A molecular dynamics modeling method for alloy steel containing multiple alloying elements

Abstract

The present disclosure discloses a molecular dynamics modeling method for alloy steel containing multiple alloying elements, which is not only used for modeling but also for further evaluation: first, an iron matrix model of a certain size and shape is established, and then a certain amount of iron atoms are replaced with a certain amount of atoms of a first type of alloying element by atomic replacement, and a certain amount of atoms of a second type of alloying element are added to the iron atom model by random insertion, and the atoms are evenly distributed to form an initial molecular dynamics model of the alloy steel; further, in order to avoid the randomly inserted atoms of the second type of alloying element from overlapping with other atoms or being too close to each other, resulting in excessive system stress and energy, the model is energy minimized, and then the model is simulated through melting, cooling and room temperature aging processes to fully eliminate gaps, structural cracks, etc. in the model and reduce stress within the model; finally, the model is verified and evaluated by means of nanoindentation simulation.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of computer simulation of material microscopic damage, and particularly relates to a molecular dynamics modeling method for alloy steel containing multiple alloy elements. Background Art

[0002] The main bearing is a key supporting part of aircraft engines and gas turbines, and is also a key part that affects the safety of engine operation. It is generally regarded as a core component that is equally important as the turbine blades. Once a failure occurs, it will cause catastrophic consequences.

[0003] The main bearings of aircraft engines and gas turbines have high technical content. They face many technical challenges in their service environment, such as high temperature, high speed, high DN value, variable load, complex and drastic operating conditions, and difficulty in monitoring their operating status. They can serve as an important criterion for measuring a country's scientific and technological and industrial strength.

[0004] Currently, most studies related to alloy steel materials for bearing steel using molecular dynamics directly adopt pure iron models. However, actual alloy steel materials contain certain other alloying elements, and directly using pure iron matrix models for research is quite different from the actual material properties.

[0005] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0006] In order to solve the above technical problems, the present disclosure discloses a molecular dynamics modeling method for alloy steel containing multiple alloying elements, characterized in that the method comprises the following steps:

[0007] S1: Obtain characteristic parameters of alloy steel, including the types of elements in the alloy, the mass fraction of various alloying elements, and the particle spacing;

[0008] S2: Construct a body-centered cubic iron matrix model with a certain size and crystal orientation, and obtain the number of iron atoms in the iron matrix model and the coordinates of each atom;

[0009] S3: In addition to iron, the atomic radius of the alloying elements that need to be added to the iron matrix model is determined according to the specific alloying elements that need to be inserted, and the existence form of various alloying elements in the iron matrix model is determined by referring to the method of the steel billet;

[0010] S4: Determine a method for adding atoms of various alloying elements into the iron matrix model based on the atomic radius of the alloying elements and the existence form of the alloying elements in the iron matrix model, including: an atomic replacement method and a random insertion method, wherein the atoms of the first type of alloying elements are selected by atomic replacement method, and the atoms of the second type of alloying elements are selected by random insertion method;

[0011] S5: determining the number of atoms of the corresponding alloying elements that need to be added to the iron matrix model based on the mass fractions of the various alloying elements obtained in step S1 and the number of iron atoms in the iron matrix model;

[0012] S6: using an atomic replacement method, randomly replacing the iron atoms in the iron matrix model with a corresponding number of atoms of the first type of alloying element, and making such atoms uniformly distributed in the iron matrix model;

[0013] S7: using a random insertion method, randomly inserting a corresponding number of atoms of the second type alloying element within the model range of the iron matrix model, and making such atoms uniformly distributed in the iron matrix model;

[0014] S8: performing energy minimization on the model processed in step S7 to eliminate the problem of atomic overlap or too small spacing caused by the randomly inserted atoms of the second type alloying element;

[0015] S9: simulating the melting process of the alloy steel on the model processed in step S8;

[0016] S10: simulating the cooling process of the alloy steel for the model processed in step S9;

[0017] S11: simulating the room temperature aging process of the alloy steel on the model processed in step S10;

[0018] S12: constructing a diamond indenter model with a diamond cubic crystal structure of a certain size and a certain crystal orientation, and obtaining the coordinates of each atom in the diamond model;

[0019] S13: Slowly press the diamond indenter model into the model processed in step S11 from above at a certain speed, obtain the indentation depth and pressure at each moment, calculate the hardness value, and then compare it with the actual hardness value of the alloy steel to evaluate the correctness of the model.

[0020] Preferably,

[0021] In step S2, the crystal directions

[100] ,

[010] and

[001] are respectively used as the X, Y and Z coordinate axis directions of the model, and the model dimensions and lattice constant a in the X, Y and Z coordinate axis directions are set to obtain the model matrix coordinate file.

[0022] Preferably,

[0023] For iron and other alloying elements, determine the atomic number and coordinates of each added atom and obtain the coordinate matrix files of various elements.

[0024] Preferably,

[0025] Except for iron, for the other alloying elements, the potential function type that characterizes the interaction force between the added elements is determined according to the added alloying elements, and the potential function between the elements in the model is set.

[0026] Preferably,

[0027] According to the coordinate matrix files of various elements and the interaction between various elements, the energy of the entire model is minimized to eliminate problems such as atomic overlap and small spacing in the model.

[0028] Preferably,

[0029] By simulating melting at 2000K, annealing from 2000K to 300K, and aging at room temperature at 300K, the residual stress in the model is reduced, making it closer to the physical and mechanical properties of real steel.

[0030] Preferably,

[0031] In step S13, the hardness and elastic modulus of the model are tested using a nanoindentation simulation method.

[0032] Preferably,

[0033] When the diamond indenter model is set as a rigid body, the diamond indenter model remains unchanged during the indentation process.

[0034] Preferably,

[0035] In step S8, the Polak-Ribiere method in the conjugate gradient (CG) algorithm is used to perform time integration on the established model to achieve energy minimization.

[0036] Preferably,

[0037] In step S9 or S10 or S11, the Nose-Hoover heat bath method in the Non-Hamiltonian equation of motion is used to perform time integration on the corresponding model to update the velocity and position of the atoms in each step.

[0038] In this way, the present disclosure innovatively proposes a molecular dynamics modeling method for alloy steel containing multiple alloying elements, which not only completes the modeling but also can evaluate the model to optimize the model, and is more in line with the physical and mechanical properties of the real material. Obviously, this is conducive to further implementation of molecular dynamics simulation and analysis.

[0039] Compared with the prior art, the present disclosure has at least the following beneficial effects:

[0040] 1) This disclosure explains the existence forms of different types of alloying elements in the iron matrix lattice in the molecular dynamics model of alloy steel;

[0041] 2) The present disclosure discloses a method for forming alloy steel by adding atoms including but not limited to chromium atoms, molybdenum atoms, vanadium atoms, and carbon atoms to an iron matrix model, which can quickly and accurately construct a molecular dynamics model of alloy steel containing any mass fraction of alloying elements;

[0042] 3) Furthermore, the present disclosure describes the interaction relationship between various elements through potential functions;

[0043] 4) Furthermore, the present disclosure relaxes the atoms of the second type alloying element randomly inserted into the model to the lowest energy position by means of energy minimization and relaxation, and fully eliminates problems such as atomic overlap and too small spacing caused by the random insertion of atoms of the second type alloying element by melting the model at high temperature, annealing at a lower temperature, and relaxing the model by aging at room temperature, thereby reducing structural defects, cracks, etc. in the model and reducing residual stress in the model;

[0044] 5) In addition, by adding a diamond indenter model, nanoindentation simulation is performed to test the hardness and elastic modulus and evaluate the correctness of the model, which is beneficial to guide the molecular dynamics modeling of alloy steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a flow chart of a molecular dynamics modeling method for M50 bearing steel in one embodiment of the present disclosure;

[0046] Figure 2 This is a diagram of an iron matrix model in one embodiment of the present disclosure;

[0047] Figure 3 This is a model diagram after adding chromium atoms in one embodiment of the present disclosure;

[0048] Figure 4 This is a model diagram after adding molybdenum atoms in one embodiment of the present disclosure;

[0049] Figure 5 This is a model diagram after adding vanadium atoms in one embodiment of the present disclosure;

[0050] Figure 6 This is a model diagram after adding carbon atoms in one embodiment of the present disclosure;

[0051] Figure 7 is a model diagram after energy minimization in one embodiment of the present disclosure;

[0052] Figure 8 is a model diagram after relaxation is completed in one embodiment of the present disclosure;

[0053] Figure 9 is a diagram of system energy changes during the relaxation process in one embodiment of the present disclosure;

[0054] Figure 10 This is a model diagram after adding a diamond indenter in one embodiment of the present disclosure;

[0055] Figure 11 In one embodiment of the present disclosure, the diamond indenter has an indentation depth of Model diagram when

[0056] Figure 12 It is a graph showing the relationship between the force and displacement of the indenter output during nanoindentation simulation in one embodiment of the present disclosure. DETAILED DESCRIPTION

[0057] In order to make those skilled in the art understand the technical solutions disclosed in this disclosure, the following will be combined with the embodiments and related appendixes. Figures 1 to 12 , the technical solutions of various embodiments are described, and the embodiments described are part of the embodiments of the present disclosure, rather than all the embodiments. The terms "first", "second", etc. used in the present disclosure are used to distinguish different objects, rather than to describe a specific order. In addition, "including" and "having" and any variations thereof are intended to cover and not exclude inclusion. For example, a process, or method, or system, or product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally also includes steps or units that are not listed, or optionally also includes other steps or units inherent to these processes, methods, systems, products or devices.

[0058] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present disclosure. The appearance of such phrases in various places in the specification does not necessarily refer to the same embodiment, nor do they constitute independent or alternative embodiments that are mutually exclusive of other embodiments. Those skilled in the art will appreciate that the embodiments described herein may be combined with other embodiments.

[0059] In one embodiment, the present disclosure discloses a molecular dynamics modeling method for alloy steel containing multiple alloying elements, characterized in that the method comprises the following steps:

[0060] S1: Obtain characteristic parameters of alloy steel, including the types of elements in the alloy, the mass fraction of various alloying elements, and the particle spacing;

[0061] S2: Construct a body-centered cubic iron matrix model with a certain size and crystal orientation, and obtain the number of iron atoms in the iron matrix model and the coordinates of each atom;

[0062] For example, determining the size is At this point, the model contains 56,790 iron atoms, and the coordinates of each iron atom can be further obtained;

[0063] S3: In addition to iron, the atomic radius of the alloying elements that need to be added to the iron matrix model is determined according to the specific alloying elements that need to be inserted, and the existence form of various alloying elements in the iron matrix model is determined by referring to the method of the steel billet;

[0064] For example, the alloying elements exemplarily include any one of the following or any combination thereof: chromium, molybdenum, vanadium, carbon, etc.; wherein the existence form of various alloying elements in the iron matrix model is determined by reference to the steel billet through literature / experimental analysis;

[0065] S4: Determine a method for adding atoms of various alloying elements into the iron matrix model based on the atomic radius of the alloying elements and the existence form of the alloying elements in the iron matrix model, including: an atomic replacement method and a random insertion method, wherein the atoms of the first type of alloying elements are selected by atomic replacement method, and the atoms of the second type of alloying elements are selected by random insertion method;

[0066] For example, chromium atoms, molybdenum atoms, and vanadium atoms are replaced by atoms, while carbon atoms are randomly inserted. Whether an atom of an alloying element belongs to the first type of alloying element or the second type of alloying element can be determined by consulting existing literature or experimentally analyzing a reference steel blank.

[0067] S5: determining the number of atoms of the corresponding alloying elements that need to be added to the iron matrix model based on the mass fractions of the various alloying elements obtained in step S1 and the number of iron atoms in the iron matrix model;

[0068] S6: using an atomic replacement method, randomly replacing the iron atoms in the iron matrix model with a corresponding number of atoms of the first type of alloying element, and making such atoms uniformly distributed in the iron matrix model;

[0069] S7: using a random insertion method, randomly inserting a corresponding number of atoms of the second type alloying element within the model range of the iron matrix model, and making such atoms uniformly distributed in the iron matrix model;

[0070] S8: performing energy minimization on the model processed in step S7 to eliminate the problem of atomic overlap or too small spacing caused by the randomly inserted atoms of the second type alloying element;

[0071] S9: simulating the melting process of the alloy steel on the model processed in step S8;

[0072] S10: simulating the cooling process of the alloy steel for the model processed in step S9;

[0073] S11: simulating the room temperature aging process of the alloy steel on the model processed in step S10;

[0074] S12: constructing a diamond indenter model with a diamond cubic crystal structure of a certain size and a certain crystal orientation, and obtaining the coordinates of each atom in the diamond model;

[0075] S13: Slowly press the diamond indenter model into the model processed in step S11 from above at a certain speed, obtain the indentation depth and pressure at each moment, calculate the hardness value, and then compare it with the actual hardness value of the alloy steel to evaluate the correctness of the model.

[0076] The above embodiments embody the main inventive concepts of the present disclosure:

[0077] First, an iron matrix model of a certain size and shape is established. Then, through atomic replacement, a certain number of iron atoms are replaced with a certain number of atoms of the first type of alloying element. Then, a certain number of atoms of the second type of alloying element are randomly inserted into the model range of the iron matrix to form an initial molecular dynamics model of the alloy steel.

[0078] Furthermore, to prevent atoms of the randomly added second-type alloying element from overlapping or being too close to other atoms, which would result in excessive stress and energy in the system, the model was energy minimized. The model was then simulated during the melting, cooling, and room-temperature aging processes to fully eliminate gaps and structural cracks in the model and reduce internal stress.

[0079] Finally, the model is verified and evaluated by means of nanoindentation simulation.

[0080] Obviously, compared with the prior art, the present disclosure achieves more accurate modeling and evaluation, which is helpful to provide guidance for the research and development of alloy steel in terms of molecular dynamics modeling.

[0081] In another embodiment,

[0082] In step S2, the crystal directions

[100] ,

[010] and

[001] are respectively used as the X, Y and Z coordinate axis directions of the model, and the model dimensions and lattice constant a in the X, Y and Z coordinate axis directions are set to obtain the model matrix coordinate file, thereby constructing a body-centered cubic structure iron matrix model with a certain size and a certain crystal direction.

[0083] In another embodiment,

[0084] For iron and other alloying elements, determine the atomic number and coordinates of each added atom and obtain the coordinate matrix files of various elements.

[0085] In another embodiment,

[0086] Except for iron, for the other alloying elements, the potential function type that characterizes the interaction force between the added elements is determined according to the added alloying elements, and the potential function between the elements in the model is set.

[0087] For example, the potential function may be the following: EAM potential function, LJ / cut potential function; in addition, regarding the type of potential function, the type of potential function that characterizes the interaction force between the added elements can be determined, for example, by consulting literature.

[0088] In another embodiment,

[0089] According to the coordinate matrix files of various elements and the interaction between various elements, the energy of the entire model is minimized to eliminate problems such as atomic overlap and small spacing in the model.

[0090] In another embodiment,

[0091] By simulating melting at 2000K, annealing from 2000K to 300K, and aging at room temperature at 300K, the residual stress in the model is reduced, making it closer to the physical and mechanical properties of real steel.

[0092] In another embodiment,

[0093] In step S13, the hardness and elastic modulus of the model are tested using a nanoindentation simulation method.

[0094] In another embodiment,

[0095] When the diamond indenter model is set as a rigid body, the diamond indenter model remains unchanged during the indentation process.

[0096] In another embodiment,

[0097] In step S8, the Polak-Ribiere method in the conjugate gradient (CG) algorithm is used to perform time integration on the established model to achieve energy minimization.

[0098] In another embodiment,

[0099] In step S9 or S10 or S11, the Nose-Hoover heat bath method in the Non-Hamiltonian equation of motion is used to perform time integration on the corresponding model to update the velocity and position of the atoms in each step.

[0100] In one embodiment, taking M50 bearing steel as an example, the present disclosure discloses a molecular dynamics modeling method for M50 bearing steel containing multiple alloying elements, comprising the following steps:

[0101] S1: Obtain the characteristic parameters of M50 bearing steel, including the types of elements in the alloy, the mass fraction of various alloying elements, and the particle spacing;

[0102] S2: constructing a body-centered cubic iron matrix model with a certain size and a certain crystal orientation, and obtaining the coordinates and corresponding numbers of each atom in the iron matrix model to obtain a model matrix coordinate file;

[0103] S3: In addition to iron, determine the atomic radius and existence form of four alloying elements that need to be added to the iron matrix model, where the four alloying elements include chromium, molybdenum, vanadium and carbon;

[0104] S4: Determine the method of adding four alloying elements to the iron matrix model;

[0105] S5: Determine the number of atoms of the four alloying elements that need to be added to the iron matrix model according to the mass fractions of the various alloying elements obtained in step S1 and the number of iron atoms in the model;

[0106] S6: Using the atomic replacement method, the iron atoms in the iron matrix model are randomly replaced with corresponding numbers of chromium atoms, molybdenum atoms, and vanadium atoms, and the three atoms are evenly distributed in the iron matrix model;

[0107] S7: Using a random insertion method, a corresponding number of carbon atoms are randomly inserted within the model range of the iron matrix model, and the carbon atoms are evenly distributed in the iron matrix model;

[0108] S8: performing time integration and energy minimization on the model processed in step S7 to eliminate problems such as atomic overlap and small spacing caused by randomly inserted carbon atoms;

[0109] S9: simulating the melting process of M50 steel on the model processed in step S8;

[0110] S10: simulating the cooling process of M50 steel for the model processed in step S9;

[0111] S11: simulating the room temperature aging process of M50 steel on the model processed in step S10;

[0112] S12: constructing a diamond indenter model with a diamond cubic crystal structure of a certain size and a certain crystal orientation, and obtaining the coordinates and corresponding numbers of each atom in the diamond model;

[0113] S13: Slowly press the diamond indenter model into the model processed in step S11 from above at a certain speed, obtain the indentation depth and pressure at each moment, calculate the nanoindentation hardness value, and then compare it with the actual M50 steel hardness value to evaluate the correctness of the model.

[0114] The above embodiment can quickly generate and evaluate a molecular dynamics model of M50 bearing steel of a certain size and shape containing multiple elements.

[0115] The above embodiments embody the main inventive concepts of the present disclosure:

[0116] First, an iron matrix model of a certain size and shape is established. Then, through atomic replacement, a certain number of iron atoms are replaced with a certain number of chromium atoms, molybdenum atoms, and vanadium atoms, respectively. Then, a certain number of carbon atoms are randomly inserted into the model range of the iron matrix to form the initial molecular dynamics model of M50 bearing steel.

[0117] Furthermore, to avoid the randomly added carbon atoms overlapping with other atoms or being too close to each other, which would lead to excessive stress and energy in the system, the model was energy minimized. Then, the model was simulated through the melting process, cooling process, and room temperature aging process to fully eliminate gaps and cracks in the model and reduce the internal stress of the model.

[0118] Finally, the model is verified and evaluated by means of nanoindentation simulation.

[0119] More specifically, taking M50 bearing steel as an example, in one embodiment, the present disclosure further discloses a molecular dynamics modeling method for M50 bearing steel containing multiple alloying elements, comprising the following steps:

[0120] (1) Obtain the characteristic parameters of M50 bearing steel, including the types of elements in the alloy, the mass fraction of each element, and the interparticle spacing;

[0121] For example, the mass fraction of carbon is 0.8%-0.85%, the mass fraction of chromium is 4%-4.5%, the mass fraction of molybdenum is 4%-4.5%, and the mass fraction of vanadium is 0.9%-1.1%;

[0122] (2) Construct a body-centered cubic iron matrix model with a certain size and a certain crystal orientation, and obtain the coordinates of each atom in the iron matrix model and its corresponding number to obtain the model matrix coordinate file; for example, the size is The number of iron atoms contained in the model is 56,790;

[0123] Use the crystal directions

[100] ,

[010] and

[001] as the X, Y and Z coordinate axis directions of the model respectively, set the model size in the X, Y and Z coordinate axis directions, the lattice constant a, and obtain the matrix coordinate matrix file;

[0124] (3) Determine the types of alloying elements that need to be added to the iron matrix model, including but not limited to chromium, molybdenum, vanadium and carbon.

[0125] It should be noted that in order to ensure that the model is close to the actual physical and mechanical properties of M50 bearing steel to the greatest extent possible while saving computer computing resources to a certain extent, the present disclosure selects four elements, chromium, molybdenum, vanadium, and carbon, and adds them to the iron matrix model to construct a molecular dynamics model of M50 bearing steel.

[0126] (4) Determine the atomic radius of the four elements and their existence forms in the iron matrix model, and then determine the method of adding the four elements to the iron matrix model;

[0127] After verification, the atomic radius of iron atoms is 126pm, the atomic radius of chromium atoms is 128pm, the atomic radius of molybdenum atoms is 139pm, the atomic radius of vanadium atoms is 132pm, and the atomic radius of carbon atoms is 77pm. It can be seen that the atomic radius of chromium, molybdenum and vanadium is close to that of iron atoms, while the atomic radius of carbon atoms is much smaller than that of iron atoms. Therefore, it can be determined that the three atoms of chromium, molybdenum and vanadium exist in the iron matrix model in the form of substitutional solid solution, while carbon atoms exist in the iron matrix model in the form of interstitial solid solution. Therefore, the three atoms of chromium, molybdenum and vanadium are added to the iron matrix model by atomic replacement, while carbon atoms are added to the iron matrix model by random insertion.

[0128] (5) determining the number of iron atoms in the iron matrix model with the determined size and the number of chromium atoms, molybdenum atoms, vanadium atoms, and carbon atoms to be added, respectively, based on the mass fraction of the alloying elements determined above;

[0129] For example, the number of iron atoms is 51,830, the number of chromium atoms, molybdenum atoms, vanadium atoms, and carbon atoms are 2,600, 1,500, 860, and 2,200 respectively;

[0130] (6) Using the atomic replacement method, the iron atoms in the iron matrix model are randomly replaced with a certain number of chromium atoms, molybdenum atoms, and vanadium atoms, and the three atoms are uniformly distributed in the iron matrix model;

[0131] (7) Using a random insertion method, a certain amount of carbon atoms are randomly inserted within the model range of the iron matrix model, while the distribution of carbon atoms in the iron matrix model is uniform;

[0132] According to the various elements replaced and randomly inserted in (6) and (7), the atomic number and coordinates of each added atom are determined, and the coordinate matrix file of each element is obtained;

[0133] Furthermore, according to the added elements, the interaction mode between the elements in the model is determined, and the potential functions between the elements in the model are set. For example, the meam potential function is used between Fe-C, the cdeam potential function is used between Fe-Cr, the meam potential function is used between Fe-Mo, the eam / fs potential function is used between Fe-V, and the meam potential function is used between Mo-Cr and Mo-V; the Lj / cut potential function is used between Cr-V, C-Cr, C-Mo and CV, and its parameters are calculated under the general force field;

[0134] (8) Using the Polak-Ribiere method in the conjugate gradient (CG) algorithm, including but not limited to, to perform time integration on the established model and perform energy minimization to eliminate problems such as atomic overlap and small spacing caused by randomly inserted carbon atoms;

[0135] (9) Using the Nose-Hoover heat bath method in the Non-Hamiltonian equation of motion to integrate time, updating the velocity and position of the atoms at each step, keeping the number of particles (N), volume (V) and temperature (T) in the system constant; relaxing the model at 2000K for 1ps to simulate the melting process of M50 steel;

[0136] (10) Using the Nose-Hoover heat bath method in the Non-Hamiltonian equation of motion, including but not limited to, time is integrated, the velocity and position of the atoms are updated at each step, and the number of particles (N), volume (V), and temperature (T) in the system are kept constant; the model is cooled uniformly from 2000K to 300K for 5ps to simulate the cooling process of M50 steel;

[0137] (11) Using the Nose-Hoover thermal bath method in the Non-Hamiltonian equation of motion, including but not limited to, time integration, updating the velocity and position of the atoms at each step, keeping the number of particles (N), volume (V), and temperature (T) in the system constant; relaxing the model at 300K for 0.5ps to simulate the room temperature aging process of M50 steel;

[0138] Therefore, according to the Nose-Hoover heat bath method in the Non-Hamiltonian motion equation used in (9), (10), and (11), the time is integrated, and the velocity and position of the atoms are updated at each step, so as to realize the melting of the model at 2000K, annealing at 2000K-300K, and aging at room temperature at 300K, so as to fully eliminate the structural defects and cracks in the model, reduce the residual stress in the model, and make it closer to some physical and mechanical properties of the real model;

[0139] (12) constructing a diamond indenter model with a diamond cubic crystal structure of a certain size and a certain crystal orientation, and obtaining the coordinates of each atom in the diamond model and its corresponding number;

[0140] (13) The diamond indenter is set as a rigid body and is slowly pressed into the M50 bearing steel model from above at a certain speed (e.g., 1 m / s). The indentation depth and the pressure on the M50 bearing steel model at each moment are obtained. The hardness value of the M50 bearing steel model is calculated and compared with the actual hardness value of the M50 steel to evaluate the correctness of the model:

[0141] i) If the evaluation is qualified, the model can be used to guide the research and development of alloy steels and various possible subsequent analyses and calculations;

[0142] ii) If the evaluation fails, any one or more of the following methods can be used to correct the model until the model evaluation passes: 1. Change the parameters in the potential function; 2. Change the potential function type; 3. Change the number of certain atoms in the model; 4. Change the distribution of the atoms of the alloying elements in the model. It should be noted that the nanoindentation simulation method is used to test the hardness value, elastic modulus value, etc. of the created model. The diamond indenter in the test is set as a rigid body and remains unchanged during the indentation process. The results are compared with the mechanical properties parameters of the real M50 steel to evaluate the established model. Among them, it is known that the Rockwell hardness value of the real M50 bearing steel is 65HRC.

[0143] More specifically, in one embodiment, referring to Figure 1 This disclosure proposes a molecular dynamics modeling method for M50 bearing steel containing multiple alloying elements, which not only achieves modeling but also enables evaluation. Specifically, the method includes the following steps:

[0144] S10: Obtain characteristic parameters of M50 bearing steel by consulting relevant data, including the types of elements contained in the alloy, the mass fraction of each element, and the particle spacing;

[0145] S20: Using serial or parallel LAMMPS software, set the model size and crystal orientation through the region command. The object of this disclosure uses the default crystal orientations

[100] ,

[010] and

[001] . The model defaults to a regular cuboid. Obtain the required potential function through the standard potential function official website and the potential function folder included in the installation package. Obtain the lattice constant of the crystal by consulting the potential function file. Run the program through the basic instructions of the LAMMPS program and the dump and run commands to obtain the iron matrix model. The model size includes but is not limited to The number of iron atoms contained in the model is 56,790;

[0146] S30: selecting elements to be added to the iron matrix model, including but not limited to chromium, molybdenum, vanadium and carbon;

[0147] S40: Determine the atomic radius of the four elements and their existence forms in the iron matrix model, and then determine the method of adding the four elements to the iron matrix model;

[0148] The atomic radius of iron atoms is 126pm, the atomic radius of chromium atoms is 128pm, the atomic radius of molybdenum atoms is 139pm, the atomic radius of vanadium atoms is 132pm, and the atomic radius of carbon atoms is 77pm. It can be seen that the atomic radius of chromium, molybdenum and vanadium is close to that of iron atoms, while the atomic radius of carbon atoms is much smaller than that of iron atoms. Therefore, the three atoms of chromium, molybdenum and vanadium exist in the iron matrix model in the state of substitutional solid solution, while carbon atoms exist in the iron matrix model in the form of interstitial solid solution; therefore, the three atoms of chromium, molybdenum and vanadium are added to the iron matrix model by atomic replacement, while carbon atoms are added to the iron matrix model by random insertion;

[0149] S50: Determine the number of atoms of various elements added to the model: In order to build a model that meets the mass fraction of each element in line with the real M50 steel, it is calculated that the number of chromium atoms added is 2600, the number of molybdenum atoms added is 1500, the number of vanadium atoms added is 630, and the number of carbon atoms inserted is 2200;

[0150] S60: Use random atomic replacement to add chromium atoms, molybdenum atoms, and vanadium atoms to the iron matrix model. At this time, the number of iron atoms in the corresponding model should be reduced by the number of other alloying elements added. The random replacement command uses:

[0151] Set type ID type / subset values ​​seed;

[0152] S70: Use random insertion to insert 2200 carbon atoms into the iron matrix model. The random insertion command is:

[0153] create_atoms type random N seed region-ID;

[0154] S80: Use the Polak-Ribiere method, including but not limited to the conjugate gradient (CG) algorithm, to perform time integration on the established model and perform energy minimization to eliminate problems such as atomic overlap and small spacing caused by randomly inserted carbon atoms. The command used is:

[0155] minimize,

[0156] The command to set the energy minimization method is: min_style cg;

[0157] S90: Use the Nose-Hoover heat bath method, including but not limited to the non-Hamiltonian equation of motion, to integrate over time, updating the velocity and position of the atoms at each step while keeping the number of particles (N), volume (V), and temperature (T) in the system constant. Relax the model at 2000K for 1ps to simulate the melting process of M50 steel. The command used is:

[0158] fix ID group-ID nvt 2000 2000 0.1;

[0159] S10: Use the Nose-Hoover heat bath method, including but not limited to the non-Hamiltonian equation of motion, to integrate time, updating the velocity and position of the atoms at each step, while keeping the number of particles (N), volume (V), and temperature (T) in the system constant. The model is cooled uniformly from 2000K to 300K for 5 ps to simulate the cooling process of M50 steel. The command used is:

[0160] fix ID group-ID nvt 2000 300 0.1;

[0161] S110: Use the Nose-Hoover thermal bath method in the non-Hamiltonian equation of motion to integrate time, updating the atomic velocities and positions at each step while keeping the number of particles (N), volume (V), and temperature (T) in the system constant. Relax the model for 0.5 ps at 300 K to simulate the room temperature aging process of M50 steel. The command used is:

[0162] fix ID group-ID nvt 300 300 0.1;

[0163] S120: Construct a diamond indenter model with a diamond cubic crystal structure of a certain size and orientation directly above the M50 steel model, and obtain the coordinates and corresponding numbers of each atom in the diamond model; the command used is:

[0164] region ID sphere xyz radius units box;

[0165] create_atoms type region region-ID;

[0166] S130: Set the diamond indenter as a rigid body, move the diamond indenter downward, and press it into the M50 bearing steel model. Obtain the indentation depth and pressure on the M50 bearing steel model at each moment. Calculate the nanoindentation hardness value of the M50 bearing steel model and compare it with the actual hardness value of M50 steel to evaluate the correctness of the model. The command used is: fix ID group-ID rigid single reinit yes.

[0167] It should be noted that the method disclosed in the present disclosure can be used with but not limited to the following software LAMMPS, Excel, MATLAB, Materials Studio and Atomsk.

[0168] See further Figure 2 The first step is to build an iron matrix model with a certain size and crystal orientation. The model size includes but is not limited to Since the lattice constant of iron is determined, the number of iron atoms contained in the model is also determined after the size is determined. This model contains 56,790 iron atoms;

[0169] See further Figure 3 , the model after adding chromium atoms into the iron matrix model by atomic replacement, including but not limited to 2600 chromium atoms;

[0170] See further Figure 4 , the model after adding molybdenum atoms into the iron matrix model by atomic replacement, including but not limited to 1500 molybdenum atoms;

[0171] See further Figure 5 , the model after adding vanadium atoms into the iron matrix model by atomic replacement, including but not limited to 630 vanadium atoms;

[0172] See further Figure 6 , a molecular dynamics model of M50 bearing steel formed by randomly inserting 2200 carbon atoms into an iron matrix model;

[0173] See further Figure 7 For the molecular dynamics model of M50 bearing steel after energy minimization, it can be seen from the model that the previously randomly distributed carbon atoms are now located in the lattice gaps of iron atoms and do not overlap with the positions of iron atoms. In addition, the carbon atoms are randomly and evenly distributed in the model.

[0174] See further Figure 8 , for the state diagram of the model after completing the relaxation process of high-temperature melting, cooling annealing and room-temperature aging, it can be seen that most atoms have moved to a certain extent compared to the initial state. At this time, most unstable factors in the model are eliminated, such as atomic overlap, gaps, cracks, etc., the structural stress in the model is released, and the system is in a relatively stable state;

[0175] See further Figure 9 ,For the system energy diagram during the entire relaxation process, it can be seen that the energy is in a low state and remains stable;

[0176] See further Figure 10 , the diamond indenter is set as a rigid body and the indenter is directly above the model The radius is The distance between the bottom end of the indenter and the M50 bearing steel model is The diamond indenter is pressed vertically downward into the substrate model, and the number of steps and the distance the indenter moves in each step are calculated to determine the depth of the indenter into the model. The hardness of the substrate model is calculated using the nanoindentation calculation formula in combination with the output force-step length file.

[0177] Figure 11 It indicates the depth of the indenter The model state at time ;

[0178] Figure 12 The graph shows the relationship between the force and displacement of the indenter output during nanoindentation simulation.

[0179] At this point, it can be understood that the present disclosure is not limited to a specific alloy steel, but can be universally used for molecular dynamics modeling of various alloy steels, and can achieve further evaluation and even provide specific means of correcting the modeling when the evaluation is unqualified until the evaluation is qualified, thereby guiding the research and development work of various alloy steels.

[0180] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0181] As described above, the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A molecular dynamics modeling method for alloy steel containing multiple alloy elements, characterized in that: The method comprises the following steps: S1: Obtain characteristic parameters of alloy steel, including the types of elements in the alloy, the mass fraction of various alloying elements, and the particle spacing; S2: Construct a body-centered cubic iron matrix model with a certain size and crystal orientation, and obtain the number of iron atoms in the iron matrix model and the coordinates of each atom; S3: In addition to iron, the atomic radius of the alloying elements that need to be added to the iron matrix model is determined according to the specific alloying elements that need to be inserted, and the existence form of various alloying elements in the iron matrix model is determined by referring to the steel billet; S4: Determine a method for adding atoms of various alloying elements into the iron matrix model based on the atomic radius of the alloying elements and the existence form of the alloying elements in the iron matrix model, including: an atomic replacement method and a random insertion method, wherein the atoms of the first type of alloying elements are selected by atomic replacement method, and the atoms of the second type of alloying elements are selected by random insertion method; S5: determining the number of atoms of the corresponding alloying elements that need to be added to the iron matrix model based on the mass fractions of the various alloying elements obtained in step S1 and the number of iron atoms in the iron matrix model; S6: using an atomic replacement method, randomly replacing the iron atoms in the iron matrix model with a corresponding number of atoms of the first type of alloying element, and making such atoms uniformly distributed in the iron matrix model; S7: using a random insertion method, randomly inserting a corresponding number of atoms of the second type alloying element within the model range of the iron matrix model, and making such atoms uniformly distributed in the iron matrix model; S8: performing energy minimization on the model processed in step S7 to eliminate the problem of atomic overlap or too small spacing caused by the randomly inserted atoms of the second type alloying element; S9: simulating the melting process of the alloy steel on the model processed in step S8; S10: simulating the cooling process of the alloy steel for the model processed in step S9; S11: simulating the room temperature aging process of the alloy steel on the model processed in step S10; S12: constructing a diamond indenter model with a diamond cubic crystal structure of a certain size and a certain crystal orientation, and obtaining the coordinates of each atom in the diamond model; S13: Slowly press the diamond indenter model into the model processed in step S11 from above at a certain speed, obtain the indentation depth and pressure at each moment, calculate the hardness value, and then compare it with the actual hardness value of the alloy steel to evaluate the correctness of the model.

2. The method according to claim 1, characterized in that In step S2, the crystal directions [100], [010] and [001] are respectively used as the X, Y and Z coordinate axis directions of the model, and the model dimensions and lattice constant a in the X, Y and Z coordinate axis directions are set to obtain the model matrix coordinate file.

3. The method according to claim 1, characterized in that For iron and other alloying elements, determine the atomic number and coordinates of each added atom and obtain the coordinate matrix files of various elements.

4. The method according to claim 3, characterized in that Except for iron, for the other alloying elements, the potential function type that characterizes the interaction force between the added elements is determined according to the added alloying elements, and the potential function between the elements in the model is set.

5. The method according to claim 4, characterized in that According to the coordinate matrix files of various elements and the interaction between various elements, the energy of the entire model is minimized to eliminate the problems of atomic overlap and small spacing in the model.

6. The method according to claim 1, wherein By simulating melting at 2000K, annealing from 2000K to 300K, and aging at room temperature at 300K, the residual stress in the model is reduced, making it closer to the physical and mechanical properties of real steel.

7. The method according to claim 1, characterized in that In step S13, the hardness and elastic modulus of the model are tested using a nanoindentation simulation method.

8. The method according to claim 1, characterized in that When the diamond indenter model is set as a rigid body, the diamond indenter model remains unchanged during the indentation process.

9. The method according to claim 1, characterized in that In step S8, the Polak-Ribiere method in the conjugate gradient CG algorithm is used to perform time integration on the established model to achieve energy minimization.

10. The method according to claim 1, characterized in that In step S9 or S10 or S11, the Nose-Hoover heat bath method in the Non-Hamiltonian equation of motion is used to perform time integration on the corresponding model to update the velocity and position of the atoms in each step.

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