Method for reducing carbon segregation of continuous casting round billet

Abstract

The invention discloses a method for reducing carbon segregation of a continuous casting round billet, the carbon element content is 0.07%-0.11%, and the method comprises the following key steps: S1, electric furnace smelting: controlling the proportion of molten iron to be 40%-70%, providing a heat source for melting scrap steel by utilizing electrode power supply and carbon-oxygen reaction in the molten iron, decarburizing through the carbon-oxygen reaction, controlling the end-point carbon content of an electric furnace to be less than or equal to 0.06%, and controlling the end-point temperature of electric furnace smelting to be more than 1600 DEG C; s2, refining furnace treatment: molten steel is transferred to a refining furnace for desulfurization, components are adjusted to a target range, and the target requirement of the carbon content is lower limit + 0.01%; the molten steel is fed into VD vacuum treatment equipment for degassing treatment, and gas impurities in the molten steel are further removed; s3, continuous casting is conducted, specifically, the temperature of a tundish is controlled to be 20-30 DEG C for casting, and the pulling speed range is 0.70-2.20 m / min; s4, sampling is carried out; s5, analyzing; and S6, evaluating the effect. And the technical problem of serious carbon segregation of the continuous casting billet is solved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a method for reducing carbon segregation in continuously cast round billets. Background Technology

[0002] With the widespread application of steel pipe products in machinery manufacturing, automotive industry, oil and gas extraction, high-temperature and high-pressure vessels, and other fields, the requirements for the internal quality of steel are becoming increasingly stringent. Carbon segregation, a common internal quality defect in continuous casting, seriously affects the yield and performance of the products. The shortcomings of existing technologies include: steel pipe products exhibit a high carbon segregation index in the thickness direction, especially noticeable in medium and high carbon steel products. While some companies have applied pulsed electromagnetic stirring to improve the uniformity of billet composition, the results are still not ideal, and the equipment investment is enormous, with a single machine investment cost exceeding 20 million yuan.

[0003] Therefore, controlling carbon segregation has become a technical challenge to be addressed in the optimization of continuous casting round billet process. Summary of the Invention

[0004] The present invention aims to provide a method for reducing carbon segregation in continuously cast billets, thereby solving the technical problem of severe carbon segregation in continuously cast billets.

[0005] The technical solution of the present invention: A method for reducing carbon segregation in continuously cast round billets includes the following process steps: S1 electric arc furnace smelting: The proportion of molten iron is controlled at 40% to 60%, and the remaining part uses scrap steel as raw material; the scrap steel is melted by using the electrodes to provide electricity and the carbon-oxygen reaction in the molten iron to provide heat source, and decarburization is carried out through the carbon-oxygen reaction at the same time, and the carbon content at the end of the electric arc furnace is controlled to be ≤0.06%; the end temperature of the electric arc furnace smelting is controlled to be above 1600℃. S2 refining furnace treatment: The molten steel is transferred to the refining furnace for desulfurization and composition adjustment to the target range, with the carbon content target requirement being the lower limit +0.01%; the molten steel is then sent to the VD vacuum treatment equipment for degassing treatment to further remove gaseous impurities from the molten steel; S3 continuous casting: The tundish temperature is controlled at 20-30℃ for casting; the casting speed range is 0.70-2.20 m / min; S4 Sampling: Cut a 20-30mm length slice on the continuous casting billet, and use a drilling and cutting equipment to drill holes from the outside to the inside. Collect the cuttings from each hole separately and label them with numbers. S5 Analysis: Component analysis is performed using a CS analyzer, and the carbon content is recorded according to the assigned number; S6 Performance Evaluation: The segregation coefficient is calculated by measuring the carbon content to evaluate the uniformity of the billet composition.

[0006] Advantages of this invention: By improving process conditions and optimizing process parameters, the carbon segregation coefficient of this invention is controlled between 0.95 and 1.05, thereby ensuring the consistency of finished product performance. Moreover, it does not require increased investment or production costs, nor does it require the introduction of new equipment technology or the upgrading of existing equipment. Attached Figure Description

[0007] Figure 1 This is a graph showing the carbon element content of flow I in Example 1.

[0008] Figure 2 This is a graph showing the carbon element content of the process in process II compared to Example 1.

[0009] Figure 3 This is a graph showing the carbon element content of flow I in Example 2.

[0010] Figure 4 This is a graph showing the carbon element content of the process II flow compared to Example 2. Detailed Implementation

[0011] The following description is based on an example.

[0012] Example 1: A method for reducing carbon segregation in continuously cast round billets Implementation conditions: The composition of molten iron is normal, the raw and auxiliary materials used are normal, and all production equipment is operating normally; Process route: 90t electric furnace - 100t ladle furnace - 100t VD furnace - four-strand arc continuous casting machine; Production specifications: φ280mm; Steel grade: 09MnCrNb steel, carbon content range: 0.07% to 0.11%.

[0013] Implementation process steps: S1 electric arc furnace smelting: A 90t electric arc furnace is used, with 72.56t of hot iron added, accounting for 60.08% of the total. 48.22t of scrap steel (including social scrap steel, self-produced scrap steel, and scrap steel slag) is used as raw material. The tapping temperature of the electric arc furnace is 1615℃, the carbon content at the tapping endpoint is 0.052%, and the tapping amount is 112.6t. During the tapping operation, 650kg of lime, 350kg of refining slag, 120kg of aluminum blocks, and a quantity of silicon manganese alloy, ferrosilicon, low-carbon manganese, and low-carbon ferrochrome are added. After tapping, 10kg of carbon powder is added and the furnace is stirred with argon gas for 5 minutes before the argon gas is turned off and the furnace is ready to be hoisted.

[0014] S2 Refining Furnace Processing: Transfer molten steel to the refining furnace, turn on argon gas, add 20kg of calcium carbide, and then power on. Continuously add 20kg each of carbon powder and silicon carbide mixture through the furnace door using an iron shovel. Adjust the argon blowing intensity according to the sound of the electric arc. After 10 minutes of power on, the temperature is measured at 1570℃, and a sample is taken for analysis; the carbon content is 0.065%. Power on and adjust the composition to the target range according to the V4 composition by adding various alloys. Repeat V4 by continuously adding 10kg each of carbon powder and silicon carbide mixture through the furnace door using an iron shovel. After 10 minutes of power on, the temperature is measured at 1603℃, and a sample is taken for analysis; the carbon content is 0.085%, and other alloy components meet the requirements. Send the molten steel into VD vacuum treatment, maintain below 67Pa for 10 minutes to break the vacuum, and measure the temperature at 1575℃. Feed in 120m of pure calcium wire, take a sample, and add 50kg of covering agent. Soft blow for 12 minutes; the carbon content is 0.093%, and other components are qualified. The temperature is measured at 1568℃, and the ladle is lifted.

[0015] S3 Continuous Casting: Produces φ280mm specification 09MnCrNb steel. The crystallizer electric stirring current intensity is 150A, the frequency is 2.5Hz, and the stirring method is alternating bidirectional, forward 8s-stop 3s-reverse 8s; the end electric stirring current intensity is 500A, the frequency is 8.0Hz, and the stirring method is continuous unidirectional; the secondary cooling water ratio setting is 0.65L / kg; the casting speed is 1.35m / min, and the superheat is 22~25℃. Figure 1 Experiment I in this invention is based on the process described in Example 1 of this invention. Figure 2 The experimental flow II follows the original process, marking the billet during the casting process to ensure that samples are taken from the same location in both flow I and flow II.

[0016] S4 Sampling: Cut the continuously cast billet into slices with a thickness of 20-30mm. Use a drilling and chip-making device to drill holes from the outside in at a depth of about 17-18mm. Collect the chips from each hole separately and label them.

[0017] S5 Analysis: Component analysis is performed using a CS analyzer, and the carbon content is recorded according to the assigned number.

[0018] S6 Effectiveness Evaluation: The analysis results are shown in Table 1 and Figure 1 In Table 1: Stream I represents the process of this invention, with a carbon segregation coefficient calculated to be 0.97–1.04; Stream II represents the comparative process, with a carbon segregation coefficient calculated to be 0.88–1.12. Figure 1 The process described in this invention results in a relatively uniform carbon content, with a minimum of 0.096%, a maximum of 0.103%, and a maximum carbon range of 0.007%, indicating a small deviation. Figure 2 The process used for comparison shows a large deviation in carbon content, with the carbon content distribution pattern resembling an "M" shape. The carbon content is lower at the edge of the billet and highest at 1 / 4 of the billet, with a minimum of 0.08% and a maximum of 0.104%, and the maximum carbon range is 0.024%.

[0019] Conclusion: The process in Example 1 can effectively reduce carbon segregation in continuously cast round billets.

[0020] Table 1 Comparison of carbon and sulfur analysis data between Example 1 and comparative processes .

[0021] Example 2: A method for reducing carbon segregation in continuously cast round billets Implementation conditions: The composition of molten iron is normal, the raw and auxiliary materials used are normal, and all production equipment is operating normally; Process route: 90t electric furnace - 100t ladle furnace - 100t VD furnace - four-strand arc continuous casting machine; Production specifications: φ280mm; Steel grade: 09MnCrNb steel, carbon content range: 0.07% to 0.11%.

[0022] Implementation process steps: S1 electric arc furnace smelting: A 90t electric arc furnace is used, with 76.06t of hot iron added, accounting for 62.36% of the total iron content. 45.91t of scrap steel (including social scrap steel, self-produced scrap steel, and scrap steel slag) are used as raw materials. The tapping temperature of the electric arc furnace is 1608℃, the carbon content at the tapping endpoint is 0.046%, and the tapping volume is 118.5t. During the tapping operation, 650kg of lime, 350kg of refining slag, 130kg of aluminum blocks, and a quantity of silicon manganese alloy, ferrosilicon, low-carbon manganese, and low-carbon ferrochrome are added. After tapping, 15kg of carbon powder is added and the furnace is stirred with argon gas for 7 minutes before the argon gas is turned off and the furnace waits for the ladle to be hoisted.

[0023] S2 Refining Furnace Processing: Transfer molten steel to the refining furnace, turn on argon gas, add 20kg of calcium carbide, and then power on. Continuously add 20kg each of carbon powder and silicon carbide mixture through the furnace door using an iron shovel. Adjust the argon blowing intensity according to the sound of the electric arc. After 12 minutes of power on, the temperature is measured at 1572℃, and a sample is taken for analysis; the carbon content is 0.068%. Power on again and adjust the composition to the target range according to the V4 composition by adding various alloys. Repeat V4 by continuously adding 10kg each of carbon powder and silicon carbide mixture through the furnace door using an iron shovel. After 10 minutes of power on, the temperature is measured at 1608℃, and a sample is taken for analysis; the carbon content is 0.083%, and other alloy components meet the requirements. Send the molten steel into VD vacuum treatment, maintain below 67Pa for 11.5 minutes to break the vacuum, and measure the temperature at 1582℃. Feed in 120m of pure calcium wire, take a sample, and add 50kg of covering agent. Soft blow for 13 minutes; the carbon content is 0.096%, and other components are qualified. The temperature is measured at 1571℃, and the ladle is lifted.

[0024] S3 Continuous Casting: Produces φ280mm specification 09MnCrNb steel. The crystallizer electric stirring current intensity is 150A, the frequency is 2.5Hz, and the stirring method is alternating bidirectional, forward 8s-stop 3s-reverse 8s; the end electric stirring current intensity is 500A, the frequency is 8.0Hz, and the stirring method is continuous unidirectional; the secondary cooling water ratio setting is 0.62L / kg; the casting speed is 1.30m / min, and the superheat is 21~27℃. Figure 3 The process of this invention is tested in the experimental I flow experiment. Figure 4 For the original process of the II-flow experiment, the billet is marked during the billet pulling process to ensure that samples are taken from the same location for both the I-flow and II-flow.

[0025] Table 2 Comparison of carbon and sulfur analysis data between Example 2 and the comparative process .

[0026] S4 Sampling: Cut the continuously cast billet into slices with a thickness of 20-30mm. Use a drilling and chip-making device to drill holes from the outside in at a depth of about 17-18mm. Collect the chips from each hole separately and label them.

[0027] S5 Analysis: Component analysis is performed using a CS analyzer, and the carbon content is recorded according to the assigned number.

[0028] S6 Effectiveness Evaluation: The analysis results are shown in Table 2. Figure 3 , Figure 4 In Table 2: Stream I represents the process of this invention, with a carbon segregation coefficient calculated to be 0.99–1.02; Stream II represents the comparative process, with a carbon segregation coefficient calculated to be 0.86–1.09. Figure 3 The process described in this invention results in a relatively uniform carbon content, with a minimum of 0.097%, a maximum of 0.101%, and a maximum carbon range of 0.004%, indicating a small deviation. Figure 4 The process used for comparison shows a large deviation in carbon content, with the carbon content distribution pattern resembling an "M" shape. The carbon content is lower at the edge of the billet and highest at 1 / 4 of the billet, with a minimum value of 0.082% and a maximum value of 0.104%, and the maximum carbon range is 0.022%.

[0029] Conclusion: The process in Example 2 can effectively reduce carbon segregation in continuously cast round billets.

Claims

1. A method for reducing carbon segregation in continuously cast round billets, characterized in that... The process includes the following steps: S1 electric arc furnace smelting: The proportion of molten iron is controlled at 40% to 60%, and the remaining part uses scrap steel as raw material; the scrap steel is melted by using the electrodes to provide electricity and the carbon-oxygen reaction in the molten iron to provide heat source, and decarburization is carried out through the carbon-oxygen reaction at the same time, and the carbon content at the end of the electric arc furnace is controlled to be ≤0.06%; the end temperature of the electric arc furnace smelting is controlled to be above 1600℃. S2 refining furnace treatment: The molten steel is transferred to the refining furnace for desulfurization and composition adjustment to the target range, with the carbon content target requirement being the lower limit +0.01%; the molten steel is then sent to the VD vacuum treatment equipment for degassing treatment to further remove gaseous impurities from the molten steel; S3 continuous casting: The tundish temperature is controlled at 20-30℃ for casting; the casting speed range is 0.70-2.20 m / min; S4 Sampling: Cut a 20-30mm length slice on the continuous casting billet, and use a drilling and cutting equipment to drill holes from the outside to the inside. Collect the cuttings from each hole separately and label them with numbers. S5 Analysis: Component analysis is performed using a CS analyzer, and the carbon content is recorded according to the assigned number; S6 Performance Evaluation: The segregation coefficient is calculated by measuring the carbon content to evaluate the uniformity of the billet composition.

Images