KR20140092800A

KR20140092800A - Method for smelting high-aluminum-low-silicon ultrapure ferritic stainless steel

Info

Publication number: KR20140092800A
Application number: KR1020147003789A
Authority: KR
Inventors: 잉티에 쑤; 자오핑 첸; 시 리
Original assignee: 바오샨 아이론 앤 스틸 유한공사
Priority date: 2011-10-25
Filing date: 2012-01-06
Publication date: 2014-07-24
Also published as: EP2772554A1; IN2014CN01547A; EP2772554B1; CN102329920A; CN102329920B; JP5833767B2; EP2772554A4; KR101787179B1; WO2013060101A1; JP2015501382A

Abstract

The present invention provides a smelting method of high aluminum low silicon super high purity ferritic stainless steel. First, the liquid steel of ferritic stainless steel is subjected to vacuum oxygen blowing decarburization and free decarburization treatment in the VOD furnace, and then the reduction process of the VOD vacuum treatment process is improved to perform preliminary deoxidation and final deoxidation, High-density aluminum ferrite was added to control the basicity of the slag in the furnace, followed by wire feed treatment and casting protection measures during the performance, and in the performance process from the VOD, a high aluminum low silicon super high purity ferrite stainless steel We have improved the pickling performance of ultrahigh purity ferritic stainless steel and improved the purity of liquid steel and the casting performance during the performance process. At the same time, it effectively inhibited the formation of magnesium aluminum sphene, a harmful impurity, and effectively removed Al ₂ O ₃ impurities. It also inhibited the oxidation of titanium in titanium-containing steels and prevented clogging of intermediate turn-off nozzles during the performance process.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method for smelting a high-purity aluminum ferrite stainless steel having a high purity,

The present invention relates to a method of smelting a kind of high aluminum low silicon super high purity ferritic stainless steel.

Ultra high purity ferritic stainless steel is a refined stainless steel, generally containing less than 150 ppm total nitrogen, less than 40 ppm total oxygen, and effectively regulating the amount, size and type of impurities. In addition, ultra high purity ferritic stainless steels act as a substitute for austenitic stainless steel and save nickel resources because they do not require nickel elements.

The smelting process of ultrahigh-purity ferritic stainless steel is generally carried out in a vacuum oxygen blowing decarburization furnace (abbreviated as VOD) under oxygen vacuum degassing and denitrification under super vacuum conditions. The general operation procedure for the VOD is as follows.

1. The AOD-treated liquid is transported to a position for VOD treatment using a ladle, and the temperature and the composition are measured and passed to a vacuum treatment chamber. After vacuum is formed, a bottom stirring. 2. Oxygen blowing and decarburization treatment is started under vacuum conditions, oxygen is blown from the upper part under the bottom stirring condition, decarburization treatment is performed, and oxygen supply stoppage is judged based on the gas component in the furnace. When the CO + CO ₂ content in the furnace gas is lower than a certain value, the oxygen supply is stopped. 3. Perform free decarburization under ultra-vacuum conditions and proceed with agitation. 4. Through the reduction process, silicon iron, aluminum, lime and fluorite are added to perform deoxidation and alloying treatment of silicon. 5. Release the vacuum. 6. Wire feed and mild agitation under atmospheric conditions, then use for casting later.

However, in the oxygen blowing and decarburizing process of the second step, not all of the supplied oxygen is used for decarburization. Since a considerable amount of oxygen enters the dissolution zone and is present in the form of chromium oxide or dissolved oxygen, deoxidation treatment must also proceed after free decarburization in the third step.

Among them, silicon and aluminum are frequently used deoxidizing elements. Each European steel company used pure silicon deoxidation technology first. The reason for this is that when deoxidized by using aluminum, a large amount of Al ₂ O ₃ impurities are produced, which adversely affects the production of most steel species, but the total oxygen content in the steel subjected to silicon deoxidation is very high, The total oxygen content reaches 60ppm or more, which affects the performance of the final product.

As the demand for ultrahigh-purity ferritic stainless steel increases, the total content of oxygen is required to be reduced to an extremely low level. Thus, people are attempting to deoxidize the silicon aluminum composite to further lower the oxygen content in the steel. Currently there are mainly patents available.

Japanese Patent No. JP20025030324 (A) discloses a smelting method of ferritic stainless steel for preventing stripe defects (tile-like shape defects) caused by silicon aluminum composite deoxidation. In the deoxidation process, silicon iron was first added to control the content of silicon to 0.20 to 3.0 wt%, and the slag basicity (mass ratio of CaO to SiO _{2 in} the slag) was controlled to 1.2 to 2.4, followed by deoxidation with aluminum . The ratio of the Al content to the Ti content in the liquid steel before casting was controlled to 0.01 to 0.10, which is the ratio of the equiaxed crystal ratio of the liquid steel in the continuous casting process (that is, the percentage of all the equiaxed crystals formed after solidification of the crystal, The equilibrium constant at the center of Billet is the diameter of the central equiaxed crystal zone and the percentage of the cast billet diameter) reaches 60%, effectively controlling the impurity content, preventing clogging of the tundish nozzle during the casting process , And the total oxygen content of the final liquid steel was maintained at a relatively low level. However, controlling the slag basicity to 1.2 to 2.4 in the above patent means that the oxygen activity of the slag is still very high, and it is difficult to lower the oxygen content of the liquid steel to an extremely low level.

The Chinese patent CN101058837, which is the name of the invention, is a smelting method of ultra high purity ferritic stainless steel, which is a decarburization method of a kind of super high purity ferritic stainless steel and a smelting method of carbonaceous material. The liquid steel is degassed by vacuum treatment, and then, under vacuum condition (degree of vacuum = 5 mbar) First, silicon iron was added and deoxidized, and further aluminum was added thereto to further deoxidize, and the deoxidizing time was 5 to 10 minutes. Subsequently, fine adjustment was made with the alloy. The above-described deoxidation method has a short processing time, good deoxidation effect, and is widely used.

However, JP2002030324 (A) and CN101058837 do not disclose a concrete method of applying aluminum to liquid steel. The density of aluminum agglomerates or aluminum granules is very low compared to the density of the liquid steel, and when added directly under the VOD vacuum condition, it floats on the upper part of the liquid steel and reacts directly with the slag to react and emit a large amount of heat, So that it is difficult to effectively perform precipitation deoxidation. When aluminum is directly added, it becomes difficult to control the aluminum content in the steel after the treatment is finished, and it becomes difficult to secure the effect of precipitation deoxidation.

At the same time, in the silicon aluminum composite deoxidation, the final content of silicon and aluminum elements has a certain influence on the deoxidation effect of the steel, the subsequent treatment and the steel texture performance. Major influences are as follows. 1) If the aluminum content in the steel is low, the effect of deoxidation is not clear. That is, the oxygen content of the liquid steel is high, and when the Ti-feeding treatment is performed in succession, a large amount of titanium oxide impurities are formed, and a large amount of titanium oxide impurities can prevent the tundishes. 2) According to the latest research, ferrite stainless steels with high silicon content (generally higher than 0.3%) affect the smoothness of the stainless steel surface due to the difficulty of pickling in subsequent processes. Therefore, in order to improve the quality of the product and ensure smooth production, most of the ultra high purity ferritic stainless steels are deoxidized to control the element content in the low silicon and high aluminum directions. Specifically, the silicon content Is controlled to 0.3% or less, and the minimum allowable value is determined according to other requirements of the steel grade. The aluminum content can be controlled within the range of 0.01 to 0.1%, effectively lowering the total oxygen content, thereby preventing oxidation of titanium in the subsequent titanium alloying process.

In the smelting of low silicon and high aluminum super high purity ferritic stainless steels, as mentioned above, it is not possible to effectively increase the aluminum content in the steel in the VOD treatment process through the related patent and the conventional method, and at the same time, The silicon content in the steel can not be controlled within a proper range unless the slag basicity control is appropriate. When the aluminum deoxidation method of the carbon steel smelting process is used, that is, when the aluminum content in the steel is increased through the Al wire feeding, the difficulty of wire feeding under the vacuum condition is so great that the vacuum process is completed, Al wire feeding can be performed only under the conditions shown in Fig. This can surely increase the aluminum content in the steel, but it can not proceed to the stirring of the stainless steel liquid steel after the Al wire feeding, so that the generated Al ₂ O ₃ impurities can not be rapidly grown and removed. In addition, under non-vacuum conditions, Al wire feeding increases the likelihood that liquid steel will absorb nitrogen and prolongs processing time. Thus, Al wire feeding under non-vacuum conditions is not a scientific method. If aluminum powder is blown under vacuum conditions, aluminum content in steel can be increased, but vacuum filling equipment is complicated and control difficulty is very large.

Thus, existing techniques and conventional operations fail to reliably address the technical problem of increasing the aluminum content in the steel and effectively controlling the silicon content under vacuum conditions.

An object of the present invention to solve the above problem is to provide a smelting method of high aluminum low silicon super high purity ferritic stainless steel.

Through the improvement of the reduction process of the VOD vacuum process, it is possible to add high-density aluminum iron, control slag basicity, and then wire-feed the process, take measures such as casting protection during the performance, High-purity ultra-high-purity ferritic stainless steel is achieved. It enhances pickling performance of ultrahigh purity ferritic stainless steel and improves purity of liquid steel and casting performance during performance. At the same time, it effectively suppresses the formation of harmful impurities, such as magnesium aluminum spinel, effectively removes Al ₂ O ₃ impurities, inhibits the oxidation of titanium in titanium-containing steels, and prevents clogging of tandem nozzles during performance.

In order to achieve the above object, the present invention takes the following technical solutions.

The invention provides a smelting method of high aluminum high silicon super low purity ferritic stainless steel, characterized by comprising the following steps.

(1) For the liquid steel of the ferritic stainless steel, the main components of the liquid steel of the ferritic stainless steel subjected to the vacuum oxygen blowing decarburization and free decarburization treatment in the VOD furnace are 10 to 23% of the chromium mass percentage , The carbon mass percentage is 0.01%, and the nitrogen mass percentage is less than 0.01%.

(2) Preliminary deoxidation: A preliminary deoxidation treatment is carried out by adding silicon iron and / or an aluminum lump in the liquid steel of the ferritic stainless steel subjected to the step (1), and slag is prepared by adding lime and fluorite, Treat for 5 to 10 minutes under strong stirring conditions.

(3) Final deoxidation: Aluminum iron is added to the liquid steel of the ferritic stainless steel obtained through the step (2) and subjected to the final deoxidation treatment. The aluminum aluminum percentage in the aluminum iron is in the range of 20 to 60% To prepare a slag, and then the slurry is stirred under a vacuum condition for 2 to 5 minutes. Followed by treatment under high vacuum and strong agitation for 12 to 18 minutes.

(4) Release the vacuum system.

(5) Under a normal pressure condition, weak stirring is performed on the liquid steel of the ferritic stainless steel for 8 to 10 minutes, then calcium wire feeding is performed on the liquid steel of the ferritic stainless steel under atmospheric pressure, After completion of the reaction, weak stirring is carried out for 5 to 10 minutes.

(6) Subsequently, weak stirring is performed for 15 to 30 minutes, and then the liquid steel of the ferritic stainless steel is subjected to performance in a protective atmosphere to finally obtain a high aluminum low silicon super high purity ferritic stainless steel.

In the smelting method for a high aluminum low silicon super high purity ferritic stainless steel provided in the present invention, in the step (2), the total added amount of the silicon iron and / or aluminum ingot is 4 to 9 kg / t, The percentage content is 70 to 80%, and the added mass of the lime takes a large value in two ranges of 4 to 6 times the added mass of the iron oxide or 2 to 3 times the added mass of the aluminum ingot. The addition mass of the fluorite is 0.05 to 0.3 times the mass of the lime added, and after the treatment of step (2), the mass content of silicon in the ferrite stainless steel is greater than 0 and less than 0.1%. The mass content of oxygen exceeds 0.01%.

In the smelting method of high aluminum low silicon super high purity ferritic stainless steel provided in the present invention, in the step (3), the amount of pure aluminum added in the aluminum iron is 2 to 6 kg / t, And the amount of fluorite added is 0.05 to 0.3 times the amount of lime. After the step (3), the silicon mass content in the liquid steel of the ferritic stainless steel is greater than 0 and less than 0.3%. The aluminum mass content is 0.01 to 0.1%, and the oxygen mass content is less than 0.003%.

In the smelting method of a high aluminum low silicon super-high purity ferritic stainless steel provided in the present invention, in the step (5), the calcium wire feeding is a pure calcium wire feeding to a liquid steel of a ferritic stainless steel, The feeding amount is 0.1 to 0.3 kg / t. After the step (5), the calcium mass content in the liquid steel of the ferritic stainless steel is 15 to 30 ppm.

In the smelting method of a high aluminum low silicon super high purity ferritic stainless steel provided in the present invention, in step (5), titanium wire feeding is performed on a liquid steel of ferritic stainless steel after calcium wire feeding and weak stirring are performed , And the amount of pure titanium in the titanium wire is 1 to 3 kg / t.

In the smelting method of high aluminum low silicon super high purity ferrite stainless steel provided in the present invention, the silicon mass percentage content is less than 0.3% and the aluminum mass percentage content is 0.01 to 0.1 %to be.

In the smelting method of high aluminum low silicon super high purity ferritic stainless steel provided by the present invention, in the step (2)

When the upper limit value of the silicon mass content in the final obtained high aluminum aluminum silicate super high purity ferritic stainless steel is required to be 0.3%, silicon iron is added in its entirety.

When it is required that the upper limit of the content of silicon mass in the final obtained high aluminum aluminum silicate super high purity ferritic stainless steel is less than or equal to 0.2%, a whole aluminum ingot is added.

When it is required that the upper limit value of the silicon mass content in the final obtained high aluminum aluminum silicate ultra high purity ferritic stainless steel is 0.2 to 0.3%, the iron iron and the aluminum lump are added, and the addition ratio of the silicon iron and aluminum lump = -0.2%) / (0.3% - upper limit value of the silicon mass content in the ultrahigh-purity high-purity ferrite stainless steel obtained in the final stage) of the aluminum low silicon super-high purity ferritic stainless steel.

In the smelting method of high aluminum low silicon super high purity ferritic stainless steel provided in the present invention, in the step (3), the aluminum iron is in a massive or spherical shape, the density is 4.5 to 6.5 g / cm ³ , 6 cm. After the process of step (3), the mass ratio of CaO and SiO ₂ in the furnace and the slag exceeds 2.8, the mass ratio of CaO and Al ₂ O ₃ of the furnace the slag is greater than 1.

In the smelting method of high aluminum low silicon super high purity ferritic stainless steel provided by the present invention,

The conditions of the high vacuum and strong stirring are to control the vacuum pressure to 800 Pa or less and control the amount of argon blowing at the bottom of the VOD to be in the range of 4 to 8 L / (min · t)

The medium strength stirring conditions are such that the vacuum pressure is controlled to 2000 Pa or less and the amount of argon blowing at the bottom of the VOD furnace is controlled in the range of 1 to 4 L / (min · t)

The weak stirring condition is that under the atmospheric pressure condition, the amount of argon blowing at the lower portion of the VOD is controlled in the range of 1 to 5 L / (min · t).

Advantageous effects of the smelting method of high aluminum low silicon super high purity ferritic stainless steel provided in the present invention are as follows.

1. It effectively improves the deoxidation efficiency of aluminum precipitation in the VOD smelting process, effectively increases the aluminum content in the steel, prevents the silicon element in the slag from returning to the liquid steel, controls the silicon content to a low level, High-purity ferritic stainless steel.

2. It is possible to prevent secondary oxidation of high-aluminum content liquid steel by casting protection measures during performance and to prevent clogging of turn-off nozzles by combining with calcium treatment, and also, in VOD process, And the aluminum content was controlled to the target content, the formed Al ₂ O ₃ impurities were sufficiently grown during the VOD agitation process to effectively float after releasing the vacuum, thereby further improving the purity of the liquid steel.

3. Aluminum in the added high-density aluminum iron can enter the liquid steel sufficiently, and MgO in the slag directly reacts with it, which greatly reduces the probability of formation of magnesium aluminum spinel and effectively prevents the formation of magnesium aluminum spinel, a harmful impurity Respectively. The effective removal of Al ₂ O ₃ impurities and the inhibition of the formation of magnesium aluminum spinel can also prevent clogging of the tundish nozzle.

4. If the aluminum content is increased and titanium alloying is required for the steel species, the oxidation of titanium can be greatly suppressed during the titanium feeding process and the yield of titanium can be increased. The present invention has an active action to prevent clogging of the nozzle due to titanium oxide.

5. The method designed in the present invention is safe and stable, has a high operability, can greatly improve the stability of the smelting and the quality of the product.

The present invention relates to the field of smelting stainless steel, and more particularly to a smelting method of ferritic stainless steel, and more particularly to a smelting method of high aluminum low silicon super high purity ferritic stainless steel.

The process principle of the present invention is as follows.

1. In the target content of silicon and aluminum in the ultrahigh-purity ferritic stainless steel required in the present invention, the silicon mass percentage content is less than 0.3% and the aluminum mass percentage content is 0.01 to 0.1%.

The main purpose of reducing the silicon content to less than 0.3% is to enhance the pickling performance of stainless steels. If the silicon content is higher than 0.3%, the pickling difficulty of the steel is increased, which affects the smoothness of the steel. Further, silicon within the above content range can secure the toughness of steel and improve the workability. The aluminum mass is 0.01 to 0.1%, which is mainly considering deoxidation effect. On the basis of thermodynamic calculations, the range of dissolved oxygen is 0.002 to 0.0025% (that is, 20 to 25 ppm) when the Al content is 0.01% in the liquid steel of ferritic stainless steels of different chromium content under the condition of 1550 캜. Since the total oxygen contains impurities, the aluminum content of the present invention is required to exceed 0.01% under the condition that the total oxygen content in the cast billet is less than 30 ppm. At the same time, the upper limit of the aluminum content is 0.1% and the upper limit of the titanium content is 0.7% when the upper limit of the aluminum content is 0.1%, considering that the aluminum-titanium content exceeds 0.15 for some titanium-containing steel types . If the aluminum content exceeds 0.1%, it is unnecessary to raise the cost of smelting.

2. Pre-deoxidation and final deoxidation

In the smelting of the ferritic stainless steel in the silicon aluminum content range, as shown in steps (2) and (3), in the present invention, preliminary deoxidation is first carried out using silicon iron and aluminum ingot, And the final deoxidization proceeds. In the present invention, there is also adopted a method of proceeding deoxidation using silicon iron, aluminum ingot and aluminum iron. The reason for this is that when aluminum is added only in the deoxidation process, the cost of aluminum iron is higher than that of silicon iron, the smelting cost is increased, and the burnt carbon becomes worse. If only the silicon iron and the aluminum ingot are added, the aluminum ingot is light and can not effectively enter the liquid steel, so that the purpose of increasing the aluminum content in the steel can not be achieved. When the final deoxidation is carried out by adding silicon iron, aluminum ingot and aluminum iron together, the bonding ability of aluminum and oxygen is much larger than the bonding ability of silicon and oxygen, so that under the situation where Cr ₂ O ₃ in slag is reduced to a basic level, It may cause an intense reaction with SiO ₂ to increase the silicon content in the steel steeply and fail to satisfy the requirement that the final silicon content is less than 0.3%. Thus, in the present invention, a method in which preliminary deoxidation is carried out by first adding iron oxide and a portion of aluminum mass. During the pre-deoxidation process, the oxygen content in the steel can not be controlled very low. Based on the equilibrium thermodynamic equations of silicon and oxygen, a large amount of silicon element can react with oxygen during the pre-deoxidation process, ensuring that the silicon content in the steel reaches a relatively low numerical range during processing. After the preliminary deoxidation treatment, aluminum is added to proceed the final deoxidation. The density of aluminum iron is larger than that of pure aluminum, so that aluminum is poured into the dissolution zone of the liquid steel, and most of the aluminum is precipitated in the liquid steel. After dissolving, the aluminum is firstly introduced into the liquid steel to realize effective precipitation deoxidation, The aluminum content in the steel can be effectively increased. Of course, some of the dissolved aluminum does not directly react to slag penetration, but does not hinder the rapid increase in aluminum content in the steel.

1) Preliminary deoxidation

In the preliminary deoxidation of step (2) of the present invention, a preliminary deoxidation treatment is carried out by adding silicon iron and / or aluminum mass having a silicon content mass percentage ratio of 70 to 80%, and the total addition amount of silicon iron and / Is 4 to 9 kg / t, and slag is prepared by adding lime and fluorite. The lime-added mass takes a large value, which is 4 to 6 times the mass of the iron-silicon-added mass, and 2 to 3 times the mass of the aluminum mass. The addition mass of fluorite is 0.05 to 0.3 times the mass of the lime added, the treatment time is 5 to 10 minutes under high vacuum and strong stirring conditions, the silicon mass content is less than 0.1% and the oxygen mass content is not less than 0.01% do.

Prior to this step, the liquid steel was immediately subjected to oxygen blowing and decarburization treatment, and dissolved solids and chromium oxide were present in large amounts. The purpose of preliminary deoxidation by adding silicon iron and aluminum ingot is to reduce the oxygen content of the steel as much as the chromium in the chromium oxide is reduced by using a silicon iron or aluminum ingot. Aluminum agglomerates have very strong reducing capacity and can react directly with Cr ₂ O _{3 in the} slag. Here, the reduction ability of silicon is examined mainly, and the reduction reaction equation of silicon is as follows.

1.5 [Si] + (Cr ₂ O ₃ ) = 2 [Cr] +1.5 (SiO ₂ )

According to the thermodynamic calculation, assuming that the thermoelectric activity based on pure water of oxides (Cr ₂ O ₃ ) and (SiO ₂ ) is 1, among calculated stainless steel having a chromium content of 18%, silicon content Exceeds 0.6%, the reaction is promoted toward the positive reaction, which means that the density of silicon iron should not be too high. Silicon iron floats on the surface of the liquid steel and reacts directly with (Cr ₂ O ₃ ) in the slag, ensuring that the silicon content is greater than 0.6% in the localized portion of the liquid steel in contact with the slag. Thus, the silicon iron selected in the present invention can satisfy the requirement that the silicon content is 70 to 80%, and the density of the silicon iron is not so high. Of course, as the lime dissolves, the SiO ₂ activity in the slag phase is lowered and the pre-deacidification by the silicon is also accelerated. In the present invention, furthermore, the progress of the pre-deoxidation by selecting aluminum is mainly for some steel grades requiring a lower content of the target silicon, and there is a related argument of the following. The amount of deoxidation of the aluminum ingot having a weight equivalent to that of silicon iron containing 75% of silicon is close to 1, so that in the range of addition of silicon iron and aluminum ingot, when the chromium content in the steel is low and the initial carbon content is low, The total content of iron and aluminum agglomerates is comparatively low. On the contrary, when the content of chromium in the steel is high and the initial carbon content is high, the total content of silicon iron and aluminum agglomerate should be relatively large. The following is an example of an analysis of two extreme situations that may occur during the production process. Based on this, the range of total added amount of silicon iron and aluminum ingot is determined. According to calculations, ferritic stainless steels having a low chromium content, for example, in the case of a steel having a chromium content of 11.6%, under the condition that the initial carbon content is 0.3% before the liquid steel enters the VOD, The blow-in amount is about 7 Nm ³ / t and can be decarburized under vacuum conditions. Experience has shown that about 2.6 to 3.45 kg of pure silicon or 3.5 to 4.6 kg of pure aluminum is required for about 30 to 40% oxygen to form chromium oxide Cr ₂ O ₃ . Considering the silicon content in the silicon iron, the lower limit of the total amount of silicon iron and aluminum ingot set in the present invention is 4 kg / t. However, in the smelting of high chrome steel, for example, in a steel having a chromium content of 22.6%, when the initial carbon content before entering the VOD is 0.6%, the oxygen intake amount per ton of steel is about 13 Nm ³ / t, It can be decarburized under the conditions. Experience has shown that about 5.6 to 7.24 kg of pure silicon or 7.5 to 9.7 kg of pure aluminum is required for about 35 to 45% oxygen to form chromium oxide Cr ₂ O ₃ . Considering the silicon content in the silicon iron, in the present invention, the upper limit of the total addition amount of the silicon iron and the aluminum ingot should be set to 9 kg / t. The amount of lime added is determined according to the amount of SiO ₂ produced, and the basicity needs to be met. The amount of the lime added in the present invention is a large value among four to six times the mass of the iron-added iron and two to three times the amount of the aluminum ingot, and the slag basicity of the furnace can be satisfied in the range of 2.8 or more. the mass ratio of the CaO and Al ₂ O ₃ greater than one. In the addition of fluorite, the main purpose is to accelerate the dissolution and melting of lime, and the amount added is determined by the degree of melting of the lime itself. According to production experience, the addition mass of fluorite is 0.05 to 0.3 times the mass of lime added. In step (2), it is required that the added silicon iron and aluminum ingot do not significantly lower the dissolved oxygen content in the steel and the oxygen content exceeds 0.01%, whereby the silicon content in the steel after the reaction is less than 0.1% . In this step, the total amount of addition of iron and aluminum ingot was determined, but in actual practice, based on the specific rate of oxygen ingestion entering decarburization, secondary combustion, loss, and dissolution during decarburization in the smelting process, The amount of oxygen to be deoxidized by the iron and aluminum masses must be determined. Since the amount of decarburization is already known, the secondary combustion rate can be analyzed based on the gas components in the furnace, and the loss can be regressed on the basis of historical values, and the ratio of oxygen entering the decomposition site can be calculated. As a result, concrete numerical values of the total amount of addition of silicon iron and aluminum ingot can be calculated, which is within the range defined in the present invention.

In the step (2) of the present invention, the addition ratio of the relevant silicon iron and / or aluminum ingot must be determined.

a. When the upper limit of the silicon mass content (ie, the target silicon content) in the final obtained high-purity aluminum high-purity super-high-purity ferritic stainless steel is required to be 0.3%, silicon iron is added in its entirety.

b. If the upper limit of the silicon mass content is required to be lower, ie the upper limit is less than 0.2% (inclusive of 0.2%), the entire aluminum mass is to be added in the final obtained high aluminum high silicon super high purity ferritic stainless steels.

c. When the upper limit value of the silicon mass content in the final obtained high aluminum aluminum silicate ultra high purity ferritic stainless steel is 0.2 to 0.35, the addition amount of silicon iron and aluminum ingot is added, and the addition ratio of the silicon iron and aluminum ingot = -0.2%) / (0.3% - upper limit value of the silicon mass content in the ultrahigh-purity high-purity ferrite stainless steel obtained in the final stage) of the low-silicon ultra-high purity ferritic stainless steel.

Among them, the upper limit value of the silicon mass content in the finally obtained high aluminum aluminum silicate ultra high purity ferritic stainless steel indicates the value that the silicon content should not be exceeded.

In the present invention, further aluminum is selected to carry out the pre-deoxidation mainly for some steel grades requiring a lower target silicon content. If the target silicon content is less than 0.3%, the above goal can be achieved by adding all of the silicon iron and controlling for the subsequent basicity. However, when it is required that the target silicon content is lower than 0.2%, it is about 0.1 to 0.2% in consideration of an increase in the amount of silicon in the final deoxidization process. Here, when silicon is increased by adding silicon iron, It can not satisfy the requirement smaller than 0.2%. Thus, in such a situation, all aluminum should be added. When the upper limit of the target silicon mass content is 0.2 to 0.3%, a mixed addition of silicon iron and an aluminum ingot is designed in the present invention, and the specific ratio is determined according to the upper limit of the content of the target silicon, and the above requirements can be satisfied.

2) Final deoxidation

In the final deoxidation step of the step (3) of the present invention, the final deoxidation treatment is carried out through a method of adding aluminum iron, wherein the aluminum mass percentage in aluminum iron is 20 to 60% and the carbon mass content is less than 0.1% , Extra iron and some trace impurities. The addition amount of pure aluminum in the aluminum iron is 2 to 6 kg / t, and the addition amount of lime and fluorite is supplemented. The addition amount of lime is 2 to 3 times of the amount of pure aluminum in aluminum iron, 0.05 to 0.3 times. After the addition of the material, the medium intensity agitation is first conducted under vacuum conditions for 2 to 5 minutes, and then, for 12 to 18 minutes under high vacuum and strong agitation conditions. After the treatment, the silicon mass content is less than 0.3%, the aluminum mass content is 0.01 to 0.1%, and the oxygen mass content is less than 0.003%.

When aluminum iron having a relatively high density is used as a deoxidizing agent for the final deoxidation, as described above, after the addition of aluminum iron, the aluminum contained therein enters the melting point of the liquid steel, which is different from that when pure aluminum is added It brings different effects. When pure aluminum is added, most of it is reacted with the oxide in the slag after the addition, so that the liquid steel does not basically melt in the slag. Production practice already proved this. The aluminum mass percentage of aluminum in the aluminum iron is 20 to 60%, which not only satisfies the range of density requirements, but also takes into consideration the following problems. That is, when the aluminum content is less than 20%, since there is a demand for the amount of pure aluminum added in the present invention, the amount of aluminum itself is excessively increased, and thus the iron content becomes too large. This not only increases the amount of carbon footprint, but also the temperature drop of the dissolution zone is too great. Calculations show that the energy released when 1 kg of aluminum participates in the reaction is equivalent to the energy of heating about 4 kg of iron from room temperature to the current temperature of the liquid steel, ie, 1700 ° C. From this it can be seen that the aluminum content in the aluminum iron must exceed 20% and the aluminum content in the aluminum iron less than 60% is primarily taken into account for the demand for density control. The density of aluminum iron should exceed 4.5 g / cm < ³ > and the corresponding aluminum content is 60%. The aluminum content of less than 0.01% is considered mainly in the control of the coal. Since the smelting steel paper is ultra low-carbon steel, the smaller the amount of coal after the addition of aluminum iron is, the better the carbon content in aluminum iron is 0.1% and the amount of aluminum iron added to the steel per tonne of 10 kg is 10 ppm, . Thus, the carbon content in the aluminum iron should be less than 0.1%, which is also a range of carbon contents achievable in the production of aluminum iron. The addition amount of aluminum iron is calculated by pure aluminum in it. The amount of pure aluminum required in the present invention is 2 to 6 kg / t. The addition of aluminum not only removes the dissolved oxygen in the steel, but also reduces Cr ₂ O ₃ in the slag that can not remove silicon iron in the pre- . It is necessary to consume about 0.5 to 2.4 kg / t of pure aluminum and further react with SiO _{2 in the} slag. The resulting amount of silicon returned is 0.1% to 0.2%, and the amount of pure aluminum consumed is 1.4 to 2.6 kg / t. It is also necessary to satisfy the target of 0.01 to 0.1% of the aluminum content of the final object, and the consumed pure aluminum is about 0.1 to 1 kg / t. As described above, the addition amount of pure aluminum obtained through the addition of the lower limit value and the addition of the upper limit value is 2 to 6 kg / t, and the addition amount of aluminum iron is a value obtained by dividing the pure aluminum addition amount by the aluminum content. The purpose of supplementing lime is to secure the mass ratio of CaO and Al ₂ O _{3 in} the furnace slag. In the present invention, it is required to stir the material at a moderate intensity for 2 to 5 minutes under a vacuum condition after adding the material at this stage. The object of the present invention is to prevent the aluminum from entering the liquid steel On the other hand, if agitation is too strong, aluminum can be sprayed onto the slag surface to prevent aluminum from entering the liquid stream. Thus, a medium intensity agitation is performed here. The high-vacuum strong agitation treatment time required in the present invention is 12 to 18 minutes, which is mainly due to the fact that Al ₂ O ₃ It is possible to ensure that the impurities are grown and sufficiently floated and removed in the weak agitation process under the following atmospheric conditions. It should also be noted that since aluminum in aluminum iron can sufficiently enter the liquid steel, when aluminum is deoxidized to a certain extent, aluminum is prevented from entering the slag directly and reducing MgO in the slag, Respectively. In stainless steels, magnesium aluminum spinel is a very harmful impurity, resulting in product defects. Since the control of aluminum and the control of silicon are realized by using aluminum iron, it can be ensured that after the treatment, the silicon mass content is less than 0.3%, the aluminum mass content is 0.01 to 0.1%, and the oxygen mass content is less than 0.003%.

Regarding the form and density of aluminum added in step (3) of the present invention, the form of aluminum iron in step (3) is massive or spherical, has a true density of 4.5 to 6.5 g / cm ³ , Is 3 to 6 cm.

The shape of the material is massive or spherical in order to facilitate manufacture and addition. If the diameter is less than 3 cm, the depth of impact will be insufficient when the aluminum iron enters the liquid steel dissolution from the bunker. However, if the size is too large, it becomes inconvenient to add the material, so that it should be less than 6 cm. The density ranges from 4.5 to 6.5 g / cm ³ due to the consideration of satisfying the requirement that 2/3 of the portion is mainly introduced into the liquid steel after the addition, and the density of the liquid steel is about 6.9 to 7.2 g / cm ³ . / cm < ³ >, and the upper limit of the density is set to 6.5 g / cm < ³ > considering that the aluminum content is 20%

In the refining step (3) in the present invention, the slag basicity to after the final deoxidation, i.e., and control the mass ratio of CaO and SiO ₂ in the slag less than 2.8, the mass ratio of the furnace slag, CaO and Al ₂ O ₃ is the first To be exceeded.

The requirement of a slag basicity of 2.8 or higher in the furnace after the final deoxidation is mainly considered from controlling the activity of SiO ₂ . Based on the CaO-SiO ₂ -Al ₂ O ₃ ternary activity, the activity coefficient of SiO ₂ is about 0.028 under pure conditions under the above basic conditions. According to the thermodynamic calculation, the activity of the equilibrium SiO _{2 in} the slag corresponding to the aluminum content of 0.01% and the silicon content of 0.3% in the steel is about 0.009, for example, the smelting of ultra high purity ferritic stainless steel of 22.6% Under this basicity condition, the mole fraction of SiO ₂ in the slag by inverse decomposition is 0.32. Since the basicity is set to at least 2.8, the white powder content of SiO ₂ is inevitably less than 26%. Based on this range, its mol fraction can generally be controlled to be less than 0.32. From this, it can be confirmed that Al does not reduce SiO ₂ in the slag under the condition of the silicon aluminum content within the basicity range. If the content of chromium is less than 22.6% for other types of steel with different chromium contents, chromium lowers the activity of silicon but increases the activity of aluminum. Therefore, based on the thermodynamic principle of smelting, And Al is not able to reduce SiO ₂ in the forward slag. In the opposite situation, the Al element can reduce SiO ₂ in the slag. There are not many steel types having a chromium content of 22.6% or more. By controlling the SiO ₂ content in the slag, it is possible to prevent the Al from reducing the SiO ₂ in the further slag. Setting the lower limit of the basicity too high results in an increase in slag , The basicity of the in-furnace slag finally determined in the present invention is at least 2.8, which is also the minimum requirement for slag basicity in the furnace. There is no requirement for the upper limit of the furnace slag basicity, if mainly requires that the aluminum content is higher, increasing the Al ₂ O ₃ in the slag, and the furnace can increase the slag basicity, and further end-furnace slag has SiO ₂ content is very It becomes low aluminum calcium slag. In other words, the slag in the furnace becomes a slag mainly composed of CaO-Al ₂ O ₃ . This is allowed by the present invention. In the present invention, it is required that the mass ratio of CaO and Al ₂ O ₃ in the furnace slag exceeds 1. It is mainly required that the mass ratio of CaO and Al ₂ O ₃ exceeds 1 in the case where the content of SiO _{2 in the} furnace slag is relatively low to be aluminum calcium slag. Thus ensuring that the furnace slag easily has the ability to absorb Al ₂ O ₃ . With respect to the aluminum calcium slag, under the condition that the mass ratio of CaO and Al ₂ O ₃ is 1.1 to 1.4, the slag in the furnace has an ability to easily absorb impurities and has very good fluidity. There is no limitation on the upper limit of the CaO and Al ₂ O ₃ in the present invention, under the circumstances, primarily non-calcium aluminum slag, allows in the range of the content of Al ₂ O ₃ low. The control of CaO content in the furnace slag was already controlled in the setting for the amount of lime added in steps (2) and (3).

3. In step (5)

1) Weak stirring

The weak agitation before pure calcium wire feeding causes the already grown Al ₂ O ₃ impurities to float and enter the slag under vacuum conditions. The weak agitation after pure calcium wire feeding promotes the entry of calcium gallate impurities of low boiling point after calcium wire feeding into the slag phase.

2) Wire feeding

A) Calcium wire feeding (i.e. calcium treatment process)

The pure calcium wire is fed to the liquid steel using a calcium treatment process, i.e., a wire feeder under normal pressure conditions. The feed amount of the pure calcium wire is 0.1 to 0.3 kg / t. After calcium wire feeding, argon is blown to the bottom under atmospheric pressure to proceed weak stirring to the liquid steel. The weak stirring is continued for 5 to 10 minutes, and after the treatment, the calcium mass content in the steel is controlled to 15 to 30 ppm.

In the present invention, since aluminum is a high-grade steel, the amount of aluminum added during the deoxidation process is relatively large. Various measures have been taken to prevent secondary oxidation by discharging Al ₂ O ₃ impurities generated in the liquid steel, but Al ₂ O ₃ still continues to block the tundishes during production. The reason for this is that, when the aluminum content is high, aluminum can reduce MgO in the slag, and the formed magnesium aluminum spinel impurities can not be easily removed. Thus, it may cause clogging. Al ₂ O ₃ impurities that have not been removed well also have the risk of blocking the tundish nozzle. In the present invention, various measures have already been taken to reduce this risk, but in order to ensure high stability of high aluminum production, the present invention avoids the risk of clogging of the tundish nozzle by using calcium treatment technology. Calcium treatment is mainly performed with Al ₂ O ₃ Thereby converting the impurity into 12CaO · 7Al ₂ O ₃ low-melting point impurity. Generally, the maximum value of the Al ₂ O ₃ content in the steel is 0.01%, and the calcium content required to convert this content of Al ₂ O ₃ to 12CaO · 7Al ₂ O ₃ is 67 ppm. Further, it is required that the dissolution amount of the calcium element itself after the calcium treatment is generally 0.09 to 0.15 times the aluminum content. If the aluminum content is 0.03, the dissolved calcium content is about 30 ppm, and the amount of pure calcium entering the liquid steel is 100 ppm, or 0.01%. Considering that the yield of calcium exceeds 30% in the calcium feeding process for high aluminum steel, it was finally determined that the feed amount of pure calcium was 0.1 to 0.3 kg / t, and finally, the control range of the calcium content was 15 to 30 ppm, satisfying the calcium treatment of the aluminum content range of the present invention, and realizing an effective modification of impurities. If the final calcium content exceeds 30 ppm, there is a risk of corroding the tundish nozzle.

B) Titanium Wire Feeding

In the smelting of titanium-containing steel, advanced titanium wire can be fed to the liquid steel of ferritic stainless steel, and the amount of pure titanium in the titanium wire is 1 to 3 kg / t, and titanium alloying can be realized. Among them, the amount of pure titanium is the amount of titanium wire feed multiplied by the titanium content in the titanium wire.

4. In step (6)

1) Mild agitation for 15 to 30 minutes

The weak agitation time causes the impurities to float forward, thereby further improving the purity of the liquid steel.

2) Playing liquid steel under a protective atmosphere

Performances under a protective atmosphere include argon gas protection for the turn-around dies nozzle, argon gas protection for the intermediate turn-off nozzles and argon gas protection over the intermediate turn-offs. The purpose is to prevent secondary oxidation of the liquid steel. In high aluminum smelting, this protection is necessary, and these are mature playing techniques that are feasible, where further description is omitted.

5. For medium intensity agitation, high vacuum agitation and weak agitation

The conditions of the medium strength stirring are that the vacuum pressure is controlled to 2000 Pa or lower and the blowing amount of the lower part of the argon gas into VOD is controlled in the range of 1 to 4 L / (min · t).

The conditions of the high vacuum and strong stirring are that the vacuum pressure is controlled to 800 Pa or lower and the blowing amount of the lower part of the argon gas into the VOD is controlled in the range of 4 to 8 L / (min · t).

The conditions of the weak stirring are to control the blowing amount of the lower portion of the argon gas into the VOD under the atmospheric pressure to a range of 1 to 5 L / (min · t).

Among them, the setting of the related parameters must be confirmed according to the production practice. The medium strength agitation under vacuum conditions should ensure that the surface of the slag does not vigorously boil and the conditions of high vacuum and strong agitation should be ensured such that spraying of the liquid steel does not affect the production and weak agitation should ensure that the slag surface is not released do. Under the above conditions, through the search for production, finally, the range of the related lower limit injection amount is determined.

It should be noted that in the present invention, a unit symbol "t" represents a tonal liquid steel, "L" represents a liter, "min" represents a minute, and "kg / t" "L / (min · t)" indicates the amount of argon gas blown into the steel per minute per minute.

Example

The method of producing low-silicon high-aluminum ferritic stainless steel by the method of the present invention and the effect obtained by combining the following embodiments will be described in detail. High-purity ferritic stainless steels, 409, 443 and 445, which produce three varieties of steel, are described as examples.

Example 1

Can process the liquid steel 120t for furnace refining VOD in the present embodiment, the ultimate degree of vacuum of less than 300Pa, and the argon gun blowing capacity of the lower part exceeds 60Nm ³ / h, the refractory material of the ray is magnesium, calcium brick work . The steel grade is 409, the amount of liquid steel is 116000 kg, or 116 t, and the initial component of the liquid steel before VOD smelting is as follows.

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.3% of C, 0.25% of Si, 11.6% of Cr, 0.010% of S, 0.025% of N, 0.55% of Mn, 0.015% of P, , The excess is Fe and trace impurity element.

The initial temperature of the liquid steel is 1580 ° C.

In this embodiment, the target of the silicon content is less than 0.26%, the aluminum content is about 0.03%, and the specific steps are as follows.

1) After oxygen blanket decarburization and free decarburization treatment on the liquid steel, the oxygen consumption is 885 Nm ³ and the free decarbonization time is 15 minutes. After the treatment, the temperature of the liquid steel is 1630 ?, and the components are as follows.

0.003% of C, 0.01% of C, 11.1% of Cr, 0.008% of S, 0.007% of N, 0.14% of Mn, 0.015% of P, 0.04% of all of O, 0.01% , The excess is Fe and trace impurity element.

2) Preliminary deoxidation The upper high limit of the silicon mass content in the final obtained high-aluminum low silicon super-purity ferrite stainless steel is required to be 0.27%. Therefore, 400 kg of silicon iron having a silicon content of 77% (that is, 3.45 kg / : 200 kg (i.e., 1.71 kg / t), a total of 600 kg (that is, 400 kg / liquid steel amount 116 t, the same as in Example 1 except for the mass of lime and fluorite) , 5.16 kg / t) was added to perform preliminary deoxidation. The slag was prepared by adding 1.6t of lime and 200kg of fluorspar. The slag was controlled by controlling the vacuum pressure to 800 Pa or less after the addition of the material, and the stirring intensity at which the lower part of the argon gas was blown was 600 L / min (i.e., 5.17 L / min · t), conversion method: 600 L / min ÷ amount of liquid steel: 116 t, conversion method within the range of Example 1 is the same as described below), and the treatment time is 8 minutes to secure initial dissolution of the lime. After the treatment, the silicon content is 0.08% and the oxygen content is 0.015%.

3) Final deoxidation, 650 kg of aluminum iron with an aluminum content of 40% was added. The aluminum iron has a diameter of 5 cm, a density of 5.4 g / cm ³ , a carbon content of 0.008%, and pure aluminum of 260 kg (i.e., 2.24 kg / t). 600 kg of lime and 50 kg of fluorite were supplemented and finally deoxidized. After the addition of the material, the amount of argon gas blown in the bottom agitation was adjusted to 150 L / min and the moderate intensity agitation was performed for 3 minutes. Subsequently, high-strength agitation is carried out, and the lower part argon blowing amount is 800 L / min (i.e., 6.90 L / (min · t)) and the processing time is 15 minutes. After the treatment, the silicon content is 0.19%, the aluminum content is 0.054%, and the oxygen content is 7.8 ppm. The main components of the furnace slag were CaO 60%, SiO ₂ 12%, Al ₂ O ₃ 17% and MgO 3%, which satisfied the requirement that the slag basicity of the furnace and the ratio of CaO and Al ₂ O ₃ should be greater than 1 . After the treatment, the temperature is 1570 ° C.

4) Vacuum was released.

5) Mild agitation for 10 minutes, stirring intensity of bottom argon gas blow is 200 L / min (ie 1.72 L / (min · t)). 20 kg of pure calcium wire (i.e., 0.17 kg / t) was added using a calcium treatment and a wire feeder. After the wire feeding, slight agitation was performed for 10 minutes and the stirring strength of the lower part of the argon gas blow was 200 L / min (I.e., 1.72 L / (min · t)). This steel requires titanium alloying through titanium wire feed. The amount of pure titanium in the titanium wire is 150 kg (i.e., 1.38 kg / t), and the final titanium is 0.1%.

6) Subsequently, slight agitation was carried out for 20 minutes and the stirring intensity of the lower part of the argon gas blowing was 180 L / min (i.e. 1.55 L / (min · t)). Playing in a protective atmosphere, both the turn-on dash nozzle and the intermediate turn-off nozzle were protected with argon blowing.

During the casting process, the aperture of the intermediate turn-off nozzles is very stable, no violent waves occur, and the total wave range is within 3%, which means that no clogging of the nozzles has occurred and no erosion of the nozzles has occurred I will express.

Finally, the liquid steel was cast into a billet, the components of which are as follows.

0.006% of C, 0.20% of Si, 11.7% of Cr, 0.001% of S, 0.008% of N, 0.23% of Mn, 0.015% of P, 0.0020% of total O, 0.09% , The excess is Fe and trace impurity element.

Among them, the silicon content was slightly increased after releasing the vacuum state, which was a small amount of SiO _{2 in the} slag Is reduced by aluminum. However, the content of aluminum was slightly lowered, and it is considered that the reason for this is that the contact between aluminum and oxygen is promoted by the lowering of temperature and the passage of time, and possible secondary oxidation, and the component thereof is slightly lowered. Aluminum added in the deoxidation process contains a certain amount of carbon, so that the carbon content is increased to some extent before the treatment but still falls within the ultra-high purity range.

In the cast billets, the amount of magnesium aluminum spinel impurities was drastically reduced as compared with the general process. The impurities mainly consisted of TiN or Ti (CN) impurities having a size of 5 μm or less and spherical calcined CaO-Al ₂ O ₃ -SiO ₂ Impurities (some of which contain a small amount of MgO) and there is no adverse effect on the performance of the steel, in particular its surface performance.

Example 2

Can process the liquid steel 120t for furnace refining VOD in the present embodiment, the ultimate degree of vacuum of less than 300Pa, and the argon gun blowing capacity of the lower part exceeds 60Nm ³ / h, the refractory material of the ray is magnesium, calcium brick work . The steel grade is 443, the amount of liquid steel is 108400 kg, or 108.4 t, and the initial component of the liquid steel before VOD smelting is as follows.

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.36% of C, 0.018% of Si, 20.8% of Cr, 0.005% of S, 0.015% of N, 0.3% of Mn, 0.010% of P, , The excess is Fe and trace impurity element.

The initial temperature of the liquid steel is 1600 ° C.

In this embodiment, the target of silicon content is less than 0.2%, the aluminum content is about 0.02%, and the specific steps are as follows.

1) After the oxygen blowing decarburization and free decarburization treatment on the liquid steel, the oxygen consumption is 1266 Nm ³ and the free decarburization time is 20 minutes. After the treatment, the temperature of the liquid steel is 1670 캜, and the components are as follows.

0.005% of C, 0.01% of Si, 19.7% of Cr, 0.004% of S, 0.004% of N, 0.14% of Mn, 0.015% of P, 0.05% , The excess is Fe and trace impurity element.

2) Preliminary deoxidation. The upper limit of the silicon mass content in the finally obtained high-aluminum high-purity ultra-high-purity ferrite stainless steel was required to be 0.2%, and all the aluminum ingots were added under these conditions. The addition of silicon iron prevented the increase of silicon. The preliminary deoxidation is carried out by adding 780 kg of the aluminum ingot (i.e., 7.20 kg / t, conversion method: 780 kg ÷ liquid steel amount 108.4 t, except for the mass of lime and fluorite in the range of Example 2, Respectively. The slag was prepared by adding 1.6t of lime and 100kg of fluorspar. The slag was controlled by controlling the vacuum pressure to 800 Pa or less after the addition of the material, and the stirring intensity to blow the lower part of the argon gas was 700 L / min (i.e., 6.46 L / min · t), conversion method: 700 L / min ÷ amount of liquid steel: 108.4 t, conversion method within the range of Example 2 is the same), and the treatment time is 6 minutes, securing initial dissolution of lime. After the treatment, the silicon content is 0.04% and the oxygen content is 0.02%.

3) Final deoxidation, 500 kg of aluminum iron (i.e., 4.61 kg / t) with an aluminum content of 40% was added. The aluminum iron has a diameter of 5 cm, density of 5.4 g / cm ³ , a carbon content of 0.01%, and pure aluminum of 200 kg (i.e., 1.85 kg / t). 400 kg of lime and 50 kg of fluorite were supplemented to carry out the final deoxidation. After the addition of the material, the amount of argon gas introduced into the bottom agitation was adjusted to 200 L / min (ie, 1.85 L / (min · t)) and the moderate intensity agitation was performed for 4 minutes. Subsequently, high-strength agitation is carried out, and the lower part of the argon gas blowing amount is 800 L / min (i.e., 7.38 L / (min · t)) and the processing time is 18 minutes. After the treatment, the silicon content is 0.20%, the aluminum content is 0.018%, and the oxygen content is 10 ppm. Furnace main component _{CaO 55%, SiO 2 2%} , Al 2 O 3 And 37%, MgO 5%, which satisfied the requirements and greater than the required ratio of CaO and Al ₂ O ₃ to the slag basicity in the furnace. After the treatment, the temperature is 1605 ° C.

4) Vacuum was released.

5) Mild agitation 9 minutes, stirring intensity of bottom argon gas blow is 200 L / min (ie 1.85 L / (min · t)). 12.8 kg of pure calcium wire (i.e., 0.12 kg / t) was added using calcium treatment and a wire feeder. After the wire feeding, slight agitation was performed for 10 minutes and the stirring strength of the lower part of the argon gas blow was 200 L / min (i.e., 1.85 L / (min · t)). This steel requires titanium alloying through titanium wire feed. The amount of pure titanium in the titanium wire is 300 kg (i.e., 2.77 kg / t), and the final titanium is 0.2%.

6) Subsequently, weak stirring was carried out for 25 minutes, and the stirring intensity of the lower part of the argon gas blowing was 160 L / min (i.e. 1.48 L / (min · t)). Playing in a protective atmosphere, both the turn-on dash nozzle and the intermediate turn-off nozzle were protected with argon blowing.

0.008% of C, 0.20% of Si, 20.8% of Cr, 0.001% of S, 0.006% of N, 0.21% of Mn, 0.015% of P, 0.0018% of total O, 0.15% , The excess is Fe and trace impurity element.

Among them, the aluminum content slightly increased because the oxygen potential of the liquid steel was further deteriorated due to the titanium wire feeding. However, the silicon content remains unchanged, because the SiO ₂ content in the slag is extremely low, preventing aluminum or titanium from further reducing the silicon in the slag during the deoxidation process. Because the added aluminum iron contains a certain amount of carbon, the carbon content has increased by a certain amount compared to before treatment but is still within the high purity range.

Example 3

Can process the liquid steel 120t for furnace refining VOD in the present embodiment, the ultimate degree of vacuum of less than 300Pa, and the argon gun blowing capacity of the lower part exceeds 60Nm ³ / h, the refractory material of the ray is magnesium, calcium brick work . The steel grade is 444, and the amount of liquid steel is 11000 kg, or 110 t. The initial components of the liquid steel before VOD smelting are as follows.

The steel sheet was found to contain 0.40% of C, 0.06% of Si, 18.8% of Si, 0.005% of S, 0.012% of N, 0.3% of Mn, 0.010% of P, 0.02% of total O, , The excess is Fe and trace impurity element.

The initial temperature of the liquid steel is 1620 ° C.

In this embodiment, the target of the silicon content is less than 0.3%, the aluminum content is about 0.04%, and the specific steps are as follows.

1) After oxygen blanket decarburization and free decarburization treatment on the liquid steel, the oxygen consumption is 1440 Nm ³ and the free decarbonization time is 20 minutes. After the treatment, the temperature of the liquid steel is 1700 ° C, and the components are as follows.

0.006% of C, 0.20% of Si, 17.4% of Cr, 0.005% of S, 0.005% of N, 0.14% of Mn, 0.015% of P, 0.05% of O, 0.01% , The excess is Fe and trace impurity element.

2) Preliminary deoxidation. The upper limit of the silicon mass content in the finally obtained high-aluminum high-purity ultra-high-purity ferritic stainless steel is required to be 0.3%. Under these conditions, silicon iron is entirely added without adding the aluminum agglomerates. 900 kg of silicon iron having a silicon content of 77% (i.e., 8.12 kg / t, conversion method: 900 kg ÷ amount of liquid steel: 110 t, the mass of lime and fluorite in the range of Example 3) ) Was added to perform preliminary deoxidation. The slag was prepared by adding 3.6 tons of lime and 200 kg of fluorspar. The slag was controlled by controlling the vacuum pressure to 400 Pa or less after the addition of the material, and the stirring strength at which the lower part of argon gas was blown was 800 L / min (i.e., 7.27 L / min · t), conversion method: 800 L / min ÷ amount of liquid steel: 110 tons, conversion method within the range of Example 3 is the same), and the treatment time was 10 minutes, and initial dissolution of lime was secured. After the treatment, the silicon content is 0.1% and the oxygen content is 0.013%.

3) Final deoxidation, 750 kg of aluminum iron (i.e., 6.82 kg / t) with an aluminum content of 47% was added. The aluminum iron has a diameter of 5 cm, a density of 5.1 g / cm ³ , a carbon content of 0.007%, and contains 350 kg of pure aluminum (i.e. 3.18 kg / t). 700 kg of lime and 200 kg of fluorite were supplemented to proceed final deoxidation. After the addition of the material, the amount of argon gas introduced into the bottom agitation was adjusted to 200 L / min (ie, 1.82 L / (min · t)) and the moderate intensity agitation was performed for 5 minutes. Subsequently, high-strength agitation is carried out, and the bottom argon blowing amount is 750 L / min (i.e., 6.82 L / (min · t)) and the processing time is 18 minutes. After the treatment, the silicon content is 0.27%, the aluminum content is 0.035%, and the oxygen content is 10 ppm. The main ingredients in the furnace are CaO 65%, SiO ₂ 18%, Al ₂ O ₃ 10% and MgO 5%, which satisfied the requirement for the slag basicity in the furnace and the ratio of CaO and Al ₂ O _{3 to} be greater than 1. After the treatment, the temperature is 1642 ° C.

4) Vacuum was released.

5) The agitation strength of the lower part argon gas blowing is 200 L / min (ie 1.82 L / (min · t)) for 10 minutes with weak agitation. After the wire feeding was completed, weak stirring was carried out for 10 minutes, and the stirring strength of the lower part of the argon gas blowing was 180 L / min. min (i.e., 1.64L / (min · t)). This steel type does not require titanium alloying and therefore does not proceed with titanium wire feeding.

6) Subsequently, weak stirring was carried out for 15 minutes and the stirring intensity of the lower part of the argon gas blowing was 180 L / min (ie 1.64 L / (min · t)). Playing in a protective atmosphere, both the turn-on dash nozzle and the intermediate turn-off nozzle were protected with argon blowing.

During the casting process, the aperture of the intermediate turn-off nozzle is very stable, no violent wave is generated, and the total wave range is within 5%, which means that no clogging of the nozzle has occurred and no erosion of the nozzle has occurred I will express.

A steel sheet comprising 0.01% of C, 0.29% of Si, 18.6% of Cr, 0.001% of S, 0.007% of N, 0.21% of Mn, 0.015% of P, 0.0017% of total O, %, And the excess is Fe and a trace impurity element.

There was a slight decrease in aluminum content but a slight increase in silicon content. This is because the content of SiO ₂ in the slag is relatively high, so that aluminum reduces the silicon in the forward slag, and since the aluminum contained in the deoxidation contains a certain amount of carbon, the carbon content is increased to some extent before the treatment, It is in the high purity range.

In the cast billet, the amount of magnesium aluminum spinel impurities was drastically reduced as compared with the general process, and the impurities were mainly spherical calcined CaO-Al ₂ O ₃ -SiO ₂ Impurities (some of which contain a small amount of MgO) and there is no adverse effect on the performance of the steel, in particular its surface performance.

In the smelting method of a kind of high aluminum low silicon super high purity ferrite stainless steel provided in the present invention, a low silicon high aluminum super high purity ferrite stainless steel having a silicon content of less than 0.3% and an aluminum content of 0.01 to 0.1% can be smelted , The total oxygen content in the bilett was less than 30 ppm, and the acid pickling performance of the product was improved. The present invention also effectively inhibited the formation of magnesium aluminum sphene, a harmful impurity, and effectively removed Al ₂ O ₃ impurities. It also inhibited the oxidation of titanium in titanium-containing steels and prevented clogging of intermediate turn-off nozzles during the performance process.

Claims

(1) For the liquid steel of the ferritic stainless steel, the main components of the liquid steel of the ferritic stainless steel subjected to the vacuum oxygen blowing decarburization and free decarburization treatment in the VOD furnace are 10 to 23% of the chromium mass percentage , A carbon mass percentage of less than 0.01%, a nitrogen mass percentage of less than 0.01%
(2) Preliminary deoxidation: A preliminary deoxidation treatment is carried out by adding silicon iron and / or an aluminum ingot to the liquid steel of the ferritic stainless steel obtained through the step (1), lime and fluorite are added to prepare slag, Treated for 5 to 10 minutes under high vacuum and strong stirring conditions,
(3) Final deoxidation: Aluminum iron is added to the liquid steel of the ferritic stainless steel obtained through the step (2) to carry out a final deoxidation treatment. The aluminum aluminum percentage in the aluminum iron is 20 to 60% To prepare a slag. The slag is then subjected to moderate strength agitation for 2 to 5 minutes under vacuum conditions, then for 12 to 18 minutes under conditions of high vacuum and strong agitation,
(4) releasing the vacuum state,
(5) Under a normal pressure condition, weak stirring is performed on the liquid steel of the ferritic stainless steel for 8 to 10 minutes, then calcium wire feeding is performed on the liquid steel of the ferritic stainless steel under atmospheric pressure, After completion of the reaction, weak stirring is carried out for 5 to 10 minutes,
(6) Subsequently, weak stirring is performed for 15 to 30 minutes, and then the ferrite stainless steel is subjected to performance under a protective atmosphere to obtain a high-aluminum low silicon ultra-high purity ferritic stainless steel High-purity ferritic stainless steel.

The method according to claim 1,
In the step (2), the total amount of the silicon iron and / or aluminum ingot is 4 to 9 kg / t, and the silicon iron percentage in the silicon iron is 70 to 80% Takes a large value in two ranges of 4 to 6 times the mass or 2 to 3 times the mass added of the aluminum ingot; Wherein the added mass of the fluorite is 0.05 to 0.3 times the mass of the lime added and after the treatment of step (2), the mass content of silicon in the liquid steel of the ferritic stainless steel is greater than 0 and less than 0.1%; Wherein the oxygen content is greater than 0.01%. &Lt; RTI ID = 0.0 > 11. < / RTI >

The method according to claim 1,
In the step (3), the amount of pure aluminum added in the aluminum iron is 2 to 6 kg / t, the amount of the lime added is 2 to 3 times the amount of pure aluminum in aluminum, and the amount of fluorite added is 0.05 To 0.3 times; After the treatment of step (3), the silicon mass content in the liquid steel of the ferritic stainless steel is greater than 0 and less than 0.3%; Wherein the aluminum mass content is 0.01 to 0.1% and the oxygen content is less than 0.003%.

The method according to claim 1,
In the step (5), the calcium wire feeding is a pure calcium wire feed to the liquid steel of the ferritic stainless steel, the pure calcium wire feed amount is 0.1 to 0.3 kg / t, and the step (5) Wherein the calcium content in the liquid steel of the ferritic stainless steel is in the range of 15 to 30 ppm after the ferritic stainless steel is finished.

The method according to claim 1,
In step (5), titanium wire feeding is performed on liquid steel of ferritic stainless steel after calcium wire feeding and weak stirring, and the amount of pure titanium in the titanium wire is 1 to 3 kg / t. High Aluminum Silicon Ultra High Purity Ferritic Stainless Steel Smelting Method.

The method according to claim 1,
Wherein the silicon mass percentage content is less than 0.3% and the aluminum mass percentage content is 0.01 to 0.1% in the finally obtained high-purity aluminum high-purity super-high-purity stainless steel.

The method according to claim 1 or 2,
In the step (2)
When the upper limit value of the silicon mass content in the final obtained high aluminum aluminum silicate ultra high purity ferritic stainless steel is 0.3%, all the silicon iron is added,
When the upper limit of the content of silicon mass in the final obtained high aluminum aluminum silicate ultra high purity ferritic stainless steel is less than or equal to 0.2%, all the aluminum ingot is added,
When the upper limit value of the silicon mass content in the final obtained high aluminum aluminum silicate ultra high purity ferritic stainless steel is 0.2 to 0.3%, silicon iron and aluminum ingot are added, and the addition ratio of the silicon iron and aluminum ingot = Wherein the upper limit of the silicon mass content in the aluminum low silicon ultra high purity ferrite stainless steel is -0.2%) / (0.3% - the upper limit value of the silicon mass content in the high aluminum super low purity ultra high purity stainless steel obtained in the final stage) Smelting Method of Silicon Ultra High Purity Ferritic Stainless Steel.

The method according to claim 1 or 3,
In step (3), the aluminum iron is lumpy or spherical, the density is 4.5 to 6.5 g / cm ³ , the diameter is 3 to 6 cm, and after the treatment of step (3) ₂ is greater than 2.8 and the mass ratio of CaO to Al ₂ O _{3 in} the furnace slag is greater than 1. The method of claim 1,

The method according to claim 1,
The conditions of the high vacuum and strong stirring are to control the vacuum pressure to 800 Pa or less and control the amount of argon blowing at the bottom of the VOD to be in the range of 4 to 8 L / (min · t)
The conditions of the medium strength stirring are to control the vacuum pressure to 2000 Pa or less and control the amount of argon blowing at the bottom of the VOD to be in the range of 1 to 4 L / (min · t) Wherein the amount of argon blowing at the bottom of the VOD furnace is controlled to be in the range of 1 to 5 L / (min · t) under the condition that the furnace temperature is below the melting point of the furnace.