Measuring method of zero strength temperature of steel

Abstract

The invention relates to a method for measuring the zero-strength temperature of steel, and the steps include: 1. taking a billet subjected to light pressure reduction during solidification as a sampling object, and performing longitudinal low-magnification and transverse low-magnification measurements on the billet sample; 2. measuring the distance h1 from the distribution line of microcracks generated by the zero plasticity temperature to the billet surface, and measuring the distance h2 from the distribution line of microcracks generated by the zero-strength temperature to the billet surface on the billet sample at low magnification; 3. The measured distances h1 and h2 are the thicknesses after pressure reduction deformation, and they are corrected to the distances h1* and h2* without light pressure reduction; 4. constructing a continuous casting solidification model by using an alternating implicit difference method, simulating the temperature distribution of the billet cross section by the model, and the billet cross sections at different positions of the billet correspond to different slice numbers; 5. calibrating the model to make it closer to the actual temperature field; 6. finding the slice number of a tension and straightening machine corresponding to light pressure reduction from the simulation result of the model, and reading the zero-strength temperature from the temperature field according to the slice number.

Description

Technical Field

[0001] The invention relates to a method for measuring zero intensity temperature. Background Art

[0002] Soft reduction technology is one of the important means to improve the segregation of ingots and improve their quality. If this technology is used improperly, it will cause serious internal cracks in the ingot, namely soft reduction cracks. Research on cracks found that when the total strain between the zero strength temperature and the zero plasticity temperature exceeds the critical strain, internal cracks will occur and expand, whether continuous or intermittent. Based on this fact, it can be concluded that the conditions for the formation of internal cracks in continuous casting ingots should be evaluated by the total strain between the ZST (zero strength temperature) and ZDT (zero plasticity temperature) applied by each roller. Therefore, it is necessary to understand the zero plasticity temperature and zero strength temperature of each steel grade when studying cracks. The zero plasticity temperature is close to the solidus temperature and can be assumed to be equal. It is difficult to obtain the zero strength temperature of a steel grade. At present, the zero strength temperature of steel is mainly measured in the laboratory by a Gleeble thermal simulator. Summary of the invention

[0003] The purpose of the invention is to provide a method for measuring the zero-strength temperature of steel.

[0004] The technical solution adopted by the present invention is: a method for measuring the zero-strength temperature of steel, comprising:

[0005] Step 1: Take samples at the position of the ingot corresponding to the tension and straightening machine under light pressure, and perform longitudinal low magnification or longitudinal low magnification and transverse low magnification on the ingot sample;

[0006] Step 2: Find the microcracks generated by zero plasticity temperature and the microcracks generated by zero strength temperature on the ingot sample at low magnification, measure the distance h1 from the distribution line of the microcracks generated by zero plasticity temperature to the ingot surface, and measure the distance h2 from the distribution line of the microcracks generated by zero strength temperature to the ingot surface;

[0007] Step 3: The measured distances h1 and h2 are the thicknesses after compression and deformation, and they are corrected and restored to the distances h1* and h2* before light compression;

[0008] Step 4: Use the alternating implicit difference method to construct a continuous casting solidification model. The temperature distribution of the cross section of the ingot is simulated by the model. The cross sections of the ingot at different positions correspond to different slice numbers. Obviously, the straightening machine that performs light pressure on the ingot also has a corresponding slice number.

[0009] Step 5: Calibrate the model to make it closer to the actual temperature field;

[0010] Step 6: Find the slice number corresponding to the tension leveler that implements light pressure from the simulation results of the model, and read the zero-intensity temperature from the temperature field according to the slice number.

[0011] Preferably, in step 1, the tensioning and straightening machine implements light pressing by single-roll pressing, so that the microcracks presented on the low magnification are clearer, and it is easier to obtain the distribution lines of microcracks generated by zero plastic temperature and zero strength temperature. Without the light pressing technology, the microcracks on the low magnification are fuzzy; multi-roll pressing will cause more microcracks on the low magnification and cause interference, and single-roll pressing is easier to distinguish. The longitudinal section low magnification is mainly measured, and the transverse low magnification is measured as a reference.

[0012] Step 1: When measuring h1 and h2, focus on measuring the longitudinal low magnification and use the lateral low magnification as a reference.

[0013] Step 2: The crack distribution law at the location of zero plastic temperature and zero strength temperature: the zero plastic temperature is close to the solidus temperature, and the solid phase ratio at the zero plastic temperature is 1, that is, h1 is the shell thickness of the billet corresponding to the straightening machine. The shell thickness refers to the thickness of the solid phase area on the surface of the billet, excluding the solid-liquid two-phase area. The microcracks generated by the zero plastic temperature are on a straight line; the microcracks generated by the zero strength temperature are near another straight line, closer to the core of the billet. Understanding this law can help operators accurately measure h1 and h2.

[0014] Step 3: Correction method for h1 and h2: h1*=h1+△e1, where h1: measured shell thickness, △e1: correction amount, △e1=h1 / l*△h, where l: measured thickness of the ingot after cooling, △h: total reduction;

[0015] H2*=h2+△e1, where h2: measured shell thickness, △e1: correction amount, △e1=h2 / l*△h, where l: measured thickness of the ingot after cooling, △h: total reduction.

[0016] Optionally, in step five, the model is calibrated by a nail shooting test, and the shell thickness of the ingot is measured by multiple nail shooting sulfur prints, and compared with the shell thickness of the model simulation results, and then the model solidification parameters are adjusted: the thermal conductivity of the liquid phase region and the solid-liquid two-phase region, until the simulation results are the same or close to the results obtained by the nail shooting test, and the model is calibrated to the state closest to the actual production situation.

[0017] Optionally, in step five, the model is calibrated by measuring the surface temperature of the ingot during the straightening process, measuring the surface temperature multiple times and comparing the results with the surface temperature in the temperature field simulated by the model, and then adjusting the model solidification parameters: thermal conductivity of the liquid phase region and the solid-liquid two-phase region, until the ingot surface temperature simulated by the model is the same as or close to the actually measured ingot surface temperature, and the model is calibrated to the state closest to the actual production situation.

[0018] Preferably, in step six, the slice number corresponds to the straightening machine, and the distances from the straightening machine to the meniscus of the continuous casting machine corresponding to different slice numbers are different. The corresponding zero intensity temperature is found from the temperature field simulated by the model through the slice number and h2*.

[0019] This application interprets the microcracks on the low-magnification longitudinal section of the ingot, and then combines the simulation results of the continuous casting solidification model to read the zero-strength temperature from the simulated temperature field on different ingot cross-sections. It is a new method for measuring the zero strength of steel grades and is no longer limited to relying on thermal simulators to detect the zero-strength temperature of steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the macrostructure of the longitudinal section of the ingot in the embodiment of the present invention;

[0021] In the figure:

[0022] h1: The distance from the zero strength temperature at the second straightening machine to the surface of the ingot, i.e. the thickness of the ingot shell (excluding the solid-liquid two-phase region);

[0023] h2: distance from the zero strength temperature at the second straightening machine to the surface of the ingot;

[0024] AB: zero plastic temperature line;

[0025] CD: zero intensity temperature line. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with embodiments. It should be understood that the embodiments are exemplary and should not constitute any limitation on the technology claimed in the present application.

[0027] This embodiment takes high carbon bearing steel as an example to measure the zero strength temperature of high carbon bearing steel. By interpreting the micro crack points on the low magnification longitudinal section of the ingot, and then combining the simulation results of the continuous casting solidification model, the zero strength temperature can be read from the temperature table. This is a new method for measuring the zero strength of steel grades, which is no longer limited to detection by thermal simulators. Specifically, the following steps are included:

[0028] (1) Taking rectangular cross-section high-carbon bearing steel as the research object, the continuous casting furnace uses a second straightening machine to perform single-roll large reduction on the continuous casting billet.

[0029] The ingot samples using the soft reduction technology were selected for longitudinal and transverse low magnification.

[0030] (2) Study the distribution law of low-magnification microcracks and measure the distance h1 from the microcracks generated at zero plasticity temperature to the surface of the ingot. Similarly, measure the distance h2 from the microcracks generated at zero strength temperature to the surface of the ingot.

[0031] (3) The measured distances h1 and h2 are the thicknesses after deformation by pressing, and need to be corrected and restored to the distances before pressing by the tensioning and leveling machine, which are h1* and h2* respectively.

[0032] (4) The alternating implicit difference method is used to construct a continuous casting solidification model. The model has an appendix that can import the temperatures corresponding to all slice numbers of the ingot into the appendix.

[0033] The model refers to the full casting strand solidification model. The default is that the multi-machine and multi-strand straightening machine is not disturbed by the flow sequence. This is the initial boundary condition of the model.

[0034] There are many slices. Simply put, the metallurgical length of the 240mm×240mm section is 20m. According to the principle of symmetry, one-fourth of the section is selected as the research object and cut into 5mm×5mm. There will be 2500000 slices. The temperature appendix data is relatively complete. The model simulation results generally use another appendix, which contains simplified results, including the center temperature of the ingot and the center temperature of the surface, but does not contain all data.

[0035] (5) Calibration model. All models simulate actual production based on assumed boundary conditions, so there will be certain deviations from the actual situation and they need to be calibrated to be more accurate.

[0036] (6) Read the zero strength temperature. Find the slice number corresponding to the tension and leveling machine from the model simulation results, and read the zero strength from the temperature table based on the slice number.

[0037] Light pressing adopts a single-roll pressing method, which is more convenient to determine the crack distribution line, and there are only two rows of light pressing cracks. According to the low-magnification microcracks in the longitudinal section of the ingot, the distance from the corresponding straightening machine to the meniscus can be found, and then the slice number n at the straightening machine can be found through the model. The specific temperature distribution of the cross section of the ingot at this position can be found from the temperature table through the slice number n. The cross section of the ingot will be divided into grids by the difference method. The grid size is the slice size. The grid nodes include the starting point of the corners, which is one more than the number of slices. Let the grid node spacing be x. Starting from the highest temperature, the temperature at the (h2* / x)th slice is the zero plastic temperature.

[0038] Note: The result of h2* / x is rounded up to the nearest integer. If it is an integer, add 1 directly.

[0039] The calculation method of zero strength temperature is the same as that of zero plasticity temperature or in the temperature table, according to the result of h1*, count the corresponding temperatures of [(h2*-h1*) / slice length] tables.

[0040] Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for measuring the zero strength temperature of steel, characterized in that: include Step 1: Take the ingot that is subjected to light pressure during the solidification process as the sampling object, and perform longitudinal low magnification or longitudinal low magnification and transverse low magnification on the ingot sample; Step 2: Find the microcracks generated by zero plasticity temperature and the microcracks generated by zero strength temperature on the ingot sample at low magnification, measure the distance h1 from the distribution line of the microcracks generated by zero plasticity temperature to the ingot surface, and measure the distance h2 from the distribution line of the microcracks generated by zero strength temperature to the ingot surface; Step 3: The measured distances h1 and h2 are the thicknesses after compression deformation. Correct them to the distances h1* and h2* without light compression; h1*=h1+△e1, where h1: measured thickness of the billet shell, △e1: correction amount, △e1=h1 / l*△h, where l: measured thickness of the billet after cooling, △h: total compression; h2*=h2+△e1, where h2: measured thickness of the billet shell, △e1: correction amount, △e1=h2 / l*△h, where l: measured thickness of the billet after cooling, △h: total compression; Step 4: Use the alternating implicit difference method to construct a continuous casting solidification model. The temperature distribution of the cross section of the ingot is simulated by the model. The cross sections of the ingot at different positions correspond to different slice numbers. Obviously, the position of the straightening machine that performs light pressure on the ingot also has a corresponding slice number. Step 5: Calibrate the model to make it closer to the actual temperature field; Step 6: Find the slice number corresponding to the tension leveler that implements light pressure from the simulation results of the model, and read the zero-intensity temperature from the temperature field according to the slice number.

2. The method for measuring the zero-strength temperature of steel according to claim 1, characterized in that: Step 1: The tensioning and straightening machine uses a single-roller pressing method to implement light pressing, so that the microcracks presented at low magnification are clearer and it is easier to obtain the distribution lines of microcracks generated by zero plasticity temperature and the distribution lines of microcracks generated by zero strength temperature.

3. The method for measuring the zero-strength temperature of steel according to claim 1, characterized in that: Step 1: When measuring h1 and h2, focus on measuring the longitudinal low magnification and use the lateral low magnification as a reference.

4. The method for measuring the zero-strength temperature of steel according to claim 1, characterized in that: Step 2: The crack distribution law at the location of zero plastic temperature and zero strength temperature: the zero plastic temperature is close to the solidus temperature, and the solid phase ratio at the zero plastic temperature is 1, that is, h1 is the shell thickness of the ingot corresponding to the straightening machine. The shell thickness refers to the thickness of the solid phase area on the surface of the ingot, excluding the solid-liquid two-phase area. The microcracks generated by the zero plastic temperature are in a straight line; The microcracks generated at zero strength temperature are near another straight line, closer to the core of the ingot.

5. The method for measuring the zero-strength temperature of steel according to claim 1, characterized in that: Step five: the model is calibrated by nail shooting test. The shell thickness of the ingot is measured by multiple nail shooting sulfur prints and compared with the shell thickness of the model simulation results. Then the model solidification parameters are adjusted: the thermal conductivity of the liquid phase region and the solid-liquid two-phase region, until the simulation results are the same as those obtained by the nail shooting test, and the model is calibrated to the state closest to the actual production situation.

6. The method for measuring the zero-strength temperature of steel according to claim 1, characterized in that: Step five, the model is calibrated by measuring the surface temperature of the ingot during the straightening process. The surface temperature is measured multiple times and the results are compared with the surface temperature in the temperature field simulated by the model. Then the model solidification parameters are adjusted: the thermal conductivity of the liquid phase region and the solid-liquid two-phase region, until the surface temperature of the ingot simulated by the model is the same as the actually measured surface temperature of the ingot, and the model is calibrated to the state closest to the actual production situation.

7. The method for measuring the zero-strength temperature of steel according to claim 1, characterized in that: Step six, the slice number corresponds to the straightening machine. The distances from the straightening machine to the meniscus of the continuous casting machine corresponding to different slice numbers are different. The corresponding zero intensity temperature is found from the temperature field simulated by the model through the slice number and h2*.

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