A method for controlling edge cracks in continuously cast slabs

Abstract

This invention discloses a method for controlling edge cracks in continuously cast slabs, belonging to the technical field of continuously cast slabs. The method includes: S1, injecting molten steel from the ladle into the tundish, controlling the temperature at 1535℃~1560℃; S2, adding protective slag to the tundish, controlling the basicity at 1.20 and the viscosity at 0.148 Pa·S1300℃, using this method for the first heat when the air temperature is below 5℃; S3, allowing molten steel to enter the crystallizer from the tundish, using a crystallizer taper of 1.1% when the air temperature is below 5℃, and 0.9% when the air temperature is above 20℃; S4, controlling the crystallizer cooling intensity: 4000 L / min for the wide side and 540 L / min for the narrow side when the air temperature is below 5℃; 4200 L / min for the wide side and 600 L / min for the narrow side when the air temperature is above 20℃; S5, controlling the ratio of secondary cooling water in the crystallizer; and S6, controlling the continuous casting speed at 0.8-1.4 m / min.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting slab technology, specifically relating to a method for controlling edge cracks in continuous casting slabs. Background Technology

[0002] In actual production, due to improper operating settings, edge cracks frequently occur in the slabs of continuous casting machines, sometimes causing quality shutdowns. This not only affects production and the subsequent hot charging schedule of the slabs, but also consumes a lot of manpower and resources for slab finishing. The incidence of edge cracks is close to 4%. Edge cracks mainly occur on the upper surface or side of the slab, 10-15mm from the corner. After subsequent rolling, depending on the degree of longitudinal crack opening, the coil exhibits product quality defects such as edge peeling, edge cracking, or even rolling defects, which seriously affect the product image and sales.

[0003] Inspection of the edge cracks in the slab revealed that most of them occurred 10–25 mm from the narrow face of the slab. Based on macroscopic morphology, metallographic analysis, and energy dispersive spectroscopy (EDS), it can be inferred that the crack formation was primarily due to the excessively rapid cooling rate on the narrow face of the mold, while the cooling rate on the wide face was slower. This resulted in stress concentration near the edge of the mold. The lower cooling rate on the narrow face also deteriorated the performance of the protective slag, leading to poor lubrication and making it more difficult for molten slag to flow into the gap between the slab and the mold. Consequently, the slag layer between the slab and the mold was thin or absent, resulting in high thermal conductivity and a rapid cooling rate, ultimately leading to the formation of edge cracks.

[0004] With increasing demands from production and the market, driven by high-paced, high-volume production, the impact of cooling, finishing, reheating, and rolling of continuously cast defective slabs on production has become exceptionally significant, especially at higher output and faster production rates. Edge cracks often occur under conditions of low casting speed, fluctuating casting speed, and high steel temperatures. Considering the relatively large temperature difference between winter and summer, and the presence of low casting speed and unstable production rates throughout the entire process, edge crack defects urgently need to be addressed. To stabilize market share, a method for controlling edge cracks in continuously cast slabs has been specifically developed. Summary of the Invention

[0005] This invention provides a method for controlling edge cracks in continuously cast slabs, which is used to control edge cracks in continuously cast slabs under normal production conditions.

[0006] The purpose of this invention is to provide a method for controlling edge cracks in continuously cast slabs, comprising:

[0007] S1. The molten steel in the ladle is injected into the tundish through the ladle turret, and the temperature is controlled at 1535℃~1560℃.

[0008] S2. Add protective slag to the tundish, control the alkalinity at 1.20, and the viscosity at 0.148 Pa·S. Use the first batch when the temperature is below 5℃.

[0009] S3. Molten steel enters the crystallizer from the tundish. When the temperature is below 5℃, the crystallizer taper is 1.1%, and when the temperature is above 20℃, the crystallizer taper is 0.9%.

[0010] S4. Control the cooling intensity of the crystallizer: when the air temperature is below 5℃, the cooling water flow rate of the crystallizer is 4000L / min for the wide side and 540L / min for the narrow side; when the air temperature is above 20℃, the cooling water flow rate is 4200L / min for the wide side and 600L / min for the narrow side.

[0011] S5. Control the cooling water ratio of the crystallizer: 0.75L / kg when the air temperature is above 20℃, and 0.70L / kg when the air temperature is below 5℃;

[0012] S6. The continuous casting speed is controlled at 0.8-1.4 m / min.

[0013] Preferably: S1 specifically refers to:

[0014] First, the steel ladle is transported to the ladle turntable by overhead crane, and the temperature of each ladle of molten steel is controlled at 1570-1595℃ upon arrival at the station.

[0015] Then, the molten steel from the ladle is poured into the intermediate ladle, and the temperature is controlled at 1535-1560℃.

[0016] The advantages and positive effects of this invention are:

[0017] This invention is applicable to the production process of continuously cast slabs, reducing the incidence of edge cracks in continuously cast slabs from 0.1% to 0.1%, effectively controlling edge cracks, increasing the hot charging rate of slabs, and reducing the input of manpower and materials. At the same time, a new crystallizer cooling system model has been developed to ensure good surface quality of cast slabs during seasonal transitions. The actual use effect is good, providing a technical reference for other steel enterprises in China, especially those whose slab edge cracks are too severe to meet production increase requirements. The application prospects are broad. Detailed Implementation

[0018] To further understand the invention's content, features, and effects, the following embodiments are provided and described in detail below:

[0019] The technical solution of this invention is as follows:

[0020] A method for controlling edge cracks in continuously cast slabs includes:

[0021] S1. The molten steel in the ladle is injected into the tundish through the ladle turret, and the temperature is controlled at 1535℃~1560℃.

[0022] S2. Add protective slag to the intermediate ladle, with its alkalinity controlled at 1.20 and viscosity controlled at 0.148 Pa·S1300℃. Use it for the first batch of casting in winter (when the temperature is below 5℃).

[0023] S3. Molten steel enters the crystallizer from the tundish. In winter, the crystallizer taper is 1.1%, and in summer, it is 0.9%.

[0024] S4. Control the cooling intensity of the crystallizer: In winter, the cooling water flow rate of the crystallizer is 4000L / min for the wide side and 540L / min for the narrow side; in summer, the cooling water flow rate is 4200L / min for the wide side and 600L / min for the narrow side.

[0025] S5. Control the cooling water ratio of the crystallizer: 0.75L / kg in summer (temperature above 20℃) and 0.70L / kg in winter.

[0026] S6. The continuous casting speed is controlled at 0.8-1.4 m / min and is stable and uniform.

[0027] The temperature of the molten steel is controlled at 1535℃~1560℃, and the temperature in winter is 5℃ higher than that in summer.

[0028] The continuous casting speed is controlled between 0.8 and 1.4 m / min. Depending on the steel grade, the casting speed in winter is 0.1 to 0.2 m / min higher than that in summer.

[0029] The following is an example of the technical methods for controlling edge cracks in continuously cast plain carbon steel Q235B slabs, specifically including:

[0030] First, the steel ladles are transported to the ladle turntable by overhead crane. The temperature of each ladle of molten steel is controlled at 1570-1595℃ upon arrival. During this process, temperature monitoring is required, and the ladle can be covered for insulation based on the temperature monitoring results.

[0031] Then, molten steel from the ladle is poured into the intermediate ladle, with the temperature controlled at 1537-1547℃. During this process, protective slag is added, with the basicity controlled at 1.20 and the viscosity controlled at 0.148 Pa·S. At 1300℃, the first furnace is poured in winter, and the black liquor surface is maintained during operation.

[0032] Finally, the molten steel enters the crystallizer via the tundish. The crystallizer taper is 1.1% in winter and 0.9% in summer. The cooling intensity of the crystallizer is controlled as follows: 4000 L / min for the wide side and 540 L / min for the narrow side in winter; 4200 L / min for the wide side and 600 L / min for the narrow side in summer. The secondary cooling water ratio is also controlled: 0.75 L / kg in summer and 0.70 L / kg in winter. The continuous casting speed is controlled between 0.8 and 1.4 m / min and kept stable and uniform to control the formation of edge cracks in the continuously cast slab.

[0033] This invention achieves the goal of controlling edge cracks in continuously cast slabs by controlling the temperature of the ladle and tundish, controlling the protective slag in the tundish, and controlling the taper of the crystallizer, the intensity of cooling water, the ratio of secondary cooling water to water volume, and finally controlling the casting speed.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A method for controlling edge cracks in continuously cast slabs, characterized in that, At least including: S1. The molten steel in the ladle is injected into the tundish through the ladle turret, and the temperature of the molten steel is controlled at 1535℃~1560℃. S2. Add protective slag to the tundish, control the alkalinity at 1.20, and the viscosity at 0.148 Pa·S. Use the first batch when the temperature is below 5℃. S3. Molten steel enters the crystallizer from the tundish. When the temperature is below 5℃, the crystallizer taper is 1.1%, and when the temperature is above 20℃, the crystallizer taper is 0.9%. S4. Control the cooling intensity of the crystallizer: when the air temperature is below 5℃, the cooling water flow rate of the crystallizer is 4000L / min for the wide side and 540L / min for the narrow side; when the air temperature is above 20℃, the cooling water flow rate is 4200L / min for the wide side and 600L / min for the narrow side. S5. Control the secondary cooling water flow rate of the crystallizer: when the air temperature is above 20℃, the secondary cooling water flow rate is 0.75L / kg; when the air temperature is below 5℃, the secondary cooling water flow rate is 0.70L / kg. S6. The continuous casting speed is controlled at 0.8-1.4 m / min.

2. The method for controlling edge cracks in continuously cast slabs according to claim 1, characterized in that, S1 specifically refers to: First, the steel ladle is transported to the ladle turntable by overhead crane, and the temperature of each ladle of molten steel is controlled at 1570-1595℃ upon arrival at the station. Then, the molten steel from the ladle is poured into the intermediate ladle, and the temperature is controlled at 1535-1560℃.