A production process of ultra-low carbon steel

Abstract

The present application relates to the technical field of metallurgy, in particular to a production process of ultra-low carbon steel. The production process comprises converter smelting, LF refining, RH refining and continuous casting. In the process, oxygen is controlled in the whole process of converter + LF + RH, and a carbon additive is used to adjust the slag, part of the slag additive is added after the converter and in the refining process to adjust the CaO / Al2O3 ratio and (FeO) content of the ladle slag, so as to reduce the oxidizability of the ladle slag. On the basis of ensuring that the molten steel is not carbonized, the Al2O3 content in the molten steel is effectively reduced by replacing part of the Al deoxidization by carbon deoxidization, the cleanliness of the molten steel is further improved, and the castability of the ultra-low carbon IF steel in the continuous casting is improved, and the quality of the ultra-low carbon steel is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a production process for ultra-low carbon steel. Background Technology

[0002] Ultra-low carbon steel (IF steel) is a type of steel with extremely low carbon content, typically not exceeding 0.03%. It is widely used in industries such as automobile manufacturing and beverage can manufacturing. To achieve good deep-drawing performance, high-quality ultra-low carbon steel requires extremely high control over elements such as C, S, and N, making production very difficult. Domestic market demand is growing rapidly. With the continuous development of the domestic automobile market, steel companies are constantly improving their automotive steel production technology, especially the smelting technology for automotive IF steel, which has made significant progress in recent years, with the RH ladle refining process playing a crucial role.

[0003] The conventional smelting process for ultra-low carbon steel is roughly as follows: hot metal converter smelting → LF (ladle refining furnace) refining → RH refining (vacuum refining) → continuous casting. To avoid over-oxidation of the molten steel, under conventional smelting processes, the target C ≤ 0.0015% must be achieved after RH vacuum decarburization. After natural decarburization in the RH vacuum furnace, the residual oxygen content in the molten steel is typically 250-400 ppm. This residual oxygen requires further Al removal, which will generate Al2O3 inclusions, causing obvious contamination of the molten steel. Summary of the Invention

[0004] In view of this, the present invention provides a production process for ultra-low carbon steel, which can effectively reduce the oxidizability of ladle slag, reduce Al2O3 inclusions in steel, and improve the quality of ultra-low carbon steel.

[0005] This invention provides a production process for ultra-low carbon steel, comprising the following steps:

[0006] (A) Converter smelting:

[0007] Molten iron is smelted in a converter, and after reaching the converter's endpoint, the steel is tapped into a ladle.

[0008] in,

[0009] The oxygen control and slag conditioning processes during the converter smelting are as follows:

[0010] If the oxygen content of the small platform is >500ppm, then add a carbon raiser, the amount of which is = (fixed oxygen value - 500ppm) × 0.1;

[0011] If the oxygen content of the small platform is ≤500ppm, no carbon raiser is added;

[0012] The endpoint of the converter is: tapping temperature 1630~1650℃, molten steel [C] ≤0.06%;

[0013] (B)LF Refining:

[0014] The molten steel obtained in step (A) is sent into the LF refining furnace and heated for LF refining. After the temperature of the molten steel meets the requirements for leaving the station, argon is stopped and a high-alumina slag conditioner is added. Then, argon is gently blown into the molten steel and it leaves the station.

[0015] in,

[0016] The amount of high-alumina slag conditioner added is determined based on the oxygen content, and the relationship is shown in equations (1) to (2):

[0017] When the oxygen activity at the outlet is ≥500ppm, the amount of high-alumina slag conditioner added is: (oxygen activity at the outlet - 550ppm) × 0.1kg / t steel × steel volume (1);

[0018] When the oxygen activity at the outlet is <550ppm, the amount of high-alumina slag conditioner added is 200kg (Equation 2).

[0019] In equations (1) and (2):

[0020] The oxygen activity at the outlet is the oxygen content in the ladle, expressed in ppm.

[0021] The amount of molten steel referred to is the amount of molten steel entering the LF refining furnace, in tons (t).

[0022] (C)RH refining:

[0023] The RH furnace is pre-vacuumed. The molten steel obtained in step (B) is sent into the RH furnace for oxygen control treatment, deoxidation and alloying, cyclic vacuum degassing, bottom argon blowing in the ladle after refining, and then high-alumina slag conditioner is added before it leaves the station.

[0024] in,

[0025] The oxygen control treatment system is selected from the following (1) to (2):

[0026] (1) If the oxygen content at the RH inlet is high, a carburizing agent shall be added upon entry; the amount of carburizing agent added shall be determined based on the molten steel [C] and molten steel [O], as shown in the table below:

[0027]

[0028] The unit for the amount of carburizing agent added is kg / t steel;

[0029] (2) If the carbon content of the RH entering the station is high, oxygen blowing shall be performed; the amount of oxygen blown shall be determined according to the carbon content of the molten steel [C] and the oxygen content of the molten steel [O], as shown in the table below:

[0030]

[0031] The unit of oxygen blowing volume is m. 3 ;

[0032] (D) Continuous casting:

[0033] The molten steel from step (C) is continuously cast to obtain ultra-low carbon steel billets.

[0034] Preferably, in step (A), during the converter smelting process, argon is blown throughout the bottom blowing of the converter; wherein, the gas supply intensity of the bottom blowing is preferably 0.005 to 0.006 Nm. 3 / (min·t).

[0035] Preferably, in step (A), the converter endpoint is: tapping temperature 1630-1650℃, molten steel [C] ≤ 0.06%;

[0036] When the molten steel [C] ≤ 0.04%, a carbon raiser is added during the tapping process to make 0.04% < molten steel [C] ≤ 0.06%.

[0037] Preferably, in step (A):

[0038] The molten iron is first pretreated and then smelted in a converter.

[0039] The pretreatment includes vanadium extraction and desulfurization.

[0040] Before tapping, thicken the slag and use a sliding plate to block the slag during tapping. The slag layer thickness in the ladle is ≤80mm, and the clearance is 250~550mm.

[0041] During the tapping process, quicklime is added to the ladle at a rate of 1.0–5.0 kg / t of steel.

[0042] Preferably, in step (B), the molten steel obtained in step (A) is fed into the LF refining furnace and a carburizing agent is added;

[0043] The amount of the carbon raiser added is 0.1 to 0.5 kg / t steel.

[0044] Preferably, in step (B):

[0045] The heating method is submerged arc heating;

[0046] During the heating process, active lime and slag-reducing agent are added; wherein, the active lime is added in 2 to 3 batches, with each batch containing 0.5 to 2.0 kg / t of steel; the slag-reducing agent is an environmentally friendly slag-reducing agent; the slag-reducing agent is added in 1 to 2 batches, with each batch containing 0.5 to 1.5 kg / t of steel;

[0047] The required temperature for molten steel leaving the station is 1570–1600℃.

[0048] Preferably, the chemical composition of the high-alumina slag conditioner, by mass percentage, includes:

[0049] Al: 10%–40%;

[0050] CaO: 15%–25%;

[0051] SiO2: ≤10%;

[0052] MgO: ≤10%;

[0053] Al2O3: 15%–35%;

[0054] H2O: ≤1.5%;

[0055] P: ≤0.050%;

[0056] S: ≤0.15%;

[0057] The particle size of the high-alumina slag conditioner is 20-40 mm.

[0058] Preferably, in step (C), the pre-vacuuming process includes: introducing an inert gas and evacuating to a vacuum level ≤2.0 mbar within 6 to 7 minutes, and evacuating to a vacuum level ≤1.0 mbar within 9 to 10 minutes.

[0059] Preferably, in step (C):

[0060] In the aforementioned system (1), after adding the carbon raiser, the gas flow rate is increased as follows: 1500 NL / min from 0 to 6 min, 1800 NL / min from 6 min to the end of deoxidation and alloying, and 1200 NL / min after the end of deoxidation and alloying.

[0061] In the aforementioned system (2), the oxygen blowing system is as follows: oxygen blowing is performed 3-4 minutes after the start of the inlet treatment. During the oxygen blowing process, the pressure is not controlled, the nozzle position is 4.0m, and the oxygen flow rate is 1600Nm. 3 / h; stop oxygen blowing after reaching the target oxygen blowing volume; increase the gas flow rate during the process as follows: 1200NL / min from the start of treatment to the end of oxygen blowing, 1800NL / min from the end of oxygen blowing to the end of deoxidation and alloying, and 1200NL / min after the end of deoxidation and alloying.

[0062] The endpoint of the oxygen control treatment is: a[O] is controlled at 250-300 ppm;

[0063] The amount of the high-alumina slag conditioner added is 0.05 to 2.5 kg / t steel.

[0064] Preferably, in step (D), during the continuous casting process, when the ladle pours molten steel into the tundish, the long nozzle of the ladle is protected by a sealing ring and argon blowing throughout the pouring process, and the weight of the molten steel in the tundish is maintained above 20t during the pouring process; the casting speed of the continuous casting is ≤1.3m / min.

[0065] To address the high oxidizing properties of IF steel ladle slag, this invention provides a production process for ultra-low carbon steel, comprising: converter smelting, LF refining, RH refining, and continuous casting, as detailed above. The key aspect is the use of a combined process of "converter + LF + RH full-process oxygen control and slag adjustment with carbon-enhancing agents." By adding slag additives after the converter furnace and during refining, the CaO / Al2O3 ratio and (FeO) content of the ladle slag are adjusted to reduce its oxidizing properties. While ensuring no carbon increase in the molten steel, carbon deoxidation replaces some Al deoxidation, effectively reducing the Al2O3 content in the molten steel, further improving its cleanliness, and consequently enhancing the castability of ultra-low carbon IF steel in continuous casting, significantly improving the quality of ultra-low carbon steel. Detailed Implementation

[0066] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0067] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0068] The term “and / or” as used herein includes any and all combinations of one or more of the related listed items.

[0069] In this document, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0070] In this article, when referring to units for data ranges, if the unit is only followed by the right endpoint, it means that the units for the left and right endpoints are the same. For example, 1630~1650℃ means that the units for the left endpoint "1630" and the right endpoint "1650" are both in℃.

[0071] This invention provides a production process for ultra-low carbon steel, comprising the following steps:

[0072] (A) Converter smelting:

[0073] Molten iron is smelted in a converter, and after reaching the converter's endpoint, the steel is tapped into a ladle.

[0074] in,

[0075] The oxygen control and slag conditioning processes during the converter smelting are as follows:

[0076] If the oxygen content of the small platform is >500ppm, then add a carbon raiser, the amount of which is = (fixed oxygen value - 500ppm) × 0.1;

[0077] If the oxygen content of the small platform is ≤500ppm, no carbon raiser is added;

[0078] The endpoint of the converter is: tapping temperature 1630~1650℃, molten steel [C] ≤0.06%;

[0079] (B)LF Refining:

[0080] The molten steel obtained in step (A) is sent into the LF refining furnace and heated for LF refining. After the temperature of the molten steel meets the requirements for leaving the station, argon is stopped and a high-alumina slag conditioner is added. Then, argon is gently blown into the molten steel and it leaves the station.

[0081] in,

[0082] The amount of high-alumina slag conditioner added is determined based on the oxygen content, and the relationship is shown in equations (1) to (2):

[0083] When the oxygen activity at the outlet is ≥500ppm, the amount of high-alumina slag conditioner added is: (oxygen activity at the outlet - 550ppm) × 0.1kg / t steel × steel volume (1);

[0084] When the oxygen activity at the outlet is <550ppm, the amount of high-alumina slag conditioner added is 200kg (Equation 2).

[0085] In equations (1) and (2):

[0086] The oxygen activity at the outlet is the oxygen content in the ladle, expressed in ppm.

[0087] The amount of molten steel referred to is the amount of molten steel entering the LF refining furnace, in tons (t).

[0088] (C)RH refining:

[0089] The RH furnace is pre-vacuumed. The molten steel obtained in step (B) is sent into the RH furnace for oxygen control treatment, deoxidation and alloying, cyclic vacuum degassing, bottom argon blowing in the ladle after refining, and then high-alumina slag conditioner is added before it leaves the station.

[0090] in,

[0091] The oxygen control treatment system is selected from the following (1) to (2):

[0092] (1) If the oxygen content at the RH inlet is high, a carburizing agent shall be added upon entry; the amount of carburizing agent added shall be determined based on the molten steel [C] and molten steel [O], as shown in the table below:

[0093]

[0094] The unit for the amount of carburizing agent added is kg / t steel;

[0095] (2) If the carbon content of the RH entering the station is high, oxygen blowing shall be performed; the amount of oxygen blown shall be determined according to the carbon content of the molten steel [C] and the oxygen content of the molten steel [O], as shown in the table below:

[0096]

[0097] The unit of oxygen blowing volume is m. 3 ;

[0098] (D) Continuous casting:

[0099] The molten steel from step (C) is continuously cast to obtain ultra-low carbon steel billets.

[0100] Regarding step (A) :

[0101] (A) Converter smelting: Molten iron is smelted in a converter, and after reaching the converter endpoint, the steel is tapped into a ladle.

[0102] In this invention, preferably, the molten iron undergoes pretreatment before being smelted in a converter. Pretreatment is typically required before smelting, and this invention does not impose any particular limitation on the pretreatment; any conventional pretreatment in the art is acceptable. Specifically, the pretreatment preferably includes vanadium extraction and desulfurization. The specific operations for vanadium extraction and desulfurization are not particularly limited; any conventional process in the art is acceptable. After pretreatment, the molten iron is fed into the converter for smelting.

[0103] In this invention, during the converter smelting process, argon is blown throughout the bottom blowing of the converter. The preferred gas supply intensity for the bottom blowing is 0.005–0.006 Nm³. 3 / (min·t), specifically 0.005Nm 3 / (min·t), 0.006Nm 3 / (min·t).

[0104] In this invention, oxygen control and slag adjustment are carried out during the converter smelting process, and the procedures are as follows:

[0105] If the oxygen content of the small platform is >500ppm, then add a carbon raiser. The amount added = (fixed oxygen value - 500ppm) × 0.1. During the calculation, do not substitute the unit ppm, but only calculate the numerical value (equivalent to (fixed oxygen value - 500ppm) / ppm). The final value is in kg. For example, if the fixed oxygen value is 650ppm, then the amount added = (650 - 500) × 0.1 = 15kg.

[0106] If the oxygen content of the small platform is ≤500ppm, no carbon raiser is added.

[0107] The oxygen content of the small platform refers to the oxygen content in the ladle measured by the oxygen analyzer in the converter, and the oxygen content in the formula also refers to this content. There are no special restrictions on the type of recarburizing agent; any conventional recarburizing agent in the field is acceptable. There are also no special restrictions on its source; any commercially available product is acceptable.

[0108] In this invention, the converter endpoint is defined as follows: tapping temperature of 1630–1650°C, and steel [C] ≤ 0.06%. Specifically, the tapping temperature can be 1630°C, 1635°C, 1640°C, 1645°C, or 1650°C. In this invention, the steel [C] refers to the carbon content in the steel. [C] represents the carbon content in the chemical composition of molten steel, which is a conventional expression in the art. In this invention, the steel [C] ≤ 0.06%, preferably 0.04% < steel [C] ≤ 0.06%. When the steel [C] ≤ 0.04%, a carbon raiser is added during the tapping process to ensure that 0.04% < steel [C] ≤ 0.06%. That is, steel can be tapped when the molten steel [C] ≤ 0.06%. When 0.04% < molten steel [C] ≤ 0.06%, no carburizing agent needs to be added during the tapping process. If the molten steel [C] ≤ 0.04%, a carburizing agent is added during the tapping process to make 0.04% < molten steel [C] ≤ 0.06%.

[0109] In this invention, steel is prepared for tapping after the converter reaches its final stage. Before tapping, a thick slag layer is formed, and a sliding plate is used to prevent slag buildup during tapping. The slag layer thickness in the ladle is ≤80mm, and the clearance is 250-550mm.

[0110] In this invention, preferably, active lime is added to the ladle during the steel tapping process. The amount of active lime added is preferably 2.5–5.0 kg / t of steel, specifically 2.5 kg / t, 3.0 kg / t, 3.5 kg / t, 4.0 kg / t, 4.5 kg / t, or 5.0 kg / t of steel.

[0111] Regarding step (B) :

[0112] (B) LF refining: The molten steel obtained in step (A) is sent into the LF refining furnace and heated for LF refining. After the temperature of the molten steel meets the requirements for leaving the station, argon is stopped and high-alumina slag conditioner is added. Then, argon is gently blown into the molten steel and it leaves the station.

[0113] LF refining refers to a ladle refining technology. The LF furnace, also known as a ladle refining furnace or ladle furnace, is an external refining technology that uses electric arc heating under vacuum conditions.

[0114] In this invention, preferably, the molten steel obtained in step (A) is fed into an LF refining furnace and a recarburizing agent is added. The preferred amount of the recarburizing agent is 0.1–0.5 kg / t steel, specifically 0.1 kg / t steel, 0.2 kg / t steel, 0.3 kg / t steel, 0.4 kg / t steel, or 0.5 kg / t steel. There are no special restrictions on the type of recarburizing agent; any conventional recarburizing agent in the art is acceptable. There are also no special restrictions on its source; any commercially available product is acceptable.

[0115] In this invention, preferably, the heating method is submerged arc heating.

[0116] In this invention, preferably, active lime and slag-reducing agent are added during the heating process, specifically in a "multi-batch, small-volume" manner. The active lime is added in 2-3 batches, with each batch containing 0.5-2.0 kg / t of steel, specifically 0.5 kg / t, 1.0 kg / t, 1.5 kg / t, and 2.0 kg / t of steel. The slag-reducing agent is an environmentally friendly agent; its type is not particularly limited and can be any conventional environmentally friendly slag-reducing agent in the field. The slag-reducing agent is added in 1-2 batches, with each batch containing 0.5-1.5 kg / t of steel, specifically 0.5 kg / t, 1.0 kg / t, and 1.5 kg / t of steel.

[0117] In this invention, preferably, the temperature requirement for molten steel leaving the station is 1570-1600℃, specifically 1570℃, 1580℃, 1590℃, or 1600℃.

[0118] In this invention, after the molten steel temperature meets the requirements for leaving the station, argon flow is stopped and a high-alumina slag conditioner is added.

[0119] In this invention, the amount of high-alumina slag conditioner added is determined based on a constant oxygen content, as shown in equations (1) to (2):

[0120] When the oxygen activity at the outlet is ≥500ppm, the amount of high-alumina slag conditioner added is: (oxygen activity at the outlet - 550ppm) × 0.1kg / t steel × steel volume (1);

[0121] When the oxygen activity at the outlet is <550ppm, the amount of high-alumina slag conditioner added is 200kg (Equation 2).

[0122] In equations (1) and (2):

[0123] The oxygen activity at the outlet is the oxygen content in the ladle, expressed in ppm.

[0124] The amount of molten steel referred to is the amount of molten steel entering the LF refining furnace, in tons (t).

[0125] (Outgoing oxygen activity -550ppm) is calculated using the absolute value;

[0126] In this calculation, the unit ppm is not substituted and only the numerical value is used (equivalent to (outlet oxygen activity - 500ppm) / ppm), and the final value is in kg. Taking an outlet oxygen activity of 600ppm and a steel volume of 100t as an example, the amount of high-alumina slag conditioner added is (600-550)×0.1kg / t×100t=500kg.

[0127] In this invention, the chemical composition of the high-alumina slag conditioner, by mass percentage, includes:

[0128] Al: 10%–40%;

[0129] CaO: 15%–25%;

[0130] SiO2: ≤10%;

[0131] MgO: ≤10%;

[0132] Al2O3: 15%–35%;

[0133] H2O: ≤1.5%;

[0134] P: ≤0.050%;

[0135] S: ≤0.15%.

[0136] In this invention, the particle size of the high-alumina slag conditioner is 20-40 mm. The high-alumina slag conditioner is in spherical form. The preparation method of the high-alumina slag conditioner is not particularly limited in this invention; it can be prepared according to a commonly used method in the art.

[0137] In this invention, after adding the high-alumina slag conditioner, argon is gently blown into the molten steel (to prevent the molten steel from churning excessively), with a blowing time of ≤2 minutes. Then, the steel is discharged from the station.

[0138] Regarding step (C) :

[0139] (C) RH refining: The RH furnace is pre-vacuumed, and the molten steel obtained in step (B) is sent into the RH furnace for oxygen control treatment, deoxidation and alloying, cyclic vacuum degassing, bottom blowing of argon in the ladle after refining, and then high-alumina slag conditioner is added before leaving the station.

[0140] In this invention, preferably, the pre-vacuuming process includes: introducing an inert gas and evacuating to a vacuum level ≤2.0 mbar within 6–7 minutes, and evacuating to a vacuum level ≤1.0 mbar within 9–10 minutes. The inert gas is preferably argon.

[0141] In this invention, the oxygen control treatment process is selected from (1) to (2).

[0142] Regarding the system (1):

[0143] (1) If the oxygen content at the RH inlet is high, a carburizing agent shall be added upon entry; the amount of carburizing agent added shall be determined based on the molten steel [C] and molten steel [O], as shown in Table 1 below:

[0144] Table 1: Reference Table for RH Carburizer Addition Amount (Unit: kg / t steel)

[0145]

[0146] The unit for the amount of carburizing agent added is kg / t steel;

[0147] In the table above, [C] refers to the carbon content in the molten steel, and [O] refers to the oxygen content. When [O] is 350 ppm and [C] is 0.02%, the amount of recarburizer added is 0.1 kg / t of steel; and so on. When the values ​​of [C] and [O] are not listed in the table, they are rounded to the values ​​listed in the table; for example, when [O] is 360 ppm and [C] is 0.026%, the rounded result is [O] 400 ppm and [C] 0.03%, and the required amount of recarburizer added is 0.1 kg / t of steel; and so on.

[0148] In this invention, the type of carbon raiser is not particularly limited, and any conventional carbon raiser in the art is acceptable; its source is not particularly limited, and any commercially available product is acceptable.

[0149] In this invention, in the above-mentioned system (1), after adding the carburizing agent, the gas flow rate is increased as follows: 1500 NL / min from 0 to 6 min (i.e., the gas flow rate is controlled at 1500 NL / min within 6 min, including the 6th minute); 1800 NL / min from 6 min until the end of deoxidation and alloying (i.e., the gas flow rate is controlled at 1800 NL / min after the 6th minute until the end of deoxidation and alloying); and 1200 NL / min after the end of deoxidation and alloying (i.e., the gas flow rate is controlled at 1200 NL / min after the end of deoxidation and alloying). The gas is preferably argon. At the beginning of step (C), the system is pre-evacuated, and after adding the carburizing agent, the gas flow rate is increased and controlled under the above-mentioned system.

[0150] In this invention, the endpoint of the oxygen control treatment is that a[O] is controlled at 250-300 ppm, specifically 250 ppm, 260 ppm, 270 ppm, 280 ppm, 290 ppm, or 300 ppm. a[O] refers to the dissolved oxygen content in the molten steel.

[0151] Regarding the system (2):

[0152] (2) If the carbon content of the RH entering the station is high, oxygen blowing shall be performed; the amount of oxygen blown shall be determined according to the carbon content of the molten steel [C] and the oxygen content of the molten steel [O], as shown in Table 2 below:

[0153] Table 2: Reference Table for Oxygen Blowing Volume at RH Station (Unit: m³) 3 )

[0154]

[0155] The unit of oxygen blowing volume is m. 3 .

[0156] In the table above, [C] refers to the carbon content in the molten steel, and [O] refers to the oxygen content. When [O] is 200 ppm and [C] is 0.030%, the oxygen blowing rate is 20 m³ / s. 3 And so on. When the values ​​of [C] and [O] are not listed in the table above, they are rounded to the values ​​listed in the table; for example, when [O] is 260ppm and [C] is 0.026%, the rounded result is [O] 300ppm and [C] 0.03%, and the oxygen blowing rate is 10m³. 3 And so on.

[0157] In this invention, the oxygen blowing system in the above-mentioned system (2) is as follows: oxygen blowing is carried out 3 to 4 minutes after the start of the inlet treatment. The pressure is not controlled during the oxygen blowing process, the gun position is 4.0m, and the oxygen flow rate is 1600Nm. 3 / h; stop oxygen blowing after the target oxygen blowing rate is reached (see Table 2 for the target oxygen blowing rate).

[0158] In this invention, in the above-mentioned system (2), the gas flow rate is increased specifically as follows: from the start of the treatment to the end of oxygen blowing, the flow rate is 1200 NL / min (i.e., the gas flow rate is controlled at 1200 NL / min from the start of the treatment to the end of oxygen blowing); from the end of oxygen blowing to the end of deoxidation and alloying, the flow rate is 1800 NL / min (i.e., the gas flow rate is controlled at 1800 NL / min from the end of oxygen blowing to the end of deoxidation and alloying); and after the end of deoxidation and alloying, the flow rate is 1200 NL / min (i.e., the gas flow rate is controlled at 1200 NL / min after the end of deoxidation and alloying). The gas is preferably argon. At the beginning of step (C), the system is first pre-evacuated, and then the gas flow rate is increased and controlled under the above-mentioned system.

[0159] In this invention, the endpoint of the oxygen control treatment is that a[O] is controlled at 250-300 ppm, specifically 250 ppm, 260 ppm, 270 ppm, 280 ppm, 290 ppm, or 300 ppm. a[O] refers to the dissolved oxygen content in the molten steel.

[0160] In this invention, the deoxidation and alloying process is not particularly limited and can be carried out according to conventional deoxidation and alloying procedures in the art. After deoxidation and alloying, cyclic vacuum degassing is performed. Preferably, the cyclic vacuum degassing time is ≥6 minutes.

[0161] In this invention, argon is blown into the ladle after refining. The argon blowing is a soft argon blowing process. The argon blowing time is ≥6 minutes.

[0162] In this invention, after the above treatment, a high-alumina slag conditioner is added before leaving the station. The high-alumina slag conditioner is the same as described in the previous technical solution and will not be repeated here. The preferred addition amount of the high-alumina slag conditioner is 0.05–2.5 kg / t steel, specifically 0.05 kg / t steel, 0.1 kg / t steel, 0.5 kg / t steel, 1.0 kg / t steel, or 1.5 kg / t steel. In this invention, argon is blown into the ladle at the bottom during the addition of the high-alumina slag conditioner. After addition, the ladle is allowed to stand for 3–10 minutes, specifically 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes. After standing, the ladle is discharged from the station.

[0163] Regarding step (D) :

[0164] (D) Continuous casting: The molten steel from step (C) is continuously cast to obtain ultra-low carbon steel billets.

[0165] In this invention, during the continuous casting process, when pouring molten steel from the ladle to the tundish, the long nozzle of the ladle is protected by a sealing ring and argon blowing throughout the pouring process, and the weight of the molten steel in the tundish is maintained above 20 tons. Furthermore, when pouring molten steel from the ladle to the tundish, the argon blowing rate is strictly controlled to ensure a stable liquid surface, and a constant pouring rate is used as much as possible. For ultra-low carbon IF steel and phosphorus-containing ultra-low carbon steel, the casting speed is ≤1.3 m / min.

[0166] To address the high oxidizing properties of IF steel ladle slag, this invention provides a smelting process. The key aspect is the use of a combined process of "converter + LF + RH full-process oxygen control and slag adjustment with carbon raisers." By adding slag additives after the converter furnace and during refining, the CaO / Al2O3 ratio and (FeO) content of the ladle slag are adjusted to reduce its oxidizing properties. While ensuring no carbon increase in the molten steel, carbon deoxidation replaces some Al deoxidation, effectively reducing the Al2O3 content in the molten steel, further improving its cleanliness, and consequently enhancing the castability of ultra-low carbon IF steel in continuous casting, significantly improving the quality of ultra-low carbon steel.

[0167] Compared with the prior art, the present invention has the following beneficial effects:

[0168] (1) This invention optimizes the process for controlling the carbon content of ultra-low carbon steel and establishes a forced decarburization process. Comprehensive technical applications show that the finished IF steel has a [C] ≤ 30 × 10⁻⁶. -6 The proportion increased from 51% to 85%, an increase of 34 percentage points.

[0169] (2) After the application of the ultra-low carbon steel ladle slag modification technology of this invention, the FeO content in the ladle slag after RH treatment decreased from 10.1%–16.3% (average 13.8%) before optimization to 6.8%–10.2% (average 7.3%), an average decrease of 6.5 percentage points; the T[O] of the tundish molten steel decreased from (30–49) × 10⁻⁶ before optimization. -6 The average is 32×10 -6 It decreased to (13~25)×10 -6 The average is 18×10 -6 On average, it decreased by 14×10 -6 The reduced oxidizing properties of IF steel ladle slag effectively improve the cleanliness of molten steel and the castability of continuous casting. The number of inclusions in the billet is significantly reduced, effectively improving the quality of IF steel products.

[0170] 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, and not for limiting the scope of the claims of the present invention.

[0171] In the following embodiments, the recarburizing agent used is Petroleum Coke Recarburizing Agent 99, sourced from Yingkou Jincheng Furnace Materials Co., Ltd. The environmentally friendly slag modifier is an improved refining slag modifier, sourced from a metallurgical auxiliary materials company. The chemical composition of the high-alumina slag modifier is: Al 35%, CaO 20%, SiO2 8%, MgO 6%, Al2O3 30%, H2O 0.85%, P 0.050%, S 0.10%; preparation is described above, and its particle size is 20–40 mm.

[0172] Example 1

[0173] (A) Converter smelting: After vanadium extraction and desulfurization pretreatment, molten iron is smelted in a converter. After reaching the converter endpoint, the steel is tapped into the ladle.

[0174] in:

[0175] During the converter smelting process, argon is blown throughout the bottom blowing process, with a gas supply intensity of 0.005 Nm. 3 / (min·t).

[0176] The oxygen control and slag conditioning procedures during converter smelting are as follows:

[0177] If the oxygen content of the small platform is >500ppm, then add a carbon raiser, the amount of which is = (fixed oxygen value - 500ppm) × 0.1; if the oxygen content of the small platform is ≤500ppm, then do not add a carbon raiser.

[0178] The oxygen content of the small platform was found to be 635 ppm. Carbon raiser was added in an amount of 13.5 kg.

[0179] The converter's endpoint was: tapping temperature 1640℃, and molten steel [C] 0.05%.

[0180] Before tapping, thick slag is applied, and a sliding plate is used to block the slag during tapping. The slag layer thickness in the ladle is 75mm, and the clearance is 350mm.

[0181] Active lime is added to the ladle during the tapping process at a rate of 3.0 kg / t steel.

[0182] (B) LF refining: The molten steel obtained in step (A) is sent into the LF refining furnace and heated for LF refining. After the temperature of the molten steel meets the requirements for leaving the station, argon is stopped and high-alumina slag conditioner is added. Then, argon is gently blown into the molten steel (to prevent the molten steel from churning) and it leaves the station.

[0183] in:

[0184] When the molten steel obtained in step (A) is fed into the LF refining furnace, a carbon raiser is added at a rate of 0.3 kg / t steel.

[0185] The heating method is submerged arc heating.

[0186] During the heating process, active lime and environmentally friendly slag remover are added; the active lime is added in 3 batches, with each batch containing 1.0 kg / t of steel; the environmentally friendly slag remover is added in 2 batches, with each batch containing 1.0 kg / t of steel.

[0187] The required temperature for molten steel leaving the station is 1590℃.

[0188] The amount of high-alumina slag conditioner added is determined based on the oxygen content. Actual testing showed the oxygen activity at the outlet was 580 ppm. Therefore, it is executed according to formula (1):

[0189] The amount of high-alumina slag conditioner added = (outlet oxygen activity - 550ppm) × 0.1kg / t steel × steel volume (1);

[0190] Specifically, the oxygen activity at the outlet is 580 ppm and the molten steel volume is 132 t. Therefore, the amount of slag conditioner added is 396 kg.

[0191] The time for micro-blowing argon is 1 minute.

[0192] (C) RH refining: The RH furnace is pre-vacuumed, and the molten steel obtained in step (B) is sent into the RH furnace for oxygen control treatment, deoxidation and alloying, cyclic vacuum degassing, bottom blowing of argon in the ladle after refining, and then high-alumina slag conditioner is added before leaving the station.

[0193] in:

[0194] The pre-vacuuming process includes: introducing argon gas and evacuating to a vacuum level of 2.0 mbar within 7 minutes, and evacuating to a vacuum level of 1.0 mbar within 10 minutes.

[0195] The oxygen control treatment process is selected from (1) to (2) above. Actual testing showed that the RH inlet [O] was 500 ppm and [C] was 0.03%. Therefore, a carbon raiser was added according to Table 1, with an addition amount of 0.2 kg / t steel. Afterwards, the argon flow rate was increased as follows: 1500 NL / min from 0 to 6 min, 1800 NL / min from 6 min until the end of deoxidation and alloying, and 1200 NL / min after the end of deoxidation and alloying. The endpoint of the oxygen control treatment was: a[O] controlled at 250 ppm.

[0196] The cyclic vacuum degassing time is 6 minutes.

[0197] The time for soft argon blowing at the bottom of the ladle is 6 minutes.

[0198] The high-alumina slag conditioner is added at a rate of 1.0 kg / t of steel. Argon is blown into the ladle during the addition process. After addition, the ladle is allowed to stand for 5 minutes before being discharged from the station.

[0199] (D) Continuous casting: The molten steel from step (C) is continuously cast to obtain ultra-low carbon IF steel billets.

[0200] in:

[0201] During the continuous casting process, when pouring molten steel from the ladle to the tundish, the long nozzle of the ladle is protected by a sealing ring and argon blowing throughout the pouring process. The weight of the molten steel in the tundish is maintained above 20 tons during the pouring. Furthermore, the argon blowing rate is strictly controlled when pouring molten steel from the ladle to the tundish to ensure a stable liquid surface, and a constant pouring rate is used as much as possible. The casting speed is 1.2 m / min.

[0202] Product Testing :

[0203] After RH treatment, the FeO content in the ladle slag was 7.8%; the T[O] in the tundish molten steel was 15 ppm; and the T[O] in the IF steel billet was 12 ppm. This demonstrates that the present invention can effectively reduce the oxidizing properties of ladle slag, decrease Al2O3 inclusions in steel, and improve the quality of ultra-low carbon steel.

[0204] Example 2

[0205] (A) Converter smelting: After vanadium extraction and desulfurization pretreatment, molten iron is smelted in a converter. After reaching the converter endpoint, the steel is tapped into the ladle.

[0206] in:

[0207] During the converter smelting process, argon is blown throughout the bottom blowing process, with a gas supply intensity of 0.006 Nm. 3 / (min·t).

[0208] The oxygen control and slag conditioning procedures during converter smelting are as follows:

[0209] If the oxygen content of the small platform is >500ppm, then add a carbon raiser, the amount of which is = (fixed oxygen value - 500ppm) × 0.1; if the oxygen content of the small platform is ≤500ppm, then do not add a carbon raiser.

[0210] Tests showed that the oxygen content of the small platform was 420 ppm, and no carbon raiser was added.

[0211] The converter's endpoint was: tapping temperature 1650℃, and steel [C] 0.06%.

[0212] Before tapping, thick slag is applied, and a sliding plate is used to block the slag during tapping. The slag layer thickness in the ladle is 70mm, and the clearance is 250mm.

[0213] Active lime is added to the ladle during the tapping process at a rate of 5.0 kg / t steel.

[0214] (B) LF refining: The molten steel obtained in step (A) is sent into the LF refining furnace and heated for LF refining. After the temperature of the molten steel meets the requirements for leaving the station, argon is stopped and high-alumina slag conditioner is added. Then, argon is gently blown into the molten steel (to prevent the molten steel from churning) and it leaves the station.

[0215] in:

[0216] When the molten steel obtained in step (A) is fed into the LF refining furnace, a carbon raiser is added at a rate of 0.1 kg / t steel.

[0217] The heating method is submerged arc heating.

[0218] During the heating process, active lime and environmentally friendly slag remover are added; the active lime is added in two batches, with each batch containing 2.0 kg / t of steel; the environmentally friendly slag remover is added in two batches, with each batch containing 0.5 kg / t of steel.

[0219] The required temperature for molten steel leaving the station is 1570℃.

[0220] The amount of high-alumina slag conditioner added is determined based on the oxygen content. Actual testing showed the oxygen activity at the outlet was 410 ppm. Therefore, it is executed according to formula (2):

[0221] The amount of high-alumina slag conditioner added = 200kg (Equation 2);

[0222] Specifically, the oxygen activity at the outlet is 410 ppm and the molten steel volume is 135 t. Therefore, the amount of slag conditioner added is 200 kg.

[0223] The time for micro-blowing argon is 2 minutes.

[0224] (C) RH refining: The RH furnace is pre-vacuumed, and the molten steel obtained in step (B) is sent into the RH furnace for oxygen control treatment, deoxidation and alloying, cyclic vacuum degassing, bottom blowing of argon in the ladle after refining, and then high-alumina slag conditioner is added before leaving the station.

[0225] in:

[0226] The pre-vacuuming process includes: introducing argon gas and evacuating to a vacuum level of 2.0 mbar within 6 minutes, and evacuating to a vacuum level of 1.0 mbar within 9 minutes.

[0227] The oxygen control treatment system is selected from (1) to (2) above; according to actual testing, the RH inlet [O] is 200ppm and [C] is 0.030%, so oxygen blowing is carried out according to Table 2, and the oxygen blowing volume is 20m³. 3 The oxygen blowing procedure is as follows: oxygen blowing begins 4 minutes after the start of inlet treatment. Pressure is not controlled during the blowing process; the nozzle position is 4.0m, and the oxygen flow rate is 1600 Nm³. 3 / h; stop oxygen blowing after reaching the target oxygen blowing rate (see Table 2 for the target oxygen blowing rate). During this period, increase the argon flow rate as follows: 1200 NL / min from the start of treatment to the end of oxygen blowing, 1800 NL / min from the end of oxygen blowing to the end of deoxidation and alloying, and 1200 NL / min after the end of deoxidation and alloying. The endpoint of the oxygen control treatment is: a[O] controlled at 300 ppm.

[0228] The cyclic vacuum degassing time is 7 minutes.

[0229] The time for soft argon blowing at the bottom of the ladle is 8 minutes.

[0230] The high-alumina slag conditioner is added at a rate of 0.8 kg / t of steel. Argon is blown into the ladle during the addition process. After addition, the ladle is allowed to stand for 3 minutes before being discharged from the station.

[0231] (D) Continuous casting: The molten steel from step (C) is continuously cast to obtain ultra-low carbon IF steel billets.

[0232] in:

[0233] During the continuous casting process, when pouring molten steel from the ladle to the tundish, the long nozzle of the ladle is protected by a sealing ring and argon blowing throughout the pouring process. The weight of the molten steel in the tundish is maintained above 20 tons during the pouring. Furthermore, the argon blowing rate is strictly controlled when pouring molten steel from the ladle to the tundish to ensure a stable liquid surface, and a constant pouring rate is used as much as possible. The casting speed is 1.3 m / min.

[0234] Product Testing :

[0235] After RH treatment, the FeO content in the ladle slag was 6.5%; the T[O] in the tundish molten steel was 13 ppm; and the T[O] in the IF steel billet was 10 ppm. This demonstrates that the present invention can effectively reduce the oxidizing properties of ladle slag, decrease Al2O3 inclusions in steel, and improve the quality of ultra-low carbon steel.

[0236] Example 3

[0237] (A) Converter smelting: After vanadium extraction and desulfurization pretreatment, molten iron is smelted in a converter. After reaching the converter endpoint, the steel is tapped into the ladle.

[0238] in:

[0239] During the converter smelting process, argon is blown throughout the bottom blowing process, with a gas supply intensity of 0.006 Nm. 3 / (min·t).

[0240] The oxygen control and slag conditioning procedures during converter smelting are as follows:

[0241] If the oxygen content of the small platform is >500ppm, then add a carbon raiser, the amount of which is = (fixed oxygen value - 500ppm) × 0.1; if the oxygen content of the small platform is ≤500ppm, then do not add a carbon raiser.

[0242] The oxygen content of the small platform was found to be 653 ppm. A carbon raiser was added in an amount of 15.3 kg.

[0243] The converter's endpoint was: tapping temperature 1630℃, and steel [C] 0.04%.

[0244] Before tapping, thick slag is applied, and a sliding plate is used to block the slag during tapping. The slag layer thickness in the ladle is 80mm, and the clearance is 550mm.

[0245] Active lime is added to the ladle during the tapping process at a rate of 2.5 kg / t of steel.

[0246] (B) LF refining: The molten steel obtained in step (A) is sent into the LF refining furnace and heated for LF refining. After the temperature of the molten steel meets the requirements for leaving the station, argon is stopped and high-alumina slag conditioner is added. Then, argon is gently blown into the molten steel (to prevent the molten steel from churning) and it leaves the station.

[0247] in:

[0248] When the molten steel obtained in step (A) is fed into the LF refining furnace, a carbon raiser is added at a rate of 0.5 kg / t steel.

[0249] The heating method is submerged arc heating.

[0250] During the heating process, active lime and environmentally friendly slag remover are added; the active lime is added in three batches, with each batch containing 0.5 kg / t of steel; the environmentally friendly slag remover is added in one batch, with each batch containing 1.5 kg / t of steel.

[0251] The required temperature for molten steel leaving the station is 1600℃.

[0252] The amount of high-alumina slag conditioner added is determined based on the oxygen content. Actual testing showed the oxygen activity at the outlet was 591 ppm. Therefore, it is executed according to formula (1):

[0253] The amount of high-alumina slag conditioner added = (outlet oxygen activity - 550ppm) × 0.1kg / t steel × steel volume (1);

[0254] Specifically, the oxygen activity at the outlet is 591 ppm and the molten steel volume is 133 t. Therefore, the amount of slag conditioner added is 541 kg.

[0255] The time for micro-blowing argon is 1 minute.

[0256] (C) RH refining: The RH furnace is pre-vacuumed, and the molten steel obtained in step (B) is sent into the RH furnace for oxygen control treatment, deoxidation and alloying, cyclic vacuum degassing, bottom blowing of argon in the ladle after refining, and then high-alumina slag conditioner is added before leaving the station.

[0257] in:

[0258] The pre-vacuuming process includes: introducing argon gas and evacuating to a vacuum level of 2.0 mbar within 6 minutes, and evacuating to a vacuum level of 1.0 mbar within 9 minutes.

[0259] The oxygen control treatment system is selected from (1) to (2) above; according to actual testing, the RH inlet [O] is 300ppm and [C] is 0.040%, so oxygen blowing is carried out according to Table 2, and the oxygen blowing volume is 25m³. 3 The oxygen blowing procedure is as follows: oxygen blowing begins 3 minutes after the start of inlet treatment. Pressure is not controlled during the blowing process; the nozzle position is 4.0m, and the oxygen flow rate is 1600 Nm³. 3 / h; stop oxygen blowing after reaching the target oxygen blowing rate (see Table 2 for the target oxygen blowing rate). During this period, increase the argon flow rate as follows: 1200 NL / min from the start of treatment to the end of oxygen blowing, 1800 NL / min from the end of oxygen blowing to the end of deoxidation and alloying, and 1200 NL / min after the end of deoxidation and alloying. The endpoint of the oxygen control treatment is: a[O] controlled at 250 ppm.

[0260] The cyclic vacuum degassing time is 6 minutes.

[0261] The time for soft argon blowing at the bottom of the ladle is 6 minutes.

[0262] The high-alumina slag conditioner is added at a rate of 2.5 kg / t of steel. Argon is blown into the ladle during the addition process. After addition, the ladle is allowed to stand for 10 minutes before being discharged from the station.

[0263] (D) Continuous casting: The molten steel from step (C) is continuously cast to obtain ultra-low carbon IF steel billets.

[0264] in:

[0265] During the continuous casting process, when pouring molten steel from the ladle to the tundish, the long nozzle of the ladle is protected by a sealing ring and argon blowing throughout the pouring process. The weight of the molten steel in the tundish is maintained above 20 tons during the pouring. Furthermore, the argon blowing rate is strictly controlled when pouring molten steel from the ladle to the tundish to ensure a stable liquid surface, and a constant pouring rate is used as much as possible. The casting speed is 1.3 m / min.

[0266] Product Testing :

[0267] After RH treatment, the FeO content in the ladle slag was 7.1%; the T[O] in the tundish molten steel was 15.6 ppm; and the T[O] in the IF steel billet was 8.2 ppm. This demonstrates that the present invention can effectively reduce the oxidizing properties of ladle slag, decrease Al2O3 inclusions in steel, and improve the quality of ultra-low carbon steel.

[0268] Comparative Example 1

[0269] (A) Converter smelting: After vanadium extraction and desulfurization pretreatment, molten iron is smelted in a converter. After reaching the converter endpoint, the steel is tapped into the ladle.

[0270] in:

[0271] During the converter smelting process, argon is blown throughout the bottom blowing process, with a gas supply intensity of 0.006 Nm. 3 / (min·t).

[0272] The converter's endpoint was: tapping temperature 1635℃, and steel [C] 0.04%.

[0273] Before tapping, thick slag is applied, and a sliding plate is used to block the slag during tapping. The slag layer thickness in the ladle is 80mm, and the clearance is 550mm.

[0274] Active lime is added to the ladle during the tapping process at a rate of 2.5 kg / t of steel.

[0275] (B) LF refining: The molten steel obtained in step (A) is sent into the LF refining furnace and heated for LF refining. After the temperature of the molten steel meets the requirements for leaving the station, argon is stopped and high-alumina slag conditioner is added. Then, argon is gently blown into the molten steel (to prevent the molten steel from churning) and it leaves the station.

[0276] in:

[0277] When the molten steel obtained in step (A) is fed into the LF refining furnace, a carbon raiser is added at a rate of 0.5 kg / t steel.

[0278] The heating method is submerged arc heating.

[0279] During the heating process, active lime and environmentally friendly slag remover are added; the active lime is added in three batches, with each batch containing 0.5 kg / t of steel; the environmentally friendly slag remover is added in one batch, with each batch containing 1.5 kg / t of steel.

[0280] The required temperature for molten steel leaving the station is 1600℃.

[0281] The dosage of high-alumina slag conditioner is 300 kg.

[0282] The time for micro-blowing argon is 1 minute.

[0283] (C) RH refining: The RH furnace is pre-vacuumed, and the molten steel obtained in step (B) is sent into the RH furnace for oxygen control treatment, deoxidation and alloying, cyclic vacuum degassing, bottom blowing of argon in the ladle after refining, and then high-alumina slag conditioner is added before leaving the station.

[0284] in:

[0285] The pre-vacuuming process includes: introducing argon gas and evacuating to a vacuum level of 2.0 mbar within 7 minutes, and evacuating to a vacuum level of 1.0 mbar within 10 minutes.

[0286] The oxygen control treatment process is selected from (1) to (2) above; actual testing showed that the RH inlet [O] was 500 ppm and [C] was 0.03%. Therefore, a carbon raiser was added according to Table 1, with an addition amount of 0.2 kg / t steel. Afterward, the argon flow rate was increased as follows: 1500 NL / min from 0 to 6 min, 1800 NL / min from 6 min to the end of deoxidation and alloying, and 1200 NL / min after the end of deoxidation and alloying. The endpoint of the oxygen control treatment was: a[O] was controlled at 250 ppm.

[0287] The cyclic vacuum degassing time is 6 minutes.

[0288] The time for soft argon blowing at the bottom of the ladle is 6 minutes.

[0289] The high-alumina slag conditioner is added at a rate of 1.0 kg / t of steel. Argon is blown into the ladle during the addition process. After addition, the ladle is allowed to stand for 5 minutes before being discharged from the station.

[0290] (D) Continuous casting: The molten steel from step (C) is continuously cast to obtain ultra-low carbon IF steel billets.

[0291] in:

[0292] During the continuous casting process, when pouring molten steel from the ladle to the tundish, the long nozzle of the ladle is protected by a sealing ring and argon blowing throughout the pouring process. The weight of the molten steel in the tundish is maintained above 20 tons during the pouring. Furthermore, the argon blowing rate is strictly controlled when pouring molten steel from the ladle to the tundish to ensure a stable liquid surface, and a constant pouring rate is used as much as possible. The casting speed is 1.2 m / min.

[0293] Product Testing :

[0294] After RH treatment, the FeO content in the ladle slag was 12.1%; the T[O] in the tundish molten steel was 22.3 ppm; and the T[O] in the IF steel billet was 14.8 ppm. It can be seen that, compared with Comparative Example 1, in Examples 1-3 of the present invention, the FeO content in the ladle slag after RH treatment was significantly reduced, the T[O] in the tundish molten steel was significantly reduced, and the Al2O3 inclusions in the IF steel billet were significantly reduced, greatly improving the quality of ultra-low carbon steel.

[0295] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A production process for ultra-low carbon steel, characterized in that, Includes the following steps: (A) Converter smelting: Molten iron is smelted in a converter, and after reaching the converter's endpoint, the steel is tapped into a ladle. in, The oxygen control and slag conditioning processes during the converter smelting are as follows: If the oxygen content of the small platform is >500ppm, then add a carbon raiser. The amount added is = (fixed oxygen value - 500ppm) × 0.1, and the unit of the amount added is kg. If the oxygen content of the small platform is ≤500ppm, no carbon raiser is added; The converter endpoint is defined as follows: tapping temperature 1630~1650℃, molten steel [C] ≤0.06%; (B) LF Refining: The molten steel obtained in step (A) is sent into the LF refining furnace and heated for LF refining. After the temperature of the molten steel meets the requirements for leaving the station, argon is stopped and a high-alumina slag conditioner is added. Then, argon is gently blown into the molten steel and it leaves the station. in, The amount of high-alumina slag conditioner added is determined based on the oxygen content, and the relationship is shown in equations (1) to (2): When the oxygen activity at the outlet is ≥500ppm, the amount of high-alumina slag conditioner added is = (oxygen activity at the outlet - 550ppm) × 0.1kg / t steel × steel volume (1); where (oxygen activity at the outlet - 550ppm) is the absolute value for calculation. When the oxygen activity at the outlet is <500ppm, the amount of high-alumina slag conditioner added is 200kg (Equation (2)); In equations (1) and (2): The oxygen activity at the outlet is the oxygen content in the ladle, expressed in ppm. The amount of molten steel referred to is the amount of molten steel entering the LF refining furnace, in tons (t). (C)RH refining: The RH furnace is pre-vacuumed, and the molten steel obtained in step (B) is sent into the RH furnace for oxygen control treatment, deoxidation and alloying, cyclic vacuum degassing, bottom argon blowing in the ladle after refining, and then high-alumina slag conditioner is added before it leaves the station. in, The oxygen control treatment system is selected from the following (1)~(2): (1) If the oxygen content at the RH inlet is high, a carburizing agent shall be added upon entry; the amount of carburizing agent added shall be determined based on the molten steel [C] and molten steel [O], as shown in the table below: The unit for the amount of carburizing agent added is kg / t steel; (2) If the carbon content of the RH entering the station is high, oxygen blowing shall be performed; the amount of oxygen blown shall be determined according to the carbon content of the molten steel [C] and the oxygen content of the molten steel [O], as shown in the table below: The unit of oxygen blowing volume is m. 3 ; (D) Continuous casting: The molten steel from step (C) is continuously cast to obtain ultra-low carbon steel billets.

2. The production process according to claim 1, characterized in that, In step (A), during the converter smelting process, argon is blown throughout the bottom blowing of the converter; wherein the gas supply intensity of the bottom blowing is 0.005~0.006 Nm. 3 / (min•t).

3. The production process according to claim 1, characterized in that, In step (A), the converter endpoint is: tapping temperature 1630~1650℃, molten steel [C] ≤0.06%; When the molten steel [C] ≤ 0.04%, a carbon raiser is added during the tapping process to make 0.04% < molten steel [C] ≤ 0.06%.

4. The production process according to claim 1, characterized in that, In step (A): The molten iron is first pretreated and then smelted in a converter. The pretreatment includes vanadium extraction and desulfurization. Before tapping, thicken the slag and use a sliding plate to block the slag during tapping. The slag layer thickness in the ladle is ≤80 mm, and the clearance is 250~550 mm. During the tapping process, active lime is added to the ladle at a rate of 1.0~5.0 kg / t steel.

5. The production process according to claim 1, characterized in that, In step (B), the molten steel obtained in step (A) is fed into the LF refining furnace and a carburizing agent is added; The amount of the carbon raiser added is 0.1~0.5 kg / t steel.

6. The production process according to claim 1, characterized in that, In step (B): The heating method is submerged arc heating; During the heating process, active lime and slag-reducing agent are added; wherein, the active lime is added in 2-3 batches, with each batch containing 0.5-2.0 kg / t of steel; the slag-reducing agent is an environmentally friendly slag-reducing agent; the slag-reducing agent is added in 1-2 batches, with each batch containing 0.5-1.5 kg / t of steel; The required temperature for molten steel leaving the station is 1570~1600℃.

7. The production process according to claim 1, characterized in that, The chemical composition of the high-alumina slag conditioner, by weight percentage, includes: Al：10%~40%； CaO: 15%~25%; SiO2: ≤10%; MgO: ≤10%; Al2O3: 15%~35%; H2O: ≤1.5%; P：≤0.050%； S：≤0.15%； The particle size of the high-alumina slag conditioner is 20~40mm.

8. The production process according to claim 1, characterized in that, In step (C), the pre-vacuuming process includes: introducing an inert gas and evacuating to a vacuum level ≤2.0 mbar within 6-7 minutes, and evacuating to a vacuum level ≤1.0 mbar within 9-10 minutes.

9. The production process according to claim 1, characterized in that, In step (C): In the aforementioned system (1), after adding the carbon raiser, the gas flow rate is increased as follows: 1500 NL / min from 0 to 6 min, 1800 NL / min from 6 min to the end of deoxidation and alloying, and 1200 NL / min after the end of deoxidation and alloying. In the aforementioned system (2), the oxygen blowing system is as follows: oxygen blowing is performed 3-4 minutes after the start of the inlet treatment. During the oxygen blowing process, the pressure is not controlled, the nozzle position is 4.0m, and the oxygen flow rate is 1600Nm. 3 / h; stop oxygen blowing after reaching the target oxygen blowing volume; increase the gas flow rate during the process as follows: 1200NL / min from the start of treatment to the end of oxygen blowing, 1800NL / min from the end of oxygen blowing to the end of deoxidation and alloying, and 1200NL / min after the end of deoxidation and alloying. The endpoint of the oxygen control treatment is: a[O] is controlled at 250~300ppm; The amount of the high-alumina slag conditioner added is 0.05~2.5 kg / t steel.

10. The production process according to claim 1, characterized in that, In step (D), during the continuous casting process, when the ladle pours molten steel into the tundish, the long nozzle of the ladle is protected by a sealing ring and argon blowing throughout the pouring process, and the weight of the molten steel in the tundish is maintained above 20t during the pouring process; the casting speed of the continuous casting is ≤1.3m / min.

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