IF steel RH decarburization final oxygen automatic control method

Abstract

The invention discloses an IF steel RH decarburization final oxygen automatic control method, and belongs to the field of steelmaking production. The method comprises the following steps: controlling oxygen in a converter: adding carbon to control oxygen according to tapping, controlling initial free oxygen before RH treatment to ensure that RH decarburization end point oxygen is in a proper range, removing the carbon adding amount of ejection steel, and executing a carbon adding and oxygen controlling measure in the tapping process; the decarburization efficiency is improved, specifically, after the diameter of the dip pipe with the pipe diameter being 850 mm is expanded, the RH ring flow is increased, so that the decarburization time is controlled, and the decarburization efficiency under the low free oxygen RH condition is guaranteed; the content of free oxygen in the molten steel is monitored in real time, and when it is monitored that the amount of steel ladle carbon removed by the free oxygen in the molten steel is insufficient, the decarburization reaction is promoted in a top lance forced oxygen supply decarburization mode. According to the method, modeling automatic control is achieved by establishing a precise calculation model of steel ladle carbon and free oxygen and calculating the OB oxygen increasing amount and the carbon adding amount, and IF steel RH decarburization end point oxygen can be effectively controlled.

Description

Technical Field

[0001] The invention relates to steelmaking production, in particular to an automatic control method for final oxygen of RH decarburization of IF steel. Background Art

[0002] The control of the final oxygen of IF steel decarburization by RH is mainly achieved by controlling the carbon-oxygen accumulation in the converter in large steel mills to improve the free oxygen of RH after decarburization. However, the effect of converter re-blowing is very demanding. The carbon-oxygen accumulation of Ma Steel's converter is controlled at 15-16, and the average oxygen when blowing is stopped is 420ppm. Due to the appropriate carbon-oxygen content, the final oxygen of IF steel decarburization is mainly controlled by natural decarburization by RH, and the final oxygen of decarburization is controlled at 260ppm.

[0003] At Baoshan Base of Shanghai Baosteel, during the treatment process, the temperature of the vacuum tank is increased by top gun coal oxygen combustion baking, the temperature drop of the treatment is reduced, and the amount of oxygen in OB temperature rise is reduced to achieve the purpose of reducing the final oxygen of decarburization. Due to the limited temperature, the carbon addition ratio is low. At the same time, the coal oxygen baking has a certain impact on the service life of the top gun sealing channel and the sealing airbag. Since the flame heating cannot exclude the cold steel in the vacuum tank from being melted into the molten steel to increase the free oxygen of the molten steel. When the carbon is high and the oxygen is low, the OB forced oxygen supply measure is adopted, and the decarburization final oxygen control performance is 280ppm.

[0004] Wuhan Iron and Steel Corporation controls the final oxygen content of decarburization in IF steel smelting with the main control method of not exceeding 450ppm. The average oxygen before treatment is 550ppm, and the ladle carbon is 458ppm. Due to the large temperature drop during treatment, the average OB oxygen content is 145Nm 3 The average final oxygen of decarburization is 380ppm. The final oxygen of decarburization is mainly controlled by not adding aluminum in the RH decarburization process. Due to the limitation of large temperature drop in the treatment process, the OB oxygen increase is mainly for heating, and the final oxygen of decarburization is at a relatively high level.

[0005] Regarding the control of the endpoint oxygen of IF steel RH decarburization, the mainstream view is that the lower the endpoint oxygen, the more conducive it is to improving the purity of molten steel, but relatively low endpoint oxygen places high demands on the RH decarburization rate and control difficulty. At the same time, there is currently no method for accurately calculating the endpoint oxygen of decarburization in large steel mills. How to combine the relationship between oxygen and carbon to calculate the amount of oxygen required for RH decarburization or the amount of oxygen added to control carbon, there is currently no successful application case. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide an automatic control method for final oxygen in RH decarburization of IF steel.

[0007] Technical solution: A method for automatic control of final oxygen in RH decarburization of IF steel, comprising the following steps:

[0008] S1. Converter oxygen control: The converter controls oxygen according to the carbon addition during steel tapping. By controlling the initial free oxygen before RH treatment, ensure that the RH decarburization endpoint oxygen is within the appropriate range, remove the carbon addition amount during steel tapping, and implement carbon addition and oxygen control measures during steel tapping;

[0009] S2. Improve decarburization efficiency: After the immersion pipe with a diameter of 850mm is expanded, the RH circulation flow rate is increased, so that the decarburization time is controlled to ensure the decarburization efficiency at a lower free oxygen RH;

[0010] S3. RH controls the end point oxygen of decarburization: the free oxygen content in the molten steel is monitored in real time. When it is detected that the amount of free oxygen in the molten steel to remove carbon from the ladle is insufficient, the decarburization reaction is promoted by forced oxygen supply and decarburization through the top gun.

[0011] Preferably, during the forced oxygen supply decarburization process of the top gun, the OB oxygen increase amount is calculated as follows: by analyzing the relationship between ladle carbon, free oxygen and the final decarburization endpoint oxygen in the natural decarburization furnace. According to the ladle carbon and oxygen before treatment, the required OB oxygen increase amount is calculated with 200ppm as the target and 230ppm as the target;

[0012] (1) Calculate the final oxygen of decarburization = (333- ladle carbon × 0.816 + 0.398 × free oxygen before treatment);

[0013] (2) Calculate the final oxygen of decarburization - target final oxygen of decarburization < -20;

[0014] (3) 0B oxygen increase = (target decarburization final oxygen - calculated decarburization final oxygen) ÷ 2;

[0015] (4) Calculate the final oxygen of decarbonization - target final oxygen of decarbonization>0;

[0016] (5) Carbon addition amount = (calculated decarburization final oxygen - target decarburization final oxygen) ÷ 100 × 70;

[0017] (6) When the ladle sample is poor, the fitting relationship between ladle carbon and free oxygen is ladle carbon = 558.9-0.3923 × free oxygen before treatment, and the ladle carbon content is calculated based on the free oxygen;

[0018] The OB oxygen content and the amount of carbon addition and oxygen control are calculated based on the actual ladle carbon and free oxygen.

[0019] Preferably, when the free oxygen in the molten steel far exceeds the carbon in the ladle, additional oxygen control is performed by adding a deoxidizer to the molten steel, and the added deoxidizer includes aluminum, silicon, manganese, and carbon.

[0020] Beneficial effects: The invention establishes an accurate calculation model for ladle carbon and free oxygen, and realizes model-based automated control of the calculation of OB oxygen addition and carbon addition, which can effectively control the IF steel RH decarburization endpoint oxygen, reduce the aluminum egg unit consumption of IF steel, and improve the purity of molten steel. The economic benefits are significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the relationship diagram between the quantity of O in steel and the inclusions in steel at the end of RH decarburization;

[0022] Figure 2 This is the relationship between O and decarburization time in steel at the end of RH decarburization;

[0023] Figure 3 It is the point diagram of natural decarburization, forced decarburization and late OB decarburization;

[0024] Figure 4 is the histogram of natural decarbonization and forced decarbonization;

[0025] Figure 5 This is the result diagram of OB decarburization oxygen content and carbon addition oxygen control content calculated by the model. DETAILED DESCRIPTION

[0026] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] Example

[0028] This embodiment provides an automatic control method for final oxygen in RH decarburization of IF steel, comprising:

[0029] (1) Converter oxygen control

[0030] The converter controls oxygen by carbon addition during steel tapping, and the target of free oxygen in RH treatment is 400ppm. The carbon addition mode for steel tapping is:

[0031]

[0032] By controlling the initial free oxygen before RH treatment, ensuring that the RH decarburization endpoint oxygen is within the appropriate range, the amount of carbon added during steelmaking is determined, and carbon addition and oxygen control measures are implemented during the steelmaking process.

[0033] (2) Improvement of decarbonization efficiency

[0034] According to research and analysis, the lower the final oxygen, the fewer inclusions in the steel, but the decarburization efficiency of the molten steel will be affected to a certain extent. Figure 1 shown.

[0035] After the oxygen at the decarburization endpoint is reduced, the decarburization time is extended. It is necessary to ensure that the decarburization time treatment rhythm is controlled under low oxygen conditions. Figure 2 shown.

[0036] The diameter of the impregnated pipe is 850mm (the refractory material is not thinned). After the diameter is expanded, the RH circulation rate increases by 9.9%, so that the decarburization time is controlled and the decarburization efficiency is guaranteed at a lower free oxygen RH.

[0037] Comparing the decarburization time of 850 immersion pipe with different steel tapping marks of 750 pipe diameter, the 850 inner diameter has a better decarburization time and the final carbon is also lower, as shown in the following table.

[0038]

[0039] (3) RH controls the end point oxygen of decarbonization

[0040] During the RH treatment, at the vacuum junction, the decarburization reaction is:

[0041] [C]+[O]→(CO)

[0042] According to the reaction form of carbon in molten steel and free oxygen under vacuum, the carbon-oxygen reaction ratio is 1:1. However, in actual production, due to the influence of oxygen in cold steel and slag in the vacuum tank, 65-70ppm of free oxygen in molten steel is required to remove 100ppm of carbon, which has a large fluctuation in production. It is necessary to accurately calculate carbon and oxygen.

[0043] In order to ensure the decarburization efficiency, it is required that there is enough free oxygen in the molten steel. When the amount of free oxygen in the molten steel to remove carbon from the ladle is insufficient, forced oxygen supply decarburization by the top gun is required to promote the decarburization reaction.

[0044] Oxygen supply and decarbonization reaction formula:

[0045] O2→2[O][C]+[O]→(CO)

[0046] Forced decarburization forms a reaction zone in the vacuum tank, and the (CO) generated by the reaction of C in the molten steel with O forms a secondary oxidation reaction with the oxygen supplied by the top gun.

[0047] [C]+[O]→(CO)(CO)+O2→CO2(-566KJ / mol)

[0048] It is beneficial to increase the temperature of the upper tank, reduce the cold steel adhesion in the vacuum tank and reduce the processing temperature drop. In terms of decarburization efficiency, compared with the end point carbon of natural decarburization, forced decarburization and late OB decarburization, the end point carbon content of natural decarburization is an average of 17.8ppm, the end point carbon content of forced decarburization is an average of 17.5ppm, and the end point carbon content of late OB decarburization is an average of 18ppm. The end point carbon of forced decarburization is lower. Figure 3 shown.

[0049] In terms of operation, by controlling the free oxygen before RH treatment and reducing the free oxygen, in terms of selection strategy, the top gun forced OB decarburization process is preferred in the RH refining furnace. The converter can further increase the carbon content of the molten steel at the end of blowing and reduce the free oxygen when blowing is stopped, which has the advantages of improving the processing efficiency and improving the purity of the molten steel. Figure 4 shown.

[0050] The final carbon content of the converter is increased and the free oxygen is reduced, and the total iron in the OB forced decarburization slag is controlled to 4.8%, which is beneficial to the improvement of the purity of the molten steel.

[0051] The calculation formula of OB oxygen increase is as follows:

[0052] By analyzing the relationship between ladle carbon, free oxygen and the final decarburization endpoint oxygen in the natural decarburization furnace, the required OB oxygen increase amount is calculated based on the ladle carbon and oxygen before treatment, with 200ppm (finished product carbon ≥ 20ppm) as the target and 230ppm (finished product carbon < 20ppm).

[0053] ① Calculate the final oxygen of decarburization = (333- ladle carbon × 0.816 + 0.398 × free oxygen before treatment);

[0054] ② Calculate the final oxygen of decarburization - target final oxygen of decarburization <-20;

[0055] ③OB oxygen increase = (target decarburization final oxygen - calculated decarburization final oxygen) ÷ 2;

[0056] ④ Calculate the final oxygen of decarbonization - target final oxygen of decarbonization>0;

[0057] ⑤Carbon addition amount = (calculated decarburization final oxygen - target decarburization final oxygen) ÷ 100 × 70. (If the calculated final oxygen is higher than the target value, add carbon to control oxygen).

[0058] ⑥ When the ladle sample is poor, the fitting relationship between ladle carbon and free oxygen is ladle carbon = 558.9-0.3923×free oxygen before treatment, and the ladle carbon content is calculated based on the free oxygen.

[0059] The model calculates the OB oxygen content and the amount of carbon addition and oxygen control based on the actual ladle carbon and free oxygen. Figure 5 shown.

[0060] The model calculation can be dynamically adjusted according to the target decarburization end oxygen value of the steel grade. The specific final oxygen target value of the steel tapping mark is as follows:

[0061] Finished product carbon upper limit ppm Decarburization endpoint oxygen target ppm ≥20 220 ＜20 240

[0062] According to the model calculation value, the target decarburization final oxygen is 230ppm, and the carbon addition oxygen control and natural decarburization areas are as follows: Figure 5 The natural decarbonization area accounts for 19.7%, and the advanced carbonization area accounts for 31.7%.

[0063] When the free oxygen in molten steel far exceeds the carbon in the ladle, a certain amount of excess oxygen will be caused after oxygen decarburization, and additional oxygen control measures are needed. Conventional deoxidizers mainly include aluminum, silicon, manganese, and carbon. Aluminum, silicon, and manganese deoxidation will produce oxidized inclusions retained in the molten steel. The main reaction product of carbon deoxidation is gas (CO), which is removed from the molten steel along with the circulating gas under vacuum.

[0064] Operation method of adding carbon first to control oxygen:

[0065] ① Carbon powder must be added within 3 minutes after the exhaust begins, and no further addition is allowed.

[0066] ②After the vacuum degree is greater than 20KPa and the circulation starts, add carbon powder. The maximum amount of carbon powder added is ≤30kg.

[0067] ③ If the second batch of carbon powder is needed, it must be added when the vacuum degree is greater than 6KPa, and the maximum amount of carbon powder added is ≤20kg. It is forbidden to add carbon when the vacuum degree is below 6KPa.

[0068] ④At 6-20KPa, the temperature drops by about 5℃ for every 30kg of carbon powder.

[0069] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An automatic control method for final oxygen in RH decarburization of IF steel, characterized in that: The following steps are involved: S1. Converter oxygen control: The converter controls oxygen according to the carbon addition during steel tapping. By controlling the initial free oxygen before RH treatment, ensure that the RH decarburization endpoint oxygen is within the appropriate range, remove the carbon addition amount during steel tapping, and implement carbon addition and oxygen control measures during steel tapping; S2. Improve decarburization efficiency: After the immersion pipe with a diameter of 850mm is expanded, the RH circulation flow rate is increased, so that the decarburization time is controlled to ensure the decarburization efficiency at a lower free oxygen RH; S3. RH controls the end point oxygen of decarburization: the free oxygen content in the molten steel is monitored in real time. When it is detected that the amount of free oxygen in the molten steel to remove carbon from the ladle is insufficient, the decarburization reaction is promoted by forced oxygen supply and decarburization through the top gun.

2. The IF steel RH decarburization final oxygen automatic control method according to claim 1, characterized in that: In the process of forced oxygen supply decarburization by top lance, the calculation method of OB oxygen increase is as follows: by analyzing the relationship between ladle carbon, free oxygen and the final decarburization end oxygen in the natural decarburization furnace. According to ladle carbon and oxygen before treatment, the required OB oxygen increase is calculated with 200ppm as the target and 230ppm as the target; (1) Calculate the final oxygen of decarburization = (333- ladle carbon × 0.816 + 0.398 × free oxygen before treatment); (2) Calculate the final oxygen of decarburization - target final oxygen of decarburization < -20; (3) 0B oxygen increase = (target decarburization final oxygen - calculated decarburization final oxygen) ÷ 2; (4) Calculate the final oxygen of decarbonization - target final oxygen of decarbonization>0; (5) Carbon addition amount = (calculated decarburization final oxygen - target decarburization final oxygen) ÷ 100 × 70; (6) When the ladle sample is poor, the fitting relationship between ladle carbon and free oxygen is ladle carbon = 558.9-0.3923 × free oxygen before treatment, and the ladle carbon content is calculated based on the free oxygen; The OB oxygen content and the amount of carbon addition and oxygen control are calculated based on the actual ladle carbon and free oxygen.

3. The IF steel RH decarburization final oxygen automatic control method according to claim 1, characterized in that: When the free oxygen in molten steel far exceeds the carbon in the ladle, additional oxygen control is carried out by adding deoxidizers to the molten steel. The added deoxidizers include aluminum, silicon, manganese and carbon.

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