Process for preparing a low-cost aluminum-conserving refining slag system

Abstract

The application discloses a low-cost aluminum-preserving refining slag system preparation process, which adopts bauxite and lime to perform refining and slagging operations, replaces a synthetic slag slagging process, does not need to adopt fluorite fluxing, is environment-friendly and effectively reduces production cost, effectively guarantees aluminum content and aluminum-oxygen balance stability in steel, and improves refining slag system stability while stabilizing refining slag system components and recycling utilization. The process can also stabilize aluminum content in steel, realizes rapid slagging in a refining process, reduces oxygen content in steel, and improves molten steel cleanliness.

Description

Technical Field

[0001] This invention relates to the field of steelmaking refining slag technology, and in particular to a low-cost aluminum-preserving refining slag preparation process. Background Technology

[0002] High aluminum loss, fluctuating aluminum content, and excessive inclusions are common problems in the production of aluminum-deoxidized steel. The main reason for these phenomena is the poor stability of the steel-slag relationship during the refining process, which prevents the maintenance of a stable balance between the steel and slag. As a result, the aluminum-oxygen balance is unstable, leading to high aluminum loss. Furthermore, this aluminum often reacts with oxygen to produce large-sized alumina inclusions that cannot be floated and removed in time, and the oxygen content in the steel cannot be reduced to the normal level in a timely manner.

[0003] To ensure the stability of the refining slag system during the refining process, the slag must form rapidly in the early stages of slag formation. Furthermore, for aluminum-deoxidized steel, the slag system must first form an aluminate slag system. A simple quicklime slag-forming process will inevitably result in a silicate slag system. During the further formation of the aluminate slag system, it will pass through the low-melting-point region of calcium oxide, causing an imbalance of aluminum and oxygen in the steel and a significant loss of aluminum. Synthetic slag or bauxite slag-forming must be used to avoid these problems.

[0004] This patent proposes a low-cost aluminum-preserving refining slag preparation process that uses bauxite and quicklime for refining and slag-making operations, replacing the synthetic slag-making process. It does not require the use of fluorite flux, is environmentally friendly, and effectively reduces production costs. While effectively ensuring the stability of aluminum content and aluminum-oxygen balance in steel, the refining slag system has stable composition and is recyclable, thus improving the stability of the refining slag system.

[0005] Reference 1: The production method of this slag system includes four steps: adding lime and aluminum granules during converter tapping, slag replenishment, argon blowing at the alloy fine-tuning station, and slag formation in the LF refining furnace. During the converter tapping process, pre-designed slag system raw materials are added to form refining and desulfurizing slag. Furthermore, the oxygen and sulfur content of the molten steel before LF furnace refining, as well as the FeO+MnO content in the top slag, are reduced through a combined top and bottom argon blowing system at the alloy fine-tuning station.

[0006] Reference 2 pertains to the field of converter slag washing technology. During converter tapping, the bottom blowing system of the ladle is opened. When one-third of the steel has been tapped, quicklime and bauxite are added. At the refining station, the slag and deoxidizer are adjusted according to different steel grade composition requirements, steel temperature, and slag conditions before heating and subsequent treatment. The advantages are shortened initial slag formation and slag melting time, reduced refining process costs, and improved steel purity.

[0007] Reference 3 provides a short-process method for recycling liquid refining slag from an LF furnace in a hot ladle. By reusing the newly generated slag from the first batch, the liquid refining slag is mixed with the molten steel to be refined in the LF furnace using an overhead crane. The mixed molten steel is then hoisted to the LF furnace for refining. This method can reduce the consumption of lime and fluorite, utilize the physical heat of the slag to achieve rapid slag formation, reduce power consumption, and lower costs by 5 yuan / t. Summary of the Invention

[0008] The purpose of this invention is to provide a low-cost aluminum-preserving refining slag preparation process that stabilizes the aluminum content in steel, enables rapid slag formation during the refining process, reduces the oxygen content in steel, and improves the cleanliness of molten steel.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] This invention discloses a low-cost process for preparing an aluminum-preserving refining slag system, the specific process steps of which are as follows:

[0011] Step 1: Production must be arranged so that both converters operate simultaneously. Both converters produce aluminum deoxidized steel. In principle, the steel grades may differ. Higher grade steel uses freshly made refining slag, while lower grade steel uses recycled refining slag. The recycling frequency shall not exceed 2 times. If both converters produce the same grade of steel, the refining slag shall not be recycled more than once.

[0012] Step 2: New refining slag preparation process: The final carbon content of the converter blowing process does not need to be guaranteed, but the tapping temperature must be ≥1610℃. Slag must be blocked during the converter tapping process. During the tapping process, bottom blowing argon gas should be activated, with an argon flow rate ≥300 NL / min. When the steel is about one-third tapped, add 2.5 kg / t - 4 kg / t of bauxite. When the steel is two-thirds tapped, add 2.5 kg / t - 4 kg / t of quicklime. After adding quicklime, add 0.5 kg / t - 3 kg / t of aluminum deoxidizer and other alloys required for the steel grade in sequence. Silicon-containing alloys must be added after the LF refining and slag-forming process is completed; after the LF is in place, add 2.5kg / t-4kg / t of quicklime and 0.5kg / t-1.5kg / t of calcium carbide, and start heating. After "white slag" is formed, add the silicon-containing alloy and continue heating to make the molten steel reach the target temperature and composition required by the steel grade; perform soft blowing or vacuum refining + soft blowing operation according to the steel grade requirements; if the steel grade requires vacuum refining, add 15-30kg of aluminum granules to the slag surface before vacuum refining; the molten steel that meets the requirements is hoisted to the ladle turret to complete the continuous casting process;

[0013] Step 3: Recycling refining slag: After the continuous casting is completed, the refining slag and residual steel in the ladle are hoisted to the tapping position at the back of the converter. After the converter tapping is completed, the ladle is moved to the hoisting position along with the ladle car, and the recycled refining slag is slowly poured into the molten steel to complete the recycling step.

[0014] Step 4: The molten steel using recycled refining slag must meet the following conditions: Carbon retention during the converter blowing process, tapping temperature ≥1560℃, and slag blocking during tapping; During the converter tapping process, add 0.5kg / t-3kg / t of aluminum deoxidizer and other alloys required for the steel grade in sequence. Silicon alloys must be added after the LF refining slag-making process; After receiving the recycled refining slag, hoist it to the LF refining furnace. After the LF is in place, add 0.5kg / t-2.5kg / t of quicklime and 0.5kg / t-1.5kg / t of calcium carbide, and start heating. During heating, add silicon alloys to ensure the molten steel reaches the target temperature and composition required for the steel grade; Perform soft blowing or vacuum refining + soft blowing operations according to the steel grade requirements; If the steel grade requires vacuum refining, add 15-30kg of aluminum granules to the slag surface before vacuum refining; The molten steel meeting the requirements is hoisted to the ladle turret to complete the continuous casting process.

[0015] Step 5: All steel grades using recycled refining slag are ordinary steel. The molten steel using recycled refining slag must meet the following conditions: tapping temperature ≥1560℃; 0.5kg / t-3kg / t of aluminum deoxidizer and other alloys required by the steel grade are added during the tapping process; after receiving the recycled refining slag, it is hoisted to the LF refining furnace. After the LF is in place, 0.5kg / t-2.5kg / t of quicklime is added and the furnace is heated until the molten steel reaches the target temperature and composition required by the steel grade; soft blowing operation is performed according to the steel grade requirements; the molten steel that meets the requirements is hoisted to the ladle turret to complete the continuous casting process.

[0016] Furthermore, the main components of the final refining slag are: CaO: 45-55%wt, Al2O3: 25-30%wt, MgO≤10%wt, SiO2≤8%wt, FeO+MnO≤1.0%wt, with the balance being impurities.

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

[0018] This invention uses bauxite and quicklime for refining slag formation, replacing the synthetic slag formation process. It eliminates the need for fluorite flux, making it environmentally friendly and effectively reducing production costs. While ensuring the stability of aluminum content and aluminum-oxygen balance in steel, the refining slag system is stable and recyclable, thus improving the stability of the refining slag system.

[0019] Compared to using synthetic slag for steel production, this patent reduces the cost per ton of steel by 20 yuan / ton, and recycling once can reduce production costs by 3.0 yuan / ton. Avoiding the use of fluorite reduces production costs by 3.2 yuan / ton. The cumulative cost reduction is 26.2 yuan / ton. When this patent covers an annual production of 20,000 tons of relevant steel grades, the annual cost reduction is 524,000 yuan. Detailed Implementation

[0020] A low-cost process for preparing aluminum-preserving refining slag system includes the following steps:

[0021] Step 1: New Refining Slag Forming Process: The final stage of converter blowing does not require guaranteed carbon content, but the tapping temperature must be ≥1610℃. Slag must be blocked during converter tapping. During converter tapping, bottom blowing argon gas is activated, with an argon flow rate ≥300 NL / min. When approximately one-third of the steel has been tapped, add 2.5 kg / t-4 kg / t of bauxite. When two-thirds of the steel has been tapped, add 2.5 kg / t-4 kg / t of quicklime. After adding quicklime, add 0.5 kg / t-3 kg / t of aluminum deoxidizer and other alloys required for the steel grade in sequence. Silicon-containing alloys must be added after the LF refining slag forming process is completed. After the LF is in place, add 2.5 kg / t-4 kg / t of quicklime and 0.5 kg / t-1.5 kg / t of calcium carbide, and begin heating. After forming "white slag," add silicon-containing alloys and continue heating until the molten steel reaches the target temperature and composition required for the steel grade. Perform soft blowing or vacuum refining + soft blowing operations according to the steel grade requirements. If the steel grade requires vacuum refining, add 15-30 kg of aluminum granules to the slag surface before vacuum refining. Molten steel meeting the requirements is then hoisted to the ladle turret to complete the continuous casting process.

[0022] Step 2: Recycling refining slag: After the ladle completes continuous casting, the refining slag and remaining steel in the ladle are hoisted to the tapping position at the back of the converter. After the converter tapping is completed, the ladle is moved to the hoisting position along with the ladle car, and the recycled refining slag is slowly poured into the molten steel to complete the recycling step.

[0023] Step 3: The molten steel using recycled refining slag must meet the following conditions: Carbon retention during converter blowing, tapping temperature ≥1560℃, and slag blocking during converter tapping; during converter tapping, add 0.5kg / t-3kg / t of aluminum deoxidizer and other alloys required for the steel grade in sequence. Silicon-containing alloys must be added after the LF refining slag-making process. Upon receiving the recycled refining slag, it is hoisted to the LF refining furnace. After the LF is in place, add 0.5kg / t-2.5kg / t of quicklime and 0.5kg / t-1.5kg / t of calcium carbide, and begin heating. During heating, add silicon-containing alloys to bring the molten steel to the target temperature and composition required for the steel grade. Perform soft blowing or vacuum refining + soft blowing operations according to the steel grade requirements. If vacuum refining is required, add 15-30kg of aluminum granules to the slag surface before vacuum refining. The compliant molten steel is hoisted to the ladle turret to complete the continuous casting process.

[0024] Step 4: The steel grades using recycled refining slag are all common steels. The molten steel using recycled refining slag must meet the following conditions: tapping temperature ≥ 1560℃; 0.5kg / t-3kg / t of aluminum deoxidizer and other alloys required for the steel grade are added during tapping. After receiving the recycled refining slag, it is hoisted to the LF refining furnace. After the LF is in place, 0.5kg / t-2.5kg / t of quicklime is added and the furnace is heated until the molten steel reaches the target temperature and composition required for the steel grade. Soft blowing is then performed according to the steel grade requirements. The compliant molten steel is hoisted to the ladle turret to complete the continuous casting process.

[0025] Table 1 shows the slag consumption per ton of steel under conventional production processes and when using the production process of this patent.

[0026] Table 1. Consumption of ton steel slag under different processes

[0027]

[0028] Compared to using synthetic slag for steel production, the implementation of this invention reduces the cost per ton of steel by 20 yuan / ton, and recycling once can reduce the production cost by 3.0 yuan / ton. Avoiding the use of fluorite reduces the production cost by 3.2 yuan / ton. The cumulative reduction in production cost is 26.2 yuan / ton. When this patent is implemented to cover the annual production of 20,000 tons of relevant steel grades, the annual cost reduction is 524,000 yuan.

[0029] 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 process for the production of a low cost aluminium preserving refining slag system, characterised in that: The specific process steps are as follows: First step: production arrangement must be two converters simultaneously producing, two converters produce steel grade are aluminum deoxidized steel grade, in principle, steel grade level exists difference, high grade steel uses new refining slag, low grade steel uses recycled refining slag, recycling times is not more than 2 times;If two converters produce same grade steel, refining slag recycling use times is not more than 1 time; Second step: new refining slag slagging process: converter blowing end does not need to ensure carbon content, must ensure tapping temperature is greater than or equal to 1610 DEG C, converter tapping process must stop slag tapping;Converter tapping process, open bottom blowing argon, argon amount is greater than or equal to 300 NL / min;Tapping close to one-third, first add bauxite 2.5kg / t-4kg / t, tapping two-thirds add lime 2.5kg / t-4kg / t;Add lime, add aluminum deoxidizer 0.5kg / t-3kg / t and other alloys required by steel grade in order, silicon containing alloy must be added after LF refining slagging process is completed;LF is in place, add lime 2.5kg / t-4kg / t, carbide 0.5kg / t-1.5kg / t, and start heating, form "white slag” after adding silicon containing alloy and continue heating, so that the molten steel reaches the target temperature and composition required by the steel grade;According to the requirements of the steel grade, soft blowing or vacuum refining + soft blowing operation is carried out;If the steel grade requires vacuum refining, add 15-30kg aluminum particles to the slag surface before vacuum refining;The molten steel meeting the requirements is hoisted to the tundish rotary table to complete the continuous casting process; Third step: recycling refining slag: after the tundish completes continuous casting, the refining slag and remaining steel in the tundish are hoisted to the converter rear tapping position with the tundish, after the converter completes tapping, the tundish is put into the hoisting position with the tundish car, the recycled refining slag is slowly poured into the molten steel, and the recycling step is completed; Fourth step: the molten steel using once recycled refining slag needs to meet the following conditions: converter blowing end carbon preservation tapping, tapping temperature is greater than or equal to 1560 DEG C, converter tapping process must stop slag tapping;Converter tapping process, add aluminum deoxidizer 0.5kg / t-3kg / t and other alloys required by steel grade in order, silicon containing alloy must be added after LF refining slagging process is completed;After receiving the recycled refining slag, hoist to LF refining furnace, add lime 0.5kg / t-2.5kg / t, carbide 0.5kg / t-1.5kg / t after LF is in place, and start heating, add silicon containing alloy during heating process, so that the molten steel reaches the target temperature and composition required by the steel grade;According to steel grade requirements, soft blowing or vacuum refining + soft blowing operation is carried out;If the steel grade requires the vacuum refining, add 15-30kg aluminum particles to the slag surface before vacuum refining;Molten steel meeting the requirements is hoisted to the tundish rotary table to complete the continuous cast process; Fifth step: the steel grade using twice recycled refining slag is all common material, the molten steel using twice recycled refining slag needs to meet the following conditions: tapping temperature is greater than or equal to 1560 DEG C;Add aluminum deoxidizer 0.5kg / t-3kg / t and other alloys required by the steel grade during tapping process. After receiving the recycled refining slag, it is hoisted to the LF refining furnace. After the LF is in place, 0.5kg / t-2.5kg / t of quicklime is added and heated until the molten steel reaches the target temperature and composition required by the steel grade. Soft blowing operation is carried out according to the steel grade requirements. Molten steel that meets the requirements is hoisted to the ladle turret to complete the continuous casting process.

2. The low cost stay-alumina refining slag series preparation process according to claim 1, characterized in that: The main components of the final refining slag are: CaO: 45-55%wt, Al2O3: 25-30%wt, MgO≤10%wt, SiO2≤8%wt, FeO+MnO≤1.0%wt, with the balance being impurities.

Images