A method for detecting high-temperature plasticity of microalloyed steel casting corner
By conducting high-temperature melting and bending straightening experiments on a thermal simulation testing machine and drawing a comparison diagram of the high-temperature plasticity of the edges and corners of the cast billet, the problem of accuracy in detecting the plasticity of the edges and corners of microalloyed steel cast billets was solved, ensuring production stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HBIS LAOTING STEEL CO LTD
- Filing Date
- 2022-07-05
- Publication Date
- 2026-04-17
AI Technical Summary
Existing technologies cannot accurately detect the high-temperature plasticity of the edges and corners of microalloyed steel billets, which may lead to misleading production processes and potential accidents.
The rapid cooling and latent heat rise processes of the billet edges and corners were simulated. High-temperature melting, plasticity, and bending straightening experiments were conducted on a thermal simulation test machine. A comparison chart of the high-temperature plasticity of the billet edges and corners was plotted to accurately detect the high-temperature plasticity of the billet edges and corners.
By simulating the actual production process, the high-temperature plasticity of the corners and edges of the billet is accurately detected, ensuring stable production and avoiding abnormal situations caused by excessively low plasticity.
Smart Images
Figure CN115326589B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an experimental method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets, belonging to the technical field of steel process performance testing in the iron and steel metallurgy industry. Background Technology
[0002] Steels containing microalloying elements such as Nb, V, and Ti are prone to cracking defects at the edges and corners of the cast billet during production. Extensive analysis and research have been conducted on this issue. The main reason is that during the continuous casting cooling process of microalloyed steel, there are significant differences in the plasticity of the billet at different temperature stages, i.e., there is a brittle temperature range. The edges and corners of the billet dissipate heat faster, and the temperature is usually lower than the internal temperature of the billet, which may cause it to enter the brittle temperature range prematurely. During continuous casting bending, the tensile stress may cause microcracks or even tensile fractures in the billet.
[0003] Previous studies on the conventional plasticity of cast billets mainly focused on directly testing the conventional plasticity of the billets. However, the actual cooling process at the edges and corners of the billets is more complex, involving rapid cooling followed by latent heat reheating. Conventional testing methods can only characterize the steady-state high-temperature plasticity of the billets and cannot accurately detect the actual high-temperature plasticity in the low-temperature region at the edges and corners. Research has found that the actual temperature reached during rapid cooling at the edges and corners of the billets has a significant impact on the high-temperature plasticity of the edges and corners. If conventional methods are used for testing, erroneous results are highly likely to be obtained, thereby misleading the formulation of production processes and even causing production accidents. Therefore, accurately detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets will play a crucial role in improving the quality of microalloyed billets. Summary of the Invention
[0004] The purpose of this invention is to provide an experimental method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets. This method simulates the process of rapid cooling and latent heat reheating at the edges and corners of billets during actual production, accurately detects and analyzes the high-temperature plasticity of the billet edges and corners, confirms whether the low-temperature zone at the edges and corners of the billet will cause abnormalities due to excessively low plasticity, ensures stable production operation, and solves the problems existing in the background technology.
[0005] The technical solution of this invention is:
[0006] An experimental method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets includes the following steps:
[0007] Step 1: Prepare the test specimen. Process the steel billet to be tested according to the high temperature tensile test standard, check whether the specimen size meets the standard, and record the specimen size.
[0008] Step Two: Conduct high-temperature melting and high-temperature tensile tests on a thermal simulation testing machine according to different experimental methods and parameters:
[0009] (1) Experiment A: High-temperature melting and fracture test of billet. The billet is heated in stages until it melts and fractures, and the melting and fracture temperature T is recorded. m Determine the high-temperature tensile insulation temperature T0, and the ratio of T0 to T m 50~70℃ lower;
[0010] (2) Experiment B: High temperature plasticity test of billet. The billet is heated to T0 in stages and held for a period of time. Then it is cooled to different test temperatures T1. After holding, a high temperature tensile test is carried out at a constant strain rate until the specimen breaks. Then it is numbered.
[0011] (3) Experiment C: Plasticity test of billet bending and straightening. The billet is heated to T0 in stages and held for a period of time. Then it is cooled to the turning test temperature T2, held for a period of time, heated to the fixed tensile test temperature T3, held for a period of time, and then subjected to a high-temperature tensile test at a constant strain rate until the specimen breaks. Then it is numbered.
[0012] Step 3: Measure the fracture diameter of the tensile fracture specimen and calculate the reduction of area.
[0013] Step 4: Based on the experimental results of Experiment B and Experiment C at different temperatures, draw a comparison diagram of the high-temperature plasticity of the billet edges and corners with the test temperature as the X-axis and the reduction of area as the Y-axis, so as to accurately determine whether there is a brittle temperature range in the billet and its edges and corners, and analyze the high-temperature plasticity of the billet edges and corners based on the experimental results.
[0014] Step 1: Prepare the specimen. The steel billet to be tested is machined into a cylindrical tensile specimen with threads at both ends, with a diameter of 10mm or 8mm×120mm. The original diameter D0 of the specimen is measured and checked to see if it meets the dimensional standard.
[0015] In step two, before the experiment, a high-temperature platinum-rhodium thermocouple is welded to the middle of the sample to check whether the thermocouple welding position is centered; then, on the thermal simulation test machine, the high-temperature melting test of the billet, the high-temperature plasticity test of the billet, and the bending and straightening plasticity test of the billet are carried out respectively.
[0016] Experiment A: The specific steps are as follows: The billet is heated in stages until it melts and fractures. Below 1200℃, the temperature is increased at a rate of 10~20℃ / s; from 1200~1350℃, the temperature is increased at a rate of 1~10℃ / s; above 1350℃, the temperature is increased at a rate of 0.1~1℃ / s. The melting point T is recorded. m Determine the high-temperature tensile insulation temperature T0, and the ratio of T0 to T m 50~70℃ lower;
[0017] Experiment B: The specific steps are as follows: The billet is heated in stages: below 1200℃, the heating rate is 10~20℃ / s; from 1200~1350℃, the heating rate is 1~10℃ / s; above 1350℃, the heating rate is 0.1~1℃ / s; T0 is held for 30~180s, then cooled to the tensile test temperature T1 at a rate of 1~10℃ / s, and held for 5~10s to eliminate the temperature gradient. The T1 temperature range is adjusted according to the steel grade, usually within the range of 1400~600℃. The tensile test strain rate is 0.01~0.001s. -1 The sample was subjected to high-temperature tensile testing until it fractured. After fracture, it was naturally cooled to room temperature, numbered and recorded. The fracture diameter was measured uniformly after the experiment was completed to reduce measurement error.
[0018] Experiment C: The specific steps are as follows: The billet is heated in stages: below 1200℃, the heating rate is 10~20℃ / s; between 1200~1350℃, the rate is 1~10℃ / s; above 1350℃, the rate is 0.1~1℃ / s. The billet is held at temperature T0 for 30~180s, then cooled to the turning test temperature T2 at a rate of 1~10℃ / s, held for a short time of 5~10s. The temperature range of T2 is adjusted according to the steel grade, usually within the range of 1200~600℃. Then, the temperature is increased again to the tensile test fixed temperature T3 at a rate of 1~10℃ / s. Temperature T3 is selected as the lowest temperature (greater than 900℃) where the reduction of area Z-value is greater than 80% according to Experiment B. This temperature is then held for a short time of 5~10s before starting the high-temperature tensile test. The tensile test strain rate is 0.01~0.001s. -1 The sample was subjected to high-temperature tensile testing until it fractured. After fracture, it was naturally cooled to room temperature, numbered and recorded. The fracture diameter was measured uniformly after the experiment was completed to reduce measurement error.
[0019] Step three: The formula for the high-temperature tensile reduction of area is:
[0020]
[0021] In the formula: Z..... High-temperature tensile reduction of area, %
[0022] D x ...High-temperature tensile fracture diameter, mm;
[0023] D0.....Original diameter of the sample, mm.
[0024] The beneficial effects of this invention are: it simulates the process of rapid cooling and latent heat reheating of the corners of the billet in actual production, draws a high-temperature plasticity diagram of the corners of the billet, comprehensively and accurately detects and analyzes the high-temperature plasticity of the corners of the billet, confirms whether the low-temperature zone of the billet and corners will cause abnormalities due to excessively low plasticity, and ensures stable production operation. Attached Figure Description
[0025] Figure 1 Photo of the cast billet:
[0026] Figure 2 This is a schematic diagram of a high-temperature plasticity test on a cast billet.
[0027] Figure 3 This is a schematic diagram of a plasticity test for bending and straightening of a cast billet.
[0028] Figure 4 The image shows a specific example of a high-temperature plasticity test on a cast billet.
[0029] Figure 5 A specific example of a plasticity test for bending and straightening of a cast billet is shown in the figure.
[0030] Figure 6 Examples of high-temperature plasticity test fracture surfaces at the edges and corners of cast billets;
[0031] Figure 7 This is an example of a comparison diagram showing the high-temperature plasticity of the edges and corners of a cast billet. Detailed Implementation
[0032] The invention will be further described below with reference to the accompanying drawings and examples.
[0033] See attached document Figure 1-7 An experimental method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets includes the following steps:
[0034] Step 1: Prepare the test specimen. Process the steel billet to be tested according to the high temperature tensile test standard, check whether the specimen size meets the standard, and record the specimen size.
[0035] Step Two: Conduct high-temperature melting and high-temperature tensile tests on a thermal simulation testing machine according to different experimental methods and parameters:
[0036] (1) Experiment A: High-temperature melting and fracture test of billet. The billet is heated in stages until it melts and fractures, and the melting and fracture temperature T is recorded. m Determine the high-temperature tensile insulation temperature T0, and the ratio of T0 to T m 50~70℃ lower;
[0037] (2) Experiment B: High temperature plasticity test of billet. The billet is heated to T0 in stages and held for a period of time. Then it is cooled to different test temperatures T1. After holding, a high temperature tensile test is carried out at a constant strain rate until the specimen breaks. Then it is numbered.
[0038] (3) Experiment C: Plasticity test of billet bending and straightening. The billet is heated to T0 in stages and held for a period of time. Then it is cooled to the turning test temperature T2, held for a period of time, heated to the fixed tensile test temperature T3, held for a period of time, and then subjected to a high-temperature tensile test at a constant strain rate until the specimen breaks. Then it is numbered.
[0039] Step 3: Measure the fracture diameter of the tensile fracture specimen and calculate the reduction of area.
[0040] Step 4: Based on the experimental results of Experiment B and Experiment C at different temperatures, draw a comparison diagram of the high-temperature plasticity of the billet edges and corners with the test temperature as the X-axis and the reduction of area as the Y-axis, so as to accurately determine whether there is a brittle temperature range in the billet and its edges and corners, and analyze the high-temperature plasticity of the billet edges and corners based on the experimental results.
[0041] In this embodiment:
[0042] Step 1: The specific steps are as follows: The steel billet to be tested is machined into a cylindrical tensile specimen with threads at both ends of Φ10mm×120mm. The thread length on one side is about 15mm. After machining, check whether the threads at both ends of the specimen match the fixture, measure the original diameter D0 of the specimen and check whether it meets the dimensional standard.
[0043] Step Two: The specific steps are as follows: Weld a high-temperature platinum-rhodium thermocouple to the center of the sample and check whether the thermocouple welding position is centered; install the fixture and sample, close the operating chamber and evacuate the vacuum, then fill with argon gas to prevent the oxide layer from interfering with the experiment. On the thermal simulation test machine, conduct the high-temperature melting test, high-temperature plasticity test, and bending straightening plasticity test of the billet respectively;
[0044] Experiment A: The specific steps are as follows: The billet is heated in stages until it melts and fractures. Below 1200℃, the temperature is increased at a rate of 10~20℃ / s; from 1200~1350℃, the temperature is increased at a rate of 1~10℃ / s; above 1350℃, the temperature is increased at a rate of 0.1~1℃ / s. The melting point T is recorded. m The temperature is 1420℃. The high-temperature tensile insulation temperature T0 is determined to be 1350℃ (lower than T). m 70℃);
[0045] Experiment B, the specific steps are as follows: Figure 4 As shown, the billet was heated in stages: below 1200℃, the temperature was increased at a rate of 10℃ / s; from 1200 to 1350℃, the temperature was increased at a rate of 5℃ / s. The billet was held at 1350℃ for 60 seconds, then cooled to the tensile test temperature T1 (1250~600℃) at a rate of 5℃ / s, held briefly for 5 seconds to eliminate the temperature gradient, and then cooled at a rate of 0.001s. -1The strain rate was subjected to high-temperature tensile testing until the specimen fractured. After fracture, the specimen was allowed to cool naturally to room temperature, and the specimens were numbered and recorded. After the experiment was completed, the fracture diameter was measured uniformly to reduce measurement errors.
[0046] Experiment C: The specific steps are as follows: Figure 5 As shown, the billet was heated in stages: below 1200℃, the temperature was increased at a rate of 10℃ / s; from 1200 to 1350℃, the rate was increased at 5℃ / s. The billet was held at 1350℃ for 60 seconds, then cooled at a rate of 5℃ / s to the transition test temperature T2 (1000~700℃), held briefly for 5 seconds to eliminate the temperature gradient; subsequently, the temperature was increased again at a rate of 5℃ / s to T3, which was the lowest temperature (1050℃) where the reduction of area Z-value was greater than 80% according to experimental method B. This temperature was then held for 5 seconds before starting the high-temperature tensile test. The strain rate for the tensile test was 0.001 s². -1 The sample was subjected to high-temperature tensile testing until it fractured. After fracture, it was naturally cooled to room temperature, numbered and recorded. The fracture diameter was measured uniformly after the experiment was completed to reduce measurement error.
[0047] Step 3: The specific steps are as follows: Figure 6 As shown, the fracture diameter D of the uniformly measured tensile fracture specimen is... x The cross-sectional reduction rate Z value is calculated using the formula for cross-sectional reduction rate.
[0048] The formula for the reduction of area during high-temperature tensile testing is:
[0049]
[0050] In the formula: Z..... High-temperature tensile reduction of area, %
[0051] D x ...High-temperature tensile fracture diameter, mm;
[0052] D0.....Original diameter of the sample, mm.
[0053] Step 4: Based on the experimental results of Experiments B and C at various test temperatures, plot a comparison diagram of the high-temperature plasticity of the billet edges and corners, with the test temperature as the X-axis and the reduction of area as the Y-axis, as shown below. Figure 7 As shown, this allows for an accurate and comprehensive determination of whether a brittle temperature range exists in the billet and its edges, and a comparative analysis is conducted based on the experimental results. Specific implementation examples:
[0055] Q420B V-containing microalloyed angle steel, the main components of which are shown in Table 1, showed cracking defects at the edges and corners of the cast billet. On-site observation revealed low-temperature blackening at the edges and corners of the cast billet, as shown in the attached table. Figure 1As shown in the figure. By using this experimental method, the high-temperature plasticity of the edges and corners of the cast billet can be comprehensively and accurately detected and analyzed, providing a basis for the analysis of the cause mechanism of cracking problems, the formulation of cracking problem solutions, and the optimization of related processes.
[0056] Table 1
[0057]
[0058] Following the experimental procedure, the fracture diameter D of each tensile fracture specimen (numbered in the high-temperature plasticity test and the bending and straightening plasticity test of the cast billet) was obtained. x And the original diameter D0 of the sample, the reduction of area Z value was calculated according to the formula, and the specific results are shown in Table 2:
[0059] Table 2
[0060]
[0061] Based on the experimental results of each test temperature in Table 2, a comparison diagram of high-temperature plasticity of the billet edges and corners is drawn with temperature variable as the X-axis and cross-sectional reduction rate as the Y-axis, thereby determining the brittle temperature range.
[0062] A comparison chart of the high-temperature plasticity of the edges and corners of the cast billet is attached. Figure 7 As shown, it is composed of a high-temperature plasticity diagram of the billet and a bending and straightening plasticity diagram of the billet. The temperature variable of the high-temperature plasticity diagram of the billet is the high-temperature tensile test temperature; the temperature variable of the bending and straightening plasticity diagram of the billet is the cooling transition temperature.
[0063] The results obtained from this experiment show that once the surface temperature of the V-containing microalloyed steel billet is too low, for example below 900℃, although the temperature may rise later, the plasticity has already deteriorated. The plasticity value will not improve with the temperature increase, but will still hover in the brittle and low plasticity region. In other words, this steel grade is very susceptible to being cooled to (too) low temperatures. At the same time, combined with the blackening of the billet edges on site, there is a rapid cooling and temperature reversal phenomenon at the edges and corners of the billet during continuous casting. If the "turning temperature" of the billet edges and corners has fallen into the trough of "bending and straightening plasticity", then the edges and corners will be in a low plasticity state when entering the bending and straightening section. In this case, it may crack under the bending and straightening action, resulting in the commonly known edge crack or corner crack phenomenon.
Claims
1. A test method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets, characterized in that: Includes the following steps: Step 1: Prepare the test specimen. Process the steel billet to be tested according to the high temperature tensile test standard, check whether the specimen size meets the standard, and record the specimen size. Step Two: Conduct high-temperature melting and high-temperature tensile tests on a thermal simulation testing machine according to different experimental methods and parameters: (1) Experiment A: high-temperature melting experiment of the casting blank, the casting blank is heated in stages until melting and breaking, and the melting temperature T is recorded m , the high-temperature tensile holding temperature T0 is determined, T0 is 50~70℃ lower than T m ; the heating stage of the casting blank is as follows: heating at a speed of 10~20℃ / s below 1200℃; heating at a speed of 1~10℃ / s at 1200~1350℃; heating at a speed of 0.1~1 ℃ / s above 1350℃; (2) Experiment B: High-temperature plasticity test of billet. The billet is heated to T0 in stages and held for a period of time. Then it is cooled to different test temperatures T1. After holding, a high-temperature tensile test is carried out at a constant strain rate until the specimen breaks. Then it is numbered. The heating stages of the billet are: below 1200℃, the heating rate is 10~20℃ / s; 1200~1350℃, the heating rate is 1~10℃ / s; above 1350℃, the heating rate is 0.1~1℃ / s. T0 is held for 30~180s. Then it is cooled to the tensile test temperature T1 at a rate of 1~10℃ / s. After holding for 5~10s, a high-temperature tensile test is carried out at a constant strain rate. (3) Experiment C: Plasticity test of billet bending and straightening. The billet is heated to T0 in stages and held for a period of time. Then it is cooled to the turning test temperature T2, held for a period of time, and then heated to the fixed tensile test temperature T3. After holding for a period of time, a high-temperature tensile test is carried out at a constant strain rate until the specimen breaks. Then it is numbered. The heating stages of the billet are: below 1200℃, the heating rate is 10~20℃ / s; 1200~1350℃, the heating rate is 1~10℃ / s; above 1350℃, the heating rate is 0.1~1℃ / s. T0 is held for 30~180s, and then cooled to the turning test temperature T2 at a rate of 1~10℃ / s. After holding for 5~10s, a high-temperature tensile test is carried out at a constant strain rate. Step 3: Measure the fracture diameter of the tensile fracture specimen and calculate the reduction of area. Step 4: Based on the experimental results of Experiment B and Experiment C at different temperatures, draw a comparison diagram of the high-temperature plasticity of the billet edges and corners with the test temperature as the X-axis and the reduction of area as the Y-axis, so as to accurately determine whether there is a brittle temperature range in the billet and its edges and corners, and analyze the high-temperature plasticity of the billet edges and corners based on the experimental results.
2. The experimental method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets according to claim 1, characterized in that: In Experiment B: the temperature T1 was 1400~600℃, and the strain rate was 0.01~0.001s. -1 .
3. The experimental method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets according to claim 1, characterized in that: In Experiment C: Temperature T2 is 1200~600℃; Temperature T3 is the lowest temperature at which the surface shrinkage rate Z value of Experiment B is greater than 80%, and should be greater than 900℃; Strain rate is 0.01~0.001s. -1 .
4. The experimental method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets according to claim 1, characterized in that: Step three: The formula for calculating the reduction of area is as follows: ， In the formula: Z..... High-temperature tensile reduction of area, % D x ...High-temperature tensile fracture diameter, mm; D0.....Original diameter of the sample, mm.
5. The experimental method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets according to claim 1, characterized in that: Step 1: The steel billet to be tested is machined into a cylindrical tensile specimen with threads at both ends, with a diameter of Φ10mm or Φ8mm×120mm, and the original diameter D0 of the specimen is measured.
6. The experimental method for detecting the high-temperature plasticity of the edges and corners of microalloyed steel billets according to claim 1, characterized in that: In step two, before the experiment, a high-temperature platinum-rhodium thermocouple is welded to the middle of the sample to check whether the thermocouple welding position is centered; then, the high-temperature melting test, high-temperature plasticity test, and bending and straightening plasticity test of the billet are carried out on the thermal simulation test machine.