A method for preventing steel leakage from high-speed billet continuous casting machine

Abstract

The present invention discloses a method for preventing breakout in a high-speed billet continuous casting machine. During continuous casting, the billet continuous casting machine operates at a casting speed of 3.5 to 5.5 m / min and a mold taper of 1.9 to 2.2% / m. The mold flux used has a melting point of 1055 to 1095°C, a melting rate of 25 to 33 seconds, and a viscosity of 0.09 to 0.13 Pa·s. When the casting speed is 3.5 to 4.0 m / min, the tundish molten steel temperature must not exceed 1535°C. When the casting speed is 4.0 to 5.5 m / min, the tundish molten steel temperature must not exceed 1530°C. The present invention controls breakout in the mold or at the foot roll section by adopting an appropriate mold copper tube taper and using a mold flux with an appropriate melting point, melting rate, and viscosity. This method achieves stable high-speed production for the billet continuous casting machine, resolves the difficulty in handling breakouts and the inability to complete production plans due to high casting speed breakouts, and improves the billet yield.

Description

Technical Field

[0001] The invention relates to a continuous casting method, in particular to a method for preventing steel leakage from a high-speed billet continuous casting machine. Background Art

[0002] During the high-speed production process of the billet continuous casting machine, three types of steel leakage often occur: steel leakage at the end of the crystallizer, steel leakage at the corner of the secondary cooling zone, and steel leakage in the middle longitudinal crack in front of the straightening machine. Although the high-speed production of the continuous casting machine can meet the demand for high-temperature steel billets, it also brings production risks. For example, the high throughput of molten steel causes great disturbance to the molten steel in the crystallizer, resulting in large fluctuations in the liquid slag layer of the protective slag and a disordered temperature field in the crystallizer. Secondly, the shell of the continuous casting billet in the secondary cooling chamber becomes thinner. If the cooling water is not replenished in time, steel leakage accidents are likely to occur. At the same time, due to the high manganese content in the steel, after reacting with the protective slag, it deteriorates the heat transfer of the crystallizer and the lubrication of the cast billet, and the probability of crack leakage increases. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preventing steel leakage in a high-speed billet continuous casting machine, so as to improve the yield rate of the billet.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: when the square billet continuous casting machine is continuously casting, the pulling speed is 3.5-5.5 m / min, and the crystallizer taper is 1.9-2.2% / m; the melting point of the protective slag used is 1055-1095°C, the melting rate is 25-33 seconds, and the viscosity is 0.09-0.13 Pa·S; when the pulling speed is 3.5-4.0 m / min, the temperature of the molten steel in the tundish shall not exceed 1535°C, and when the continuous casting machine pulling speed is 4.0-5.5 m / min, the temperature of the molten steel in the tundish shall not exceed 1530°C.

[0005] Furthermore, when the pulling speed is 3.5-4.5 m / min, the consumption of protective slag is 0.42-0.50 kg / ton of steel; when the pulling speed is 4.5-5.5 m / min, the consumption of protective slag is 0.45-0.55 kg / ton of steel.

[0006] Furthermore, during the continuous casting, the gap between the surface of the crystallizer foot roller and the four surfaces of the casting billet should not be greater than 2 mm.

[0007] Furthermore, the secondary cooling water system of the billet continuous casting machine must be arranged for full-process cooling, with at least 4 cooling sections, and each cooling section is not less than 1.5m in length.

[0008] The beneficial effects of the above technical solution are as follows: by adopting an appropriate mold copper tube back taper and using mold slag with an appropriate melting point, melting rate, and viscosity, the present invention controls breakout within the mold or at the bottom roll section, thereby achieving stable high-speed production in a billet continuous casting machine. This invention stabilizes high-speed production in the continuous casting machine, ensuring smooth production, and resolving the difficulties associated with high-speed breakout, which can hinder production schedules. It also improves billet yield and has broad prospects for widespread application. DETAILED DESCRIPTION

[0009] The present invention will be further described in detail below with reference to specific embodiments.

[0010] The method for preventing steel breakout in a high-speed billet continuous casting machine is applicable to plain carbon steel and low-alloy steel, and is particularly applicable to steel with a Mn content ranging from 1.20 to 1.60%. Preferably, the steel has the following composition ratio (by weight): C 0.17 to 0.27%, Mn 1.20 to 1.60%, Si 0.30 to 0.90%, S 0 to 0.047%, P 0 to 0.045%, V 0.013 to 0.050%, Nb 0.0080 to 0.020%, and the balance is Fe and unavoidable impurities.

[0011] The method for preventing steel leakage from a high-speed billet continuous casting machine adopts the following process:

[0012] (1) The cross-section of the billet continuous casting machine is 150 mm × 150 mm to 180 mm × 180 mm, the billet arc radius is 9 to 12 m, and the casting speed of the continuous casting machine during the production process is 3.5 to 5.5 m / min. When the casting speed is 3.5 to 4.0 m / min, the temperature of the molten steel in the tundish shall not exceed 1535°C; when the casting speed is 4.0 to 5.5 m / min, the temperature of the molten steel in the tundish shall not exceed 1530°C.

[0013] (2) During direct rolling of the billet continuous casting machine, the effective height of the crystallizer is 900-1000 mm, and the inverted taper of the crystallizer is 1.9-2.2% / m.

[0014] (3) The mold slag used has a melting point of 1055-1095°C, a melting rate of 25-33 seconds, and a viscosity of 0.09-0.13 Pa·s. At a casting speed of 3.5-4.5 m / min, the mold slag consumption is 0.42-0.50 kg / ton of steel; at a casting speed of 4.5-5.5 m / min, the mold slag consumption is 0.45-0.55 kg / ton of steel.

[0015] (4) During continuous casting, the gap between the surface of the crystallizer foot roller and the four surfaces of the billet should not be greater than 2 mm; in this way, it can ensure that the continuous casting billet enters the foot roller section after leaving the crystallizer. At this time, the four surfaces of the continuous casting billet can be squeezed by the foot roller in four directions, ensuring that the shape of the continuous casting billet is not deformed, reducing the occurrence of corner cracks, and preventing the billet from leaking steel in the foot roller section.

[0016] (5) During continuous casting, the gap between the rollers of each section in the second cooling zone of the square billet continuous casting machine and the outer arc of the arc template does not exceed 2 mm; in this way, the stress / strain generated by the continuous casting billet during operation is less than the critical stress / strain of the crack, thereby avoiding steel leakage in the second cooling section of the billet, that is, further controlling steel leakage in the second cooling section through high arc accuracy.

[0017] (6) During continuous casting, the distance between the end of the water system in the secondary cooling zone of the square billet continuous casting and the air cooling zone of the first roller of the straightening machine shall not exceed 3m; thus, by reducing the distance to the air cooling zone before straightening, the temperature return of the billet can be effectively controlled, thereby controlling the steel leakage during the temperature return of the billet.

[0018] (7) The secondary cooling water system of the billet continuous casting machine is pure water cooling with a water pressure of 1.8 to 2.2 MPa. The secondary cooling water system of the billet continuous casting machine must be arranged for full-process cooling. The secondary cooling zone has at least 4 cooling sections, and the length of each cooling section is not less than 1.5 m. The secondary cooling water system of the billet continuous casting machine is equipped with water bars from the crystallizer foot roll to the straightening machine. Water spray cooling is carried out during production, and the maximum water flow in each section is not less than 5 t / h.

[0019] (8) For each row of water nozzles in the secondary cooling water system of the billet continuous casting machine, the distance error between the inner and outer arc water nozzles and the billet surface shall not exceed 2mm; the distance error between the side arc water nozzles and the billet surface shall not exceed 2mm. For each row of water nozzles in the secondary cooling water system of the billet continuous casting machine, the inner and outer arc water nozzles and the side arc water nozzles shall be of the same model.

[0020] Example 1: The method for preventing steel leakage in a high-speed billet continuous casting machine is specifically described as follows.

[0021] There are two rows of crystallizer foot rollers, four in each row, arranged on four sides, with a total of eight foot rollers in two rows. The gap between the surface of the crystallizer foot rollers and the four surfaces of the ingot is 0.1mm. The gap between the rollers of each section of the secondary cooling zone and the outer arc of the ingot is 0.1mm. The distance between the last section of the secondary cooling zone water system (secondary cooling zone section 4) and the first roller of the straightening machine is 2.53m. The taper of the crystallizer copper tube is 2.0% / m, and the total length of the secondary cooling zone is 11.8 meters. When pouring steel, the temperature of the molten steel in the tundish is 1534℃, the pulling speed is 3.6m / min, the melting point of the protective slag is 1065℃, the consumption of protective slag is 0.436kg / t, the total water volume of the secondary cooling zone is 80.42 tons per hour, and 45.08 tons of ingots are produced per hour. The water volume of the secondary cooling zone is 1.78l / kg, which enables normal production. There is no leakage of steel from longitudinal cracks at corners or leakage before straightening when pouring steel. The steel composition of this embodiment is shown in Table 1 below;

[0022] Table 1: Composition of the steel described in Example 1 (wt%)

[0023] C Mn P S Si V Nb 0.24 1.39 0.029 0.032 0.33 0.035 0.0093 0.25 1.42 0.027 0.036 0.34 0.035 0.0091

[0024] In Table 1, the balance of the components is Fe and inevitable impurities.

[0025] Example 2: The method for preventing steel leakage in a high-speed billet continuous casting machine is specifically described as follows.

[0026] There are two rows of crystallizer foot rollers, four in each row, arranged on four sides, with a total of eight foot rollers in two rows. The gap between the surface of the crystallizer foot rollers and the four surfaces of the ingot is 0.1mm. The gap between the rollers of each section of the secondary cooling zone and the outer arc of the ingot is 0.1mm. The distance between the last section of the secondary cooling zone water system (secondary cooling zone section 4) and the first roller of the straightening machine is 2.53m. The taper of the crystallizer copper tube is 2.0% / m, and the total length of the secondary cooling zone is 11.8 meters. When pouring steel, the temperature of the molten steel in the tundish is 1532℃, the pulling speed is 3.7m / min, the melting point of the protective slag is 1065℃, the consumption of protective slag is 0.447kg / t, the total water volume of the secondary cooling zone is 82.74 tons per hour, and 46.33 tons of ingots are produced per hour. The water volume of the secondary cooling zone is 1.79l / kg, which enables normal production. There is no leakage of steel from longitudinal cracks at corners or leakage before straightening when pouring steel. The steel composition of this embodiment is shown in Table 2 below;

[0027] Table 2: Composition of the steel described in Example 2 (wt%)

[0028] C Mn P S Si V Nb 0.24 1.39 0.025 0.031 0.34 0.035 0.012 0.24 1.42 0.022 0.036 0.34 0.034 0.0108

[0029] In Table 2, the balance of the components is Fe and inevitable impurities.

[0030] Example 3: The method for preventing steel leakage in a high-speed billet continuous casting machine is specifically described as follows.

[0031] There are two rows of crystallizer foot rollers, four in each row, arranged on four sides, with a total of eight foot rollers in two rows. The gap between the surface of the crystallizer foot rollers and the four surfaces of the ingot is 0.1mm. The gap between the rollers of each section of the secondary cooling zone and the outer arc of the ingot is 0.1mm. The distance between the last section of the secondary cooling zone water system (secondary cooling zone section 4) and the first roller of the straightening machine is 2.53m. The taper of the crystallizer copper tube is 2.0% / m, and the total length of the secondary cooling zone is 11.8 meters. When pouring steel, the temperature of the molten steel in the tundish is 1528℃, the pulling speed is 4.2m / min, the melting point of the protective slag is 1060℃, the consumption of protective slag is 0.462kg / t, the total water volume of the secondary cooling zone is 94.08 tons per hour, and 52.59 tons of ingots are produced per hour. The water volume of the secondary cooling zone is 1.79l / kg, which enables normal production. There is no leakage of steel from longitudinal cracks at corners or leakage before straightening when pouring steel. The steel composition of this embodiment is shown in Table 3 below;

[0032] Table 3: Composition of the steel described in Example 3 (wt%)

[0033] C Mn P S Si V Nb 0.24 1.38 0.024 0.034 0.33 0.034 0.0083 0.24 1.33 0.03 0.03 0.32 0.034 0.0134

[0034] In Table 3, the balance of the components is Fe and inevitable impurities.

[0035] Example 4: The method for preventing steel leakage in a high-speed billet continuous casting machine is specifically described as follows.

[0036] There are two rows of crystallizer foot rollers, four in each row, arranged on four sides, with a total of eight foot rollers in two rows. The gap between the surface of the crystallizer foot rollers and the four surfaces of the ingot is 0.1mm. The gap between the rollers of each section of the secondary cooling zone and the outer arc of the ingot is 0.1mm. The distance between the last section of the secondary cooling zone water system (secondary cooling zone section 4) and the first roller of the straightening machine is 2.53m. The taper of the crystallizer copper tube is 2.0% / m, and the total length of the secondary cooling zone is 11.8 meters. When pouring steel, the temperature of the molten steel in the tundish is 1528℃, the pulling speed is 4.7m / min, the melting point of the protective slag is 1060℃, the consumption of protective slag is 0.482kg / t, the total water volume of the secondary cooling zone is 104.92 tons per hour, and 58.85 tons of ingots are produced per hour. The water volume of the secondary cooling zone is 1.78l / kg, which enables normal production. There is no leakage of steel from longitudinal cracks at corners or leakage before straightening when pouring steel. The steel composition of this embodiment is shown in Table 4 below;

[0037] Table 4: Composition of the steel described in Example 4 (wt%)

[0038] C Mn P S Si V Nb 0.23 1.37 0.025 0.025 0.31 0.033 0 0.25 1.39 0.033 0.026 0.32 0.035 0

[0039] In Table 4, the balance of the components is Fe and inevitable impurities.

[0040] Example 5: The method for preventing steel leakage in a high-speed billet continuous casting machine is specifically described as follows.

[0041] There are two rows of crystallizer foot rollers, four in each row, arranged on four sides, with a total of eight foot rollers in two rows. The gap between the surface of the crystallizer foot rollers and the four surfaces of the ingot is 0.1mm. The gap between the rollers of each section of the secondary cooling zone and the outer arc of the ingot is 0.1mm. The distance between the last section of the secondary cooling zone water system (secondary cooling zone section 4) and the first roller of the straightening machine is 2.53m. The taper of the crystallizer copper tube is 2.0% / m, and the total length of the secondary cooling zone is 11.8 meters. When pouring steel, the temperature of the molten steel in the tundish is 1525℃, the pulling speed is 5.0m / min, the melting point of the protective slag is 1053℃, the consumption of protective slag is 0.522kg / t, the total water volume of the secondary cooling zone is 115.32 tons per hour, and 62.61 tons of ingots are produced per hour. The water volume of the secondary cooling zone is 1.85l / kg, which enables normal production. There is no leakage of steel from longitudinal cracks at corners or leakage before straightening when pouring steel. The steel composition of this embodiment is shown in Table 5 below;

[0042] Table 5: Composition of the steel described in Example 5 (wt%)

[0043] C Mn P S Si V Nb 0.23 1.33 0.028 0.029 0.32 0.033 0 0.24 1.34 0.045 0.036 0.31 0.034 0

[0044] In Table 5, the balance of the components is Fe and inevitable impurities.

[0045] Example 6: The method for preventing steel leakage in a high-speed billet continuous casting machine is specifically described as follows.

[0046] There are two rows of crystallizer foot rollers, four in each row, arranged on four sides, with a total of eight foot rollers in two rows. The gap between the surface of the crystallizer foot rollers and the four surfaces of the ingot is 0.1mm. The gap between the rollers of each section of the secondary cooling zone and the outer arc of the ingot is 0.1mm. The distance between the last section of the secondary cooling zone water system (secondary cooling zone section 4) and the first roller of the straightening machine is 2.53m. The taper of the crystallizer copper tube is 2.0% / m, and the total length of the secondary cooling zone is 11.8 meters. When pouring steel, the temperature of the molten steel in the tundish is 1518℃, the pulling speed is 5.5m / min, the melting point of the protective slag is 1050℃, the consumption of protective slag is 0.532kg / t, the total water volume of the secondary cooling zone is 129.30 tons per hour, and 68.87 tons of ingots are produced per hour. The water volume of the secondary cooling zone is 1.88l / kg, which enables normal production. There is no leakage of steel from longitudinal cracks at corners or leakage before straightening when pouring steel. The steel composition of this embodiment is shown in Table 6 below;

[0047] Table 6: Composition of the steel described in Example 6 (wt%)

[0048] C Mn P S Si V Nb 0.24 1.37 0.028 0.033 0.33 0.032 0 0.25 1.41 0.023 0.026 0.42 0.035 0

[0049] In Table 6, the balance of the components is Fe and inevitable impurities.

[0050] Implementation effect statistics:

[0051] In steel companies, continuous casting is organized by ladle pouring, and the number of breakouts is calculated using the breakout rate. The definition of the breakout rate varies from company to company, making it difficult to standardize. This method defines the breakout rate as: breakouts / 10,000 tons of ingots, meaning the number of breakouts per 10,000 tons of ingots produced.

[0052] Before using this method, the steel leakage rate was 7.6 times / 10,000 tons, mainly due to steel leakage from longitudinal cracks in corners and steel leakage before straightening. With the implementation of the above-mentioned processes of this method, the steel leakage rate gradually decreased. According to the monthly output statistics, it was 5.5 times / 10,000 tons, 3.4 times / 10,000 tons, and 1.2 times / 10,000 tons respectively. After all the above-mentioned processes were adopted, the steel leakage rate can be stably controlled at 0 times / 10,000 tons.

Claims

1. A method for preventing steel breakout in a high-speed billet continuous casting machine, characterized in that: When the billet continuous casting machine is continuously casting, the casting speed is 3.5-5.5 m / min, the mold taper is 1.9-2.2% / m; the mold slag used has a melting point of 1055-1095°C, a melting speed of 25-33 seconds, and a viscosity of 0.09-0.13 Pa·s; when the casting speed is 3.5-4.0 m / min, the molten steel temperature in the tundish shall not exceed 1535°C; when the casting speed of the continuous casting machine is 4.0-5.5 m / min, the molten steel temperature in the tundish shall not exceed 1530°C; When the pulling speed is 3.5-4.5 m / min, the mold slag consumption is 0.42-0.50 kg / ton of steel; when the pulling speed is 4.5-5.5 m / min, the mold slag consumption is 0.45-0.55 kg / ton of steel; During the continuous casting, the gap between the surface of the mold foot roller and the four surfaces of the cast billet shall not exceed 2 mm, the gap between each section of the supporting rollers in the secondary cooling zone of the billet continuous casting machine and the outer arc of the arc template shall not exceed 2 mm, and the end of the water system in the secondary cooling zone of the billet continuous casting machine shall not be more than 3 meters away from the air cooling zone of the first roller of the tension straightener; The water system layout of the secondary cooling zone of the billet continuous casting machine must be full-process cooling, with at least 4 cooling sections, and each cooling section is not less than 1.5m in length.