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CN-118910365-B - Production process of high-cleanliness ultra-low carbon steel

CN118910365BCN 118910365 BCN118910365 BCN 118910365BCN-118910365-B

Abstract

The invention belongs to the technical field of ferrous metallurgy, in particular to a production process of high-cleanliness ultra-low carbon steel, which is characterized in that RH decarburization treatment is adopted for molten steel, the molten steel is sent into a VOD furnace, after reaching the vacuum requirement, the VOD is sent down from a top lance to the slag surface for blowing hydrogen, simultaneously blowing through the bottom air brick, deoxidizing molten steel by blowing hydrogen at the bottom, deoxidizing the steel slag by blowing hydrogen at the top of the steel slag, simultaneously carrying out top slag modification, alloying after breaking the air, and avoiding deoxidizing alloy in the process. The invention has higher safety and effective treatment of gas emission, reduces the oxidizing property of slag by top-blown hydrogen, reduces the secondary oxidation of slag to molten steel, improves the recovery rate of Fe in slag, reduces iron loss, improves the alloy yield under the condition of low oxygen, reduces the alloy oxidation consumption, has good dynamics condition, is beneficial to the efficient floating of inclusions in the molten steel, obviously improves the cleanliness of the molten steel, and is beneficial to the improvement of the mechanical property of the steel and the light weight of automobiles.

Inventors

  • BAO YANPING
  • Lv Ziyu

Assignees

  • 北京科技大学

Dates

Publication Date
20260505
Application Date
20240724

Claims (5)

  1. 1. The production process of the high-cleanliness ultra-low carbon steel is characterized in that RH+VOD duplex control is adopted to control molten steel, the molten steel is sent into a VOD furnace after being decarburized by RH, hydrogen is blown from a top lance to the slag surface after the VOD meets the vacuum degree requirement, meanwhile, the bottom air brick is used for blowing, the bottom hydrogen is blown to deoxidize the molten steel, the top part is used for blowing hydrogen to deoxidize the slag surface and simultaneously carrying out top slag modification, alloying is carried out after the breaking, and deoxidized alloy is not used in the process; the production process specifically comprises KR pretreatment, converter smelting, RH, VOD and continuous casting; The ladle car is started to an RH station, vacuumizing is started to start circulation, a five-stage or four-stage vacuum pump is adopted to vacuumize to 5-15 KPa to keep vacuum degree, an oxygen lance is started to forcedly decarbonize, the oxygen blowing intensity is 1200-4200 NL/t Steel and method for producing same /min, the oxygen blowing time is 5-18 min, and a three-stage pump, a two-stage pump, a three-stage pump are sequentially started at intervals of 1min after decarbonizing is finished, A primary pump, after the primary pump is started, maintaining the vacuum degree of the vacuum chamber to be less than or equal to 67Pa, and maintaining the vacuum degree for 5-20 min for natural decarburization; breaking the blank and discharging after decarburization is finished, wherein the discharge requirement [ C ] content is less than or equal to 15 multiplied by 10 -6 , and the temperature of molten steel is required to be 1662-1688 ℃; directly feeding the molten steel into a VOD station without adding a top slag modifier after RH is discharged, after the molten steel enters the VOD station, capping the steel ladle, starting vacuum treatment, continuously reducing the vacuum degree when the vacuum degree reaches 1500-2500 Pa, and then adjusting the vacuum degree of a vacuum chamber to be less than or equal to 67Pa, blowing hydrogen-inert gas mixed gas with the hydrogen ratio of 10-50%, wherein the blowing strength is 1500-4500 NL/t Steel and method for producing same /min, the blowing time is 8-20 min, simultaneously blowing hydrogen-inert gas mixed gas with the hydrogen ratio of 10-50% through a bottom air brick, performing bottom blowing through a plurality of bottom blowing holes, wherein the air supply strength is total 1200-6000 NL/t Steel and method for producing same /min, the blowing time is 8-30 min, the vacuum degree is continuously reduced when the blowing amount reaches 50%, the vacuum degree of a vacuum chamber is not more than 67Pa when the blowing hydrogen is finished, the blowing time is 5-15 min, the blowing auxiliary degassing is performed to molten steel by using the bottom blowing air brick, the blowing air strength is total 1200-4500 NL/t Steel and method for producing same /min, the required temperature of molten steel in the VOD discharge station is 1585-1630 ℃, the content of molten steel [ C ] is 15× -6 , [ O ] is not more than 15×770×5X7N10X7X10 ] [ 10 ] and [ 5×7X10X10X ] is not more than 15×35X ] and the blowing time is not more than 35×10X5×35X5.
  2. 2. The process for producing high-cleanliness ultra-low carbon steel according to claim 1, wherein the KR pretreatment is used for desulfurizing molten iron, and the [ S ] content in the treated molten iron is required to be less than or equal to 50 multiplied by 10 -6 .
  3. 3. The production process of the high-cleanliness ultra-low carbon steel according to claim 1, wherein the ratio of steel scraps fed into a converter is controlled to be less than or equal to 22%, the FeO content at the end of the converting is controlled to be less than or equal to 25% by weight, the required temperature at the end of the converting is controlled to be 1690-1710 ℃, the content of end point [ C ] is controlled to be (320-480) multiplied by 10 -6 , the content of end point [ P ] is controlled to be less than or equal to 90 multiplied by 10 -6 , the content of end point [ S ] is controlled to be less than or equal to 55 multiplied by 10 -6 , the content of end point [ O ] is more than or equal to 480 multiplied by 10 -6 , a carbonless ladle is adopted for tapping, and lime of 0.8-3.5 kg/t Steel and method for producing same is added for tapping.
  4. 4. The production process of the high-cleanliness ultra-low carbon steel according to claim 1 is characterized in that the alloy quantity is required to be added according to the calculation of the component of VOD tapping molten steel, soft blowing is carried out for 5-10 min after the alloy is added to ensure that the molten steel component is uniform, the temperature of the molten steel is required to be controlled to be 1570-1595 ℃ after the alloying, the [ C ] content is less than or equal to 15×10 -6 ℃, the [ Si ] content is less than or equal to 55×10 -6 , the [ Mn ] content is 900×10 -6 -1300×10 -6 , the [ P ] content is less than or equal to 90×10 -6 , the [ S ] content is less than or equal to 50×10 -6 , [ Ti ] content is less than or equal to 110×10 -6 , [ Als ] content is less than or equal to 15×10 -6 , [ O ] content is less than or equal to 15×10 -6 , [ N ] content is less than or equal to 30×10 -6 , and the [ H ] content is less than or equal to 3×10 -6 .
  5. 5. The production process of the high-cleanliness ultra-low carbon steel is characterized in that protective casting measures are adopted in continuous casting, secondary oxidation of molten steel is strictly prevented, the temperature of a tundish is controlled to be 1554-1570 ℃, an ultra-low carbon covering agent is adopted in a crystallizer covering agent, protective casting is carried out in the whole continuous casting process, and oxygenation is required to be less than 3ppm and nitrogen is required to be increased to be less than 3ppm.

Description

Production process of high-cleanliness ultra-low carbon steel Technical Field The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a production process of high-cleanliness ultra-low carbon steel. Background In the production process of ultra-low carbon steel, scholars have proposed to blow hydrogen for deoxidation in the AOD, RH, RH +VD refining step, and the clean deoxidation mode avoids oxide inclusion, but because of the diffusion of oxygen between slag steel interfaces, when the oxygen content is lower than the slag/steel oxygen content balance point, the steel transmits oxygen into slag to realize diffusion deoxidation, and when the oxygen content is higher than the slag/steel oxygen content balance point, the slag transmits oxygen into the steel to generate secondary oxidation. The oxygen content can be reduced to a lower level by the way of clean deoxidation such as hydrogen blowing deoxidation, but if the oxygen content in the slag is controlled unstably, the final oxygen content control can be poor, and when the top slag modifier is used at present, some problems which cannot be avoided in the prior art still exist: (1) When the top slag is pre-deoxidized by adopting a pre-deoxidizing agent, the adding amount is too small to pre-deoxidize the slag efficiently, and when the adding amount is too large, the fluidity and other performances of the refining slag are affected, and Al 2O3 is also generated to diffuse into molten steel; (2) Smoke dust can be generated in the process of adding the modifier to the surface of ladle slag after tapping, so that the environment is polluted; (3) When the addition amount of the modifier is calculated inaccurately, the fluctuation of the total iron content of the ladle top slag is larger; (4) The RH dip pipe has thicker slag layer after being put in, and is difficult to mix after adding the top slag modifier, molten steel is exposed due to bottom blowing, and the mixing effect is poor due to insufficient bottom blowing flow; (5) Too high FeO content in the slag can increase iron loss. Disclosure of Invention In order to solve the problems in the prior art, the main purpose of the invention is to provide a production process of high-cleanliness ultra-low carbon steel. In order to solve the technical problems, according to one aspect of the present invention, the following technical solutions are provided: The production process of high-cleanliness ultra-low carbon steel is characterized by that it utilizes RH+VOD double control, after the molten steel adopts RH decarburization treatment, the molten steel is fed into VOD furnace, after the VOD reaches the vacuum level requirement the top lance is down to slag surface to blow hydrogen, at the same time the bottom air brick is used for blowing, the bottom is used for blowing hydrogen to deoxidize molten steel, and the top is used for blowing hydrogen to deoxidize steel slag on the slag surface, at the same time making top slag modification, after the steel slag is broken, making alloying, and in the course no deoxidized alloy is used. As a preferable scheme of the production process of the high-cleanliness ultra-low carbon steel, the production process specifically comprises KR pretreatment, converter smelting, RH, VOD and continuous casting. As a preferable scheme of the production process of the high-cleanliness ultra-low carbon steel, KR pretreatment is adopted to desulfurize molten iron, and the [ S ] content in the treated molten iron is required to be less than or equal to 50 multiplied by 10 -6. The production process of the high-cleanliness ultra-low carbon steel has the advantages that the ratio of steel scraps fed into a converter is controlled to be less than or equal to 22%, the FeO content at the end of the converter is 22wt%, the required temperature at the end of the converter is controlled to be 1690-1710 ℃, the content of the end point [ C ] is controlled to be (320-480) multiplied by 10 -6, the content of the end point [ P ] is less than or equal to 90 multiplied by 10 -6, the content of the end point [ S ] is less than or equal to 55 multiplied by 10 -6, the content of the end point [ O ] is more than or equal to 480 multiplied by 10 -6, a carbonless ladle is adopted for tapping, and 0.8-3.5 kg/t Steel and method for producing same of lime is added for tapping. The production process of the high-cleanliness ultra-low carbon steel comprises the steps of starting a ladle car to an RH station, starting vacuumizing and circulating, vacuumizing to 5-15 kPa to keep the vacuum degree by adopting a five-stage/four-stage vacuum pump, starting forced decarburization by a lower oxygen lance, starting a three-stage pump, a two-stage pump and a one-stage pump at intervals of 1min after decarburization, starting the one-stage pump, maintaining the vacuum degree of a vacuum chamber to be less than or equal to 67Pa, keeping the vacuum degree of 5-20 min for natural decarbu