阅读说明：本技术 一种超低碳钢精炼炉渣改质的方法 (Method for modifying ultra-low carbon steel refining slag ) 是由 马文俊 陈斌 龚坚 黄福祥 李海波 高攀 刘道正 陈建光 赵彦伟 刘国梁 朱克然 于 2020-05-11 设计创作，主要内容包括：本发明公开了一种超低碳钢精炼炉渣改质的方法,所述方法包括：测定转炉钢液的终点氧含量；将所述转炉钢液出钢,获得出钢钢液,在所述出钢过程中根据所述终点氧含量向所述转炉钢液中加入2～4kg/吨钢的小粒白灰；根据所述终点氧含量,向所述出钢钢液的渣面加入1.5～2.5kg/吨钢的第一缓释脱氧剂,获得含第一改质渣的钢液；将所述含第一改质渣的钢液进行脱碳处理,获得脱碳钢液；测定所述脱碳钢液的氧含量,根据所述脱碳钢液的氧含量向所述脱碳钢液的渣面加入0.5～1.3kg/吨钢的第二缓释脱氧剂,后钢包加盖,包盖内喷吹燃气和氧气燃烧加热渣面促进化渣。RH结束后精炼炉渣中FeO含量可稳定控制在3％以下。(The invention discloses a method for modifying ultra-low carbon steel refining slag, which comprises the following steps: measuring the end point oxygen content of the converter molten steel; tapping the converter molten steel to obtain tapped molten steel, and adding small-particle lime of 2-4 kg/ton steel into the converter molten steel according to the end point oxygen content in the tapping process; adding 1.5-2.5 kg/ton of first slow-release deoxidizer into the slag surface of the molten steel to obtain molten steel containing first modified slag according to the end-point oxygen content; performing decarburization treatment on the molten steel containing the first modified slag to obtain decarburization molten steel; and measuring the oxygen content of the decarburized molten steel, adding a second slow-release deoxidizer of 0.5-1.3 kg/ton of steel to the slag surface of the decarburized molten steel according to the oxygen content of the decarburized molten steel, covering a steel ladle, and blowing gas and oxygen into the steel ladle to combust and heat the slag surface to promote slagging. After RH is finished, the FeO content in the refining slag can be stably controlled below 3 percent.)

1. A method for upgrading ultra-low carbon steel refinery slag, comprising:

measuring the end point oxygen content of the converter molten steel;

tapping the converter molten steel to obtain tapped molten steel, and adding small-particle lime of 2-4 kg/ton steel into the converter molten steel according to the end point oxygen content in the tapping process;

adding 1.5-2.5 kg/ton of first slow-release deoxidizer into the slag surface of the molten steel to obtain molten steel containing first modified slag according to the end-point oxygen content;

performing decarburization treatment on the molten steel containing the first modified slag to obtain decarburization molten steel;

and measuring the oxygen content of the decarburized molten steel, adding 0.5-1.3 kg/ton of second slow-release deoxidizer to the slag surface of the decarburized molten steel according to the oxygen content of the decarburized molten steel, and covering a steel ladle to obtain the modified ultra-low carbon steel refining slag.

2. The method for upgrading ultra-low carbon steel refining slag according to claim 1, wherein the mass fraction of the metallic aluminum in the first slow-release deoxidizer is 55 to 65 percent; the mass fraction of the metal aluminum in the second slow-release deoxidizer is 40-50%.

3. The method for modifying ultra-low carbon steel refinery slag according to claim 1, wherein, when the steel output is 1/5-1/3, small white ash of 2-4 kg/ton steel is added according to the terminal oxygen content per ton steel during the steel output process; the particle size of the small lime particles is less than 500 mm.

4. The method for modifying ultra-low carbon steel refining slag according to claim 1, wherein a first slow-release deoxidizer of 1.5 to 2.5 kg/ton steel is added to the slag surface of the molten steel to be tapped according to the terminal oxygen content, comprising:

when the end point oxygen content is less than or equal to 400ppm, the addition amount of the small-particle lime is 2.0-2.5 kg per ton of steel;

when the end point oxygen content is 400-550 ppm, the addition amount of the small lime particles is 2.5-3.0 kg per ton of steel;

when the end point oxygen content is 550-700 ppm, the addition amount of the small lime particles is 3.0-3.5 kg per ton of steel;

and when the final oxygen content is more than or equal to 700ppm, the addition amount of the small lime particles is 3.5-4.0 kg per ton of steel.

5. The method for modifying ultra-low carbon steel refining slag according to claim 1, wherein a first slow-release deoxidizer of 1.5 to 2.5 kg/ton steel is added to the slag surface of the molten steel to be tapped according to the terminal oxygen content, comprising:

when the end-point oxygen content is less than or equal to 400ppm, the addition amount of the first slow-release deoxidizer is 1.5-1.8 kg per ton of steel;

when the final oxygen content is 400-550 ppm, the addition amount of the first slow-release deoxidizer is 1.8-2.0 kg/ton of steel;

when the end-point oxygen content is 550-700 ppm, the addition amount of the first slow-release deoxidizer is 2.0-2.2 kg per ton of steel;

when the final oxygen content is more than or equal to 700ppm, the addition amount of the first slow-release deoxidizer is 2.2-2.5 kg per ton of steel.

6. The method of modifying ultra-low carbon steel refinery slag according to claim 1, wherein the second slow-release deoxidizer is added to the surface of the molten decarburization steel in an amount of 0.5 to 1.3 kg/ton based on the oxygen content of the molten decarburization steel, and comprises:

when the oxygen content of the decarbonized steel liquid is less than or equal to 200ppm, the addition amount of the second slow-release deoxidizer is 0.5-0.7 kg per ton of steel;

when the oxygen content of the decarbonized steel liquid is 200-350 ppm, the addition amount of the second slow-release deoxidizer is 0.7-0.9 kg per ton of steel;

when the oxygen content of the decarbonized steel liquid is 350-500 ppm, the addition amount of the second slow-release deoxidizer is 0.9-1.1 kg per ton of steel;

when the oxygen content of the decarbonized steel liquid is more than or equal to 500ppm, the addition amount of the second slow-release deoxidizer is 1.1-1.3 kg per ton of steel.

7. The method for modifying ultra-low carbon steel refinery slag according to claim 1, wherein said second slow-release deoxidizer is added to said molten decarburization steel at a waiting position of a cast slab.

8. The method for modifying ultra-low carbon steel refinery slag according to claim 7, wherein a rotary distributor and said ladle roaster are installed in said waiting position, and said second slow-release deoxidizer is added on the surface of the slag by using the rotary distributor according to the oxygen content of the obtained decarburized molten steel.

9. The method for modifying ultra-low carbon steel refinery slag as claimed in claim 1, wherein secondary slagging is carried out by covering steel ladle and heating slag surface by combustion of coke oven gas, wherein gas flow rate is 200-400 m during secondary slagging³The flow rate of oxygen is 150-300 m³The oxygen/fuel ratio is controlled in terms of complete combustion.

10. The method for modifying ultra-low carbon steel refining slag according to claim 1, wherein the ultra-low carbon steel is an ultra-low carbon steel with a finished carbon content of 0.0020 to 0.0010%; the method is suitable for 150-350 t large steel ladles.

Technical Field

The invention relates to the technical field of steel making, in particular to a method for modifying ultra-low carbon steel refining slag.

Background

In the RH vacuum refining process of the ultra-low carbon steel, oxygen in molten steel is required to be decarburized, so that the molten steel is not deoxidized in the tapping process, and the oxygen content in the molten steel is usually 300-800 ppm. Meanwhile, the oxidability of the slag is high, the content of FeO is 8-15%, and after the molten steel is subjected to Al deoxidation after decarburization is completed, oxygen in the slag can be continuously transferred to the molten steel, so that the cleanliness of the molten steel is influenced.

In order to reduce the transfer of oxygen in the slag to molten steel, a traditional converter after-furnace slag modification process is developed, and a slow-release deoxidizer is added to the slag surface in the tapping process or after tapping to reduce the oxidability of the slag. However, in the RH decarburization process, because the oxygen potential of the molten steel is higher than that of the slag, the molten steel flows circularly, so that the oxygen is transferred to the slag by the molten steel, the oxidability of the slag is increased, and the oxygen is transferred to the molten steel by the slag after deoxidation. Although some enterprises add the slow-release deoxidizer again on the slag surface after finishing RH to carry out secondary slag modification, the slag surface temperature is low, the slag melting effect of the slow-release deoxidizer added secondarily is poor, and a large amount of unmelted slow-release deoxidizer exists on the slag surface, so that the slag components are uneven, and the secondary modification effect is poor.

The prior patent CN107858474B of the applicant relates to a method for controlling the oxidability and adsorbability of ultra-low carbon steel slag, which comprises the following steps: slag stopping and tapping are adopted during converter smelting, the tapping time is controlled to be 4-6 minutes, and the thickness of a slag layer is controlled to be less than or equal to 80 mm; adding lime and fluorite in the converter tapping process; performing on-line bottom blowing argon in the converter tapping process, and closing bottom blowing when the converter tapping is finished; closing bottom blowing, and adding a first high-calcium aluminum slag ball to the slag surface after the slag surface is calm; covering a steel ladle after the first high-calcium aluminum slag ball is added, and carrying out RH refining on the steel ladle; in the RH refining process, taking a slag sample after decarburization is finished, analyzing components and content of the slag, and measuring the content of dissolved oxygen in the molten steel; and adding a second high-calcium aluminum slag ball and lime or bauxite into the slag surface after finishing the RH refining, and covering the steel ladle. Although the method can reduce the oxidability of the ultra-low carbon steel slag and improve the adsorbability of the ultra-low carbon steel slag, the slag melting effect is not ideal in the process of long-term use by the applicant.

Therefore, the development of a method for modifying ultra-low carbon steel refining slag can reduce the oxidability of the ultra-low carbon steel slag and further improve the secondary slagging effect, and becomes a key problem for the research of metallurgical workers.

Disclosure of Invention

The invention aims to provide a method for modifying ultra-low carbon steel refining slag, which can stably control the oxidability of the ultra-low carbon steel slag and greatly improve the slag melting effect.

In order to accomplish the above objects, the present invention provides a method for upgrading ultra-low carbon steel refinery slag, the method comprising:

measuring the end point oxygen content of the converter molten steel;

tapping the converter molten steel to obtain tapped molten steel, and adding small-particle lime of 2-4 kg/ton steel into the converter molten steel according to the end point oxygen content in the tapping process;

adding 1.5-2.5 kg/ton of first slow-release deoxidizer into the slag surface of the molten steel to obtain molten steel containing first modified slag according to the end-point oxygen content;

performing decarburization treatment on the molten steel containing the first modified slag to obtain decarburization molten steel;

and measuring the oxygen content of the decarburized molten steel, adding 0.5-1.3 kg/ton of second slow-release deoxidizer to the slag surface of the decarburized molten steel according to the oxygen content of the decarburized molten steel, and covering a steel ladle to obtain the modified ultra-low carbon steel refining slag.

Further, the mass fraction of the metal aluminum in the first slow-release deoxidizer is 55-65%; the mass fraction of the metal aluminum in the second slow-release deoxidizer is 40-50%.

Further, when the steel tapping amount is 1/5-1/3 in the converter steel tapping process, adding small-particle lime of 2-4 kg/ton steel according to the terminal oxygen content per ton steel; the particle size of the small lime particles is less than 500 mm.

Further, according to the end point oxygen content, a first slow release deoxidizer of 1.5-2.5 kg/ton steel is added to the slag surface of the molten steel, and the first slow release deoxidizer comprises:

when the end point oxygen content is less than or equal to 400ppm, the addition amount of the small-particle lime is 2.0-2.5 kg per ton of steel;

when the end point oxygen content is 400-550 ppm, the addition amount of the small lime particles is 2.5-3.0 kg per ton of steel;

when the end point oxygen content is 550-700 ppm, the addition amount of the small lime particles is 3.0-3.5 kg per ton of steel;

and when the final oxygen content is more than or equal to 700ppm, the addition amount of the small lime particles is 3.5-4.0 kg per ton of steel.

Further, according to the end point oxygen content, a first slow release deoxidizer of 1.5-2.5 kg/ton steel is added to the slag surface of the molten steel, and the first slow release deoxidizer comprises:

when the end-point oxygen content is less than or equal to 400ppm, the addition amount of the first slow-release deoxidizer is 1.5-1.8 kg per ton of steel;

when the final oxygen content is 400-550 ppm, the addition amount of the first slow-release deoxidizer is 1.8-2.0 kg/ton of steel;

when the end-point oxygen content is 550-700 ppm, the addition amount of the first slow-release deoxidizer is 2.0-2.2 kg per ton of steel;

when the final oxygen content is more than or equal to 700ppm, the addition amount of the first slow-release deoxidizer is 2.2-2.5 kg/ton of steel.

Further, adding a second slow-release deoxidizer of 0.5-1.3 kg/ton steel to the slag surface of the decarburized molten steel according to the oxygen content of the decarburized molten steel, wherein the second slow-release deoxidizer comprises:

when the oxygen content of the decarbonized steel liquid is less than or equal to 200ppm, the addition amount of the second slow-release deoxidizer is 0.5-0.7 kg per ton of steel;

when the oxygen content of the decarbonized steel liquid is 200-350 ppm, the addition amount of the second slow-release deoxidizer is 0.7-0.9 kg per ton of steel;

when the oxygen content of the decarbonized steel liquid is 350-500 ppm, the addition amount of the second slow-release deoxidizer is 0.9-1.1 kg per ton of steel;

when the oxygen content of the decarbonized steel liquid is more than or equal to 500ppm, the addition amount of the second slow-release deoxidizer is 1.1-1.3 kg per ton of steel.

Further, the second slow-release deoxidizer is added into the decarburization molten steel at a casting blank waiting position.

And further, a rotary distributor and the steel ladle roaster are additionally arranged at the waiting position, the second slow-release deoxidizer is added on the slag surface of the steel ladle by adopting the rotary distributor according to the oxygen content of the obtained decarburized molten steel, and the steel ladle roaster is adopted by covering the steel ladle.

Further, covering a steel ladle, and heating the slag surface by using coke oven gas combustion to carry out secondary slagging, wherein in the secondary slagging process, the gas flow is 200-400 m³The flow rate of oxygen is 150-300 m³The oxygen/fuel ratio is controlled in terms of complete combustion.

Further, the ultra-low carbon steel is an ultra-low carbon steel grade with the finished product carbon content of 0.0020-0.0010%; the method is suitable for 150-350 t large steel ladles.

The decarburization treatment of the present invention is generally referred to as RH refining; the oxygen content of the decarbonized molten steel is the oxygen content of the decarbonized molten steel.

The terms "first", "second", and the like used in the present invention do not denote order, and may be understood as nouns.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

the invention provides a method for modifying ultra-low carbon steel refining slag, which dynamically controls the adding amount of small-particle lime and a first slow-release deoxidizer through the end-point oxygen content after a converter is started; according to the oxygen content of the decarburized molten steel, the adding amount of the second slow-release deoxidizer is dynamically controlled, the modification effect is improved, and the consumption of the modifier is reduced. Meanwhile, after a second slow-release deoxidizer is added, the ladle roaster is lowered, and the slag surface is heated by using the combustion of coke oven gas, so that the effect of modifying secondary slag is promoted. By adopting the method, the FeO content in the refining slag can be stably controlled below 3 percent after RH is finished, thereby effectively reducing oxygen transmission from the slag to the molten steel and improving the cleanliness of the molten steel.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

FIG. 1 is a flowchart of a method for upgrading ultra-low carbon steel refinery slag according to an embodiment of the present invention.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.

Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, 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 invention belongs. If there is a conflict, the present specification will control.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

In order to solve the technical problems, the embodiment of the invention provides the following general ideas:

to achieve the above objects, the present embodiment provides a method for modifying ultra-low carbon steel refining slag, comprising:

step 1, when the steel tapping amount is 1/5-1/3 in the converter steel tapping process, adding small-particle lime in a graded manner according to the end point oxygen content of converter molten steel:

when the end point oxygen content is less than or equal to 400ppm, the addition amount of the small-particle lime is 2.0-2.5 kg per ton of steel;

when the end point oxygen content is 400-550 ppm, the addition amount of the small lime particles is 2.5-3.0 kg per ton of steel;

when the end point oxygen content is 550-700 ppm, the addition amount of the small lime particles is 3.0-3.5 kg per ton of steel;

and when the final oxygen content is more than or equal to 700ppm, the addition amount of the small lime particles is 3.5-4.0 kg per ton of steel.

According to the invention, the addition amount of the small-particle lime is controlled in a stepped manner through the end-point oxygen content, so that the phosphorus and phosphorus removal effect is good, the oxygen content in the molten steel is not too low, and the RH decarburization difficulty is reduced. In the step, small-particle lime is added to dephosphorize and dephosphorize; if the addition amount of the small lime is too low, the phosphorus and phosphorus content in the top slag is still higher, and if the addition amount of the small lime is too high, Ca in the small lime reacts with oxygen in the molten steel, so that the oxygen content in the molten steel is too low, and the RH decarburization difficulty is increased.

First, the addition of small particle lime solves the problem of desulfurization. According to the invention, small-particle lime is added when the steel tapping amount is 1/5-1/3, so that slag, molten steel and small-particle lime can be fully mixed by utilizing the impact of steel flow in the steel tapping process, and the desulfurization efficiency is improved:

the small lime particles are alkaline oxides to generate O, and the O in the slag is increased^2-The concentration is increased, so that the slag alkalinity is increased to facilitate desulfurization. If small particle limeToo little addition of O in the slag^2-The concentration is reduced, the desulphurization is not facilitated, meanwhile, because the molten steel requires certain oxygen content to complete the decarburization reaction, according to the C-O balance, the O content is low, the C content at the end point of the converter is higher, the RH decarburization pressure can be increased, and because the RH decarburization capability is limited; if the small lime is added too much, O in the slag^2-The concentration is increased, and according to C-O balance, the high O content can add a large amount of Al deoxidation in the RH process, so that Al is caused₂O₃The inclusion is increased.

Secondly, the addition of small-particle lime can solve the dephosphorization problem. Phosphorus is an important harmful element in steel, the outstanding harm of phosphorus to steel is cold brittleness, the phosphorus can obviously reduce the toughness of steel, particularly the tempering toughness and the impact toughness, and the toughness is obviously deteriorated under the low-temperature condition.

When the FeO in the converter smelting is very low, lime can not be well melted, and obviously dephosphorization can not be carried out; however, if (FeO) is too high, dephosphorization of (CaO) will be diluted. Because the molten steel requires certain oxygen content to complete decarburization reaction, certain (FeO) can be obtained from furnace slag by utilizing the balance relation of steel slag, a certain amount of small-particle lime is added into a steel ladle to ensure the alkalinity of slag particles in the steel ladle, favorable conditions for dephosphorization are formed in a converter steel tapping steel ladle, meanwhile, the impact of steel flow on the liquid level of the steel ladle and the stirring of low argon blowing of the steel ladle on the molten steel in the steel ladle are added, and a gas-liquid system fluid flow behavior is formed in the steel ladle to promote chemical reaction inside the molten steel formed in the steel ladle, so that the effect of dephosphorization in the steel ladle in the molten steel tapping process is achieved. Ideally, the chemical reaction formula of dephosphorization of molten steel in the ladle is shown as formula (1) -formula (4):

2[P]+5[O]＝(P₂O₅) (1)

(P₂O₅)+4(CaO)＝(CaO.P₂O₅) (2)

[O]+[Fe]＝(FeO) (3)

2[P]+5[FeO]+4(CaO)＝(4CaO.P₂O₅)+5[Fe](4)

CaO is P₂O₅The main factor of the reduction, increasing (CaO) to saturation content, can increase CaO (alkalinity) also increases the concentration of free CaO (not bound to acidic oxides) and causes P₂O₅Improvement of or steel [ P ]]. If the small-particle lime is added too much, the slag becomes thick due to the excessive CaO in the slag, and the dephosphorization capability of the slag is reduced. If the addition amount of the small lime particles is too small, the dephosphorization effect cannot be well achieved.

The reason why the small-sized lime is added in a stepwise manner according to the terminal oxygen content in the embodiment of the invention is to synthesize the analysis, and dynamically control the addition amount of the small-sized lime according to different terminal oxygen contents, so that the problems of desulfurization and dephosphorization are successfully solved, and the oxygen content in the molten steel is appropriate, thereby ensuring RH decarburization.

Step 2, after tapping, closing ladle bottom blowing, and adding a first slow-release deoxidizer of 1.5-2.5 kg/ton steel on a ladle slag surface in a stepped manner by adopting a rotary distributor according to the end point oxygen content:

when the end-point oxygen content is less than or equal to 400ppm, the addition amount of the first slow-release deoxidizer is 1.5-1.8 kg per ton of steel;

when the final oxygen content is 400-550 ppm, the addition amount of the first slow-release deoxidizer is 1.8-2.0 kg/ton of steel;

when the end-point oxygen content is 550-700 ppm, the addition amount of the first slow-release deoxidizer is 2.0-2.2 kg per ton of steel;

when the final oxygen content is more than or equal to 700ppm, the addition amount of the first slow-release deoxidizer is 2.2-2.5 kg/ton of steel.

The first slow-release deoxidizer contains 55 to 65 percent of metallic aluminum; aims to reduce the oxidability of the steel ladle top slag and ensure the proper oxygen content in the molten steel, thereby ensuring the RH decarburization. If the content of the metallic aluminum is less than 55 percent, the oxidability of the ladle top slag cannot be well reduced; if the content of the metallic aluminum is more than 65%, the content of oxygen in the molten steel is too low, and the difficulty of RH decarburization is increased.

Because the high content of the ladle slag (FeO) can influence the purity of the molten steel, influence the purity of the molten steel and influence the yield of the alloy. Therefore, after tapping is finished, the first slow-release deoxidizer is added to the surface of the ladle in a certain amount, and the first slow-release deoxidizer has the following effects:

on one hand, the first slow-release deoxidizer is added to reduce the content of FeO in ladle slag so as to eliminate FeO introduced by the increase of the amount of the ladle slag caused by tapping in formula (5);

on the other hand, Al in the first slow-release deoxidizer and FeO in the ladle top slag are subjected to reduction reaction to generate Al₂O₃Then combined with CaO in the slag and slag charge and small-sized lime which is not completely reacted to generate 3CaO & Al with lower melting point₂O₃Or 12CaO 7Al₂O₃Further reducing the oxidability of the ladle top slag and preventing the increase of the dissolved oxygen in the subsequent refining process, see formula (5) and formula (6).

3(FeO)+2Al→(Al2O₃)+3[Fe](5)

12(CaO)+7(Al₂O₃)→(12CaO·7Al₂O₃) (6)

From the analysis, it is important to know how to add the first slow-release deoxidizer according to the end-point oxygen content, and the embodiment of the invention adds the first slow-release deoxidizer step by step, so that the oxidability of the steel ladle top slag can be reduced, and the oxygen content in the molten steel is appropriate, thereby ensuring RH decarburization. If the first slow-release deoxidizer is added too little, the oxidability of the ladle top slag cannot be well reduced; if the first slow-release deoxidizer is added too much, the oxygen content in the molten steel is too low, and the difficulty of RH decarburization is increased.

And 3, obtaining decarburized molten steel after RH refining is empty, driving the ladle car out of a vacuum treatment position to a waiting position, additionally installing a ladle roaster and a rotary distributor at the waiting position, and adopting a rotary distributor to add a second slow-release deoxidizer on the slag surface of the ladle in a stepped manner according to the oxygen content of the decarburized molten steel (namely the oxygen content before RH aluminum addition):

when the oxygen content of the decarbonized steel liquid is less than or equal to 200ppm, the addition amount of the second slow-release deoxidizer is 0.5-0.7 kg per ton of steel;

when the oxygen content of the decarbonized steel liquid is 200-350 ppm, the addition amount of the second slow-release deoxidizer is 0.7-0.9 kg per ton of steel;

when the oxygen content of the decarbonized steel liquid is 350-500 ppm, the addition amount of the second slow-release deoxidizer is 0.9-1.1 kg per ton of steel;

when the oxygen content of the decarbonized steel liquid is more than or equal to 500ppm, the addition amount of the second slow-release deoxidizer is 1.1-1.3 kg per ton of steel.

The oxygen content of the decarbonized steel liquid in the invention is the oxygen content of the decarbonized molten steel.

The second slow-release deoxidizer contains 40-50% of metallic aluminum. Aims to reduce the oxidability of the steel ladle top slag and ensure the proper oxygen content in the molten steel, thereby ensuring the RH decarburization. If the content of the metallic aluminum is less than 40 percent, the oxidability of the ladle top slag cannot be well reduced; if the content of the metallic aluminum is more than 50 percent, the oxygen content in the molten steel is too low, and the difficulty of RH decarburization is increased. The amount of the second slow-release deoxidizer containing the metallic aluminum is less than that of the first slow-release deoxidizer containing the metallic aluminum, because the oxidation of the top slag of the steel ladle is greatly reduced by adding the first slow-release deoxidizer, and the oxidation of the slag is increased if the amount of the second slow-release deoxidizer containing the metallic aluminum is too high.

In the step, after RH refining is broken, the second slow-release deoxidizer is added according to the oxygen content of the decarburized steel liquid, and because the oxygen potential during converter tapping depends on Al generated by aluminum deoxidation₂O₃The slag can meet the requirement of slagging when entering the furnace slag; the second slow-release deoxidizer with proper amount is added to reduce the deoxidation product Al₂O₃The generation of impurities improves the cleanliness of molten steel. The second slow-release deoxidizer is added on the slag surface of the steel ladle by adopting a rotary distributor, so that the reaction is quicker and more uniform; the key is how to add the second slow-release deoxidizer according to the oxygen content of the decarbonized steel liquid, if the second slow-release deoxidizer is added too little, the oxygen potential is too low to meet the requirement of slagging; if too much second slow-release deoxidizer is added, the oxidation of the slag is increased. The embodiment of the invention further adopts a method of adding the second slow-release deoxidizer step by step according to the oxygen content of the decarburized steel liquid, so that the Al content in the slag can be improved₂O₃Without causing an increase in the oxidizability of the slag.

Step 4, reducing after adding the second slow-release deoxidizerThe ladle roaster arranged on the waiting position heats the slag surface by utilizing the combustion of coke oven gas, thereby promoting the effect of modifying secondary slag; the step is combined with the step 1-3, and the slag surface is heated by utilizing the combustion of the coke oven gas, so that the secondary slag modification effect is greatly improved. Preferably, in the secondary slagging process, the gas flow is 200-400 m³The flow rate of oxygen is 150-300 m³The oxygen/fuel ratio is controlled in terms of complete combustion. If the gas flow is less than 200m³The heat quantity of the coke oven gas during combustion and heating is insufficient, so that the secondary slag modification effect is poor; if the gas flow is more than 400m³The oxygen demand of the coke oven gas combustion increases and the cost is increased; oxygen blowing amount is the oxygen amount required for complete combustion, and if the oxygen flow rate is less than 150m³The flow rate of oxygen is more than 300m³The heat quantity is too high, the cost is increased, residual oxygen exists in the slag, the slag transfers oxygen to molten steel, and the cleanliness of the molten steel is reduced.

From the above, it can be seen that the method for modifying ultra-low carbon steel refining slag provided by the invention is based on the mutual cooperation of the steps 1-4: after the converter is started, dynamically controlling the addition of the small-particle lime and the first slow-release deoxidizer according to the end-point oxygen content; after RH is finished, the adding amount of the second slow-release deoxidizer is dynamically controlled according to the oxygen content of the liquid decarbonization steel, so that the modification effect is improved, and the consumption of the modifier is reduced. Meanwhile, after a second slow-release deoxidizer is added, the ladle roaster is lowered, and the slag surface is heated by using the combustion of coke oven gas, so that the effect of modifying secondary slag is promoted. By adopting the method, the oxidability of the ultra-low carbon steel slag can be stably controlled, and the slag melting effect is greatly improved. After RH is finished, the FeO content in the refining slag can be stably controlled below 5%, so that oxygen transmission from the slag to molten steel is effectively reduced, and the cleanliness of the molten steel is improved.

Hereinafter, a method for upgrading ultra low carbon steel refining slag according to the present application will be described in detail with reference to examples, comparative examples and experimental data.

The following examples and comparative examples all used cast steel grades as high grade pipeline steel SDC06, the main components of which are shown in Table 1.

TABLE 1 main component/% of test steel

Finished component C	Finished product ingredient Si	Finished component Mn	Finished component P	Finished product ingredient S	Finished product ingredient Alt
						0.0013	0.01	0.14	0.011	0.006	0.035

Adding small-particle lime of 2-4 kg/ton steel according to the end point oxygen content when the steel tapping amount is 1/5-1/3 in the converter steel tapping process; after tapping, closing ladle bottom blowing, and adding a slow-release deoxidizer of 1.5-2.5 kg/ton steel on the slag surface of the ladle by adopting a rotary distributor according to the end-point oxygen content; after RH refining is broken, the ladle car is driven out of a vacuum treatment position to a waiting position, a ladle roaster and a rotary distributor are additionally arranged at the waiting position, and a slow-release deoxidizer of 0.5-1.3 kg/ton steel is added on the slag surface of the ladle by the rotary distributor according to the oxygen content of the decarbonized steel liquid; after the slow release deoxidizer is added, the ladle roaster is lowered, the slag surface is heated by utilizing the combustion of coke oven gas, the effect of secondary slag modification is promoted, and the process parameters of each group are shown in table 2.

TABLE 2 Process parameters for each group

Wherein the steps of comparative example 1 are the same as those of example 3 except that the ladle roaster installed at the waiting position is not lowered in the secondary slagging process; comparative example 2 the same procedure as in example 3 was repeated except that the first slow-release deoxidizer was not added; comparative example 3 the procedure of example 3 was followed except that the second sustained-release deoxidizer was not added.

In examples 1 to 4 and comparative examples 1 to 2, immediately after completion of RH, a slag sample was taken and subjected to automatic rapid analysis of the slag, and the results of the measurement of dissolved oxygen in molten steel were shown in the oxygen content in decarburized steel liquid in Table 2, and the results of the analysis of each group were shown as the results of SiO analysis of the slag₂Content, MgO content, Feot content, CaO content, and Al₂O₃The contents are shown in Table 3.

TABLE 3

Lowering the ladle roaster for secondary slagging after adding 0.5-1.3 kg/ton steel slow-release deoxidizer after finishing RH, analyzing the slag after secondary slagging, and analyzing the Feot content, CaO content and Al content of the slag according to the analysis results of each group₂O₃The contents are shown in Table 4.

TABLE 4

As can be seen from tables 3 to 4, the Feot content in the final steel slag of examples 1 to 4 of the present invention was greatly reduced as compared with comparative examples 1 to 2; the slag melting effect of the embodiments 1 to 4 of the invention is better.

In summary, according to the method for modifying ultra-low carbon steel refining slag provided by the invention, after a converter is started, the addition amount of small-particle lime and a first slow-release deoxidizer is dynamically controlled according to the final oxygen content; after RH is finished, the adding amount of the second slow-release deoxidizer is dynamically controlled according to the oxygen content of the liquid decarbonization steel, so that the modification effect is improved, and the consumption of the modifier is reduced. Meanwhile, after a second slow-release deoxidizer is added, the ladle roaster is lowered, and the slag surface is heated by using the combustion of coke oven gas, so that the effect of modifying secondary slag is promoted. By adopting the method, the FeO content in the refining slag can be stably controlled below 3 percent after RH is finished, thereby effectively reducing oxygen transmission from the slag to the molten steel and improving the cleanliness of the molten steel.

Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.