A converter smelting method for efficiently removing Mn from molten steel

Abstract

This invention discloses a converter smelting method for efficiently removing Mn from molten steel. The specific process steps and parameters are as follows: (1) Raw material ratio: During the converter smelting process, the scrap steel ratio is controlled at 15-20%, and low-manganese scrap steel is selected, requiring the manganese content of the scrap steel to be ≤0.30%; (2) Initial slag formation and blowing: The mass percentage of the initial converter slag composition is controlled as follows: basicity R (CaO / SiO2) ≥2.0, FeO ≥20%, MgO ≥8.0%; (3) Later slag formation and blowing: After the first slag dumping, the lance is blown again. At this time, the mass percentage of the converter slag composition is adjusted as follows: basicity R (CaO / SiO2) ≥2.8, FeO ≥20%, MgO ≥10.0%; (4) Slag blocking during tapping. This invention aims to solve the problems of low demanganese rate and unqualified final steel composition when smelting high-manganese content molten iron into industrial pure iron and clean steel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and particularly relates to a converter smelting method for efficiently removing Mn from molten steel. It is especially suitable for the efficient removal of manganese in the process of smelting high-manganese-content molten iron into industrial pure iron and clean steel. Background Technology

[0002] In steel smelting, to control the cost of molten iron preparation, enterprises often use high-manganese ore for ironmaking, resulting in an average manganese content of ≥0.45% in the molten iron. However, when smelting industrial pure iron and clean steel, the requirements for the content of impurities such as manganese in the molten steel are stringent. The existing converter smelting process has a low demanganese rate, making it difficult to effectively remove manganese from high-manganese molten iron. This easily leads to substandard final steel composition, failing to meet the production quality requirements of industrial pure iron and clean steel, and restricting the application of high-manganese molten iron in the smelting of high-quality steel grades. Summary of the Invention

[0003] The purpose of this invention is to provide a converter smelting method for efficiently removing Mn from molten steel, aiming to solve the problems of low manganese removal rate and unqualified final steel composition when smelting industrial pure iron and clean steel from molten iron with high manganese content. This method achieves efficient removal of manganese from high manganese molten iron and stably produces industrial pure iron with extremely low total impurity content and uniform composition.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a converter smelting method for efficiently removing Mn from molten steel. The specific process steps and parameters are as follows:

[0006] (1) Raw material ratio: During the converter smelting process, the scrap steel ratio is controlled at 15-20%, and low manganese content scrap steel is selected, requiring the manganese content of the scrap steel to be ≤0.30%;

[0007] (2) Initial slag formation and blowing: The mass percentage of the initial converter slag composition is controlled as follows: basicity R (CaO / SiO2) ≥ 2.0, FeO ≥ 20%, MgO ≥ 8.0%; when the oxygen supply accounts for 60%-70% of the total oxygen supply, the slag is removed once by lifting the lance, and the amount of slag removed accounts for ≥ 85% of the total slag. At this time, the steel composition is controlled as 0.30% ≤ C ≤ 0.65%, and the steel temperature is controlled as 1540℃ ≤ T ≤ 1570℃.

[0008] (3) Slag formation and blowing in the later stage: After the first slag dumping, the slag is blown again. At this time, the composition of the slag formation mass percentage in the converter is adjusted to basicity R (CaO / SiO2) ≥2.8, FeO ≥20%, MgO ≥10.0%; continue blowing until the oxygen supply ends, control the elemental composition of the molten steel to be 0.020%≤C≤0.040%, the free oxygen content at the end of the molten steel to be 700ppm≤[O]≤1000ppm, and the temperature of the molten steel at the end of the end to be 1570℃≤T≤1610℃;

[0009] (4) Slag blocking during steel tapping: After the oxygen supply ends and the slag is dumped, steel tapping is carried out by using a double sliding slag blocking method with the slide plate in front and behind.

[0010] Furthermore, in step (2), the target C content of the molten steel is 0.50%.

[0011] Furthermore, in step (2), the target temperature of the molten steel is 1560℃.

[0012] Furthermore, in step (3), the target C of the steel element mass percentage composition is controlled to be 0.030%.

[0013] Furthermore, in step (3), the target free oxygen content [O] at the end of the molten steel is 800 ppm.

[0014] Furthermore, in step (3), the target temperature of the final molten steel is 1600℃.

[0015] Furthermore, this method is applicable to smelting high-manganese-content molten iron in a 100t converter, wherein the average mass percentage content of Mn is 0.45%, and the molten iron feed rate is 85t / furnace.

[0016] Furthermore, the initial converter slag composition mass percentage is controlled as follows: basicity R (CaO / SiO2) = 2.2, FeO = 23%, MgO = 8.5%; the later slag composition is controlled as follows: slag basicity R (CaO / SiO2) = 3.0, FeO = 22%, MgO = 10.5%.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0018] This invention achieves efficient removal of Mn from high-manganese molten iron (average ≥0.45%) by controlling the composition and timing of slag formation in converter smelting, combined with the reaction mechanism of Mn in the converter molten pool, and adopting a process approach of high oxidizing power, low temperature, and large slag volume.

[0019] 1. Improved Manganese Removal Efficiency: By precisely controlling the slag composition, blowing parameters, and slag formation timing, combined with the reaction mechanism of Mn in the converter molten pool, efficient removal of manganese from high-manganese molten iron (average ≥0.45%) is achieved. This solves the problem of low manganese removal rate in traditional processes, ensuring that the manganese content of the final molten steel meets the quality requirements of industrial pure iron and clean steel. Under this implementation method, the manganese removal rate of a 150t converter reaches 94.5%, the average manganese content (Mn) of the final molten steel is ≤0.025%, and the contents of other impurity elements (P≤0.006%, S≤0.004%) all meet the quality standards of industrial pure iron. The uniformity deviation of the molten steel composition is ≤0.001%, with no unqualified composition.

[0020] 2. Stable steel quality: The process parameters are precise and controllable, which can stably produce industrial pure iron with extremely low total impurity content and uniform composition, effectively avoiding the problem of unqualified final steel composition caused by excessive manganese, and improving the qualification rate of steel products.

[0021] 3. Optimized raw material utilization: This process is adapted to the smelting requirements of high manganese content molten iron. It can make full use of molten iron prepared from high manganese ore to smelt high-quality steel grades. While controlling the cost of molten iron preparation, it expands the application scenarios of high manganese molten iron and improves the production efficiency of enterprises.

[0022] 4. Highly operable process: The parameters such as slag composition, blowing temperature, and oxygen supply of the converter are clearly defined, and the operation steps such as lifting the lance to pour slag and blocking slag to tap steel are standardized, making it easy to promote and apply in the existing converter smelting production lines of steel enterprises without the need for large-scale equipment modification. Detailed Implementation

[0023] This implementation method is based on the smelting of high-manganese-content molten iron (average Mn value 0.45%, molten iron feed rate 85t / furnace) in a 100t converter. The goal is to smelt industrial pure iron. All auxiliary material additions are measured in kg / ton of steel. The entire process strictly follows the aforementioned process parameter control principles. Combined with the Mn element "hump" reaction mechanism, efficient removal of manganese is achieved. The detailed implementation steps and data parameters are as follows:

[0024] 1. Raw material preparation and furnace loading

[0025] The scrap steel ratio is controlled at 18% (low-manganese scrap steel, Mn content 0.25%), and the scrap steel input is 15.3t / furnace; the molten iron input has an Mn content of 0.45%, a C content of 4.2%, a Si content of 0.5%, and a P content of 0.08%. Basic preparation of auxiliary materials for the furnace input includes: quicklime (CaO content 90%), lightly calcined dolomite (MgO content 45%), and iron pellets (FeO content 85%). The particle size of all auxiliary materials is controlled between 5-30mm to avoid pulverization affecting the slag-forming effect.

[0026] 2. Initial slag formation and blowing stage

[0027] (1) Initial addition of slag-forming auxiliary materials (kg / ton of steel)

[0028] Quicklime: 45kg / t, lightly calcined dolomite: 22kg / t, iron balls: 18kg / t. The auxiliary materials are fed into the furnace simultaneously with the molten iron and scrap steel, and stirred by bottom blowing argon gas (argon gas flow rate 0.8m³ / min·t). (2) Initial slag composition control

[0029] The alkalinity R (CaO / SiO2) = 2.2, FeO = 23%, and MgO = 8.5%, which meets the initial process requirements of R ≥ 2.0, FeO ≥ 20%, and MgO ≥ 8.0%.

[0030] (3) Blowing parameters and lance lifting and slag removal

[0031] The top and bottom blowing process is adopted. The oxygen pressure of the top lance is 0.8MPa and the oxygen flow rate is 3.5m³ / min·t. When the oxygen supply reaches 65% of the total oxygen supply, the lance is lifted and the slag is dumped. The amount of slag dumped accounts for 88% of the total slag (to remove the initial high manganese slag and avoid the return of manganese to phosphorus and manganese).

[0032] (4) State of molten steel during slag removal

[0033] The steel has a C content of 0.52% (meeting the requirement of 0.30%≤C≤0.65%, close to the target of 0.50%) and a steel temperature of 1558℃ (meeting the requirement of 1540℃≤T≤1570℃, close to the target of 1560℃). At this point, the Mn content in the steel has decreased from 0.45% to 0.12%, thus initially achieving efficient removal of manganese.

[0034] 3. Later stage of slag formation and blowing

[0035] (1) Amount of slag-forming auxiliary materials added in the later stage (kg / ton of steel)

[0036] After the first slag dumping, immediately add 20 kg / t of quicklime, 15 kg / t of lightly calcined dolomite, and 8 kg / t of iron balls. After adding, continue bottom blowing argon gas stirring (argon gas flow rate 1.0 m³ / min·t) to quickly form a new slag system. (2) Control of slag composition in the later stage

[0037] After adding auxiliary materials, the basicity of the slag system R (CaO / SiO2) = 3.0, FeO = 22%, and MgO = 10.5%, which meets the process requirements of R ≥ 2.8, FeO ≥ 20%, and MgO ≥ 10.0% in the later stage, maintaining a highly oxidizing slag system and continuously removing manganese.

[0038] (3) Control of blowing parameters in the later stage

[0039] The oxygen pressure of the top lance is adjusted to 0.9-1.2 MPa and the oxygen flow rate is 3.2-4.0 m³ / min·t. The blowing continues until the total oxygen supply reaches 100%, at which point the oxygen supply is stopped. Throughout the process, the temperature of the molten pool is controlled to rise slowly to avoid the reduction of manganese due to high temperature. (4) Core indicators of molten steel after oxygen supply ends

[0040] The molten steel has a C content of 0.032% (compliant with 0.020%≤C≤0.040%, close to the target of 0.030%), a final free oxygen content [O] of 820ppm (compliant with 700ppm≤[O]≤1000ppm, close to the target of 800ppm), and a final molten steel temperature of 1595℃ (compliant with 1570℃≤T≤1610℃, close to the target of 1600℃). The final Mn content of the molten steel is reduced to 0.008%, meeting the stringent requirements for manganese in industrial pure iron. 4. Slag blocking and steel tapping stage

[0041] After oxygen supply is completed, the late-stage smelting slag is first removed (90% of the slag is removed), and then steel is tapped using a double-sliding slag-blocking process with a sliding plate. The slag-blocking plug is linked to the sliding plate for control. The slag-blocking efficiency during the tapping process is ≥98%, which avoids slag entering the ladle and causing secondary pollution of the molten steel.

[0042] During the tapping process, silicon-manganese alloy is added simultaneously (addition amount 0.3kg / t) to ensure the uniformity of the steel composition. After tapping, argon gas is blown into the bottom of the ladle for soft stirring (argon gas flow rate 0.3m³ / min·t, stirring time 8min) to further remove inclusions in the steel.

[0043] 5. Principles for fine-tuning process parameters

[0044] If the Mn content of the molten iron entering the furnace is higher than 0.50% (e.g., 0.50%-0.60%), the following minor adjustments can be made:

[0045] The initial addition of iron pellets is increased by 2-3 kg / t, which increases the FeO content of the initial slag system to 25%-28% and enhances its oxidizing properties.

[0046] The amount of slag dumped in a single lifting gun is increased to over 90%, further removing high-manganese slag;

[0047] The amount of lightly calcined dolomite added in the later stage is increased by 1-2 kg / t to ensure MgO ≥ 11% and improve slag fluidity. After fine-tuning, the demanganese removal rate can still be stabilized at over 97%, ensuring that the final molten steel Mn content meets the standard.

[0048] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A converter smelting method for efficiently removing Mn from molten steel, characterized in that, The specific process steps and parameters are as follows: (1) Raw material ratio: During the converter smelting process, the scrap steel ratio is controlled at 15-20%, and low manganese content scrap steel is selected, requiring the manganese content of the scrap steel to be ≤0.30%; (2) Initial slag formation and blowing: The mass percentage of the initial converter slag composition is controlled as follows: basicity R (CaO / SiO2) ≥ 2.0, FeO ≥ 20%, MgO ≥ 8.0%; when the oxygen supply accounts for 60%-70% of the total oxygen supply, the slag is removed once by lifting the lance, and the amount of slag removed accounts for ≥ 85% of the total slag. At this time, the steel composition is controlled as 0.30% ≤ C ≤ 0.65%, and the steel temperature is controlled as 1540℃ ≤ T ≤ 1570℃. (3) Slag formation and blowing in the later stage: After the first slag dumping, the slag is blown again. At this time, the composition of the slag formation mass percentage in the converter is adjusted to basicity R (CaO / SiO2) ≥2.8, FeO ≥20%, MgO ≥10.0%; continue blowing until the oxygen supply ends, control the elemental composition of the molten steel to be 0.020%≤C≤0.040%, the free oxygen content at the end of the molten steel to be 700ppm≤[O]≤1000ppm, and the temperature of the molten steel at the end of the end to be 1570℃≤T≤1610℃; (4) Slag blocking during steel tapping: After the oxygen supply ends and the slag is dumped, steel tapping is carried out by using a double sliding slag blocking method with the slide plate in front and behind.

2. The converter smelting method for efficiently removing Mn from molten steel according to claim 1, characterized in that, In step (2), the target C content of the molten steel is 0.50%.

3. The converter smelting method for efficiently removing Mn from molten steel according to claim 1, characterized in that, In step (2), the target temperature of the molten steel is 1560℃.

4. The converter smelting method for efficiently removing Mn from molten steel according to claim 1, characterized in that, In step (3), the target C for the mass percentage composition of elements in molten steel is controlled to be 0.030%.

5. The converter smelting method for efficiently removing Mn from molten steel according to claim 1, characterized in that, In step (3), the target free oxygen content [O] at the end of the molten steel is 800 ppm.

6. The converter smelting method for efficiently removing Mn from molten steel according to claim 1, characterized in that, In step (3), the target temperature of the final molten steel is 1600℃.

7. The converter smelting method for efficiently removing Mn from molten steel according to claim 1, characterized in that, This method is applicable to smelting high-manganese-content molten iron in a 100t converter, where the average mass percentage of Mn is 0.45% and the molten iron feed rate is 85t / furnace.

8. The converter smelting method for efficiently removing Mn from molten steel according to claim 1, characterized in that, The initial converter slag composition was controlled at the following mass percentages: basicity R (CaO / SiO2) = 2.2, FeO = 23%, MgO = 8.5%; the later slag composition was controlled at: basicity R (CaO / SiO2) = 3.0, FeO = 22%, MgO = 10.5%.