A numerical simulation method for hydrogen permeation process of enameled steel sheet

Abstract

The present invention relates to a numerical simulation method for the hydrogen permeation process of an enameled steel plate, and belongs to the technical field of enameled steel quality control methods. The technical scheme of the present invention is: (1) minimizing the energy of the initial model to obtain the optimal structure; (2) fully relaxing the iron / hydrogen model to reach an equilibrium state; (3) fixing the temperature and pressure of the system, and studying the motion state of hydrogen atoms in iron matrix models of different thicknesses during heating and cooling. The beneficial effects of the present invention are: the construction of iron matrix models of different thicknesses and the observation of the motion state and position of hydrogen atoms are relatively simple, achieving a detailed understanding of the microstructure of the enameled steel plate during temperature changes, and facilitating simulation operations and process predictions.

Description

Technical Field

[0001] The invention relates to a numerical simulation method for a hydrogen permeation process of an enameled steel plate, belonging to the technical field of enameled steel quality control methods. Background Art

[0002] In recent years, the application of enameled steel plates has played a pivotal role in the national economy. Enameled steel plates refer to composite materials obtained by firing enamel on the surface of a metal blank through enameling technology. Since enameled steel plates have the advantages of strong formability inherent in metals and corrosion resistance and strong decorativeness of enamel, the target market of enameled steel plates has extended from the traditional daily necessities industry to the fields of construction, metallurgy and chemical equipment. Enameled steel plates for different purposes are required to have different comprehensive properties. Common problems of enameled steel plates during use include scale explosion, cracks in the enamel layer, bubbles in the enamel and pores. Among them, scale explosion is the most common and fatal problem of enameled products, and the time of occurrence is difficult to predict.

[0003] Fish scale refers to the phenomenon that the enamel layer on the surface of the enameled product peels off in a half-moon shape of varying sizes and depths, and adheres to the surface like fish scales. The occurrence of fish scale defects will cause the metal matrix inside the enameled product to contact the external environment, thereby reducing the service performance of the enameled product. In order to improve the anti-fish scale performance of enameled steel plates, domestic and foreign scholars have conducted a lot of research on the fish scale mechanism of enameled steel plates. The study found that the fish scale phenomenon of enameled steel plates is caused by excessive pressure of hydrogen precipitated in the steel plates. During the production process of enameled products, the steel plates undergo two hydrogen-producing reactions, the first one is during pickling, and the second one is during the enamel firing process. During pickling, iron reacts with acid, the metal is dissolved and hydrogen is precipitated, and the precipitated hydrogen does not volatilize completely, but is partially dissolved in the steel plate in the form of hydrogen atoms. On the other hand, during the enamel firing process, since the clay contains crystal water, a dehydration process will occur, and part of the water in the melt will be discharged. However, since the water contained is discharged slowly, some of the water will inevitably react with the iron. Part of the hydrogen released by the reaction will evaporate, and the other part will dissolve in the steel plate.

[0004] When a large amount of hydrogen atoms are dissolved in the steel plate, the enameling temperature is high, and the solubility of hydrogen increases with the temperature. After the enameled product cools down, the hydrogen in the steel reaches supersaturation at room temperature, and the hydrogen will diffuse outward. Since the hardened porcelain layer is impermeable to hydrogen, a large amount of hydrogen atoms will combine between the porcelain layer and the steel plate to form hydrogen. When the pressure of hydrogen exceeds the limit of the porcelain layer, it will break through the porcelain layer and cause scale explosion.

[0005] Currently, the recognized methods for testing the anti-scale burst performance of enameled steel plates are mainly hydrogen penetration method and enameling method. The enameling method is generally used for base enamels with a tendency to scale burst. The enameled steel plate is then heated in an oven, and the anti-scale burst performance of the steel plate is tested by comparing the number of scale burst defects on the enameled base enamel steel plate. The hydrogen penetration method generally enamels the steel plate on one side, and uses hydrogen to cathode charge the enameled steel plate under standard acid solution, temperature and current density. The time when the first scale burst appears on the steel plate represents the anti-scale burst performance of the steel plate. The long time used indicates that the diffusion rate of hydrogen in the steel plate is slow, and the number of hydrogen atoms entering the steel plate in the same time under the same process is small, which is beneficial to improve the anti-scale burst performance of the enameled steel plate. Compared with the enameling method, the hydrogen penetration method has a short cycle and simple operation, so it is widely used.

[0006] Patent CN102192933A discloses a method for measuring hydrogen permeation of the enamel scale explosion sensitivity of cold-rolled steel plates. The sample is fastened between two electrolytic cells and electrolyte is poured into the two electrolytic cells at the same time; the potential value of the sample is measured, and after the potential value stabilizes, the sample is charged with hydrogen; the computer records the potential-time curve of the sample, and when the potential-time curve appears a straight line approximately parallel to the horizontal axis, the test is stopped; the hydrogen permeation time is obtained through the potential-time curve and the anti-enamel scale explosion sensitivity value is calculated based on the hydrogen permeation time.

[0007] In the hydrogen permeation experiment, the hydrogen atoms in the enameled steel plate exist in the gaps of the metal lattice. The diffusion of hydrogen atoms refers to the process of hydrogen atoms in the gap position migrating to another gap position. The diffusion rate of hydrogen atoms in the steel plate can be judged by the penetration time or diffusion coefficient of hydrogen atoms in the steel plate. Therefore, observing the change law of the microstructure during the movement of hydrogen atoms in the enameled steel plate from the atomic scale is very helpful for improving the anti-scale explosion property of the enameled steel plate.

[0008] In actual production, it takes a lot of effort to experimentally observe the microscopic motion state of hydrogen atoms in enameled steel plates. Summary of the invention

[0009] The present invention aims to provide a numerical simulation method for the hydrogen permeation process of an enameled steel plate, adopts a molecular dynamics simulation method to observe the motion state of hydrogen atoms in an iron matrix with different process parameters, and controls the heating temperature, holding time and cooling rate in the subsequent heating and cooling processes by simulating the state of hydrogen atoms adhering to the surface of the steel plate after pickling and enameling, so that the number of hydrogen atoms in the enameled steel plate in the use state is significantly reduced, and the occurrence of scale explosion is reduced; the construction of iron matrix models with different thicknesses and the observation of the motion state and position of hydrogen atoms are relatively simple, and a detailed understanding of the microstructure of the enameled steel plate during the temperature change process is achieved, which facilitates simulation operations and process predictions, and effectively solves the above-mentioned problems existing in the background technology.

[0010] The technical solution of the present invention is: a numerical simulation method for the hydrogen permeation process of an enameled steel plate, comprising the following steps: (1) minimizing the energy of the initial model to obtain an optimal structure; (2) fully relaxing the iron / hydrogen model to reach an equilibrium state; (3) fixing the temperature and pressure of the system to study the motion state of hydrogen atoms in iron matrix models of different thicknesses during heating and cooling.

[0011] In the step (1), the initial model energy is minimized using a conjugate gradient algorithm.

[0012] In the step (2), the iron / hydrogen model is fully relaxed to reach an equilibrium state under the NPT ensemble.

[0013] In the step (3), the temperature and pressure of the system are adjusted using the Nose-Hoover method and the Berendsen method, and the simulation is carried out under an isothermal and isobaric ensemble; the hydrogen permeation simulation process of the enameled steel plate is as follows: first, the steel plate with hydrogen atoms attached to the surface after pickling and enameling is heated and fired, then subjected to heat preservation treatment, cooled after the heat preservation is completed, and finally the process of hydrogen atoms permeating into the enameled steel plate is completed.

[0014] The beneficial effects of the present invention are as follows: a molecular dynamics simulation method is used to observe the motion state of hydrogen atoms in an iron matrix with different process parameters; by simulating the state of hydrogen atoms adhering to the surface of a steel plate after pickling and enameling, the heating temperature, holding time and cooling rate in the subsequent heating and cooling processes are controlled, so that the number of hydrogen atoms in the enameled steel plate under use is significantly reduced, and the occurrence of scale explosion is reduced; the construction of iron matrix models with different thicknesses and the observation of the motion state and position of hydrogen atoms are relatively simple, so a detailed understanding of the microstructure of the enameled steel plate during temperature changes is achieved, and simulation operations and process predictions are convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram of the iron / hydrogen model of different thicknesses under the initial equilibrium state of the present invention.

[0016] Figure 2 It is a diagram of the iron / hydrogen model of different thicknesses during the heating and heat preservation process of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the invention implementation cases clearer, the technical solutions in the implementation cases of the present invention will be clearly and completely described below in conjunction with the drawings in the implementation cases. Obviously, the implementation cases described are only a small part of the implementation cases of the present invention, rather than all the implementation cases. Based on the implementation cases in the present invention, all other implementation cases obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0018] A numerical simulation method for the hydrogen permeation process of enameled steel plate comprises the following steps: (1) minimizing the energy of the initial model to obtain the optimal structure; (2) fully relaxing the iron / hydrogen model to reach an equilibrium state; (3) fixing the temperature and pressure of the system and studying the motion state of hydrogen atoms in iron matrix models of different thicknesses during heating and cooling.

[0019] In the step (1), the initial model energy is minimized using a conjugate gradient algorithm.

[0020] In the step (2), the iron / hydrogen model is fully relaxed to reach an equilibrium state under the NPT ensemble.

[0021] In the step (3), the temperature and pressure of the system are adjusted using the Nose-Hoover method and the Berendsen method, and the simulation is carried out under an isothermal and isobaric ensemble; the hydrogen permeation simulation process of the enameled steel plate is as follows: first, the steel plate with hydrogen atoms attached to the surface after pickling and enameling is heated and fired, then subjected to heat preservation treatment, cooled after the heat preservation is completed, and finally the process of hydrogen atoms permeating into the enameled steel plate is completed.

[0022] In practical applications, the method of the present invention is used to simulate the effect of substrate thickness on the motion state of hydrogen atoms in the substrate during hydrogen penetration. Other simulation process parameters are the same as those in the conventional enameled steel plate production process to prepare an enameled steel plate model.

[0023] The iron / hydrogen model is constructed by an iron layer and a hydrogen layer. The three coordinate axes X, Y, and Z are along the

[100] ,

[010] , and

[001] crystal directions respectively, and the iron / hydrogen interface is parallel to the Z plane. The interatomic interaction potential function uses the embedded atom potential.

[0024] Example:

[0025] like Figure 1 and Figure 2 The figure shows four iron / hydrogen models with different iron matrix thicknesses, with a total number of atoms of about 100,000, 125,000, 150,000 and 175,000 respectively. The iron / hydrogen model is energy minimized and fully relaxed to reach equilibrium; then the model is kept warm for 60ps at T=30K and pressure P=0GPa, and then cooled. As the thickness of the model matrix increases, the number of hydrogen traps increases, which reduces the diffusion rate of hydrogen atoms in iron, thereby improving the anti-scale explosion performance of the enameled steel sheet. The numerical simulation method has great application value for simulating the enameling and cooling process of enameled steel sheets, and has great reference value in process research and development and improvement. The model has a good predictive and guiding role in improving the anti-scale explosion performance of enameled steel sheets.

Claims

1. A numerical simulation method for hydrogen permeation process of enameled steel sheet, characterized in that The method includes the following steps: (1) minimizing the energy of the initial model to obtain the optimal structure; (2) fully relaxing the iron / hydrogen model to reach an equilibrium state; (3) fixing the temperature and pressure of the system and studying the motion state of hydrogen atoms in the iron matrix model of different thicknesses during heating and cooling; In the step (1), the initial model energy is minimized using a conjugate gradient algorithm; in the step (2), the iron / hydrogen model is fully relaxed to reach an equilibrium state under the NPT ensemble; in the step (3), the temperature and pressure of the system are adjusted using the Nose-Hoover method and the Berendsen method, and the simulation is carried out under an isothermal and isobaric ensemble; the hydrogen permeation simulation process of the enameled steel plate is as follows: first, the steel plate with hydrogen atoms attached to the surface after pickling and enameling is heated and fired, then subjected to a heat preservation treatment, cooled after the heat preservation is completed, and finally the process of hydrogen atoms permeating into the enameled steel plate is completed.

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