Method for improving recovery of ferromolybdenum in converter process

Abstract

This invention belongs to the technical field of iron and steel smelting, specifically relating to a method for improving the recovery rate of ferromolybdenum in the converter process. The method involves alloying during the tapping process, with bottom-blowing argon in the ladle and an argon flow rate controlled in a "small-large-small" manner. When the converter has tapped half its capacity, the ferromolybdenum alloy is added in batches. This method solves the problem of low and fluctuating molybdenum recovery rate in the ferromolybdenum alloy process in the converter. It not only provides a foundation for improving the performance and stability of subsequent products but also reduces alloy consumption and costs in the converter process.

Description

Technical Field

[0001] This invention belongs to the technical field of iron and steel smelting, specifically relating to a method for improving the recovery rate of ferromolybdenum in the converter process. Background Technology

[0002] In the production of low-alloy steel, molybdenum can increase the solid solubility of microalloying elements such as niobium, vanadium, and titanium in austenite, and delay the precipitation of carbonitrides of these microalloying elements, thereby improving the strength and low-temperature performance of the steel. Therefore, ferromolybdenum is often added for microalloying treatment in the production of high-strength steel, low-temperature resistant steel, fire-resistant steel, and alloy structural steel.

[0003] In existing production processes, ferromolybdenum alloying is generally added before adding molten iron to the converter. This method facilitates the melting of ferromolybdenum and improves the uniformity of molybdenum in the molten steel. However, due to the high oxidizing properties within the converter, the ferromolybdenum recovery rate is generally low, typically around 92%. Furthermore, factors such as slag residue from converter decomposition and slag splashing during furnace protection cause significant fluctuations in the ferromolybdenum recovery rate.

[0004] Patent CN113801975A provides a method for improving the yield of ferromolybdenum alloy. This patent improves the ferromolybdenum recovery rate by controlling the converter end temperature and the converter end oxygen content; using a forklift to alloy ferromolybdenum after tapping; and continuously blowing argon gas at the bottom during alloying.

[0005] However, this method has a low degree of automation, and because the density of the ferromolybdenum alloy is lower than that of molten steel, it floats on the surface of the molten steel after being added, resulting in uneven distribution of molybdenum in the molten steel and increasing the risk of fluctuations in molybdenum recovery rate. Furthermore, this method requires continuous bottom-blowing of argon gas into the ladle after adding the ferromolybdenum alloy, with the argon gas flow rate maintained at 20–90 m³ / h. 3 The rate of argon gas consumption will increase, and in order to ensure that the slag in the ladle does not overflow during high-flow-rate argon bottom blowing, the ladle clearance must be maintained at 500mm to 650mm, which will cause production difficulties in the RH furnace.

[0006] Patent CN101525718A provides an alloying process for stabilizing and precisely controlling the molybdenum content in steel. This patent stabilizes the molybdenum content in steel by controlling the converter tapping temperature; adding alloying materials and ferromolybdenum when the steel is 1 / 5 to 1 / 4 tapped; and using a large volume of argon gas for stirring and adding ferromolybdenum during refining throughout the tapping process.

[0007] However, this method has the following drawbacks: (1) When ferromolybdenum and other alloys (ferrochrome, ferromanganese, ferrosilicon, etc.) are added at the same time, the temperature of the molten steel is 1680-1740℃, which is far above 600℃. At temperatures of 600℃ and above, molybdenum will be rapidly oxidized into molybdenum trioxide and molybdenum dioxide. This leads to the oxidation of molybdenum in ferromolybdenum, thereby reducing the recovery rate of molybdenum in ferromolybdenum. (2) The use of high-flow-rate bottom blowing argon in the ladle will increase the exposed area and time of the molten steel, and increase the nitrogen absorption of the molten steel. Especially when aluminum deoxidation is used, the nitrogen absorption of the molten steel is 20-50ppm, which leads to large fluctuations in the nitrogen content of the molten steel, thereby reducing the stability of the steel strength and low-temperature toughness. At the same time, the use of high-flow-rate bottom blowing argon will increase the consumption of argon. In order to ensure that the slag in the ladle does not overflow when the argon is blown at a high flow rate, the ladle must be kept clear, generally within the range of 500mm to 650mm, which will cause production difficulties in the RH furnace.

[0008] Patent CN101413044A discloses an alloy addition method to improve the yield of ferromolybdenum. This patent improves the recovery rate of molybdenum in ferromolybdenum by controlling the converter tapping temperature; adding the alloy to a high-level silo; adding the alloy and ferromolybdenum when the tapping volume reaches 1 / 2; and using high-flow-rate argon agitation throughout the tapping process. However, this method has the following drawbacks: The constant high-flow-rate bottom blowing of argon into the ladle, requiring molten steel surface agitation, results in a longer exposed area and time for the molten steel, increasing nitrogen absorption. In particular, the patent uses aluminum particles for deoxidation, further enhancing the nitrogen absorption capacity of the molten steel, with nitrogen absorption fluctuating between 20-50 ppm. This leads to large fluctuations in nitrogen content in the molten steel, reducing the stability of the steel's strength and low-temperature toughness. Simultaneously, the constant high-flow-rate bottom blowing of argon increases argon consumption, and to prevent slag overflow during high-flow-rate bottom blowing, the ladle clearance generally needs to be maintained at 500mm-650mm, causing difficulties in RH furnace production. Summary of the Invention

[0009] The purpose of this invention is to provide a method for improving the recovery rate of ferromolybdenum alloy in the converter process, solving the problem of low and fluctuating molybdenum recovery rate in the ferromolybdenum alloy in the converter process. This method can not only provide a foundation for improving the performance and stability of subsequent products, but also reduce alloy consumption in the converter process and reduce alloy usage costs.

[0010] The specific technical solution is as follows:

[0011] A method for improving the recovery rate of ferromolybdenum in the converter process involves alloying during the converter tapping process. The specific operation is as follows:

[0012] When the molten steel has been poured to 1 / 4 full, alloys other than ferromolybdenum are added to the molten steel in the ladle according to the steel composition requirements; when the molten steel has been poured to 3 / 4 full, all alloys other than ferromolybdenum that meet the steel composition requirements are added.

[0013] Adding the alloy when the molten steel has reached 1 / 4 of its pour length ensures that it is thoroughly agitated in the ladle under the impact of the molten steel, thus improving the uniformity of elements in the molten steel. Adding the alloy (excluding ferromolybdenum) first reduces the oxygen content in the molten steel, thereby preventing excessive oxidation of molybdenum in the ferromolybdenum and improving the molybdenum recovery rate.

[0014] When the molten steel has been poured to half its capacity, ferromolybdenum is added to the molten steel in the ladle in batches, and the ferromolybdenum is added completely before the end of the tapping process.

[0015] During the alloying process in the steel tapping process, bottom blowing argon is initiated in the molten steel ladle: the initial argon flow rate in the molten steel ladle is controlled at 0-20 m³ / s. 3 / h; During the middle stage of steelmaking, the argon gas flow rate in the ladle is controlled at 20-50m³ / h. 3 / h; the argon gas flow rate in the ladle during the later stages of tapping is controlled at 10-20m³ / h. 3 / h; After tapping, the argon gas flow rate is controlled at 5-10m³ / h. 3 / h, it is advisable to allow the liquid level to fluctuate slightly.

[0016] In addition to reducing argon consumption, this method of controlling the argon flow rate has the following advantages: Initially, the ladle contains less molten steel, resulting in a lower bottom-blowing argon flow rate; during the middle stages of tapping, the ladle contains more molten steel, allowing for a higher bottom-blowing argon flow rate. This ensures thorough mixing of the deoxidizer, alloying agents, and ferromolybdenum, leading to a more uniform steel composition. Maintaining the flow rate at 20-50 m³ / min... 3 Within the flow rate range of / h, this ensures sufficient stirring while also preventing excessive exposure of the molten steel surface to air, thereby reducing the amount of nitrogen absorbed by the molten steel. Later, the bottom-blowing argon flow rate is reduced to further ensure that the molten steel surface is not excessively exposed to air and to reduce the amount of nitrogen absorbed by the molten steel.

[0017] Furthermore, the specific control of argon flow rate in the bottom blowing of the molten steel ladle in the method for improving the ferromolybdenum recovery rate in the converter process is as follows:

[0018] From the start of tapping until one-quarter of the tapping time, the argon flow rate is controlled between 0-20 m³ / s. 3 / h;

[0019] During the period from 1 / 4 to 3 / 4 of the tapping time, the argon flow rate is controlled at 20-50 m³ / h. 3 / h;

[0020] From 3 / 4 of the tapping time to the completion of tapping, the argon gas flow rate is controlled at 10-20 m³ / h. 3 / h.

[0021] Furthermore, in the method for improving the recovery rate of ferromolybdenum in the converter process, the particle size of the ferromolybdenum is 20-40 mm. Using low-particle-size ferromolybdenum increases the contact area between the ferromolybdenum alloy and the molten steel, which is beneficial to increasing the melting rate of the ferromolybdenum.

[0022] Furthermore, the other alloys used in the method for improving the recovery rate of ferromolybdenum in the converter process include ferrosilicon manganese, medium-carbon ferromanganese, or high-carbon ferromanganese. GB / T3795-2014 specifies the specific content of medium-carbon and high-carbon ferromanganese, with medium-carbon ferromanganese grades divided into FeMn82C1.0, FeMn82C1.5, and FeMn78C2.0. High-carbon ferromanganese grades are divided into FeMn78C8.0, FeMn74C7.5, and FeMn68C7.0. The absence of aluminum-containing alloys is to avoid high aluminum content in the molten steel, which would lead to excessive nitrogen absorption.

[0023] Furthermore, in the method for improving the recovery rate of ferromolybdenum in the converter process, ferromolybdenum is added to the molten steel in 1-2 batches.

[0024] Furthermore, the amount of ferromolybdenum added in the method for improving the ferromolybdenum recovery rate in the converter process is calculated according to formula (1):

[0025]

[0026] In the formula, t MoFe The amount of ferromolybdenum added is expressed in kg / t steel; wt Mo The target molybdenum content for this steel grade is the median limit, %; wt′ Mo The molybdenum content in ferromolybdenum, %; R Mo The molybdenum recovery rate of ferromolybdenum alloy, %.

[0027] The content of ferromolybdenum is specified by the national standard GB / T3649-2008. The "median limit" refers to the arithmetic mean of the upper and lower limits of the content of a certain element. For example, if the molybdenum content ranges from 0.15% to 0.25%, its "median limit" is (0.15% + 0.25%) / 2 = 0.20%.

[0028] When producing the first furnace, the "molybdenum recovery rate" is calculated based on the theoretical recovery rate; when producing the second furnace, the "molybdenum recovery rate" can be calculated using the recovery rate of the previous furnace; when producing the third furnace, the "molybdenum recovery rate" is calculated by summing the recovery rates of the first two furnaces and then averaging them; when producing the fourth furnace, the "molybdenum recovery rate" is calculated by summing the recovery rates of the first three furnaces and then averaging them; and so on, that is, the "molybdenum recovery rate" of the Nth furnace is the arithmetic average of all molybdenum recovery rates from the first furnace to the (N-1)th furnace.

[0029] Furthermore, in the method for improving the recovery rate of ferromolybdenum in the converter process, a sliding plate is used to block slag at the end of the tapping stage to ensure that no slag is discharged from the molten steel.

[0030] The beneficial effects of the present invention are as follows: the method for improving the recovery rate of ferromolybdenum alloy in the converter process is to carry out alloying during the steel tapping process, to open the bottom blowing argon in the ladle, and to add ferromolybdenum alloy with a particle size of 20-40mm in batches when the converter tapping reaches 1 / 2.

[0031] Under conditions that meet production requirements, the method described in this invention can improve and stabilize the molybdenum recovery rate in ferromolybdenum alloys during the production process. The molybdenum recovery rate using this method can reach 96.0%–97.7%, with an average recovery rate of 96.9% and a fluctuation range of only 0.8%–0.9%. Furthermore, the amount of ferromolybdenum added is reduced by at least 6% compared to existing processes, lowering the production cost of alloying in the converter production process. Specific advantages are as follows:

[0032] (1) Adding ferromolybdenum alloy during the tapping process and using the impact of molten steel to stir the ferromolybdenum alloy and homogenize it.

[0033] (2) No additional equipment such as forklifts is needed, which reduces the investment in production equipment and thus reduces production costs.

[0034] (3) The present invention adopts the control method of "argon flow rate in small-large-small", which does not require restrictions on the clearance of the steel ladle, and the process is highly usable. Moreover, compared with the continuous, full-process high-flow-rate bottom blowing argon in the existing process, the method of the present invention greatly reduces the consumption of energy media such as argon, thereby reducing process costs.

[0035] (4) By carrying out deoxidation and ferromolybdenum alloying in different stages during the steelmaking process, the present invention greatly improves the molybdenum yield and stability of ferromolybdenum, reduces the amount of ferromolybdenum added, and reduces the alloying production cost. Attached Figure Description

[0036] Figure 1 This is a graph showing the relationship between the argon flow rate control in the molten steel ladle and the tapping time in Example 1. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0038] 1. Method for determining molybdenum content in ferromolybdenum: According to the lead molybdate gravimetric method in the national standard GB / T3649-2008, the sample is dissolved in dilute nitric acid, EDTA complexes the iron, and in the presence of acetic acid and ammonium acetate, ammonium acetate is added to precipitate molybdenum to form lead molybdate. After filtration, washing, ignition, and weighing, the sample is then weighed.

[0039] 2. R Mo The value is calculated based on the lowest recovery rate derived from multiple production runs using the content described in this patent.

[0040] 3. The molybdenum recovery rate of ferromolybdenum alloy in each heat is calculated as follows:

[0041] Molybdenum recovery rate = (Measured percentage of molybdenum in steel × 1000) / (wt')Mo ×t MoFe )×100%.

[0042] Example 1

[0043] When a steel plant produces Q690D steel, the specific production steps and key process control points for improving the ferromolybdenum recovery rate in the converter process, as described in this invention, are as follows:

[0044] When the molten steel has been poured to 1 / 4 of its capacity, alloys such as metallic manganese, ferrosilicon, ferrochrome, and ferroniobium are added to the molten steel in the ladle according to the steel composition requirements; when the molten steel has been poured to 3 / 4 of its capacity, all alloys except ferromolybdenum that meet the steel composition requirements are added.

[0045] When the molten steel has been poured to 1 / 2, ferromolybdenum with a particle size of 20-40mm is added to the molten steel in the ladle in two batches. The addition of ferromolybdenum is completed before the end of tapping.

[0046] During the alloying process in the steel tapping process, the bottom blowing of argon gas is initiated in the ladle. The specific details of argon gas flow control are as follows: Figure 1 As shown:

[0047] During the initial 0-1 minute, the argon flow rate in the molten steel ladle is controlled at 0-20 m³ / min. 3 / h;

[0048] During the first 1-3 minutes of tapping, the argon flow rate in the ladle should be controlled at 20-50 m³ / min. 3 / h;

[0049] During the last 3-4 minutes of tapping, the argon flow rate in the ladle should be controlled at 10-20 m³ / s. 3 / h;

[0050] After tapping (4 minutes), the argon gas flow rate is controlled at 10 m³ / min. 3 / h, keep the liquid level slightly moving.

[0051] Slide plates are used to block slag at the end of the tapping process to ensure that molten steel does not drip slag.

[0052] The amount of ferromolybdenum added in this embodiment is calculated according to formula (1):

[0053]

[0054] In the formula, wt Mo =0.22%, wt′ Mo = 55.1% (measured molybdenum content in ferromolybdenum), R Mo =96%;

[0055] Substituting the above values ​​into equation (1) yields t. MoFe= 4.16 kg / t, which means 4.16 kg of ferromolybdenum is added to 1 ton of steel.

[0056] Five heats of molten steel were produced continuously using the above method. The molybdenum recovery rate and production cost of the ferromolybdenum alloy for each heat are shown in Table 1.

[0057] Table 1. Statistics of relevant data for each furnace batch

[0058]

[0059]

[0060] Comparative Example 1

[0061] When a steel plant produces Q690D steel, ferromolybdenum is added to the converter along with scrap steel before the converter process. The particle size of the ferromolybdenum is 10-100mm.

[0062] The calculation formula remains the same as formula (1):

[0063]

[0064] In the formula, wt Mo =0.22%, wt' Mo = 55.1% (measured molybdenum content in ferromolybdenum), R Mo =90%;

[0065] Substituting the above values ​​into equation (1) yields t. MoFe = 4.44 kg / t, which means 4.16 kg of ferromolybdenum is added to 1 ton of steel.

[0066] Five heats of molten steel were produced consecutively using the method of Comparative Example 1. The molybdenum element recovery rate and production cost of each heat of ferromolybdenum alloy are shown in Table 2.

[0067] Table 2 shows the statistical data of each furnace in the comparative example.

[0068]

[0069]

[0070] As shown in Tables 1 and 2, the method described in this invention can meet the requirements for molybdenum alloying in converters, achieving a molybdenum recovery rate of 96.0%–97.7%, with an average recovery rate of 96.9% and a fluctuation range of -0.9%–0.9%, all of which are superior to Comparative Example 1. Comparative Example 1 achieved a molybdenum recovery rate of only 89.9%–94.4%, with an average recovery rate of 91.8% and a fluctuation range of -1.9%–2.6%.

[0071] The method described in this invention eliminates the need to add alloys during the refining process, thus avoiding increased operational difficulty and intensity. Furthermore, adding alloys during the refining process necessitates increasing bottom-blowing argon gas, exposing the molten steel and increasing nitrogen absorption, leading to greater fluctuations in nitrogen content within the molten steel.

[0072] Furthermore, when adding alloys during the refining process, the alloys can only be added to the surface of the molten steel, even though the density of ferromolybdenum is 9.0-9.5 t / m³. 3 (Density increases with increasing molybdenum content), compared to the density of steel (7.85 t / m³). 3 The molybdenum content is large, but the difference is not significant. Therefore, thorough stirring is necessary to ensure uniform molybdenum content in the molten steel. Furthermore, the temperature of the molten steel during the refining process is generally lower (40-60℃) than that during converter tapping, which is also unfavorable for the melting of ferromolybdenum and hinders the uniform distribution of molybdenum in the steel.

[0073] Using the method described in this invention, the cost of alloy steel per ton is 64.43 yuan / ton, which is 4.34 yuan less than that of Comparative Example 1 (68.76 yuan / ton). This indicates that the method described in this invention has a good effect on reducing the production cost of alloy steel in converters and has good economic benefits.

Claims

1. A method for improving the recovery rate of ferromolybdenum in a converter process, characterized in that, Alloying is performed during the converter tapping process, eliminating the need to add alloys during the refining process. The specific operation is as follows: When the molten steel has been poured to 1 / 4 of its capacity, alloys other than ferromolybdenum are added to the molten steel in the ladle according to the steel composition requirements; when the molten steel has been poured to 3 / 4 of its capacity, all alloys other than ferromolybdenum that meet the steel composition requirements are added. When the molten steel has been poured to half its capacity, ferromolybdenum is added to the molten steel in the ladle in batches, and the ferromolybdenum is added completely before the end of the tapping process. The amount of ferromolybdenum added is calculated according to formula (1): （1） In the formula, The amount of ferromolybdenum added is expressed in kg / t steel. The target molybdenum content for this steel grade is the median limit, % . The molybdenum content in ferromolybdenum, % R Mo The molybdenum recovery rate of ferromolybdenum alloy, % During the alloying process in the steel tapping process, the bottom blowing argon gas in the molten steel ladle is activated; the specific control of the argon gas flow rate in the bottom blowing argon gas in the molten steel ladle is as follows: From the start of tapping until one-quarter of the tapping time, the argon flow rate is controlled between 0-20 m³ / s. 3 / h; During the period from 1 / 4 to 3 / 4 of the tapping time, the argon flow rate is controlled at 20-50 m³ / h. 3 / h; From 3 / 4 of the tapping time to the completion of tapping, the argon gas flow rate is controlled at 10-20 m³ / h. 3 / h; After tapping, the argon gas flow rate is controlled at 5-10 m³ / h. 3 / h; Other alloys include ferrosilicon, medium-carbon ferromanganese, or high-carbon ferromanganese, but do not include aluminum-containing alloys.

2. The method for improving the recovery rate of ferromolybdenum in the converter process according to claim 1, characterized in that, The particle size of the ferromolybdenum is 20-40 mm.

3. The method for improving the recovery rate of ferromolybdenum in the converter process according to claim 1, characterized in that, The ferromolybdenum was added to the molten steel in the ladle in two batches.

4. The method for improving the recovery rate of ferromolybdenum in the converter process according to claim 1, characterized in that, Slag blocking is used at the end of the steel tapping process.

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