A production method for improving the center quality of a cast slab

Abstract

The application discloses a production method for improving the core quality of a casting blank, comprising the following steps: S1, KR method desulfurization and adding a composite MgO-CaO desulfurizer; S2, top and bottom combined blowing smelting, adding slagging materials and aluminum blocks for deoxidization in the tapping process, and adding carbon and manganese alloy for deoxidization and alloying; S3, adopting LF+RH process for refining, and performing magnesium metallurgical treatment modification after RH vacuum treatment; S4, lifting the molten steel to a ladle for pouring; S5, adjusting the tundish nozzle height in the pouring process, and performing cooling in a strong cooling mode, and adopting a positive dazzle mode for oscillation of the crystallizer; S6, adopting multi-point pressing down after the molten steel enters the fan-shaped section, and performing large pressing down operation in the horizontal section; S7, cutting the head blank, and using the head blank for rolling protocol products, and determining the rolling steel grade by flaw detection scanning of the first blank; S8, performing purging inspection after the blank is cooled by piling, and performing edge grinding.The application has the advantages of improving the cleanliness of the molten steel, reducing the internal impurities of the casting blank, and improving the core quality of the casting blank.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to a production method for improving the quality of the core of a cast billet. Background Technology

[0002] As continuously cast billets continue to extend to wider and thicker specifications, their quality directly affects the progress of product development. Billet quality includes composition control, improved cleanliness, and refinement of the continuous casting process.

[0003] Currently, harmful elements such as phosphorus, sulfur, oxygen, nitrogen, and hydrogen are often added to molten steel. These inclusions greatly reduce the cleanliness of the molten steel and damage the overall quality of the billet. At the same time, during the casting process, the temperature and flow field of the liquid core are unstable, which easily leads to secondary oxidation. Inclusions can enter the crystallizer, affecting the internal quality of the steel plate. Slag entrapment is serious during the initial and final casting processes, ultimately resulting in a lower pass rate for steel plate flaw detection and poor quality of the billet core. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of excessive impurities and poor quality in the core of existing cast billets. It provides a production method to improve the core quality of cast billets, which can improve the cleanliness of molten steel, reduce internal impurities in the cast billet, optimize continuous casting technology and improve the quality of the cast billet, thereby achieving the goal of improving the core quality of the cast billet.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A production method for improving the quality of the core of a cast billet, comprising the following steps: S1: After the molten iron is sampled for temperature measurement upon entering the station, desulfurization is carried out using the KR method to ensure that the molten iron temperature is 1250±50℃ and the amount of composite MgO-CaO desulfurizing agent added is 1500±50kg. S2: The amount of molten iron charged is 160-180t. The converter adopts top and bottom blowing smelting. During the tapping process, slag-forming materials and aluminum blocks are added for deoxidation, and carbon and manganese alloys are added for deoxidation and alloying. S3: Refining is carried out using the LF+RH process. After RH vacuum treatment, magnesium metallurgical treatment is performed to modify and purify the molten steel. After magnesium treatment, the steel is stirred for 15-20 minutes. S4: Molten steel is hoisted to the ladle for pouring, with the long nozzle inserted to a depth of 130-180mm, a pouring speed of 0.6-1.3m / min, and a superheat of 30-40℃; S5: During the casting process, adjust the height of the tundish nozzle, raise the height of the upper nozzle to 500mm, and insert the lower nozzle to a depth of 900~1100mm. Use strong cooling method for cooling. The flow rate of the wide face of the crystallizer is 5500~6000L / min, and the flow rate of the narrow face is 900~1200L / min. The crystallizer is vibrated in a positive oscillation mode with an amplitude of 5~15mm and a vibration frequency of 200~300 times / min. S6: After the molten steel enters the fan-shaped section, it is pressed down at multiple points. When it enters the horizontal section, a large pressing operation is performed, with a pressing amount of 8-12mm. S7: First blank cutting. The first blank is required to be ≥5500mm. The first blank is cut to 3000mm. The second blank is cut according to the order requirements, to 3000~6000mm. The first blank is used to roll the contracted product. The steel grade to be rolled is determined by flaw detection scanning of the first blank. S8: After the billet has been cooled for 48 hours, it should be blown and inspected, and the edges should be ground to a thickness of 100~200mm.

[0006] Furthermore, the chemical composition and mass percentage of the cast billet are as follows: C: 0.02%~0.20%, Si: 0.05%~0.40%, Mn: 0.5%~2.0%, P≤0.025%, S≤0.015%, Al: 0.010%~0.050%, Mg: 0.0008%~0.0018%, N≤0.0060%, H≤0.0002%, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, the chemical composition and mass percentage of the cast billet are as follows: C: 0.09%, Si: 0.23%, Mn: 0.89%, P: 0.011%, S: 0.003%, Al: 0.026%, Mg: 0.0013%, N: 0.0053%, H: 0.0001%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, the chemical composition and mass percentage of the billet are as follows: C: 0.17%, Si: 0.18%, Mn: 0.69%, P: 0.013%, S: 0.011%, Al: 0.041%, Mg: 0.0013%, N: 0.00443%, H: 0.0001%, with the balance being Fe and unavoidable impurities.

[0009] Compared with the prior art, the advantages of the technical solution of the present invention are as follows: (1) The present invention adopts BOF, LF&RH process, which improves the cleanliness of molten steel, reduces the influence of harmful elements such as phosphorus, sulfur, oxygen, nitrogen and hydrogen on the quality of billet, improves the overall quality of billet, and magnesium treatment improves the morphology of inclusions, which is conducive to removing the influence of inclusions in molten steel and reducing the aggregation of segregated elements. At the same time, magnesium metallurgy technology can effectively improve the welding effect, which is conducive to the market development and application of plate varieties. (2) This invention optimizes the process of the long nozzle of the ladle and the process of the upper and lower nozzles of the middle ladle, improves the steady-state casting effect, is conducive to the stability of the temperature and flow field of the liquid core, improves the core quality of the billet, and also reduces the secondary oxidation during the casting process, slows down the rate at which inclusions are brought into the crystallizer and affect the internal quality of the steel plate, and improves the obstacle efficiency of large-sized inclusions, reduces the slag entrapment situation during the opening and closing processes, and improves the steel plate flaw detection pass rate and inclusion rating. (3) The present invention adopts a high superheat and low casting speed casting method, combined with cooling control, and strong pressing, which helps to form a coarse columnar crystal structure, which is interlaced at the liquid core and broken during the rolling process, thereby forming a fine interlaced grain structure; this newly developed billet structure can effectively refine the grain size of the structure and achieve the purpose of improving the quality of the billet core. Attached Figure Description

[0010] Figure 1 This is a low-magnification tissue photograph from Example 1 of the present invention. Detailed Implementation Example 1

[0011] To make the present invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates a production method for improving the core quality of a cast billet. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0012] This embodiment provides a production method for improving the core quality of a cast billet. The chemical composition and mass percentage of the cast billet are as follows: C: 0.09%, Si: 0.23%, Mn: 0.89%, P: 0.011%, S: 0.003%, Al: 0.026%, Mg: 0.0013%, N: 0.0053%, H: 0.0001%, with the balance being Fe and unavoidable impurities. The production method specifically includes: (1) After the molten iron is sampled for temperature measurement upon entering the station, desulfurization is carried out by the KR method to ensure that the temperature of the molten iron is 1286℃ and the amount of composite MgO-CaO desulfurizing agent added is 1500kg. (2) The amount of molten iron charged is 167t. The converter adopts top and bottom blowing smelting. During the tapping process, slag-forming materials and aluminum blocks are added for deoxidation, and carbon and manganese alloys are added for deoxidation and alloying. (3) The refining process adopts the LF→RH process for refining. After RH vacuum treatment, magnesium metallurgical treatment is carried out to modify and purify the molten steel. After magnesium treatment, the steel is stirred for 17 minutes. (4) The molten steel is hoisted to the ladle for pouring, the long nozzle is inserted to a depth of 160mm, the pouring speed is 0.9m / min, and the superheat is 37℃; (5) During the casting process, adjust the height of the tundish nozzle, raise the height of the upper nozzle to 500mm, and insert the lower nozzle to 990mm. Use strong cooling method for cooling. The flow rate of the wide face of the crystallizer is 5800L / min, and the flow rate of the narrow face is 980L / min. The crystallizer is vibrated in the positive oscillation mode with an amplitude of 13mm and a vibration frequency of 280 times / min. (6) After the molten steel enters the fan-shaped section, it is pressed down at multiple points. When it enters the horizontal section, a large pressing operation is carried out, with a pressing amount of 9mm. (7) Head blank cutting: The head blank is marked as 6500mm. The first blank is cut to 3000mm. The second blank is cut to 4200mm according to the order requirements. The head blank is used to roll the contracted product. The steel grade to be rolled is determined by flaw detection scanning of the first blank. (8) After the billet has been cooled for 48 hours, it is blown and inspected, and the edges are ground to 130mm. Example 2

[0013] This embodiment provides a production method for improving the core quality of a cast billet. The chemical composition and mass percentage of the cast billet are as follows: C: 0.17%, Si: 0.18%, Mn: 0.69%, P: 0.013%, S: 0.011%, Al: 0.041%, Mg: 0.0013%, N: 0.00443%, H: 0.0001%, with the balance being Fe and unavoidable impurities. The production method specifically includes: (1) After the molten iron is sampled for temperature measurement upon entering the station, desulfurization is carried out by the KR method to ensure that the temperature of the molten iron is 1230℃ and the amount of composite MgO-CaO desulfurizing agent added is 1550kg; (2) The amount of molten iron charged is 175t. The converter adopts top and bottom blowing smelting. During the tapping process, slag-forming materials and aluminum blocks are added for deoxidation, and carbon and manganese alloys are added for deoxidation and alloying. (3) The refining process adopts the LF→RH process for refining. After RH vacuum treatment, magnesium metallurgical treatment is carried out to modify and purify the molten steel. After magnesium treatment, the steel is stirred for 19 minutes. (4) The molten steel is hoisted to the ladle for pouring, the long nozzle is inserted to a depth of 170mm, the pouring speed is 1.1m / min, and the superheat is 31℃; (5) During the casting process, adjust the height of the tundish nozzle, raise the height of the upper nozzle to 500mm, insert the lower nozzle to 1010mm, use strong cooling method for cooling, the flow rate of the wide face of the crystallizer is 5900L / min, the flow rate of the narrow face is 1100L / min, the crystallizer is vibrated in the positive oscillation mode with an amplitude of 6mm and a vibration frequency of 210 times / min. (6) After the molten steel enters the fan-shaped section, it is pressed down at multiple points. When it enters the horizontal section, a large pressing operation is carried out, with a pressing amount of 10mm. (7) Head blank cutting: The head blank is marked as 5800mm. The first blank is cut to 3000mm. The second blank is cut to 3600mm according to the order requirements. The head blank is used to roll the contracted product. The steel grade to be rolled is determined by flaw detection scanning of the first blank. (8) After the billet has been cooled for 48 hours, it is blown and inspected, and the edges are ground to 160mm.

[0014] This invention improves the effect of steel modification by controlling the steady state of the smelting process and the continuous casting process, and monitors the quality of the product through flaw detection equipment, resulting in a significant improvement in the quality of the cast billet.

[0015] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A production method for improving the quality of the core of a cast billet, characterized in that: S1: After the molten iron is sampled for temperature measurement upon entering the station, desulfurization is carried out using the KR method to ensure that the molten iron temperature is 1250±50℃ and the amount of composite MgO-CaO desulfurizing agent added is 1500±50kg. S2: The amount of molten iron charged is 160-180t. The converter adopts top and bottom blowing smelting. During the tapping process, slag-forming materials and aluminum blocks are added for deoxidation, and carbon and manganese alloys are added for deoxidation and alloying. S3: Refining is carried out using the LF+RH process. After RH vacuum treatment, magnesium metallurgical treatment is performed to modify and purify the molten steel. After magnesium treatment, the steel is stirred for 15-20 minutes. S4: Molten steel is hoisted to the ladle for pouring, with the long nozzle inserted to a depth of 130-180mm, a pouring speed of 0.6-1.3m / min, and a superheat of 30-40℃; S5: During the casting process, adjust the height of the tundish nozzle, raise the height of the upper nozzle to 500mm, and insert the lower nozzle to a depth of 900~1100mm. Use strong cooling method for cooling. The flow rate of the wide face of the crystallizer is 5500~6000L / min, and the flow rate of the narrow face is 900~1200L / min. The crystallizer is vibrated in a positive oscillation mode with an amplitude of 5~15mm and a vibration frequency of 200~300 times / min. S6: After the molten steel enters the fan-shaped section, it is pressed down at multiple points. When it enters the horizontal section, a large pressing operation is performed, with a pressing amount of 8-12mm. S7: First blank cutting. The first blank is required to be ≥5500mm. The first blank is cut to 3000mm. The second blank is cut according to the order requirements, to 3000~6000mm. The first blank is used to roll the contracted product. The steel grade to be rolled is determined by flaw detection scanning of the first blank. S8: After the billet has been cooled for 48 hours, it should be blown and inspected, and the edges should be ground to a thickness of 100~200mm.

2. The production method for improving the core quality of a cast billet according to claim 1, characterized in that: The chemical composition and mass percentage of the billet are as follows: C: 0.02%~0.20%, Si: 0.05%~0.40%, Mn: 0.5%~2.0%, P≤0.025%, S≤0.015%, Al: 0.010%~0.050%, Mg: 0.0008%~0.0018%, N≤0.0060%, H≤0.0002%, with the balance being Fe and unavoidable impurities.

3. The production method for improving the core quality of a cast billet according to claim 1, characterized in that: The chemical composition and mass percentage of the billet are as follows: C: 0.09%, Si: 0.23%, Mn: 0.89%, P: 0.011%, S: 0.003%, Al: 0.026%, Mg: 0.0013%, N: 0.0053%, H: 0.0001%, with the balance being Fe and unavoidable impurities.

4. The production method for improving the core quality of a cast billet according to claim 1, characterized in that: The chemical composition and mass percentage of the billet are as follows: C: 0.17%, Si: 0.18%, Mn: 0.69%, P: 0.013%, S: 0.011%, Al: 0.041%, Mg: 0.0013%, N: 0.00443%, H: 0.0001%, with the balance being Fe and unavoidable impurities.

5. The production method for improving the core quality of a cast billet according to claim 1, characterized in that: (1) After the molten iron is sampled for temperature measurement upon entering the station, desulfurization is carried out by the KR method to ensure that the temperature of the molten iron is 1286℃ and the amount of composite MgO-CaO desulfurizing agent added is 1500kg. (2) The amount of molten iron charged is 167t. The converter adopts top and bottom blowing smelting. During the tapping process, slag-forming materials and aluminum blocks are added for deoxidation, and carbon and manganese alloys are added for deoxidation and alloying. (3) The refining process adopts the LF→RH process for refining. After RH vacuum treatment, magnesium metallurgical treatment is carried out to modify and purify the molten steel. After magnesium treatment, the steel is stirred for 17 minutes. (4) The molten steel is hoisted to the ladle for pouring, the long nozzle is inserted to a depth of 160mm, the pouring speed is 0.9m / min, and the superheat is 37℃; (5) During the casting process, adjust the height of the tundish nozzle, raise the height of the upper nozzle to 500mm, and insert the lower nozzle to 990mm. Use strong cooling method for cooling. The flow rate of the wide face of the crystallizer is 5800L / min, and the flow rate of the narrow face is 980L / min. The crystallizer is vibrated in the positive oscillation mode with an amplitude of 13mm and a vibration frequency of 280 times / min. (6) After the molten steel enters the fan-shaped section, it is pressed down at multiple points. When it enters the horizontal section, a large pressing operation is carried out, with a pressing amount of 9mm. (7) Head blank cutting: The head blank is marked as 6500mm. The first blank is cut to 3000mm. The second blank is cut to 4200mm according to the order requirements. The head blank is used to roll the contracted product. The steel grade to be rolled is determined by flaw detection scanning of the first blank. (8) After the billet has been cooled for 48 hours, it is blown and inspected, and the edges are ground to 130mm.

6. The production method for improving the core quality of a cast billet according to claim 1, characterized in that: (1) After the molten iron is sampled for temperature measurement upon entering the station, desulfurization is carried out by the KR method to ensure that the temperature of the molten iron is 1230℃ and the amount of composite MgO-CaO desulfurizing agent added is 1550kg; (2) The amount of molten iron charged is 175t. The converter adopts top and bottom blowing smelting. During the tapping process, slag-forming materials and aluminum blocks are added for deoxidation, and carbon and manganese alloys are added for deoxidation and alloying. (3) The refining process adopts the LF→RH process for refining. After RH vacuum treatment, magnesium metallurgical treatment is carried out to modify and purify the molten steel. After magnesium treatment, the steel is stirred for 19 minutes. (4) The molten steel is hoisted to the ladle for pouring, the long nozzle is inserted to a depth of 170mm, the pouring speed is 1.1m / min, and the superheat is 31℃; (5) During the casting process, adjust the height of the tundish nozzle, raise the height of the upper nozzle to 500mm, insert the lower nozzle to 1010mm, use strong cooling method for cooling, the flow rate of the wide face of the crystallizer is 5900L / min, the flow rate of the narrow face is 1100L / min, the crystallizer is vibrated in the positive oscillation mode with an amplitude of 6mm and a vibration frequency of 210 times / min. (6) After the molten steel enters the fan-shaped section, it is pressed down at multiple points. When it enters the horizontal section, a large pressing operation is carried out, with a pressing amount of 10mm. (7) Head blank cutting: The head blank is marked as 5800mm. The first blank is cut to 3000mm. The second blank is cut to 3600mm according to the order requirements. The head blank is used to roll the contracted product. The steel grade to be rolled is determined by flaw detection scanning of the first blank. (8) After the billet has been cooled for 48 hours, it is blown and inspected, and the edge is ground 160mm.

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