Method for achieving low-superheat-degree casting in steelmaking continuous casting process

Abstract

The invention provides a method for achieving low-superheat-degree casting in the steelmaking continuous casting process, and relates to the technical field of metallurgy. The method comprises the steps that in the molten steel continuous casting process, a steel ladle covering agent is added into a steel ladle, molten steel is shielded to prevent high-temperature molten steel from being exposed, permanent layer bricks of the wall and the bottom of the steel ladle are of a concave structure, and heat dissipation of the molten steel of the wall and the bottom of the steel ladle is reduced through the low heat conductivity characteristic of air; steel ladle long nozzle protective casting is adopted from a steel ladle to a tundish, and a covering agent is adopted for covering the molten steel surface of the tundish to prevent the molten steel surface of the tundish from being exposed; water gap protection casting is adopted from the tundish to the crystallizer, casting powder covering protection casting is adopted for the crystallizer, and the tundish molten steel level is prevented from being exposed. According to the method, through protective casting in the molten steel continuous casting process and special structures of the steel ladle wall and the steel ladle bottom, the temperature reduction of the molten steel in the casting process can be effectively reduced, and casting of the molten steel within the theoretical liquidus temperature range of 5-20 DEG C (low superheat degree) is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for realizing low superheat casting in a steelmaking continuous casting process. Background Art

[0002] High-quality steel is widely used in parts with high performance requirements, and the product quality requirements are very high. Most high-quality steels are made by continuous casting, which is a process of metal solidification, mainly in the continuous casting mold. The metal solidification structure in the continuous casting mold can directly affect the organizational properties of the final steel product. In order to ensure the fluidity of the molten steel in the casting system, a temperature higher than the theoretical liquidus line of metal solidification is required, which is professionally called "superheat". On the one hand, the size of "superheat" determines the grain size of the continuous casting billet solidification process. A smaller superheat can generate smaller grains, which can improve the product performance of the steel; on the other hand, a smaller superheat can significantly reduce the component segregation and looseness in the solidification process, essentially improving the product performance and quality of the steel. During the continuous casting process, since the theoretical liquidus temperature of the molten steel is around 1500°C, in order to ensure the fluidity of the molten steel during the casting process, it is necessary to determine a reasonable tapping temperature for the intermittent tapping process based on the temperature loss during the casting process. According to experience: the tapping process time is 3 to 6 minutes, the average temperature drop is 10°C / min, and the general temperature drop is 40 to 60°C; the argon blowing time is generally 3 to 5 minutes, and the temperature drop caused by argon blowing is 4 to 6°C / min, and the general temperature drop is 25-30°C; the temperature drop of the molten steel during ladle transportation and standing is generally 1 to 1.5°C / min; the temperature drop of the molten steel in the ladle during casting is generally 1-1.5°C / min, and the casting time is 30-45min; the temperature drop caused by heat dissipation on the surface of the tundish during casting is generally 0.3°C / min. To compensate for these temperature drops, the tapping temperature will be increased, but among these temperature drops, only the tapping temperature increased to compensate for the temperature drops in the ladle and the tundish will directly affect the increase in superheat. The superheat of molten steel casting is set to 20-40°C during operation, resulting in coarse grains in the ingot and prone to segregation and porosity defects. Therefore, reducing the temperature drop in the ladle and the tundish during the casting process can directly reduce the continuous casting superheat, directly improve the quality of the ingot, and indirectly improve the performance of steel products. Summary of the invention

[0003] In order to solve the above technical problems existing in the prior art, an embodiment of the present invention provides a method for realizing low superheat casting in the steelmaking continuous casting process. The technical solution is as follows:

[0004] A method for achieving low superheat casting in a steelmaking continuous casting process, comprising:

[0005] During the continuous casting of molten steel, full protection casting is implemented. Ladle covering agent is added to the ladle to completely shield the molten steel to avoid exposure of high-temperature molten steel. The permanent layer bricks of the ladle wall and the ladle bottom are concave structures, which use the low thermal conductivity of air to reduce the temperature loss of molten steel on the ladle wall and bottom.

[0006] From the ladle to the tundish, the ladle long nozzle is used to protect the casting, and the tundish uses a covering agent to cover the molten steel surface to avoid the tundish steel surface being exposed;

[0007] From the tundish to the crystallizer, the sprue is used to protect the casting, and the crystallizer is covered with protective slag to protect the casting, so as to avoid the exposure of the molten steel surface in the tundish.

[0008] Each of the permanent layer bricks of the ladle wall is a vertical concave structure, with one side of the brick being flat and the other side being thick at the top and bottom and thin in the middle. The upper and lower parts have the same thickness, and the thickness of the middle part is one-fifth to four-fifths of the thickness of the upper and lower parts. The upper and lower parts have the same height, and the height of the middle part is one-quarter to three-quarters of the height of the entire brick. The slope of the connection between the upper and lower parts and the middle part is 10°-70°.

[0009] The plane side of the permanent layer bricks of the ladle wall is close to the steel shell of the ladle, and the other side is close to the working layer of the ladle wall.

[0010] Each of the permanent layer bricks at the bottom of the ladle is a horizontal concave structure, with a flat bottom surface and a top surface that is thick on both sides and thin in the middle. The thickness of the two side parts is the same, and the thickness of the middle part is one-fifth to four-fifths of the thickness of the two side parts. The width of the two side parts is the same, and the width of the middle part is one-quarter to three-quarters of the width of the entire brick; the slope of the connection between the two side parts and the middle part is 10°-70°.

[0011] The flat side of the permanent layer bricks at the bottom of the ladle is close to the steel shell of the ladle, and the top surface is close to the working layer at the bottom of the ladle.

[0012] The thickness of the ladle covering agent in the ladle is not less than 5 cm.

[0013] The tundish is operated with a large dose of covering agent to always maintain "black slag" operation.

[0014] The initial covering agent for tundish casting occupies one third of the volume of the tundish, the height of the covering agent is not less than 20 cm during the casting process, and the long shroud of the ladle is always at least 20 cm below the covering agent surface.

[0015] The crystallizer uses a large dose of protective slag to protect the casting and always maintains "black slag" operation.

[0016] During the mold protection slag casting process, the height of the protection slag is not less than 5 cm, and during the nozzle protection casting, the nozzle is always below the covering agent surface.

[0017] The method can cast at a temperature range of 5°C-20°C.

[0018] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0019] The above scheme, by modifying the shape of the permanent layer bricks on the ladle wall and the bottom of the ladle, "replaces" the heat-conducting part of the ladle from a thermal conductivity of 0.2-0.5 W / (m·K) to a thermal conductivity of 0.026W / (m·K), thereby greatly reducing the temperature loss from the ladle wall and the bottom of the ladle during the casting process of the molten steel, and reducing the temperature drop rate of the molten steel in the ladle during the casting process from 1-1.5℃ / min to 0.5-0.7℃ / min; by modifying the thermal conductivity of the molten steel level in the ladle, the molten steel level in the tundish and the molten steel level in the crystallizer during the casting process to 0.02W / The covering of the (m·K) covering agent reduces the cooling rate of the temperature drop caused by the heat dissipation on the surface of the tundish from 0.3℃ / min to 0.1℃ / min, so that the increased tapping temperature to compensate for the temperature drop of the ladle and the tundish will directly affect the reduction of the temperature of the superheat increase, so that the superheat of the molten steel casting is set to 20-40℃ in normal operation to achieve casting within the range of 5℃-20℃ (low superheat), which can generate smaller ingot grains, improve the product performance of steel, significantly reduce the component segregation and looseness in the solidification process, and essentially improve the product performance and quality of steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 It is a schematic diagram of the whole device involved in a method for realizing low superheat casting in a steelmaking continuous casting process provided by an embodiment of the present invention;

[0022] Figure 2 It is a schematic diagram of a ladle structure involved in a method for realizing low superheat casting in a steelmaking continuous casting process provided by an embodiment of the present invention;

[0023] Figure 3 It is a schematic diagram of a permanent layer brick structure of a wall covering involved in a method for realizing low superheat casting in a steelmaking continuous casting process provided by an embodiment of the present invention;

[0024] Figure 4 It is a schematic diagram of a permanent layer brick structure of a bottom cladding involved in a method for realizing low superheat casting in a steelmaking continuous casting process provided by an embodiment of the present invention.

[0025] Among them: 1- ladle covering agent; 2- ladle; 3- ladle long nozzle; 4- tundish covering agent; 5- tundish; 6- tundish nozzle; 7- crystallizer; 8- crystallizer protective slag; 9- slag line area ladle wall working layer; 10- ladle wall permanent layer brick; 11- ladle wall working layer in molten steel area; 12- ladle bottom working layer; 13- ladle bottom air permeable brick; 14- ladle bottom permanent layer brick; 15- nozzle seat brick; 16- ladle bottom nozzle; 17- ladle steel shell. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0027] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0028] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0029] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0030] The embodiment of the present invention provides a method for achieving low superheat casting in a steelmaking continuous casting process. Figure 1 and Figure 2 As shown, the method may include the following steps:

[0031] A method for achieving low superheat casting in a steelmaking continuous casting process, comprising:

[0032] During the continuous casting of molten steel, a ladle covering agent 1 is added to the ladle 2 to completely shield the molten steel to prevent the high-temperature molten steel from being exposed. The permanent layer bricks 10 of the ladle wall and the permanent layer bricks 14 of the ladle bottom are both concave structures to reduce the temperature loss of the molten steel on the ladle wall and the ladle bottom.

[0033] From the ladle 2 to the tundish 5, the ladle long nozzle 3 is used to protect the casting, and the tundish 5 uses the tundish covering agent 4 to cover the molten steel surface to avoid the tundish steel surface being exposed;

[0034] From the tundish 5 to the crystallizer 7, the tundish water inlet 6 is used to protect the casting, and the crystallizer 7 is covered with crystallizer protection slag 8 to protect the casting, so as to avoid the exposure of the tundish steel liquid surface.

[0035] like Figure 3 The permanent layer bricks of the ladle wall are vertical concave structures. One side of the brick is flat, and the other side is thick at the top and bottom and thin in the middle. The thickness of the upper and lower parts is the same, and the thickness of the middle part is one-fifth to four-fifths of the thickness of the upper and lower parts. The upper and lower parts are the same height, and the height of the middle part is one-quarter to three-quarters of the height of the entire brick. The slope at the connection between the upper and lower parts and the middle part is 10°-70°.

[0036] The plane side of the permanent layer brick 10 of the ladle wall is close to the ladle steel shell 17, and the other side is close to the ladle wall working layer, wherein the upper half of the ladle wall working layer is the slag line area ladle wall working layer 9, and the lower half is the molten steel area ladle wall working layer 11.

[0037] like Figure 4 The permanent layer bricks 14 at the bottom of the ladle are horizontal concave structures, the bottom surface of the bricks is flat, the top surface is thick on both sides and thin in the middle, the thickness of the two side parts is the same, the thickness of the middle part is one-fifth to four-fifths of the thickness of the two side parts, and the width of the two side parts is the same, the width of the middle part is one-quarter to three-quarters of the width of the entire brick, and the slope of the connection between the two side parts and the middle part is 10°-70°.

[0038] The flat side of the permanent layer bricks 14 of the ladle bottom is close to the ladle steel shell 17 , and the top surface is close to the ladle bottom working layer 12 .

[0039] like Figure 2 The bottom of the ladle is conventionally provided with bottom air bricks 13 and bottom water inlet 16, and water inlet seat bricks 15 are arranged around the bottom water inlet 16.

[0040] In the specific application process,

[0041] First, by modifying the shape of the permanent layer bricks on the ladle wall and bottom, the heat-conducting part of the ladle is "replaced" with a thermal conductivity of 0.2-0.5 W / (m·K) to a thermal conductivity of 0.026 W / (m·K), thereby greatly reducing the amount of molten steel flowing from the ladle wall and bottom during casting, and reducing the temperature drop rate of the molten steel in the ladle from 1-1.5℃ / min to 0.5-0.7℃ / min during casting.

[0042] Secondly, by covering the molten steel levels in the ladle, the tundish and the crystallizer with a covering agent with a thermal conductivity of 0.02W / (m·K) during the casting process, the cooling rate caused by heat dissipation on the surface of the tundish was reduced from 0.3℃ / min to 0.1℃ / min.

[0043] Finally, through the whole process protection casting, the increased tapping temperature to compensate for the temperature drop of the ladle and the tundish will directly affect the reduction of the temperature of the superheat increase, so that the superheat of the molten steel casting is set to 20-40℃ in normal operation to achieve casting within the range of 5℃-20℃ (low superheat), which can generate smaller ingot grains, improve the product performance of the steel, significantly reduce the component segregation and looseness in the solidification process, and essentially improve the product performance and quality of the steel.

[0044] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for achieving low superheat casting in a steelmaking continuous casting process, characterized in that: The method comprises: During the continuous casting of molten steel, a ladle covering agent is added to the ladle to completely shield the molten steel and avoid exposure of high-temperature molten steel. The permanent layer bricks on the ladle wall and the ladle bottom are both concave in structure to reduce the temperature loss of the molten steel on the ladle wall and the ladle bottom. From the ladle to the tundish, the ladle long nozzle is used to protect the casting, and the tundish uses a covering agent to cover the molten steel surface to avoid the tundish steel surface being exposed; From the tundish to the crystallizer, the water nozzle is used for protection casting, and the crystallizer is covered with protective slag for protection casting to avoid the exposure of the crystallizer steel liquid surface.

2. The method for realizing low superheat casting in steelmaking continuous casting process according to claim 1, characterized in that: Each of the permanent layer bricks of the ladle wall is a vertical concave structure, with one side of the brick being flat and the other side being thick at the top and bottom and thin in the middle. The thickness of the upper and lower parts is the same, and the thickness of the middle part is one-fifth to four-fifths of the thickness of the upper and lower parts. The upper and lower parts are the same height, and the height of the middle part is one-quarter to three-quarters of the height of the entire brick. The slope of the connection between the upper and lower parts and the middle part is 10°-70°.

3. The method for realizing low superheat casting in steelmaking continuous casting process according to claim 2, characterized in that: The plane side of the permanent layer bricks of the ladle wall is close to the steel shell of the ladle, and the other side is close to the working layer of the ladle wall.

4. The method for realizing low superheat casting in steelmaking continuous casting process according to claim 1, characterized in that: Each brick of the permanent layer bricks at the bottom of the ladle is a horizontal concave structure, the bottom surface of the brick is flat, the top surface is thick on both sides and thin in the middle, the thickness of the two side parts is the same, the thickness of the middle part is one-fifth to four-fifths of the thickness of the two side parts, and the width of the two side parts is the same, the width of the middle part is one-quarter to three-quarters of the width of the entire brick; the slope of the connection between the two side parts and the middle part is 10°-70°.

5. The method for realizing low superheat casting in steelmaking continuous casting process according to claim 4, characterized in that: The flat side of the permanent layer bricks at the bottom of the ladle is close to the steel shell of the ladle, and the top surface is close to the working layer at the bottom of the ladle.

6. The method for realizing low superheat casting in steelmaking continuous casting process according to claim 1, characterized in that: The thickness of the ladle covering agent in the ladle is not less than 5 cm.

7. The method for realizing low superheat casting in steelmaking continuous casting process according to claim 1, characterized in that: The initial covering agent for tundish casting occupies one third of the volume of the tundish, the height of the covering agent is not less than 20 cm during the casting process, and the long shroud of the ladle is always at least 20 cm below the covering agent surface.

8. The method for realizing low superheat casting in steelmaking continuous casting process according to claim 1, characterized in that: During the mold protection slag casting process, the height of the protection slag is not less than 5 cm, and during the nozzle protection casting, the nozzle is always below the covering agent surface.

9. The method for realizing low superheat casting in steelmaking continuous casting process according to claim 1, characterized in that: The method can cast at a temperature range of 5°C-20°C.

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