A process for smelting high-phosphorus weathering steel through decarburization and phosphorus retention.

Abstract

This invention discloses a process for smelting high-phosphorus weathering steel through decarburization and phosphorus retention. The process involves using a decarburization converter to decarburize blast furnace hot metal to obtain semi-steel, which is then tapped to a ladle at 1330–1420°C and slag removed. The semi-steel undergoes deep decarburization and reduction in an AOD converter, with alloying elements added according to the steel grade composition. The alloyed steel is then transported to an LF furnace for refining, where alloys are added to fine-tune the composition according to the steel grade's chemical requirements. Finally, the refined steel is transported to a continuous casting platform for casting, yielding high-phosphorus weathering steel slabs. This invention utilizes a decarburization converter without adding any alkaline slag-forming agents, achieving efficient decarburization and phosphorus retention to obtain semi-steel with a phosphorus content close to that of the original hot metal, resulting in low smelting costs. The semi-steel's entry into the AOD converter significantly improves the decarburization and chromium retention conditions, increasing the AOD furnace's production efficiency. The LF furnace's white slag formation, deep desulfurization, temperature increase, and alloy composition fine-tuning ensure the purity and castability of the molten steel, creating favorable conditions for the slab continuous casting process.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, specifically relating to a process for smelting high-phosphorus weathering steel through decarburization and phosphorus retention. Background Technology

[0002] For most steel grades, phosphorus is one of the harmful elements. It easily segregates in the steel and causes brittleness during processing, leading to a deterioration in the steel's performance. Therefore, a lower phosphorus content is generally preferred. Weathering steel is a low-alloy steel between ordinary steel and stainless steel. Phosphorus in it is a beneficial element, improving the steel's weather resistance and hardness, enhancing impact resistance, and reducing iron loss. Currently, the conventional converter process for smelting weathering steel requires the addition of large amounts of ferrophosphorus alloy to reach the required phosphorus content range because the phosphorus content at the converter tapping point is already low. Therefore, this method fails to fully utilize the phosphorus resources in the molten iron, resulting in resource waste and high smelting costs.

[0003] In existing reports, high-phosphorus steel is generally smelted using deep desulfurized hot metal with minimal slag, utilizing low basicity and weak stirring to increase the final phosphorus content of the molten steel to 0.05%. Patent application number 200410047045.0 discloses a method for smelting phosphorus-containing steel, employing rapid heating in a converter to remove carbon and retain phosphorus, creating high-phosphorus slag, and adding phosphate rock or phosphate ore to the converter to increase the final phosphorus content. Patent application number 201410334836.5 discloses a top-and-bottom blowing converter method for smelting phosphorus-containing steel, using low basicity slag formation in the converter and adding iron-containing carbon balls to control the final phosphorus content at 0.05–0.065%. (Application number 201110240361 is also mentioned.) Patent application X discloses a converter smelting method for phosphorus-containing steel. By controlling the oxygen lance position and oxygen supply intensity, and reducing the addition of alkaline slagging agents, the final phosphorus content can be controlled at around 0.030%, thus reducing the amount of ferrophosphorus added. Patent application No. 201610622221.1 discloses a method for controlling the final phosphorus content of molten steel in a converter. This involves normal dephosphorization steelmaking in the previous heat, retaining slag as needed for phosphorus increase, and then smelting phosphorus-containing steel. However, relying on high-phosphorus slag for phosphorus increase has limited effectiveness. Application No. 2018115024... Patent application No. 16.8 discloses a method for smelting high-phosphorus steel in a converter, employing a slag-retention and low-slag smelting method to reduce the consumption of slag-forming materials and ferrophosphorus alloys, thereby reducing iron loss caused by large slag volumes. During the blowing process, the oxygen lance uses a high-low-low position, which can control the final phosphorus content to 0.05-0.06%. Patent application No. 202210017613.0 discloses a method for producing high-phosphorus steel, in which steel slag is used to partially or completely replace quicklime as flux during the steelmaking process, combined with a reasonable oxygen supply system, slag-forming system, and final control. While using various processes to meet phosphorus content requirements, the consumption of quicklime and the cost of alloys are reduced. However, due to the high lime content in steel slag, the final phosphorus content after decarburization cannot achieve the goal of high-phosphorus steel production. The invention patent application No. 202010362481.6 discloses a method for preparing ultra-low carbon high-phosphorus steel, which involves desulfurizing molten iron, performing converter blowing, and vacuum decarburizing the molten steel while adding phosphorus-containing substances to adjust the phosphorus content in the molten steel, ultimately obtaining ultra-low carbon high-phosphorus steel. However, a large amount of ferrophosphorus alloy still needs to be added in the end.

[0004] The above processes for producing high-phosphorus steel all use conventional converter low-alkalinity slag making, or add iron ore and phosphorus-containing steel slag to partially increase phosphorus. However, due to the strong oxidation reaction of converter decarburization, some phosphorus in the molten iron will inevitably be oxidized during converter decarburization. For high-phosphorus weathering steel with a phosphorus content ≥0.070%, the phosphorus retention effect is limited, and additional iron phosphate is required. Summary of the Invention

[0005] Based on the above, the purpose of this invention is to provide a process for smelting high-phosphorus weathering steel through decarburization and phosphorus retention. The process adopts a three-step method of "BOF+AOD+LF" for decarburization and phosphorus retention. The decarburization converter completes part of the decarburization task to obtain semi-steel. High-phosphorus iron ore is added during the smelting of semi-steel to adjust the phosphorus content of the semi-steel. This can make the phosphorus content in the semi-steel basically close to the initial phosphorus content in the molten iron, which can reduce costs and significantly improve the decarburization and chromium retention conditions of the AOD converter, thereby increasing production efficiency.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A process for smelting high-phosphorus weathering steel by decarburization and phosphorus retention includes the following steps:

[0008] S1. Decarburization converter smelting: Decarburization is carried out on blast furnace molten iron using a decarburization converter to obtain semi-steel. The chemical composition of the semi-steel, by mass percentage, is: C 2.0~3.0%, Si≤0.10%, Mn≤0.10%, P 0.070~0.150%, S 0.02~0.06%, with the remainder being Fe and unavoidable impurities.

[0009] S2, tapping half steel: tapping the half steel from S1 into the ladle, wherein the tapping temperature of the half steel is 1330~1420℃; then the ladle filled with half steel is hoisted to the slag removal station for slag removal, so that the slag layer thickness on the liquid surface inside the ladle is ≤50mm;

[0010] S3, AOD converter smelting: After slag removal from S2, the molten iron ladle is placed in an AOD converter for deep decarburization and reduction. During the reduction stage, the slag basicity is controlled at 1.5-2.5, and aluminum particles are added for deep deoxidation. Then, according to the composition of the steel grade, one or more alloying elements, such as Cu, Ni, Cr, Nb, Si, Mn, or Ti, are added for alloying. The chemical composition of the alloyed steel, by mass percentage, is: C≤0.15%, Si 0.25-0.75%, Mn 0.20-1.50%, P 0.070-0.150%, S≤0.010%, Cu≤0.55%, Ni≤0.65%, Cr≤1.25%, with the remainder being Fe and unavoidable impurities.

[0011] S4 and LF furnace refining: The alloyed molten steel from S3 is hoisted to the LF furnace for refining. 8–12 kg / t of refining slag and 6–10 kg / t of lime are added. The temperature is increased at a rate of 2–5 °C / min for 10–20 minutes, followed by rapid white slag desulfurization to ensure the sulfur content of the molten steel leaving the furnace is ≤0.010%. Alloys are added to fine-tune the steel composition according to the chemical composition control requirements of the steel grade. Specifically, the Al content in the steel is adjusted in the LF furnace by feeding aluminum wire, controlling it to be between 0.020% and 0.040%.

[0012] S5, Slab Continuous Casting: The molten steel refined from S4 is hoisted to the continuous casting platform for casting to obtain high-phosphorus weather-resistant steel slabs.

[0013] As a further preferred embodiment of the technical solution of the present invention, in S1, the blast furnace molten iron used in decarburization converter smelting contains 0.070 to 0.150% P.

[0014] Furthermore, in S1, only high-phosphorus iron ore is added as a coolant during decarburization converter smelting. The chemical composition of the high-phosphorus iron ore, by mass percentage, is: P≥0.50%, with the remainder being Fe and unavoidable impurities.

[0015] Furthermore, 10-100 kg / t of high-phosphorus iron ore is added to the decarburized converter 1-3 minutes after oxygen supply, without adding any other alkaline slagging agents such as lime or dolomite.

[0016] Furthermore, the oxygen supply pressure of the decarburization converter is set at 0.65–0.75 MPa, which is 0.5–1 MPa lower than the normal smelting pressure of the converter, and the total oxygen supply time is 4–7 minutes.

[0017] Furthermore, in S3, top-gun oxygen blowing is used for decarbonization in the early stage of the decarbonization phase, with an oxygen supply intensity of 1.0–1.5 m³ / s. 3 ·min -1 For steel of / t, stop supplying oxygen to the top lance when the carbon content reaches 0.20%–0.30%; for side-blown oxygen-argon mixture, the oxygen supply intensity is 0.5–0.7 m. 3 ·min -1 / t steel, argon gas supply intensity 0.5~0.7m 3 ·min -1 / t steel, oxygen-argon ratio is 1:1; after the carbon content reaches 0.04%~0.06%, it enters the reduction stage. Argon gas is introduced into the side tuyeres at the bottom of the furnace, and 2.0~2.4Kg / t steel of Ca-Si powder is added through the top hopper for reduction.

[0018] Furthermore, during the decarburization stage, the top-blown oxygen supply accounts for 60% of the total oxygen supply, and during the reduction stage, the argon gas supply intensity at the side tuyeres at the furnace bottom is 1.5–2.0 m³ / s. 3 ·min -1 / t steel.

[0019] Furthermore, in S3, the AOD converter smelting uses silicon-manganese alloy with Mn, and the insufficient Si is made up with ferrosilicon. The Mn and Si in the steel are added in the AOD converter according to the lower limit of the target composition of the steel grade. Then, in step S4, after entering the LF furnace, the Mn and Si content is finely adjusted to the middle limit required by the steel grade.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention employs a decarburization converter without adding any alkaline slag-forming agents to efficiently decarburize and retain phosphorus to obtain semi-steel. High-phosphorus iron ore is added during the smelting of the semi-steel to adjust its phosphorus content, resulting in semi-steel with a phosphorus content close to that of the original molten iron, thus reducing smelting costs. The semi-steel is then smelted in an AOD converter, significantly improving the decarburization and chromium retention conditions and increasing the AOD furnace's production efficiency. The LF furnace produces white slag for deep desulfurization, and the heating and fine-tuning of alloy composition ensure the purity and castability of the molten steel, creating favorable conditions for the slab continuous casting process. Attached Figure Description

[0022] Figure 1 This is a flowchart of the process for smelting high-phosphorus weathering steel by decarburization and phosphorus retention according to the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] Example 1

[0025] like Figure 1 As shown, a process for smelting high-phosphorus weathering steel through decarburization and phosphorus retention, taking the production of SPA-H high-strength weathering steel slabs for containers in a 100-ton converter at a certain factory as an example, includes the following steps:

[0026] After the molten iron from the blast furnace is transported to the steel plant via a ladle, it is not pretreated for desulfurization, thus avoiding the loss of vanadium slag and the temperature drop during the process caused by slag removal during pretreatment.

[0027] 10.5t of high-phosphorus iron ore and 101.5t of molten iron were charged into the decarburization converter. The mass fraction of each element in the molten iron is shown in Table 1. The remainder consists of iron and unavoidable impurities.

[0028] Table 1. Mass fraction of each element in molten iron in Example 1

[0029]

[0030] Oxygen is blown into the converter through an oxygen lance for smelting. After blowing oxygen for 1 minute, a coolant is added. The coolant is made of high-phosphorus iron ore and the amount added is 25 kg / t of steel.

[0031] The oxygen supply pressure was controlled at 0.78 MPa. Due to the high cooling intensity and long low-temperature cooling time of the molten pool, the carbon-oxygen reaction was inhibited, and the oxygen supply time was extended. At 6 minutes and 29 seconds of blowing, the furnace flame was observed; the carbon flame was initially visible. The oxygen lance was immediately lifted, and the temperature was measured at 1406℃. After the semi-steel was tapped, samples were taken for testing, yielding a semi-steel with a carbon content of 2.26% and a phosphorus content of 0.120%. Through decarburization in the decarburization converter, enhanced cooling intensity, and extended oxygen supply time, the carbon content in the molten iron was oxidized to 2.26%. Simultaneously, the addition of high-phosphorus iron ore increased phosphorus content, achieving a phosphorus content of 0.120% in the semi-steel. The decarburization converter completed a large portion of the decarburization task while preserving phosphorus, maximizing the utilization of phosphorus resources in the molten iron.

[0032] The decarburized semi-steel is tapped into the molten iron ladle at a temperature of 1406℃. The ladle, filled with semi-steel, is then hoisted to the slag removal station for slag removal, and the slag layer thickness on the liquid surface is measured to be 30mm.

[0033] The semi-steel, after slag removal, is added to the AOD converter for decarburization and reduction. The addition amount is 103t. In the early stage of decarburization, top-lance oxygen blowing is used for decarburization, and the oxygen supply intensity is 1.0m. 3 ·min -1 For steel of / t, stop supplying oxygen to the top lance when the carbon content reaches 0.28%; for side-blown oxygen-argon mixture, the oxygen supply intensity is 0.7m. 3 ·min -1 / t steel, argon gas supply intensity 0.6m 3 ·min -1 / t steel; after the carbon content reaches 0.06%, it enters the reduction stage. Argon gas is introduced into the side tuyeres at the bottom of the furnace, and 2.0Kg / t steel of Ca-Si powder is added through the top hopper of the furnace for reduction.

[0034] The steel is treated with silicon-manganese alloy to produce Mn and Si, with ferrosilicon used to make up any shortfall. Mn and Si are added to the steel at the lower limit in the AOD converter, followed by the addition of ferrochrome and ferronickel for microalloying. The slag basicity is controlled at 1.8. After AOD treatment, the steel composition is: C: 0.08%, Si: 0.30%, Mn: 0.30%, P: 0.120%, S: 0.008%, Cr: 0.35%, Ni: 0.15%, with the balance being iron and unavoidable impurities. Due to the low carbon content of the semi-steel, smelting in the AOD converter significantly improves the decarburization and chromium retention conditions of the AOD furnace, thereby increasing the production efficiency of the AOD furnace.

[0035] The molten steel after AOD converter smelting was argon-blown and temperature-measured at the LF furnace treatment station. High-power submerged arc heating was then applied to the semi-molten steel, with 8 kg / t of refining slag and 6 kg / t of lime added. After 10 minutes of heating, the steel temperature reached 1583℃, allowing for rapid white slag formation and deep desulfurization. The sulfur content at the outlet was 0.008%. Alloys were added to fine-tune the composition. The Al content in the steel was controlled to 0.025% in the LF refining furnace using aluminum wire feed. The LF furnace's white slag formation and deep desulfurization, temperature increase, and fine-tuning of the alloy composition ensured the purity and castability of the molten steel. The molten steel entered the slab continuous casting process with good castability. The chemical composition of the LF-treated steel is shown in Table 4.

[0036] Table 2 Chemical composition of molten steel after LF treatment in Example 1

[0037]

[0038] The molten steel refined by LF is hoisted to the continuous casting platform for casting. During the casting process, the ladle is covered, the tundish is covered with a covering agent, the long nozzle is protected by argon, and an immersion nozzle is used to avoid secondary oxidation of the molten steel. Special protective slag for weathering steel is used during the casting process to obtain high phosphorus weathering steel slabs.

[0039] Example 2

[0040] like Figure 1 As shown, a process for smelting high-phosphorus weathering steel through decarburization and phosphorus retention, taking the production of atmospheric corrosion resistant 09CuPCrNi weathering steel slabs in a 100-ton converter at a certain plant as an example, includes the following steps:

[0041] After the molten iron from the blast furnace is transported to the steel plant via molten iron ladle, it is not subjected to pretreatment and desulfurization, thus avoiding the loss of vanadium slag and the loss of temperature drop during the process caused by slag removal during pretreatment.

[0042] 110 tons of molten iron were added to the decarburization converter. The mass fraction of each element in the molten iron is shown in Table 3. The remainder consists of iron and unavoidable impurities.

[0043] Table 3 Mass fraction of each element in molten iron in Example 2

[0044]

[0045] Oxygen is blown into the converter through an oxygen lance for smelting. After blowing oxygen for 1 minute, a coolant is added. The coolant is made of high-phosphorus iron ore and the amount added is 90 kg / t of steel.

[0046] The oxygen supply pressure was controlled at 0.72 MPa. Due to the high cooling intensity and long cooling time of the molten pool, the carbon-oxygen reaction was inhibited, and the oxygen supply time was extended. After 5 minutes and 45 seconds of blowing, the furnace flame was observed; when the carbon flame first appeared, the oxygen lance was immediately lifted, and the temperature was measured at 1349℃. After the semi-steel was produced, samples were taken for testing, yielding a semi-steel with a carbon content of 2.55% and a phosphorus content of 0.095%. Through decarburization in a decarburizing converter, enhanced cooling intensity, and extended oxygen supply time, the carbon content in the molten iron was oxidized to 2.55%. Simultaneously, the addition of high-phosphorus iron ore increased phosphorus content, achieving a phosphorus content of 0.095% in the semi-steel, maximizing the utilization of phosphorus resources in the molten iron.

[0047] The decarburized semi-steel is tapped into the molten iron ladle at a temperature of 1349℃. The ladle, filled with semi-steel, is then hoisted to the slag removal station for slag removal, and the slag layer thickness on the liquid surface is measured to be 30mm.

[0048] The semi-steel, after slag removal, is added to the AOD converter for decarburization and reduction. The addition amount is 105t. In the early stage of decarburization, top-lance oxygen blowing is used for decarburization, and the oxygen supply intensity is 1.2m. 3 ·min -1 For steel of / t, stop supplying oxygen to the top lance when the carbon content reaches 0.24%; for side-blown oxygen-argon mixture, the oxygen supply intensity is 0.6m. 3 ·min -1 / t steel, argon gas supply intensity 0.6m 3 ·min -1 / t steel; after the carbon content reaches 0.05%, it enters the reduction stage. Argon gas is introduced into the side tuyeres at the bottom of the furnace, and 2.2Kg / t steel of Ca-Si powder is added through the top hopper of the furnace for reduction.

[0049] The steel is treated with silicon-manganese alloy to produce Mn and Si, with ferrosilicon used to make up any deficiencies. The Mn and Si content in the steel is kept below the lower limit in the AOD converter. Then, copper plates, ferrochrome, and ferronickel are added for microalloying. The slag basicity is controlled at 1.8. The composition of the molten steel after AOD treatment is: C: 0.07%, Si: 0.10%, Mn: 0.35%, P: 0.095%, S: 0.010%, Cu: 0.35%, Cr: 0.45%, Ni: 0.35%, with the balance being iron and unavoidable impurities. Due to the low carbon content of the semi-steel, smelting in the AOD converter significantly improves the decarburization and chromium retention conditions of the AOD furnace, thereby increasing the production efficiency of the AOD furnace.

[0050] After AOD converter smelting, the molten steel was purged with argon and its temperature measured at the LF furnace treatment station. High-power submerged arc heating was then applied to the semi-molten steel, with 12 kg / t steel refining slag and 10 kg / t steel lime added. After heating for 20 minutes and measuring the steel temperature at 1552℃, rapid white slag desulfurization was performed. The sulfur content at the outlet was 0.008%. Alloys were added to fine-tune the composition. Als in the steel was added through an aluminum feeder in the LF refining furnace. The acid-soluble aluminum content in the molten steel exiting the LF furnace was 0.033%. The LF furnace white slag desulfurization, temperature increase, and fine-tuning of the alloy composition ensured the purity and castability of the molten steel. The molten steel proceeded to the next process with good castability. The chemical composition of the molten steel after LF treatment is shown in Table 4.

[0051] Table 4 Chemical composition of molten steel after LF treatment in Example 2

[0052]

[0053] The molten steel refined by LF is hoisted to the continuous casting platform for casting. During the casting process, the ladle is covered, the tundish is covered with a covering agent, the long nozzle is protected by argon, and an immersion nozzle is used to avoid secondary oxidation of the molten steel. Special protective slag for weathering steel is used during the casting process to obtain high phosphorus weathering steel slabs.

[0054] Example 3

[0055] like Figure 1 As shown, a process for smelting high-phosphorus weathering steel through decarburization and phosphorus retention, taking the production of uncoated weathering steel bridge structural steel 355GNH weathering steel slabs in a 100-ton converter at a certain factory as an example, includes the following steps:

[0056] After the molten iron from the blast furnace is transported to the steel plant via molten iron ladle, it is not subjected to pretreatment and desulfurization, thus avoiding the loss of vanadium slag and the loss of temperature drop during the process caused by slag removal during pretreatment.

[0057] 5 tons of scrap steel were charged into the decarburization converter, and 105 tons of molten iron were added. The mass fraction of each element in the molten iron is shown in Table 5, with the remainder being iron and unavoidable impurities.

[0058] Table 5. Mass fraction of each element in molten iron in Example 3

[0059]

[0060] Oxygen is blown into the converter through an oxygen lance for smelting. After blowing oxygen for 1 minute, a coolant is added. The coolant is made of high-phosphorus iron ore and the amount added is 50 kg / t of steel.

[0061] The oxygen supply pressure was controlled at 0.66 MPa. Due to the high cooling intensity and long cooling time of the molten pool, the carbon-oxygen reaction was inhibited, and the oxygen supply time was extended. After 6 minutes of blowing, the furnace flame was observed. When the carbon flame first appeared, the oxygen lance was immediately lifted, and the temperature was measured at 1385℃. After the semi-steel was produced, a sample was taken for testing, and the semi-steel had a carbon content of 2.92% and a phosphorus content of 0.075%. By decarburizing in a decarburizing converter, enhancing the cooling intensity, and extending the oxygen supply time, the carbon content in the molten iron was oxidized to 2.92%. At the same time, the phosphorus-enhancing effect of adding high-phosphorus iron ore was achieved, and the phosphorus content in the semi-steel reached 0.075%, maximizing the utilization of phosphorus resources in the molten iron.

[0062] The decarburized semi-steel is tapped into the molten iron ladle at a temperature of 1385℃. The ladle, filled with semi-steel, is then hoisted to the slag removal station for slag removal, and the slag layer thickness on the liquid surface is measured to be 45mm.

[0063] The semi-steel, after slag removal, is added to the AOD converter for decarburization and reduction. The addition amount is 103t. In the early stage of decarburization, top-lance oxygen blowing is used for decarburization, and the oxygen supply intensity is 1.5m. 3 ·min -1 For steel of / t, stop supplying oxygen to the top lance when the carbon content reaches 0.20%; for side-blown oxygen-argon mixture, the oxygen supply intensity is 0.5m. 3 •min -1 / t steel, argon gas supply intensity 0.5m 3 •min -1 / t steel; after the carbon content reaches 0.04%, it enters the reduction stage. Argon gas is introduced into the side tuyeres at the bottom of the furnace, and 2.4Kg / t steel of Ca-Si powder is added through the top hopper of the furnace for reduction.

[0064] The steel is treated with silicon-manganese alloy to produce Mn and Si, with ferrosilicon used to make up any shortfall. The Mn and Si content in the steel is increased to the lower limit in the AOD converter. Then, copper plates, ferrochrome, and ferronickel are added for microalloying. The slag basicity is controlled at 2.5. The composition of the molten steel after AOD treatment is: C: 0.12%, Si: 0.50%, Mn: 1.25%, P: 0.075%, S: 0.004%, Cu: 0.60%, Cr: 1.05%, Ni: 0.20%, with the balance being iron and unavoidable impurities. Due to the low carbon content of the semi-steel, smelting in the AOD converter significantly improves the decarburization and chromium retention conditions of the AOD furnace, thereby increasing the production efficiency of the AOD furnace.

[0065] After AOD converter smelting, the molten steel is purged with argon and its temperature is measured at the LF furnace treatment station. High-power submerged arc heating is then applied to the semi-molten steel, with 10 kg / t of refining slag and 8 kg / t of lime added. After heating for 15 minutes to reach 1533℃, rapid white slag formation and deep desulfurization are performed. The sulfur content at the outlet is 0.010%. Alloys are added to fine-tune the composition. Als in the steel is added through an aluminum feeder in the LF refining furnace. The acid-soluble aluminum content in the molten steel exiting the LF furnace is 0.040%. The deep desulfurization using white slag formation in the LF furnace, along with the heating and fine-tuning of the alloy composition, ensures the purity and castability of the molten steel. The molten steel then enters the slab continuous casting process with good castability. The chemical composition of the molten steel after LF treatment is shown in Table 6.

[0066] Table 6. Chemical composition of molten steel after LF treatment in Example 3.

[0067]

[0068] The molten steel refined by LF is hoisted to the continuous casting platform for casting. During the casting process, the ladle is covered, the tundish is covered with a covering agent, the long nozzle is protected by argon, and an immersion nozzle is used to avoid secondary oxidation of the molten steel. Special protective slag for weathering steel is used during the casting process to obtain high phosphorus weathering steel slabs.

Claims

1. A process for smelting high-phosphorus weathering steel through decarburization and phosphorus retention, characterized in that, The three-step decarbonization and phosphorus retention method using BOF+AOD+LF includes the following steps: S1. Decarburization converter smelting: Decarburization converter is used to decarburize molten iron from blast furnace to obtain semi-steel. The chemical composition of the semi-steel, by mass percentage, is: C 2.0~3.0%, Si≤0.10%, Mn≤0.10%, P 0.070~0.150%, S 0.02~0.06%, with the remainder being Fe and unavoidable impurities. No alkaline slagging agents are added to the decarburization converter, achieving efficient decarburization and phosphorus retention to obtain semi-steel. High-phosphorus iron ore is added during the smelting of the semi-steel to adjust its phosphorus content. S2, tapping half steel: tapping the half steel from S1 into the ladle, wherein the tapping temperature of the half steel is 1330~1420℃; then the ladle filled with half steel is hoisted to the slag removal station for slag removal, so that the slag layer thickness on the liquid surface inside the ladle is ≤50mm; S3, AOD converter smelting: After slag removal from S2, the molten iron ladle is placed in an AOD converter for deep decarburization and reduction. During the reduction stage, the slag basicity is controlled at 1.5-2.5, and aluminum particles are added for deep deoxidation. Then, according to the composition of the steel grade, one or more alloying elements, such as Cu, Ni, Cr, Nb, Si, Mn, or Ti, are added for alloying. The chemical composition of the alloyed steel, by mass percentage, is: C≤0.15%, Si 0.25-0.75%, Mn 0.20-1.50%, P 0.070-0.150%, S≤0.010%, Cu≤0.55%, Ni≤0.65%, Cr≤1.25%, with the remainder being Fe and unavoidable impurities. S4 and LF furnace refining: The alloyed molten steel from S3 is hoisted to the LF furnace for refining. 8–12 kg / t of refining slag and 6–10 kg / t of lime are added. The temperature is increased at a rate of 2–5 °C / min for 10–20 minutes, followed by rapid white slag desulfurization to ensure the sulfur content (S) of the molten steel leaving the furnace is ≤0.010%. Alloys are added to fine-tune the steel composition according to the chemical composition control requirements of the steel grade. Specifically, the Al content in the steel is adjusted in the LF furnace by feeding aluminum wire, controlling it to 0.020–0.040%. S5, Slab Continuous Casting: The molten steel refined from S4 is hoisted to the continuous casting platform for casting to obtain high-phosphorus weather-resistant steel slabs.

2. The process for smelting high-phosphorus weathering steel by decarburization and phosphorus retention according to claim 1, characterized in that, In S1, the blast furnace iron used in decarburization converter smelting contains 0.070% to 0.150% P.

3. The process for smelting high-phosphorus weathering steel by decarburization and phosphorus retention according to claim 2, characterized in that, In S1, high-phosphorus iron ore is added as a coolant during decarburization converter smelting. The chemical composition of the high-phosphorus iron ore, by mass percentage, is: P≥0.50%, with the remainder being Fe and unavoidable impurities.

4. A process for smelting high-phosphorus weathering steel by decarburization and phosphorus retention according to any one of claims 1-3, characterized in that, After oxygen is supplied to the decarburized converter for 1-3 minutes, add 10-100 kg / t of high-phosphorus iron ore.

5. The process for smelting high-phosphorus weathering steel by decarburization and phosphorus retention according to claim 4, characterized in that, The oxygen supply pressure of the decarburization converter is set at 0.65-0.80 MPa, which is 0.5-1 MPa lower than the normal smelting pressure of the converter, and the total oxygen supply time is 4-7 minutes.

6. A process for smelting high-phosphorus weathering steel by decarburization and phosphorus retention according to any one of claims 1-3 and 5, characterized in that, In S3, top-gun oxygen blowing is used for decarbonization in the early stage of the decarbonization phase, with an oxygen supply intensity of 1.0–1.5 m³ / s. 3 ·min -1 For steel of / t, stop supplying oxygen to the top lance when the carbon content reaches 0.20%–0.30%; for side-blown oxygen-argon mixture, the oxygen supply intensity is 0.5–0.7 m. 3 ·min -1 / t steel, argon gas supply intensity 0.5~0.7m 3 ·min -1 / t steel, oxygen-argon ratio is 1:1; after carbon content reaches 0.04%~0.06%, it enters the reduction stage. Argon gas is introduced into the side tuyeres at the bottom of the furnace, and 2.0~2.4Kg / t steel of Ca-Si powder is added through the top hopper of the furnace for reduction, and the composition of the molten steel is adjusted to the control target.

7. The process for smelting high-phosphorus weathering steel by decarburization and phosphorus retention according to claim 6, characterized in that, During the decarburization stage, the top-blown oxygen supply accounts for 60% of the total oxygen supply, and during the reduction stage, the argon gas supply intensity at the side tuyeres at the furnace bottom is 1.5–2.0 m³ / h. 3 ·min -1 / t steel.

8. A process for smelting high-phosphorus weathering steel by decarburization and phosphorus retention according to any one of claims 1-3, 5, and 7, characterized in that, In S3, the AOD converter smelting uses silicon-manganese alloy with Mn, and the insufficient Si is made up with ferrosilicon. The Mn and Si in the steel are added in the AOD converter according to the lower limit of the target composition of the steel grade. Then, in step S4, after entering the LF furnace, the Mn and Si content is finely adjusted to the middle limit required by the steel grade.

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