A preparation process for high casting speed of weathering steel thin slab

Abstract

The present invention discloses a preparation process for high drawing speed of weathering steel thin slab, belonging to the field of iron and steel production, which includes converter smelting, LF furnace refining, and then continuous casting to obtain thin slab. The composition of the weathering steel includes Cu, Cr, and Ti. In the converter smelting process, deoxidation is not carried out during the tapping process of the converter, and copper and chromium are added additionally. The mass ratio of the components of the molten steel after the converter is: C < 0.05%, Cr 0.2% - 0.25%, Cu 0.15% - 0.2%. In the LF furnace refining process, the following steps are completed in sequence: heating up to ≥ 1580°C; adding phosphorus, copper, and chromium; blowing argon for decarburization; adding ferrosilicon alloy to make the component Si 0.20 - 0.22%; adding aluminum wire for deoxidation; desulfurization, ferromanganese alloying, slag making; soft blowing under differential flow stirring; feeding calcium-ferrite cored wire, soft blowing for the second time after calcium treatment, closing argon gas, and adding carbon-free basic covering agent for heat preservation; in the continuous casting process, the drawing speed is increased to 4.9 m / min. Compared with the prior art, it has the characteristics of low cost and high casting drawing speed.

Description

Technical Field

[0001] The divisional application of the present invention "A low-cost and stable casting production method for weathering steel based on thin slabs" (2022101019175) relates to a steel production method, in particular, a high-speed drawing process for weathering steel thin slabs. Background Art

[0002] Weathering steel is mainly used in container manufacturing and has a large demand. Currently, weathering steel is produced on a fully headless thin slab production line, which has the advantages of low cost, thin specifications, and stable performance.

[0003] However, in actual production, ferrosilicon, ferromanganese, ferrochrome, ferrophosphorus, copper plate, and aluminum deoxidizers are added all at once during the converter discharge process. Lime is added to the refining furnace for slag adjustment, desulfurization, fine-tuning of alloy composition, and titanium-ferroalloy and calcium treatment. High carbon requirements are imposed on the converter discharge, with the final carbon content required to be less than 0.035%. The large alloy load and long smelting times result in high converter over-oxygen levels, high deoxidizer costs, and a high number of oxidizing inclusions. During the continuous casting process, mold level fluctuations and thermocouple fluctuations can affect casting speed stability, especially at speeds above 4.6 m / min, where fluctuations can exceed 1.5. Rapid casting speed reductions can result in the current rolled specification not meeting demand, necessitating a transition to thicker gauges, impacting product delivery times. Summary of the Invention

[0004] The technical task of the present invention is to address the deficiencies of the above-mentioned existing technologies and provide a high-speed drawing process for preparing weathering steel thin slabs. This method improves the smelting path of molten steel, adjusts the order of alloy addition, changes the method of alloy addition, etc., so as to remove inclusions in the steel and improve the purity of the molten steel. At the same time, it further reduces the production cost of weathering steel, stabilizes the crystallizer liquid level and thermocouple fluctuations, and increases the casting drawing speed, thereby achieving low cost, high quality and large output of weathering steel.

[0005] The technical solution for solving the technical problem is: a high-speed drawing process for preparing weathering steel thin slabs, comprising: converter smelting, LF furnace refining, and then continuous casting to obtain thin slabs, wherein the weathering steel comprises Cu, Cr, and Ti, and is characterized in that: in the converter smelting process, deoxidation is not performed during the converter discharge process, and copper and chromium are added; the mass ratio of the components of the molten steel after the converter is: C < 0.05%, Cr 0.2%-0.25%, and Cu 0.15%-0.2%; in the LF furnace refining process, the following are sequentially completed: heating to ≥1580°C; adding phosphorus, copper, and chromium; argon blowing for decarburization; adding ferrosilicon alloy to a Si content of 0.20-0.22%; adding aluminum wire for deoxidation; desulfurization, ferromanganese alloying, and slag formation; soft blowing under differential flow stirring; feeding calcium iron cored wire, soft blowing for a second time after calcium treatment, turning off argon, and adding a carbon-free alkaline covering agent for heat preservation; and increasing the drawing speed to 4.9 m / min during the continuous casting process.

[0006] Further, in the argon blowing and decarburization during the refining in the LF furnace, the stirring time is determined according to the carbon content upon arrival and the oxygen content in the steel. When the oxygen content in the steel is greater than 350 ppm, the stirring time does not exceed 5 min; for every 20 ppm decrease in oxygen, the stirring time is extended by 1 min, with a maximum not exceeding 10 min. The decarburization reaction is carried out in this way until the carbon content of the molten steel is reduced to less than 0.035%.

[0007] Further, in the phosphorus, copper, and chromium supplementation during the refining in the LF furnace, the supplementation is targeted according to P 0.06% - 0.07%, Cu 0.23% - 0.24%, and Cr 0.26 - 0.28%.

[0008] Further, in the desulfurization, ferromanganese alloying, and slag formation during the refining in the LF furnace, specifically, lime is added first, ferromanganese alloy is supplemented, the manganese content is finely adjusted to 0.35 - 0.45%, lime is supplemented after alloying, and aluminum pellets and calcium carbide are added by power supply to adjust the slag; after the desulfurization slag is made, argon is blown and stirred to ensure that the S content of the molten steel is < 0.005%; after the slag formation is completed, ferro-titanium cored wire is fed.

[0009] Further, the mass ratio of the components of the molten steel after the above refining is: C 0.035 - 0.045%, S ≤ 0.003%, P 0.075 - 0.095%, Cu 0.25 - 0.29%, Cr 0.30 - 0.35%, Si 0.30 - 0.50%, Mn 0.40 - 0.50%, Als 0.015 - 0.050%.

[0010] Compared with the prior art, the present invention has the following prominent beneficial effects:

[0011] 1. Reducing the carbon requirement for tapping from the converter, which can effectively reduce the consumption of iron and steel materials and the consumption of deoxidizers; protecting the refractories of the converter, improving the furnace campaign life, and reducing the cost of aluminum product deoxidizers by about 0.15 Kg / t;

[0012] 2. Adding ferrosilicon and ferromanganese separately to reduce the formation of silicomanganese salt inclusions and reduce the usage amount of deoxidizers during the LF refining process;

[0013] 3. Replacing ferro-titanium alloy with ferro-titanium cored wire can effectively improve the recovery rate of titanium element, ensure stable composition, and at the same time reduce the generation of iron oxide and titanium nitride compounds;

[0014] 4. Forming an annular flow field through differential flow control to improve the floating efficiency of inclusions and improve the purity of molten steel.

[0015] 5. Stabilizing the fluctuations of the liquid level and thermocouple during the continuous casting process of the endless rolling production line, and the casting speed can be increased to 4.9 m / min. Specific Embodiments

[0016] The present invention will be further described below in conjunction with specific embodiments.

[0017] The present invention relates to a high drawing speed preparation process for weathering steel thin slab, including: converter smelting, LF furnace refining, then continuous casting to obtain thin slab, and entering subsequent continuous rolling, cooling, and coiling process flows. And, the hot metal does not need pretreatment.

[0018] The following are specific production steps and parameters. The steel grade produced is weathering steel, and the composition contains components such as Cu, Cr, Ti, etc.

[0019] 1. Converter smelting

[0020] The existing standard requires that the carbon content in the converter tapping is ≤0.035%. In the present invention, the requirement for the carbon content in the converter tapping is reduced, and the carbon content in the argon station is less than 0.05% is sufficient. By reducing the requirement for the carbon content in the converter tapping, the consumption of iron and steel materials can be effectively reduced, the consumption of deoxidizers can be reduced, and the cost of aluminum product deoxidizers is reduced by about 0.15 Kg / t; at the same time, the converter refractories can be protected and the furnace campaign life can be improved.

[0021] The existing standard range of [O] in the converter end steel water is 600 ppm - 1000 ppm. In the present invention, overblowing of the converter is reduced, and the end point oxygen is reduced (300 - 400 ppm), which is beneficial to reducing the consumption of iron and steel materials and protecting the furnace lining refractories;

[0022] During the converter tapping process, no deoxidation is carried out. According to the target range of Cr 0.2% - 0.25% and Cu 0.15% - 0.2%, ferrochromium and copper plates are added as supplements;

[0023] The mass ratio of the components of the steel water after the converter is: C < 0.05%, Cr 0.2% - 0.25%, Cu 0.15% - 0.2%, and there are no control requirements for other components.

[0024] 2. LF furnace refining

[0025] During the LF furnace refining process, deoxidation, desulfurization, addition of alloy components, and removal of inclusions are carried out in the LF furnace; in the following steps, the raw material addition amount is based on matching 300 t of steel water volume.

[0026] (1) Heating and temperature rising

[0027] Oxygen determination and sampling are carried out when the LF furnace enters the station, and heating and temperature rising are carried out to raise the temperature of the steel water to ≥1580°C;

[0028] (2) Phosphorus, copper, and chromium supplementation

[0029] According to the arriving composition, add phosphorus by making up to the target of 0.06%-0.07%, and add ferrosilicon and copper plates according to the composition of Cu 0.23%-0.24% and Cr 0.26-0.28%; in the optimized plan, add ferrosilicon and copper plates according to Cu 0.23% and Cr 0.26.

[0030] (3) Argon blowing for decarburization

[0031] Adjust the bottom argon blowing of the ladle to the bypass valve, with the pipeline pressure greater than 1.6 bar, ensuring the overall tumbling of the molten steel surface, so as to promote the further reaction of residual oxygen and carbon in the steel to generate CO gas and reduce the carbon and oxygen content in the steel;

[0032] The stirring time depends on the arriving carbon content and the oxygen situation in the steel. When the oxygen in the steel is greater than 350 ppm, the stirring time does not exceed 5 min; for every 20 ppm decrease in oxygen, the stirring time is extended by 1 min, with a maximum of 10 min, and the decarburization reaction is carried out in this way until the carbon content of the molten steel is reduced to less than 0.035%.

[0033] (4) Adding ferrosilicon alloy

[0034] Add ferrosilicon alloy until the silicon content reaches 0.20-0.22% for silicon alloying; in the optimized plan, add according to the target of Si 0.20%.

[0035] (5) Adding aluminum wire for deoxidation

[0036] Then add 1000-1500 meters of aluminum wire for deoxidation;

[0037] (6) Desulfurization, alloying, slag making

[0038] After deoxidation, add the first batch of lime 2500-3500 Kg, and add low-carbon ferromanganese or medium-carbon ferromanganese alloy. If the molten steel design also contains Ni or other alloys, they are also added together with the ferromanganese alloy at this time, and the manganese content is finely adjusted to 0.35-0.45%; in the optimized plan, add according to the lower limit; add silicon and manganese alloys separately to reduce the formation of silicate inclusions and reduce the consumption of deoxidizers during LF refining;

[0039] After alloying, add lime ≤1200 Kg, power on and add aluminum pellets and calcium carbide to adjust the slag. Add 15-35 Kg of aluminum pellets and 20-30 Kg of calcium carbide each time. In the optimized plan, add 10-20 Kg of calcium carbide per minute;

[0040] After making the desulfurization slag, adjust the argon flow rate to 80 m 3 / h and stir for 5-8 min. Ensure that the S in the molten steel is less than 0.005%;

[0041] According to the slag condition, if white slag does not appear, add lime ≤500 Kg / time;

[0042] After slag making is completed, 350 - 450 meters of ferrotitanium cored wire is fed. The titanium content in the ferrotitanium cored wire is 70%, and the ratio of iron to powder is 170:396. Replacing ferrotitanium alloy with ferrotitanium cored wire can effectively improve the recovery rate of titanium element, ensure stable composition, and reduce the generation of iron oxide and titanium nitride compounds at the same time.

[0043] (7) Soft blowing

[0044] Differential flow stirring: A total of 6 minutes in two stages, 3 minutes for each stage. In the first stage, the argon gas of the A - side permeable core is opened to the bypass state, and the flow rate on the B - side is 50 - 80 m 3 / h. After 3 minutes, in the second stage, the argon gas of the B - side permeable core is opened to the bypass state, and the flow rate on the A - side is 50 - 80 m 3 / h. In this way, an annular flow field is formed to promote the floating and adsorption of inclusions. By controlling the differential flow to form an annular flow field, the floating efficiency of inclusions is improved, and the purity of molten steel is enhanced.

[0045] After differential flow control, adjust the soft blowing of argon for 8 - 15 minutes (the diameter of the argon flower exposed on the molten steel surface is 50 - 100 mm), feed 280 m of calcium - iron cored wire (Ca content > 97%), and perform the second soft blowing for 8 - 12 minutes after calcium treatment. The argon gas flow rate during soft blowing is 10 - 30 m 3 / h.

[0046] Turn off the argon gas, add a carbon - free basic covering agent for heat preservation, and the molten steel is sent to the continuous casting machine when leaving the station.

[0047] The mass ratio of the components of the molten steel after refining is: C 0.035 - 0.045%, S ≤ 0.003%, P 0.075 - 0.095%, Cu 0.25 - 0.29%, Cr 0.30 - 0.35%, Si 0.30 - 0.50%, Mn 0.40 - 0.50%, Als 0.015 - 0.050%.

[0048] 3. Continuous casting

[0049] The molten steel formed by LF furnace refining enters the continuous casting and rolling production line. During the continuous casting process, the liquid level and thermocouple fluctuation are < 1. Due to the high purity of the molten steel, thin slab billets with a specification of 1.0 - 2.5 mm can be obtained.

[0050] The thin slab billets go through rough rolling, finish rolling, laminar flow cooling, and coiling to obtain hot - rolled strip steel with different thicknesses.

[0051] In order to better compare the process of this application and the prior art, a comparative experiment was conducted.

[0052] The hot metal pretreatment and converter smelting methods of each example group and the control group are the same, and the difference lies in the LF furnace refining process.

[0053] In the converter smelting process: the converter overblows by 30%, no deoxidizer alloy is added during the tapping process of the converter, and the mass ratio of the components of the molten steel after the converter is controlled according to C < 0.05%, Cr 0.23%, Cu 0.18%, and there are no control requirements for other components.

[0054] The mass ratio of the components of the molten steel after refining in each example group and the control group is controlled according to C 0.038%, S 0.0025%, P 0.079%, Cu 0.26%, Cr 0.33%, Si 0.34%, Mn 0.45%, Als 0.025%.

[0055] The LF furnace refining process of each example group operates according to the parameter range disclosed in the above steps.

[0056] In the LF furnace refining process of the control group:

[0057] (1) Heating and temperature rising

[0058] Oxygen is determined and sampled when the LF furnace enters the station, heated and the temperature of the molten steel is raised to 1590°C;

[0059] (2) Argon blowing and decarburization

[0060] The oxygen content at arrival is 380 ppm, and the stirring time is 5 min; the carbon content after stirring is 0.034%;

[0061] (3) Deoxidation

[0062] 1500 meters of aluminum wire is added;

[0063] (4) Desulfurization, alloying, and slag making

[0064] After deoxidation, 2000 Kg of the first batch of lime is added (for a molten steel volume of 300 t), and according to the preset component control requirements, low-carbon ferromanganese, copper plates, low-carbon ferrochromium, and ferrosilicon are sequentially added. The power is supplied for 2 minutes, and the slag surface turns green. Then 400 Kg of lime is continuously added, and the power is supplied for 3 minutes until the slag surface turns white. Desulfurization stirring is carried out, and the argon is opened to 50 m 3 / h for stirring for 15 min, and the S in the steel is reduced to 0.006%. After desulfurization to [S] ≤ 0.003%, 20 - 30 kg of aluminum particles are added to the slag surface, stirred for 1 - 2 min, and then re-slagging is carried out before titanium alloying. The titanium alloying target is controlled according to the internal control at 0.025 - 0.045%.

[0065] (5) Soft blowing

[0066] The set flow rate of the 2 gas permeable cores of the ladle is 15 - 25 m 3 / h, with the same flow rate, ensuring that the argon flower diameter is the size of a basketball.

[0067] The comparison of the results of each group is shown in the following table

[0068] Usage amount of deoxidizer Recovery rate of titanium element Purity of molten steel Maximum stable casting speed Example 1 3.1 Kg / t 92％ Fluctuation 0.5 4.9 m / min Example 2 3.25 Kg / t 94.5％ Fluctuation 0.4 4.9 m / min Example 3 3.08 Kg / t 90.3％ Fluctuation 0.6 4.9 m / min Control group 3.53 Kg / t 72.3％ Fluctuation 1.8 4.5 m / min

[0069] As can be seen from the results of each group, using the method of the present invention can reduce the consumption of deoxidizer in the LF refining process, effectively improve the recovery rate of titanium element, improve the purity of molten steel by increasing the floating efficiency of inclusions, and the maximum stable casting speed can be increased to 4.9 m / min. When the casting speed of the control group exceeds 4.6 m / min, the fluctuation will reach more than 1.5. Therefore, the maximum stable casting speed can only reach 4.5 m / min, and when the continuous casting speed decreases rapidly, it will cause the current specifications of rolling not to meet the requirements, and it is necessary to transition to thicker specifications, affecting the product delivery time.

[0070] It should be noted that specific embodiments of the present invention have been described in detail. For those skilled in the art, various obvious changes made without departing from the spirit and scope of the present invention are within the protection scope of the present invention.

Claims

1. A preparation process for high casting speed of weathering steel thin slab, comprising: Converter smelting, LF furnace refining, and then continuous casting to obtain thin slab. The weathering steel composition includes Cu, Cr, Ti, and is characterized in that: In the converter smelting process, deoxidation is not carried out during the tapping process of the converter, and copper and chromium are added. The mass ratio of the composition of the molten steel after the converter is: C < 0.05%, Cr 0.2% - 0.25%, Cu 0.15% - 0.2%; there are no control requirements for other components; In the LF furnace refining process, the following are completed in sequence: heating up to ≥1580°C; adding phosphorus, copper, and chromium; blowing argon for decarburization; adding ferrosilicon alloy until the composition Si is 0.20 - 0.22%; adding aluminum wire for deoxidation; desulfurization, ferromanganese alloying, slag making; soft blowing under differential flow stirring; feeding calcium-ferrite cored wire, soft blowing for the second time after calcium treatment, closing argon, and adding carbon-free basic covering agent for heat preservation; among them: in the blowing argon decarburization of the LF furnace refining, the stirring time is determined according to the carbon content at arrival and the oxygen content in the steel. When the oxygen content in the steel is greater than 350 ppm, the stirring time does not exceed 5 min; for every 20 ppm decrease in oxygen, the stirring time is extended by 1 min, and the maximum does not exceed 10 min, and the decarburization reaction is carried out in this way until the carbon content of the molten steel is reduced to less than 0.035%; In the continuous casting process, the casting speed is increased to 4.9 m / min.

2. The process for preparing weathering steel thin slab with high casting speed according to claim 1, characterized in that: In the addition of phosphorus, copper, and chromium in the LF furnace refining, the addition is targeted according to P 0.06% - 0.07%, Cu 0.23% - 0.24%, Cr 0.26 - 0.28%.

3. The high drawing speed preparation process of weathering steel thin slab according to claim 1, characterized in that: In the desulfurization, ferromanganese alloying, and slag making in the LF furnace refining, specifically, first add lime, add ferromanganese alloy, fine-tune the manganese content to 0.35 - 0.45%, add lime after alloying, and send electricity to add aluminum particles and calcium carbide to adjust the slag; after making the desulfurization slag, blow argon and stir to ensure that the sulfur content of the molten steel S < 0.005%; after the slag making is completed, feed the ferrotitanium cored wire.