A method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron

Abstract

This invention discloses a method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron, belonging to the field of iron and steel metallurgical technology. This method optimizes desulfurization, slag removal, and converter smelting processes to stably smelt molten iron with a manganese content ≤0.50% and a sulfur content ≥0.050% into steel with a manganese content ≤0.02% and a sulfur content ≤0.003%, suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and in particular relates to a method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron. Background Technology

[0002] The steel industry is currently experiencing a growing demand for ultra-low manganese and low-sulfur steel, but traditional smelting methods are insufficient to achieve this under conditions of high manganese and high-sulfur molten iron. When the manganese content in molten iron is ≤0.50% and the sulfur content is ≥0.050%, it is difficult to stably control the manganese content in molten steel to ≤0.02% and the sulfur content to ≤0.003%.

[0003] The main issues include:

[0004] 1. Hot metal pretreatment stage: After conventional KR desulfurization, the sulfur content can only be reduced to about 0.005%, and manganese cannot be effectively removed;

[0005] 2. Converter smelting stage: The existing bottom blowing process is prone to manganese reduction (final Mn≥0.05%). Summary of the Invention

[0006] The purpose of this invention is to provide an industrial production method for smelting molten iron with a manganese content ≤0.50% and a sulfur content ≥0.050% into molten steel with a manganese content ≤0.02% and a sulfur content ≤0.003% by optimizing desulfurization, slag removal, and converter smelting processes.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron, comprising:

[0009] Hot metal pretreatment:

[0010] Two steps to remove the scum:

[0011] Stirring depth: 5-6m; First stage stirring, i.e., the first slag removal: speed 70-90r / min, add calculated desulfurizing agent; Second stage stirring, i.e., the second slag removal: speed ≥100r / min; deep desulfurization is carried out.

[0012] Iron molten metal conditions: Temperature ≥1300℃, silicon content ≤0.4%, scrap steel addition amount 45t;

[0013] First slag removal: Quickly remove 2 / 3 of the desulfurization slag;

[0014] Second slag removal: Add 1-2 kg / t of thickening agent, let stand for 5 minutes, and then remove the slag. The slag removal rate should be ≥99%. The amount of desulfurizing agent added should be calculated based on the removal of 0.25-0.30 kg / t of desulfurizing agent per 0.001% of sulfur. At the same time, sufficient stirring time and speed should be matched to meet the requirement of complete melting of the desulfurizing agent.

[0015] Converter smelting:

[0016] Choose a high-carbon oxygen-product converter;

[0017] Based on the blowing time, the converter bottom blowing control model is adjusted in stages, the ratio of molten iron and scrap steel fed into the furnace is adjusted, the converter slag making mode and slag ratio are adjusted, and a reasonable oxygen lance position control mode is used.

[0018] The converter smelting process is controlled in stages. In the early stage of converter blowing, after the ignition is normal, the first batch of material is added and the reaction in the furnace is carefully observed to prevent splashing. In the middle stage of blowing, the slag melting and the temperature of the molten pool are controlled. In the middle and late stages of blowing, the temperature of the molten pool and the carbon content are measured by the auxiliary lance. In the late stage of blowing, the material is added according to the TSC measurement to control the final temperature and oxygen content.

[0019] Control the bottom blowing flow rate in stages:

[0020]

[0021] The total charge of the converter is 295-305t, and the temperature of the molten iron entering the furnace must be ≥1300℃. The silicon content of the molten iron and the corresponding weight of scrap steel are shown in the table below:

[0022]

[0023] Gun position control mode:

[0024]

[0025] Slag removal system:

[0026] The initial batch of materials added during the early stage of smelting consists of 6-7 tons of quicklime, 3 tons of acidic pellets, and 2-3 tons of raw dolomite.

[0027] During the mid-stage of the blowing process, to ensure slag melting, add 1-2 tons of quicklime and 3-5 tons of acidic pellets. Control the process temperature (TSC measurement temperature) to 1540℃-1570℃, and maintain a carbon content of 0.15%≤C≤0.45%.

[0028] After TSC in the later stage of blowing, the ratio of active lime to iron oxide scale should be greater than 1:1.5. The final temperature should be controlled between 1590-1630℃ and the final oxygen should be between 700ppm and 1100ppm.

[0029] After the endpoint sample is taken, according to the residual manganese content, when the manganese content is ≥0.04%, spot blowing treatment is carried out. The ratio of quicklime to iron sheet added during spot blowing is greater than 1:2.5. After spot blowing, the temperature is between 1590-1610℃, and the endpoint oxygen is not less than 700ppm.

[0030] Furthermore, the two slag removal processes are as follows: 80 r / min for the first 10 minutes and 120 r / min for the last 12 minutes.

[0031] Furthermore, the desulfurizer composition by mass ratio includes: lime:fluorite = 8-10:1.

[0032] Furthermore, the composition of the slag-collecting agent by mass percentage is: SiO2: 65%-75%, Al2O3: 8%-18%, H2O≤1.0%; this ratio can effectively adsorb the molten iron slag that has not been completely removed.

[0033] Furthermore, the high-carbon oxygen product converter has a value greater than 0.0025.

[0034] Furthermore, the stirring depth is 5.4m.

[0035] Furthermore, according to this method, deep demanganese removal in the converter can stably reduce the manganese content of the continuously cast molten steel to below 0.02%, and the final sulfur content can be stably controlled to below 0.003%.

[0036] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0037] According to this method, deep demanganese removal in the converter can stably reduce the manganese content of the continuously cast molten steel to below 0.02%, and the final sulfur content can be stably controlled to below 0.003%.

[0038] Improve the purity of molten steel through process optimization. Detailed Implementation

[0039] A method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron includes:

[0040] Hot metal pretreatment:

[0041] 1. Desulfurizing agent composition by mass ratio: lime:fluorite = 9:1;

[0042] The composition of the slag-coating agent by mass ratio is: SiO2: 65%~75%, Al2O3: 8%~18%, H2O≤1.0%;

[0043] 2. Staged mixing:

[0044] The speed was 80 rpm for the first 10 minutes and 120 rpm for the next 12 minutes.

[0045] 3. Two steps to remove the scum:

[0046] - Desulfurizing agent dosage: Add 0.25~0.30 kg / t of desulfurizing agent to remove 0.001% sulfur. - Stirring control: Time ≥ 22 min, speed ≥ 100 r / min.

[0047] - Mixing depth: 5.4m; First stage mixing: 80r / min, adding calculated desulfurizing agent; Second stage mixing: ≥100r / min. Deep desulfurization is performed.

[0048] - Molten iron conditions: Temperature ≥1300℃, silicon content ≤0.4%, scrap steel addition amount 45t.

[0049] First slag removal: Quickly remove 2 / 3 of the desulfurization slag.

[0050] Second slag removal: Add 1~2 kg / t of thickening agent, let stand for 5 minutes, then remove the slag, with a removal rate ≥99%. Add enough desulfurizer at once to meet the slag requirements for ultra-deep desulfurization. The amount of desulfurizer added is calculated based on removing 0.25~0.30 kg / t of desulfurizer per 0.001% of sulfur. Simultaneously, ensure sufficient stirring time and speed to guarantee complete melting of the desulfurizer.

[0051] Converter smelting:

[0052] Choose a high carbon oxygen product converter (preferably greater than 0.0025).

[0053] Based on the blowing time, the converter bottom blowing control model is adjusted in stages, and the ratio of molten iron and scrap steel fed into the furnace is adjusted; the converter slag forming mode and slag material ratio are adjusted, and a reasonable oxygen lance position control mode is used.

[0054] The converter smelting process is controlled in stages. In the early stage of converter blowing, after normal ignition, the first batch of material is added, and the reaction inside the furnace is carefully observed to prevent splashing. In the middle stage of blowing, the slag melting and molten pool temperature are controlled, and in the later stage of blowing, the molten pool temperature and carbon content are measured using a secondary lance. In the later stage of blowing, material replenishment is carried out based on TSC measurements to control the final temperature and oxygen content.

[0055] Control the bottom blowing flow rate in stages:

[0056]

[0057] The total charge of the converter is 295~305t, and the temperature of the molten iron entering the furnace must be ≥1300℃. The silicon content of the molten iron and the corresponding weight of scrap steel are shown in the table below:

[0058]

[0059] Gun position control mode:

[0060]

[0061] Slag removal system:

[0062] The initial batch of materials added during the early stage of smelting consists of 6 to 7 tons of quicklime, 3 tons of acidic pellets, and 2 to 3 tons of raw dolomite.

[0063] During the mid-stage of the blowing process, to ensure slag melting, add 1 to 2 tons of quicklime and 3 to 5 tons of acidic pellets. Control the process temperature, with the TSC measurement temperature controlled at 1540℃-1570℃, and the carbon content 0.15%≤C≤0.45%.

[0064] After TSC in the later stage of blowing, the ratio of active lime to iron oxide scale should be greater than 1:1.5. The final temperature should be controlled between 1590-1630℃ and the final oxygen should be between 700ppm and 1100ppm.

[0065] After the endpoint sample is taken, according to the residual manganese content, when the manganese content is ≥0.04%, spot blowing treatment is carried out. The ratio of quicklime to iron sheet added during spot blowing is greater than 1:2.5. After spot blowing, the temperature is between 1590-1610℃, and the endpoint oxygen is not less than 700ppm.

[0066] Case 1

[0067] The molten iron had a manganese content of 0.41% and a sulfur content of 0.053%. 3527 kg of desulfurizing agent and 300 kg of thickening slag agent were added, with a stirring time of 27 minutes. The sulfur content of the molten iron entering the furnace was 0.001%. During the smelting process, 7.2 t of quicklime, 6.2 t of acidic pellets, and 2.1 t of raw dolomite were added. The converter TSC temperature was 1568℃, with a carbon content of 0.28%. After TSC, 1.2 t of quicklime and 2.5 t of iron oxide scale were added. The converter final temperature was 1610℃, with an oxygen content of 960 ppm. The final manganese content was 0.017%, and the sulfur content was 0.0022%.

[0068] Case 2

[0069] The molten iron had a manganese content of 0.43% and a sulfur content of 0.055%. 3762 kg of desulfurizing agent and 300 kg of thickening slag agent were added, with a stirring time of 28 minutes. The sulfur content of the molten iron entering the furnace was 0.001%. During the smelting process, 6.9 t of quicklime, 6.1 t of acidic pellets, and 1.7 t of raw dolomite were added. The converter TSC temperature was 1555℃, and the carbon content was 0.38%. After TSC, 2.1 t of quicklime and 3.4 t of iron oxide scale were added. The converter final temperature was 1609℃, the oxygen content was 1011 ppm, and the final manganese content was 0.013% and the sulfur content was 0.0024%.

[0070] Comparison Case 3

[0071] The molten iron had a manganese content of 0.43% and a sulfur content of 0.051%. The desulfurizing agent dosage was 3950 kg, and the stirring time was 27 min. The sulfur content of the molten iron entering the furnace was 0.001%, and no thickening agent was added. During the smelting process, 6.5 t of quicklime, 0 t of acidic pellets, 2.1 t of raw dolomite, and 5.3 t of iron oxide scale were added. The converter TSC temperature was 1561℃, and the carbon content was 0.29%. After TSC, 2.3 t of quicklime and 2.8 t of iron oxide scale were added. The converter final temperature was 1611℃, the oxygen content was 1034 ppm, and the final manganese content was 0.042% and the sulfur content was 0.0051%.

[0072] Meanwhile, taking Patent 1 (A method for producing ultra-low manganese steel using a high-manganese molten iron converter_202010364676.4) as an example: its manganese content cannot be stably reduced to below 0.02% (as in its Examples 1 and 3); and taking Patent 2 (A new process for smelting low-phosphorus and low-sulfur steel_202110844353.X) as another example: its finished product sulfur content cannot be stably reduced to below 0.003% (it is 0.0034%).

[0073] 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 method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron, characterized in that: include: Hot metal pretreatment: Two steps to remove the scum: Stirring depth: 5-6m; First stage stirring, i.e., the first slag removal: speed 70-90r / min, add calculated desulfurizing agent; Second stage stirring, i.e., the second slag removal: speed ≥100r / min; deep desulfurization is carried out. Molten iron conditions: Temperature ≥ 1300℃; First slag removal: Quickly remove 2 / 3 of the desulfurization slag; Second slag removal: Add 1-2 kg / t of thickening agent, let stand for 5 minutes, and then remove the slag. The slag removal rate should be ≥99%. The amount of desulfurizing agent added should be calculated based on the removal of 0.25-0.30 kg / t of desulfurizing agent per 0.001% of sulfur. At the same time, sufficient stirring time and speed should be matched to meet the requirement of complete melting of the desulfurizing agent. Converter smelting: Choose a high-carbon oxygen-product converter; Based on the blowing time, the converter bottom blowing control model is adjusted in stages, the ratio of molten iron and scrap steel fed into the furnace is adjusted, the converter slag making mode and slag ratio are adjusted, and a reasonable oxygen lance position control mode is used. The converter smelting process is controlled in stages. In the early stage of converter blowing, after the ignition is normal, the first batch of material is added and the reaction in the furnace is carefully observed to prevent splashing. In the middle stage of blowing, the slag melting and the temperature of the molten pool are controlled. In the middle and late stages of blowing, the temperature of the molten pool and the carbon content are measured by the auxiliary lance. In the late stage of blowing, the material is added according to the TSC measurement to control the final temperature and oxygen content. Control the bottom blowing flow rate in stages: The total charge of the converter is 295-305t, and the temperature of the molten iron entering the furnace must be ≥1300℃. The silicon content of the molten iron and the corresponding weight of scrap steel are shown in the table below: Gun position control mode: Slag removal system: The initial batch of materials added during the early stage of smelting consists of 6-7 tons of quicklime, 3 tons of acidic pellets, and 2-3 tons of raw dolomite. During the mid-stage of the blowing process, to ensure slag melting, add 1-2 tons of quicklime and 3-5 tons of acidic pellets. Control the process temperature (TSC measurement temperature) to 1540℃-1570℃, and maintain a carbon content of 0.15%≤C≤0.45%. After TSC in the later stage of blowing, the ratio of active lime to iron oxide scale should be greater than 1:1.

5. The final temperature should be controlled between 1590-1630℃ and the final oxygen should be between 700ppm and 1100ppm. After the endpoint sample is taken, according to the residual manganese content, when the manganese content is ≥0.04%, spot blowing treatment is carried out. The ratio of quicklime to iron sheet added during spot blowing is greater than 1:2.

5. After spot blowing, the temperature is between 1590-1610℃, and the endpoint oxygen is not less than 700ppm.

2. The method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron according to claim 1, characterized in that: The two slag removal operations were performed at 80 r / min for the first 10 minutes and 120 r / min for the last 12 minutes.

3. The method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron according to claim 1, characterized in that: The desulfurizing agent composition by mass ratio includes: lime:fluorite = 8-10:

1.

4. The method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron according to claim 1, characterized in that: The composition of the slag-forming agent by mass percentage is as follows: SiO2: 65%-75%, Al2O3: 8%-18%, H2O≤1.0%.

5. The method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron according to claim 1, characterized in that: The high-carbon oxygen product converter has a value greater than 0.0025.

6. The method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron according to claim 1, characterized in that: Stirring depth: 5.4m.

7. The method for smelting ultra-low manganese and ultra-low sulfur steel using high-manganese and high-sulfur molten iron according to claim 1, characterized in that: According to this method, deep demanganese removal in the converter can stably reduce the manganese content of the continuously cast molten steel to below 0.02%, and the final sulfur content can be stably controlled to below 0.003%.

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