A method for direct tapping of molten iron by pre-desulfurization in high-speed rail steel smelting process

Abstract

The present invention belongs to the field of metallurgical technology, and relates to a method for direct iron tapping in the process of high-speed rail steel smelting by pre-desulfurization of molten iron. After the molten iron desulfurization starts to be blown, according to the existing secondary model, before the blowing ends, the molten iron temperature is measured online, and the actual consumption ratio of magnesium powder and lime is calculated; according to the deviation between the molten iron temperature, the actual consumption ratio of magnesium powder and lime and the calculated value of the secondary model, the type and amount of magnesium powder and lime added are controlled, and then the S content at the end of the molten iron is guaranteed by controlling the bottom blowing gas flow rate. The present invention can tap iron at the end of desulfurization and blowing without re-blowing, and the production smelting cycle is reduced by 3.5 minutes on average, reducing the production cost by 12.5 yuan / ton. Compared with the traditional molten iron pre-desulfurization process, the present invention effectively improves the production efficiency of molten iron pre-desulfurization and reduces the production cost.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a method for pre-desulfurizing molten iron and directly tapping iron in a high-speed rail steel smelting process. Background Art

[0002] As the support of the railway, rails are an important foundation. Because it involves human life safety issues, rail steel has the most stringent quality requirements compared to other steels. At present, most high-quality steel on the market requires molten iron pretreatment during smelting. On the one hand, the sulfur content in the finished product can be controlled at an extremely low level. On the other hand, the desulfurization of molten iron pretreatment can reduce the desulfurization pressure of off-furnace refining, so that off-furnace refining can better remove non-metallic inclusions in molten steel. In the process of high-quality steel smelting, molten iron pretreatment, as a basic treatment method, is responsible for providing low-sulfur molten iron for converter smelting, reducing the desulfurization burden of subsequent refining processes, and improving the internal quality of molten steel. Therefore, molten iron pretreatment is a necessary condition for high-quality steel smelting.

[0003] Due to the special nature of railway rails, aluminum-free deoxidation technology is used in the smelting process. The refining is controlled by low-basicity slag, and the desulfurization ability is weak. This further requires that the sulfur content in the molten iron needs to be controlled to a very low level in the molten iron pretreatment process before entering the converter to meet the high-speed rail standard requirements. However, in the traditional smelting process of high-speed rail steel, the long process of molten iron pretreatment brings great cost pressure to the steel mill. Whether it is the composite injection method or the KR stirring method desulfurization, after the desulfurizer reacts with the molten iron, it is necessary to take samples and send them to the laboratory for analysis. Only after the test results are qualified can the iron be directly tapped; if the test results are unqualified, it is necessary to spray, sample, analyze again, and then tap the iron. It takes 3-5 minutes from sampling to the reporting of the test results, and 10-12 minutes for spraying, sampling, and analysis again. The lengthy molten iron desulfurization cycle, waiting for samples, and slag removal seriously affect the improvement of production efficiency and the reduction of costs.

[0004] Patent CN201711165245.X provides a method for controlling the sulfur content in the pre-desulfurization process of molten iron. The core idea is to achieve low-cost pre-desulfurization of molten iron by controlling the use of desulfurizers in different stages of injection. However, it is still impossible to achieve direct iron tapping at the end point and achieve the goal of efficient production.

[0005] Patent CN201510791844.7 provides a method for controlling the sulfur content at the KR endpoint. The core idea is to establish a standardized operation mode to replace the conventional experience operation method and improve the overall desulfurization efficiency, but it does not involve the optimization of the desulfurization process flow. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for direct iron tapping by pre-desulfurization of molten iron in the high-speed rail steel smelting process. Through process innovation, iron tapping without waiting for samples can be achieved, the efficiency of molten iron pre-desulfurization can be improved, and the production cost can be reduced.

[0007] The technical solution adopted by the present invention is: after the desulfurization of molten iron begins to be blown, according to the existing secondary model, before the end of the blown, the molten iron temperature is measured online and the actual consumption ratio of magnesium powder and lime is calculated;

[0008] (1) If there are deviations between the molten iron temperature, the actual consumption ratio of magnesium powder and lime and the values ​​calculated by the secondary model, that is, the difference between the molten iron temperature and the target temperature is ≥10°C, and the deviation between the actual consumption ratio of magnesium powder and lime and the values ​​calculated by the secondary model is ≥5%, then ≤0.8 kg / t of magnesium powder is added, and the blowing time calculated by the secondary model is delayed by 3 minutes as the blowing end point. At the same time, during the blowing process, the purge gas is set at 200±10 Nm 3 / h flow rate is controlled until the blowing is completed, and then the iron is tapped; this operation is carried out under the most unfavorable conditions where the temperature calculated by the secondary model, the actual consumption ratio of magnesium powder and lime are all deviated, and the strong desulfurizer magnesium powder is added to create conditions for continued desulfurization of the molten iron. At the same time, at the end point, the conditions for continued desulfurization are created by continuing to blow nitrogen, and then the bottom blowing control with the maximum flow rate is used to achieve strong stirring of the molten pool, so as to maximize the hit of the S content of the molten iron end point.

[0009] (2) If the molten iron temperature is hit, and there is a deviation between the actual consumption ratio of magnesium powder and lime and the value calculated by the secondary model, that is, the difference between the molten iron temperature and the target temperature is less than 10°C, and the actual consumption ratio of magnesium powder and lime deviates from the value calculated by the secondary model by ≥5%, then ≤0.5kg / t of magnesium powder and ≤1.5kg / t of lime are added, and the blowing time calculated by the secondary model is delayed by 2 minutes as the blowing end point. At the same time, during the blowing process, the purge gas is ≤180Nm 3 / h flow rate is controlled until the blowing is completed, and then the iron is tapped; this operation is carried out under the unfavorable condition that the consumption ratio of magnesium powder and lime calculated by the model deviates from the actual one, and a certain proportion of magnesium powder and lime are added to create conditions for continued desulfurization of the molten iron, and then a large-flow bottom blowing control method is used to achieve strong stirring of the molten pool, so that the S content of the molten iron endpoint is hit.

[0010] (3) If there is a deviation between the molten iron temperature and the value calculated by the secondary model, the actual consumption ratio of magnesium powder and lime is on target, that is, the difference between the molten iron temperature and the target temperature is ≥10°C, and the deviation between the actual consumption ratio of magnesium powder and lime and the value calculated by the secondary model is less than 5%,

[0011] When the molten iron temperature is positively deviated from the target temperature, lime ≤2.5kg / t is added, and the blowing time calculated by the secondary model is delayed by 2.5min as the blowing end point. During the blowing process, the purge gas is ≤180Nm3 / h flow rate is controlled until the blowing is completed and then the iron is tapped;

[0012] When the molten iron temperature is negative to the target temperature, magnesium powder ≤0.5kg / t is added, and the blowing time calculated by the secondary model is delayed by 1.5min as the blowing end point. During the blowing process, the purge gas is ≤180Nm 3 / h flow rate is controlled until the blowing is completed and then the iron is tapped;

[0013] This operation is to use lime to fully reduce the temperature and increase the activity coefficient of MnS to promote the hit of the endpoint composition, under the premise that there is a positive deviation between the temperature calculated by the secondary model and the actual temperature; under the premise that there is a negative deviation between the temperature calculated by the secondary model and the actual temperature, add an appropriate amount of magnesium powder to continue to improve the desulfurization efficiency of the molten steel and ensure the hit of the endpoint sulfur content; the above two situations are assisted by a bottom blowing control method with a certain flow rate to achieve the stirring of the molten iron, laying the foundation for the hit of the endpoint composition.

[0014] The present invention measures the temperature of molten iron online 3 minutes before the end of blowing.

[0015] In the method (1) of the present invention, 0.6-0.8 kg / t of magnesium powder is added.

[0016] In the method (2) of the present invention, 0.2-0.5 kg / t of magnesium powder and 0.8-1.5 kg / t of lime are added.

[0017] In (3) of the present invention, when the molten iron temperature-target temperature has a positive deviation, 1.5-2.5 kg / t of lime is added; when the molten iron temperature-target temperature has a negative deviation, 0.3-0.5 kg / t of magnesium powder is added.

[0018] In (2) and (3) of the present invention, the purge gas is 150-180 Nm 3 / h flow rate is controlled until the blowing is completed.

[0019] If the molten iron temperature, the actual consumption ratio of magnesium powder and lime are all hit, that is, the difference between the molten iron temperature and the target temperature is less than 10C°, and the deviation between the actual consumption ratio of magnesium powder and lime and the calculated value of the secondary model is less than 5%, blowing and tapping are carried out according to the secondary model.

[0020] The beneficial effect of adopting the above technical scheme is that the traditional high-speed rail steel smelting molten iron pretreatment process adopts the method of spraying desulfurizer, sampling and analysis, and then choosing to spray again or tap iron according to the result, which affects the improvement of production efficiency. However, under the steelmaking process conditions of the secondary calculation model, the present invention performs process control according to the measurement of the auxiliary gun, and can tap iron at the end of desulfurization blowing without re-blowing. The production smelting cycle is reduced by an average of 3.5 minutes, and the production cost is reduced by 12.5 yuan / ton, realizing high-efficiency and low-cost smelting of desulfurization, which can be applied to the steelmaking process on a large scale, is easy to operate and has stable effect. Compared with the traditional molten iron pre-desulfurization process, the present invention can effectively improve the production efficiency of molten iron pre-desulfurization and reduce production costs. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with the embodiments. Example 1

[0022] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0023] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1350℃. The actual consumption ratio of magnesium powder and lime was 1:3.2. The target temperature calculated by the secondary model was 1320℃, and the consumption ratio of magnesium powder and lime was 1:3.5. In view of this situation, 0.6kg / t of magnesium powder was added, and the blowing time calculated by the secondary model was delayed by 3 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 210Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.002%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.2 minutes compared with the normal furnace. Example 2

[0024] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0025] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1320℃. The actual consumption ratio of magnesium powder and lime was 1:3.5. The target temperature calculated by the secondary model was 1330℃, and the consumption ratio of magnesium powder and lime was 1:3.8. In view of this situation, 0.8kg / t of magnesium powder was added, and the blowing time calculated by the secondary model was delayed by 3 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 190Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.001%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.8 minutes compared with the normal furnace. Example 3

[0026] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0027] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1310℃. The actual consumption ratio of magnesium powder and lime was 1:3.2. The target temperature calculated by the secondary model was 1305℃, and the consumption ratio of magnesium powder and lime was 1:3.5. In view of this situation, 0.2kg / t of magnesium powder and 0.8kg / t of lime were added, and the blowing time calculated by the secondary model was delayed by 2 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 150Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.002%, which is no more than 0.004% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 2.9 minutes compared with the normal furnace. Example 4

[0028] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0029] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1320℃. The actual consumption ratio of magnesium powder and lime was 1:3.5. The target temperature calculated by the secondary model was 1318℃, and the consumption ratio of magnesium powder and lime was 1:3.8. In view of this situation, 0.5kg / t of magnesium powder and 1.5kg / t of lime were added, and the blowing time calculated by the secondary model was delayed by 2 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 180Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.004%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.1 minutes compared with the normal furnace. Example 5

[0030] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0031] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1310℃. The actual consumption ratio of magnesium powder and lime was 1:3.4. The target temperature calculated by the secondary model was 1340℃, and the consumption ratio of magnesium powder and lime was 1:3.5. In view of this situation, 1.5kg / t of lime was added, and the blowing time calculated by the secondary model was delayed by 2.5 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 150Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.003%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.5 minutes compared with the normal furnace. Example 6

[0032] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0033] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1305℃. The actual consumption ratio of magnesium powder and lime was 1:3.2. The target temperature calculated by the secondary model was 1320℃, and the consumption ratio of magnesium powder and lime was 1:3.3. In view of this situation, 2.5kg / t of lime was added, and the blowing time calculated by the secondary model was delayed by 2.5 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 180Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.003%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.5 minutes compared with the normal furnace. Example 7

[0034] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0035] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1350℃. The actual consumption ratio of magnesium powder and lime was 1:3.7. The target temperature calculated by the secondary model was 1320℃, and the consumption ratio of magnesium powder and lime was 1:3.8. In view of this situation, 0.3kg / t of magnesium powder was added, and the blowing time calculated by the secondary model was delayed by 1.5 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 150Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.002%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.2 minutes compared with the normal furnace. Example 8

[0036] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0037] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1360℃. The actual consumption ratio of magnesium powder and lime was 1:3.8. The target temperature calculated by the secondary model was 1315℃, and the consumption ratio of magnesium powder and lime was 1:3.9. In view of this situation, 0.5kg / t of magnesium powder was added, and the blowing time calculated by the secondary model was delayed by 1.5 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 180Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.001%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.3 minutes compared with the normal furnace. Example 9

[0038] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0039] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1318℃. The actual consumption ratio of magnesium powder and lime was 1:3.5. The target temperature calculated by the secondary model was 1341℃, and the consumption ratio of magnesium powder and lime was 1:3.7. In view of this situation, 0.7kg / t of magnesium powder was added, and the blowing time calculated by the secondary model was delayed by 3 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 200Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.003%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.6 minutes compared with the normal furnace. Example 10

[0040] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0041] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and the actual consumption ratio of magnesium powder and lime was 1:3.3. The target temperature calculated by the secondary model was 1304°C, and the consumption ratio of magnesium powder and lime was 1:3.5. In view of this situation, 0.4kg / t of magnesium powder and 1.0kg / t of lime were added, and the blowing time calculated by the secondary model was delayed by 2 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 166Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.001%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 2.8 minutes compared with the normal furnace. Embodiment 11

[0042] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0043] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1306℃. The actual consumption ratio of magnesium powder and lime was 1:3.4. The target temperature calculated by the secondary model was 1318℃, and the consumption ratio of magnesium powder and lime was 1:3.5. In view of this situation, 2.2kg / t of lime was added, and the blowing time calculated by the secondary model was delayed by 2.5 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 175Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.004%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.3 minutes compared with the normal furnace. Example 12

[0044] This embodiment takes a ladle with a nominal capacity of 120 tons as an example to illustrate that during the smelting of high-speed rail steel, during the pretreatment of molten iron, blowing and control are performed according to the calculation amount of the secondary model.

[0045] The molten iron temperature was measured online 3 minutes before the end of the first blowing, and it was 1344℃. The actual consumption ratio of magnesium powder and lime was 1:3.6. The target temperature calculated by the secondary model was 1321℃, and the consumption ratio of magnesium powder and lime was 1:3.7. In view of this situation, 0.4kg / t of magnesium powder was added, and the blowing time calculated by the secondary model was delayed by 1.5 minutes as the blowing end point. At the same time, during the blowing process, the purge gas flow rate was 160Nm 3 / h until the blowing is completed, and then the iron is tapped. After this tapping, the S content of the molten iron is 0.002%, which is no more than 0.005% lower than the standard requirement, meeting the quality requirements of high-speed rail steel and achieving unequal tapping. The smelting time is reduced by 3.2 minutes compared with the normal furnace.

Claims

1. A method for direct tapping of molten iron by pre-desulfurization in the high-speed rail steel smelting process, characterized in that: After the hot metal desulfurization starts, the hot metal temperature is measured online and the actual consumption ratio of magnesium powder and lime is calculated before the end of the blowing according to the existing secondary model; (1) If there are deviations between the molten iron temperature, the actual consumption ratio of magnesium powder and lime and the values ​​calculated by the secondary model, that is, the difference between the molten iron temperature and the target temperature is ≥10°C, and the deviation between the actual consumption ratio of magnesium powder and lime and the values ​​calculated by the secondary model is ≥5%, then 0.6-0.8 kg / t of magnesium powder is added, and the blowing time calculated by the secondary model is delayed by 3 minutes as the blowing end point. At the same time, during the blowing process, the purge gas is adjusted at 200±10 Nm 3 / h maximum flow rate is controlled until the blowing is completed and then the iron is tapped; (2) If the molten iron temperature is hit, and there is a deviation between the actual consumption ratio of magnesium powder and lime and the value calculated by the secondary model, that is, the difference between the molten iron temperature and the target temperature is less than 10°C, and the actual consumption ratio of magnesium powder and lime is ≥5% different from the value calculated by the secondary model, then 0.2-0.5 kg / t of magnesium powder and 0.8-1.5 kg / t of lime are added, and the blowing time calculated by the secondary model is delayed by 2 minutes as the blowing end point. At the same time, during the blowing process, the purge gas is ≤180 Nm 3 / h flow rate is controlled until the blowing is completed and then the iron is tapped; (3) If there is a deviation between the molten iron temperature and the value calculated by the secondary model, the actual consumption ratio of magnesium powder and lime is on target, that is, the difference between the molten iron temperature and the target temperature is ≥10°C, and the deviation between the actual consumption ratio of magnesium powder and lime and the value calculated by the secondary model is less than 5%, When the target temperature - molten iron temperature is a positive deviation, lime is added at 1.5-2.5 kg / t, and the blowing time calculated by the secondary model is delayed by 2.5 min as the blowing end point. During the blowing process, the purge gas is ≤180 Nm 3 / h flow rate is controlled until the blowing is completed and then the iron is tapped; When the target temperature - molten iron temperature is a negative deviation, 0.3-0.5 kg / t of magnesium powder is added, and the blowing time calculated by the secondary model is delayed by 1.5 min as the blowing end point. During the blowing process, the purge gas is ≤180 Nm 3 / h flow rate is controlled until the blowing is completed and then the iron is tapped; In (2) and (3), the purge gas is 150-180 Nm 3 / h flow rate is controlled until the blowing is completed.

2. The method for direct tapping of molten iron during high-speed rail steel smelting according to claim 1, characterized in that: Measure the temperature of the molten iron online 3 minutes before the end of blowing.