Creep life prediction method of Cr-mo-v heat-resistant steel based on physical mechanism of dislocation and precipitate evolution

Abstract

The application discloses a Cr-Mo-V heat-resistant steel creep life prediction method based on dislocation and precipitated phase evolution physical mechanism, and comprises the following steps: obtaining high-temperature service working conditions and related material parameters of a metal material structure; based on microstructure evolution rules of the metal material structure under high-temperature service load, a dislocation evolution model and a precipitated phase evolution model are established, and a whole-process creep rate change model and a cumulative creep damage model considering microstructure evolution are established; a finite element model is established in a finite element software, each model equation is written through a user-defined subroutine and introduced into the finite element model, and creep damage numerical simulation is carried out; a creep failure judgment basis is set, the obtained cumulative creep damage is compared with the creep failure judgment basis, and the creep life is determined. The application can organically combine microstructure changes in the material high-temperature service process with macroscopic creep response, and avoids the problem that a traditional experience extrapolation method is difficult to reflect the influence of organization evolution.

Description

Technical Field

[0001] This invention relates to the field of creep life evaluation technology for high-temperature structural materials, specifically to a method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution. Background Technology

[0002] Metallic materials undergo creep deformation over time under high-temperature loads, and the life assessment results directly affect the safe operation of high-temperature pressure-bearing components and high-temperature structural parts. Existing high-temperature creep life assessment methods mostly use empirical relationships between temperature, stress, and life for fitting or extrapolation. Although convenient for engineering applications, these methods mainly rely on macroscopic experimental data and cannot reflect the impact of the continuous evolution of the material's microstructure on creep behavior and life during service. Especially under long-term service conditions, empirical extrapolation methods struggle to balance the rationality of the mechanism with the stability of the prediction.

[0003] Especially for precipitation-strengthened high-temperature metallic materials, factors such as dislocation multiplication and recovery, coarsening of precipitates and attenuation of strengthening capacity, and increase in actual stress caused by changes in sample cross-section all jointly affect creep rate and life evolution during service. Extrapolating life solely based on empirical parameters makes it difficult to simultaneously consider the coupling relationship between dislocation evolution, particle strengthening attenuation, and accelerated creep in the later stages of service. Therefore, this invention presents a creep life prediction method for Cr-Mo-V heat-resistant steel based on the physical mechanisms of dislocation and precipitate evolution. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution, thereby solving the problem that existing life assessment methods are unable to reflect the microstructure evolution and the decay of strengthening capabilities during service.

[0005] The technical solution adopted in this invention is as follows: A method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution includes the following steps: S1. Obtain the high-temperature service conditions, initial microstructure parameters, and material-related constants of metallic structural components; S2. Analyze the dislocation evolution law of metallic structural components under high-temperature service loads, and establish a dislocation evolution model under high-temperature service loads. S3. Analyze the evolution law of precipitates in metallic structural components under high-temperature service loads, establish a precipitate evolution model that can identify effective strengthening precipitates, and calculate the internal stress of metallic structural components due to precipitate strengthening based on the identified effective strengthening precipitates. S4. Based on the dislocation evolution law and precipitate evolution law of metallic structural components under high temperature service load, establish a creep rate change model and cumulative creep damage model that consider the microstructure evolution during high temperature service. S5. Establish a finite element model based on the dimensional parameters of the metal material structural component, and introduce the relevant parameters obtained in step S1. At the same time, write and import the models established in steps S2 to S4 into the finite element model through user-defined subroutines to obtain a finite element analysis model that considers the evolution of microstructure. Use this model to simulate the creep damage of the metal material structural component during service and obtain the cumulative creep damage during service. S6. Set the criteria for judging creep failure of metal structural components, and compare and analyze the cumulative creep damage obtained in step S6 during service with the criteria for judging creep failure to determine its creep life.

[0006] Furthermore, the dislocation evolution model established in step S2 is as follows: ; ; In the formula, For dislocation density, To accumulate creep strain, For creep rate, Taylor factor Burgers vector, This is the constant related to the dislocation advance distance. For dynamic recovery constant, For dislocation line tension, For dislocation climb mobility, As a self-diffusion pre-index factor, Boltzmann's constant, The equivalent stress for the current state, It is the self-diffusion activation energy. The gas constant is... This refers to the service temperature.

[0007] In the dislocation evolution model of the above technical solution, the first term The first term is work hardening, indicating that dislocation multiplication leads to an increase in dislocation density; the second term... The third term is a dynamic response term, indicating that dislocation annihilation and rearrangement during deformation lead to a decrease in dislocation density; This is a static response term, indicating that under high temperature conditions, dislocations approach and annihilate each other through climb, leading to a decrease in dislocation density.

[0008] Furthermore, the precipitation phase evolution model established in step S3 includes: An evolution model of the average radius of precipitates is established by using time-controlled precipitate coarsening. The evolution model of the average radius of precipitates is as follows: ; In the formula, The average radius of the precipitate at the current moment, The average radius of the precipitated phase at the initial time. The coarsening rate constant of the precipitated phase, For time; A precipitate particle size distribution model is established using an exponential distribution method. The precipitate particle size distribution model is as follows: ; ; ; In the formula, for At time , the radius is The number density of the precipitated phase per unit area. For particle size distribution reference number density, The particle size distribution coefficient is... for The radius of the precipitate at time t is variable. Set a threshold for the radius of the precipitated phase, that is, calculate the number density of precipitated phases with a radius greater than or equal to the set threshold; The spacing between planar squares. This represents the volume fraction of the precipitated phase.

[0009] Furthermore, the precipitation phase evolution model established in step S3 also includes: Effectively enhance the precipitate particle size distribution model: ; In the formula, To effectively enhance the number density of the precipitated phase per unit area, To effectively enhance the radius of the precipitated phase, , To effectively enhance the critical radius of the precipitated phase, and , For Friedel spacing; Effective model for calculating the average spacing of precipitates: ; In the formula, To effectively enhance the average spacing of precipitates; The internal stress generated by the effective strengthening of precipitated phases in metallic structural components is: ; In the formula, To strengthen internal stress through precipitated phase, For the precipitate strengthening constant, This is the shear modulus of metallic materials.

[0010] In the above technical solutions, only those with dimensions greater than or equal to the critical dimension are actually available. Precipitation phases contribute to creep strengthening, therefore it is necessary to identify effective strengthening precipitates and calculate the internal stress of metallic structural components due to precipitate strengthening based on the identified effective strengthening precipitates.

[0011] Furthermore, the creep rate change model considering the entire process of microstructure evolution established in step S4 is as follows: ; ; In the formula, To unify the effective creep stress, The creep rate function, is the dislocation strengthening constant.

[0012] In the above technical solution, based on the established whole-process creep rate variation model, the creep deformation (initial creep, steady-state creep, and accelerated creep) of metallic structural components throughout the entire process can be analyzed to assess material life and safe operation. In the whole-process calculation, this model can continuously track the creep rate. When the creep rate reaches a local minimum and begins to rise continuously, the material is determined to have transitioned from the steady-state creep stage to the accelerated creep stage in the later stages of service. Preferably, if adjacent time steps satisfy... and Then the first Each time step corresponds to a state point that is determined as the end point of steady-state creep, and the subsequent stage is determined as the accelerated creep stage in the later stage of service.

[0013] Furthermore, the unified effective creep stress in the whole-process creep rate change model established in step S4 is: ; In the formula, To strengthen internal stress through precipitated phase, For dislocation strengthening stress, and .

[0014] In the above technical solution, for constant load uniaxial creep specimens, The actual stress is taken as follows: ,or, ; In the formula, For actual stress, For external load, This represents the current actual cross-sectional area. For nominal applied stress, This represents the current cumulative creep strain; For in-service structural components The equivalent stress of the critical parts of the structural component is obtained through stress analysis or finite element calculation. The von Mises equivalent stress is preferred.

[0015] Furthermore, the cumulative creep damage model established in step S4 is as follows: ; In the formula, The damage variable takes values ​​from 0 to 1. The rate of change of the damage variable with respect to time. , , These are the parameters for the creep damage model.

[0016] In the above technical solution, the established cumulative creep damage model is an explicit damage accumulation model. During the calculation process, for the first... For each time step, explicit integration is used: ; In the formula, For the first The time step and the first The time difference between steps.

[0017] The beneficial effects of this invention are as follows: This invention establishes a method for evaluating the high-temperature creep life of metallic materials, focusing on dislocation evolution, precipitate coarsening, precipitate strengthening attenuation, true stress rise, and damage accumulation. It organically combines microstructural changes and macroscopic creep response during high-temperature service, avoiding the problem that traditional empirical extrapolation methods struggle to reflect the influence of microstructural evolution. Furthermore, this invention employs a unified solution method for effective creep stress and the entire creep rate, enabling continuous description of steady-state creep and accelerated creep in the later stages of service within the same computational system. This method is applicable not only to whole-process creep life prediction but also to state assessment and remaining life analysis at a given service time. It can also be further combined with step integral or finite element methods to achieve engineering applications of complex metallic components. Attached Figure Description

[0018] Figure 1 This is a flowchart of the high-temperature creep life evaluation method of the present invention. Detailed Implementation

[0019] This invention provides a method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0020] Reference Figure 1 This embodiment provides a method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution, including the following steps: S1. Obtain the high-temperature service conditions, initial microstructure parameters, and material-related constants of metallic structural components; S2. Analyze the dislocation evolution law of metallic structural components under high-temperature service loads, and establish a dislocation evolution model under high-temperature service loads. S3. Analyze the evolution law of precipitates in metallic structural components under high-temperature service loads, establish a precipitate evolution model that can identify effective strengthening precipitates, and calculate the internal stress of metallic structural components due to precipitate strengthening based on the identified effective strengthening precipitates. S4. Based on the dislocation evolution law and precipitate evolution law of metallic structural components under high temperature service load, establish a creep rate change model and cumulative creep damage model that consider the microstructure evolution during high temperature service. S5. Establish a finite element model based on the dimensional parameters of the metal material structural component, and introduce the relevant parameters obtained in step S1. At the same time, write and import the models established in steps S2 to S4 into the finite element model through user-defined subroutines to obtain the finite element analysis model of microstructure evolution. Use this model to simulate creep damage during the service process of the metal material structural component and obtain the cumulative creep damage during the service process. S6. Set the criteria for judging creep failure of metal structural components, and compare and analyze the cumulative creep damage obtained in step S6 during service with the criteria for judging creep failure to determine its creep life.

[0021] Specifically, the dislocation evolution model established in step S2 above is as follows: (1); (2); In the formula, For dislocation density, For the current cumulative creep strain, For creep rate, Taylor factor Burgers vector, This is the constant related to the dislocation advance distance. For dynamic recovery constant, For dislocation line tension, For dislocation climb mobility, As a self-diffusion pre-index factor, Boltzmann's constant, The equivalent stress for the current state, It is the self-diffusion activation energy. The gas constant is... This refers to the service temperature.

[0022] Specifically, the precipitation phase evolution model established in step S3 above includes: An evolution model of the average radius of precipitates is established by using time-controlled precipitate coarsening. The evolution model of the average radius of precipitates is as follows: (3); In the formula, The average radius of the precipitate at the current moment, The average radius of the precipitated phase at the initial time. The coarsening rate constant of the precipitated phase, For time; A precipitate particle size distribution model is established using an exponential distribution method. The precipitate particle size distribution model is as follows: (4); (5); (6); In the formula, for At time , the radius is The number density of the precipitated phase per unit area. For particle size distribution reference number density, The particle size distribution coefficient is... for The radius of the precipitate at time t is variable. Set a threshold for the radius of the precipitated phase, that is, calculate the number density of precipitated phases with a radius greater than or equal to the set threshold; The spacing between planar squares. This represents the volume fraction of precipitated phase at the current moment.

[0023] In addition, in step S3 above, only dimensions greater than or equal to the critical dimension actually exist. Precipitation phases contribute to creep strengthening, therefore it is necessary to identify effective strengthening precipitates and calculate the internal stress of metallic structural components due to precipitate strengthening based on the identified effective strengthening precipitates. Therefore, based on the above precipitate evolution model, an evolution model capable of identifying effective strengthening precipitates should be established, including: Effectively enhance the precipitate particle size distribution model: (7); (8); (9); In the formula, To effectively enhance the number density of the precipitated phase per unit area, To effectively enhance the radius of the precipitated phase, To effectively enhance the critical radius of the precipitated phase, For Friedel spacing; Effective model for calculating the average spacing of precipitates: (10); In the formula, To effectively enhance the average spacing of precipitates; The internal stress generated by the effective strengthening of precipitated phases in metallic structural components is: (11); In the formula, To strengthen internal stress through precipitated phase, For the precipitate strengthening constant, This is the shear modulus of metallic materials.

[0024] Specifically, the creep rate change model considering the entire process of microstructure evolution established in step S4 above is as follows: (12); (13); In the formula, To unify the effective creep stress, The creep rate function, It is the dislocation strengthening constant; The above-mentioned unified effective creep stress for: (14); and (15).

[0025] In the formula, To strengthen internal stress through precipitated phase, This is dislocation strengthening stress.

[0026] The equivalent stress of the aforementioned current external effects The values ​​vary depending on the service conditions; for constant load uniaxial creep specimens... The actual stress is taken as follows: ,or, (16); In the formula, For actual stress, For external load, This represents the current actual cross-sectional area. For nominal applied stress, This represents the current cumulative creep strain; For structural components in service engineering projects Based on the current load-bearing state, geometric dimensions, and effective cross-sectional area of ​​the structural components, the equivalent stress at the critical locations of the structural components needs to be obtained through stress analysis or finite element calculations. The von Mises equivalent stress is preferred.

[0027] In this embodiment, the established full-process creep rate variation model can analyze the creep deformation (initial creep, steady-state creep, and accelerated creep) of metallic structural components throughout the simulation process to assess material life and safe operation. During the full-process simulation calculation, this model can continuously track the creep rate. When the creep rate reaches a local minimum and begins to rise continuously, the material is determined to have transitioned from the steady-state creep stage to the accelerated creep stage in the later stages of service. Preferably, if adjacent time steps satisfy... ,and Then the first Each time step corresponds to a state point that is considered the end of steady-state creep, and the subsequent stages are defined as the accelerated creep stage in the later stages of service. Furthermore, during the steady-state creep stage, the increase in actual stress and the evolution of internal strengthening are roughly balanced. This corresponds to the near-steady-state value near the minimum creep rate; however, in the later stages of service, as the actual stress continues to increase and the particle reinforcement diminishes, The creep rate increases again, thus accelerating the creep process.

[0028] Specifically, the cumulative creep damage model established in step S4 above is as follows: (17); In the formula, The damage variable takes values ​​from 0 to 1. The rate of change of the damage variable with respect to time. , , These are the parameters for the creep damage model.

[0029] In the above technical solution, the established cumulative creep damage model is an explicit damage accumulation model. During the calculation process, for the first... For each time step, explicit integration is used: (18); In the formula, For the first The time step and the first The time difference between steps.

[0030] Specifically, in step S5 above, the finite element model of the metal material structural component is established in the Abaqus finite element software. At the same time, the above formulas (1)-(18) are written by user-defined subroutines (UDF) and embedded in the Abaqus finite element software for secondary development, so as to obtain the finite element analysis model of microstructure evolution. This model can more accurately simulate the creep damage of the metal material structural component during service and obtain the cumulative creep damage during service.

[0031] Based on the above formulas (1)-(18), the high-temperature service condition parameters of the metal material structural components that need to be obtained in step S1 above include at least: temperature, nominal applied stress, and cumulative service time. The initial parameters of the microstructure include at least: initial dislocation density, initial average radius of precipitates, volume fraction of precipitates, and a threshold value for the radius of precipitates; Material-related constants include at least: Taylor factor, Burgers vector, shear modulus, dislocation line tension, dynamic recovery constant, dislocation advance distance-related constant, precipitate coarsening rate constant, precipitate strengthening constant, dislocation strengthening constant, Friedel spacing, self-diffusion pre-exponential factor, Boltzmann constant, self-diffusion activation energy, gas constant, and creep damage model parameters.

[0032] This embodiment takes the microstructure and mechanical state of Cr-Mo-V steel (uniaxial constant load specimen) after 1000 h of service at a service temperature of 474K and a nominal applied stress of 200MPa as the research object, and predicts its creep life by using a creep life prediction method for Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution.

[0033] To facilitate the calculation of each model in the evaluation method of this embodiment, this embodiment first obtains the initial microstructure parameters and related material constants of Cr-Mo-V steel under high-temperature service conditions through literature data of similar materials, material database queries, short-time creep test inversion or microstructure characterization results, as shown in Table 1 below.

[0034] Table 1. Relevant material parameters of Cr-Mo-V steel under high-temperature service conditions. Using the finite element model established in this embodiment, a numerical simulation of creep damage is performed under the above conditions to obtain the cumulative creep damage during service, and the cumulative creep damage amount is calculated. As a failure criterion, the remaining life of the structural component is predicted. Finite element simulation shows that when... At that time, the predicted lifespan of the structural component was 10,000 hours. Since it has already been in service for 1,000 hours, its remaining lifespan is 9,000 hours.

[0035] It should be noted that any parts not mentioned in this invention can be achieved by using or referencing existing technologies.

[0036] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution, characterized in that, Including the following steps: S1. Obtain the high-temperature service conditions, initial microstructure parameters, and material-related constants of the metallic structural components; S2. Analyze the dislocation evolution law of metallic structural components under high-temperature service loads, and establish a dislocation evolution model under high-temperature service loads. S3. Analyze the evolution law of precipitates in metallic structural components under high-temperature service loads, establish a precipitate evolution model that can identify effective strengthening precipitates, and calculate the internal stress of metallic structural components due to precipitate strengthening based on the identified effective strengthening precipitates. S4. Based on the dislocation evolution law and precipitate evolution law of metallic structural components under high temperature service load, establish a creep rate change model and cumulative creep damage model that consider the microstructure evolution during high temperature service. S5. Establish a finite element model based on the dimensional parameters of the metal material structural component, and introduce the relevant parameters obtained in step S1. At the same time, write and import the models established in steps S2 to S4 into the finite element model through user-defined subroutines to obtain a finite element analysis model that considers the evolution of microstructure. Use this model to simulate the creep damage of the metal material structural component during service and obtain the cumulative creep damage during service. S6. Set the criteria for judging creep failure of metal structural components, and compare and analyze the cumulative creep damage obtained in step S6 during service with the criteria for judging creep failure to determine its creep life.

2. The method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution as described in claim 1, characterized in that, The dislocation evolution model established in step S2 is as follows: ； ； In the formula, For dislocation density, To accumulate creep strain, For creep rate, Taylor factor Burgers vector, This is the constant related to the dislocation advance distance. For dynamic recovery constant, For dislocation line tension, For dislocation climb mobility, As a self-diffusion pre-index factor, Boltzmann's constant, The equivalent stress for the current state, It is the self-diffusion activation energy. The gas constant is For temperature.

3. The method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution as described in claim 2, characterized in that, The precipitation phase evolution model established in step S3 includes: An evolution model of the average radius of precipitates is established by using time-controlled precipitate coarsening. The evolution model of the average radius of precipitates is as follows: ； In the formula, The average radius of the precipitate at the current moment, The average radius of the precipitated phase at the initial time. The coarsening rate constant of the precipitated phase, For time; A precipitate particle size distribution model is established using an exponential distribution method. The precipitate particle size distribution model is as follows: ； ； ； In the formula, for At time , the radius is The number density of the precipitated phase per unit area. For particle size distribution reference number density, The particle size distribution coefficient is... for The radius of the precipitate at time t is variable. Set a threshold for the radius of the precipitated phase, that is, calculate the number density of precipitated phases with a radius greater than or equal to the set threshold; The spacing between planar squares, This represents the volume fraction of the precipitated phase.

4. The method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution according to claim 3, characterized in that, The precipitate evolution model established in step S3 also includes: Effective enhancement of precipitate particle size distribution model: ； In the formula, To effectively enhance the number density of the precipitated phase per unit area, To effectively enhance the radius of the precipitated phase, , To effectively enhance the critical radius of the precipitated phase, and , For Friedel spacing; Effective model for calculating the average spacing of precipitates: ； In the formula, To effectively enhance the average spacing of precipitates; The internal stress generated by the effective strengthening of precipitated phases in metallic structural components is: ； In the formula, To strengthen internal stress through precipitated phase, For the precipitate strengthening constant, This is the shear modulus of metallic materials.

5. The method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution according to claim 4, characterized in that, The creep rate change model considering the entire process of microstructure evolution established in step S4 is as follows: ； In the formula, To unify the effective creep stress, The creep rate function, is the dislocation strengthening constant.

6. The method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution according to claim 5, characterized in that, In the whole-process creep rate change model established in step S4, the unified effective creep stress is: ； In the formula, To strengthen internal stress through precipitated phase, For dislocation strengthening stress, and .

7. The method for predicting the creep life of Cr-Mo-V heat-resistant steel based on the physical mechanism of dislocation and precipitate evolution according to claim 6, characterized in that, The cumulative creep damage model established in step S4 is as follows: ； In the formula, The damage variable takes values ​​from 0 to 1. The rate of change of the damage variable with respect to time. , , These are the parameters for the creep damage model.

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