Method and System for Controlling Nitrogen Content of Low-Carbon High-Nitrogen Steel

Abstract

The present invention discloses a method for controlling the nitrogen content of a low-carbon high-nitrogen steel, comprising the following steps: S1. After the molten steel enters the RH station, start vacuum pumping, control the vacuum degree within the set vacuum degree range, select nitrogen as the lifting gas, and increase the nitrogen content of the incoming molten steel at the set nitrogen flow rate; S2. Under the condition that each element of the molten steel approaches or reaches the RH target value, measure the nitrogen increase rate at the set vacuum degree range and nitrogen flow rate; S3. Calculate the nitrogen content at the current moment in real time based on the nitrogen increase rate; S4. Determine whether to increase or remove nitrogen based on the nitrogen content at the current moment. If increasing nitrogen, calculate the RH breaking vacuum time based on the nitrogen increase rate. If removing nitrogen, calculate the RH breaking vacuum time based on the nitrogen removal rate. This method avoids the influence of the vacuum tank sealing performance, the change of the nitrogen activity coefficient caused by the change of the chemical composition of the molten steel during the RH production process, and the differences such as the nitrogen content when entering the RH on the nitrogen increase rate of the RH, can adapt to different converters and RH processes, and realizes the precise control of the nitrogen content of the molten steel.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy. More specifically, the present invention relates to a method and system for controlling the nitrogen content of a low-carbon high-nitrogen steel. Background Art

[0002] Generally, nitrogen in steel is a harmful element. When the nitrogen content in steel is high, when heated in the temperature range of 250-450 °C, its surface turns blue, nitrides precipitate, causing distortion of the metal lattice and generating a large internal stress, thereby deteriorating the plasticity and impact toughness of the steel, making the steel brittle, which is called "blue brittleness". However, for some special-purpose steels, nitrogen is an important alloying element. For example, for cold-rolled grain-oriented electrical steel, in order to obtain an oriented electrical steel product with excellent electromagnetic properties, it is required to precisely control the nitrogen content and acid-soluble aluminum content in the steel during the smelting process of the oriented electrical steel, so that a certain number of finely dispersed AlN particles precipitate in the steel strip after hot rolling and normalizing processes, inhibiting the growth of primary grains, and promoting the full growth of secondary recrystallization grains and the formation of a favorable Goss texture during the high-temperature annealing process. Therefore, the nitrogen content of oriented silicon steel is usually controlled at 70 ppm to 130 ppm. Too high or too low will cause incomplete secondary recrystallization of the finished product, affecting the electromagnetic properties of the final product.

[0003] Chinese Patent (Authorized Publication No.: CN 104962698 B) published "a method for precisely controlling the nitrogen content of oriented electrical steel". Its technical solution is mainly: bottom blowing nitrogen throughout the converter process. After the molten steel reaches the RH station, argon is initially used as the lifting gas, refined for 5 minutes under an ultimate vacuum of ≤67 Pa, and then the RH lifting gas is switched to nitrogen for the first nitrogen addition; after the first nitrogen addition, the RH lifting gas is switched to argon, and the vacuum degree of RH is 2-3 KPa. After treatment, the nitrogen content of the molten steel is sampled and analyzed to calculate the first nitrogen addition rate; when the RH refining reaches 40 minutes, the lifting gas is switched to nitrogen, and according to the gap between the nitrogen content of the molten steel after the first nitrogen addition and the target value, the second nitrogen addition time is determined according to the first nitrogen addition rate. The disadvantages of this technical solution are: 1) Bottom blowing nitrogen throughout the converter process results in a low nitrogen recovery rate. The N content at the RH station is 0.0028%, 0.0027%, and 0.0027% respectively, and the nitrogen addition effect is not good; 2) After the lifting gas is switched to argon after the first nitrogen addition, the molten steel is in a denitrification state. Therefore, during this period, the nitrogen content of the molten steel gradually decreases. Thus, the second nitrogen addition time calculated by the method of "determining the second nitrogen addition time according to the gap between the nitrogen content of the molten steel after the first nitrogen addition and the target value and according to the first nitrogen addition rate" is inaccurate; in addition, this method always assumes that the nitrogen content of the molten steel is lower than the upper limit of the control range after the first nitrogen addition. In fact, after the converter blows nitrogen throughout the process and the first nitrogen addition at the RH ends, the nitrogen content of the molten steel may have exceeded the upper limit of the nitrogen content control. How to control the nitrogen content in this case is not mentioned in this patent. Summary of the Invention

[0004] The present invention provides a method for controlling the nitrogen content of a low-carbon high-nitrogen steel, aiming to improve the control accuracy of the nitrogen content of the low-carbon high-nitrogen steel.

[0005] The present invention is implemented as follows. A method for controlling the nitrogen content of a low-carbon high-nitrogen steel, the method comprising the following steps:

[0006] S1. After the molten steel enters the RH station, start to evacuate the vacuum, control the vacuum degree within the set vacuum degree range, select nitrogen as the lifting gas, and increase the nitrogen content of the incoming molten steel at the set nitrogen flow rate;

[0007] S2. Under the condition that each element of the molten steel approaches or reaches the RH target value, measure the nitrogen increase rate at the set vacuum degree range and nitrogen flow rate;

[0008] S3. Calculate the nitrogen content at the current moment in real time based on the nitrogen increase rate;

[0009] S4. Determine whether to increase or remove nitrogen based on the nitrogen content at the current moment. If increasing nitrogen, calculate the RH breaking vacuum time based on the nitrogen increase rate; if removing nitrogen, calculate the RH breaking vacuum time based on the nitrogen removal rate.

[0010] Furthermore, the control method for the chemical composition of the molten steel is specifically as follows:

[0011] After the molten steel enters the RH station, take a steel sample Ⅰ for inspection. According to the test results of the steel sample Ⅰ, calculate the RH target values of each element of the molten steel to be hit or the carbon increasing agent and alloy required to approach the RH target values, and add the carbon increasing agent and alloy to adjust the chemical composition of the molten steel for the first time;

[0012] After the set time Ⅰ for adding the carbon increasing agent and alloy, take a steel sample Ⅱ for inspection;

[0013] According to the test results of the steel sample Ⅱ, calculate the carbon increasing agent and alloy required to hit the RH target values of each element of the molten steel to finely adjust the chemical composition of the molten steel, and perform the second adjustment on the chemical composition of the molten steel.

[0014] Furthermore, the method for obtaining the nitrogen increase rate is specifically as follows:

[0015] After the set time Ⅰ after adding the carbon increasing agent and alloy during the first adjustment of the chemical composition of the molten steel, take an oxygen-nitrogen sample Ⅰ. After taking the oxygen-nitrogen sample Ⅰ, take an oxygen-nitrogen sample Ⅱ after the set time Ⅱ, and record the sampling moments of the oxygen-nitrogen sample Ⅰ and the oxygen-nitrogen sample Ⅱ;

[0016] Based on the nitrogen content growth rate between the oxygen-nitrogen sample Ⅰ and the oxygen-nitrogen sample Ⅱ, it is the nitrogen increase rate at the set vacuum degree range and nitrogen flow rate;

[0017] Among them, the set time Ⅰ is the reaction and homogenization time of the carbon increasing agent or alloy and the molten steel.

[0018] Furthermore, the calculation formula for the nitrogen addition rate is as follows:

[0019] Nitrogen addition rate = (Nitrogen content in oxygen-nitrogen sample II - Nitrogen content in oxygen-nitrogen sample I) ÷ (Sampling time of oxygen-nitrogen sample II - Sampling time of oxygen-nitrogen sample I)

[0020] Furthermore, the method for obtaining the denitrification rate is as follows:

[0021] Control the chemical composition of the molten steel to be close to the RH target value, and control the nitrogen content of the molten steel to be around the upper limit of the RH target range for nitrogen content. Take an oxygen-nitrogen sample III to analyze the nitrogen content;

[0022] Switch the lifting gas to argon, and control the RH vacuum degree within the set vacuum degree range and the lifting gas flow rate to the set flow rate. After a certain period of time, take an oxygen-nitrogen sample IV to analyze the nitrogen content. Among them, the denitrification rate = (Nitrogen content in oxygen-nitrogen sample III - Nitrogen content in oxygen-nitrogen sample IV) ÷ (Sampling time of oxygen-nitrogen sample IV - Sampling time of oxygen-nitrogen sample III).

[0023] Furthermore, the calculation formula for the nitrogen content at the current moment is as follows:

[0024] Nitrogen content at the current moment = Nitrogen content in oxygen-nitrogen sample II + (Current moment - Sampling time of oxygen-nitrogen sample II) × Nitrogen addition rate.

[0025] Furthermore, the determination method for nitrogen addition or denitrification at the current moment is as follows:

[0026] When the nitrogen content at the current moment < RH target value of nitrogen content, nitrogen addition is required at the current moment, and the lifting gas remains nitrogen;

[0027] When the nitrogen content at the current moment > RH target value of nitrogen content, denitrification is required at the current moment, and the lifting gas is switched from nitrogen to argon.

[0028] Furthermore, the first adjustment process of the chemical composition of the molten steel is as follows:

[0029] For elements with unstable alloy recovery rates, calculate the carbonaceous agent and alloy required to make the element in the molten steel close to the RH target value according to the test results of steel sample I;

[0030] For elements with stable alloy recovery rates, calculate the alloy required to make the element in the molten steel reach the RH target value according to the test results of steel sample I.

[0031] Furthermore, the current moment is any moment when the test result of oxygen-nitrogen sample II is received and after.

[0032] The present invention is implemented as follows. A nitrogen content control system for low-carbon high-nitrogen steel, the system includes:

[0033] A control unit, connected to an input unit and a prompting unit;

[0034] The input unit is used to input the denitrification rate of the current low-carbon high-nitrogen steel type, and the detection results of oxygen-nitrogen samples and steel samples, and send them to the control unit; after the collection times of the oxygen-nitrogen samples and the steel samples are reached, the control unit issues a reminder through the prompting unit;

[0035] The control unit controls the nitrogen content of the low-carbon high-nitrogen steel during the RH treatment process based on the above nitrogen content control method for the low-carbon high-nitrogen steel.

[0036] The present invention provides a method for automatically controlling the nitrogen content of low-carbon high-nitrogen steel. This method avoids the influence of factors such as the sealing performance of the vacuum tank, the change in the activity coefficient of nitrogen caused by the change in the chemical composition of the molten steel during the RH production process, and the difference in the nitrogen content at the RH inlet on the nitrogen increase rate of the RH, can adapt to different converters and RH processes, and realizes the precise control of the nitrogen content of the molten steel. Description of the Drawings

[0037] Figure 1 It is a flow chart of the nitrogen content control method for the low-carbon high-nitrogen steel provided by the embodiment of the present invention;

[0038] Figure 2 It is a schematic structural diagram of the nitrogen content control system for the low-carbon high-nitrogen steel provided by the embodiment of the present invention. Detailed Embodiments

[0039] The following is a more detailed description of the specific embodiments of the present invention by referring to the drawings and describing the embodiments, so as to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0040] The nitrogen increase process of the molten steel is the dissolution reaction of nitrogen in the molten steel. The main factors affecting the solubility of N in the molten steel are: nitrogen partial pressure and alloy composition. The greater the nitrogen partial pressure, the greater the solubility of nitrogen in the steel. Under certain nitrogen partial pressure conditions, the molten steel composition has a great influence on the solubility of nitrogen in the steel.

[0041] During the top-bottom combined blowing converter smelting, the top blowing gas is oxygen, and the bottom blowing gas is argon or nitrogen, and the bottom blowing gas can be switched. During the converter smelting, the top lance continuously supplies oxygen to keep a high oxygen potential at the molten steel-slag interface. Oxygen, as a surface-active element, hinders the nitrogen in the air from entering the molten steel and also inhibits the escape of nitrogen in the molten steel. Therefore, the denitrification and nitrogen increase processes exist simultaneously, and the nitrogen increase effect depends on the denitrification rate and the nitrogen increase rate. When the bottom blowing gas is argon, the nitrogen content at the converter end point generally remains at about 15-30 ppm; when the bottom blowing gas is nitrogen, the denitrification rate is generally less than the nitrogen increase rate. Therefore, bottom blowing nitrogen can achieve nitrogen increase during the converter blowing process.

[0042] Based on the above idea, the present invention proposes a method for controlling the nitrogen content of a low-carbon high-nitrogen steel. Herein, the low-carbon high-nitrogen steel refers to: the RH target range of the C content is 0.020% - 0.070%; the RH target range of the N content is 0.0050% - 0.0120%, and the rest are alloying elements such as Si, Mn, P, S, Als, etc., iron, and inevitable residual elements. Combining Figure 1 The above method for controlling the nitrogen content will be described. This method specifically includes the following steps:

[0043] S1. After the molten steel enters the RH station, take a steel sample Ⅰ for inspection, start to evacuate, control the vacuum degree at 5 Kpa - 8 Kpa, select nitrogen as the lifting gas, and increase the nitrogen content of the incoming molten steel at a set nitrogen flow rate.

[0044] In the embodiment of the present invention, the lifting gas is blown in through the gas pipeline arranged in the RH riser pipe. Under the combined action of the lifting gas and the high vacuum degree in the vacuum tank, the continuous circulation of the molten steel in the vacuum tank is realized to achieve the expected metallurgical effect. If the nitrogen content of the molten steel is lower than the RH target value of the nitrogen content, nitrogen is selected as the lifting gas; if the nitrogen content in the molten steel is higher than the RH target value of the nitrogen content, argon is selected as the lifting gas. In addition, the flow rate of nitrogen at the time of entering the station is set according to the steel grade, and its value range is 130 Nm 3 / h - 170 Nm 3 / h.

[0045] S2. In order to make the subsequent nitrogen increase rate stable, it is best to minimize the fluctuation of the chemical composition of the molten steel as much as possible. Before taking the oxygen-nitrogen sample Ⅰ, adjust the chemical composition of the molten steel to be close to the RH target value. Add a carburizer and alloy according to the test results of the steel sample Ⅰ to adjust the chemical composition of the molten steel so that the chemical composition of the molten steel reaches or is close to the RH target value, and the RH target value is within the RH target range of the corresponding component.

[0046] In the embodiment of the present invention, due to the unstable recovery rates of the carburizer and aluminum-containing alloy, if the addition amounts of the carburizer or aluminum-containing alloy are calculated based on hitting the RH target values of the C content and the Als content, it is easy to exceed the standard of the C content and the Als content in the molten steel. Therefore, the addition amounts of the carburizer and aluminum-containing alloy are based on hitting values close to the RH target values of the C content and the Als content, such as: RH target value of the C content - 0.005%, RH target value of the Als content - 0.005%. For the remaining components such as the Mn element, since the recovery rate of ferromanganese alloy is stable, the addition amount of ferromanganese alloy is targeted at hitting the RH target value of the Mn content.

[0047] S3. After the set time Ⅰ for adding the carburizer and alloy, take the oxygen-nitrogen sample Ⅰ and the steel sample Ⅱ for inspection, and take the oxygen-nitrogen sample Ⅱ for inspection after the set time Ⅱ after taking the oxygen-nitrogen sample Ⅰ;

[0048] The set duration I is set as the reaction and homogenization time of the recarburizer or alloy with the molten steel. The reason for taking the oxygen-nitrogen sample I after the recarburizer or alloy is added for the set duration I (3 minutes - 10 minutes) is that at this time, the elements in the molten steel are already close to the target values, and the subsequent nitrogen increasing rate remains relatively stable. The nitrogen increasing rate calculated based on the test results of the oxygen-nitrogen sample I is highly representative. The oxygen-nitrogen sample is taken by inserting the sampling component of the oxygen-nitrogen analyzer into the molten steel and then sent to the laboratory for inspection after being fully cooled by air cooling. The time interval from the moment of taking the oxygen-nitrogen sample to obtaining the nitrogen content analysis result is about 14 - 20 minutes.

[0049] After taking the oxygen-nitrogen sample I, take the oxygen-nitrogen sample II after the set duration II. The set duration II is generally set to 3 minutes to 8 minutes. The reasons are as follows: If the interval time between the two oxygen-nitrogen samples is too short, the nitrogen content increment is small, and when there are certain deviations in the analysis results of the oxygen-nitrogen samples, it is easy to increase the deviation of the calculated result of the nitrogen increasing rate; if the interval time between the two oxygen-nitrogen samples is too long, the time to obtain the nitrogen content result of the oxygen-nitrogen sample II is too late, which may cause the nitrogen content in the molten steel to be much higher than the upper limit of the nitrogen content target range.

[0050] S4. Add recarburizer and alloy to finely adjust the chemical composition of the molten steel according to the test results of the steel sample II, so that the chemical composition of the molten steel reaches the target value. Therefore, the addition amounts of recarburizer, ferrosilicon, ferromanganese, ferrophosphorus, ferrosulfur, and aluminum shot are all targeted at hitting the RH target values of the corresponding components.

[0051] S5. Calculate the nitrogen increasing rate under the current nitrogen gas flow rate and vacuum degree range based on the nitrogen content difference between the oxygen-nitrogen sample I and the oxygen-nitrogen sample II, and calculate the nitrogen content at the current moment in real time based on the nitrogen increasing rate. The current moment is generally any moment when the test results of the oxygen-nitrogen sample II are received and later;

[0052] In the embodiment of the present invention, the calculation formula of the nitrogen increasing rate is specifically as follows:

[0053] Nitrogen increasing rate = (nitrogen content in the oxygen-nitrogen sample II - nitrogen content of the oxygen-nitrogen sample I) ÷ (sampling moment of the oxygen-nitrogen sample II - sampling moment of the oxygen-nitrogen sample I), unit: % / min;

[0054] Nitrogen content at the current moment = nitrogen content in the oxygen-nitrogen sample II + (current moment - sampling moment of the oxygen-nitrogen sample II) × nitrogen increasing rate; unit: %.

[0055] S6. Determine whether to increase or remove nitrogen based on the nitrogen content at the current moment. If it is to increase nitrogen, calculate the RH breaking vacuum time based on the nitrogen increasing rate. If it is to remove nitrogen, calculate the RH breaking vacuum time based on the nitrogen removing rate. Calculate the time to reach the RH target value of the nitrogen content based on the nitrogen increasing rate, that is, the RH breaking vacuum time. When breaking vacuum in RH, at this time, the nitrogen content in the molten steel may just be at the RH target value of the nitrogen content, or may be very close to the RH target value of the nitrogen content.

[0056] In the embodiment of the present invention, when the nitrogen content at the current moment < the RH target value of the nitrogen content, the lifting gas remains nitrogen, and the RH breaking time is estimated based on the nitrogen increasing speed. When the nitrogen content at the current moment is equal to the RH target value of the nitrogen content, breaking occurs and the RH treatment ends. When the nitrogen content at the current moment > the RH target value of the nitrogen content, the lifting gas is switched from nitrogen to argon for nitrogen removal, and the breaking time is estimated based on the nitrogen removal speed.

[0057] It should be noted that due to the slow nitrogen increasing speed, it is defaulted that the temperature adjustment of the molten steel in the RH process has been completed. Since the temperature adjustment has no obvious correlation with the nitrogen adjustment and is an existing technology, the present application does not elaborate on the temperature adjustment of the molten steel in detail. When the chemical composition and temperature adjustment of the molten steel at the current moment are completed, as long as the nitrogen content reaches the RH target value of the nitrogen content, breaking can occur.

[0058] In the embodiment of the present invention, the method for determining the nitrogen removal speed is as follows: The nitrogen removal speed is related to the RH vacuum degree, the nitrogen content of the molten steel, the chemical composition of the steel grade, etc., and can be experimentally determined by simulating the RH process of the steel grade to be smelted in production practice. First, control the chemical composition of the molten steel to be close to the target value, control the nitrogen content of the molten steel to be around the upper limit of the RH target range of the nitrogen content, take the oxygen-nitrogen sample III to analyze the nitrogen content, and then switch the lifting gas to argon, and control the RH vacuum degree to be within the set vacuum degree range and the lifting gas flow rate to be the set flow rate. After a period of time, take the oxygen-nitrogen sample IV to analyze the nitrogen content; Nitrogen removal speed = (Nitrogen content in oxygen-nitrogen sample III - Nitrogen content in oxygen-nitrogen sample IV) ÷ (Sampling time of oxygen-nitrogen sample IV - Sampling time of oxygen-nitrogen sample III), unit: % / min.

[0059] Figure 2 It is a schematic structural diagram of the nitrogen content control system for the low-carbon high-nitrogen steel provided by the embodiment of the present invention. This system includes:

[0060] A control unit, connected to the input unit and the prompt unit;

[0061] The input unit is used to input the nitrogen removal speed, the detection results of the oxygen-nitrogen sample and the steel sample of the current low-carbon high-nitrogen steel grade, and send them to the control unit.

[0062] After reaching the collection time of the oxygen-nitrogen sample and the steel sample, the control unit issues a reminder through the prompt unit;

[0063] The control unit controls the nitrogen content of the low-carbon high-nitrogen steel during the RH treatment process based on the above-mentioned nitrogen content control method for the low-carbon high-nitrogen steel.

[0064] To further elaborate on the idea of the present invention, the following takes the smelting of low-carbon high-nitrogen steel in a 300T RH refining furnace as an example to further illustrate the present invention.

[0065] Example 1, the chemical composition control requirements of the low-carbon high-nitrogen steel are shown in Table 1, and the rest are iron and inevitable residual elements.

[0066] Table 1 RH control requirements for the chemical composition of the low-carbon high-nitrogen steel in Examples 1 and 2

[0067]

[0068] (1) Determination of the RH denitrification rate for this type of steel grade: When producing RH low-carbon high-nitrogen steel, first control the chemical composition of the molten steel to be close to the target value and control the nitrogen content of the molten steel to about 0.0090%. Take an oxygen-nitrogen sample to analyze the nitrogen content. Subsequently, switch the lifting gas to argon, set the RH vacuum degree, and the lifting gas flow rate within the normal range for this steel grade. After 8 minutes, take an oxygen-nitrogen sample to analyze the nitrogen content. The denitrification rate = the amount of nitrogen content reduction ÷ (the time difference between the two oxygen-nitrogen sample sampling times) = 0.0030% ÷ 8 = 0.000375% / min. This value is collected as input into the system;

[0069] (2) After the molten steel enters the RH, take steel sample Ⅰ for inspection, then start to evacuate the vacuum. Set the lifting gas to nitrogen, and the nitrogen flow rate is set to 170 Nm 3 / h, and the vacuum degree is controlled at 6 Kpa to increase the nitrogen content of the molten steel when it enters the station;

[0070] (3) The analysis results of the C content, Mn content, and Als content of steel sample Ⅰ are 0.022%, 0.08%, and 0.012% respectively. Adjust the chemical composition by adding carburizer / alloy according to the composition of steel sample Ⅰ. Among them, the addition amount of carburizer is calculated with the target of hitting "0.035%", the addition amount of ferromanganese is calculated with the target of hitting "0.20%", and the addition amount of aluminum shot is calculated with the target of hitting "0.020%". Add 41 kg of carburizer, 416 kg of low-carbon ferromanganese, and 25 kg of aluminum shot respectively;

[0071] (4) 5 minutes after adding the above carburizer and alloy, take oxygen-nitrogen sample Ⅰ and steel sample Ⅱ for inspection. When taking oxygen-nitrogen sample Ⅰ, click "Take oxygen-nitrogen sample Ⅰ" and record the time of taking oxygen-nitrogen sample Ⅰ;

[0072] (5) 6 minutes after taking oxygen-nitrogen sample Ⅰ, take oxygen-nitrogen sample Ⅱ for inspection; when taking oxygen-nitrogen sample Ⅱ, click "Take oxygen-nitrogen sample Ⅱ" and record the time of taking oxygen-nitrogen sample Ⅱ;

[0073] (6) The analysis results of the C content, Mn content, and Als content of steel sample Ⅱ are 0.041%, 0.198%, and 0.018% respectively. Since the C content and Mn content are already close to or exceed the target values, no further adjustment is made. Add 6 kg of aluminum shot according to the composition of steel sample Ⅱ to adjust the Als of the molten steel to the "RH target value";

[0074] (7) Since the oxygen and nitrogen analysis takes a certain amount of time, the analysis results of oxygen and nitrogen sample I and oxygen and nitrogen sample II are received 18 minutes after taking oxygen and nitrogen sample I and 15 minutes after taking oxygen and nitrogen sample II respectively. The nitrogen contents of oxygen and nitrogen sample I and oxygen and nitrogen sample II are 0.0025% and 0.0037% respectively. Then the nitrogen increase rate is automatically calculated as follows: nitrogen increase rate = (0.0037% - 0.0025%) ÷ 6 min = 0.0002% / min;

[0075] (8) As time goes on, the nitrogen content of the molten steel is calculated in real time. When the analysis result of the nitrogen content of oxygen and nitrogen sample II is received on site, the nitrogen content of the molten steel = the nitrogen content of oxygen and nitrogen sample II + (the time when the nitrogen content analysis result of oxygen and nitrogen sample II is received - the sampling time of oxygen and nitrogen sample II) × nitrogen increase rate = 0.0037% + 15 × 0.0002% = 0.0067%;

[0076] (8) Calculate the nitrogen content of the molten steel at the time when the analysis result of the nitrogen content of oxygen and nitrogen sample II is received. The N content is 0.0067%, which is < the RH nitrogen content target value (0.0070%). The lifting gas is kept as nitrogen to continue increasing the nitrogen content. After continuing to increase the nitrogen content for 1.5 minutes, the real-time N content of the molten steel is calculated to reach 0.0070%, and then the RH breaks the vacuum and the RH treatment ends. The main parameters of the RH process are shown in Table 2.

[0077] Table 2 Main parameters of the RH process in Example 1

[0078]

[0079]

[0080] Example 2: The chemical composition of the low-carbon high-nitrogen steel is shown in Table 1, and the rest are iron and inevitable residual elements.

[0081] Determination of the RH denitrification rate for this type of steel: When producing RH low-carbon high-nitrogen steel, first control the chemical composition of the molten steel close to the target value and control the nitrogen content of the molten steel to about 0.0090%. Take oxygen and nitrogen samples to analyze the nitrogen content. Subsequently, switch the lifting gas to argon, set the RH vacuum degree and the lifting gas flow rate within the normal range of this steel type, and after 8 minutes, take oxygen and nitrogen samples to analyze the nitrogen content. The denitrification rate = the amount of nitrogen content reduction ÷ (the time difference between the sampling times of the two oxygen and nitrogen samples) = 30 ÷ 8 = 0.000375% / min. This value is collected as input into the system;

[0082] (2) After the molten steel enters the RH, take steel sample I for inspection, and then start to evacuate. The lifting gas is set as nitrogen, and the nitrogen flow rate is set as 210 Nm 3 / h, and the vacuum degree is controlled at 7.8 Kpa to increase the nitrogen content of the molten steel when it enters the station;

[0083] (3) The analysis results of the C content, Mn content, and Als content in Steel Sample I are 0.028%, 0.05%, and 0.016% respectively. According to the composition of Steel Sample I, a carbon additive and alloys are added to adjust the chemical composition. Among them, the addition amount of the carbon additive is calculated with the target of hitting "0.035%", the addition amount of ferromanganese is calculated with the target of hitting "0.20%", and the addition amount of aluminum shot is calculated with the target of hitting "0.020%". 22 kg of carbon additive, 508 kg of low-carbon ferromanganese, and 12 kg of aluminum shot are added respectively:

[0084] (4) Six minutes after adding the carbon additive and alloys, Oxygen-Nitrogen Sample I and Steel Sample II are sent for inspection. When taking Oxygen-Nitrogen Sample I, click "Take Oxygen-Nitrogen Sample I" and record the time of taking Oxygen-Nitrogen Sample I;

[0085] (5) Four minutes after taking Oxygen-Nitrogen Sample I, Oxygen-Nitrogen Sample II is sent for inspection; when taking Oxygen-Nitrogen Sample II, click "Take Oxygen-Nitrogen Sample II" and record the time of taking Oxygen-Nitrogen Sample II;

[0086] (6) The analysis results of the C content, Mn content, and Als content in Steel Sample II are 0.042%, 0.21%, and 0.026% respectively. Since the C content, Mn content, and Als content are all close to or exceed the target values, the composition is no longer adjusted;

[0087] (7) Since the analysis of the oxygen-nitrogen sample takes a certain amount of time, the analysis results of Oxygen-Nitrogen Sample I and Oxygen-Nitrogen Sample II are received 14 minutes after taking Oxygen-Nitrogen Sample I and 17 minutes after taking Oxygen-Nitrogen Sample II respectively. The nitrogen contents of Oxygen-Nitrogen Sample I and Oxygen-Nitrogen Sample II are 0.0036% and 0.0049% respectively. The nitrogen increase rate is automatically calculated, and the nitrogen increase rate = (0.0049% - 0.0036%) ÷ 4 min = 0.0003% / min;

[0088] (8) As time goes on, the nitrogen content of the molten steel is calculated in real time. When the nitrogen content analysis result of Oxygen-Nitrogen Sample II is received on-site, the real-time nitrogen content of the molten steel = the nitrogen content of Oxygen-Nitrogen Sample II + (the time when the nitrogen content analysis result of Oxygen-Nitrogen Sample II is received - the sampling time of Oxygen-Nitrogen Sample II) × the nitrogen increase rate = 0.0049% + 17 * 0.0003% = 0.0104%;

[0089] (9) Since the real-time N content of the molten steel is calculated to be 0.0104% when the nitrogen content analysis result of Oxygen-Nitrogen Sample II is received, which is > the RH nitrogen content target value (0.0070%), a signal is output, and the lifting gas is switched to argon for denitrification. After continuing denitrification for 9.1 minutes, the real-time N content of the molten steel is calculated to reach 0.0070%, and the RH breaks the vacuum, and the RH treatment ends. The main parameters of the RH process are shown in Table 3.

[0090] Table 3 Main Parameters of the RH Process in Example 2

[0091]

[0092]

[0093] Example 3: The chemical composition control requirements for low-carbon high-nitrogen steel are shown in Table 4, and the rest are iron and inevitable residual elements.

[0094] Table 4 RH control requirements for the chemical composition of low-carbon high-nitrogen steel in Example 3

[0095]

[0096] (1) Determination of the RH denitrification rate for this type of steel grade: When producing this type of steel grade, first control the chemical composition of the molten steel close to the target value and control the nitrogen content of the molten steel to about 0.0110%. Take an oxygen-nitrogen sample to analyze the nitrogen content. Subsequently, switch the lifting gas to argon, set the RH vacuum degree, and the lifting gas flow rate within the normal range for this steel grade. After 8 minutes, take an oxygen-nitrogen sample to analyze the nitrogen content. The denitrification rate = the amount of nitrogen content reduction ÷ (the time difference between the two oxygen-nitrogen sample sampling times) = 0.0038% ÷ 8 = 0.000475% / min. Collect this value as input into the system;

[0097] (2) After the molten steel enters the RH, take steel sample Ⅰ for inspection, and then start vacuum pumping. Set the lifting gas to nitrogen, and the nitrogen flow rate is set to 210 Nm 3 / h, and control the vacuum degree to 7.5 Kpa to increase the nitrogen content of the molten steel when it enters the station;

[0098] (2) The analysis results of the C content, Si content, Mn content, P content, and Als content of steel sample Ⅰ are 0.031%, 1.53%, 1.09%, 0.015%, and 0.068% respectively. Adjust the chemical composition by adding carburizer and alloys according to the composition of steel sample Ⅰ. Among them, the addition amount of the carburizer is calculated with the goal of hitting "0.040%", and the addition amounts of alloys such as ferrosilicon, ferromanganese, and ferrophosphorus are calculated with the goals of hitting the "RH Si content target value", "RH Mn content target value", and "RH P content target value". The addition amount of aluminum shot is calculated with the goal of hitting 0.795%. Add 45 kg, 603 kg, 745 kg, 455 kg, and 2280 kg of carburizer, ferrosilicon, ferromanganese, ferrophosphorus, and aluminum shot respectively:

[0099] (3) 8 minutes after adding the carburizer and alloys, send oxygen-nitrogen sample Ⅰ and steel sample Ⅱ for inspection. When taking oxygen-nitrogen sample Ⅰ, click "Take oxygen-nitrogen sample Ⅰ" and record the time when oxygen-nitrogen sample Ⅰ is taken;

[0100] (4) 3 minutes after taking oxygen-nitrogen sample Ⅰ, send oxygen-nitrogen sample Ⅱ for inspection; when taking oxygen-nitrogen sample Ⅱ, click "Take oxygen-nitrogen sample Ⅱ" and record the time when oxygen-nitrogen sample Ⅱ is taken;

[0101] (5) The analysis results of the C content, Si content, Mn content, P content, and Als content of the steel sample II are 0.047%, 1.66%, 1.32%, 0.051%, and 0.806% respectively. Since the C content, Mn content, P content, and Als content in the steel sample II have all approached or exceeded the target values, the composition is no longer adjusted. According to the composition of the steel sample II, 175 kg of ferrosilicon is added to adjust the Si content of the molten steel to the "RH target value";

[0102] (6) Since it takes a certain amount of time for the oxygen and nitrogen sample analysis, the analysis results of the oxygen and nitrogen sample I and the oxygen and nitrogen sample II are received 16 minutes after taking the oxygen and nitrogen sample I and 15 minutes after taking the oxygen and nitrogen sample II respectively. The nitrogen contents of the oxygen and nitrogen sample I and the oxygen and nitrogen sample II are 0.0045% and 0.0061% respectively. The nitrogen increase rate is automatically calculated as follows: nitrogen increase rate = (0.0061% - 0.0045%) ÷ 3 min = 0.00053% / min;

[0103] (7) As time goes on, the nitrogen content of the molten steel is calculated in real time. When the analysis result of the nitrogen content of the oxygen and nitrogen sample II is received on site, the real-time nitrogen content of the molten steel = the nitrogen content of the oxygen and nitrogen sample II + (the time when the analysis result of the nitrogen content of the oxygen and nitrogen sample II is received - the sampling time of the oxygen and nitrogen sample II) × the nitrogen increase rate = 0.0061% + 15 × 0.00053% = 0.0141%;

[0104] (8) Since the real-time N content of the molten steel is calculated to be 0.0141% when the analysis result of the nitrogen content of the oxygen and nitrogen sample II is received, which is > the RH nitrogen content target value (0.0090%), a signal is output to switch the lifting gas to argon for denitrification. After continuing denitrification for 10.7 minutes, the real-time N content of the molten steel is calculated to reach 0.0090%, and the RH breaks the vacuum, and the RH treatment ends. The main parameters of the RH process are shown in Table 4.

[0105] Table 4 Main parameters of the RH process in Example 3

[0106]

[0107] The present invention has been described exemplarily. Obviously, the specific implementation of the present invention is not limited by the above methods. As long as various non-substantive improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for controlling the nitrogen content of a low-carbon high-nitrogen steel, characterized in that, The method includes the following steps: S1. After the molten steel enters the RH station, start vacuum pumping, control the vacuum degree within the set vacuum degree range, select nitrogen as the lifting gas, and increase the nitrogen content of the incoming molten steel at the set nitrogen flow rate; S2. Under the condition that each element of the molten steel reaches the RH target value, measure the nitrogen increasing speed at the set vacuum degree range and nitrogen flow rate; S3. Calculate the nitrogen content at the current moment in real time based on the nitrogen increasing speed; S4. Determine whether to increase or remove nitrogen based on the nitrogen content at the current moment. If it is to increase nitrogen, calculate the RH breaking vacuum time based on the nitrogen increasing speed. If it is to remove nitrogen, calculate the RH breaking vacuum time based on the nitrogen removing speed; The control method of the molten steel chemical composition is as follows: Take a steel sample Ⅰ for inspection after the molten steel enters the RH station. Calculate the carbon increasing agent and alloy required to reach the RH target value of each element according to the test results of the steel sample Ⅰ, and add the carbon increasing agent and alloy to adjust the chemical composition of the molten steel for the first time; Take a steel sample Ⅱ for inspection after the set time Ⅰ for adding the carbon increasing agent and alloy; Calculate the carbon increasing agent and alloy required to reach the RH target value of each element according to the test results of the steel sample Ⅱ, finely adjust the chemical composition of the molten steel, and conduct the second adjustment of the chemical composition of the molten steel; The method for obtaining the nitrogen increasing speed is as follows: After the set time Ⅰ after adding the carbon increasing agent and alloy during the first adjustment of the molten steel chemical composition, take an oxygen-nitrogen sample Ⅰ. After the set time Ⅱ after taking the oxygen-nitrogen sample Ⅰ, take an oxygen-nitrogen sample Ⅱ, and record the sampling moments of the oxygen-nitrogen sample Ⅰ and the oxygen-nitrogen sample Ⅱ; The nitrogen content growth speed between the oxygen-nitrogen sample Ⅰ and the oxygen-nitrogen sample Ⅱ is the nitrogen increasing speed at the set vacuum degree range and nitrogen flow rate; Among them, the set time Ⅰ is the reaction and homogenization time of the carbon increasing agent and alloy with the molten steel.

2. The method for controlling the nitrogen content of the low-carbon high-nitrogen steel according to claim 1, characterized in that, The calculation formula of the nitrogen increasing speed is as follows: Nitrogen increasing speed = (nitrogen content in the oxygen-nitrogen sample Ⅱ - nitrogen content in the oxygen-nitrogen sample Ⅰ) ÷ (sampling moment of the oxygen-nitrogen sample Ⅱ - sampling moment of the oxygen-nitrogen sample Ⅰ).

3. The method for controlling the nitrogen content of the low-carbon high-nitrogen steel according to claim 1, wherein The method for obtaining the nitrogen removing speed is as follows: Control the molten steel chemical composition to reach the RH target value, and control the nitrogen content of the molten steel to the upper limit of the nitrogen content RH target range. Take an oxygen-nitrogen sample Ⅲ to analyze the nitrogen content; Switch the lifting gas to argon, and control the RH vacuum degree within the set vacuum degree range and the lifting gas flow rate within the set flow rate range. After a period of time, take an oxygen-nitrogen sample Ⅳ to analyze the nitrogen content. Among them, the nitrogen removing speed = (nitrogen content in the oxygen-nitrogen sample Ⅲ - nitrogen content in the oxygen-nitrogen sample Ⅳ) ÷ (sampling time of the oxygen-nitrogen sample Ⅳ - sampling time of the oxygen-nitrogen sample Ⅲ).

4. The method for controlling the nitrogen content of the low-carbon high-nitrogen steel according to claim 1, characterized in that, The calculation formula of the nitrogen content at the current moment is as follows: Nitrogen content at the current moment = nitrogen content in the oxygen-nitrogen sample Ⅱ + (current moment - sampling moment of the oxygen-nitrogen sample Ⅱ) × nitrogen increasing speed.

5. The method for controlling the nitrogen content of the low-carbon high-nitrogen steel according to claim 1, characterized in that, The determination method of whether it is to increase or remove nitrogen at the current moment is as follows: When the nitrogen content at the current moment < RH target value of the nitrogen content, nitrogen needs to be increased at the current moment, and the lifting gas remains nitrogen; When the nitrogen content at the current moment > RH target value of the nitrogen content, nitrogen needs to be removed at the current moment, and the lifting gas is switched from nitrogen to argon.

6. The method for controlling the nitrogen content of the low-carbon high-nitrogen steel according to any one of claims 1 or 2, characterized in that, The current moment is any moment when the test result of the oxygen-nitrogen sample Ⅱ is received and after that.

7. A nitrogen content control system for a low-carbon high-nitrogen steel, characterized in that, The system includes: A control unit, connected to an input unit and a prompt unit; An input unit, configured to input the denitrification rate of the current low-carbon and high-nitrogen steel grade, the detection results of oxygen-nitrogen samples and steel samples, and send them to the control unit; after the collection time of the oxygen-nitrogen samples and steel samples is reached, the control unit issues a reminder through the prompting unit; A control unit, which controls the nitrogen content of the low-carbon and high-nitrogen steel during the RH treatment process based on the nitrogen content control method of the low-carbon and high-nitrogen steel according to any one of claims 1 to 6.

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