A computational method for simulating the evolution of slab pit defects during rolling

Abstract

The present invention discloses a calculation method for simulating the evolution of concave pit defects in a slab during the rolling process. It belongs to the field of finite element analysis methods, and the specific steps are as follows: 1. In the finite element analysis software, draw three-dimensional graphics of the roll and the slab according to the actual dimensions; 2. Add concave pit defects with a radius of r0 to the slab; 3. Add a fillet with a radius of r1 at the edge of the concave pit defect with r0; 4. Set the material properties, initial conditions, and boundary conditions; 5. Perform meshing; 6. Calculate the rolling process to obtain the geometric shape of the concave pit defect after rolling. The technical problem to be solved by the present invention is a finite element calculation method for simulating the evolution of concave pit defects in a slab during the rolling process, which is used to study the evolution law of concave pit defects during the rolling process, so as to optimize the billet grinding and rolling processes; the present invention realizes the numerical simulation of the evolution of concave pit defects in a slab during the rolling process, can replace most on-site tests, improves efficiency and saves costs.

Description

Technical Field

[0001] The present invention belongs to the field of finite element analysis methods, and relates to a calculation method for simulating the evolution of a slab pit defect during a rolling process; more specifically, it relates to a finite element calculation method for simulating the evolution of a slab pit defect during a rolling process. Background Art

[0002] In the prior art, in the production of hot-rolled steel plates, the surface defects of the ingots may be repaired during the hot rolling process, or may be inherited to the surface of the finished steel plate. For pit defects on the surface of the ingots, the measures currently adopted by most steel mills are to grind the ingots to a certain thickness until the pits completely disappear. If the pit defects can be "healed" during the hot rolling process and the final product can meet the corresponding quality standards, then this kind of grinding based on the standard of no surface defects is not necessary, because it will produce a large amount of grinding, resulting in increased costs and waste.

[0003] In addition to being affected by the size of the pits themselves, the evolution of the pits is also affected by many other process factors, such as rolling temperature and reduction. In the actual production process, there are many possibilities for the arrangement and combination of these factors. It is difficult to test these different combinations of process parameters one by one on the production site. Using numerical simulation methods to study is a feasible method. At present, there have been many studies on the numerical simulation of steel billet rolling processing. These studies assume that the billet surface is a complete plane without defects. However, for billets with surface pit defects, it is necessary to solve the model convergence problem caused by the change in geometric shape, and the conventional model cannot be used directly. Summary of the invention

[0004] Purpose of the invention: The purpose of the invention is to provide a calculation method for simulating the evolution of the pit defect of the casting billet during the rolling process, which is used to study the evolution law of the pit defect during the rolling process and provide data support for optimizing the billet grinding and rolling process. This method can replace most of the field tests, improve efficiency and save costs.

[0005] Technical solution: The calculation method for simulating the evolution of the pit defect of the casting billet during the rolling process described in the present invention has the following specific operation steps:

[0006] (1) Draw the 3D graphics of the roll and the billet according to the actual size in the finite element analysis software;

[0007] (2) Add a pit defect with a radius of r0 to the ingot; wherein the value of the pit defect r0 is selected according to the actual situation;

[0008] (3) Add a fillet with a radius of r1 at the edge of the r0 pit defect;

[0009] (4) Set material properties and initial and boundary conditions;

[0010] (5) Perform dissection;

[0011] (6) Calculate the rolling process to obtain the geometric shape of the pit defect after rolling.

[0012] Furthermore, in step (1), the rolling roller is in the shape of a hollow cylinder, and the shape of the ingot is in the shape of a cuboid.

[0013] Furthermore, in step (3), the value of r1 must satisfy r1 <r0 / 5。

[0014] Furthermore, in step (4), setting material properties and initial conditions and boundary conditions specifically refers to:

[0015] (4.1) Set the density, elastic modulus, yield strength, Poisson's ratio and hardening function model of the ingot at rolling temperature;

[0016] Set the initial displacement and speed to 0, or set them to the calculation results after the last rolling pass;

[0017] (4.2), for the roller, the deformation can be ignored and its properties can be set to rigid, that is, its deformation can be ignored;

[0018] (4.3) Set the displacement, rotation speed and rotation direction of the roller;

[0019] (4.4) Set the contact conditions and friction coefficient between the roll and the ingot.

[0020] Furthermore, in step (5), the steps of performing the segmentation are specifically as follows:

[0021] (5.1) Divide one bottom surface of the roller into a quadrilateral and then sweep it along the axis to complete the hexahedral division of the entire roller;

[0022] (5.2) With the pit as the center, a rectangular area is divided on the ingot, and the distance between each face of the rectangular area and the pit is ≥10r0;

[0023] (5.3) Divide the blank area outside the rectangular block divided near the pit into hexahedrons; the maximum size of the unit cell is set to 2 cm;

[0024] (5.4) The rectangular area divided near the pit is divided into tetrahedrons, and the unit size growth rate in the area does not exceed 1.2; the maximum size of the unit where the pit surface and the fillet surface are located is set to r1.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following characteristics: The technical problem to be solved by the present invention is a finite element calculation method for simulating the evolution of pit defects in the casting billet during the rolling process, which is used to study the evolution law of pit defects in the rolling process, so as to optimize the billet grinding and rolling process; the present invention realizes the numerical simulation of the evolution of pit defects in the casting billet during the rolling process, which can replace most of the on-site tests, improve efficiency and save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is an operation flow chart of the present invention;

[0027] Figure 2 It is a schematic diagram of the cross section of the roller in the present invention;

[0028] Figure 3 Schematic diagram of the splitting of the ingot in the present invention; wherein (a) is a splitting diagram of 1 / 4 of the ingot, and (b) is a splitting diagram of 1 / 4 of the ingot near the pit defect;

[0029] Figure 4 It is a comparison diagram of the change of the pit profile before and after rolling in the present invention; wherein, (a) is a comparison diagram of the cross section parallel to the rolling direction, and (b) is a comparison diagram of the cross section perpendicular to the rolling direction. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific embodiments, which is not intended to limit the scope of protection of the present invention:

[0031] like Figure 1 The specific operation steps of the calculation method for simulating the evolution of the pit defect of the casting billet during the rolling process described in the present invention are as follows:

[0032] (1) In the finite element analysis software, draw the 3D graphics of the roll and the billet according to the actual size. The shape of the roll is a hollow cylinder, and the shape of the billet is a cuboid;

[0033] (2) Add a pit defect with a radius of r0 to the ingot, where the value of r0 is selected according to the actual situation;

[0034] (3) Add a fillet with a radius of r1 to the edge of the pit. The value of r1 must satisfy r1 <r0 / 5;

[0035] (4) Set material properties, initial conditions and boundary conditions:

[0036] (a) Setting the density, elastic modulus, yield strength, Poisson's ratio and hardening function model of the ingot at rolling temperature;

[0037] Set the initial displacement and speed to 0 (for the first pass calculation) or to the calculation result after the last rolling pass is completed;

[0038] (b) For the roller, the deformation can be ignored and its properties can be set to rigid, that is, its deformation can be ignored;

[0039] (c) Setting the displacement (pressing amount), rotation speed and rotation direction of the roller;

[0040] (d) Setting the contact conditions between the roll and the ingot and the friction coefficient;

[0041] (5) Perform segmentation according to the following steps:

[0042] (a) A bottom surface of the roller (hollow cylinder) is quadrilateralized and then swept along the axis to complete the hexahedral division of the entire roller;

[0043] (b) With the pit as the center, a rectangular area is divided on the billet, and the distance between each face of the rectangular area and the pit is not less than 10r0;

[0044] (c) Divide the blank area outside the rectangular block near the pit into hexahedrons. The maximum size of the unit cell is set to 2 cm;

[0045] (d) tetrahedron partitioning is performed on the rectangular area partitioned near the pit, and the growth rate of the unit size in the area does not exceed 1.2;

[0046] The maximum size of the unit where the pit surface and the fillet surface are located is set to r1;

[0047] (6) Calculate the rolling process to obtain the geometric shape of the pit defect after rolling.

[0048] Example 1

[0049] This example calculates the evolution of a Φ10 hemispherical pit defect on the surface of a billet with an initial thickness of 150 mm during a rolling pass with a reduction of 20 mm. The pit is located at the center of the upper surface of the billet, and considering the symmetry, only 1 / 4 of the entire system is modeled.

[0050] Draw a hollow cylinder with an outer diameter of 505mm, an inner diameter of 305mm, a length of 1200mm, and an axis direction of the y-axis as a roller. The roller is set to be rigid, with a displacement of -10mm in the z-direction; the rotation speed is 3rad / s. Draw a cuboid with a height (z-direction) of 75mm, a width of 1000mm (y-direction), and a length of 1200mm (x-direction); add a pit with a radius of 5mm at the midpoint of one side in the x-direction, and add a fillet with a radius of 1mm at the upper edge of the pit; the density of the ingot is set to 7.5g / cm 3, elastic modulus is 100 GPa, yield strength is 9 MPa, Poisson's ratio is 0.3, and the hardening function adopts Ludvik model, in which k = 84 MPa and n = 0.67. The initial displacement and velocity of the casting are set to 0.

[0051] One bottom surface of the roller is aligned with the side surface of the ingot, and symmetry boundary conditions are set on the bottom and side surfaces of the ingot; the contact method between the working surface of the roller and the surface of the ingot is set to a penalty function, and the friction coefficient is set to 0.6.

[0052] The roll was split and the results were as follows: Figure 2 As shown; a rectangular area is divided near the pit defect of the ingot, and the distance between each surface of the rectangular area and the center of the pit is 50 mm. The ingot is segmented, wherein the maximum growth rate of the unit size in the rectangular area divided near the pit defect is set to 1.2, and the result is as follows Figure 3 shown.

[0053] Perform rolling calculations and visualize the data after calculations are completed. The pit contours before and after rolling are as follows: Figure 4 As shown; the results show that after one rolling, the pit depth dropped from 5mm to 3.4mm, and the pit was elongated to 14mm along the rolling direction, with no change in the width direction.

[0054] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A calculation method for simulating the evolution of a slab pit defect during rolling, characterized in that: The specific steps are as follows: (1) Draw the 3D graphics of the roll and the billet according to the actual size in the finite element analysis software; (2) Add a pit defect with a radius of r0 to the ingot; wherein the value of the pit defect r0 is selected according to the actual situation; (3) Add a fillet with a radius of r1 at the edge of the r0 pit defect; (4) Set material properties, initial conditions and boundary conditions. The specific steps are as follows: (4.1) Set the density, elastic modulus, yield strength, Poisson's ratio and hardening function model of the ingot at rolling temperature; Set the initial displacement and speed to 0, or set them to the calculation results after the last rolling pass; (4.2), for the roller, the deformation can be ignored and its properties can be set to rigid, that is, its deformation can be ignored; (4.3) Set the displacement, rotation speed and rotation direction of the roller; (4.4) Setting the contact conditions and friction coefficient between the roll and the billet; (5) Perform segmentation. The specific steps are as follows: (5.1) Divide one bottom surface of the roller into a quadrilateral and then sweep it along the axis to complete the hexahedral division of the entire roller; (5.2) With the pit as the center, a rectangular area is divided on the ingot, and the distance between each face of the rectangular area and the pit is ≥10r0; (5.3) Divide the blank area outside the rectangular block divided near the pit into hexahedrons; the maximum size of the unit cell is set to 2 cm; (5.4) Tetrahedron division is performed on the rectangular area divided near the pit, and the unit size growth rate in the area does not exceed 1.2; the maximum size of the unit where the pit surface and the fillet surface are located is set to r1; (6) Calculate the rolling process to obtain the geometric shape of the pit defect after rolling.

2. The calculation method for simulating the evolution of a slab pit defect during rolling according to claim 1, characterized in that: In step (1), the rolling roller is in the shape of a hollow cylinder, and the shape of the ingot is in the shape of a cuboid.

3. The calculation method for simulating the evolution of a casting slab pit defect during rolling according to claim 1, characterized in that: In step (3), the value of r1 satisfies r1 <r0 / 5。

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