A method for preventing cold steel from sticking in vacuum tank during RH refining process and its application

Abstract

The present invention discloses a method and application for preventing cold steel from sticking in a vacuum tank during RH refining, and belongs to the technical field of iron and steel metallurgy refining. The method of the present invention combines the analysis of thermodynamic and kinetic conditions of vacuum degassing, and by matching the relationship between the vacuum degree, circulating gas flow rate and waste gas volume in different degassing stages, the problem of excessive splashing of molten steel in the RH vacuum process is avoided to the greatest extent, so that the splashing droplets are only distributed in the high-temperature area at the lower part of the RH vacuum tank, which greatly reduces the possibility of splashing molten steel condensing into cold steel when it encounters cold. The method for preventing cold steel from sticking in a vacuum tank during RH refining is used in the preparation of products such as steel and steel billets. Since there is no risk of cold steel nodules falling off, the molten steel is cleaner, the composition control is more precise, and the obtained product has better performance and higher stability.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy refining, and more specifically, relates to a method for preventing cold steel from sticking in a vacuum tank during RH refining and its application. Background Art

[0002] RH refining has become an essential process for high-end products. In the existing production process, the molten steel splashes a lot during the vacuum degassing process due to the degassing reaction. The connection position of the RH upper tank and the lower tank needs to be connected with a flange. Since the flange is a steel product, a water cooling device needs to be added around it to avoid flange deformation due to service conditions. In actual production, the temperature of the joint position is low due to water cooling. The splashed molten steel solidifies and adheres to the upper and lower positions of the joint due to the quenching. With the increase of RH refining furnaces, the cold steel at the joint position accumulates thicker and thicker, and there is a risk of falling off at any time. The overall falling of the cold steel at the joint will lead to abnormal composition of the molten steel, which seriously affects the production rhythm matching and RH efficient production in the steelmaking process. At the same time, the falling of cold steel nodules will also affect the cleanliness and temperature of the molten steel, and affect the stability of the production process control. Therefore, the RH refining furnace needs to wash the cold steel after a certain number of furnaces, which affects the production rhythm, reduces the operation rate of the RH refining furnace, and greatly increases the difficulty of production organization and production cost.

[0003] The existing methods for treating cold steel in the RH vacuum refining process mainly include (1) post-treatment of cold steel, which is basically based on oxygen blowing and melting, or oxygen blowing plus fuel, such as patent CN111549203A, but it is not suitable for steel types with relatively high requirements for non-metallic oxide inclusions, and the oxygen blowing operation is not conducive to the control of inclusions in steel; (2) The main methods for preventing cold steel slag and molten steel from solidifying and adhering in the vacuum tank are: a. Changing the internal structure of the vacuum tank to increase the temperature of the refractory near the water-cooled flange to avoid the splashing molten steel from pre-cooling and condensing inside the vacuum tank. This method has the problem of high equipment modification cost, such as patent CN110408743A; b. Controlling the vacuum in the early stage of vacuum blowing The vacuum degree can alleviate the splashing of molten steel. If only the vacuum degree is considered without combining the waste gas volume and the circulation flow rate during the degassing process, the intensity of the reaction cannot be effectively controlled. Theoretically, the splashing problem of molten steel cannot be solved, such as patents CN107828938A and CN102443682A; c. Nitrogen is added to the molten steel before vacuum treatment, so that a large amount of high-temperature gas escapes during the RH refining process, and the cold steel in the vacuum tank is heated and melted into the molten steel, such as CN111979377A. Since it takes a lot of time to denitrify the molten steel, this method will obviously increase the RH treatment time. In addition, the escape of a large amount of gas will cause more serious molten steel splashing, which is not conducive to the prevention and treatment of cold steel nodules. Summary of the invention

[0004] 1. Problem to be solved

[0005] Aiming at the problem of cold steel sticking in a vacuum tank during RH refining, the present invention provides a method for preventing cold steel sticking in a vacuum tank during RH refining, which can avoid excessive splashing of molten steel during RH refining and reduce the probability of splashing molten steel condensing into cold steel when it is cold. The method can be applied to the preparation of steel.

[0006] 2. Technical solution

[0007] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0008] Before RH refining vacuum treatment, the oxygen content of molten steel is controlled to be 10-25ppm, the carbon content is 3200-8000ppm, the nitrogen content is not more than 100ppm, the ladle top slag is reducing slag, the sum of TFe and MnO content in the slag is ≤3%, and the product of carbon and oxygen is 80000ppm 2 -200000ppm 2 If the carbon-oxygen product is too high, the reaction will be violent and the molten steel will easily splash. If the carbon-oxygen product is too low, the decarburization and deoxidation efficiency will be low, affecting the quality of the molten steel.

[0009] The gas flow rate is controlled during vacuum refining as follows:

[0010] The gas flow rate during 0-16min is 180-220Nl / min, the gas flow rate during 17-24min is 270-340Nl / min, and the gas flow rate during 25min to breaking through the air is 600-1000Nl / min.

[0011] Control vacuum degree and exhaust gas volume as follows:

[0012] The vacuum refining process lasts 0-5min, the vacuum degree of the vacuum tank is 85KPa~60KPa, and the waste gas volume is controlled at 710~3200kg / h;

[0013] The vacuum refining process lasts 6-10 minutes, the vacuum degree of the vacuum tank is 59KPa~30KPa, and the waste gas volume is controlled at 1000~3000kg / h;

[0014] The vacuum refining process lasts 11-13 minutes, the vacuum degree of the vacuum tank is 29Pa~18KPa, and the waste gas volume is controlled at 900-2100kg / h;

[0015] The vacuum refining process lasts 14-16 minutes, the vacuum degree of the vacuum tank is 17KPa~8KPa, and the waste gas volume is controlled at 500~300kg / h;

[0016] The vacuum refining process lasts 16-18 minutes, the vacuum degree of the vacuum tank is 7KPa~6KPa, and the waste gas volume is controlled at 300~330kg / h;

[0017] The vacuum refining process lasts 19-21 minutes, the vacuum degree of the vacuum tank is 5KPa~3KPa, and the waste gas volume is controlled at 260~340kg / h;

[0018] The vacuum refining process lasts 22-24 minutes, the vacuum degree of the vacuum tank is 2KPa~0.2KPa, and the waste gas volume is controlled at 240~320kg / h;

[0019] The vacuum refining process takes 25 minutes until the air breaks, the vacuum degree of the vacuum tank is less than 0.1KPa, and the waste gas volume is ≤300kg / h.

[0020] During the vacuum refining process, the opening area of ​​the test observation hole near the vacuum main valve is controlled, and the start and stop of the multi-stage vacuum pump are coordinated to achieve online adjustment and control of the vacuum degree in the vacuum tank.

[0021] During the RH refining process, carbon and oxygen react violently to generate CO during carbon deoxidation, and a large amount of gas is generated, causing molten steel to splash. Since the temperature of the upper part of the vacuum chamber is relatively low, the splashed molten steel is easily condensed in the water cooling area to form nodules. Therefore, the present invention combines the thermodynamic and kinetic conditions of vacuum degassing (N, H, O) and analyzes the relationship between the vacuum degree, circulating gas flow rate and waste gas volume in different degassing stages to avoid the problem of excessive splashing of molten steel during the RH vacuum process to the greatest extent, so that the splashing droplets are only distributed in the high-temperature area at the bottom of the RH vacuum tank, which greatly reduces the possibility of splashing molten steel condensing into cold steel when it encounters cold, reduces the frequency of RH vacuum tank nodules and tank washing, improves the operating rate of RH equipment, and reduces costs and increases efficiency.

[0022] The present invention controls the vacuum degree and waste gas volume during the stage to achieve control of the CO generation rate. The greater the vacuum degree, the more intense the reaction. In the early stage of refining, the CO generation speed is fast and the generation amount is large. Therefore, the waste gas volume is adjusted. On the one hand, it is to avoid excessive gas pressure due to the generation of a large amount of gas in the vacuum tank, which inhibits the continued reaction and discharges the generated waste gas containing a large amount of CO. On the other hand, the vacuum degree is controlled within a lower range to reduce the intensity of CO generation. As the reaction proceeds, oxygen is consumed and the CO generation rate decreases. Therefore, the vacuum degree of the vacuum tank is increased to make the reaction proceed in the direction of the product and increase the decarburization rate. The control of the vacuum degree and the waste gas volume is adjusted according to the CO generation rate during the refining process. Further, the product of carbon and oxygen in the molten steel is controlled to be 80,000 ppm. 2 -200000ppm 2 , in order to achieve a balance between the depth of carbon deoxidation and the intensity of the reaction. While ensuring carbon deoxidation, the generation rate of CO is controlled to avoid the problem of excessive splashing of molten steel during the RH vacuum process to the greatest extent, so that the splashing droplets are only distributed in the high-temperature area at the bottom of the RH vacuum tank, greatly reducing the possibility of splashing molten steel condensing into cold steel when it encounters cold.

[0023] The method for preventing cold steel from sticking in the vacuum tank during RH refining is used in the preparation of steel, steel billets and other products. Since there is no risk of cold steel nodules falling off, the molten steel is cleaner, the composition control is more precise, and the product performance is better and more stable. In addition, the frequency of RH vacuum tank nodule removal and tank washing is reduced, the operating rate of RH equipment is improved, and the production efficiency is improved.

[0024] 3. Beneficial effects

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention combines the thermodynamic and kinetic conditions of vacuum degassing and matches the relationship between the vacuum degree, circulating gas flow rate and exhaust gas volume in different degassing stages to avoid the problem of excessive splashing of molten steel during the RH vacuum process to the greatest extent, so that the splashing droplets are only distributed in the high-temperature area at the lower part of the RH vacuum tank, greatly reducing the possibility of splashing molten steel condensing into cold steel when it encounters cold;

[0027] (2) The composition of the product obtained by the method of the present invention is more accurately controlled, and the product has better performance and higher stability;

[0028] (3) The present invention reduces the frequency of RH vacuum tank tumor removal and tank cleaning, improves the operating rate of RH equipment, and reduces costs and increases efficiency. DETAILED DESCRIPTION

[0029] The following illustrates exemplary embodiments of the present invention that can be implemented. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention, it should be understood that other embodiments can be implemented and that various changes can be made to the present invention without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but is merely for illustration and does not limit the description of the characteristics and features of the present invention, in order to propose the best mode for performing the present invention, and is sufficient to enable those skilled in the art to implement the present invention. Therefore, the scope of the present invention is limited only by the appended claims.

[0030] The technical scheme is further explained by taking the example of producing medium-high carbon steel in a 120-ton RH refining furnace of a certain factory. The cold steel and aluminum attenuation of the vacuum tanks of the four newly-launched RH vacuum tanks after using 25 furnaces are compared and analyzed. Among them, vacuum tanks No. 1-3 adopt the technical scheme of the present invention. The specific situation is: the test steel types are 50Mn and S48C. Before the RH refining vacuum treatment, the oxygen content of the molten steel is 11-24ppm, the carbon content is 3200-8000ppm, and the product of carbon and oxygen is 80000ppm. 2 -200000ppm 2 , the ladle top slag is reducing slag, and the sum of TFe and MnO content in the slag is ≤2.7%;

[0031] During the vacuum refining process, the gas flow rate is increased from 0 to 16 minutes to 180-220 Nl / min, from 17 to 24 minutes to 270-340 Nl / min, and from 25 minutes to breaking the vacuum to 600-1000 Nl / min.

[0032] The vacuum refining process lasts 0-5min, the vacuum degree of the vacuum tank is 85KPa~60KPa, and the waste gas volume is controlled at 710~3200kg / h;

[0033] The vacuum refining process lasts 6-10 minutes, the vacuum degree of the vacuum tank is 59KPa~30KPa, and the waste gas volume is controlled at 1000~3000kg / h;

[0034] The vacuum refining process lasts 11-13 minutes, the vacuum degree of the vacuum tank is 29Pa~18KPa, and the waste gas volume is controlled at 900-2100kg / h;

[0035] The vacuum refining process lasts 14-16 minutes, the vacuum degree of the vacuum tank is 17KPa~8KPa, and the waste gas volume is controlled at 500~300kg / h;

[0036] The vacuum refining process lasts 17-18 minutes, the vacuum degree of the vacuum tank is 7KPa~6KPa, and the waste gas volume is controlled at 300~330kg / h;

[0037] The vacuum refining process lasts 19-21 minutes, the vacuum degree of the vacuum tank is 5KPa~3KPa, and the waste gas volume is controlled at 260~340kg / h;

[0038] The vacuum refining process lasts 22-24 minutes, the vacuum degree of the vacuum tank is 2KPa~0.2KPa, and the waste gas volume is controlled at 240~320kg / h;

[0039] The vacuum refining process takes 25 minutes until the air breaks, the vacuum degree of the vacuum tank is less than 0.1KPa, and the waste gas volume is ≤300kg / h.

[0040] The online regulation and control of the vacuum degree in the vacuum tank is achieved by controlling the opening area of ​​the test observation hole near the vacuum main valve and coordinating the start and stop of the multi-stage vacuum pump.

[0041] Vacuum tank No. 4 adopts the conventional vacuuming scheme, that is, it reaches the ultimate vacuum (less than 100Pa) at the fastest speed, and breaks the air after completing the degassing task. The specific conditions of the 4 vacuum tanks after 25 furnace tests are shown in the following table.

[0042] Table 1 Comparison of Experiments of Examples 1-3

[0043] Serial number Cold steel condition of tank body Aluminum attenuation rate (outbound / inbound) Is it necessary to wash the tank? Example 1 No obvious cold steel bonding 0.74 no Example 2 No obvious cold steel bonding 0.80 no Example 3 No obvious cold steel bonding 0.77 no Comparative Example 1 Cold steel bonding is serious 0.61 need

[0044] It can be seen from the results of the embodiment that after adopting the technical solution, the cold steel situation in the vacuum tank is well controlled, the aluminum attenuation rate in the vacuum treatment process is stably controlled, the tank washing frequency is low, the continuous operation rate of the RH refining furnace is high, and costs are reduced and efficiency is increased.

Claims

1. A method for preventing cold steel from sticking in a vacuum tank during RH refining, characterized in that: Control vacuum degree and exhaust gas volume as follows: The vacuum refining process lasts 0-5min, the vacuum degree of the vacuum tank is 85KPa~60KPa, and the waste gas volume is controlled at 710~3200kg / h; The vacuum refining process lasts 6-10 minutes, the vacuum degree of the vacuum tank is 59KPa~30KPa, and the waste gas volume is controlled at 1000~3000kg / h; The vacuum refining process lasts 11-13 minutes, the vacuum degree of the vacuum tank is 29Pa~18KPa, and the waste gas volume is controlled at 900-2100kg / h; The vacuum refining process lasts 14-16 minutes, the vacuum degree of the vacuum tank is 17KPa~8KPa, and the waste gas volume is controlled at 500~300kg / h; The vacuum refining process lasts 17-18 minutes, the vacuum degree of the vacuum tank is 7KPa~6KPa, and the waste gas volume is controlled at 300~330kg / h; The vacuum refining process lasts 19-21 minutes, the vacuum degree of the vacuum tank is 5KPa~3KPa, and the waste gas volume is controlled at 260~340kg / h; The vacuum refining process lasts 22-24 minutes, the vacuum degree of the vacuum tank is 2KPa~0.2KPa, and the waste gas volume is controlled at 240~320kg / h; The vacuum refining process lasts 25 minutes until the air is broken, the vacuum degree of the vacuum tank is less than 0.1KPa, and the waste gas volume is ≤300kg / h; During the vacuum refining process, the gas flow rate is controlled as follows: 0-16min boost gas flow rate is 180-220NL / min, 17-24min boost gas flow rate is 270-340NL / min, 25min to air breaking boost gas flow rate is 600-1000NL / min; Before RH refining vacuum treatment, the product of carbon and oxygen in molten steel is controlled to 80000ppm 2 -200000ppm 2 , the oxygen content is 10~25ppm, and the carbon content is 3200~8000ppm.

2. The method for preventing cold steel from sticking in a vacuum tank during RH refining according to claim 1, characterized in that: The nitrogen content of molten steel is not more than 100ppm.

3. The method for preventing cold steel from sticking in a vacuum tank during RH refining according to claim 2, characterized in that: During the vacuum refining process, the opening area of ​​the test observation hole near the vacuum main valve is controlled, and the start and stop of the multi-stage vacuum pump are coordinated to achieve online adjustment and control of the vacuum degree in the vacuum tank.

4. The method for preventing cold steel from sticking in a vacuum tank during RH refining according to claim 3, characterized in that: The ladle top slag is reducing slag, and the sum of TFe and MnO contents in the slag is ≤3%.

5. An application of the method for preventing cold steel from sticking in a vacuum tank during RH refining process according to any one of claims 1 to 4, characterized in that: Used in steel preparation technology.