Molten steel nitrogen increasing method and accurate nitrogen control model

Abstract

The invention discloses a molten steel nitrogen increasing method and a precise nitrogen control model, and belongs to the technical field of ferrous metallurgy smelting. The invention provides a molten steel nitrogen increasing method and a precise nitrogen control model. The control method comprises the steps that the target nitrogen content of vanadium microalloyed low alloy steel is controlled; nitrogen is increased according to the converter feeding iron-steel ratio; converter bottom blowing nitrogen increasing; adding nitrogen to converter end point carbon; the adding sequence of the converter deoxidizer is controlled; alloy nitrogen increasing; nitrogen is increased during tapping; blowing nitrogen at the bottom of the steel ladle to increase nitrogen; and a matching model of the target nitrogen content, the iron-steel ratio, end point carbon and ladle bottom blowing nitrogen increase is established. The steel ladle bottom blowing nitrogen flow is adjusted according to different in-furnace iron-steel ratios, the end point carbon content and the tapping time, the target nitrogen content is achieved through accurate control, effective utilization of nitrogen is improved, the rolled metal performance is stabilized, the waste steel amount is reduced, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy and smelting technology, specifically to a method for increasing nitrogen in molten steel and a precise nitrogen control model. Background Technology

[0002] Currently, low-alloy steels mainly use V, Nb, and Ti for microalloying. V is more stable and cheaper than Nb and Ti, and its applications are more widespread. V is a strong carbide and nitride forming element, and it readily forms stable, insoluble, tiny, dispersed carbonitride particles in steel. During solidification, these carbonitrides continuously precipitate extremely fine particles, resulting in a strong precipitation strengthening effect. In addition, the precipitation of carbonitrides refines the ferrite grains, thereby strengthening the steel. The nitrogen content in the steel plays a crucial role in the strengthening effect of V, but excessive nitrogen content reduces the toughness and toughness of the steel, leading to "blue brittleness."

[0003] The nitrogen (V) in steel is obtained by adding alloys such as vanadium-nitrogen and ferrovanadium, while the nitrogen (N) is obtained by adding alloys such as vanadium-nitrogen alloys and nitriding, as well as blowing in nitrogen gas. Due to the complexity of the steelmaking process, the nitrogen content in steel generally fluctuates significantly due to various production process factors, including the iron-to-steel ratio, final carbon content, deoxidizer addition method, and blowing volume. This leads to large and unstable fluctuations in the properties of rolled products and low effective utilization of N. To reduce nitrogen content fluctuations and mitigate the harmful effects of excessive N content, measures such as increasing alloy content are often taken, resulting in excessively high production costs.

[0004] Therefore, how to stably control the nitrogen content in vanadium microalloyed low alloy steel is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the above-mentioned prior art, the purpose of this invention is to provide a method for increasing nitrogen content in molten steel and a precise nitrogen control model. This is used to precisely control the nitrogen content in vanadium microalloyed low-alloy steel, stabilize rolling performance, and reduce production costs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a method for increasing nitrogen content in molten steel, comprising: during the steelmaking process, adjusting the nitrogen content (N) of vanadium microalloyed low-alloy steel according to the target nitrogen content (N) of the steel. 目标 The nitrogen increase amounts N1 (for the iron-to-steel ratio), N2 (for the vanadium-nitrogen alloy), N3 (for the tapping time), and N4 (for the final carbon nitrogen increase) are controlled to obtain the ladle bottom-blowing nitrogen amount N5. This amount is then used for ladle bottom blowing to achieve nitrogen increase in molten steel. The formula for calculating the ladle bottom-blowing nitrogen amount N5 is as follows: Nitrogen gas volume N5 for bottom blowing of ladle = (N 目标 -N1-N2-N3-N4).

[0007] Furthermore, the nitrogen increase N1 in the iron-to-steel ratio is related to the iron-to-steel ratio T.铁钢比 The relationship is as follows: N1=a*T 铁钢比 +b, Where a = -110, b = 130, T 铁钢比 It ranges from 0.6 to 1.0.

[0008] In some implementations, the higher the iron-to-steel ratio in the converter feed, the lower the nitrogen content in the steel.

[0009] Furthermore, low-alloy steel is microalloyed using vanadium-nitrogen alloys, with the nitrogen addition amount N2 and the total amount of vanadium-nitrogen alloy added Q being... 钒氮 And Q 出钢量 The relationship is as follows: N2=Q 钒氮 *Q 氮含量 *Q 收得率 / Q 出钢量 .

[0010] Furthermore, when tapping steel from the converter, a deoxidizer is added first, followed by a vanadium-nitrogen alloy, with a time interval of 30-100 seconds between the addition of the deoxidizer and the vanadium-nitrogen alloy.

[0011] Furthermore, the nitrogen increase N3 during tapping time is related to the tapping time T. 出钢时间 The relationship is as follows: N3=c*T 出钢时间 +d, Where c=4 and d=-8, Steel tapping time T 出钢时间 The time is 2-5 minutes. Less than 2 minutes is recorded as 2 minutes, and more than 5 minutes is recorded as 5 minutes.

[0012] In some implementations, the longer the converter tapping time, the higher the nitrogen content in the steel.

[0013] Furthermore, the final carbon-to-nitrogen increase (N4) is related to the tapping time (T). 终点碳 The relationship between them is as follows: N4=e*T 终点碳 +f, Where e = 5555.6, f = -1.1, The endpoint carbon content is 0.02%-0.2%, with values ​​below 0.02% recorded as 0.02% and values ​​above 0.2% recorded as 0.2%.

[0014] In some implementations, the lower the carbon content at the converter endpoint, the lower the nitrogen content in the steel.

[0015] Furthermore, the nitrogen increase amount N5 from bottom blowing in the ladle and the nitrogen amount T from bottom blowing in the ladle... 钢包底吹 The relationship is as follows: N5=j*T 钢包底吹+h, Where j=2.36, h=1.64, The nitrogen flow rate for bottom blowing in the ladle is 20-1000 L / min.

[0016] In some implementations, the amount of nitrogen blown into the ladle, T 钢包底吹 The larger the diameter, the higher the nitrogen content in the steel.

[0017] Furthermore, once the amount of nitrogen gas blown into the ladle reaches the calculated amount, it automatically switches to argon gas blown into the ladle.

[0018] A second aspect of the present invention provides a precise nitrogen control model constructed using the aforementioned method for increasing nitrogen content in molten steel.

[0019] A third aspect of the present invention provides the application of the aforementioned method for increasing nitrogen content in molten steel in the control of nitrogen content in steel.

[0020] The beneficial effects of this invention are: This invention effectively solves the problem of large fluctuations in nitrogen content caused by numerous influencing factors in the actual production of vanadium-nitrogen microalloyed low-alloy steel HRB400E. It achieves precise control of nitrogen content, improves the effective utilization of nitrogen, and stabilizes the performance of rolled steel. This invention has strong practical guidance; currently, statistics show that the qualified rate of precise nitrogen content control (target nitrogen content ±10ppm) for HRB400E steel reaches over 90%, with stable nitrogen content control and minimal fluctuations. This makes a significant contribution to improving rolled steel performance, reducing scrap steel volume, and lowering alloy costs. Detailed Implementation

[0021] 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.

[0022] Before obtaining the nitrogen quantity calculation method of this invention, two main methods were used: (1) Controlling the nitrogen blowing time. Based on the nitrogen content detection of the previous batch, the normal nitrogen blowing quantity for this batch was controlled at 5-15 min. If the nitrogen content detected in the previous batch was high, the nitrogen blowing time for this batch was controlled at the lower limit; if the nitrogen content detected in the previous batch was low, the nitrogen blowing time for this batch was controlled at the upper limit. (2) Controlling the nitrogen blowing quantity. Based on the nitrogen content detection of the previous batch, the normal nitrogen blowing quantity for this batch was controlled at 2-10 m³ / min. 3 To control the nitrogen content, if the nitrogen content was high in the previous furnace, the nitrogen blowing amount in this furnace will be controlled at the lower limit; if the nitrogen content was low in the previous furnace, the nitrogen blowing amount in this furnace will be controlled at the upper limit.

[0023] The two methods mentioned above are mainly based on the nitrogen content detection of the previous batch and the nitrogen blowing operation is carried out based on experience. They do not take into account the influence of nitrogen content, iron-to-steel ratio, tapping time, and final carbon content on nitrogen content in the actual production process. As a result, the nitrogen content in the final product fluctuates greatly and is unstable. Therefore, there is an urgent need for more accurate nitrogen content calculation and nitrogen increase methods.

[0024] 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.

[0025] The test materials used in the embodiments of this invention, unless otherwise specified, are all conventional test materials in the art and can be purchased through commercial channels.

[0026] Example 1: Smelting of HRB400E-1 steel The HRB400E (HRB400E-1) steel grade adopts vanadium-nitrogen microalloying, with a target vanadium content of 0.033% and a target nitrogen content of 0.011% (110ppm). The specific smelting steps are as follows: (1) 32 tons of scrap steel were added to the converter and 135 tons of molten iron were added.

[0027] (2) High-pressure oxygen is blown into the molten pool through the oxygen lance at the top of the converter. During the oxygen blowing process, lime, dolomite and other slag-forming agents are added. The oxygen reacts with impurities such as carbon, silicon, manganese and phosphorus in the molten iron to carry out decarburization, dephosphorization and desulfurization.

[0028] (3) Temperature measurement and sampling: The temperature of molten steel is measured multiple times during smelting, and samples are taken to analyze the composition and determine the smelting process.

[0029] (4) When the final carbon content is 0.08% and the temperature is 1620℃, the target requirements for steel composition and temperature are met. Then, oxygen blowing is stopped and the steel tapping operation is carried out.

[0030] (5) During the tapping process, a deoxidizer (silicon-calcium-barium) is added to the ladle to remove oxygen from the molten steel. At the same time, alloy materials (carbon powder, high manganese, silicon-manganese, vanadium-nitrogen) are added to adjust the steel composition. The deoxidizer is added first, followed by the vanadium-nitrogen alloy. The time interval between the addition of the deoxidizer and the vanadium-nitrogen alloy is guaranteed to be more than 30 seconds.

[0031] (6) When the endpoint [C] ≥ 0.10%, no deoxidizer is added; when the endpoint [C] < 0.10%, 0.2 kg / t of silicon-calcium-barium steel is added for every 0.01% decrease. 160 kg of carbon powder, 400 kg of high manganese, 2070 kg of silicon-manganese, and 74 kg of vanadium-nitrogen are added by weighing in the silo.

[0032] (7) During the tapping process, the tapping time is automatically identified and recorded as 3 minutes.

[0033] (8) One minute after the steel tapping begins, argon gas is introduced through the automatic nitrogen-argon switching system of the ladle car.

[0034] (9) The online roller scale weighed 158 tons of molten steel in one furnace.

[0035] (10) The converter steel output per heat was 158 tons, the vanadium-nitrogen alloy nitrogen content was 16%, the yield was 60%, the addition amount was 74 kg, the iron-to-steel ratio was 0.854 (135 tons of hot metal / 158 tons of steel), the tapping time was 3 min, the final carbon content was 0.08%, and the target nitrogen content was 0.011% (110 ppm). The relationship between nitrogen increase N1 due to iron-to-steel ratio and iron-to-steel ratio is: N1 = a * Tiron-to-steel ratio + b, where a and b are coefficients, a = -110 and b = 130. Nitrogen increase N1 due to iron-to-steel ratio in a heat run = -110 * 0.854 + 130 = 36.06 (ppm); The relationship between the nitrogen addition amount (N2) and the total amount of vanadium-nitrogen alloy added is: N2 = Qvanadium * Qnitrogen content * Q yield / Q tapping amount. The nitrogen addition amount (N2) for a single heat of vanadium-nitrogen alloy is: N2 = 74 * 16% * 60% / 158 * 1000 = 44.96 (ppm). The relationship between nitrogen increase (N3) and tapping time is: N3 = c * T_tapping time + d, where c and d are coefficients, c = 4 and d = -8. Tapping times less than 2 minutes are calculated as 2 minutes, and tapping times greater than 5 minutes are calculated as 5 minutes. Nitrogen increase per heat tapping time (N3) = 4 * 3 - 8 = 4 (ppm). The relationship between the final carbon-nitrogen increase (N4) and the tapping time is: N4 = e * Tfinal carbon + f = 5555.6 * Tfinal carbon - 1.1, where e and f are coefficients, e is 5555.6, and f is -1.1. The final carbon content is calculated as 0.02% if it is below 0.02%, and as 0.20% if it is above 0.2%. The final carbon-nitrogen increase for a heat is N4 = 5555.6 * 0.08% - 1.1 = 3.34 (ppm). The relationship between the nitrogen increase N5 from bottom blowing in the ladle and the total nitrogen volume from bottom blowing in the ladle is: N5 = j * T_bottom blowing in the ladle + h, where j and h are coefficients, j is 2.36 and h is 1.64. Therefore, the nitrogen increase N5 from bottom blowing in the ladle for a heat is calculated as: N5 = 2.36 * T_bottom blowing in the ladle + 1.64. (11) The nitrogen increase amount N5 from bottom blowing of the ladle in this heat is automatically calculated. N5 = (target N - N1 - N2 - N3 - N4) = (110 - 36.06 - 44.96 - 4 - 3.34) = 21.64; the nitrogen increase amount T_bottom blowing of the ladle in this heat = (N5 - 1.64) / 2.36 = (21.64 - 1.64) / 2.36 = 8.47. To achieve the target nitrogen content of 110 ppm, the nitrogen increase amount from bottom blowing of the ladle in this heat is 8.47 m³ / s. 3 .

[0036] (12) After the calculation is completed, the automatic nitrogen-argon switching system of the ladle car starts to switch to nitrogen blowing. When the amount of nitrogen blown into the ladle for this heat reaches the calculated amount of 8.47m³, the nitrogen will be introduced. 3 Then, it automatically switches to bottom-blowing argon gas from the ladle.

[0037] Example 2: Smelting of HRB400E-2 steel The HRB400E (HRB400E-2) steel grade adopts vanadium-nitrogen microalloying, with a target vanadium content of 0.042% and a target nitrogen content of 0.012% (120ppm). The specific smelting steps are as follows: (1) 34 tons of scrap steel were added to the converter and 134 tons of molten iron were added.

[0038] (2) High-pressure oxygen is blown into the molten pool through the oxygen lance at the top of the converter. During the oxygen blowing process, lime, dolomite and other slag-forming agents are added. The oxygen reacts with impurities such as carbon, silicon, manganese and phosphorus in the molten iron to carry out decarburization, dephosphorization and desulfurization.

[0039] (3) Temperature measurement and sampling: The temperature of molten steel is measured multiple times during smelting, and samples are taken to analyze the composition and determine the smelting process.

[0040] (4) The final carbon content is 0.10% and the temperature is 1630℃, which meets the target requirements for steel composition and temperature. Oxygen blowing is stopped and steel tapping is carried out.

[0041] (5) During the tapping process, a deoxidizer (silicon-calcium-barium) is added to the ladle to remove oxygen from the molten steel. At the same time, alloy materials (carbon powder, high manganese, silicon-manganese, vanadium-nitrogen) are added to adjust the steel composition. The deoxidizer is added first, followed by the vanadium-nitrogen alloy. The time interval between the addition of the deoxidizer and the vanadium-nitrogen alloy is guaranteed to be more than 40 seconds.

[0042] (6) When the endpoint [C] ≥ 0.10%, no deoxidizer is added; when the endpoint [C] < 0.10%, 0.2 kg / t of silicon-calcium-barium steel is added for every 0.01% decrease. 120 kg of carbon powder, 450 kg of high manganese, 2150 kg of silicon-manganese, and 100 kg of vanadium-nitrogen are added by weighing in the silo.

[0043] (7) During the tapping process, the tapping time is automatically identified and recorded as 3.5 min.

[0044] (8) One minute after the steel tapping begins, argon gas is introduced through the automatic nitrogen-argon switching system of the ladle car.

[0045] (9) The online roller scale weighed 159 tons of molten steel in one furnace.

[0046] (10) The converter output was 159 tons, the nitrogen content of the vanadium-nitrogen alloy was 15.4%, the yield was 60%, the addition amount was 100 kg, the iron-to-steel ratio was 0.843 (134 tons of hot metal / 159 tons of steel), the tapping time was 3.5 min, the final carbon content was 0.10%, and the target nitrogen content was 0.012% (120 ppm). The relationship between nitrogen increase N1 due to iron-to-steel ratio and iron-to-steel ratio is: N1 = a * Tiron-to-steel ratio + b, where a and b are coefficients, a = -110 and b = 130. Nitrogen increase N1 due to iron-to-steel ratio in a heat run = -110 * 0.843 + 130 = 37.27 (ppm); The relationship between the nitrogen addition amount (N2) and the total amount of vanadium-nitrogen alloy added is: N2 = Qvanadium * Qnitrogen content * Q yield / Q tapping amount. The nitrogen addition amount (N2) for a single heat of vanadium-nitrogen alloy is: N2 = 100 * 15.4% * 60% / 159 * 1000 = 58.11 (ppm). The relationship between nitrogen increase (N3) and tapping time is: N3 = c * T_tapping time + d, where c and d are coefficients, c = 4 and d = -8. Tapping times less than 2 minutes are calculated as 2 minutes, and tapping times greater than 5 minutes are calculated as 5 minutes. Nitrogen increase per heat tapping time (N3) = 4 * 3.5 - 8 = 6 (ppm). The relationship between the final carbon-nitrogen increase (N4) and the tapping time is: N4 = e * Tfinal carbon + f = 5555.6 * Tfinal carbon - 1.1, where e and f are coefficients, e is 5555.6, and f is -1.1. The final carbon content is calculated as 0.02% if it is below 0.02%, and as 0.20% if it is above 0.2%. The final carbon-nitrogen increase for a heat is N4 = 5555.6 * 0.10% - 1.1 = 4.46 (ppm). The relationship between the nitrogen increase N5 from bottom blowing in the ladle and the total nitrogen volume from bottom blowing in the ladle is: N5 = j * T_bottom blowing in the ladle + h, where j and h are coefficients, j is 2.36 and h is 1.64. Therefore, the nitrogen increase N5 from bottom blowing in the ladle for a heat is calculated as: N5 = 2.36 * T_bottom blowing in the ladle + 1.64. (11) Automatically calculate the nitrogen increase N5 from bottom blowing in the ladle for this heat. Nitrogen increase N5 = (Target N - N1 - N2 - N3 - N4) = (110 - 37.27 - 58.11 - 6 - 4.46) = 14.16; Nitrogen increase T_bottom blowing = (N5 - 1.64) / 2.36 = (14.16 - 1.64) / 2.36 = 5.31. To achieve the target nitrogen content of 120 ppm, the nitrogen increase T_bottom blowing for this heat is 5.31 m³ / min. 3 .

[0047] (12) After the calculation is completed, the automatic nitrogen-argon switching system of the ladle car starts to switch to nitrogen blowing. When the amount of nitrogen blown into the ladle for this heat reaches the calculated amount of 5.31m³, the nitrogen will be introduced. 3Then, it automatically switches to bottom-blowing argon gas from the ladle.

[0048] This invention has strong practical guidance. Statistical analysis shows that the pass rate of nitrogen content control (target nitrogen content ±10ppm) in HRB400E steel reaches over 90%, with stable nitrogen content control and small fluctuations, which makes a significant contribution to improving the performance of rolled products and reducing alloy costs.

[0049] 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 method for increasing nitrogen content in molten steel, characterized in that, include: In the steelmaking process, based on the target nitrogen content (N) of vanadium microalloyed low alloy steel... 目标 The nitrogen increase amounts N1 (for the iron-to-steel ratio), N2 (for the vanadium-nitrogen alloy), N3 (for the tapping time), and N4 (for the final carbon nitrogen increase) are controlled to obtain the ladle bottom-blowing nitrogen amount N5. This amount is then used for ladle bottom blowing to achieve nitrogen increase in molten steel. The formula for calculating the ladle bottom-blowing nitrogen amount N5 is as follows: Nitrogen gas volume N5 for bottom blowing of ladle = (N 目标 -N1-N2-N3-N4).

2. The method for increasing nitrogen content in molten steel according to claim 1, characterized in that, Nitrogen increase N1 in iron-to-steel ratio and iron-to-steel ratio T 铁钢比 The relationship is as follows: N1=a*T 铁钢比 +b, Where a = -110, b = 130, T 铁钢比 It ranges from 0.6 to 1.

0.

3. The method for increasing nitrogen content in molten steel according to claim 1, characterized in that, Low-alloy steel is microalloyed using vanadium and nitrogen. The amount of nitrogen added (N2) and the amount of vanadium and nitrogen alloy added (Q) are related. 钒氮 And Q 出钢量 The relationship is as follows: N2=Q 钒氮 *Q 氮含量 *Q 收得率 / Q 出钢量 。 4. The method for increasing nitrogen content in molten steel according to claim 1, characterized in that, When tapping steel from the converter, the deoxidizer is added first, followed by the vanadium-nitrogen alloy. The time interval between the addition of the deoxidizer and the vanadium-nitrogen alloy is 30-100 seconds.

5. The method for increasing nitrogen content in molten steel according to claim 1, characterized in that, Nitrogen increase N3 during tapping time and tapping time T 出钢时间 The relationship is as follows: N3=c*T 出钢时间 +d, Where c=4 and d=-8, Steel tapping time T 出钢时间 The time is 2-5 minutes. Less than 2 minutes is recorded as 2 minutes, and more than 5 minutes is recorded as 5 minutes.

6. The method for increasing nitrogen content in molten steel according to claim 1, characterized in that, The final carbon-nitrogen increase (N4) and the tapping time (T) 终点碳 The relationship between them is as follows: N4=e*T 终点碳 +f, Where e = 5555.6, f = -1.1, The endpoint carbon content is 0.02%-0.2%, with values ​​below 0.02% recorded as 0.02% and values ​​above 0.2% recorded as 0.2%.

7. The method for increasing nitrogen content in molten steel according to claim 1, characterized in that, Nitrogen increase amount N5 and nitrogen volume T of bottom blowing in ladle 钢包底吹 The relationship is as follows: N5=j*T 钢包底吹 +h, Where j=2.36, h=1.64, The nitrogen flow rate for bottom blowing in the ladle is 20-1000 L / min.

8. The method for increasing nitrogen content in molten steel according to claim 1, characterized in that, Once the nitrogen gas volume at the bottom of the ladle reaches the calculated amount, it will automatically switch to argon gas at the bottom of the ladle.

9. The precise nitrogen control model constructed by the steel nitrogen increase method according to any one of claims 1-8.

10. The application of the nitrogen enrichment method for molten steel according to any one of claims 1-8 in the control of nitrogen content in steel.