Visual analysis method for grain change in medium plate casting blank heating furnace

Abstract

The invention relates to the technical field of grain refinement of medium-thickness plate casting blanks, in particular to a visual analysis method for grain change in a medium-thickness plate casting blank heating furnace. The method specifically comprises the following steps: S1, processing a sample; s2, grinding the sample, and then cleaning and blow-drying the sample; s3, putting the prepared sample into a crucible, then putting the crucible into an ultrahigh-temperature imaging type heating furnace of a high-temperature laser confocal microscope system, vacuumizing, and introducing inert or reducing gas; s4, simulating the heating process of the casting blank heating furnace by using the ultrahigh-temperature imaging type heating furnace, wherein the heating process is divided into four stages; s5, selecting a single-frame picture which is clear in austenite grain boundary display and does not grow obviously, and exporting the single-frame picture; and S6, analyzing the picture. And the grain change condition in the blank in the medium-thickness plate casting blank heating process can be observed in real time, and the production process can be accurately adjusted and guided in combination with an austenite grain growth model.

Description

Technical Field

[0001] The present invention relates to the technical field of medium and thick plate casting slab grain refinement, and in particular to a method for visualizing grain changes in a medium and thick plate casting slab heating furnace. Background Art

[0002] The billet heating furnace is a device used to heat the billet, and it plays a vital role in the metal processing process. Before rolling, the billet needs to be austenitized in the heating furnace to obtain a single-phase austenite structure, achieve composition homogenization, and reduce deformation resistance. The heating process is roughly divided into two stages: heating and soaking. During the heating stage, the billet is heated from the furnace entry temperature to 1100-1200°C at a certain heating rate. Under normal circumstances, the final temperature of the billet during the heating stage is 1150-1200°C, and the soaking time is in the range of 30-60 minutes. The austenite grain size is mainly affected by the heating rate, final temperature, and soaking time.

[0003] In plate production, achieving a fine grain size is a fundamental starting point for developing production processes. The size of the initial austenite grains during billet heating significantly influences the changes in austenite grain size during subsequent rolling. Smaller grains increase the number of grains per unit volume, resulting in more grain boundaries and greater grain boundary resistance, which in turn increases the material's yield strength. Grain boundaries confine and homogenize plastic deformation within a material, and the presence of numerous grain boundaries effectively retards crack propagation. Therefore, grain refinement can improve the material's toughness. Grain refinement also has varying degrees of impact on tensile strength, brittle transition temperature, work hardening index, and reduction of area. The overall trend is an increase in tensile strength, but the impact is relatively less pronounced than on yield strength. Therefore, grain refinement can improve the yield strength ratio, reduce the brittle transition temperature, and increase the work hardening index. Therefore, grain refinement can improve both strength and toughness, and is a key objective in developing press working processes.

[0004] Medium and thick plate products are mainly used in engineering machinery, shipbuilding, pressure vessels, energy, construction and other fields. They have a wide range of uses and a wide variety of varieties, and occupy an extremely important position in the national economy. Some application areas have complex environments and require products with high comprehensive performance, such as high strength and toughness, ultra-low temperature toughness, corrosion resistance and wear resistance, easy welding, and yield strength ratio. With the continuous advancement of enterprise production technology, medium and thick plate products have changed from the past practice of mainly achieving specified performance by adding alloys, and now pay more attention to improving the comprehensive performance of products through means such as fine grain strengthening and precipitation strengthening. Since fine grain strengthening not only improves the strength of the plate but also improves the toughness, the control of the original grain size and the suppression of grain growth by deformation recrystallization have become the most basic starting points for formulating medium and thick plate production process systems. However, it is currently impossible to observe the changes in the grains inside the billet in real time in the billet heating furnace, which has become a shortcoming that restricts grain size research. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention provides a visual analysis method for grain changes in a medium and thick plate casting furnace, which can observe the grain changes inside the billet during the heating process of the medium and thick plate casting in real time, and combined with the austenite grain growth model, it can accurately adjust and guide the production process.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A visual analysis method for grain changes in a medium and thick plate casting furnace specifically comprises the following steps:

[0008] S1: Processing medium and heavy plate ingot samples into disc specimens;

[0009] S2: Grind the sample, then clean and dry it;

[0010] S3: The prepared sample is placed in a crucible, which is then placed in an ultra-high temperature imaging heating furnace of a high-temperature laser confocal microscope system, where it is evacuated and an inert or reducing gas is introduced.

[0011] S4: An ultra-high temperature imaging heating furnace is used to simulate the heating process of the slab heating furnace. The heating process is divided into four stages: the first stage is the heating source preheating stage, the second stage is the heating stage, the third stage is the soaking stage, and the fourth stage is the cooling stage.

[0012] S5: Ensure that more than 10 complete grains are captured within the field of view. Observe the grain changes inside the sample in real time during the second and third stages. Select single-frame images with clear austenite grain boundaries and no obvious growth for export.

[0013] S6: Analyze the images and compare the austenite grain sizes under different heating rates, soaking temperatures, and soaking times to find out the variation pattern between austenite grain size and process parameters.

[0014] According to the austenite grain growth kinetics equation:

[0015]

[0016] The heating rate v correction term is introduced to establish a multivariate nonlinear regression model:

[0017]

[0018] Where: D is the austenite grain size, μm;

[0019] D0 is the initial grain size, μm;

[0020] K is the kinetic constant;

[0021] v is the heating rate, °C / s;

[0022] α is the heating rate index;

[0023] t is the soaking time, min;

[0024] n is the time index;

[0025] R is the gas constant, J / (mol·K);

[0026] T is the soaking temperature, °C;

[0027] Q is the activation energy of grain boundary migration, kJ / mol;

[0028] According to the characteristics of different steel grades, D0, K, n, α, R, and Q are determined and substituted into equations (1) and (2) to obtain the relationship between austenite grain size and heating rate, soaking temperature, and soaking time.

[0029] Furthermore, in S1, the medium and thick plate ingot sample is processed into a disc sample by wire cutting.

[0030] Furthermore, in S1, the diameter of the disc sample is 3 to 7 mm, and the height is 2 to 4 mm.

[0031] Furthermore, in S2, after one end surface of the disc sample is ground and polished with sandpaper, the sample is placed in an ultrasonic vibration cleaner and vibrated and cleaned with an ethanol solution, and then blown dry for use.

[0032] Furthermore, the high-temperature laser confocal microscope system in S3 consists of an optical system with high-speed laser scanning and imaging capabilities, an ultra-high-temperature imaging furnace, an imaging heating and high-temperature tension and compression unit, a motorized workbench, a control system, and auxiliary systems. It is currently the only device capable of real-time laser scanning imaging, recording, and analysis of high-temperature, dynamic objects. Due to its high scanning frequency (15-120 frames / second), high observation temperature (up to 1750°C), ability to accommodate a variety of experimental atmospheres, and real-time online observation capabilities, it is an advanced research tool in the fields of metal materials, semiconductor materials, and ceramic materials.

[0033] Furthermore, in S3, the sample is placed in an alumina ceramic crucible, which is then placed on a bracket in an ultra-high temperature imaging heating furnace and the furnace cover is closed; vacuuming and introducing argon are repeated 2 to 3 times.

[0034] Furthermore, in S4, the first stage is heated to 200°C at a temperature lower than 200°C / min, the second stage is heated to the final temperature of the heating furnace insulation stage at a heating rate of 200-600°C / min, the third stage is heated at the final temperature for 30-60 minutes, and the fourth stage is cooled to room temperature at a cooling rate of 30-800°C / min.

[0035] Compared with the existing method, the present invention has the following beneficial effects:

[0036] 1. The present invention prepares a small sample of the ingot and uses an ultra-high temperature imaging heating furnace to simulate the heating process of the ingot heating furnace, that is, the two stages of heating and soaking, to achieve real-time online observation of the changes in the grains inside the sample. During the heating and soaking stages, the changes in the austenite grains inside the sample can be observed online in real time. The austenite grain sizes at different heating rates and soaking temperatures can be compared and analyzed to find out the change rules. A parameter model of the austenite grain size and the heating rate, soaking temperature, and soaking time can be established, which is helpful to formulate a suitable heating process in the ingot heating furnace and obtain good finished product performance. This solves the current shortcoming that the grain changes inside the billet cannot be observed in real time in the ingot heating furnace. The experimental method is simple, easy to operate, and the experimental results are reliable, which is helpful to formulate a suitable heating process in the ingot heating furnace and obtain good finished product performance.

[0037] 2. The present invention repeats the process of vacuuming and introducing argon gas 2 to 3 times. The observation process is carried out in a vacuum environment and protected by an inert gas to ensure that the sample is not contaminated.

[0038] 3. The present invention places the sample into an alumina ceramic crucible. Compared with graphite or metal crucibles, alumina ceramics are more durable in high temperature and corrosive environments and have lower long-term use costs. Alumina ceramic crucibles are an ideal choice for high temperature and corrosive environments, and are particularly suitable for application scenarios with high requirements for purity, stability and durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the first figure derived during the casting change process of Example 1 of the present invention.

[0040] Figure 2 This is the second figure derived during the casting process of Example 1 of the present invention.

[0041] Figure 3 This is the third figure derived during the casting process of Example 1 of the present invention.

[0042] Figure 4 This is the fourth figure derived during the casting change process of Example 1 of the present invention.

[0043] Figure 5 This is the first figure derived during the casting change process of Example 2 of the present invention.

[0044] Figure 6 This is the second figure derived during the casting change process of Example 2 of the present invention.

[0045] Figure 7 This is the third figure derived during the casting change process of Example 2 of the present invention.

[0046] Figure 8 This is the fourth figure derived during the casting change process of Example 2 of the present invention. DETAILED DESCRIPTION

[0047] The present invention discloses a method for visual analysis of grain changes in a heating furnace for medium and thick plate casting. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters for implementation. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0048] A visual analysis method for grain changes in a medium and thick plate casting furnace specifically comprises the following steps:

[0049] 1. Sampling: The medium and thick plate ingot samples are processed into disc samples with a diameter of 3 to 7 mm and a height of 2 to 4 mm by wire cutting.

[0050] 2. Sample Preparation: Grind the sample in accordance with GB / T13298 "Methods for the Examination of Metal Microstructures." Auxiliary devices may be used during the grinding process to ensure that the two end faces of the disc remain parallel. After sanding and polishing one end face of the disc sample, place the sample in an ultrasonic vibrator and clean it with ethanol solution. Then, blow dry and set aside.

[0051] 3. The experimental equipment of this invention utilizes a high-temperature laser confocal scanning microscope system with tension and compression capabilities. It is an analytical instrument used in the field of materials science. The high-temperature laser confocal microscope system consists of an optical system with high-speed laser scanning and imaging capabilities, an ultra-high-temperature imaging heating furnace, an imaging-type high-temperature tension and compression unit, a motorized workbench, a control system, and auxiliary systems. It is currently the only device capable of real-time laser scanning imaging, recording, and analysis of high-temperature, dynamic objects. Due to its high scanning frequency (15-120 frames / second), high observation temperature (up to 1750°C), ability to accommodate a variety of experimental atmospheres, and real-time online observation capabilities, it is an advanced research tool in the fields of metal materials, semiconductor materials, ceramic materials, and other fields.

[0052] The prepared sample was placed in an alumina ceramic crucible, which was then placed on the high-temperature heating furnace bracket of a high-temperature laser confocal microscope and the furnace lid was closed. Vacuuming and introducing argon gas were repeated 2 to 3 times to eliminate water vapor and oxidizing atmosphere in the furnace.

[0053] 4. Temperature control program setting. The program is divided into four stages. The first stage is the heating source preheating stage, heating to 200℃ at a heating rate of less than 200℃ / min; the second stage is the heating stage, heating to the final temperature of the heating furnace holding stage at a heating rate of 200-600℃ / min; the third stage is the soaking time at the final temperature for 30-60 minutes, which is used to simulate the soaking process of the heating furnace to obtain a single-phase austenite structure; the fourth stage is the cooling stage, cooling to room temperature at a cooling rate of 30-800℃ / min, and observing the precipitates and solid-state phase transformation behavior.

[0054] 5. Observe the grain evolution process. Select an appropriate magnification to ensure that at least 10 complete grains are captured within the field of view. During the heating and soaking stages, observe the grain evolution within the specimen in real time. Select single-frame images with clear austenite grain boundaries and no apparent growth for export.

[0055] 6. Analyze the pictures and compare the austenite grain sizes under different heating rates, soaking temperatures, and soaking times to find out the changing pattern between austenite grain size and process parameters;

[0056] According to the austenite grain growth kinetics equation:

[0057]

[0058] The heating rate v correction term is introduced to establish a multivariate nonlinear regression model:

[0059]

[0060] Where: D is the austenite grain size, μm;

[0061] D0 is the initial grain size, μm;

[0062] K is the kinetic constant;

[0063] v is the heating rate, °C / s;

[0064] α is the heating rate index;

[0065] t is the soaking time, min;

[0066] n is the time index;

[0067] R is the gas constant, J / (mol·K);

[0068] T is the soaking temperature, °C;

[0069] Q is the activation energy of grain boundary migration, kJ / mol;

[0070] According to the characteristics of different steel grades, D0, K, n, α, R, and Q are determined and substituted into equations (1) and (2) to obtain the relationship between austenite grain size and heating rate, soaking temperature, and soaking time.

[0071] Example 1:

[0072] Visual analysis of grain changes in a Q355B ingot heating furnace.

[0073] 1. Sampling: The medium and heavy plate ingot samples were processed by wire cutting into disc specimens with a diameter of 5 mm and a height of 3 mm.

[0074] 2. Sample preparation. Grind the specimens in accordance with GB / T13298, "Methods for the Examination of Metal Microstructures." After grinding and polishing one end of the disc specimen with 120#, 400#, 600#, or 1000# sandpaper, place the specimen in an ultrasonic oscillator and clean it with ethanol solution, then blow dry for later use.

[0075] 3. Test Preparation: Place the prepared sample into an alumina ceramic crucible, then place it on the high-temperature heating furnace bracket of a high-temperature laser confocal microscope and secure the furnace lid. Repeat the process of vacuuming and introducing argon twice to eliminate water vapor and oxidizing atmosphere in the furnace.

[0076] 4. Temperature control program settings. The program is divided into four stages: heating rate gradient: 1°C / s, 3°C / s, 5°C / s, 10°C / s; soaking temperature gradient: 1050°C, 1100°C, 1150°C, 1200°C; soaking time: fixed at 60 minutes.

[0077] 5. Observe the grain change process. Select the magnification of 275 times. During the heating and soaking stages, observe the grain changes inside the sample in real time. Figure 1-4 As shown, during the soaking stage at 1100°C, a single frame image showing clear austenite grain boundaries and no apparent growth was selected for export. The austenite grain intercept was measured to be 117.7 μm. Comparing and analyzing the austenite grain sizes at different heating rates and soaking temperatures to identify the patterns of change will help develop a suitable heating process within the slab heating furnace and achieve good finished product performance. Table 1 shows the grain size measurement data for Example 1.

[0078] Table 1 Grain size measurement data of Example 1

[0079] Steel Type Heating rate (℃ / s) Temperature (℃) Grain size (μm) Q355B steel 1 1050 42.3 Q355B steel 10 1200 158.6

[0080] Before the experiment, the initial grain size D0 of 45# steel was measured to be 28 μm. According to formula (2), nonlinear regression was performed on the Q355B steel data:

[0081]

[0082] Using the least squares method we get:

[0083]

[0084] A model relationship between austenite grain size, heating rate and soaking temperature was constructed to guide the adjustment of production process parameters.

[0085] Example 2:

[0086] Visual analysis process of grain changes in the heating furnace for 45# casting billets.

[0087] 1. Sampling: Cut the medium and heavy plate ingot sample into a disc sample with a diameter of 3mm and a height of 2mm;

[0088] 2. Sample preparation. Grind the specimens in accordance with GB / T13298, "Methods for the Examination of Metal Microstructures." After grinding and polishing one end of the disc specimen with 120#, 400#, 600#, or 1000# sandpaper, place the specimen in an ultrasonic oscillator and clean it with ethanol solution, then blow dry for later use.

[0089] 3. Test Preparation: Place the prepared sample into an alumina ceramic crucible, then place it on the high-temperature heating furnace bracket of a high-temperature laser confocal microscope and secure the furnace lid. Repeat the process of evacuating the furnace and introducing argon three times to eliminate water vapor and oxidizing atmosphere.

[0090] 4. Temperature control program settings. The program is divided into four stages: heating rate gradient: 1°C / s, 3°C / s, 5°C / s, 10°C / s; soaking temperature gradient: 1050°C, 1100°C, 1150°C, 1200°C; soaking time: fixed at 60 minutes.

[0091] 5. Observation of grain change process. Select the magnification of 275 times, and observe the grain change inside the sample in real time during the heating and soaking stages, such as Figure 5-8 As shown, during the soaking stage at 1200°C, a single frame image showing clear austenite grain boundaries and no apparent growth was selected for export. The austenite grain intercept was measured to be 136.9 μm. Comparing and analyzing the austenite grain sizes at different heating rates and soaking temperatures to identify the patterns of change will help develop an appropriate heating process within the slab heating furnace and achieve good finished product performance. Table 2 shows the grain size measurement data for Example 2.

[0092] Table 2 Grain size measurement data of Example 2

[0093] Steel Type Heating rate (℃ / s) Temperature (℃) Grain size (μm) 45# steel 5 1150 132.7 45# steel 10 1100 68.5

[0094] Before the experiment, the initial grain size D0 of 45# steel was measured to be 22 μm. According to formula (2), nonlinear regression was performed on the data of 45# steel:

[0095]

[0096] Using the least squares method we get:

[0097]

[0098] A model relationship between austenite grain size, heating rate and soaking temperature was constructed to guide the adjustment of production process parameters.

[0099] This method prepares small cast specimens and uses an ultra-high-temperature imaging furnace to simulate the heating process within a cast furnace, namely the two stages of heating and soaking. This allows real-time online observation of grain changes within the specimens. The observation process is protected by an inert gas atmosphere, ensuring that the specimens are not contaminated. The experimental method is simple, easy to use, and provides reliable results, facilitating the development of appropriate furnace heating processes for cast specimens, resulting in superior finished product performance.

[0100] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A visual analysis method for grain changes in a medium and thick plate casting furnace, characterized in that: The specific steps include: S1: Processing medium and heavy plate ingot samples into disc specimens; S2: Grind the sample, then clean and dry it; S3: The prepared sample is placed in a crucible, which is then placed in an ultra-high temperature imaging heating furnace of a high-temperature laser confocal microscope system, where it is evacuated and an inert or reducing gas is introduced. S4: An ultra-high temperature imaging heating furnace is used to simulate the heating process of the slab heating furnace. The heating process is divided into four stages: the first stage is the heating source preheating stage, the second stage is the heating stage, the third stage is the soaking stage, and the fourth stage is the cooling stage. S5: Ensure that more than 10 complete grains are captured within the field of view. Observe the grain changes inside the sample in real time during the second and third stages. Select single-frame images with clear austenite grain boundaries and no obvious growth for export. S6: Analyze the images and compare the austenite grain sizes under different heating rates, soaking temperatures, and soaking times to find out the variation pattern between austenite grain size and process parameters. According to the austenite grain growth kinetics equation: The heating rate v correction term is introduced to establish a multivariate nonlinear regression model: Where: D is the austenite grain size, μm; D0 is the initial grain size, μm; K is the kinetic constant; v is the heating rate, °C / s; α is the heating rate index; t is the soaking time, min; n is the time index; R is the gas constant, J / (mol·K); T is the soaking temperature, °C; Q is the activation energy of grain boundary migration, kJ / mol; According to the characteristics of different steel grades, D0, K, n, α, R, and Q are determined and substituted into equations (1) and (2) to obtain the relationship between austenite grain size and heating rate, soaking temperature, and soaking time.

2. The method for visually analyzing grain changes in a medium and thick plate casting furnace according to claim 1, characterized in that: In S1, the medium and heavy plate ingot samples were processed into disc specimens by wire cutting.

3. The method for visually analyzing grain changes in a medium and thick plate casting furnace according to claim 1, characterized in that: In S1, the diameter of the disc sample is 3 to 7 mm and the height is 2 to 4 mm.

4. The method for visually analyzing grain changes in a medium and thick plate casting furnace according to claim 1, characterized in that: In S2, after one end surface of the disc sample is ground and polished with sandpaper, the sample is placed in an ultrasonic vibration cleaner for vibration cleaning with an ethanol solution, and then blown dry for use.

5. The method for visualizing and analyzing grain changes in a medium and thick plate casting furnace according to claim 1, characterized in that: In S3, the high-temperature laser confocal microscope system consists of an optical system with high-speed laser scanning imaging function, an ultra-high temperature imaging heating furnace, an imaging heating high-temperature stretching and compression unit, an electric workbench, a control system and an auxiliary system.

6. The method for visualizing and analyzing grain changes in a medium and thick plate casting furnace according to claim 1, characterized in that: In S3, the sample is placed in an alumina ceramic crucible, which is then placed on a bracket in an ultra-high temperature imaging heating furnace and the furnace cover is closed; vacuuming and introducing argon gas are repeated 2 to 3 times.

7. The method for visualizing and analyzing grain changes in a medium and thick plate casting furnace according to claim 1, characterized in that: In S4, the first stage is heating to 200°C at a rate lower than 200°C / min, the second stage is heating to the final temperature of the heating furnace insulation stage at a heating rate of 200-600°C / min, the third stage is soaking time at the final temperature for 30-60 minutes, and the fourth stage is cooling to room temperature at a cooling rate of 30-800°C / min.

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