Method for reducing generation of inclusions in cold-rolled low-carbon steel

Abstract

The invention discloses a method for reducing inclusions generated by cold-rolled low-carbon steel, and belongs to the technical field of low-carbon steel preparation. The production process of the cold-rolled low-carbon steel comprises the steps of molten iron pretreatment, converter smelting, RH refining and continuous casting. By controlling the S content in the molten iron after molten iron pretreatment, adopting the converter smelting and RH refining processes and adopting an alloy containing a silicon element to replace an aluminum alloy for deoxidation, generation of aluminum oxide inclusions is reduced, and the surface quality of a cold rolled material is improved. The production of inclusions in the steel can be reduced, and the quality of the cold-rolled low-carbon steel product is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-carbon steel preparation, and particularly relates to a method for reducing the generation of inclusions in cold-rolled low-carbon steel. Background Art

[0002] Cold-rolled low-carbon steel is widely used in the automotive and household appliance industries, and has relatively strict requirements for the surface quality of the rolled plate. There are many reasons affecting the surface quality of the rolled plate, but large-sized inclusions, especially those located in the surface layer of the continuous casting billet, are important reasons for causing surface defects in cold-rolled plates. Non-metallic inclusions in steel are important factors affecting the cleanliness of molten steel and the quality of steel products. For low-carbon aluminum-killed steel, a large number of clustered Al2O3 inclusions will be formed after aluminum deoxidation. Such inclusions will directly affect the pouring effect of molten steel and the mechanical properties of steel products.

[0003] Cold-rolled low-carbon steel has the characteristics of high oxygen content at the tapping of the converter, short refining treatment time, and high casting machine drawing speed. A high oxygen content at the tapping of the converter will increase the amount of inclusions generated after deoxidation. A short refining treatment time results in insufficient floating of the generated inclusions. A high casting machine drawing speed is likely to cause large fluctuations in the liquid level and result in slag entrainment. Chinese invention patent CN109487039A discloses a method for controlling inclusions in ultra-low-carbon steel based on a straight-barrel type vacuum refining device. The ladle is transported to the straight-barrel type vacuum refining station, and the ladle is lifted. The immersion tube is inserted 50 mm below the molten steel surface, and the argon blowing nozzles on the same semi-circular circumference as the eccentric bottom blowing nozzle on the ladle wall of the immersion tube are blown with strong argon, and the argon blowing nozzles on the opposite side are blown with weak argon. The immersion tube is inserted 200 mm below the molten steel surface, and the eccentric bottom blowing argon of the ladle is turned on. The immersion tube is inserted 400 - 500 mm below the molten steel surface, and it is quickly pumped to the ultimate vacuum degree. The argon blowing flow rate is finely adjusted until the top slag is pushed to the weak blowing side of the immersion tube wall to the minimum area. After decarburization treatment, a molten steel sample is taken for oxygen determination, and then the molten steel is deoxidized and the CaO / Al2O3 in the top slag system is controlled to be 1.2 - 2.0. After breaking the vacuum, the ladle is taken out. By denaturing the Al2O3 inclusions generated by deep deoxidation into calcium aluminate inclusions with low melting points, the amount of Al2O3 inclusions in the continuous casting molten steel is reduced, thereby reducing the amount of Al2O3 inclusions adhered to the nozzle wall during the process of pouring the molten steel through the tundish nozzle into the mold, and avoiding the occurrence of nozzle clogging. However, this method requires major modifications to existing equipment and has extremely high operating requirements, and is not suitable for industrial mass production. Therefore, researching and developing a method for reducing the generation of inclusions in cold-rolled low-carbon steel at low cost, easy to operate, and environmentally friendly based on existing equipment is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for reducing the generation of inclusions in cold-rolled low-carbon steel. The present invention can reduce the generation of inclusions in steel, reduce the usage amount of aluminum alloy in production, meet the requirements of green and low-carbon manufacturing, and improve the product quality of cold-rolled low-carbon steel.

[0005] The object of the present invention is achieved in the following manner:

[0006] The present invention provides a method for reducing the generation of inclusions in cold-rolled low-carbon steel. The production process of cold-rolled low-carbon steel is: hot metal pretreatment → converter smelting → RH refining → continuous casting;

[0007] (1) [S] in the hot metal ≤ 0.005% after hot metal pretreatment;

[0008] (2) The carbon content at the end of converter smelting is controlled at 0.04% - 0.10%, the converter end temperature is controlled at 1650 - 1750 °C. After the blowing is completed, no alloying operation is carried out, and the steel is directly tapped. 1 - 5 kg / t of quicklime is added after tapping;

[0009] (3) Lift the ladle to the RH refining position, determine the oxygen content after entering the station to obtain [O] 进站 (ppm), and carry out oxygen blowing decarburization operation according to the oxygen value entering the station, the vacuum degree ≤ 1 kPa, and the treatment time ≥ 5 min;

[0010] (4) After the decarburization of the molten steel is completed, determine the oxygen content of the molten steel to obtain [O] end (ppm). After determining the oxygen content, add ferrosilicon alloy to calm the molten steel according to the following formula: the addition amount of ferrosilicon (kg) = (the upper limit of the silicon component target ÷ 2) × the weight of the molten steel (t) × 1000 ÷ the silicon content of the alloy;

[0011] (5) Calculate the "remaining oxygen value of the molten steel after silicon deoxidation": The remaining oxygen value of the molten steel is calculated according to the following formula: the remaining oxygen value of the molten steel = [O] 终点 (ppm) - the addition amount of ferrosilicon (kg) × (32 / 28) ÷ (the weight of the molten steel (t) × 1000) × 1000000 × α, where α = 30% - 40%;

[0012] (6) When the "remaining oxygen value of the molten steel after silicon deoxidation" > 100, the addition amount of aluminum alloy (kg) = the remaining oxygen value of the molten steel after silicon deoxidation (ppm) × (the weight of the molten steel (t) ÷ (650 - 720)) + (the target aluminum content (%) × the weight of the molten steel (t) × 1000 ÷ the aluminum content of the alloy ÷ the yield); when the "remaining oxygen value of the molten steel after silicon deoxidation" ≤ 100, the addition amount of aluminum alloy (kg) = 100 × (the weight of the molten steel (t) ÷ (650 - 720)) + (the target aluminum content (%) × the weight of the molten steel (t) × 1000 ÷ the aluminum content of the alloy ÷ the yield);

[0013] (7) After the composition of the molten steel is uniform, break the vacuum and remove it.

[0014] Based on the above technical solution, further, the chemical elements and weight percentages of the cold-rolled low-carbon steel are as follows: C ≤ 0.080%, Si ≤ 0.15%, Mn: 0.10% - 0.50%, P ≤ 0.030%, S ≤ 0.030%, Al ≤ 0.10%, and the balance is iron and inevitable impurities.

[0015] Based on the above technical solution, further, the chemical elements and weight percentages of the cold-rolled low-carbon steel are as follows: C: 0.0001% - 0.020%, Si ≤ 0.12%, Mn: 0.10% - 0.50%, P ≤ 0.010%, S ≤ 0.008%, Al ≤ 0.030%, and the balance is iron and inevitable impurities.

[0016] Based on the above technical solution, further, [S] in the hot metal after hot metal pretreatment in step (1) ≤ 0.001%.

[0017] Based on the above technical solution, further, the converter end temperature in step (2) is controlled at 1680 - 1700 °C, the ladle hanging temperature is controlled at 1630 - 1670 °C, and 1 - 3 kg / t of steel quicklime is added after tapping;

[0018] Based on the above technical solution, further, the oxygen blowing amount in step (3) is calculated according to the following formula: Oxygen blowing amount (Nm 3 ) = ([C] initial (ppm) + 250 - [O] 进站 (ppm)) × [steel weight (t) ÷ (850 - 920)].

[0019] Based on the above technical solution, further, the vacuum degree in step (3) is controlled at 0.1 - 1 kPa, and the treatment time is 5 - 20 min.

[0020] Based on the above technical solution, further, the silicon content in the ferrosilicon alloy in step (4) is 50 - 90%.

[0021] Based on the above technical solution, further, after the ferrosilicon alloy is added and circulated for 2 - 10 min in step (6), aluminum alloy is added, and the aluminum content in the aluminum alloy is 50 - 100%.

[0022] The beneficial effects of the present invention compared with the prior art are as follows:

[0023] 1. The present invention uses an alloy containing silicon elements to replace aluminum alloy for deoxidation, reducing the generation of alumina inclusions and improving the surface quality of cold-rolled materials.

[0024] 2. The method of the present invention reduces the usage amount of aluminum alloy, reduces production costs, and reduces carbon emissions. Specific embodiments

[0025] The present invention will be described in detail below in conjunction with embodiments. However, the implementation manners of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, without creative efforts, obtaining other similar embodiments all fall within the protection scope of the present invention.

[0026] Example 1

[0027] Taking a 200t converter as an example, [C]: 0.010%, upper limit of [Si]: 0.030%, [Mn]: 0.20%, [P]: 0.010%, [S]: 0.008%, [Al]: 0.030%, and the balance is Fe and inevitable impurities. The production process flow is hot metal pretreatment → converter smelting → RH refining → continuous casting; it includes the following steps:

[0028] (1) Hot metal pretreatment, [S] in the treated hot metal: 0.001%;

[0029] (2) Converter smelting, the converter end temperature is 1680°C, the converter smelting end carbon content is 0.082%, no alloying operation is carried out after the blowing is completed, and the steel is directly tapped. The ladle hanging temperature is 1640°C, and 400 kg of quicklime is added after tapping;

[0030] (3) The steel ladle is hoisted to the RH refining position. After entering the station, the oxygen content [O] 进站 (ppm): 281 ppm. According to the incoming oxygen value, oxygen blowing decarburization operation is carried out. According to the oxygen blowing amount (Nm 3 ) = ([C] initial (ppm) + 250 - [O] 进站 (ppm)) × [steel weight (t) ÷ 885] is calculated, and the oxygen blowing amount is 178 Nm 3 ; the lowest vacuum degree of the vacuum treatment is 0.1 kPa, the vacuum degree < 1 kPa, and the time is 7 min;

[0031] (4) After the steel water decarburization is completed, the steel water is oxygen-determined. The oxygen-determination result [O] 终点 (ppm): 255 ppm. Ferrosilicon is added to calm the steel water. The ferrosilicon addition amount = (upper limit of the silicon component target ÷ 2) × steel water weight (t) × 1000 ÷ alloy silicon content. The ferrosilicon addition amount (kg) = 0.015% × 200 × 1000 ÷ 75% = 40 kg;

[0032] (5) Judge the "remaining oxygen value of the molten steel after silicon deoxidation": According to [O] 终点 (ppm) - ferrosilicon addition amount × (32 ÷ 28) ÷ (steel water weight (t) × 1000) × 1000000 × α, α = 35%, calculate: 255 - 40 × (32 / 28) ÷ 200 ÷ 1000 × 1000000 × 35% = 175 > 100;

[0033] (6) After adding ferrosilicon for 3 minutes in the cycle, add aluminum alloy to calm the molten steel. "The remaining oxygen value in the molten steel after silicon deoxidation" > 100. The addition amount of aluminum alloy (kg) = the remaining oxygen value in the molten steel after silicon deoxidation × (molten steel weight (t) ÷ 685) + (target aluminum content (%) × molten steel weight (t) × 1000 ÷ alloy aluminum content ÷ recovery rate); The addition amount of aluminum alloy (kg) = 175 × (200 ÷ 685) + (0.030% × 200 × 1000 ÷ 100% ÷ 100%) = 111 kg;

[0034] (7) After 5 minutes of cycling, break the vacuum and remove.

[0035] If completely using aluminum deoxidation, 148 kg of aluminum is required, while in this embodiment, the addition amount of aluminum is reduced by 37 kg, and the weight of alumina inclusions generated is reduced by 71 kg.

[0036] Example 2

[0037] Taking a 200 t converter as an example, [C]: 0.010%, [Si] upper limit: 0.030%, [Mn]: 0.20%, [P]: 0.010%, [S]: 0.008%, [Al]: 0.030%, and the balance is Fe and inevitable impurities. The production process flow is hot metal pretreatment → converter smelting → RH refining → continuous casting; it includes the following steps:

[0038] (1) Hot metal pretreatment, [S] in the treated hot metal: 0.001%;

[0039] (2) The converter end temperature is 1690 °C, the converter smelting end carbon content is 0.046%, no alloying operation is carried out after blowing, directly tapping, the hanging ladle temperature is 1650 °C, and 400 kg of quicklime is added after tapping;

[0040] (3) Hang the molten steel ladle at the RH refining position. After entering the station, determine the oxygen [O] 进站 (ppm): 421 ppm. Carry out oxygen blowing decarburization operation according to the inlet oxygen value. According to the oxygen blowing amount (Nm 3 ) = ([C] initial (ppm) + 250 - [O] 进站 (ppm)) × [molten steel amount (t) ÷ 885] to calculate, the oxygen blowing amount is 65 Nm 3 ; The lowest vacuum degree for vacuum treatment is 0.1 kPa, and the time when the vacuum degree < 1 kPa is 7 minutes;

[0041] (4) After the molten steel decarburization is completed, determine the oxygen of the molten steel. The oxygen determination result [O] 终点(ppm): 173 ppm. Add ferrosilicon to calm the molten steel. The addition amount of ferrosilicon = (upper limit of target silicon composition ÷ 2) × weight of molten steel (t) × 1000 ÷ silicon content in the alloy. The addition amount of ferrosilicon (kg) = 0.015% × 200 × 1000 ÷ 75% = 40 kg;

[0042] (5) Judge the "remaining oxygen value of molten steel after silicon deoxidation": According to [O] 终点 (ppm) - addition amount of ferrosilicon × (32 / 28) ÷ (weight of molten steel (t) × 1000) × 1000000 × α, α = 35%. Calculate: 173 - 40 × 32 ÷ 28 ÷ 200 ÷ 1000 × 1000000 × 35% = 93 < 100;

[0043] (6) After 3 minutes of ferrosilicon addition cycle, add aluminum alloy to calm the molten steel. "Remaining oxygen value of molten steel after silicon deoxidation" < 100. The addition amount of aluminum alloy (kg) = 100 × (weight of molten steel (t) ÷ 685) + (target aluminum composition (%) × weight of molten steel (t) × 1000 ÷ aluminum content in the alloy ÷ recovery rate). The addition amount of aluminum alloy (kg) = 100 × (200 ÷ 685) + (0.030% × 200 × 1000 ÷ 100% ÷ 100%) = 89 kg;

[0044] (7) After 5 minutes of cycle, break the vacuum and remove.

[0045] If completely using aluminum for deoxidation, 122 kg of aluminum is needed, while in this example, the addition amount of aluminum is reduced by 33 kg, and the weight of alumina inclusions generated is reduced by 63 kg.

[0046] Example 3

[0047] Taking a 200 t converter as an example, [C]: 0.0002%, [Si] upper limit: 0.12%, [Mn]: 0.40%, [P]: 0.010%, S]: 0.008%, [Al]: 0.030%, and the balance is Fe and unavoidable impurities. The production process flow is hot metal pretreatment → converter smelting → RH refining → continuous casting; including the following steps:

[0048] (1) Hot metal pretreatment, [S] in the treated hot metal: 0.001%;

[0049] (2) The converter end temperature is 1700 °C, the carbon content at the end of converter smelting is 0.065%, no alloying operation is carried out after blowing, directly tapping, the ladle hanging temperature is 1660 °C, and 400 kg of quicklime is added after tapping;

[0050] (3) Hang the molten steel ladle at the RH refining position. After entering the station, determine the oxygen [O] 进站 (ppm): 550 ppm. Carry out oxygen blowing and decarburization operation according to the inlet oxygen value. According to the oxygen blowing amount (Nm3 ) = ([C] initial (ppm) + 250 - [O] 进站 (ppm)) × [steel weight (t) ÷ 885], oxygen blowing volume 79 Nm 3 ; The lowest vacuum degree for vacuum treatment is 0.1 kPa, the vacuum degree < 1 kPa, and the time is 10 min;

[0051] (4) After the decarburization of the molten steel is completed, the oxygen in the molten steel is determined, and the oxygen determination result [O] 终点 (ppm): 370 ppm. Ferrosilicon is added to calm the molten steel. The addition amount of ferrosilicon = (upper limit of the target silicon component ÷ 2) × molten steel weight (t) × 1000 ÷ silicon content in the alloy. The addition amount of ferrosilicon (kg) = 0.06% × 200 × 1000 ÷ 75% = 160 kg;

[0052] (5) Judge the "remaining oxygen value of the molten steel after silicon deoxidation": According to [O] 终点 (ppm) - addition amount of ferrosilicon × (32 / 28) ÷ (molten steel weight (t) × 1000) × 1000000 × α, α = 35%, calculate: (370 - 160 × 32 ÷ 28 ÷ 200 ÷ 1000 × 1000000 × 35%) = 50 < 100;

[0053] (6) After 3 minutes of the ferrosilicon addition cycle, aluminum alloy is added to calm the molten steel. The "remaining oxygen value of the molten steel after silicon deoxidation" < 100. The addition amount of aluminum alloy (kg) = 100 × (molten steel weight (t) ÷ 685) + (target aluminum component (%) × molten steel weight (t) × 1000 ÷ aluminum content in the alloy ÷ recovery rate). The addition amount of aluminum alloy (kg) == 100 × (200 ÷ 685) + (0.030% × 200 × 1000 ÷ 100% ÷ 100%) = 89 kg;

[0054] (7) After 5 minutes of cycling, break the vacuum and remove.

[0055] If aluminum deoxidation is completely adopted, 329 kg of aluminum needs to be used. In this embodiment, the addition amount of aluminum is reduced by 240 kg, and the weight of alumina inclusions generated is reduced by 461 kg.

[0056] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; the technical solutions recorded in the foregoing embodiments are modified, or some or all of the technical features are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for reducing the generation of inclusions in cold-rolled low-carbon steel, characterized in that, The production process of cold-rolled low-carbon steel is: hot metal pretreatment → converter smelting → RH refining → continuous casting; (1) [S] in the hot metal after hot metal pretreatment ≤ 0.005%; (2) The carbon content at the end of converter smelting is controlled at 0.04% - 0.10%, the converter end temperature is controlled at 1650 - 1750 °C. After the blowing is completed, alloying operation is not carried out, and the steel is directly tapped. After tapping, 1 - 5 kg / t of steel quicklime is added; (3) Lift the ladle to the RH refining position, measure the oxygen content after entering the station to obtain [O] 进站 (ppm), perform oxygen blowing decarburization operation according to the incoming oxygen value, the vacuum degree ≤ 1 kPa, and the treatment time ≥ 5 min; (4) After the decarburization of the molten steel is completed, the oxygen content of the molten steel is measured to obtain [O] 终点 (ppm). After the oxygen measurement, ferrosilicon alloy is added to the molten steel for calming according to the following formula. The addition amount of ferrosilicon (kg) = (upper limit of the target silicon component ÷ 2) × molten steel weight (t) × 1000 ÷ silicon content of the alloy; (5) Calculate the "remaining oxygen value of molten steel after silicon deoxidation": The remaining oxygen value of molten steel is calculated according to the following formula: Remaining oxygen value of molten steel = [O] 终点 (ppm) - Amount of ferrosilicon added (kg) × (32 / 28) ÷ (Weight of molten steel (t) × 1000) × 1000000 × α, where α = 30% - 40%; (6) When the "remaining oxygen value of the molten steel after silicon deoxidation" > 100, the addition amount of aluminum alloy (kg) = the remaining oxygen value of the molten steel after silicon deoxidation (ppm) × (molten steel weight (t) ÷ (650 - 720)) + (target component aluminum (%) × molten steel weight (t) × 1000 ÷ alloy aluminum content ÷ recovery rate); when the "remaining oxygen value of the molten steel after silicon deoxidation" ≤ 100, the addition amount of aluminum alloy (kg) = 100 × (molten steel weight (t) ÷ (650 - 720)) + (target component aluminum (%) × molten steel weight (t) × 1000 ÷ alloy aluminum content ÷ recovery rate); (7) After the molten steel composition is uniform, it is evacuated and removed.

2. The method according to claim 1, characterized in that The chemical elements and weight percentages of the described cold-rolled low-carbon steel are: C ≤ 0.080%, Si ≤ 0.15%, Mn: 0.10% - 0.50%, P ≤ 0.030%, S ≤ 0.030%, Al ≤ 0.10%, and the balance is iron and inevitable impurities.

3. The method according to claim 1, characterized in that, In step (1), [S] in the hot metal after hot metal pretreatment ≤ 0.001%.

4. The method according to claim 1, characterized in that In step (2), the converter end temperature is controlled at 1680 - 1700 °C, the ladle hanging temperature is controlled at 1630 - 1670 °C, and 1 - 3 kg / t of steel quicklime is added after tapping.

5. The method according to claim 1, characterized in that, In step (3), the oxygen blowing amount is calculated according to the following formula: Oxygen blowing amount (Nm 3 ) = ([C]initial (ppm) + 250 - [O] 进站 (ppm)) × [Steel amount (t) ÷ (850 - 920)].

6. The method according to claim 1, characterized in that In step (3), the vacuum degree is controlled at 0.1 - 1 kPa, and the treatment time is 5 - 20 min.

7. The method according to claim 1, wherein In step (4), the silicon content in the ferrosilicon alloy is 50 - 90%.

8. The method according to claim 1, characterized in that, In step (6), the aluminum alloy is added after the ferrosilicon alloy is added and circulated for 2 - 10 min. The aluminum content in the aluminum alloy is 50 - 100%.