CN114563437A - Method for testing crack formation temperature of continuous casting billet - Google Patents
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Abstract
The invention provides a method for testing the crack formation temperature of a continuous casting billet, which belongs to the field of metal material detection, and particularly comprises the steps of dissecting the cracks of the casting billet obtained in the actual production of continuous casting, extracting the size information of the cracks, and etching the cracks to obtain the size and thickness conditions of oxidation dots around the cracks; prefabricating cracks on the surface of an original casting blank without cracks, and placing the casting blank in a high-temperature furnace to study the oxidation behavior of a prefabricated crack sample; dissecting the prefabricated crack for analysis, drawing the thickness of the oxidation dot layer with the oxidation temperature and time, and determining the oxidation temperature and time interval by comparing the thickness of the oxidation dot layer of the actual crack with the drawing; and (4) placing the surface temperature curve of the casting blank in a graph, wherein the intersection area of the graph is the forming temperature of the cracks of the casting blank. The test method has the characteristics of accuracy and quantification, is suitable for various ferrous/nonferrous metals and alloys, and can be used for a long time only by measuring the map once for specific metals.
Description
Technical Field
The invention belongs to the field of metal material detection, and particularly relates to a method for testing crack formation temperature of a continuous casting billet.
Background
According to incomplete statistics, about 50% of defects in various defects of a casting blank are defects related to cracks. Common cracks in the continuous casting process are mainly divided into surface cracks and internal cracks, and the surface cracks of the casting blank are one of the main problems which trouble the quality improvement of the casting blank. The quality of the surface quality of the casting blank directly influences the quality of rolled materials, the yield of products and the cost, and the systematic prevention and control technology of the surface cracks of the casting blank is the core competitive force of products of enterprises.
Scientists speculate the crack formation mechanism through the dissection of the crack, and the judgment of the crack generation position is important for the speculation of the crack formation mechanism. At present, most metallurgists judge whether cracks are generated during continuous casting or rolling according to existence of decarburized layers around the cracks and judge whether the cracks are generated in a continuous casting crystallizer or a secondary cooling section according to the types of the cracks (transverse cracks, longitudinal cracks, corner cracks and the like).
The present inventors proposed a method of oxidizing by pre-cracking, and published an article named High-temperature oxidation floor of surface cracks in low alloy steel bloom in corosion Science journal at 4.1.2022, and determined the crack formation temperature by measuring the thickness information of oxidized spots around the crack at different temperatures, but it was only applicable to a High temperature range of 1000 ℃ or more, because it was difficult to form oxidized spots around the crack at 1000 ℃ or less, which resulted in the above method being not applicable. Therefore, the invention further provides the steps of extracting the humidity information below 1000 ℃ during continuous casting, introducing water vapor with the same humidity under the experimental environment, and simulating the oxidation condition of the oxide layer at the periphery of the crack, so that the forming temperature of the crack in the whole continuous casting process can be simulated, namely the crack can be detected at the temperature of 700 ℃ and 1200 ℃.
Disclosure of Invention
The invention provides a method for quantitatively and accurately judging crack formation temperature.
A method for testing the crack formation temperature of a continuous casting billet is characterized by comprising the following steps:
1) dissecting casting blank cracks obtained in the actual continuous casting production, and extracting crack size information including the width, depth, expansion angle and the like of the cracks;
2) etching the cracks to obtain whether oxidation dots exist around the cracks or not, and the size of the oxidation dots and the thickness of the oxidation dot layer;
3) prefabricating cracks on the surface of an original casting blank without cracks, wherein the size and the trend of the prefabricated cracks are required to be consistent with those of actual cracks;
4) sealing the prefabricated crack sample, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature, breaking the pipe sealing, and preserving heat for different times to study the oxidation behavior of the prefabricated crack sample;
5) dissecting the prefabricated crack to analyze the size of the peripheral oxidation dots and the thickness of the oxidation dot layer, drawing the thickness of the oxidation dot layer with the oxidation temperature and time, and marking the thickness of the oxidation dot layer of the actual crack in the drawing to determine the oxidation temperature and time interval;
6) the surface temperature curve of the casting blank is arranged in the upper graph, and the intersection area of the graphs is the crack forming temperature of the casting blank.
Further, the dissection of the crack in the step 1) may be two-dimensional dissection observed by using an optical microscope/electron microscope, or may be three-dimensional dissection performed by using equipment such as industrial CT.
Further, etching the cracks in the step 2) is performed by using 1-5% of nitric acid alcohol, and etching time is 5-500 s.
Further, the pre-crack in the step 3) may be performed by wire cutting, laser cutting, broaching, striking, or the like.
Further, the sample sealing tube in the step 4) can be protected by inert gas atmosphere or vacuum.
Further, the preset temperature of the high-temperature furnace in the step 4) is any temperature between 700 ℃ and 1300 ℃.
Further, when the preset temperature in the step 4) is between 700 and 1000 ℃, water vapor with the volume fraction of between 30 and 50 percent and the flow rate of between 1 and 60L/h is required to be introduced into the high-temperature furnace; when the preset temperature is between 1000 and 1300 ℃, water vapor does not need to be introduced.
Further, the heat preservation time in the step 4) is any time between 1 and 200 minutes.
Further, when the preset temperature in the step 5) is between 700 and 1000 ℃, the problem that no oxidation dot layer exists around the crack at low temperature is solved by detecting the information of the oxidation layer around the crack.
The invention provides a method for judging the crack formation temperature of a continuous casting billet, and the method is not reported in documents. The judgment method has the characteristics of accuracy and quantification, is expected to be widely applied to the aspect of continuous casting defect detection, and can even be expanded to the field of defect detection of nonferrous metals and alloys.
The method has the following advantages:
1) the crack formation temperature determined by the method has the characteristics of accuracy and quantification, and the original qualitative judgment mode is broken through.
2) For steel grades with specific components, only one experiment is needed to obtain an oxidation dot layer and temperature and time pattern, and the oxidation dot layer and the temperature and time pattern can be used for a long time subsequently.
3) The invention can be widely applied to various steel types, even to the fields of nonferrous metals, alloys and the like.
Drawings
Fig. 1 shows two-dimensional anatomical crack size and propagation information of an actual casting blank according to an embodiment of the present invention.
FIG. 2 shows the size of the oxide dots and the thickness of the oxide dots of an actual ingot according to an embodiment of the present invention.
FIG. 3 is a graph showing the size information of a pre-crack according to an embodiment of the present invention.
FIG. 4 is a graph of an oxidation dot pattern, i.e., a thickness of an oxidation dot layer as a function of temperature and time, according to a first embodiment of the present invention.
FIG. 5 shows the surface quality of a slab after the process is improved according to an embodiment of the present invention.
Fig. 6 shows oxide layer information of practical casting blanks according to the second and third embodiments of the present invention.
Fig. 7 is a diagram of an oxide layer map, i.e., a relationship between oxide layer thickness and temperature and time according to the second embodiment of the present invention.
FIG. 8 is an oxide layer pattern of three-way steam according to an embodiment of the present invention.
FIG. 9 shows the microstructure of the surface of a casting blank after adjusting the secondary cooling water process according to the third embodiment of the invention.
Detailed Description
Example one
Performing two-dimensional dissection on casting blank cracks obtained in actual continuous casting production, and extracting size information such as the width, depth, expansion angle and the like of the cracks as shown in figure 1; the chemical composition (wt.%) of the slab steel grade is shown in the following table:
| C | Si | Mn | P | S | Cr | Mo | Al |
| 0.36~0.40 | 0.2~0.3 | 0.74~0.80 | ＜0.02 | 0.02~0.03 | 1.12~1.18 | 0.18~0.2 | 0.01~0.04 |
etching the crack with 2% nitric acid alcohol to obtain the size of the oxidized dots around the crack and the thickness of the oxidized dot layer, as shown in FIG. 2; prefabricating cracks on the surface of an original casting blank without cracks in a wire cutting mode, wherein the size and the trend of the prefabricated cracks are required to be matched with those of actual cracks, and the size and the trend are shown in figure 3; carrying out vacuum tube sealing on the prefabricated crack sample, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature (1000, 1050, 1100, 1150 and 1200 ℃), breaking the tube sealing, and keeping the temperature for different times (10, 20, 30, 40, 50, 60, 120 and 180 minutes) so as to research the oxidation behavior of the prefabricated crack sample; dissecting the prefabricated crack to analyze the size of the peripheral oxidation dots and the thickness of the oxidation dot layer, and plotting the thickness of the oxidation dot layer with the oxidation temperature and time, as shown in FIG. 4, and marking the thickness of the oxidation dot layer of the actual crack in the graph (thick line) to determine the possible oxidation temperature and time interval; the temperature curve of the surface of the casting blank is placed in the upper graph (a sphere), and the intersection area of the graphs is the forming temperature of the cracks of the casting blank. Through the analysis, the crack formation temperature of the casting blank is determined to be 1120 ℃, the surface temperature of the casting blank is in the crystallizer, and no crack appears on the surface of the casting blank after the components of the casting powder in the crystallizer and the vibration parameters of the crystallizer are adjusted, as shown in figure 5, the test method is practical.
Example two
Three-dimensional dissection is carried out on casting blank cracks obtained in the actual continuous casting production, and size information such as the width, the depth and the expansion angle of the cracks is extracted; etching the crack by 4% nitric acid alcohol to obtain the size of an oxidation dot at the periphery of the crack and the thickness of the oxidation dot layer; the results in fig. 4 are fully applicable since the steel type is the same as in example one, but as shown in fig. 6, it was found that there is no oxidation dot around the crack, i.e. the oxidation dot information is outside the range of fig. 4, indicating that the crack formation temperature is below 1000 ℃. Prefabricating cracks on the surface of an original casting blank without cracks in a laser cutting mode, wherein the size and the trend of the prefabricated cracks are required to be matched with those of actual cracks; sealing the prefabricated crack sample by high-purity argon, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature (700, 750, 800, 850, 900 and 950 ℃), breaking the sealed pipe and preserving the heat for different times (1, 2, 5, 10, 20, 30, 40, 50, 60, 120 and 180 minutes) so as to research the oxide layer information around the prefabricated crack; dissecting the prefabricated crack to analyze the thickness condition of the peripheral oxide layer of the prefabricated crack, drawing the thickness of the oxide layer with the oxidation temperature and time, and marking the thickness of the oxide layer of the actual crack in the drawing (a thick line) to determine a possible oxidation temperature and time interval; the temperature curve of the surface of the casting blank is placed in the upper graph (a sphere), and the intersection area of the graphs is the forming temperature of the cracks of the casting blank. However, as shown in fig. 7, there is no intersection between the two, so the result shows that the method is still inaccurate.
EXAMPLE III
Three-dimensional dissection is carried out on casting blank cracks obtained in the actual continuous casting production, and size information such as the width, the depth and the expansion angle of the cracks is extracted; etching the crack by 4% nitric acid alcohol to obtain the size of an oxidation dot at the periphery of the crack and the thickness of the oxidation dot layer; the results in fig. 4 are fully applicable since the steel type is the same as in example one, but as shown in fig. 6, it was found that there is no oxidation dot around the crack, i.e. the oxidation dot information is outside the range of fig. 4, indicating that the crack formation temperature is below 1000 ℃. Prefabricating cracks on the surface of an original casting blank without cracks in a laser cutting mode, wherein the size and the trend of the prefabricated cracks are required to be matched with those of actual cracks; sealing the prefabricated crack sample by high-purity argon, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature (700, 750, 800, 850, 900 and 950 ℃), introducing water vapor with the volume fraction of 30% and the flow rate of 60L/h into the high-temperature furnace, breaking the sealed tube, and preserving the heat for different times (1, 2, 5, 10, 20, 30, 40, 50, 60, 120 and 180 minutes) so as to research the oxide layer information on the periphery of the prefabricated crack sample; dissecting the prefabricated crack to analyze the thickness condition of the peripheral oxide layer of the prefabricated crack, drawing the thickness of the oxide layer with the oxidation temperature and time, and marking the thickness of the oxide layer of the actual crack in the drawing (a thick line) to determine a possible oxidation temperature and time interval; the temperature profile of the surface of the ingot is placed in the upper graph (sphere), as shown in fig. 8, the intersection region of the graphs is the temperature at which cracks form in the ingot. Through analysis, the method is accurate, and the simulation is identical with the experimental result. The result shows that the forming temperature of the crack is between 820 and 850 ℃, the crack is formed in a continuous casting secondary cooling area, the surface temperature of the casting blank before the casting blank enters light pressure is kept away from between 820 and 850 ℃ by adjusting the proportion of secondary cooling water and secondary cooling water, the optimized casting blank surface sample is taken for observation, no crack is generated on the casting blank surface, and the microstructure is shown in figure 9.
Example four
Carrying out two-dimensional dissection on casting blank cracks obtained in actual continuous casting production, and extracting size information such as the width, depth, expansion angle and the like of the cracks; etching the cracks by 1% nitric acid alcohol to obtain the size of an oxidation dot at the periphery of the cracks and the thickness of the oxidation dot layer; prefabricating cracks on the surface of an original casting blank without cracks in a sample hammering mode, wherein the size and the trend of the prefabricated cracks are required to be matched with those of actual cracks; carrying out vacuum tube sealing on a prefabricated crack sample, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature (700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300 ℃), introducing water vapor with the volume fraction of 50% and the flow rate of 1L/h into the high-temperature furnace when the preset temperature is between 700 and 1000 ℃, breaking the tube sealing, and preserving heat for different times (1, 2, 5, 10, 20, 30, 40, 50, 60, 120, 180 minutes) so as to research the oxidation behavior of the prefabricated crack sample; dissecting the prefabricated crack to analyze the size of the peripheral oxidation dots, the thickness of the oxidation dot layer and the thickness of the oxidation layer, drawing the thickness of the oxidation dot layer with the oxidation temperature and the oxidation time, and marking the thickness of the oxidation dot layer of the actual crack in the drawing to determine a possible oxidation temperature and time interval; the surface temperature curve of the casting blank is arranged in the upper graph, and the intersection area of the graphs is the forming temperature of the cracks of the casting blank.
Comparative example 1
Carrying out two-dimensional dissection on casting blank cracks obtained in actual continuous casting production, and extracting size information such as the width, depth, expansion angle and the like of the cracks; etching the cracks by 1% nitric acid alcohol to obtain the size of an oxidation dot at the periphery of the cracks and the thickness of the oxidation dot layer; prefabricating cracks on the surface of an original casting blank without cracks in a sample hammering mode, wherein the size and the trend of the prefabricated cracks are required to be matched with those of actual cracks; carrying out vacuum tube sealing on a prefabricated crack sample, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature (700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250 and 1300 ℃), then introducing water vapor with the volume fraction of 20% into the high-temperature furnace when the preset temperature is 700-1000 ℃, breaking the tube sealing and preserving the heat for different times (1, 2, 5, 10, 20, 30, 40, 50, 60, 120 and 180 minutes) so as to research the oxidation behavior of the prefabricated crack sample; dissecting the prefabricated crack to analyze the size of the peripheral oxidation dots, the thickness of the oxidation dot layer and the thickness of the oxidation layer, drawing the thickness of the oxidation dot layer with the oxidation temperature and the oxidation time, and marking the thickness of the oxidation dot layer of the actual crack in the drawing to determine a possible oxidation temperature and time interval; the surface temperature curve of the casting blank is arranged in the upper graph, and the intersection area of the graphs is the forming temperature of the cracks of the casting blank. However, the results show that when the volume fraction of the water vapor is less than 30%, the simulation result is greatly different from the actual result, and the result is inaccurate.
Comparative example No. two
Carrying out two-dimensional dissection on casting blank cracks obtained in actual continuous casting production, and extracting size information such as the width, depth, expansion angle and the like of the cracks; etching the cracks by 1% nitric acid alcohol to obtain the size of an oxidation dot at the periphery of the cracks and the thickness of the oxidation dot layer; prefabricating cracks on the surface of an original casting blank without cracks in a sample hammering mode, wherein the size and the trend of the prefabricated cracks are required to be matched with those of actual cracks; carrying out vacuum tube sealing on a prefabricated crack sample, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature (700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300 ℃), introducing water vapor with the volume fraction of 60% into the high-temperature furnace when the preset temperature is 700-1000 ℃, breaking the tube sealing and preserving the heat for different times (1, 2, 5, 10, 20, 30, 40, 50, 60, 120, 180 minutes) so as to research the oxidation behavior of the prefabricated crack sample; dissecting the prefabricated cracks to analyze the size of the oxidation dot layer and the thickness of the oxidation layer of the periphery of the prefabricated cracks, drawing the thickness of the oxidation dot layer with the oxidation temperature and time, and marking the thickness of the oxidation dot layer of the actual cracks in the drawing to determine possible oxidation temperature and time intervals; the surface temperature curve of the casting blank is arranged in the upper graph, and the intersection area of the graphs is the forming temperature of the cracks of the casting blank. However, the results show that when the volume fraction of the water vapor is greater than 50%, the simulation result is greatly different from the actual result, and the result is inaccurate.
Comparative example No. three
Performing two-dimensional dissection on casting blank cracks obtained in actual continuous casting production, and extracting size information such as the width, depth and expansion angle of the cracks; etching the cracks by 1% nitric acid alcohol to obtain the size of an oxidation dot at the periphery of the cracks and the thickness of the oxidation dot layer; prefabricating cracks on the surface of an original casting blank without cracks in a sample hammering mode, wherein the size and the trend of the prefabricated cracks are required to be matched with those of actual cracks; carrying out vacuum tube sealing on the prefabricated crack sample, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature (700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300 ℃), introducing water vapor with the volume fraction of 50% and the flow rate of 0.5L/h into the high-temperature furnace when the preset temperature is between 700 and 1000 ℃, breaking the tube sealing and preserving the heat for different times (1, 2, 5, 10, 20, 30, 40, 50, 60, 120 and 180 minutes) so as to research the oxidation behavior of the prefabricated crack sample; dissecting the prefabricated crack to analyze the size of the oxidation dot layer and the thickness of the oxidation layer of the periphery of the prefabricated crack, drawing the thickness of the oxidation dot layer with the oxidation temperature and time, and marking the thickness of the oxidation dot layer of the actual crack in the drawing to determine a possible oxidation temperature and time interval; the surface temperature curve of the casting blank is arranged in the upper graph, and the intersection area of the graphs is the forming temperature of the cracks of the casting blank. However, the result shows that when the flow rate of the water vapor is less than 1L/h, the humidity in the furnace chamber cannot be ensured, and the simulation result is greatly different from the actual result, and the result is inaccurate.
Comparative example No. four
Carrying out two-dimensional dissection on casting blank cracks obtained in actual continuous casting production, and extracting size information such as the width, depth, expansion angle and the like of the cracks; etching the cracks by 1% nitric acid alcohol to obtain the size of an oxidation dot at the periphery of the cracks and the thickness of the oxidation dot layer; prefabricating cracks on the surface of an original casting blank without cracks in a sample hammering mode, wherein the size and the trend of the prefabricated cracks are required to be matched with those of actual cracks; carrying out vacuum tube sealing on a prefabricated crack sample, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature (700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300 ℃), introducing water vapor with the volume fraction of 30% and the flow rate of 70L/h into the high-temperature furnace when the preset temperature is between 700 and 1000 ℃, breaking the tube sealing, and preserving heat for different times (1, 2, 5, 10, 20, 30, 40, 50, 60, 120, 180 minutes) so as to research the oxidation behavior of the prefabricated crack sample; dissecting the prefabricated cracks to analyze the size of the oxidation dot layer and the thickness of the oxidation layer of the periphery of the prefabricated cracks, drawing the thickness of the oxidation dot layer with the oxidation temperature and time, and marking the thickness of the oxidation dot layer of the actual cracks in the drawing to determine possible oxidation temperature and time intervals; the surface temperature curve of the casting blank is arranged in the upper graph, and the intersection area of the graphs is the forming temperature of the cracks of the casting blank. However, the result shows that when the flow rate of the water vapor is more than 60L/h, the temperature in the furnace chamber is reduced more severely, and the preset temperature cannot be ensured, so that the simulation result is greatly different from the actual result, and the result is inaccurate.
The above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and it should be understood by those skilled in the art that the specific embodiments of the present invention can be modified or substituted with equivalents with reference to the above embodiments, and any modifications or equivalents without departing from the spirit and scope of the present invention are within the scope of the claims to be appended.
Claims (7)
1. A method for testing the crack formation temperature of a continuous casting billet is characterized by comprising the following steps:
a. dissecting the casting blank cracks obtained in the actual continuous casting production, and extracting crack size information including the width, depth, expansion angle and the like of the cracks;
b. etching the cracks to obtain whether oxidation dots exist around the cracks or not, and the size of the oxidation dots and the thickness of the oxidation dot layer;
c. prefabricating cracks on the surface of an original casting blank without cracks, wherein the size and the trend of the prefabricated cracks are required to be consistent with those of actual cracks;
d. sealing the prefabricated crack sample, then placing the prefabricated crack sample in a high-temperature furnace, heating the high-temperature furnace to a preset temperature, breaking the pipe sealing, and preserving heat for different times to study the oxidation behavior of the prefabricated crack sample; the preset temperature of the high-temperature furnace is 700-1000 ℃, and steam with the volume fraction of 30-50% and the flow rate of 1-60L/h is introduced into the high-temperature furnace;
e. dissecting the prefabricated cracks to analyze the size of peripheral oxidation dots and the thickness of an oxidation dot layer, drawing the thickness of the oxidation dot layer, the oxidation temperature and the oxidation time, and marking the thickness of the oxidation dot layer of the actual cracks in the drawing to determine the oxidation temperature and the time interval;
g. the surface temperature curve of the casting blank is arranged in the upper graph, and the intersection area of the graphs is the forming temperature of the cracks of the casting blank.
2. The method for testing the crack formation temperature of a slab as claimed in claim 1, wherein: and c, dissecting the cracks in the step a by adopting two-dimensional dissection observed by an optical mirror/electron microscope or three-dimensional dissection carried out by industrial CT equipment.
3. The method for testing the crack formation temperature of the continuous casting slab as claimed in claim 1, wherein the etching of the crack in the step b is performed by using 1% -5% by mass of nitric alcohol, and the etching time is 5-500 s.
4. The method for testing the crack formation temperature of the continuous casting billet according to claim 1, wherein the pre-crack in the step c is performed by linear cutting, laser cutting, broaching and/or striking.
5. The method for testing the crack formation temperature of the continuous casting slab as claimed in claim 1, wherein the sample tube sealing in the step d is performed in an inert gas atmosphere protection mode or a vacuum protection mode.
6. The method for testing the crack formation temperature of the continuous casting slab as claimed in claim 1, wherein the predetermined temperature of the high temperature furnace in the step d is between 1000 ℃ and 1300 ℃, and water vapor is not required to be introduced.
7. The method for testing the crack formation temperature of a continuous casting slab as claimed in claim 1, wherein the holding time in step d is 1-200 minutes.
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