Semi-steel steelmaking method of SPA-H weathering resistant steel for slagging by using furnace slag

Abstract

The invention discloses a semi-steel steelmaking method for SPA-H weathering resistant steel using roughing slag for slagging, which comprises the following steps of: smelting semi-steel in a converter, and adding the roughing slag of a steelmaking furnace as a slagging material for slagging in the blowing process; the roughing slag of the steel smelting furnace is added in two batches, the first batch of roughing slag is added from the blowing oxygen step to 40%-50%, and the adding amount is 70%-80% of the total mass; the adding time of the second batch is from the blowing oxygen step to 60%-70%, and the adding amount is 20%-30% of the total mass; in the blowing process, the lance position of an oxygen lance is controlled in a high-low-low mode, the lance position in the early stage of the oxygen blowing process is 1.7-1.8 m, the lance position in the middle stage of the oxygen blowing process is 1.55-1.65 m, and the lance position in the later stage of the oxygen blowing process is 1.4-1.45 m. The method can safely and stably use the tapping slag in the steelmaking process, controls the dephosphorization rate in a suitable range, realizes cyclic utilization of the tapping slag of the steelmaking furnace in the steelmaking process, avoids resource waste, reduces the steelmaking production cost, and has the characteristics of good safety, low cost, energy conservation and environmental protection.

Description

Technical Field

[0001] This invention relates to a steelmaking method, and more particularly to a semi-steelmaking method for SPA-H weathering steel using under-furnace slag. Background Technology

[0002] Semi-steel is an intermediate product formed after molten iron undergoes a vanadium extraction process in a converter. Compared to molten iron, semi-steel has a lower content of elements such as silicon, manganese, and carbon, making it less prone to slag formation and resulting in lower dephosphorization efficiency during the semi-steel steelmaking process. In traditional processes, slag from steelmaking furnaces is generally used for outsourced magnetic separation or directly discharged as waste. This incurs processing and transportation costs, while the iron and MgO in the slag are not fully utilized, leading to resource waste.

[0003] Since most of the slag from steelmaking furnaces is pre-melted material and contains some iron oxide, all of which are beneficial for slag formation, using slag alone can easily cause explosive blowouts during converter blowing, creating safety hazards. Furthermore, excessive slag formation accelerates the dephosphorization reaction efficiency, resulting in a large amount of ferrophosphorus alloying and wasting costs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a safe and stable semi-steelmaking method for SPA-H weathering steel using under-furnace slag.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: the semi-steel is smelted in a converter, and slag from the steelmaking furnace is added as slag-forming material during the blowing process; the slag from the steelmaking furnace is added in two batches, the first batch is added when the oxygen blowing step reaches 40% to 50%, and the amount added is 70% to 80% of the total mass; the second batch is added when the oxygen blowing step reaches 60% to 70%, and the amount added is 20% to 30% of the total mass; during the blowing process, the oxygen lance position is controlled in a high-low-low mode, with the lance position at 1.7 to 1.8m in the early stage of the oxygen blowing process, 1.55 to 1.65m in the middle stage, and 1.4 to 1.45m in the later stage.

[0006] Furthermore, the total amount of slag added to a single furnace in the steelmaking furnace is 4000-6000 kg.

[0007] Furthermore, the oxygen pressure during the oxygen blowing process is between 0.75 and 0.85 MPa, and the oxygen supply intensity is between 3.0 and 3.6 Nm. 3 / (t·min).

[0008] Furthermore, the final temperature of the converter smelting is 1610–1630°C.

[0009] Furthermore, the composition and mass content of the slag from the steelmaking furnace meet the following requirements: CaO > 35%, SiO2 < 8%, MgO > 15%, P < 5%, S < 1%.

[0010] The beneficial effects of adopting the above technical solution are as follows: This invention uses steelmaking furnace slag to replace all conventional slag-forming materials. Through a high-level silo, steelmaking furnace slag is added to the converter in batches during the converter blowing process. Combined with optimized adjustment of the blowing lance position, the direct oxygen supply ratio is maximized, avoiding excessive slag melting. While not affecting the decarburization process, a certain degree of dephosphorization is achieved, and converter blowout is avoided. Therefore, furnace slag can be used safely and stably in the steelmaking process, and the dephosphorization rate is controlled within an appropriate range, achieving the goal of safe and low-cost production of SPA-H weathering steel. This invention realizes the recycling of steelmaking furnace slag in the steelmaking process, avoiding resource waste, reducing the cost of slag-forming materials in the SPA-H weathering steel smelting process, lowering steelmaking production costs, and reducing the discharge of steelmaking waste, thus contributing to environmental protection. Therefore, this invention has the characteristics of good safety, low cost, energy saving, and environmental protection. Detailed Implementation

[0011] The present invention will now be described in further detail with reference to specific embodiments.

[0012] This method for semi-steelmaking of SPA-H weathering steel using underflow slag is carried out in a converter using semi-steel as raw material. The composition and mass content of the semi-steel are: C 3.0-3.3%, P < 0.140%, Si < 0.1%, Ti < 0.1%, with the balance being iron and other unavoidable elements.

[0013] In the converter smelting process, slag from the steelmaking furnace is added during the blowing process to replace all conventional slag-forming materials, serving as the slag-forming material. The slag is a mixture, mainly consisting of steel slag scattered under the furnace during the tapping process, lime and lightly calcined dolomite scattered during the charging process, and molten iron scattered under the furnace during the molten iron charging process. The composition and mass content of the slag from the steelmaking furnace must meet the following requirements: CaO > 35%, SiO2 < 8%, MgO > 15%, P < 5%, S < 1%. The slag from the steelmaking furnace needs to be dried and crushed, and the particle size of the slag from the steelmaking furnace is less than 10 cm. The total amount of slag from the steelmaking furnace added per furnace is 4000-6000 kg. Because SPA-H weathering steel has certain requirements for the final phosphorus content, to avoid excessive dephosphorization and waste of ferrophosphorus alloy, the addition time of the furnace slag needs to be delayed. Rapid heating is used to suppress the converter dephosphorization reaction. The furnace slag is added in two batches. The first batch is added when the oxygen blowing rate reaches 40%–50%, and the amount added is 70%–80% of the total mass. The second batch is added when the oxygen blowing rate reaches 60%–70%, and the amount added is 20%–30% of the total mass. No materials are allowed to be added 1–2 minutes before the oxygen blowing ends, and the process continues until the oxygen blowing is complete.

[0014] During the blowing process, top-blown oxygen is used throughout the converter oxygen blowing process, supplemented by bottom-blown argon for stirring. Because the slag below the furnace contains some iron oxide, it easily causes slagging in the converter. Therefore, the converter lance position needs to be lowered to reduce the proportion of indirect oxygen supply and avoid excessive slagging. The oxygen lance position is controlled in a high-low-low mode: the lance position is 1.7–1.8m in the early stage of the oxygen blowing process, and the bottom-blown argon flow rate is controlled at 350 Nm³. 3 / h; During the oxygen blowing process, the gun position is 1.55-1.65m, and the bottom blowing argon flow rate is controlled at 400Nm. 3 / h; During the later stage of the oxygen blowing process, the gun position is 1.4–1.45m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; During the oxygen blowing process, the maximum range of a single adjustment of the oxygen lance position, i.e., the vertical adjustment range of the oxygen lance, is <0.2m / time; The oxygen pressure during the oxygen blowing process is 0.75~0.85Mpa, and the oxygen supply intensity is 3.0~3.6Nm. 3 / (t·min). The final temperature of the converter smelting is 1610~1630℃.

[0015] After blowing, the steel is tapped, with a clearance of 400-600 mm left in the ladle. Bottom-blown argon gas is used for stirring throughout the tapping process. The alloys required for SPA-H weathering steel are added during tapping. Before tapping is completed, a sliding plate and infrared slag detection are used to prevent slag buildup. The converter is then turned to complete the furnace operation. The composition and mass content of the obtained qualified molten steel are: C 0.07-0.10%, P 0.07-0.10%, Cu 0.25-0.35%, with the balance being iron and other unavoidable elements. Example 1

[0016] A steel plant has a 150t converter with a semi-steel loading of 170t. The semi-steel composition is: C 3.2%, Si 0.02%, Ti 0.01%, P 0.135%.

[0017] During the converter blowing process, the first batch of steelmaking furnace slag (2800 kg) was added when the oxygen blowing rate reached 40%; the second batch (1200 kg) was added when the oxygen blowing rate reached 70%. The composition of the steelmaking furnace slag used was: CaO 41%, SiO2 4.7%, MgO 18%, P 2.5%, S 0.22%. In the early stages of oxygen blowing, the oxygen lance position was controlled at 1.75 m, and the bottom-blown argon flow rate was controlled at 350 Nm³. 3 / h; During the mid-stage oxygen blowing, the oxygen lance position is controlled at 1.65m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; During the later stages of oxygen blowing, the oxygen lance position is controlled at 1.45m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; total oxygen blowing time 11min; oxygen pressure controlled at 0.70~0.85Mpa during oxygen blowing, oxygen supply intensity 3.0~3.6Nm 3 / (t·min). The final temperature measurement was 1625℃. The composition of the molten steel sample after tapping was: C 0.075%, P 0.080%, Cu 0.27%.

[0018] In this embodiment, a total of 4000 kg of steelmaking furnace slag was used per furnace, with a slag-forming material consumption cost of 0 yuan. Since steelmaking furnace slag is a self-produced waste, there is no procurement cost, and the unit price of the slag-forming material is 0 yuan / ton. In contrast, the unit price of conventional slag-forming materials, light-burned dolomite, is 320 yuan / ton, and the unit price of raw dolomite is 80 yuan / ton. Subsequent embodiments and comparative examples will use this unit price to calculate costs. Example 2

[0019] A steel plant has a 150t converter with a semi-steel charge of 173t. The semi-steel composition is: C 3.3%, Si 0.04%, Ti 0.02%, P 0.130%.

[0020] During the converter blowing process, the first batch of steelmaking furnace slag (3500 kg) is added when the oxygen blowing reaches 50%; the second batch (1500 kg) is added when the oxygen blowing reaches 70%. The composition of the steelmaking furnace slag used is: CaO 40.5%, SiO2 3.9%, MgO 19.4%, P 2.2%, S 0.35%. In the early stages of oxygen blowing, the oxygen lance position is controlled at 1.80 m, and the bottom-blown argon flow rate is controlled at 350 Nm³. 3 / h; During the mid-stage oxygen blowing, the oxygen lance position is controlled at 1.60m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; During the later stages of oxygen blowing, the oxygen lance position is controlled at 1.40m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; Total oxygen blowing time 11.5min; Oxygen pressure controlled at 0.70~0.85Mpa during oxygen blowing, oxygen supply intensity 3.0~3.6Nm 3 / (t·min). The final temperature measurement was 1620℃. The composition of the molten steel sample after tapping was: C 0.080%, P 0.075%, Cu 0.26%.

[0021] In this embodiment, a total of 5000 kg of slag was used per furnace, and the cost of slag-making material was 0 yuan. Example 3

[0022] A steel plant has a 150t converter with a semi-steel charge of 175t. The semi-steel composition is: C 3.28%, Si 0.02%, Ti 0.03%, P 0.137%.

[0023] During the converter blowing process, the first batch of steelmaking furnace slag (4500 kg) was added when the oxygen blowing rate reached 40%; the second batch (1500 kg) was added when the oxygen blowing rate reached 70%. The composition of the steelmaking furnace slag used was: CaO 39.5%, SiO2 4.2%, MgO 18.2%, P 2.4%, S 0.41%. In the early stage of oxygen blowing, the oxygen lance position was controlled at 1.75 m, and the bottom-blown argon flow rate was controlled at 350 Nm³. 3 / h; During the mid-stage oxygen blowing, the oxygen lance position is controlled at 1.60m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; During the later stages of oxygen blowing, the oxygen lance position is controlled at 1.45m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; total oxygen blowing time 11min; oxygen pressure controlled at 0.70~0.85Mpa during oxygen blowing, oxygen supply intensity 3.0~3.6Nm 3 / (t·min). The final temperature measurement was 1615℃. The composition of the molten steel sample after tapping was: C 0.075%, P 0.078%, Cu 0.28%.

[0024] In this embodiment, a total of 6000 kg of slag was used per furnace, and the cost of slag-making material was 0 yuan. Example 4

[0025] A steel plant has a 150t converter with a semi-steel charge of 175t. The semi-steel composition is: C 3.20%, Si 0.023%, Ti 0.017%, P 0.131%.

[0026] During the converter blowing process, the first batch of steelmaking furnace slag (3150 kg) was added when the oxygen blowing rate reached 40%; the second batch (1350 kg) was added when the oxygen blowing rate reached 70%. The composition of the steelmaking furnace slag used was: CaO 44%, SiO2 3.9%, MgO 17.6%, P 2.37%, S 0.29%. In the early stages of oxygen blowing, the oxygen lance position was controlled at 1.70 m, and the bottom-blown argon flow rate was controlled at 350 Nm³. 3 / h; During the mid-stage oxygen blowing, the oxygen lance position is controlled at 1.55m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; During the later stages of oxygen blowing, the oxygen lance position is controlled at 1.40m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; total oxygen blowing time 12min; oxygen pressure controlled at 0.70~0.85Mpa during oxygen blowing, oxygen supply intensity 3.0~3.6Nm 3 / (t﹒min). The final temperature measurement was 1618℃. The composition of the molten steel sample after tapping was: C 0.080%, P 0.081%, Cu 0.26%.

[0027] In this embodiment, a total of 4500 kg of slag was used per furnace, and the cost of slag-making material consumption was 0 yuan. Example 5

[0028] A steel plant has a 150t converter with a semi-steel charge of 169t. The semi-steel composition is: C 3.30%, Si 0.041%, Ti 0.035%, P 0.139%.

[0029] During the converter blowing process, the first batch of steelmaking furnace slag (4400 kg) was added when the oxygen blowing reached 50%; the second batch (1100 kg) was added when the oxygen blowing reached 80%. The composition of the steelmaking furnace slag used was: CaO 42.5%, SiO2 3.76%, MgO 16.9%, P 2.25%, S 0.16%. In the early stage of oxygen blowing, the oxygen lance position was controlled at 1.75m, and the bottom-blown argon flow rate was controlled at 350 Nm³. 3 / h; During the mid-stage oxygen blowing, the oxygen lance position is controlled at 1.60m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; During the later stages of oxygen blowing, the oxygen lance position is controlled at 1.45m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; total oxygen blowing time 12min; oxygen pressure controlled at 0.70~0.85Mpa during oxygen blowing, oxygen supply intensity 3.0~3.6Nm 3 / (t·min). The final temperature measurement was 1618℃. The composition of the molten steel sample after tapping was: C 0.075%, P 0.077%, Cu 0.27%.

[0030] In this embodiment, a total of 5500 kg of slag was used per furnace, and the cost of slag-making material was 0 yuan.

[0031] Comparative Example 1: A steel plant has a 150t converter with a semi-steel loading of 170t. The semi-steel composition is: C 3.1%, Si 0.033%, Ti 0.025%, P 0.129%.

[0032] During the converter blowing process, the first batch of slag-forming materials is added when the oxygen blowing reaches 40%, consisting of 2000 kg of light-burned dolomite and 1000 kg of raw dolomite. The second batch of slag-forming materials is added when the oxygen blowing reaches 70%, consisting of 500 kg of light-burned dolomite. In the early stages of oxygen blowing, the oxygen lance position is controlled at 1.85 m, and the bottom-blown argon flow rate is controlled at 350 Nm³. 3 / h; During the mid-stage oxygen blowing, the oxygen lance position is controlled at 1.70m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; During the later stages of oxygen blowing, the oxygen lance position is controlled at 1.60m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; oxygen blowing time 11.5min; oxygen pressure controlled at 0.70~0.85Mpa, oxygen supply intensity 3.0~3.6Nm 3 / (t·min). The final temperature measurement was 1625℃. The composition of the molten steel sample after tapping was: C 0.081%, P 0.079%, Cu 0.26%.

[0033] This comparative example uses a total of 2500 kg of lightly calcined dolomite and 1000 kg of raw dolomite per furnace, with a slag-forming material consumption cost of 880 yuan.

[0034] Comparative Example 2: A steel plant has a 150t converter with a semi-steel charge of 172t. The semi-steel composition is: C 3.3%, Si 0.011%, Ti 0.017%, P 0.135%.

[0035] During the converter blowing process, the first batch of slag-forming materials is added when the oxygen blowing reaches 40%, consisting of 2100 kg of light-burned dolomite and 800 kg of raw dolomite. The second batch of slag-forming materials is added when the oxygen blowing reaches 70%, consisting of 600 kg of light-burned dolomite and 500 kg of raw dolomite. In the early stages of oxygen blowing, the oxygen lance position is controlled at 1.85 m, and the bottom-blown argon flow rate is controlled at 350 Nm³. 3 / h; During the mid-stage oxygen blowing, the oxygen lance position is controlled at 1.75m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; During the later stages of oxygen blowing, the oxygen lance position is controlled at 1.60m, and the bottom-blown argon flow rate is controlled at 400Nm. 3 / h; oxygen blowing time 11.5min; oxygen pressure controlled at 0.70~0.85Mpa, oxygen supply intensity 3.0~3.6Nm 3 / (t·min). The final temperature measurement was 1628℃. The composition of the molten steel sample after tapping was: C 0.077%, P 0.075%, Cu 0.27%.

[0036] This comparative example uses a total of 2700 kg of lightly calcined dolomite and 1300 kg of raw dolomite per furnace, with a slag-forming material consumption cost of 968 yuan.

Claims

1. A semi-steelmaking method for SPA-H weathering steel using under-furnace slag, characterized in that: The semi-steel is smelted in a converter, and slag from the steelmaking furnace is added as slag-forming material during the blowing process. The slag from the steelmaking furnace is added in two batches. The first batch is added when the oxygen blowing rate reaches 40% to 50%, and the amount added is 70% to 80% of the total mass. The second batch is added when the oxygen blowing rate reaches 60% to 70%, and the amount added is 20% to 30% of the total mass. During the blowing process, the oxygen lance position is controlled in a high-low-low mode. The lance position is 1.7 to 1.8m in the early stage of the oxygen blowing process, 1.55 to 1.65m in the middle stage, and 1.4 to 1.45m in the later stage.

2. The semi-steelmaking method for SPA-H weathering steel using under-furnace slag as described in claim 1, characterized in that: The total amount of slag added to a single steelmaking furnace is 4000-6000 kg.

3. The semi-steelmaking method for SPA-H weathering steel using under-furnace slag as described in claim 1, characterized in that: The oxygen blowing process is carried out at an oxygen pressure of 0.75–0.85 MPa, with an oxygen supply intensity of 3.0–3.6 Nm. 3 / (t·min).

4. The semi-steelmaking method for SPA-H weathering steel using under-furnace slag as described in claim 1, characterized in that: The final temperature of the converter smelting is 1610–1630℃.

5. A semi-steelmaking method for SPA-H weathering steel using under-furnace slag as described in any one of claims 1-4, characterized in that: The composition and mass content of the slag under the steelmaking furnace meet the following requirements: CaO > 35%, SiO2 < 8%, MgO > 15%, P < 5%, S < 1%.