Smelting method for reducing inclusions in RH vacuum furnace channel washing water steel

Abstract

The invention discloses a smelting method for reducing inclusions in RH vacuum furnace channel washing water, and belongs to the technical field of smelting. When the LF refining furnace is used for smelting the channel washing water, an aluminum source is not added into the channel washing water, and only heating treatment is carried out; when the RH vacuum furnace starts tank washing treatment, the light treatment mode is started firstly, the treatment mode is switched to the treatment mode after residual oxygen in the vacuum chamber is eliminated, the RH vacuum furnace completes carbon deoxidation tank washing operation, and the inclusions in the RH vacuum furnace channel washing water are reduced. According to the method, inclusions generated by deoxidation of the aluminum product are reduced, the purity of molten steel is improved, DS inclusions are obviously reduced, and meanwhile the risk of continuous casting flocculation flow is reduced; the use of aluminum products is reduced, so that the alloy cost is effectively reduced. The secondary refining period of the LF refining furnace is shortened, the power consumption per ton of steel is reduced, the generation of aluminum oxide inclusions is reduced, and the lime consumption of the LF refining furnace is indirectly reduced.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a smelting method for reducing inclusions in molten steel washed in an RH vacuum furnace. Background Technology

[0002] The RH process, also known as the vacuum circulation degassing method for molten steel, is a vacuum treatment technology for molten steel jointly developed in 1956 by Ruhrstahl and Heraeus in Germany. Its name is derived from the initials of the two companies' names. This technology uses argon gas to drive the molten steel to circulate between a vacuum chamber and a ladle. It utilizes the principle of hydrogen escape and the refinement of molten steel droplets under vacuum conditions to remove gases such as hydrogen, nitrogen, and oxygen.

[0003] Before each production run, RH vacuum refining requires coordinating the molten steel for tank washing to remove residual oxygen generated during baking and cooling of the steel within the vacuum chamber. According to "CN 104004887 B A method for reducing the high oxygen content in an RH vacuum chamber," ordinary molten steel, after deoxidation and heating, is first used as the tank washing steel to clean the vacuum chamber before subsequent vacuum refining of special steel grades. Similar existing processes typically involve adjusting the Al content in the tank washing steel to the upper limit of the internal composition control, then adding 0.015 wt%, heating it to a suitable temperature, and then transferring it to the RH vacuum furnace for tank washing. The aluminum lost during the tank washing process is replenished later in the RH vacuum furnace treatment. However, the existing process has the following drawbacks: 1. Repeated addition of aluminum products leads to significant alloy cost consumption, with an average ALs loss of approximately 0.045wt%; 2. The production process generates a large amount of alumina inclusions, contaminating the molten steel and increasing the risk of turbulence in continuous casting; 3. Due to the large amount of alumina inclusions generated, when the molten steel is returned to the LF refining furnace for secondary refining, 200-300 kg of lime needs to be added per 100 tons of molten steel to adjust the calcium-aluminum ratio of the slag and adsorb inclusions; 4. The extended refining and smelting cycle caused by removing inclusions leads to increased power consumption per ton of steel. Therefore, a targeted smelting method needs to be developed to solve the above problems. Summary of the Invention

[0004] In view of the above-mentioned prior art, the purpose of this invention is to provide a smelting method for reducing inclusions in molten steel washed in an RH vacuum furnace.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a smelting method for reducing inclusions in molten steel washed in an RH vacuum furnace, comprising the following steps: (1) When using the LF refining furnace to smelt the molten steel for washing the tank, no aluminum source is added to the molten steel for washing the tank; only the temperature is raised. After the treatment, the molten steel for washing the tank enters the RH vacuum furnace. (2) When the RH vacuum furnace starts the tank cleaning process, first start the light treatment mode to eliminate residual oxygen in the vacuum chamber; in the light treatment mode, control the vacuum degree to not exceed 20 kPa; (3) After the residual oxygen in the vacuum chamber is eliminated, switch to this treatment mode, control the vacuum degree to be no higher than 133KPa, and the total treatment time to be no less than 15min; then the RH vacuum furnace completes the carbon deoxidation washing tank operation to reduce the inclusions in the molten steel washed by the RH vacuum furnace.

[0006] Furthermore, in step (2), under light treatment mode: argon is selected as the circulating gas, and the circulating gas flow rate is 700±100NL / min.

[0007] Furthermore, in step (2), under light treatment mode, after the vacuum main valve is opened, the surface of the steel liquid in the large tank is kept slightly agitated, and treatment continues for 6±1 min. When the CO content in the gas is less than 0.3%, the oxygen value is measured to be ≤20 ppm, which is considered to be the elimination of residual oxygen in the vacuum chamber.

[0008] Furthermore, in step (3), under this processing mode, the circulating gas is 1500±100NL / min, and the aluminum alloy is replenished until the composition reaches the upper limit of the internal control.

[0009] Furthermore, in step (3), under this processing mode, when the vacuum level drops to <67pa, the deep vacuum time begins; to ensure that the vacuum chamber reaches the preheated state, the RH deep vacuum time is ≥8min.

[0010] The beneficial effects of this invention are: This invention, when using an LF refining furnace to smelt molten steel for washing, does not add an aluminum source to the molten steel; it only performs a temperature increase. When the RH vacuum furnace begins the washing process, it first starts in a light treatment mode. After the residual oxygen in the vacuum chamber is eliminated, it switches to this treatment mode. The RH vacuum furnace completes the carbon deoxidation washing operation, reducing inclusions in the molten steel. This method reduces inclusions generated by aluminum deoxidation, improves the purity of the molten steel, significantly reduces DS-type inclusions, and reduces the risk of continuous casting turbulence. It also reduces the use of aluminum products, thereby effectively reducing alloy costs, saving approximately 58 kg of aluminum granules per molten steel washing process. It shortens the secondary refining cycle of the LF refining furnace by approximately 10 minutes, reduces power consumption per ton of steel by 1.6 kWh / t, and indirectly reduces lime consumption in the LF refining furnace by 200-300 kg by reducing the formation of alumina inclusions. Detailed Implementation

[0011] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0012] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0013] The current conventional process involves smelting molten steel in an LF refining furnace for washing. First, the aluminum content is adjusted to the upper limit of the internal control + 0.015%, and then the temperature is raised to a suitable temperature before being hoisted into an RH vacuum furnace for washing. During the later stages of RH vacuum furnace treatment, aluminum lost during the washing process is replenished, with an average loss of about 0.045%. This results in multiple aluminum replenishments, leading to significant product consumption, and also generates a large amount of alumina inclusions during the production process.

[0014] This invention is applicable to the smelting of medium and high carbon steel. When smelting steels with low carbon content (<0.1%), such as cold heading steel 6A and ship plate steel B, only aluminum can be added to remove residual oxygen. Because removing residual oxygen in the vacuum chamber by using the carbon content of the steel can easily lead to violent carbon-oxygen reactions, slag overflow and overturning in the ladle, or even explosions, if too much residual oxygen is present, most washing tanks use aluminum to remove residual oxygen in the vacuum chamber. This invention, by switching the vacuum treatment mode and adjusting the circulating gas volume, ensures that the surface of the molten steel in the large ladle is only slightly agitated, thus ensuring that the carbon-oxygen reaction in the vacuum chamber proceeds slowly. This achieves the purpose of removing residual oxygen in the vacuum chamber while reducing the generation of inclusions.

[0015] This invention utilizes the fact that carbon has a greater affinity for oxygen than silicon and aluminum under vacuum conditions. The improvement lies in the fact that, under vacuum conditions, carbon in molten steel reacts with residual oxygen in the vacuum chamber to generate CO gas, thus achieving the tank cleaning function. The equilibrium reaction equation is: [C] + [O] = CO↑. By observing the splashing of molten steel in the vacuum chamber and the CO content in the gas analyzer, the RH vacuum furnace processing mode and circulating gas volume are adjusted to ensure that the splashing generated by the carbon-oxygen reaction in the vacuum chamber is within a normal safe range. Slight agitation of the molten steel surface in the ladle further promotes the reaction between the carbon in the molten steel and the residual oxygen in the vacuum chamber. This achieves deoxidation while ensuring that the violent carbon-oxygen reaction does not lead to slag overflow, ladle overturning, or even explosions that seriously threaten safe production.

[0016] The test materials used in the embodiments of the present invention, unless otherwise specified, are all conventional test materials in the art and can be purchased through commercial channels.

[0017] Example 1: A smelting method for reducing inclusions in molten steel washed in an RH vacuum furnace Taking the production of steel grade 45# as an example, the amount of molten steel used in this operation is 120 tons. The specific operating steps are as follows: When smelting molten steel in a LF refining furnace, no aluminum source is added to the molten steel; only heating is performed. After heating, the molten steel enters an RH vacuum furnace, and vacuum treatment begins. First, a light treatment mode is activated: the vacuum level is controlled at 6.7 kPa, argon is selected as the circulating gas, and the circulating gas flow rate is 700 ± 100 NL / min. After the vacuum main valve is opened, the carbon in the steel begins to react with the residual oxygen in the vacuum chamber, causing the molten steel to churn and splash. The splashing is observed, and the circulating gas flow rate is finely adjusted as needed to ensure that the surface of the molten steel in the large ladle is slightly agitated. At this point, the gas analyzer detects a CO content of approximately 30%. Treatment continues for 6 ± 1 min. When the gas analyzer detects a CO content of less than 0.3%, an oxygen value of ≤20 ppm is measured using a constant oxygen probe, indicating that the residual oxygen in the vacuum chamber has been cleaned. The process then switches to the main treatment mode: the vacuum level is controlled not to exceed 133 kPa, the circulating gas flow rate is gradually adjusted to 1400 NL / min, and aluminum alloy is added until the composition reaches the internal control limit. When the vacuum level continues to decrease to <67 Pa (at this point, approximately 3-4 minutes have passed since entering this processing mode), the deep vacuum time (also known as RH pure degassing time) begins. To ensure the vacuum chamber reaches a preheated state, the RH deep vacuum time is ≥8 minutes, and the overall processing time (from the start of vacuum processing to the end of vacuum processing) is ≥15 minutes. The RH vacuum furnace then completes the carbon deoxidation washing tank operation.

[0018] Estimate the carbon deoxidation dosage C and aluminum deoxidation dosage AL in molten steel respectively; the formula for calculating carbon deoxidation dosage C is as follows: C = (KM) / Q Wherein, K represents oxygen return in the vacuum chamber, which is generally 200-600 ppm; M represents residual oxygen at the end of deoxygenation, which is generally around 20 ppm; and Q represents the carbon-oxygen consumption coefficient of 1.333.

[0019] The slag flow in the vacuum chamber is large, and the estimated oxygen return value K in the vacuum chamber is 400 ppm. The estimated residual oxygen M at the end of deoxidation is 20 ppm. According to the calculation, the carbon deoxidation dosage C of the molten steel is 0.0436%.

[0020] The formula for calculating the amount of aluminum (AL) used for deoxidation is as follows: AL = (KM) / Q / D / B T 1000 Wherein, K represents oxygen return in the vacuum chamber, which is generally 200-600 ppm; M represents residual oxygen at the end of deoxidation, which is generally around 20 ppm; Q represents the aluminum-oxygen consumption coefficient of 0.89; D represents the aluminum particle grade; and B represents the aluminum particle yield.

[0021] The vacuum chamber has a large slag flow rate. The estimated oxygen return value K in the vacuum chamber is 400 ppm, the estimated residual oxygen M at the end of deoxidation is 20 ppm, the aluminum particle grade D is 98%, and the aluminum particle recovery rate B is 90%. It is calculated that the molten steel saved by smelting and washing the tank in a single smelting process is 58 kg of AL.

[0022] The composition of the molten steel was tested. The sampling times were after the molten steel was smelted in the LF refining furnace (before molten steel washing) and after the molten steel was smelted in the RH furnace (after molten steel washing). The content of the main elements in the molten steel was tested, and the results are shown in Table 1 below.

[0023] Table 1. Content of major elements in molten steel Microscopic inclusion content analysis of molten steel from the washing tank for casting and rolling showed no excessive levels of DS-type inclusions, resulting in a 100% pass rate for microscopic inclusion content. This invention reduces inclusions generated during the deoxidation of aluminum products, improves the purity of molten steel, and significantly reduces DS-type inclusions.

[0024] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that upon arrival of molten steel, processing begins directly in this processing mode, and the circulating gas flow rate can be quickly adjusted to 1200-1400 L / min. Since there is no carbon-oxygen reaction in the molten steel within the vacuum chamber, there is no need to monitor the waste analyzer data, nor is it necessary to control the processing mode to reduce molten steel spraying within the vacuum chamber.

[0025] Taking the production of steel grade 45# as an example, the amount of molten steel used in this operation is 120 tons. The specific operating steps are as follows: When smelting molten steel in an LF refining furnace, no aluminum source is added to the molten steel; only heating is performed. After heating, the molten steel enters an RH vacuum furnace, and vacuum treatment begins. Using this treatment mode: control the vacuum level to no higher than 133 kPa, adjust the circulating gas to 1400 NL / min, and add aluminum alloy until the composition reaches the upper limit of the internal control. When the vacuum level continues to decrease to <67 Pa (after approximately 3-4 minutes of this treatment mode), the deep vacuum time (also known as RH pure degassing time) begins. To ensure the vacuum chamber reaches a preheated state, the RH deep vacuum time is ≥8 minutes, and the overall treatment time (from the start to the end of vacuum treatment) is ≥15 minutes. The aluminum lost during the later stages of RH vacuum furnace treatment is replenished, with an average loss of 0.045% based on experience. This results in significant aluminum consumption from repeated replenishments and the generation of large amounts of alumina inclusions during production. The RH vacuum furnace completes the carbon deoxidation washing operation.

[0026] The composition of the molten steel was tested. The sampling times were after the molten steel was smelted in the LF refining furnace (before molten steel washing) and after the molten steel was smelted in the RH furnace (after molten steel washing). The content of the main elements in the molten steel was tested, and the results are shown in Table 2 below.

[0027] Table 2. Content of major elements in molten steel The secondary refining cycle, power consumption per ton of steel, and consumption of auxiliary materials such as lime and silicon carbide in the secondary smelting of the LF refining furnace were statistically analyzed for Example 1 and Comparative Example 1. The results are shown in Table 3.

[0028] Table 3 Secondary refining cycle, power consumption per ton of steel, and auxiliary material consumption for secondary smelting in the LF refining furnace As can be seen, using the method of Example 1, the secondary refining cycle of the LF refining furnace is shortened by approximately 10 minutes, and the power consumption per ton of steel is reduced by about 2 kWh / t. Due to the reduction in alumina inclusion formation, the lime consumption of the LF refining furnace is indirectly reduced by 100-250 kg. This invention solves the problems of a long secondary refining cycle in the LF refining furnace, high power consumption per ton of steel, and high consumption of auxiliary materials such as lime and silicon carbide in the secondary smelting process.

[0029] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A smelting method for reducing inclusions in molten steel washed in an RH vacuum furnace, characterized in that, Includes the following steps: (1) When using the LF refining furnace to smelt the molten steel for washing the tank, no aluminum source is added to the molten steel for washing the tank; only the temperature is raised. After the treatment, the molten steel for washing the tank enters the RH vacuum furnace. (2) When the RH vacuum furnace starts the tank cleaning process, first start the light treatment mode to eliminate residual oxygen in the vacuum chamber; in the light treatment mode, control the vacuum degree to not exceed 20 kPa; (3) After the residual oxygen in the vacuum chamber is eliminated, switch to this treatment mode, control the vacuum degree to be no higher than 133KPa, and the total treatment time to be no less than 15min; then the RH vacuum furnace completes the carbon deoxidation washing tank operation to reduce the inclusions in the molten steel washed by the RH vacuum furnace.

2. The smelting method for reducing inclusions in molten steel washed in an RH vacuum furnace according to claim 1, characterized in that, In step (2), under light treatment mode: argon is selected as the circulating gas, and the circulating gas flow rate is 700±100NL / min.

3. The smelting method for reducing inclusions in molten steel washed in an RH vacuum furnace according to claim 2, characterized in that, In step (2), under light treatment mode, after the vacuum main valve is opened, the surface of the steel liquid in the large tank is kept slightly agitated, and treatment continues for 6±1 min. When the CO content in the gas is less than 0.3%, the oxygen value is measured to be ≤20 ppm, which is considered to be the elimination of residual oxygen in the vacuum chamber.

4. The smelting method for reducing inclusions in molten steel washed in an RH vacuum furnace according to claim 1, characterized in that, In step (3), under this processing mode, the circulating gas is 1500±100NL / min, and the aluminum alloy is replenished until the composition reaches the upper limit of the internal control.

5. The smelting method for reducing inclusions in molten steel washed in an RH vacuum furnace according to claim 1, characterized in that, In step (3), under this processing mode, when the vacuum level drops to <67pa, the deep vacuum time begins; to ensure that the vacuum chamber reaches the preheated state, the RH deep vacuum time is ≥8min.

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