Method for producing ultra-low carbon steel

Abstract

The invention provides a method for producing ultra-low carbon steel. The method comprises a converter process, an LF refining process, an RH refining process and a continuous casting process. In the converter process, the slag amount of the converter is controlled; in the LF refining process, a carbonaceous foaming agent is added to foam the refining slag, and an aluminum-based modifier is added to deoxidize the slag; in the RH refining process, lime is added into the slag at the beginning of RH refining, and a magnesium material is added to adjust the slag at the end of RH refining; and in the continuous casting process, the amount of residual molten steel in a steel ladle during multi-furnace continuous casting is controlled. According to the method for producing the ultra-high carbon steel, through the technological means of strictly controlling the converter working procedure, the LF refining working procedure, the RH refining working procedure and the continuous casting working procedure, the oxidability of the slag can be effectively controlled, the cleanliness of the molten steel is improved, and the occurrence rate of inclusion defects of cold-rolled sheets is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for producing ultra-low carbon steel. Background Art

[0002] Ultra-low carbon steel with high cleanliness is used in the fields of automobiles, home appliances, etc. due to its excellent ultra-deep drawing performance. The top slag control effect is particularly critical to its quality improvement. If the oxygen potential of the top slag of the RH refining ladle is high, in the subsequent process, the top slag of the ladle will continue to transfer oxygen to the molten steel, resulting in a large amount of Al2O3 inclusions in the molten steel, which will deteriorate the cleanliness of the molten steel; in the continuous casting process, if too much high-oxidizing top slag is drawn into the molten steel and enters the tundish, it will inevitably increase the oxidizing property of the top slag of the tundish, aggravate the secondary oxidation of the molten steel, and cause more serious nozzle blockage during casting, seriously affecting the quality of the ingot and finished product, and reducing production efficiency.

[0003] At present, the main ultra-low carbon steel production process at home and abroad is the short process of converter-RH-continuous casting. However, due to the differences in equipment conditions and steelmaking process characteristics of each steel mill, in steel mills that use the long process of converter-LF-RH-continuous casting to produce ultra-low carbon steel, the contact time between the top slag and the molten steel is longer, the problem of excessive oxidation of the top slag is more prominent, and the cleanliness control of the molten steel is more difficult.

[0004] The Chinese patent with publication number CN110643779A discloses a method for controlling the production of ultra-low carbon steel top slag, which controls the top blowing time and bottom blowing gas supply intensity in the converter process, and controls the basicity and TFe content of the converter final slag; controls the insertion depth of the immersion tube, increases the gas flow, alloying process time and soft blowing time in the RH refining process; after sedation, reaches the continuous casting process through full-process protection casting, plug rod argon blowing and other measures; cancels the use of top slag modifiers, and achieves good control of the top slag oxidizability. However, when the converter endpoint control is unstable, the cancellation of the use of top slag modifiers cannot cope with various working conditions in actual production, resulting in large fluctuations in the control level of top slag oxidizability, and it is difficult to effectively improve the cleanliness of molten steel.

[0005] The Chinese patent with publication number CN111910040A discloses a method for stable control of the oxidizability of ultra-low carbon steel top slag, which prevents the transfer of oxygen in the steel to the top slag by modifying the top slag after the converter; in the RH oxygen blowing and heating process, oxygen blowing and aluminum addition are carried out simultaneously to prevent excessive oxygen blowing, resulting in excessive oxygen content in the steel; in the oxygen blowing and decarburization process, the oxygen blowing flow of the top gun is controlled to avoid a sharp increase in the oxygen content in the steel, resulting in the transfer of oxygen in the steel to the top slag; in the continuous casting process, the oxygen atmosphere and the liquid level of the tundish are controlled to avoid the contact between oxygen in the air and the top slag or the wall of the tundish; the invention significantly reduces the TFe content of the top slag of the RH inlet and RH outlet ladle, and the castability of the molten steel is significantly improved. However, although this method comprehensively considers the influence of oxygen in the top slag and oxygen in the steel on the oxidizability of the top slag, it needs to blow oxygen and add aluminum to heat the molten steel, which is bound to cause a significant increase in Al2O3 inclusions in the steel, thereby deteriorating the cleanliness of the molten steel, and does not consider the influence of the top slag composition on the adsorption capacity of inclusions in the steel.

[0006] The Chinese patent with publication number CN116287566A discloses a top slag modification process for ultra-low carbon steel, which is modified by adding pre-deoxidized carbon powder, lime, medium carbon ferromanganese and aluminum particles at the end of converter blowing, and then using the top slag to transfer oxygen to the molten steel during the RH decarburization process to achieve the second step of modification, and finally adding aluminum particles again after the RH treatment is completed to complete the third step of modification. The invention reasonably controls the oxidizability of the ladle top slag through staged modification, so that the oxidizability of the top slag can be utilized as a resource; however, the method also does not propose corresponding measures to control the oxidizability of the ladle top slag during the ladle casting process.

[0007] In view of the above problems, it is necessary to develop a method for controlling the top slag of ultra-low carbon steel produced by the converter-LF-RH-continuous casting process. Summary of the invention

[0008] The technical problem solved by the present invention is to provide a method for producing ultra-low carbon steel. The production method provided by the present application can effectively control the oxidizability of slag, improve the cleanliness of molten steel, and reduce the occurrence rate of inclusion defects.

[0009] In view of this, the present application provides a method for producing ultra-low carbon steel, comprising: a converter process, a LF refining process, a RH refining process and a continuous casting process;

[0010] In the converter process, controlling the amount of slag discharged from the converter;

[0011] In the LF refining process, a carbonaceous foaming agent is added to foam the refined slag, and an aluminum-based modifier is added to deoxidize the slag;

[0012] In the RH refining process, lime is added to the slag at the beginning of RH refining, and magnesium materials are added to adjust the slag at the end of RH refining;

[0013] In the continuous casting process, control the amount of molten steel remaining in the ladle during continuous casting of multiple furnaces.

[0014] Preferably, in the converter process, the means for controlling the amount of slag discharged from the converter is to use a slide plate to block the slag during steel tapping, and the average slag thickness of the slag discharged is less than 50 mm.

[0015] Preferably, in the LF refining process, the carbonaceous foaming agent includes one or more of SiC, calcium carbide and carbon powder;

[0016] And / or, the amount of the carbon foaming agent added is 1.5-2.5 kg / t steel;

[0017] And / or, the foaming time is greater than 10 min.

[0018] Preferably, in the LF refining process, the amount of the aluminum-based modifier added is calculated according to formula (I):

[0019]

[0020] Where: Q1 is the amount of aluminum-based modifier added, kg; Δw(FeO) is the FeO reduction content of the ladle top slag, %; A is the surface area of ​​the ladle top slag after LF refining, m 2 ; h is the thickness of the top slag of the ladle at the end of LF refining, m; ρ S is the density of ladle top slag, kg / m 3 ;M Al 、M FeO are the relative atomic masses of Al and FeO, kg / mol; w(Al) is the content of metal Al in the modifier, %;

[0021] The aluminum-based modifier includes one of metal Al+CaCO3, metal Al+CaO+Al2O3+SiO2, metal Al+CaO+CaF, metal Al+CaO and pure metal Al particles.

[0022] Preferably, in the RH refining process, the amount of lime added is determined based on the mass fraction ratio of CaO to Al2O3 in the slag being greater than 2.0.

[0023] Preferably, in the RH refining process, the amount of lime added is calculated according to formula (II):

[0024] Q2=A·h·ρ S ·[λ·w(Al2O3) LF -w(CaO) LF ] (Ⅱ);

[0025] Where: Q2 is the amount of lime added, kg; A is the surface area of ​​the top slag of the ladle at the end of LF refining, m 2; h is the thickness of the ladle top slag at the end of LF refining, m; ρ S is the density of ladle top slag, kg / m 3 ;λ is the ratio of slag w(CaO) / w(Al2O3) after adding lime to adjust the slag,λ>2.0;w(Al2O3) LF Al2O3 content in slag at the end of LF refining, %; w(CaO) LF is the CaO content in the slag after LF refining, %.

[0026] Preferably, in the RH refining process, the magnesia material includes MgO, and the magnesia material is added so that the MgO content in the slag is 10% to 15%.

[0027] Preferably, the amount of the magnesium material added is calculated according to formula (III):

[0028]

[0029] Where: Q3 is the amount of magnesium material added, kg; A is the surface area of ​​the ladle top slag after RH refining, m 2 ; h is the thickness of the ladle top slag at the end of RH refining, m; ρ S is the density of ladle top slag, kg / m 3 ; β is the target value of MgO content in slag after adding magnesia material, %; w(MgO) RH is the MgO content in the slag at the end of RH refining, %; α is the MgO content in the magnesia material, %.

[0030] Preferably, the remaining molten steel amount is calculated according to formula (IV):

[0031]

[0032] Where: W1 is the amount of remaining molten steel in casting, t; W total is the total mass of molten steel in the ladle, t; γ is the slag control coefficient, which is 5 to 10.

[0033] Preferably, in the continuous casting process, the remaining molten steel amount in the tundish during the casting process is controlled and calculated according to formula (V):

[0034]

[0035] Where: W2 is the amount of molten steel remaining in the tundish during continuous casting, t; W tundish is the maximum tonnage of molten steel cast in the tundish, t; η is the control coefficient of the remaining molten steel in the tundish, which is taken as 1.5~2.0.

[0036] The present application provides a method for producing ultra-low carbon steel, which comprises: a converter process, an LF refining process, an RH refining process and a continuous casting process; specifically, in the converter process, the amount of slag in the converter process is controlled, so that the amount of slag in the converter can be controlled at a lower level; in the LF refining process, a carbonaceous foaming agent is added to promote the foaming of the refined slag, improve the heating effect of LF refining, shorten the LF refining cycle, and inhibit the transfer of oxygen in the steel liquid to the slag, effectively controlling the oxidizability of the slag; and at the same time, an aluminum-based modifier is added to the furnace to improve the foaming effect of the LF refining process. The slag is deoxidized to reduce the oxidizability of the refined slag. In the RH refining process, lime is added to adjust the slag at the beginning of RH refining to reduce the FeO activity. Magnesium materials are added to adjust the slag at the end to thicken the slag and further reduce the FeO activity of the slag. The RH refining and slag reaction during the refining process are controlled. In the continuous casting process, the amount of molten steel remaining in the ladle during continuous casting of multiple furnaces is controlled to control the amount of slag under the ladle, reduce the oxidizability of the slag in the middle ladle, inhibit the secondary oxidation of the molten steel, reduce the nodule rate of the nozzle, and improve the cleanliness of the molten steel. Therefore, the method for producing ultra-high carbon steel provided by the present application can effectively control the oxidizability of the slag, improve the cleanliness of the molten steel, and reduce the incidence of cold rolling inclusion defects by strictly controlling the process means of each process of the converter process, the LF refining process, the RH refining process, and the continuous casting process. DETAILED DESCRIPTION

[0037] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0038] In view of the need to control the slag oxidation and molten steel cleanliness of ultra-low carbon steel in the prior art, the present application provides a method for producing ultra-low carbon steel, which controls the amount of slag discharged from the converter and uses a carbon foaming agent in the LF refining process to inhibit the transfer of oxygen in the molten steel to the slag, effectively controlling the slag oxidation. Lime is added to the slag at the beginning of the RH refining process, and magnesium materials are added to adjust the slag at the end of the RH refining process, which can effectively reduce the FeO activity of the slag and control the slag reaction during the RH refining and calming process. At the same time, during the continuous casting process, by controlling the amount of molten steel remaining in the ladle, the secondary oxidation of the molten steel can be inhibited, which is beneficial to improving the cleanliness of the molten steel. Therefore, the method for producing ultra-low carbon steel provided in the present application can achieve the control of top slag, effectively control the slag oxidation, improve the cleanliness of the molten steel, and thereby reduce the occurrence of inclusion defects in cold-rolled plates. Specifically, an embodiment of the present invention discloses a method for producing ultra-low carbon steel, including: a converter process, a LF refining process, an RH refining process, and a continuous casting process;

[0039] In the converter process, controlling the amount of slag discharged from the converter;

[0040] In the LF refining process, a carbonaceous foaming agent is added to foam the refined slag, and an aluminum-based modifier is added to deoxidize the slag;

[0041] In the RH refining process, lime is added to the slag at the beginning of RH refining, and magnesium materials are added to adjust the slag at the end of RH refining;

[0042] In the continuous casting process, control the amount of molten steel remaining in the ladle during continuous casting of multiple furnaces.

[0043] In the method for producing ultra-low carbon steel provided in the present application, the processes involved include: a converter process, a LF refining process, a RH refining process and a continuous casting process.

[0044] Before the converter process, raw material preparation, ironmaking, and molten iron pretreatment are performed according to the composition of the ultra-low carbon steel. The above steps are performed according to means well known to those skilled in the art, and there is no particular limitation in this application. In this application, the ultra-low carbon steel is an ultra-low carbon steel well known to those skilled in the art, and there is no particular limitation in this application. For example, the ultra-low carbon steel can be M3A35 series ultra-low carbon steel, M3A30 series ultra-low carbon steel, or other ultra-low carbon steel.

[0045] After the above treatment, the obtained molten steel is put into a converter. In the converter process, the amount of slag in the converter is controlled during the steel tapping process, specifically, a process method of using a slide plate to block the slag is used to improve the success rate of slag blocking, and the average slag thickness of the slag is controlled to be less than 50 mm, specifically, the average slag thickness can be controlled to be 40 mm or 30 mm. In addition, the converter process is carried out according to technical means well known to those skilled in the art, and this application has no special restrictions on this.

[0046] After the converter process, the obtained molten steel is subjected to LF refining. In this process, a carbonaceous foaming agent is used to promote the foaming of the refining slag, improve the LF heating effect, shorten the LF refining cycle, and inhibit the transfer of oxygen in the molten steel to the slag, which can effectively control the oxidizability of the slag; at the same time, an aluminum-based modifier is used to deoxidize the slag to reduce the oxidizability of the refining slag. The carbonaceous foaming agent includes one or more of SiC, calcium carbide and carbon powder; the amount of the carbonaceous foaming agent added is added according to the height of the slag after foaming being more than 2 times the thickness of the original slag layer, and the slag is allowed to foam continuously for more than 10 minutes; more specifically, the amount of the carbonaceous foaming agent added is 1.5-2.5kg / t steel, and more specifically, the amount of the carbonaceous foaming agent added is 1.6-2.0kg / t steel. The aluminum-based modifier includes metal Al+CaCO3, metal Al+CaO+Al2O3+SiO2, metal Al+CaO+CaF, metal Al+CaO, pure metal Al particles, etc. The amount of the aluminum-based modifier added is calculated according to formula (I):

[0047]

[0048] Where: Q1 is the amount of aluminum-based modifier added, kg; Δw(FeO) is the FeO reduction content of the ladle top slag, %; A is the surface area of ​​the ladle top slag after LF refining, m 2 ; h is the thickness of the ladle top slag at the end of LF refining, m; ρ S is the density of ladle top slag, kg / m 3 ;M Al 、M FeO are the relative atomic masses of Al and FeO, kg / mol respectively; w(Al) is the metal Al content of the modifier, %.

[0049] In addition, the present application has no particular limitation on other process means in the LF refining process, and the process may be carried out according to methods well known to those skilled in the art.

[0050] After LF refining, the molten steel after LF refining is subjected to RH refining. At the beginning of the RH refining process, excessive lime is added to the slag to adjust the slag to reduce the FeO activity; the amount of lime added is determined based on the control of the mass fraction ratio of CaO to Al2O3 in the slag to be above 2.0, that is, w(CaO) / w(Al2O3) in the slag>2.0; specifically, the amount of lime added is calculated according to formula (II):

[0051] Q2=A·h·ρ S ·[λ·w(Al2O3) LF -w(CaO) LF ] (Ⅱ);

[0052] Where: Q2 is the amount of lime added, kg; A is the surface area of ​​the top slag of the ladle at the end of LF refining, m 2 ; h is the thickness of the ladle top slag at the end of LF refining, m; ρ S is the density of ladle top slag, kg / m 3 ;λ is the ratio of slag w(CaO) / w(Al2O3) after adding lime to adjust the slag,λ>2.0;w(Al2O3) LF Al2O3 content in slag at the end of LF refining, %; w(CaO) LF is the CaO content in the slag after LF refining, %.

[0053] At the end of RH refining, a magnesia material is added to thicken the slag, so as not to reduce the FeO activity of the slag, and to control the slag adjustment reaction during the RH refining and calming process; the MgO content in the slag is controlled to be 10-15%, and the magnesia material includes MgO; specifically, the amount of the magnesia material added is calculated according to formula (III):

[0054]

[0055] Where: Q3 is the amount of magnesium material added, kg; A is the surface area of ​​the ladle top slag after RH refining, m 2 ; h is the thickness of the top slag of the ladle at the end of RH refining, m; ρ S is the density of ladle top slag, kg / m 3 ; β is the target value of MgO content in slag after adding magnesia material, %; w(MgO) RH is the MgO content in the slag at the end of RH refining, %; α is the MgO content in the magnesia material, %.

[0056] In addition, the present application has no particular limitation on other process means in the RH refining process, and the process may be carried out according to methods well known to those skilled in the art.

[0057] The present application finally performs a continuous casting process, further controls the amount of slag in the ladle to reduce the oxidizability of the slag in the middle ladle; specifically controls the amount of molten steel remaining in each ladle casting during multi-furnace continuous casting, and stabilizes the amount of molten steel remaining during the middle ladle casting, ensuring less slag; the calculation of the amount of molten steel remaining in the ladle is performed according to formula (IV):

[0058]

[0059] Where: W1 is the remaining molten steel in ladle casting, t; W total is the total mass of molten steel in the ladle, t; γ is the slag control coefficient, which is 5 to 10.

[0060] The calculation of the remaining molten steel volume during the tundish re-casting is performed according to formula (V):

[0061]

[0062] Where: W2 is the amount of molten steel remaining in the tundish during continuous casting, t; W tundish is the maximum tonnage of molten steel cast in the tundish, t; η is the control coefficient for the remaining molten steel in the tundish, which is taken as 1.5~2.0.

[0063] In addition, the present application has no special restrictions on other process means in the continuous casting and refining process, and the process is carried out according to methods well known to those skilled in the art.

[0064] The present invention provides a method for producing ultra-low carbon steel, comprising: a converter process, an LF refining process, an RH refining process and a continuous casting process; in each of the above processes, the amount of slag in the steel-making process of the converter process is controlled, and a carbon foaming agent is used in the LF refining process to promote the foaming of the refining slag, improve the LF heating effect, shorten the LF refining cycle, and at the same time, inhibit the transfer of oxygen in the molten steel to the slag, effectively control the oxidizability of the slag, and deoxidize the slag to reduce the oxidizability of the refining slag; at the beginning of the RH refining process, an excessive amount of lime is added to the slag to adjust the slag, and then a magnesium material is added to adjust the slag at the end of the RH refining to thicken the slag, which can effectively reduce the FeO activity of the slag, control the RH refining and sedation process steel slag reaction; during continuous casting, the amount of slag in the ladle is controlled to reduce the oxidizability of the slag in the middle ladle, inhibit the secondary oxidation of the molten steel, and is conducive to further improving the cleanliness of the molten steel. Therefore, the method for producing ultra-low carbon provided by the present application can effectively control the oxidizability of the slag, improve the purity of the molten steel, and reduce the incidence of inclusion defects in the cold-rolled plate.

[0065] In order to further understand the present invention, the method for producing ultra-low carbon steel provided by the present invention is described in detail below in conjunction with embodiments, and the protection scope of the present invention is not limited by the following embodiments.

[0066] Example 1

[0067] Take the production of M3A35 series ultra-low carbon steel with a titanium content of 0.08% and a carbon content of less than 20ppm using the converter-LF-RH-continuous casting process as an example, with a capacity of 200t converter

[0068] 1) After the converter smelting of ultra-low carbon steel is completed, a slide plate is used to block the slag during steel tapping, and the average slag thickness is controlled at 40mm; when the ladle reaches the LF refining process, a certain amount of corundum slag and other raw materials need to be added to make refined slag, and 300kg of calcium carbide foaming agent is added to the slag surface before electric heating begins;

[0069] 2) After adopting the new LF refining foaming agent operation process, it was measured that the height of the slag after foaming was more than 2.3 times of the original slag layer, the electric heating heating rate increased from the original 2.1℃ / min to 2.5℃ / min, the heating rate increased by about 19%, the heating time was shortened from the original 16min to 13min, and the LF process time was shortened from 28min to 25min;

[0070] According to the test, the FeO mass fraction in the LF incoming slag is 23%, and the average slag thickness after LF slag making is 80mm. Based on the ladle diameter of 3.7m, the surface area of ​​the ladle top slag is estimated to be about 11m 2 , ladle top slag density 3000kg / m 3 ; According to calculation, 200kg of metal Al content modifier with 35% is added at the end of LF to deoxidize the slag;

[0071] 3) The molten steel after LF refining is subjected to RH refining process. The slag composition is detected before RH enters the station. The mass fraction of FeO in the top slag is 13%, the mass fraction of CaO in the top slag is 30%, and the mass fraction of Al2O3 in the top slag is 18%. The parameters related to the top slag of the ladle adopt the values ​​in process 2); after calculation, 400kg of lime is added to the slag surface before the start of refining, and the w(CaO) / w(Al2O3) of the top slag entering the RH station reaches 2.5; after testing, the MgO content of the top slag of the ladle at the end of RH is 5%, the target value of MgO content is 10%, and the average thickness of the top slag of the ladle at the end of RH is 90mm; after calculation, 185kg of magnesia refractory powder (MgO content 90%) is added at the end of RH, and the MgO content of the top slag of the RH exiting the station is 10.1% after adding, and the FeO content of the top slag is 8% with the addition of the top slag modifier;

[0072] 4) After the RH refining process, it reaches the continuous casting process. According to the slag amount control formula, η=1.7 and γ=7 are taken respectively. The weight of molten steel during the 75-ton ladle re-pouring of the continuous casting furnace is controlled to be above 45 tons, and the remaining molten steel in the ladle is above 30 tons, which greatly reduces the possibility of slag rolling and ensures that the molten steel has a high cleanliness during ladle casting.

[0073] After the application of the above top slag control technology, the FeO content of the ladle top slag in the tundish casting process was reduced to 7%, the top slag w(CaO) / w(Al2O3) was reduced to 1.8, the TO content of the molten steel in the tundish was reduced to 16ppm, and the incidence of inclusion defects in cold-rolled plates was reduced to below 10%.

[0074] Example 2

[0075] Take the production of M3A30 series ultra-low carbon steel with a titanium content of 0.06% and a carbon content of less than 20ppm using the converter-LF-RH-continuous casting process as an example, with a capacity of 120t converter

[0076] 1) After the converter smelting of ultra-low carbon steel is completed, a slide plate is used to block the slag during steel tapping, and the average slag thickness is controlled at 30 mm; when the ladle reaches the LF refining process, a certain amount of corundum slag and other raw materials need to be added to make refined slag, and about 200 kg of calcium carbide foaming agent is added to the slag surface before electric heating begins;

[0077] 2) After adopting the new LF refining foaming agent operation process, it was measured that the height of the slag after foaming was more than 2.2 times of the original slag layer, the electric heating heating rate increased from the original 2.2℃ / min to 2.8℃ / min, the heating rate increased by about 27%, the heating time was shortened from the original 13min to 10min, and the LF process time was shortened from 23min to 20min;

[0078] According to the test, the FeO mass fraction in the LF incoming slag is 20%, and the average slag thickness after LF slag making is 65mm. Based on the ladle diameter of 3.0m, the surface area of ​​the ladle top slag is estimated to be about 7m 2 , ladle top slag density 3000kg / m 3 ; It is calculated that at the end of LF, 50kg of a modifier with a metal Al content of 40% is added to deoxidize the slag;

[0079] 3) The molten steel after LF refining is subjected to RH refining process, and the slag composition is detected at the RH station. The mass fraction of FeO in the top slag is 15%, the mass fraction of CaO in the top slag is 35%, and the mass fraction of Al2O3 in the top slag is 20%. The parameters related to the top slag of the ladle adopt the values ​​in process 2); after calculation, 100kg of lime is added to the slag surface before the start of refining, and the w(CaO) / w(Al2O3) of the top slag of the RH station reaches 2.1; after testing, the MgO content of the top slag of the RH ladle is 6% at the end of RH, the target value of MgO content is 15%, and the average thickness of the top slag of the RH ladle is 75mm at the end of RH; after calculation, 196kg of magnesia refractory powder (MgO content 85%) is added at the end of RH, and the MgO content of the top slag of the RH station is 14.8%, and the FeO content of the top slag is less than 10% with the addition of the top slag modifier;

[0080] 4) After the RH refining process, the continuous casting process is reached. According to the slag amount control formula, η=1.65 and γ=6 are taken respectively. The weight of molten steel during the continuous casting furnace 50-ton ladle re-pouring is controlled to be above 30 tons, and the remaining molten steel in the ladle is above 20 tons, which greatly reduces the possibility of slag rolling and ensures that the molten steel has a high cleanliness during ladle casting.

[0081] After the application of the above top slag control technology, the FeO content of the ladle top slag in the tundish casting process was reduced to 9%, the top slag w(CaO) / w(Al2O3) was reduced to 1.5, the TO content of the molten steel in the tundish was reduced to 20ppm, and the incidence of inclusion defects in cold-rolled plates was reduced to below 15%.

[0082] Comparative Example 1

[0083] Take the production of M3A35 series ultra-low carbon steel with a titanium content of 0.08% and a carbon content of less than 20ppm using the converter-LF-RH-continuous casting process as an example, with a capacity of 200t converter

[0084] 1) After the converter smelting of ultra-low carbon steel is completed, a slide plate is used to block the slag during steel tapping. The average thickness of the slag on the top of the ladle is 40 mm as measured at the argon blowing station. When the ladle reaches the LF refining process, a certain amount of corundum slag and other raw materials need to be added to make refined slag. After adding about 150 kg of calcium carbide foaming agent to the slag surface, electric heating begins;

[0085] 2) After adopting the LF refining foaming agent operation process, it was measured that the height of the slag after foaming was more than 1.2 times of the original slag layer, the electric heating heating rate was 2.1°C / min, the heating time was 16min, and the LF process time was 28min;

[0086] According to the test, the FeO mass fraction in the slag entering the LF station is 20%, and no deoxidation operation is performed on the slag at the end of LF;

[0087] 3) The molten steel after LF refining is subjected to RH refining process, and the slag composition is detected at the RH station, and the FeO mass fraction of the top slag is 21%; no lime is added at the beginning of RH refining, and the w(CaO) / w(Al2O3) of the top slag at the RH station is 3.0; no magnesium modifier is added at the end of RH refining, and the MgO content of the top slag at the RH station is 6%;

[0088] 4) When the continuous casting process is reached, the remaining steel in the ladle and the casting liquid level of the tundish are not controlled. Almost all the molten steel in the ladle has been cast. When the 75-ton tundish is replaced, the weight of the molten steel is less than 20 tons.

[0089] After testing, the FeO content of the ladle top slag during the tundish casting process was 19%, the top slag w(CaO) / w(Al2O3) was 3.5, the TO content of the molten steel in the tundish reached 30ppm, and the incidence of inclusion defects in cold-rolled plates was above 35%.

[0090] Comparative Example 2

[0091] Take the production of M3A30 series ultra-low carbon steel with a titanium content of 0.06% and a carbon content of less than 20ppm using the converter-LF-RH-continuous casting process as an example, with a capacity of 120t converter

[0092] 1) After the converter smelting of ultra-low carbon steel is completed, a slide plate is used to block the slag during steel tapping. The average thickness of the top slag of the ladle is 30 mm as measured at the argon blowing station. When the ladle reaches the LF refining process, a certain amount of corundum slag and other raw materials need to be added to make refined slag. After adding about 100 kg of calcium carbide foaming agent to the slag surface, electric heating begins;

[0093] 2) After adopting the LF refining foaming agent operation process, it was measured that the height of the slag after foaming was more than 1.1 times of the original slag layer, the electric heating heating rate was 2.2°C / min, the heating time was 13min, and the LF process time was 23min;

[0094] According to the test, the FeO mass fraction in the slag entering the LF station is 21%, and no deoxidation operation is performed on the slag at the end of LF;

[0095] 3) The molten steel after LF refining is subjected to RH refining process, and the slag composition is detected at the RH station, and the FeO mass fraction of the top slag is 23%; no lime is added at the beginning of RH refining, and the w(CaO) / w(Al2O3) of the top slag at the RH station is 3.0; no magnesium modifier is added at the end of RH refining, and the MgO content of the top slag at the RH station is 7%;

[0096] 4) After the RH refining process, the continuous casting process is reached. The remaining steel in the ladle and the casting liquid level of the tundish are not controlled. Almost all the molten steel in the ladle is cast. The weight of the molten steel is less than 10 tons when the 50-ton tundish is replaced.

[0097] After testing, the FeO content of the ladle top slag during the tundish casting process was 20%, the top slag w(CaO) / w(Al2O3) was 3.3, the TO content of the molten steel in the tundish reached 35ppm, and the incidence of inclusion defects in cold-rolled plates was above 40%.

[0098] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0099] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for producing ultra-low carbon steel, comprising: Converter process, LF refining process, RH refining process and continuous casting process; In the converter process, controlling the amount of slag discharged from the converter; In the LF refining process, a carbonaceous foaming agent is added to foam the refined slag, and an aluminum-based modifier is added to deoxidize the slag; In the RH refining process, lime is added to the slag at the beginning of RH refining, and magnesium materials are added to adjust the slag at the end of RH refining; In the continuous casting process, control the amount of molten steel remaining in the ladle during continuous casting of multiple furnaces.

2. The method according to claim 1, characterized in that: In the converter process, the means for controlling the amount of slag discharged from the converter is to use a slide plate to block the slag during steel tapping, and the average slag thickness of the slag discharged is less than 50 mm.

3. The method according to claim 1, characterized in that In the LF refining process, the carbonaceous foaming agent includes one or more of SiC, calcium carbide and carbon powder; And / or, the amount of the carbon foaming agent added is 1.5-2.5 kg / t steel; And / or, the foaming time is greater than 10 min.

4. The method according to claim 1, characterized in that: In the LF refining process, the amount of the aluminum-based modifier added is calculated according to formula (I): Where: Q1 is the amount of aluminum-based modifier added, kg; Δw(FeO) is the FeO reduction content of the ladle top slag, %; A is the surface area of ​​the ladle top slag after LF refining, m 2 ; h is the thickness of the ladle top slag at the end of LF refining, m; ρ S is the density of ladle top slag, kg / m 3 ;M Al 、M FeO are the relative atomic masses of Al and FeO, kg / mol; w(Al) is the content of metal Al in the modifier, %; The aluminum-based modifier includes one of metal Al+CaCO3, metal Al+CaO+Al2O3+SiO2, metal Al+CaO+CaF, metal Al+CaO and pure metal Al particles.

5. The method according to claim 1, characterized in that In the RH refining process, the amount of lime added is determined according to the mass fraction ratio of CaO to Al2O3 in the slag being greater than 2.

0.

6. The method according to claim 1 or 5, characterized in that: In the RH refining process, the amount of lime added is calculated according to formula (II): Q2=A·h·ρ S ·[λ·w(Al2O3) LF -w(CaO) LF ] (Ⅱ); Where: Q2 is the amount of lime added, kg; A is the surface area of ​​the top slag of the ladle at the end of LF refining, m 2 ; h is the thickness of the ladle top slag at the end of LF refining, m; ρ S is the density of ladle top slag, kg / m 3 ;λ is the ratio of slag w(CaO) / w(Al2O3) after adding lime to adjust the slag,λ>2.0;w(Al2O3) LF Al2O3 content in slag at the end of LF refining, %; w(CaO) LF is the CaO content in the slag after LF refining, %.

7. The method according to claim 1, characterized in that In the RH refining process, the magnesia material includes MgO, and the magnesia material is added so that the MgO content in the slag is 10% to 15%.

8. The method according to claim 1 or 7, characterized in that: The amount of magnesium material added is calculated according to formula (III): Where: Q3 is the amount of magnesium material added, kg; A is the surface area of ​​the ladle top slag after RH refining, m 2 ; h is the thickness of the ladle top slag at the end of RH refining, m; ρ S is the density of ladle top slag, kg / m 3 ; β is the target value of MgO content in slag after adding magnesia material, %; w(MgO) RH is the MgO content in the slag at the end of RH refining, %; α is the MgO content in the magnesia material, %.

9. The method according to claim 1, characterized in that: The remaining amount of molten steel is calculated according to formula (IV): Where: W1 is the amount of remaining molten steel in casting, t; W total is the total mass of molten steel in the ladle, t; γ is the slag control coefficient, which is 5 to 10.

10. The method according to claim 1, characterized in that In the continuous casting process, the remaining molten steel volume in the tundish during the casting process is controlled and calculated according to formula (V): Where: W2 is the amount of molten steel remaining in the tundish during continuous casting, t; W tundish is the maximum tonnage of molten steel cast in the tundish, t; η is the control coefficient of the remaining molten steel in the tundish, which is taken as 1.5~2.0.

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