Casting process control method of high-alloy pipe billet steel rectangular billet

Abstract

The invention discloses a casting process control method for a high-alloy pipe billet steel rectangular billet. The casting process control method comprises the steps that S1, large ladle protection casting is conducted; s2, tundish protection pouring is carried out; s3, protective casting of a crystallizer; s4, an electromagnetic stirring technology is adopted at the position of the crystallizer and the position close to the solidification tail end of the casting blank, and proper current and frequency are controlled; s5, carrying out secondary cooling; and S6, a soft reduction process is adopted, specifically, according to the solidification characteristic in the steel grade continuous casting process, a reduction process of 0-0-2-4-6-4-0 is adopted to control core segregation. The method has the advantages that the surface quality of the casting blank is stable, the surface detection qualification rate and the inner detection qualification rate of the rolled metal are improved, and the product quality is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of manufacturing process of pipe materials for thermal power boilers, and particularly relates to a method for controlling the casting process of high alloy steel rectangular billets. Background Technology

[0002] High-alloy tube billet steel contains alloying elements such as Cr, Mo, V, and Nb. During continuous casting, the core of the billet is short, making it prone to porosity and cracks. Furthermore, high-alloy tube billet steel has high requirements for the surface quality of the billet. Low carbon content billet surfaces are prone to defects such as dents, cracks, and pits. Therefore, a suitable continuous casting control method is the key to controlling the quality of high-alloy tube billet steel billets.

[0003] Currently, the general production process involves sequentially passing the steel in a ladle, tundish, crystallizer, secondary cooling, and cutting. This process utilizes protective sleeves, an inert gas environment, covering agents, and crystallizer flux to protect the molten steel and prevent secondary oxidation. A general-purpose flux is used in the crystallizer. However, this method easily results in cast billets with defects such as depressions and cracks, which severely affect the quality of the rolled product. Currently, the surface inspection pass rate for high-alloy tube billets is only around 60%. To ensure the surface quality of the rolled product, 1.5mm of peeling is required on one side, leading to high production costs. Furthermore, the internal inspection pass rate is only 40%–60%, resulting in low market competitiveness. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of easy dents and cracks in the cast billet, low flaw detection pass rate, and high production cost during the casting of high alloy steel tube billets. It provides a method for controlling the casting process of rectangular billets of high alloy steel tube billets, which can ensure stable surface quality of the cast billet, improve the pass rate of surface and internal flaw detection of rolled products, and enhance product quality.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for controlling the casting process of high-alloy steel rectangular billets, the specific steps of which are as follows: S1, Ladle Protection Casting: A long ladle nozzle is used, and the connection parts are inert gas atmosphere to prevent secondary oxidation of molten steel; S2, tundish protection pouring: S21, Perform the pouring operation in an inert environment; S22 adopts an integral submerged nozzle, and the appropriate nozzle insertion depth is controlled in the crystallizer to prevent secondary oxidation and slag entrapment of molten steel. S23 uses a double-layer covering agent for the tundish. When the weight of the molten steel in the tundish reaches 15t after the ladle is started to pour, 160kg of carbon-free covering agent is added evenly to the tundish. When the weight of the tundish reaches 28t, another 160kg of carbon-free covering agent is added evenly to the tundish. Then, an appropriate amount of heat-insulating covering agent is added to the tundish. The entire pouring process ensures that the surface of the molten steel in the tundish is stable and not exposed. S3, Crystallizer-protected pouring: S31 uses a mold protective slag, which fully covers the surface of the molten steel in the mold throughout the entire casting process, maintaining a slag layer of appropriate thickness to prevent secondary oxidation of the molten steel. S32 uses a special crystallizer protective slag with a basicity of 1.0~1.1, a viscosity of 0.6~0.7 Pa.s, and a TC of 18%~20%, according to the characteristics of the steel grade. This slag lubricates the billet, ensures an appropriate cooling rate and uniform heat transfer, and prevents slag accumulation, thus preventing surface depressions, cracks, and indentations. S33, crystallizer vibration parameters: crystallizer vibration frequency 175cpm, controlling the depth of vibration marks on the surface of the billet to ensure uniform cooling of the billet surface; S34, the radius of curvature of the copper tube in the crystallizer is 20mm, which reduces the cooling intensity at the corner of the billet and prevents longitudinal depression at the corner of the billet; S4. Electromagnetic stirring technology is used at the crystallizer position and near the solidification end of the billet to control the appropriate current and frequency to control the shrinkage of the billet, increase the equiaxed crystals of the billet, and improve segregation. S5, secondary cooling; S6 adopts a light reduction process: based on the solidification characteristics during the continuous casting process of the steel grade, a 0-0-2-4-6-4-0 reduction process is adopted to control core segregation and ensure the quality of the core of the billet.

[0006] Furthermore, in step S5, the secondary cooling needs to be combined with the casting machine design capacity. For a 250*300 cross section, at an appropriate drawing speed, a water volume of 0.20~0.21L / kg should be used, and the straightening temperature should be controlled at 980℃~1000℃ to avoid the generation of straightening cracks.

[0007] Furthermore, in step S5, the secondary cooling gas pressure is controlled at 0.55~0.65MPa, and the gas flow rate is controlled at 170m³ / h. 3 / h, to ensure the intensity and uniformity of secondary cooling of the billet, and to avoid thermal stress cracks in the billet.

[0008] Furthermore, in step S32, the special crystallizer protective slag has an basicity of 1.0, a viscosity of 0.65 Pa·s, and a TC of 18.2%.

[0009] Furthermore, in step S32, the basicity of the special crystallizer protective slag is 1.05, the viscosity is 0.68 Pa·s, and the TC is 19.2%.

[0010] Furthermore, in step S32, the basicity of the special crystallizer protective slag is 1.1, the viscosity is 0.69 Pa·s, and the TC is 19.6%.

[0011] Furthermore, in step S5, the secondary cooling gas pressure is controlled at 0.60 MPa, and the air flow rate is controlled at 170 m³ / h. 3 / h.

[0012] In the technical solution of this invention, by improving the control process parameters of the casting process, the surface quality of the billet is stably controlled, thereby increasing the surface inspection qualification rate of rolled products from less than 60% to more than 90%, which greatly improves product quality. Round steel that fails the surface inspection only needs to be spot-ground to meet the release conditions, and the internal inspection qualification rate is increased to 100%, ensuring the excellent quality of the high alloy tube billet steel produced, and improving the stability and service life of pipeline materials for thermal power boilers. Detailed Implementation Example 1

[0013] To make the present invention clearer, the following description further illustrates a method for controlling the casting process of a high-alloy steel rectangular billet. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention.

[0014] This embodiment provides a method for controlling the casting process of high-alloy steel rectangular billets, characterized in that: S1, Ladle Protection Casting: A long ladle nozzle is used, and the connection parts are inert gas atmosphere to prevent secondary oxidation of molten steel.

[0015] S2, tundish protection pouring: S21, Perform the pouring operation in an inert environment; S22 adopts an integral submerged nozzle, and the appropriate nozzle insertion depth is controlled in the crystallizer to prevent secondary oxidation and slag entrapment of molten steel. S23 uses a double-layer covering agent for the tundish. When the weight of the molten steel in the tundish reaches 15t after the ladle is started to pour, 160kg of carbon-free covering agent is added evenly to the tundish. When the weight of the tundish reaches 28t, another 160kg of carbon-free covering agent is added evenly to the tundish. Then, an appropriate amount of heat-insulating covering agent is added to the tundish. The entire pouring process ensures that the surface of the molten steel in the tundish is stable and not exposed.

[0016] S3, Crystallizer-protected pouring: S31 uses a mold protective slag, which fully covers the surface of the molten steel in the mold throughout the entire casting process, maintaining a slag layer of appropriate thickness to prevent secondary oxidation of the molten steel. S32 uses a special crystallizer protective slag with an basicity of 1.0, a viscosity of 0.65 Pa·s, and a TC of 18.2%. S33, crystallizer vibration parameters: crystallizer vibration frequency 175cpm, controlling the depth of vibration marks on the surface of the billet to ensure uniform cooling of the billet surface; S34, the copper tube of the crystallizer has a radius of 20mm, which reduces the cooling intensity at the corner of the billet and prevents longitudinal depression at the corner of the billet.

[0017] S4 employs electromagnetic stirring technology at the crystallizer location and near the solidification end of the billet to control appropriate current and frequency, thereby controlling billet shrinkage, increasing equiaxed crystals, and improving segregation.

[0018] S5, secondary cooling: S51, combined with the casting machine design capabilities, uses a specific water volume of 0.20L / kg at an appropriate drawing speed for a 250*300 cross section, and controls the straightening temperature at 980℃~1000℃ to avoid the generation of straightening cracks; S52, secondary air conditioning pressure controlled at 0.60MPa, air flow rate controlled at 170m³ / h. 3 / h, to ensure the intensity and uniformity of secondary cooling of the billet, and to avoid thermal stress cracks in the billet.

[0019] S6 adopts a light reduction process: based on the solidification characteristics during the continuous casting process of the steel grade, a 0-0-2-4-6-4-0 reduction process is adopted to control core segregation and ensure the quality of the core of the billet.

[0020] Wherein, 0-0-2-4-6-4-0 represents the amount of compression at each stage. Example 2

[0021] This embodiment provides a method for controlling the casting process of high-alloy steel rectangular billets, characterized in that: S1, Ladle Protection Casting: A long ladle nozzle is used, and the connection parts are inert gas atmosphere to prevent secondary oxidation of molten steel.

[0022] S2, tundish protection pouring: S21, Perform the pouring operation in an inert environment; S22 adopts an integral submerged nozzle, and the appropriate nozzle insertion depth is controlled in the crystallizer to prevent secondary oxidation and slag entrapment of molten steel. S23 uses a double-layer covering agent for the tundish. When the weight of the molten steel in the tundish reaches 15t after the ladle is started to pour, 160kg of carbon-free covering agent is added evenly to the tundish. When the weight of the tundish reaches 28t, another 160kg of carbon-free covering agent is added evenly to the tundish. Then, an appropriate amount of heat-insulating covering agent is added to the tundish. The entire pouring process ensures that the surface of the molten steel in the tundish is stable and not exposed.

[0023] S3, Crystallizer-protected pouring: S31 uses a mold protective slag, which fully covers the surface of the molten steel in the mold throughout the entire casting process, maintaining a slag layer of appropriate thickness to prevent secondary oxidation of the molten steel. S32 uses a special crystallizer protective slag with an basicity of 1.05, a viscosity of 0.68 Pa·s, and a TC of 19.2%. S33, crystallizer vibration parameters: crystallizer vibration frequency 175cpm, controlling the depth of vibration marks on the surface of the billet to ensure uniform cooling of the billet surface; S34, the copper tube of the crystallizer has a radius of 20mm, which reduces the cooling intensity at the corner of the billet and prevents longitudinal depression at the corner of the billet.

[0024] S4 employs electromagnetic stirring technology at the crystallizer location and near the solidification end of the billet to control appropriate current and frequency, thereby controlling billet shrinkage, increasing equiaxed crystals, and improving segregation.

[0025] S5, secondary cooling: S51, combined with the casting machine design capabilities, uses a specific water content of 0.21L / kg at an appropriate drawing speed for a 250*300 cross section, and controls the straightening temperature at 980℃~1000℃ to avoid the generation of straightening cracks; S52, the secondary cooling gas pressure is controlled at 0.60MPa and the gas flow rate is controlled at 170m3 / h to ensure the intensity and uniformity of secondary cooling of the billet and avoid thermal stress cracks in the billet. S6 adopts a light reduction process: based on the solidification characteristics during the continuous casting process of the steel grade, a 0-0-2-4-6-4-0 reduction process is adopted to control core segregation and ensure the quality of the core of the billet. Example 3

[0026] This embodiment provides a method for controlling the casting process of high-alloy steel rectangular billets, characterized in that: S1, Ladle Protection Casting: A long ladle nozzle is used, and the connection parts are inert gas atmosphere to prevent secondary oxidation of molten steel.

[0027] S2, tundish protection pouring: S21, Perform the pouring operation in an inert environment; S22 adopts an integral submerged nozzle, and the appropriate nozzle insertion depth is controlled in the crystallizer to prevent secondary oxidation and slag entrapment of molten steel. S23 uses a double-layer covering agent for the tundish. When the weight of the molten steel in the tundish reaches 15t after the ladle is started to pour, 160kg of carbon-free covering agent is added evenly to the tundish. When the weight of the tundish reaches 28t, another 160kg of carbon-free covering agent is added evenly to the tundish. Then, an appropriate amount of heat-insulating covering agent is added to the tundish. The entire pouring process ensures that the surface of the molten steel in the tundish is stable and not exposed.

[0028] S3, Crystallizer-protected pouring: S31 uses a mold protective slag, which fully covers the surface of the molten steel in the mold throughout the entire casting process, maintaining a slag layer of appropriate thickness to prevent secondary oxidation of the molten steel. S32 uses a special crystallizer protective slag with an basicity of 1.1, a viscosity of 0.69 Pa·s, and a TC of 19.6%. S33, crystallizer vibration parameters: crystallizer vibration frequency 175cpm, controlling the depth of vibration marks on the surface of the billet to ensure uniform cooling of the billet surface; S34, the copper tube of the crystallizer has a radius of 20mm, which reduces the cooling intensity at the corner of the billet and prevents longitudinal depression at the corner of the billet.

[0029] S4 employs electromagnetic stirring technology at the crystallizer location and near the solidification end of the billet to control appropriate current and frequency, thereby controlling billet shrinkage, increasing equiaxed crystals, and improving segregation.

[0030] S5, secondary cooling: S51, combined with the casting machine design capabilities, uses a specific water volume of 0.20L / kg at an appropriate drawing speed for a 250*300 cross section, and controls the straightening temperature at 980℃~1000℃ to avoid the generation of straightening cracks; S52, secondary air conditioning pressure controlled at 0.60MPa, air flow rate controlled at 170m³ / h. 3 / h, to ensure the intensity and uniformity of secondary cooling of the billet, and to avoid thermal stress cracks in the billet.

[0031] S6 adopts a light reduction process: based on the solidification characteristics during the continuous casting process of the steel grade, a 0-0-2-4-6-4-0 reduction process is adopted to control core segregation and ensure the quality of the core of the billet.

[0032] 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 method for controlling the casting process of a high-alloy steel rectangular billet, characterized in that: S1, large-bottle protection pouring: adopts large-bottle long nozzle, and the connection part is inert gas atmosphere; S2, tundish protection pouring: S21, Perform the pouring operation in an inert environment; S22 adopts an integral submersible nozzle, and the appropriate nozzle insertion depth is controlled inside the crystallizer; S23 uses a double-layer covering agent for the tundish. When the weight of the molten steel in the tundish reaches 15t after the ladle is started to pour, 160kg of carbon-free covering agent is added evenly to the tundish. When the weight of the tundish reaches 28t, another 160kg of carbon-free covering agent is added evenly to the tundish. Then, an appropriate amount of heat-insulating covering agent is added to the tundish. The entire pouring process ensures that the surface of the molten steel in the tundish is stable and not exposed. S3, Crystallizer-protected pouring: S31 uses mold protective slag, which fully covers the surface of the molten steel in the mold throughout the entire casting process, maintaining a slag layer of appropriate thickness. For S32, a special crystallizer protective slag with a basicity of 1.0~1.1, a viscosity of 0.6~0.7 Pa.s, and a TC of 18%~20% is used according to the characteristics of the steel grade to lubricate the billet and ensure an appropriate cooling rate and uniform heat transfer. S33, crystallizer vibration parameters: crystallizer vibration frequency 175cpm, controlling the depth of vibration marks on the surface of the billet; S34, the radius of the copper tube in the crystallizer is 20mm, which reduces the cooling intensity at the corner of the billet; S4. Electromagnetic stirring technology is used at the crystallizer position and near the end of the billet solidification to control appropriate current and frequency. S5, secondary cooling; S6 adopts a light reduction process: based on the solidification characteristics during the continuous casting process of the steel grade, a 0-0-2-4-6-4-0 reduction process is adopted to control core segregation.

2. The method for controlling the casting process of high-alloy steel rectangular billets according to claim 1, characterized in that: In step S5, the secondary cooling needs to be combined with the casting machine design capacity. For a 250*300 cross section, the water content should be 0.20~0.21L / kg at an appropriate drawing speed, and the straightening temperature should be controlled at 980℃~1000℃.

3. The method for controlling the casting process of high-alloy steel rectangular billets according to claim 1 or 2, characterized in that: In step S5, the secondary cooling gas pressure is controlled at 0.55~0.65MPa, and the gas flow rate is controlled at 170m³ / h. 3 / h.

4. The method for controlling the casting process of high-alloy steel rectangular billets according to claim 1 or 2, characterized in that: In step S32, the special crystallizer protective slag has an alkalinity of 1.0, a viscosity of 0.65 Pa·s, and a TC of 18.2%.

5. The method for controlling the casting process of high-alloy steel rectangular billets according to claim 1 or 2, characterized in that: In step S32, the basicity of the special crystallizer protective slag is 1.05, the viscosity is 0.68 Pa·s, and the TC is 19.2%.

6. The method for controlling the casting process of high-alloy steel rectangular billets according to claim 1 or 2, characterized in that: In step S32, the basicity of the special crystallizer protective slag is 1.1, the viscosity is 0.69 Pa·s, and the TC is 19.6%.

7. The method for controlling the casting process of high-alloy steel rectangular billets according to claim 3, characterized in that: In step S5, the secondary cooling gas pressure is controlled at 0.60 MPa, and the gas flow rate is controlled at 170 m³ / h. 3 / h.