Method for removing manganese during the tapping of a converter

Abstract

The application discloses a method for removing manganese in a converter tapping process and belongs to the technical field of iron and steel metallurgy. The method increases the oxidizability of molten steel and top slag by adopting a slag tapping method during tapping, reduces the manganese content in the molten steel, and then adopts a slag skimming method to remove manganese, inhibit manganese return and not affect the composition of the molten steel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to a method for demanganese removal during the tapping process of a converter. Background Technology

[0002] Low-manganese steel (such as industrial pure iron) is increasingly favored by users due to its excellent physical properties. Currently, the internationally accepted method for converter smelting of low-manganese steel is as follows: low-manganese molten iron is used (manganese content ≤ 0.10%), employing either double-slag or twin-slag converter smelting. The final stage relies on a large slag volume (≥ 130 kg / t), low temperature (tapping temperature ≤ 1620℃), and high oxidizing properties (oxygen value > 700 ppm) for manganese removal. Its disadvantages are as follows: First, the cost of smelting low-manganese steel is high, mainly because low-manganese molten iron requires the purchase of special low-manganese ore, increasing the cost of molten iron. Simultaneously, twin-slag or twin-slag smelting results in significant iron loss and high steel material costs. Second, the high oxidizing properties of the molten steel affect its purity. Third, relying on over-blowing to remove manganese at the final stage leads to severe corrosion of the furnace lining refractory materials, posing a significant safety risk. Summary of the Invention

[0003] The purpose of this invention is to provide a method for demanganese removal during the converter tapping process. This method involves increasing the oxidizability of molten steel and top slag by using a slag-feeding method during tapping to reduce the manganese content in the molten steel, and then using a slag-removing method to achieve demanganese removal and inhibit manganese reversion without affecting the composition of the molten steel.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A method for demanganese during the tapping process of a converter steelmaking process includes the following steps:

[0006] (I) Converter final carbon temperature control

[0007] 1) Using molten iron and scrap steel as raw materials, the converter adopts the single slag method for smelting. The lime in the converter is controlled at 20-60 kg / t steel, and the light-burned dolomite is controlled at 10-50 kg / t steel.

[0008] 2) The converter process temperature is controlled at 1550-1590℃, and the process carbon content is controlled at 0.10-0.60wt%.

[0009] 3) The converter endpoint temperature is controlled at 1600-1680℃, the converter endpoint oxygen is controlled within 450-700ppm, and the endpoint Mn is 0.02-0.06wt%.

[0010] (II) Control of slag discharge during converter tapping

[0011] 1) Converter boiling tapping, no alloying or deoxidizing agents are added during the tapping process;

[0012] 2) Determine the slag amount based on the difference between the final Mn composition and the finished product Mn composition, and control the slag amount to 4-16 kg / t steel;

[0013] 3) After slag removal, add 2-4 kg / t of quicklime, and utilize the oxidizing properties of the converter slag for manganese removal to start the bottom blowing of argon gas in the large tank. The argon gas flow rate is 90-150 Nm. 3 / h, stir for 90s-120s and then turn off the argon gas;

[0014] 4) After argon blowing is completed, take a sample for temperature measurement and send it to the laboratory for analysis;

[0015] (III) Slag Removal from Molten Steel

[0016] The molten steel is slag-removed to obtain the molten steel after slag removal.

[0017] Furthermore, in step (i) 1), the deoxidizer includes aluminum wire segments, aluminum-iron alloys, and other aluminum-containing alloys.

[0018] Further, in step (a) 1), the composition of the molten iron is: C: 4.0-5.0 wt%, Si: 0.2-0.80 wt%, Mn: 0.11-0.30 wt%, P: ≤0.15 wt%, S: ≤0.060 wt%, with the balance being iron and unavoidable impurities.

[0019] In step 1), the mass of scrap steel accounts for 5-11% of the total mass of molten iron and scrap steel.

[0020] Furthermore, in step (1) 3), after the endpoint test, iron oxide scale is added to the furnace at a rate of 1.9–5 kg / t steel, followed by argon blowing and stirring for 1–3 minutes, with the argon flow rate controlled at 5–20 Nm. 3 / min, further in-furnace demanganese removal.

[0021] Furthermore, in step (ii), the converter slag obtained from converter boiling tapping has the following composition: CaO: 35-45 wt%, SiO2: 8-12 wt%, TFe: 18-27 wt%, MgO: 6-9 wt%, MnO: 1-3 wt%, P2O5: 1.8-3.5 wt%, S: 0.02-0.06 wt%, with the balance being unavoidable impurities.

[0022] Further, in step (ii) 2), based on the difference between the Mn content at the endpoint and the Mn content in the finished product, the Mn content in the finished product is 0.02-0.05 wt%, and the standard for the amount of slag is determined, as shown in Table 1;

[0023] Table 1

[0024] ＜0.01 4～6 0.01～0.02 7～9 0.021～0.03 9～11 0.031 or higher 14～16

[0025] Furthermore, in step (ii) 2), based on the tapping time (s) and slag amount (kg / t steel) of the previous furnace, the slag dropping time is determined using formula ①: Slag dropping time = Slag amount * Tapping time of the previous furnace / 500 (time is rounded to one decimal place), and the slag amount is precisely controlled by the slag dropping time.

[0026] Furthermore, in step (ii) 2), the slag blocking is done by a sliding plate, and the sliding plate is closed after the slag discharge time is reached.

[0027] Furthermore, in step (iii), the slag removal operation of the molten steel is as follows:

[0028] 1) After sampling, the molten steel is hoisted to the slag removal position for slag removal.

[0029] 2) Tilt the molten steel ladle so that the slag surface is level with the lower edge of the ladle opening at a 20-30° angle;

[0030] 3) The operator uses the slag remover to remove the solidified slag.

[0031] Furthermore, in step 2), the molten steel ladle is tilted to 20-30° to ensure that the slag surface is flush with the lower edge of the ladle opening.

[0032] Furthermore, the molten steel, after the slag has been removed, enters the corresponding refining station for further processing.

[0033] Further, the refined molten steel is poured into a casting machine to form billets.

[0034] This invention fully utilizes the high temperature, high oxidizing power, and high basicity characteristics of converter slag. At the end of the tapping process, the amount of slag is precisely controlled by adjusting the tapping time. Deep demanganese removal is achieved by increasing the oxidizing power of the top slag (Top slag TFe content 20-30%). After demanganese removal, the molten steel undergoes a slag removal process to remove the high-manganese slag from the surface, resulting in molten steel with the required composition for casting. This invention is safe and reliable, eliminating the need to purchase low-manganese molten iron, employ twin-slag or double-blow converter smelting, and avoids increasing the oxidizing power of the molten steel through methods such as overblowing, thereby reducing the cost of steel feedstock and refractory materials.

[0035] The beneficial effects of this invention are:

[0036] (1) This invention simplifies the production process of low manganese steel. The converter does not need to adopt a double-slag or double-slag smelting method to achieve the purpose of deep demanganese removal of low manganese steel.

[0037] (2) After demanganese removal, the molten steel is treated by removing the high manganese slag from the surface of the molten steel to ensure that the composition is qualified before casting, which can improve the quality of the molten steel.

[0038] (3) The present invention is safe and reliable. It does not remove manganese through overblowing or other methods, which can reduce the production cost of low manganese steel. Detailed Implementation

[0039] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0040] Example 1

[0041] A method for demanganese removal during the converter steelmaking process includes the following process route: converter—argon station—slag removal—refining—casting machine, smelting industrial pure iron DDCT-1, with a steel output of 260t and a finished product Mn≤0.02wt%, including the following steps:

[0042] 1) The converter feed rate is 260 tons, including 25 tons of scrap steel. The scrap steel used is pure scrap steel. The molten iron is treated by slag removal, which requires that the slag be completely removed. Molten iron composition: C: 4.5wt%, Si: 0.3wt%, Mn: 0.28wt%, P: 0.15wt%, S: 0.002wt%, with the balance being iron and unavoidable impurities.

[0043] 2) The converter adopts the single slag method for smelting. The quicklime in the converter is controlled at 40 kg / t, and the light-burned dolomite is controlled at 10 kg / t.

[0044] 3) Sub-gun process test, process temperature controlled at 1580℃, process carbon content controlled at 0.40wt%;

[0045] 4) The converter endpoint temperature is controlled at 1660℃, the converter endpoint oxygen is controlled at 500ppm, and the endpoint Mn content is measured to be 0.032wt%.

[0046] 5) After the endpoint test, add 0.5 tons of iron oxide scale to the furnace, then perform bottom blowing argon stirring for 1 minute, adjusting the bottom blowing flow rate to 900 Nm. 3 / h;

[0047] 6) Steel is tapped from a converter using boiling water, without the addition of alloys or deoxidizers during the tapping process;

[0048] 7) Slag blocking adopts sliding plate slag blocking. Based on the Mn content of 0.032% sampled at the converter endpoint, the difference between it and the finished product Mn (calculated with finished product Mn as 0.02wt%) is calculated. Based on the tapping time of the previous ladle of steel of 325s, the slag discharge amount is calculated to be about 8kg / t, and the slag discharge time is 4s.

[0049] 8) Converter slag composition: CaO: 42%, SiO2: 10%, TFe: 26%, MgO: 8%, MnO: 2.5%, P2O5: 2.5%, S: 0.04%, with the balance being unavoidable impurities.

[0050] 9) After tapping and slag removal, add 600 kg of quicklime and 90 Nm of argon gas. 3 / h, after blowing argon gas for 105s, the Mn content of the argon station sample was 0.017%; using the oxidative demanganese properties of the converter final slag, the TFe content of the top slag of the molten steel ladle was 26%.

[0051] 10) After taking the argon station sample, hoist it into the molten steel slag removal position to carry out slag removal operations;

[0052] 11) After entering the slag removal position, tilt the molten steel ladle to 25° to ensure that the slag surface is flush with the ladle opening;

[0053] 12) Operate the slag remover to remove the solidified slag inside the ladle, exposing the molten steel surface;

[0054] 13) After slag removal is completed, the molten steel is hoisted to the refining furnace for treatment. Once the molten steel is qualified, it is cast into the machine.

[0055] DDCT-1 finished product composition: C: 0.0018wt%, Si: 0.0035wt%, Mn: 0.017wt%, P: 0.002wt%, S: 0.0021%, Als: 0.001wt%, balance is iron and unavoidable impurities.

[0056] Example 2

[0057] A method for demanganese removal during the converter steelmaking process includes the following process route: converter—argon station—slag removal—refining—casting machine, smelting industrial pure iron DYCT-1 steel, with a steel output of 258t and a finished product Mn≤0.03wt%, including the following steps:

[0058] A method for demanganese removal during the converter steelmaking process includes the following process route: converter—argon station—slag removal—refining—casting machine, producing industrial pure iron DYCT-1 steel with a tapping rate of 260t and a finished product Mn ≤ 0.03wt%, comprising the following steps:

[0059] 1) The converter feed rate is 258 tons, including 28 tons of scrap steel. The scrap steel used is pure scrap steel. The molten iron is treated by slag removal, which requires that the slag be completely removed. Molten iron composition: C: 4.4wt%, Si: 0.2wt%, Mn: 0.27wt%, P: 0.12wt%, S: 0.002wt%, with the balance being iron and unavoidable impurities.

[0060] 2) The converter adopts the single slag method for smelting. The quicklime and lightly calcined dolomite in the converter are controlled at 42 kg / t and 12 kg / t respectively.

[0061] 3) Sub-gun process test, process temperature controlled at 1585℃, process carbon content controlled at 0.42wt%;

[0062] 4) The converter endpoint temperature is controlled at 1666℃, the converter endpoint oxygen is controlled at 520ppm, and the endpoint Mn content is measured to be 0.045wt%.

[0063] 5) After the endpoint test, add 0.5 tons of iron oxide scale to the furnace, then perform bottom blowing argon stirring for 1 minute, adjusting the bottom blowing flow rate to 900 Nm. 3 / h;

[0064] 6) Steel is tapped from a converter using boiling water, without the addition of alloys or deoxidizers during the tapping process;

[0065] 7) Slag blocking adopts sliding plate slag blocking. Based on the Mn content of 0.045wt% sampled at the converter endpoint, the difference between it and the finished product Mn (calculated with finished product Mn as 0.03wt%) is calculated. Based on the tapping time of the previous ladle of steel of 350s, the slag discharge amount is calculated to be about 8kg / t, and the slag discharge time is 6s.

[0066] 8) Converter slag composition: CaO: 45wt%, SiO2: 12wt%, TFe: 25wt%, MgO: 8.5wt%, MnO: 2.5wt%, P2O5: 2.8wt%, S: 0.04wt%, with the balance being unavoidable impurities.

[0067] 9) After tapping and slag removal, add 600 kg of quicklime and 90 Nm of argon gas. 3 / h, after blowing argon gas for 105s, the Mn content of the argon station sample was 0.022wt%; using the oxidative properties of the converter final slag for demanganese removal, the TFe content of the top slag of the molten steel ladle was 25%.

[0068] 10) After taking the argon station sample, hoist it into the molten steel slag removal position to carry out slag removal operations;

[0069] 11) After entering the slag removal position, tilt the molten steel ladle to 27° to ensure that the slag surface is flush with the ladle opening;

[0070] 12) Operate the slag remover to remove the solidified slag inside the ladle, exposing the molten steel surface;

[0071] 13) After slag removal is completed, the molten steel is hoisted to the refining furnace for treatment. Once the molten steel is qualified, it is cast into the machine.

[0072] DYCT-1 finished product composition: C: 0.0018wt%, Si: 0.0035wt%, Mn: 0.022wt%, P: 0.0025wt%, S: 0.0025wt%, Als: 0.001wt%, balance is iron and unavoidable impurities.

Claims

1. A method for demanganese removal during the tapping process of a converter steelmaking process, characterized in that, Includes the following steps: (a) Converter final carbon temperature control 1) Using molten iron and scrap steel as raw materials, the converter adopts the single slag method for smelting. The lime in the converter is controlled at 20~60kg / t steel, and the light calcined dolomite is controlled at 10~50kg / t steel. 2) The converter process temperature is controlled at 1550–1590℃, and the process carbon content is controlled at 0.10–0.60 wt%. 3) The converter final temperature is controlled at 1600–1680℃, the converter final oxygen content is controlled within the range of 450–700 ppm, and the final Mn content is 0.02–0.06 wt%. (ii) Control of slag discharge during converter tapping 1) Converter boiling tapping, no alloying or deoxidizing agents are added during the tapping process; 2) Determine the slag amount based on the difference between the final Mn composition and the finished product Mn composition, and control the slag amount to 4~16 kg / t steel; 3) After slag removal, add 2-4 kg / t of quicklime. Utilize the oxidizing properties of the final converter slag for manganese removal by starting the bottom-blowing argon gas in the large tank. The argon gas flow rate is 90-150 Nm³. 3 / h, stir for 90s-120s and then turn off the argon gas; 4) After argon blowing is completed, take a sample; (iii) Slag removal from molten steel The molten steel is slag-removed to obtain the molten steel after slag removal; In step (ii) 2), when the difference between the final Mn composition and the finished product Mn composition is <0.01wt%, the slag discharge rate is controlled at 4~6kg / t steel; when the difference between the final Mn composition and the finished product Mn composition is 0.01~0.02wt%, the slag discharge rate is controlled at 7~9kg / t steel; when the difference between the final Mn composition and the finished product Mn composition is 0.021~0.03wt%, the slag discharge rate is controlled at 9~11kg / t steel; when the difference between the final Mn composition and the finished product Mn composition is greater than 0.031wt%, the slag discharge rate is controlled at 14~16kg / t steel. In step (ii) 2), based on the tapping time and slag amount of the previous furnace, the slag feeding time is determined using formula ①, and the slag feeding amount is precisely controlled by adjusting the slag feeding time: Slag discharge time = slag discharge volume Formula ① for steel tapping time on furnace / 500 The unit for tapping time of the previous furnace is seconds (s), the unit for slag amount is kg / t steel, and the unit for slag discharge time is seconds (s), with the time rounded to one decimal place.

2. The method according to claim 1, characterized in that, In step (1), the composition of the molten iron is: C: 4.0~5.0wt%, Si: 0.2~0.80wt%, Mn: 0.11~0.30wt%, P: ≤0.15wt%, S: ≤0.060wt%, with the balance being iron and unavoidable impurities.

3. The method according to claim 1, characterized in that, In step (1), the mass of scrap steel accounts for 5-11% of the total mass of molten iron and scrap steel.

4. The method according to claim 1, characterized in that, In step (1) 3), after the endpoint test, add iron oxide scale to the furnace at a rate of 1.9~5 kg / t steel, then blow argon and stir for 1~3 minutes, with the argon flow rate controlled at 5~20 Nm. 3 / min.

5. The method according to claim 1, characterized in that, In step (ii), the converter slag obtained by boiling tapping in the converter has the following composition: CaO: 35~45wt%, SiO2: 8~12wt%, TFe: 18~27wt%, MgO: 6~9wt%, MnO: 1~3wt%, P2O5: 1.8~3.5wt%, S: 0.02~0.06wt%, with the balance being unavoidable impurities.

6. The method according to claim 1, characterized in that, In step (ii) 2), the slag blocking is a sliding plate slag blocking.

7. The method according to claim 1, characterized in that, In step (three), the slag removal operation of molten steel is as follows: 1) After sampling, the molten steel is hoisted to the slag removal position for slag removal; 2) Tilt the ladle to ensure the slag surface is flush with the bottom edge of the ladle opening; 3) The operator uses the slag remover to remove the slag completely.

8. The method according to claim 7, characterized in that, In step (3) 2), the molten steel ladle is tilted to 20~30°.