CN111172353A

CN111172353A - Method for controlling cleanliness of molten steel and smelting control method for preventing nozzle nodulation in pouring process of sulfur-containing aluminum-containing steel

Info

Publication number: CN111172353A
Application number: CN202010008206.4A
Authority: CN
Inventors: 曾令宇; 张波; 余大华; 余衍丰; 张志明; 刘志龙; 刘志明; 胡现锋; 赵科; 黄继利; 覃小锋; 任世岗; 徐忠; 孙忠权; 周楠; 敖永明; 黎莉; 余雷
Original assignee: SGIS Songshan Co Ltd
Current assignee: SGIS Songshan Co Ltd
Priority date: 2020-01-03
Filing date: 2020-01-03
Publication date: 2020-05-19

Abstract

A method for controlling the cleanliness of molten steel and a smelting control method for preventing nozzle nodulation in the pouring process of sulfur-containing and aluminum-containing steel, belonging to the smelting field. The method for controlling the cleanliness of molten steel comprises the following steps. Smelting the blast furnace molten iron without desulfurization in a converter, and carrying out deoxidation, alloying and tapping slag washing in sequence to remove impurities when the converter taps. Refining the converter tapping by an LF furnace under the condition of not adjusting acid-soluble aluminum. Namely, a slagging agent is added in the tapping to control the composition of the refining slag, and the refining slag is deoxidized by a deoxidizer after the slag is melted. The above process monitors the sulfur content in the molten steel and adjusts the sulfur content of the molten steel to a first target value with ferrosulfur. Refining the LF furnace steel by using an RH furnace, and optionally feeding aluminum according to the acid-soluble aluminum content of the LF furnace steel in the process to adjust the aluminum content to a second target value. And performing calcium treatment after finishing the RH furnace refining. The process improves the purity of the molten steel, avoids the problem of nodulation when the molten steel is poured, and can also control the rising of a stopper rod curve.

Description

Method for controlling cleanliness of molten steel and smelting control method for preventing nozzle nodulation in pouring process of sulfur-containing aluminum-containing steel

Technical Field

The application relates to the field of smelting, in particular to a method for controlling cleanliness of molten steel and a smelting control method for preventing nozzle nodulation in a pouring process of sulfur-containing aluminum-containing steel.

Background

The smelting process for smelting sulfur-containing and aluminum-containing steel is the key to ensure the stable stopper curve of molten steel in the pouring process. If the smelting process is unreasonable, the purity of the molten steel is poor, so that the nozzle nodulation of the molten steel in the casting process is serious, the stopper rod curve obviously rises, the nozzle nodulation falls off in the casting process, and the defect of macroscopic inclusion is generated, which is a defect that the molten steel for automobiles is not allowed to exist. Therefore, how to effectively control the cleanliness of molten steel and avoid the rising of a stopper curve during pouring becomes a difficult problem to be solved urgently by practitioners in the industry.

The inventors have found that some of the existing practices for controlling nodules present problems to varying degrees.

For example, molten steel is smelted by a converter or an electric furnace, refined in an LF ladle, and deoxidized in a ladle furnace by using aluminum particles and calcium carbide. The composition of the slag from the refining station comprises the following components in percentage by mass: CaO 50-60%, MgO 4-7%, SiO₂10 to 14 percent of Al₂O₃22 to 28 percent, the T.Fe content is less than 1.5 percent, and the sulfur content is 0.2 to 0.6 percent; the content of the refined product in the later stage is 1.0-2.4%.

The method uses aluminum particles and calcium carbide for deoxidation, and uses high alkalinity and high Al for refining final slag₂O₃And (4) content refining slag composition. And carrying out calcium treatment on the molten steel in an LF furnace, and adjusting the sulfur content. The yield of sulfur is low and unstable, the sulfur needs to be adjusted for many times, and the waste of alloy cost is large. The slag reacts violently with the ferrous sulfate powder added at the last stage of ladle refining, so that oxygen in the slag is transferred to steel and further reacts with Al in molten steel to generate a large amount of Al₂O₃And (4) inclusion.

After the RH furnace treatment is finished, the floating removal of the inclusion is promoted through soft blowing control, the inclusion in the molten steel cannot be completely removed, the quality of the molten steel is not pure, and the plug rod curve is easy to obviously rise.

In another practice, molten steel is smelted by a converter, and is added in the refining process of an LF furnaceAdding active lime, fluorite and aluminum pills to make refined slag. The refining slag comprises the following components in percentage by weight: 42-48% of CaO and SiO₂10 to 15% of Al₂O₃20-25%, MgO 8-12%, FeO + MnO 0.3-0.8%, CaF₂2-5%, the alkalinity of refining slag is 2.5-4.0, and the later stage of LF refining is to feed calcium silicate wires into molten steel by 0.8-1.2 m/ton;

adjusting sulfur in the RH furnace process, and carrying out soft blowing on the mixture to a casting machine for casting. The treatment method uses high alkalinity and high Al₂O₃Content refining slag system. And (3) carrying out calcium treatment on the molten steel after the LF furnace treatment is finished, deforming the impurities, adjusting the sulfur content in an RH furnace, and finishing the soft blowing after the vacuum treatment.

The control stability of the content of sulfur and sulfur is poor when the RH treatment of the process is finished, the sulfur reacts with the slag violently in the sulfur increasing process, a large amount of oxygen in the slag enters the steel and reacts with Al in the steel to generate a large amount of Al₂O₃The inclusions are difficult to float upward and be removed by short-time soft blowing. The stopper rod rises obviously during the pouring process.

Disclosure of Invention

Based on the defects, the application provides a method for controlling the cleanliness of molten steel and a smelting control method for preventing nozzle nodulation in the pouring process of sulfur-containing aluminum-containing steel, so as to partially or completely improve and even solve the problems of low molten steel cleanliness and easiness in nozzle nodulation in the related technology.

The application is realized as follows:

in a first aspect, examples of the present application provide a method of controlling cleanliness of molten steel that can be used to make sulfur-containing, aluminum-containing steels to inhibit the problem of accretion during the pouring of the molten steel.

The method for controlling the cleanliness of the molten steel comprises the following steps:

the blast furnace molten iron is sent into a converter for smelting without desulfurization pretreatment, and deoxidation, alloying and slag washing are sequentially carried out when the converter taps.

And carrying out primary refining treatment on converter tapping through an LF (ladle furnace) under the condition of not adjusting acid-soluble aluminum. Wherein the first refining process comprises: adding a slagging agent to control the composition of refining slag in the converter tapping, deoxidizing by a deoxidizing agent after the slag is melted, monitoring the sulfur content in molten steel in the first refining treatment process, and adjusting the sulfur content of the molten steel to a first target value by ferrosulfur.

And carrying out secondary refining treatment on the LF furnace steel tapping by using the RH furnace, and optionally feeding aluminum according to the acid-soluble aluminum content of the LF furnace steel tapping in the secondary refining treatment process to adjust the aluminum content of the molten steel to a second target value.

And performing calcium treatment after finishing the RH furnace refining.

With reference to the first aspect, in a first possible embodiment of the first aspect of the present application, the deoxidizer used in the first refining treatment step is a slag surface deoxidizer.

In combination with the first possible embodiment of the first aspect, in a second possible embodiment of the first aspect of the present application, the slag surface deoxidizing agent includes a single-component deoxidizing agent and a multi-component deoxidizing agent.

Optionally, the single-component deoxidizer comprises 70 silicon carbide, the multi-component deoxidizer comprises calcium carbide, aluminum particles and synthetic slag, and the mass ratio of the total mass of the calcium carbide, the aluminum and the synthetic slag to the mass of the 70 silicon carbide is 0.5-2.

With reference to the first aspect, in a third possible implementation manner of the first aspect of the present application, the first refining process further includes any one or more of the following definitions:

I) and the converter tapping is transferred to the LF furnace without adding fluorite and fluorite balls.

II) the slagging agent comprises lime and slag charge with alkalinity of 0.5, and the mass ratio of the lime to the slag charge is 0.5-0.8.

III) the alkalinity of the refining slag is 1.5 to 3.0, and the components in percentage by mass are as follows: 42-48% of CaO and 20-30% of SiO₂10-20% of Al₂O₃3-8% of MgO, and the sum of TFe and MnO is less than or equal to 1.5%.

With reference to the first aspect, in a fourth possible implementation manner of the first aspect of the present application, a method includes: and soft blowing treatment is carried out after the calcium treatment.

In a fifth possible embodiment of the first aspect of the present application in combination with the first aspect, in the steps of deoxidation, alloying and slag washing at the time of tapping from the converter, the deoxidation is performed by adding ferroaluminum to the molten steel for refining.

In a sixth possible embodiment of the first aspect of the present application in combination with the first aspect, in the steps of deoxidizing, alloying, and slag washing at the time of tapping from the converter, the alloying is performed by refining by adding ferro-aluminum, a carburant, ferrosilicon, ferro-silico-ferromanganese, low-carbon ferrochrome, and high-carbon ferrochrome to the molten steel.

With reference to the first aspect or the fifth or sixth possible embodiment of the first aspect, in a seventh possible embodiment of the first aspect of the present application, in the deoxidizing, alloying, and slag washing step at the time of tapping from the converter, the inclusion removal treatment includes adding slag lime and synthetic slag to the molten steel for refining.

Optionally, the amount of the slag material lime is 2-3 kg/ton of molten steel, and the amount of the synthetic slag is 2-3 kg/ton of molten steel.

With reference to the seventh possible embodiment of the first aspect, in an eighth possible embodiment of the first aspect of the present application, the deoxidation, alloying and inclusion removal treatment at converter tapping includes:

adding aluminum iron when the converter tapping amount reaches 1/4.

Adding carburant, ferrosilicon, ferro-silico-manganese, low-carbon ferromanganese, low-carbon ferrochrome and high-carbon ferrochrome when the steel output of the converter reaches 1/3.

When the steel tapping amount of the converter reaches 3/4, slag charge lime and synthetic slag are added.

In a second aspect, examples of the present application provide a smelt control method for preventing nozzle clogging during a casting process of a sulfur-containing, aluminum-containing steel.

The smelting control method comprises the following steps:

smelting the blast furnace molten iron without desulfurization pretreatment by using a converter, and controlling the carbon content of the smelting end point of the converter to be lower than the target carbon content of the sulfur-containing and aluminum-containing steel.

Carrying out slagging treatment in the converter tapping process, wherein the slagging treatment comprises a deoxidation step, an alloying step and a slagging agent adding step, the deoxidation step comprises adding aluminum iron when the converter tapping reaches 1/4 volume of the converter, the alloying step comprises adding an alloying reagent to control the content of target elements of molten steel within a preset range when the converter tapping reaches 1/3 volume of the converter, and the slagging agent adding step comprises adding slag charge lime and synthetic slag when the converter tapping reaches 3/4 volume of the converter.

Feeding molten steel tapped from a converter into an LF furnace without adding fluorite or fluorite balls, refining under the conditions of monitoring the sulfur content of the molten steel and supplementing ferrosulfur to obtain outbound molten steel with the expected sulfur content and acid-soluble aluminum content, wherein the refining method comprises the step of adding lime and low-alkalinity slag with alkalinity of 0.5 into the molten steel to form CaO with the alkalinity of 1.5-3.0 and the components of CaO of 42-48% and SiO of 20-30%₂10-20% of Al₂O₃And 3-8% of MgO, and less than or equal to 1.5% of TFe + MnO, and then adding a composite deoxidizer and 70 silicon carbide for deoxidation.

Transferring the outbound molten steel of the LF furnace to an RH furnace for refining, wherein the refining method comprises the following steps: when the molten steel arrives at a station, the acid-soluble aluminum content is controlled by feeding aluminum, then vacuum treatment is carried out, and pure calcium feeding and soft blowing treatment are carried out after the vacuum treatment is finished so as to lead inclusions to float.

Has the advantages that:

in the implementation process, the method for controlling the cleanliness of the molten steel provided by the embodiment of the application obtains effective control on the cleanliness of the molten steel, so that the problem of accretion in the pouring process of the molten steel obtained by the method is restrained.

Firstly, in the smelting stage (primary smelting) of the converter, the sulfur content of the molten iron in the blast furnace can be ensured to meet the requirement of the final product (sulfur-containing steel and aluminum-containing steel) on the sulfur content without desulfurization pretreatment, and simultaneously, impurities caused by subsequent operations (such as adding more sulfur iron or sulfur iron wires) for adjusting the sulfur content can be avoided, so that the molten steel can be controlled to have relatively better castability. In addition, the tapping is first deoxidized to produce Al by performing the blast furnace molten iron converter smelting in the order of deoxidation, alloying and slag washing₂O₃Adding alloy to ensure the alloy is fully melted, and removing impuritiesCan absorb Al₂O₃Thereby obtaining good deoxidation and inclusion removal effects.

Second, aluminum is an important deoxidizer during the ladle refining stage, which is partially dissolved into the steel during the steelmaking process. This fraction of aluminum is called acid-soluble aluminum because it can be dissolved by acid. The content of acid-soluble aluminum is advantageous in reducing dissolved oxygen in steel and refining the crystal grains of steel, but high acid-soluble aluminum may cause the generation of alumina inclusions during molten steel casting. While calcium is generally selected for suppressing the inclusions to turn them into acid-soluble aluminum, calcium as a desulfurizing agent also causes unnecessary changes and fluctuations in the sulfur content. Therefore, under the condition of not adjusting acid-soluble aluminum, the alkalinity of the slag can be effectively controlled to inhibit the reaction of the acid-soluble aluminum and the slag, and the combined deoxidation, the deoxidization by a deoxidizer and the slagging deoxidation, and the combination of the adjustment of the sulfur content can control the total oxygen and the inclusion in the steel to proper content.

Thirdly, in the vacuum circulation degassing refining stage, the molten steel exists in the form of boiling small liquid drops under vacuum condition and has large degassing surface area, thereby facilitating degassing. In addition, the hot surface of the molten steel in the process is always provided with slag covered on the surface, so the temperature difference is small. The reaction of molten steel and slag is greatly reduced in the stage, and the content of aluminum is stable, so that the adjustment of the content of aluminum in the stage is favorable for controlling the aluminum of the poured steel to reach the expected content, the Als loss in the process is small, and the Al is reduced₂O₃And (4) generating.

Furthermore, calcium is adopted to denature the aluminum oxide inclusions after the vacuum cycle degassing refining is finished, and the problem that a large amount of CaS inclusions are generated by sulfur reaction in steel when calcium is added in other stages can be avoided.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments or the prior art of the present application, the drawings used in the description of the embodiments or the prior art will be briefly described below.

FIG. 1 is a stopper rod curve during the casting preparation of a sulfur-containing, aluminum-containing steel of example 1 of the present application;

FIG. 2 is a stopper rod curve during the casting preparation of a sulfur-containing, aluminum-containing steel of example 2 of the present application;

FIG. 3 is a stopper rod curve during the casting preparation of the sulfur-containing aluminum-containing steel of comparative example 1 of the present application.

Detailed Description

Pig iron is a product obtained by smelting iron ore in a blast furnace, and steel is a product obtained by smelting pig iron (molten iron/liquid pig iron). Both steel and pig iron are iron-based alloys and both contain elements such as carbon, silicon, manganese, sulfur, phosphorus, and the like. One of the main differences between the two is that the carbon content is different, wherein the mass fraction of carbon in pig iron is more than 2%, and the mass fraction of carbon in steel is less than 2%. The steel making is mainly to smelt by various means to reduce carbon in pig iron and remove harmful impurities, and then a proper amount of alloy elements are added according to the requirements on the performance of steel products, so that the steel with excellent performance is obtained. At present, the equipment (steel making furnace) involved in steel making mainly comprises a converter and an electric furnace, and the converter (such as oxygen converter steel making) is the main equipment and development direction.

The main purpose of steel making as described above is to remove part of carbon in pig iron and to remove unnecessary impurity elements and the like in pig iron. Specifically, steel making comprises the steps of removing elements such as carbon, oxygen, phosphorus, sulfur and the like, removing gas and impurities, adjusting the components and content of the elements, and controlling the temperature in the smelting process. In terms of flow, steel making generally mainly includes blast furnace iron making to obtain molten iron, then converter primary smelting is performed on the molten iron, and then external refining/secondary refining is performed. In actual steel making operation, these objects can be partially achieved by means of oxidation, slagging, deoxidation and the like.

Wherein, the oxidation can also realize decarburization to a certain extent, and the generated carbon oxides can play roles of stirring molten steel, homogenizing components and temperature, removing gas and inclusions, providing heat energy and the like. The slag/furnace slag can control the oxidation-reduction reaction process of each element in the molten steel and absorb the non-metallic inclusions in the molten steel. In addition, the slag covers the liquid surface of the molten steel, so that heat loss can be reduced, the molten steel can be prevented from absorbing gas, and the slag can absorb iron and the like evaporated from the molten steel.

Therefore, it is an important topic to be faced by practitioners in the art how to select a smelting process to control the smelting process so as to obtain steel with a target quality.

The present inventors worked on the study of sulfur-containing and aluminum-containing steels. The sulfur-containing aluminum-containing steel is a metal material with large consumption, wide application range and a wide variety. The sulfur-containing and aluminum-containing steel is particularly widely applied to the fields of precision equipment, automobile parts and the like. The sulfur-containing and aluminum-containing steel is generally required to have a sulfur content of 0.010 to 0.050% and an aluminum content or acid-soluble aluminum content of 0.010 to 0.050%. In practice, in the process of manufacturing the sulfur-containing and aluminum-containing steel, aluminum element is added into the steel to refine crystal grains so as to toughen the steel, and sulfur element is added into the steel so as to strengthen the cutting processing performance of the steel. However, the high contents of sulfur and aluminum in steel lead to the generation of a large amount of inclusions such as manganese sulfide and aluminum oxide in the steel during the smelting stage.

In view of the above, the inventors have studied the smelting process of sulfur-containing aluminum-containing steel, and tried to propose a method for controlling the smelting process thereof so as to control the cleanliness of molten steel, thereby being beneficial to suppressing the nozzle clogging problem occurring in the molten steel pouring process. In addition, the nozzle nodulation phenomenon is effectively restrained, so that the rising condition of the stopper rod curve during molten steel pouring is relieved or even eliminated.

Embodiments of the present application will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present application and should not be construed as limiting the scope of the present application. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In the present application, the process proposed by the inventor is given as an example of a method for controlling molten steel cleanliness, a smelting control method for preventing nozzle clogging in a pouring process of sulfur-containing aluminum-containing steel, and the following is specifically described for the above scheme:

a method for controlling molten steel cleanliness applied to a smelting process for manufacturing sulfur-containing aluminum-containing steel comprises the following steps S101 to S104.

And S101, smelting blast furnace molten iron without desulfurization pretreatment in a converter, and sequentially carrying out deoxidation, alloying and slag washing during converter tapping.

In practice, the inventor realizes that if the blast furnace molten iron is subjected to molten iron desulphurization pretreatment, the sulfur content in the molten iron is reduced, so that more sulfur iron needs to be added in the subsequent LF refining process to reach the corresponding sulfur content, and further, impurities caused by alloy entrainment are increased, and the castability of the molten steel is influenced.

In the example, when tapping from a converter, deoxidation is mainly performed by adding a deoxidizer to molten steel. The deoxidizer reacts with oxygen to produce deoxidized products that are insoluble in molten steel and float up from the molten steel, thereby entering the slag. Whereas the addition of the desired ferroalloy or metal to the steel is alloying in order to adjust the content of alloying elements in the steel to achieve the compositional range of the target steel grade specification. Slag washing can remove inclusions, and the inclusions generated in the process are transferred to slag charge from molten steel.

The inventor finds that the sequence of deoxidation, alloying and slag washing (slag washing can remove inclusions) in the smelting process of the converter has a significant influence on the castability of the molten steel. In the example of the application, the molten steel is deoxidized by adding a deoxidizer first, so that the deoxidized product (mainly Al) is obtained₂O₃) As early as possible, adding alloy to ensure the alloy to be fully melted, and then carrying out slag washing. The operation mode of slag washing is as follows: adding lime and synthetic slag, under the action of bottom blowing and stirring during tapping, promoting the melting of slag charge and absorbing deoxidation product Al₂O₃And the aim of improving the purity of the molten steel is fulfilled. If a different sequence of processes from the above-described three operation sequences of deoxidation, alloying and slag washing is adopted, the effect of removing the deoxidation products in the steel is deteriorated, thereby affecting the castability of the molten steel.

The oxygen content of molten steel tapped from a converter (the oxidability of the molten steel) has different influences on the quality of steel and the alloy absorption rate. Thus, deoxidation of the tap may improve the subsequent handling of the molten steel. According to different steel grades and performance requirements, the deoxidizer has different choices. Examples of the deoxidizer include ferromanganese, ferrosilicon, silico-calcium alloy, silico-aluminum alloy, and aluminum. In the example, deoxidation is carried out by adding ferroaluminum to molten steel for refining. The ferro-aluminum reacts with oxygen to produce oxides, thereby removing the oxygen. Further, the deoxidation effect can be increased by selecting the adding mode of the aluminum iron. For example, when the tapping amount of the converter reaches 1/4 (that is, when the converter capacity is V, the tapping amount reaches 1/4, which means that the discharge amount of molten steel from the converter is V/4), the aluminum and iron are added. Subsequently, when the steel output of the converter reaches 1/3, carburant, ferrosilicon, ferro-silico-manganese, low-carbon ferromanganese, low-carbon ferrochrome and high-carbon ferrochrome can be added for alloying operation; when the steel tapping amount of the converter reaches 3/4, slag charge lime and synthetic slag are added for slag washing operation.

In the examples, alloying is mainly to adjust the contents of elements such as C (carbon), Si (silicon), Mn (manganese), and Cr (chromium) in steel in molten steel. Correspondingly, alloy such as carburant, ferrosilicon, ferro-silico-manganese, low-carbon ferromanganese, low-carbon or high-carbon ferrochrome and the like is adopted as an alloying reagent. In operation, after the molten steel is deoxidized, alloying agents are added to the steel to be melted in the molten steel and react and interact with various elements.

The inclusion removal is achieved by slag washing. In the example, slag is formed by molten steel, and slag is used for absorbing impurities, so that the impurities are removed from the molten steel. In the example, the slag washing is carried out by using a combination of lime and synthetic slag. Wherein, lime can be used as a flux and an alkalinity regulator and is used together with the synthetic slag to facilitate the lime to dissolve and absorb impurities (mainly aluminum and partial impurities such as phosphorus). The amount of lime is, for example, 2 to 3 kg/ton of molten steel, and the amount of synthetic slag is, for example, 2 to 3 kg/ton of molten steel.

After the converter smelting (primary smelting), the quality of the molten steel tapped from the converter is improved. In order to further remove other elements of the steel, so as to control the purity of the molten steel, the refining is continuously selected, and the molten steel treatment effect of one or more selected from deoxidation, desulfurization, dephosphorization, decarburization, inclusion removal, alloying and fine adjustment of components is realized. Such refining may be referred to as secondary refining or secondary refining, and a description of the subsequent steps (mainly referred to as step S102 and step S103 in the present example) will be clarified.

And step S102, performing first refining treatment by an LF (ladle furnace) under the condition of not adjusting acid-soluble aluminum. The first refining process includes: the method comprises the steps of mixing a slagging agent in converter tapping, namely, adding the slagging agent (slagging material) into LF to control the composition of refined slag, deoxidizing by using a deoxidizing agent after slagging is completed, monitoring the sulfur content in molten steel in the first refining treatment process, and gradually adjusting the sulfur content of the molten steel to the inner control range of steel components by using ferro-sulphur (or ferro-sulphur wires) (for example, the error can be controlled to be +/-0.003%).

The operation of adjusting sulfur and Al in the LF furnace refining process without adjusting acid-soluble aluminum is illustrated by the following description.

By the desulfurization reaction formula: (O)^2-)+〔S〕＝(S^2-) It is known that oxygen in the slag is transferred to the steel as the desulfurization proceeds, and the oxygen content in the steel increases. At this time, when the content of Als (acid-soluble aluminum) in the steel is high, aluminum in the steel participates in the deoxidation reaction of molten steel to form solid Al₂O₃。

The reduction of the oxygen content in the steel will intensify the desulphurisation reaction. Particularly in the LF process, the bottom blowing stirring effect creates better reaction kinetic conditions. The reaction is stronger as the content of Als in the steel is higher. On one hand, the yield of sulfur is reduced, and the usage amount of alloy is increased, so that the production cost is increased; on the other hand, as the desulfurization reaction proceeds, Als in the steel is lost. The higher the content of Als in steel, the more obvious the loss of Als caused by desulfurization reaction, and the more Al is produced₂O₃The more.

Al in steel₂O₃The content has obvious influence on the castability of molten steel, and Al in the steel₂O₃When the impurities are not removed in time, the impurities are easy to be enriched at the position of a stopper rod water gap, so that the castability of molten steel is poor, and the stopper rod is obviously raised. Therefore, the Als is not adjusted during the refining process in the LF furnace. Molten steel is treated in an RH furnace, because the molten steel is pumped into a vacuum chamber for degassing, steel slag does not react, Als is adjusted in the process, the Als in the steel does not participate in the desulfurization reaction, and the S, Als content in the steel can be adjustedIs stably controlled so that a large amount of Al can be avoided₂O₃And (4) generation of inclusions.

In general, the LF furnace refining process is performed after step S101 is performed, and the molten steel smelted by the converter is subjected to a first refining process to remove various unnecessary elements and substances.

During the first refining treatment, the smelting is carried out to remove the undesired elements mainly by slagging. Therefore, refining is usually carried out by using a slag-forming agent, for example, fluorite and fluorite balls are selected as the slag-forming agent. However, fluorite used as a slag former easily erodes a lining, pollutes the environment, and is expensive to use. Therefore, in order to avoid problems in terms of environment and the like, in the example, the converter tapping can be transferred to the LF furnace without adding fluorite and fluorite pellets. As a substitute for fluorite, exemplary slag formers include lime, and alkalinity (CaO/SiO)₂) 0.5 slag charge and the ratio of the mass of lime to the mass of slag charge is 0.5 to 0.8 (e.g. 0.6 or 0.7).

The refining slag produced by the slag former is selected according to the following components: the alkalinity of the refining slag is 1.5 to 3.0 (such as 1.6, 1.8, 1.9, 2.3, 2.6 or 2.8), and the refining slag comprises the following components in percentage by mass: 42-48% CaO, 20-30% SiO₂，10～20％Al₂O₃3-8% of MgO, and the sum of TFe and MnO is less than or equal to 1.5%. In other examples, the refining slag comprises the following components in percentage by mass: 44-47% CaO, 23-27% SiO₂，12～16％Al₂O₃，4～8％MgO，TFe+MnO≤0.5％。

The slag system ensures that the sulfur yield in the refining process is stable, the sulfur control precision is high, the slag fluidity is good, and meanwhile, Al in the slag is good₂O₃Low content, Al adsorbed by slag₂O₃The capability is stronger, the impurity adsorption effect is good, and the method is a favorable factor for preventing the nozzle from nodulation.

The slagging with lime and slag charge is carried out when the converter taps steel to a refining furnace, and then deoxidation of the slag surface is carried out after slagging is completed, for example, deoxidation is carried out by adding a deoxidizer on the slag surface. Lime and slag can be added into the converter and the LF respectively by 50% by mass.

In the present example, a slag surface deoxidizing agent is used for deoxidizing the slag surface. Illustratively, the slag surface deoxidizer can be a single-component deoxidizer or a multi-component deoxidizer. Or a combination of multi-component deoxidizers. Among them, the one-component deoxidizer is, for example, 70 silicon carbide. The multi-component deoxidizer is composed of, for example, calcium carbide, aluminum particles, and synthetic slag, and the ratio of the total mass of the calcium carbide, aluminum, and synthetic slag to the mass of 70 silicon carbide is 0.5 to 2.0 (e.g., 0.5, 0.8, 1.0, 1.4, 1.5, 1.8). Deoxidizer is added into steel, and the oxygen content in slag can be reduced through diffusion deoxidation reaction with slag. Meanwhile, the deoxidation product has a good foaming effect, and can keep a good reducing atmosphere in the LF furnace treatment process, so that the content of TFe + MnO in slag can be effectively controlled to be less than or equal to 1.5%, a good deoxidation effect in the refining process is ensured, the heat loss in the refining process can be reduced, and the heating and temperature rising efficiency is improved.

Illustratively, as an alternative, the deoxidizer is, for example, a slag surface complex deoxidizer of 0.7 to 1.0kg/t (e.g., 0.73kg/t, 0.75kg/t, 0.82kg/t, 0.86kg/t, 0.9kg/t, 0.94kg/t or 0.97kg/t) and 70 silicon carbide of 0.3 to 0.5kg/t (e.g., 0.4 kg/t). The deoxidizer is combined according to the above mode, the deoxidizing speed is high, the process slag is easier to foam, the submerged arc effect in the refining process is good, the effect of preventing secondary oxidation of molten steel in the LF refining process is better, and the deoxidizer is beneficial to preventing nozzle nodulation.

And S103, carrying out second refining treatment on the LF furnace steel by using an RH furnace, and optionally feeding aluminum according to the acid-soluble aluminum content of the LF furnace steel during the second refining treatment to adjust the aluminum content of the molten steel to a second target value (the error can be controlled to be +/-0.015%).

The second refining treatment is carried out using an RH furnace, and since the acid-soluble aluminum is not controlled in step S102, it is possible to select to monitor the acid-soluble aluminum content in this step and to select to feed aluminum in combination with the situation to control the acid-soluble aluminum content. In other words, if the acid-soluble aluminum content is insufficient, aluminum wire is added to supplement aluminum; if the acid-soluble aluminum meets the design requirements, no supplemental aluminum is required.

Since the RH furnace refining is performed under a vacuum condition, in the example, a high vacuum processing time of 18 to 21 minutes (for example, 19 minutes or 20 minutes) at not more than 0.266KPa (for example, 0.2KPa, 0.15KPa, 0.10KPa, 0.05KPa, 0.02KPa) is selected, and inclusions in steel are further removed by floating up by a long vacuum processing, thereby improving castability of molten steel.

And step S104, performing calcium treatment after RH furnace refining is finished.

The calcium treatment is carried out by adding calcium (pure calcium, for example, in an amount of 0.02 kg to 0.05 kg) to the molten steel so as to obtain Al₂O₃The inclusion is denatured, and the condition that the castability of molten steel is deteriorated due to a large amount of CaS inclusion generated by the reaction with sulfur in steel is avoided. Calcium is a strong deoxidizer and has a low boiling point, and can be quickly turned into steam after entering molten steel, and can react with oxygen and oxides in the steel to generate calcium oxides in the floating process, so that the content of the calcium oxides in the steel is reduced, the removal of non-metallic inclusions in the molten steel is facilitated, and the purity of the steel is improved. Further, the soft blow treatment is performed after the calcium treatment.

In view of the fact that the control method can control the molten steel purity in the smelting process of the sulfur-containing and aluminum-containing steel, the control method can be used for controlling the problem of nozzle nodulation during molten steel pouring, namely avoiding the nozzle nodulation. Therefore, the example also provides a smelting control method for preventing nozzle nodulation in the pouring process of the sulfur-containing and aluminum-containing steel, which comprises the following steps:

the blast furnace molten iron is directly transferred into a converter for smelting without desulfurization pretreatment, and the carbon content of the smelting end point of the converter is controlled to be lower than the target carbon content of the sulfur-containing aluminum-containing steel. And carrying out slagging treatment in the converter tapping process. The slagging treatment mainly comprises a deoxidation step, an alloying step and a slagging agent adding step. Wherein the deoxidation step is to add aluminum iron when tapping the steel from the converter for 1/4 of the capacity of the converter. The alloying step comprises the step of adding an alloying reagent to control the content of target elements of the molten steel within a preset range when the converter taps 1/3 of the capacity of the converter. The step of adding the slag former comprises the step of adding slag charge lime and synthetic slag when the tapping of the converter reaches the volume of 3/4 of the converter.

Molten steel tapped from converter without additionAnd adding fluorite or fluorite balls, directly feeding into the LF furnace, and refining under the conditions of monitoring the sulfur content of the molten steel and supplementing ferrosulfur so as to obtain the outbound molten steel with the expected sulfur content. The refining method in the step comprises the steps of adding a compound deoxidizer and 70 silicon carbide into molten steel for deoxidation, and adding lime and low-alkalinity slag with alkalinity of 0.5-1.0 to form the slag with the alkalinity of 1.5-3.0, wherein the components of the slag comprise 42-48% of CaO and 20-30% of SiO₂，10～20％Al₂O₃3 to 8 percent of MgO and less than or equal to 1.5 percent of TFe + MnO.

The implementation of the above process achieves at least one or more of the following effects:

(1) through optimizing the refining deoxidation and the refining slag composition, the lower oxygen content of the molten steel is ensured, the yield of sulfur is improved, the stable control of the sulfur is ensured, and meanwhile, no fluorite or fluorite-containing balls are added in the process from the converter to the LF, so that the influence on the environment is reduced.

(2) Als is not adjusted in the LF refining furnace process, so that the Als in the steel does not participate in slag reaction basically under the condition that the alkalinity of the slag is 1.5-3.0, and a large amount of Al is prevented₂O₃The generation of inclusions improves the castability of molten steel.

(3) And the LF refining furnace gradually adds sulfur iron wires or sulfur iron to adjust sulfur according to the process sample, the sulfur content in steel is stably controlled, and the sulfur content can be stably controlled within a target value of +/-0.003 percent after LF is finished.

(4) The RH furnace feeds aluminum wires to Als internal control target +0.015 percent according to the content of Als discharged from the LF station, steel and slag basically do not react in the RH treatment process, the yield of the Al wires is stable, and the RH treatment does not adjust sulfur.

(5) The RH furnace is subjected to high vacuum treatment for 18-21 minutes at the pressure of less than or equal to 0.266KPa, inclusions in steel are further floated and removed through long-time vacuum treatment, and the castability of molten steel is improved.

(6) The RH furnace vacuum treatment is ended by suitableCalcium content of (1), Al in steel₂O₃The inclusion is denatured, and the phenomenon that the castability of molten steel is deteriorated due to a large amount of CaS inclusion generated by the reaction with sulfur in steel is avoided.

(7) And the soft blowing control after the vacuum treatment is finished further promotes the floating removal of the inclusion, so that the castability of the molten steel is improved.

Some examples of the application of the above process are listed below.

Example 1

The control requirements of the components of a finished product of a certain steel grade containing sulfur and aluminum are as follows: c: 0.19 to 0.21%, 0.20 to 0.30% of Si, 0.70 to 0.80% of Mn, 0.80 to 0.90% of Cr, and Als; 0.010-0.030 percent of the total weight of the alloy, 0.015 percent of the target, less than or equal to 0.025 percent of P and 0.020-030 percent of S.

The smelting process comprises the following steps:

the blast furnace molten iron is transferred into a converter for smelting without pretreatment and desulfurization, and the end point carbon of the converter is controlled according to 0.08-0.15%.

2.3kg/t of aluminum and iron are added into 1/3 of the steel tapping, 2/3 of the steel tapping is added with alloy elements of C, Si, Mn and Cr to adjust the components of the molten steel to the lower limit of the range, 3/4 of the steel tapping is added with 3.0kg/t of slag charge lime and 2.5kg/t of synthetic slag. The slag charge is added in the tapping process for removing impurities through slag washing, and the heat preservation and the like are carried out in the process of conveying the steel to the LF refining furnace.

The LF refining furnace is added with lime 2.0kg/t and low-alkalinity slag 4.5kg/t at the station (the LF refining furnace is transported to an LF refining plant at the station, and the LF furnace slagging treatment is firstly carried out at the time). After the slag is melted, 0.8kg/t of slag surface compound deoxidizer and 0.4kg/t of 70 silicon carbide are added. Gradually adding ferrosulfur or ferrosulfur wire according to the process sample to adjust the sulfur content, and controlling the sulfur content of the refining furnace out of the station: 0.022-0.028%.

And feeding Al wires to the RH refining furnace to increase the content of Als to 0.030-0.036%. The technological parameters of RH refining furnace refining are high vacuum treatment time of 18 minutes under 0.266KPa or less, pure calcium line feeding of 0.04kg/t, and soft blowing time of 10-15 minutes.

And (3) pouring after the molten steel is smelted, wherein the result shows that no nozzle nodulation exists in the pouring process of the casting machine, and the stopper rod curve is stable, as shown in figure 1.

Example 2

The control requirements of the components of a finished product of the steel containing sulfur and aluminum are that C is 0.34-0.38%, Si is 0.60-0.75%, Mn is 0.95-1.05%, Cr is 0.10-0.0.25%, V is 0.25-0.35%, Als is less than or equal to 0.030%, P is less than or equal to 0.025%, and S is less than or equal to 0.040-0050%.

The specific process steps are as follows:

smelting blast furnace molten iron in a converter, wherein the end point carbon of the converter is controlled according to 0.08-0.25%. Specifically, 1.5kg/t of aluminum and iron are added into 1/3 of the steel tapping, 2/3 of the steel tapping is added with alloy elements such as C, Si, Mn, Cr, V and the like to adjust the components of the molten steel to the lower limit of the range, 3.0kg/t of slag material lime is added into 3/4 of the steel tapping, and 2.5kg/t of synthetic slag is added.

The converter tapping is transferred to an LF refining furnace, 2.0kg/t of lime and 4.5kg/t of low-alkalinity slag are added at the station of the refining furnace, 0.8kg/t of slag surface compound deoxidizer and 0.5kg/t of 70 silicon carbide are added after the slag is melted. And gradually adding ferrosulfur or ferrosulfur wires according to the process sample to adjust the sulfur content, and controlling the sulfur content of the outlet station to be 0.042-0.048%.

And transferring the LF refining furnace tapping into an RH refining furnace, and feeding Al wires to increase Als to 0.030% when RH arrives at a station. The RH furnace treats the molten steel for 21 minutes under high vacuum at the pressure of less than or equal to 0.266KPa, a pure calcium line is fed for 0.03kg/t, the soft blowing time is 10-15 minutes, no nozzle nodulation occurs in the casting process of the casting machine, and the stopper curve is stable, which is shown in figure 2.

Comparative example 1

S45C sulfur-containing steel is produced, and the sulfur-containing steel comprises the following components in percentage by mass: c: 0.42% -0.48%, Si: 0.15% -0.350%, Mn: 0.50% -0.80%, P < 0.025%, S: 0.015% -0.30%, Cr: 0.10% -0.20%, A1: 0.020-0.32%.

S45C the sulfur-containing steel is produced by adopting an LD converter smelting process, an LF refining process, an RH vacuum refining process and a continuous casting blank forming process.

The production process comprises the following steps:

the molten iron is smelted in a converter after being desulfurized, and the sulfur content is less than or equal to 0.020 percent after the final sample application of the converter is subjected to spectral analysis.

Smelting blast furnace molten iron in a converter, wherein the end point carbon of the converter is controlled according to 0.08-0.25%. Specifically, 1.5kg/t of aluminum and iron are added in 1/3 of the steel tapping, 2/3 of the steel tapping is added with alloy elements such as C, Si, Mn, Cr and the like to adjust the components of the molten steel to the lower limit of the range, 3.0kg/t of slag charge lime is added in 3/4 of the steel tapping, and 2.5kg/t of synthetic slag is added.

The converter tapping is transferred to an LF refining furnace, 2.0kg/t of lime and 4.5kg/t of low-alkalinity slag are added at the station of the refining furnace, 0.8kg/t of slag surface compound deoxidizer and 0.5kg/t of 70 silicon carbide are added after the slag is melted. In the LF process, aluminum is added by feeding aluminum wires, the Al is controlled to be 0.030-0.040% after LF is finished, sulfur is not adjusted in the LF process, the alkalinity of LF final slag is 5-8, and the ratio of CaO: 58 to 62 percent of sulfur, 8 to 12 percent of SiO2, 25 to 30 percent of Al2O3, and less than or equal to 1.0 percent of TFe + MnO, 0.025 percent of sulfur is adjusted by a sulfur iron bin in the RH process, 0.03 kg/ton of pure calcium is fed after the vacuum treatment is finished, the soft blowing time is 10 to 15 minutes, the pure calcium is cast on a casting machine for casting, and the stopper curve obviously rises as shown in figure 3.

According to the structural comparison of the embodiment 1, the embodiment 2 and the comparative example 1, the scheme of the invention can obtain better molten steel pouring effect. In the pouring process, the stopper rod works more stably, the stopper rod does not rise obviously, and the stopper rod fluctuates and rises obviously in the pouring of molten steel in the comparative example 1. Therefore, the problem of nozzle nodulation of sulfur-containing aluminum-containing steel in the pouring process is solved by optimizing a refining deoxidation method, refining slag system control and an RH furnace vacuum treatment process, and the stopper rod curve in the pouring process is stable and controllable.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for controlling cleanliness of molten steel is applied to smelting sulfur-containing and aluminum-containing steel, and is characterized by comprising the following steps:

sending the blast furnace molten iron into a converter for smelting without desulfurization pretreatment, and sequentially carrying out deoxidation, alloying and slag washing when tapping from the converter;

performing a first refining process by an LF furnace without adjusting acid-soluble aluminum, the first refining process comprising: adding a slagging agent in an LF furnace to control the composition of refining slag, introducing a deoxidizing agent to deoxidize after the slag is melted, monitoring the sulfur content in molten steel in the first refining treatment process, adjusting the sulfur content of the molten steel to the lower limit of an outbound control range by ferrosulfur, and gradually adjusting the sulfur content in the steel to the internal control requirement range of the steel according to the analysis result of a subsequent sample;

carrying out secondary refining treatment on the LF furnace steel tapping by using an RH furnace, and optionally feeding aluminum according to the acid-soluble aluminum content of the LF furnace steel tapping in the secondary refining treatment process to adjust the aluminum content of the molten steel to +/-0.015% of a control target;

and performing calcium treatment after finishing the RH furnace refining.

2. The method for controlling cleanliness of molten steel according to claim 1, wherein the deoxidizer used in the first refining process step is a slag surface deoxidizer.

3. The method of controlling cleanliness of molten steel according to claim 2,

the slag surface deoxidizer comprises a single-component deoxidizer and a multi-component deoxidizer;

optionally, the single-component deoxidizer comprises 70 silicon carbide, the multi-component deoxidizer comprises calcium carbide, aluminum particles and synthetic slag, and the mass ratio of the total mass of the calcium carbide, the aluminum particles and the synthetic slag to the mass of the 70 silicon carbide is 0.5-2.0.

4. The method of controlling molten steel cleanliness according to claim 1, wherein the first refining process further includes any one or more of the following limitations:

I) the converter tapping is transferred to the LF furnace without adding fluorite and fluorite balls;

II) the slagging agent comprises lime and slag charge with alkalinity of 0.5, and the mass ratio of the lime to the slag charge is 0.5-0.8;

III), the alkalinity of the refining slag is 1.5 to 3.0, and the refining slag comprises the following components in percentage by mass: 42-48% of CaO and 20-30% of SiO₂10-20% of Al₂O₃，38 percent of MgO, and less than or equal to 1.5 percent of TFe + MnO.

5. The method of controlling cleanliness of molten steel according to claim 1, comprising: soft blowing treatment, and the soft blowing treatment is carried out after the calcium treatment.

6. The method for controlling cleanliness of molten steel according to claim 1, wherein the deoxidation is performed by adding ferro-aluminum to the molten steel for refining in the steps of deoxidation, alloying and slag washing at the time of tapping from the converter.

7. The method for controlling cleanliness of molten steel according to claim 1, wherein in the steps of deoxidation, alloying and slag washing at the time of tapping from the converter, the alloying is performed by adding a carburant, ferrosilicon, silicoferromanganese, low-carbon ferromanganese, low-carbon ferrochrome and high-carbon ferrochrome to the molten steel for refining.

8. The method for controlling cleanliness of molten steel according to claim 1, 6 or 7, wherein in the steps of deoxidation, alloying and slag washing at the time of tapping from the converter, the inclusion removal treatment includes adding slag lime and synthetic slag to the molten steel for refining;

9. The method of controlling cleanliness of molten steel according to claim 8, wherein the deoxidation, alloying and inclusion removal processes performed at the time of tapping from the converter include:

adding aluminum iron when the converter tapping amount reaches 1/4;

adding a carburant, ferrosilicon, ferro-silico-manganese, low-carbon ferromanganese, low-carbon ferrochrome and high-carbon ferrochrome when the steel output of the converter reaches 1/3;

10. A smelting control method for preventing nozzle nodulation in a pouring process of sulfur-containing and aluminum-containing steel is characterized by comprising the following steps:

smelting the blast furnace molten iron without desulfurization pretreatment by using a converter, and controlling the carbon content of the smelting end point of the converter to be lower than the target carbon content of the sulfur-containing and aluminum-containing steel;

carrying out slagging treatment in the converter tapping process, wherein the slagging treatment comprises a deoxidation step, an alloying step and a slagging agent adding step, the deoxidation step comprises adding aluminum iron when the converter tapping reaches 1/4 volume of the converter, the alloying step comprises adding an alloying agent to control the content of target elements of molten steel within a preset range when the converter tapping reaches 1/3 volume of the converter, and the slagging agent adding step comprises adding slag charge lime and synthetic slag when the converter tapping reaches 3/4 volume of the converter;

feeding molten steel tapped from a converter into an LF furnace without adding fluorite or fluorite balls, refining under the conditions of monitoring the sulfur content of the molten steel and supplementing ferrosulfur to obtain outbound molten steel with the expected sulfur content and acid-soluble aluminum content, wherein the refining method comprises the step of adding lime and low-alkalinity slag with alkalinity of 0.5-1.0 into the molten steel to form CaO with the alkalinity of 1.5-3.0 and the components of CaO of 42-48% and SiO of 20-30%₂10-20% of Al₂O₃3-8% of MgO and less than or equal to 1.5% of TFe + MnO, and then deoxidizing by adding a composite deoxidizer and 70 silicon carbide;