cracking is a significant problem, but there are no mature methods for predicting cracking tendency. This invention presents a cracking tendency detection method based on XRD residual stress testing and three-point bending fracture toughness testing, forming a quantitative evaluation index to facilitate accurate determination of the cracking tendency of hard alloys such as nuclear-grade valve sealing surfaces. Furthermore, based on databases and machine learning models, it can quickly achieve efficient synergistic optimization of alloy composition, additive manufacturing process, and post-processing, efficiently designing and fabricating valve sealing surfaces with low cracking tendency. It eliminates components and processes with high cracking tendency, enabling proactive design and significantly reducing trial-and-error costs. Targeted low-cracking-tendency optimization schemes are provided according to different materials and performance requirements, effectively solving the sealing surface cracking problem. Compared to traditional trial-and-error methods, this significantly improves efficiency and brings considerable economic benefits to the fabrication of nuclear-grade valve sealing surfaces. Simultaneously, this technology has good universality and scalability, not limited to nuclear-grade valve sealing surface applications, but also providing technical support for applications such as the design of hard materials and dissimilar metal interfaces under high stress and complex working conditions. Currently, there is no clear detection method for the cracking tendency of valve sealing surfaces. This invention combines residual stress and cracking tests to propose a clear evaluation method and a method for preparing valve sealing surfaces with low cracking tendency.

[0053] like Figure 1 As shown, the method for preparing the valve sealing surface with low cracking tendency of the present invention specifically includes the following steps:

[0054] Step 1: Design of the sealing surface composition of nuclear-grade valves.

[0055] Composition pre-design was carried out for different sealing surface alloy systems and different alloy element additions, and phase balance calculations and solidification path simulations were performed to clarify the solidification and precipitation rules of low melting point phases and hard and brittle phases.

[0056] Phase equilibrium calculations include the following steps:

[0057] Equilibrium thermodynamic calculations are performed using the CALPHAD method. The material composition (e.g., Stellite6 cobalt-based alloy, Norem02 iron-based alloy, or composition with different alloying elements) is input to calculate the phase composition and equilibrium volume fraction of precipitated phases, identifying the types and precipitation temperature ranges of low-melting-point and brittle phases. Low-melting-point and brittle phases are more prone to cracking; therefore, their precipitation should be suppressed during composition and process design.

[0058] Solidification path simulation includes the following steps:

[0059] Non-equilibrium solidification path simulation was performed using the Scheil module of Thermo-Calc software to determine the non-equilibrium precipitation patterns of low-melting-point and hard-brittle phases during additive manufacturing. This information guides the formulation of subsequent additive manufacturing process parameters and post-processing techniques. Additive manufacturing involves rapid cooling, which is a non-equilibrium thermodynamic process. Understanding non-equilibrium thermodynamic processes can guide the optimization of process parameters (such as heat input and cooling rate) or post-processing techniques (such as using heat treatment for microstructure optimization).

[0060] Step 2: Additive manufacturing process selection and path design.

[0061] Based on the pre-designed composition, and combined with the influence of process parameters such as heat source power, feeding speed, and heat source moving speed in finite element simulation, as well as the effect of additive manufacturing deposition path on the stress field, the additive manufacturing process parameters and deposition path are preliminarily designed. If the average residual stress on the surface layer is always higher than 400 MPa, post-processing methods need to be introduced to determine the processing parameters of the sealing surface and complete the sample preparation.

[0062] The process parameters include one or more of the following: heat source power, feeding speed, heat source moving speed, defocusing amount (ring laser heat source), and protective gas flow rate.

[0063] In some embodiments, the laser powder feeding process parameters are: laser power 1800-2500W, defocusing amount -1 to -4mm, scanning speed 4-10mm / s, powder feeding speed 8-25g / min, and protective gas flow rate 12-30L / min;

[0064] In some embodiments, the laser wire feeding process parameters are: laser power 1400-2200W, defocusing amount -1 to -4mm, scanning speed 5-9mm / s, wire feeding speed 2-8mm / s, wire feeding diameter 1.2-1.6mm, and protective gas flow rate 10-20L / min.

[0065] Depositional pathways include radial deposition, circumferential deposition, and continuous reciprocating deposition. The angle of the depositional direction of each sedimentary layer can also be changed during the depositional process.

[0066] Finite element simulation uses commercial finite element software (such as ABAQUS, ANSYS, etc.) to import material properties, heat source equations and temperature fields into the software, and uses the birth and death element method to model the valve sealing surface workpiece as a whole and simulate the multiaxial stress field distribution.

[0067] Post-processing includes stepped slow cooling and multi-stage aging treatment. The decision to introduce post-processing methods depends on the stress field simulation results; the main purpose is to further alleviate residual stress caused by rapid cooling during the preparation process. If the stress field simulation results show that the average residual stress on the surface layer consistently exceeds 400 MPa, then post-processing methods are necessary to gradually release residual stress and further reduce the tendency to crack.

[0068] Specifically, in some embodiments, the preparation steps used in additive manufacturing include:

[0069] Medium frequency induction furnace melting: Under argon protection (flow rate ≥ 50 L / min), a single material (such as Stellite6 cobalt-based alloy or Norem02 iron-based alloy) is melted to 1550 ± 50℃, with staged feeding: the first stage is 10% pre-melting for 5 minutes, followed by 3 feedings (5 minutes apart, each feeding amount is 20%).

[0070] Powder preparation: vacuum atomization powdering, particle size distribution 80-270 mesh (d 50 =100±10μm), oxygen content ≤0.03%;

[0071] Wire preparation: After induction melting, the wire is drawn to a diameter of 0.8-1.2 mm (tolerance ±0.05 mm) with a surface roughness Ra≤1.6 μm.

[0072] Step 3: Testing and evaluation of the tendency of the sealing surface to crack.

[0073] XRD residual stress test and three-point bending fracture toughness test were performed on the sample to verify the results of sealing surface composition optimization and process optimization, and to form a quantitative evaluation criterion for the cracking tendency of the sealing surface. At the same time, the hardness of the sample was evaluated to meet the basic service requirements.

[0074] According to standard GB / T 39520-2020, the XRD residual stress test includes the following steps: select a surface position far away from the edge of the valve sealing surface, and calculate the residual stress based on the degree of XRD diffraction peak shift.

[0075] According to standard GB / T 21143-2014, the three-point bending fracture toughness test includes the following steps: Based on a micro three-point bending fixture (the radius of curvature of the loading point R=0.1mm), a micron-sized notch (50μm wide and 200μm deep, made by electrical discharge machining) is prepared on the surface of the cladding layer of the sealing surface, and the strain field at the tip of the notch is monitored in real time using digital image correlation (DIC) (resolution 0.1μm).

[0076] The quantitative assessment criteria for the tendency of the sealing surface to crack are: the average residual stress of the surface layer should be ≤400MPa; and / or, room temperature fracture toughness. K IC ≥25MPa·m 1 / 2 If the surface hardness is low, it is considered to have a low tendency to crack. Simultaneously, the average surface hardness of the valve sealing surface must be ≥38 HRC to meet basic service requirements.

[0077] Step 4: Construct a multi-parameter machine learning model.

[0078] A machine learning model is constructed to integrate alloy composition, additive manufacturing process parameters and deposition path, post-processing techniques, residual stress, and cracking tendency (XRD residual stress test and three-point bending fracture toughness test results). This model is used to establish a mapping relationship between composition, process, and cracking tendency, enabling efficient collaborative optimization and proactive design across multiple parameters. Once the machine learning model is built, it will be continuously validated and iteratively optimized.

[0079] Machine learning models include one of the following algorithms: decision tree, support vector machine, k-nearest neighbors, random forest, artificial neural network, adaptive boosting model, etc.

[0080] Step 5: Preparation of valve sealing surfaces with low cracking tendency.

[0081] Based on the predetermined valve sealing surface composition and the corresponding model analysis results, the corresponding preparation process is output to prepare a low-cracking valve sealing surface.

[0082] Example 1: In this example, a Stellite6 cobalt-based alloy sealing surface is prepared on a 304 stainless steel valve seat substrate.

[0083] Step 1: Pre-design of the composition of the sealing surface of nuclear-grade valves.

[0084] Phase equilibrium calculations and solidification path simulations were performed to clarify the phase transformation laws and solidification precipitation laws of the low-melting-point phase and the hard-brittle phase. The microstructure was controlled by a Co matrix and M... 23 C6 and Cr7C3 carbides precipitate, Fe3C, σ The content of phases such as Laves is <5%.

[0085] Step 2: Additive manufacturing process selection and path design.

[0086] A laser-fed powder feeding process was employed, using Stellite6 cobalt-based alloy powder with a particle size of 80-270 mesh and an oxygen content ≤0.03%. A finite element three-dimensional model was constructed, with a cladding layer thickness of 3 mm. The effects of different process parameters and deposition paths on the stress field distribution were analyzed, resulting in the following process parameter ranges: laser power 1800-2000 W, defocusing amount -2 to -3 mm, scanning speed 6-8 mm / s, and powder feeding speed 8-12 g / min. The cladding path adopted a zigzag scanning pattern, with each layer approximately 0.4-0.6 mm thick and a scanning interval of 0.1-0.3 mm. Adjacent layers were rotated 180° to optimize fusion. A two-stage aging heat treatment was used: first-stage aging at 750℃ for 1-4 h followed by water quenching; second-stage aging at 550℃ for 6-10 h followed by air cooling. Samples were prepared using the above process.

[0087] Step 3: Testing and evaluation of the tendency of the sealing surface to crack.

[0088] The samples were subjected to hardness testing to confirm that they met the hardness requirements. XRD residual stress testing and three-point bending fracture toughness testing were also performed to analyze the cracking tendency.

[0089] Step 4: Construct a multi-parameter machine learning model.

[0090] The system constructs machine learning models of alloy composition, additive manufacturing process parameters and deposition path, post-processing process, residual stress and cracking tendency, and verifies and iteratively optimizes them to build a mapping relationship between "composition-process-cracking tendency".

[0091] Step 5: Preparation of valve sealing surfaces with low cracking tendency.

[0092] Based on the predetermined valve sealing surface composition and the corresponding model analysis results, a corresponding fabrication process is output to prepare a low-cracking valve sealing surface. The optimized fabrication process parameters are: laser power 2000W, defocusing amount -2mm, scanning speed 8mm / s, and powder feeding speed 10g / min. The cladding path adopts a zigzag scanning pattern, with each layer approximately 0.5mm thick, a scanning interval of 0.3mm, and adjacent layers rotated 180° to optimize fusion. A two-stage aging heat treatment is employed: first-stage aging at 750℃ for 2 hours, followed by water quenching; second-stage aging at 550℃ for 8 hours, followed by air cooling.

[0093] like Figure 2 and Figure 3 As shown, the surface residual stress of the prepared low-cracking valve sealing surface is 320-360 MPa, and the room temperature fracture toughness is... K IC =35.9 MPa·m 1 / 2 Crack penetration testing showed no obvious cracks in the sample, and the tendency for cracking on the sealing surface was significantly reduced. The surface hardness of the valve sealing surface was 38-43 HRC, which met the hardness evaluation and indicated good service performance.

[0094] Example 2: In this example, a Norem02 iron-based alloy sealing surface is prepared on a 304 stainless steel valve seat substrate.

[0095] Step 1: Pre-design of the composition of the sealing surface of nuclear-grade valves.

[0096] Phase equilibrium calculations and solidification path simulations were performed using Thermo-Calc (TCFE9 database) and the Scheil model to clarify the phase transformation laws and solidification precipitation laws of the low-melting-point phase and the hard-brittle phase. The microstructure was controlled by an austenitic matrix and Cr7C3 carbide precipitation, with Fe3C... σ The content of phases such as Laves is <5%.

[0097] Step 2: Additive manufacturing process selection and path design.

[0098] Laser wire feeding was employed using Norem02 iron-based alloy powder with a particle size of 80-270 mesh and an oxygen content ≤0.03%. A finite element three-dimensional model was constructed with a cladding layer thickness of 3 mm. The effects of different process parameters and deposition paths on the stress field distribution were analyzed, resulting in the following process parameter ranges: laser power 1600-2000 W, scanning speed 5-7 mm / s, wire feeding speed 4-6 mm / s, and protective gas flow rate 15-20 L / min. A serpentine scanning path was used for the cladding, with a layer thickness of 0.6-1.0 mm, a scanning interval of 0.3-0.5 mm, and an overlap rate of 30-50%. Stepped slow cooling was employed, from 800℃ to 600℃ at a rate ≤5℃ / min, followed by air cooling below 600℃. A first-stage aging process followed by heat treatment was used: first-stage aging at 600-800℃ for 2-4 hours, followed by water quenching; second-stage aging at 400-600℃ for 4-8 hours, followed by air cooling. Samples were prepared using the above process.

[0099] Step 3: Testing and evaluation of the tendency of the sealing surface to crack.

[0100] The cracking tendency was analyzed by combining XRD residual stress test and three-point bending fracture toughness test.

[0101] Step 4: Construct a multi-parameter machine learning model.

[0102] The system constructs machine learning models of alloy composition, additive manufacturing process parameters and deposition path, post-processing process, residual stress and cracking tendency, and verifies and iteratively optimizes them to build a mapping relationship between "composition-process-cracking tendency".

[0103] Step 5: Preparation of valve sealing surfaces with low cracking tendency.

[0104] Based on the predetermined valve sealing surface composition and the corresponding model analysis results, a corresponding fabrication process is output to prepare a low-cracking valve sealing surface. The optimized fabrication process parameters are: laser power 2000W, scanning speed 5mm / s, wire feed speed 4mm / s, and protective gas flow rate 20L / min. The cladding path adopts a "serpentine" scanning method, with a layer thickness of approximately 0.9mm, a scanning interval of 0.4mm, and an overlap rate of 40%. Stepped slow cooling is adopted from 800℃ to 600℃ at a rate ≤5℃ / min, followed by air cooling below 600℃. Heat treatment is performed after a first-stage aging process: first-stage aging at 700℃ for 2 hours, followed by water quenching; second-stage aging at 500℃ for 6 hours, followed by air cooling.

[0105] The surface residual stress of the prepared low-cracking valve sealing surface is 265-290 MPa, and the room temperature fracture toughness is [not specified]. K IC =27.6 MPa·m 1 / 2Crack penetration testing showed no obvious cracks in the sample, and the tendency for the sealing surface to crack was significantly reduced. The surface hardness of the valve sealing surface was 40-46 HRC, which met the hardness assessment and indicated good service performance.

[0106] Currently, most studies rely on crack observation to determine the cracking tendency of sealing surfaces, a method characterized by low accuracy and large errors. This invention addresses the problem of brittle cracking in nuclear-grade valve sealing surfaces by presenting a method for assessing the cracking tendency of valve sealing surfaces and a method for preparing valve sealing surfaces with low cracking tendency. The specific implementation process involves: designing the composition and analyzing phase transformation laws through thermodynamic calculations; designing additive manufacturing process parameters and paths; improving stress distribution by combining finite element simulation of the stress field and post-processing design; proposing a cracking tendency assessment method based on residual stress analysis and fracture toughness; and constructing a machine learning model to grasp the quantitative relationship between multiple parameters and the cracking tendency of valve sealing surfaces, ultimately forming a mature technology and assessment method for preparing nuclear-grade valve sealing surfaces with low cracking tendency. This technology fills the gap in the control and assessment of cracking tendency in the field of nuclear-grade valve sealing surfaces, achieving efficient synergistic optimization and proactive design of alloy composition, additive manufacturing process, and post-processing process. It significantly reduces trial-and-error costs, minimizes unnecessary experiments, accelerates the research and application of advanced nuclear power generation technologies, reduces R&D costs, and improves efficiency.

[0107] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0108] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method of evaluating a valve seat cracking tendency, characterized by, The method comprises the following steps: a pre-design of the sealing surface composition is performed based on phase equilibrium calculation and solidification path simulation; a preliminary design of the additive manufacturing process parameters and deposition path is performed based on the pre-designed composition, and a sample is prepared; XRD residual stress testing and three-point bending fracture toughness testing are performed on the sample, and based on the testing results, an evaluation criterion for the cracking tendency of the sealing surface is formed; The evaluation criterion of the cracking tendency of the sealing surface is that the average residual stress of the surface layer of the valve sealing surface is ≤400 MPa, and the room temperature fracture toughness is ≥25 MPa·m K IC ≥25 MPa·m 1 / 2 , and the low cracking tendency is determined. the phase equilibrium calculation comprises the following steps: performing equilibrium thermodynamic calculation based on the CALPHAD method, inputting the material composition, calculating the phase composition and precipitated phase equilibrium volume fraction, and determining the type and precipitation temperature range of low-melting-point phases and hard and brittle phases; the solidification path simulation comprises the following steps: performing non-equilibrium solidification path simulation using the Scheil module of Thermo-Calc software to determine the non-equilibrium precipitation rules of low-melting-point phases and hard and brittle phases in the additive manufacturing process, and guiding the subsequent additive manufacturing process parameters and post-processing process formulation; the finite element simulation is performed by importing the material properties and heat source equation into the finite element software, modeling the whole valve sealing surface workpiece using the birth and death element method, and simulating the stress field distribution; if the stress field distribution result of the finite element simulation shows that the average residual stress of the surface layer is always higher than 400 MPa, a post-processing process needs to be introduced in the finite element simulation process; the post-processing process comprises stepwise slow cooling or multi-stage aging treatment.

2. The evaluation method according to claim 1, characterized in that The process parameters include one or more of heat source power, feeding speed, heat source moving speed, defocusing amount, and protective gas flow.

3. The evaluation method according to claim 1, characterized in that The deposition path includes radial deposition, circumferential deposition, and continuous reciprocating deposition.

4. The evaluation method according to claim 1, characterized in that During the XRD residual stress testing and three-point bending fracture toughness testing of the sample, hardness testing is simultaneously performed on the sample, and the average hardness of the surface layer of the sample is greater than or equal to 38 HRC.

5. A method of establishing an evaluation model of a valve seat cracking tendency, characterized by, The evaluation method comprises any one of claims 1-4.

6. The method of establishing an evaluation model according to claim 5, wherein, The establishment method further comprises the following steps: Based on the composition of the sealing surface, the additive manufacturing process parameters and deposition path, the post-processing process, the XRD residual stress testing data and the three-point bending fracture toughness testing data, an evaluation model for the cracking tendency of the valve sealing surface is established based on a machine learning method.

7. An assessment model of a valve seat cracking propensity, characterized by, The evaluation model is established by the establishment method of claim 5 or 6.

8. A method of making a valve seat having a low propensity for cracking, the method comprising: The evaluation model of claim 7 is used to output the corresponding preparation process based on the composition of the sealing surface, and to prepare the valve sealing surface with low cracking tendency.

Images