JP5833767B2 - Smelting method of high aluminum low silicon ultra pure ferritic stainless steel - Google Patents

Description

  The present invention relates to the field of smelting stainless steel, specifically to a method for smelting ferritic stainless steel, and more specifically to a method for smelting high aluminum low silicon ultrapure ferritic stainless steel.

  Ultra-pure ferritic stainless steel is a superior product in ferritic stainless steel, and generally requires a total content of carbon nitrogen of less than 150 ppm and a total oxygen content of less than 40 ppm, and the number, size and type of inclusions are Well controlled and ultra-pure ferritic stainless steel is partially replaced by austenitic stainless steel. Since inclusion of nickel element is not required, the effect of saving nickel resources is exhibited.

  As a smelting process of ultra-pure ferritic stainless steel, oxygen blown deep decarburization and denitrification treatment is generally performed in a vacuum oxygen decarburization furnace (abbreviated as VOD furnace) under the ultra-vacuum condition. The operation is as follows.

1. AOD treated steel hot pot (contains molten metal) is transported to the VOD treatment room, temperature and components are measured, if passed, enter the vacuum processing chamber, first vacuum and bottom stirring Second, oxygen decarburization treatment is performed under vacuum conditions, head oxygen blowing decarburization is performed under bottom stirring conditions, and it is determined whether or not to stop the oxygen blowing depending on the components of the furnace gas, and CO + CO ₂ in the furnace gas When the content of oxygen is lower than the prescribed value, stop blowing oxygen; 3. Free decarburize under ultra-vacuum conditions and stir vigorously; 4. Reduce process, ie ferrosilicon, aluminum, lime and firefly Add stones, deoxidize and silicon alloy; 5; break the vacuum; 6; feed the wire to atmospheric conditions, stir softly, and finally feed to casting.

  However, in the process of oxygen decarburization in the above step (2), the blown oxygen is not completely used for decarburization, and a substantial part of oxygen enters the melting tank, and chrome oxide or dissolved oxygen Since it exists in the form, it is necessary to perform further deoxygenation treatment after the free decarburization in step (3).

Of these, silicon and aluminum are commonly used deoxygenating elements. Each European steel company first uses pure silicon deoxygenation technology, and when aluminum deoxygenation is adopted as the cause, a large amount of inclusions of Al ₂ O ₃ are produced, which adversely affects many types of steel. However, the total oxygen content in the silicon deoxygenated steel is very high and the total oxygen in the billet is above 60 ppm, which affects the performance of the final product.

  As the demand for ultra-pure ferritic stainless steel is increasing and its total oxygen content is also required to be at a very low level, people are trying to reduce the oxygen content in steel to further reduce the silicon aluminum composite deoxygenation. Try the process. There are mainly the following patent documents concerning the silicon aluminum composite deoxygenation process.

Japanese Patent JP20020303324 (A) discloses a method of smelting ferritic stainless steel for preventing stripe pattern defects (also called waveform defects) by silicon aluminum composite deoxygenation. First, ferrosilicon is added to the deoxygenation process, the target silicon content is controlled to 0.20 to 3.0 wt%, and the slag alkalinity (the mass ratio of CaO to SiO _{2 in} the slag) is 1.2 to 2.4. It is required that the ratio of the Al content and the Ti content of the steel bath be in the range of 0.01 to 0.10 before being deoxidized with aluminum and finally cast. This method refers to the equiaxed crystal ratio (equiaxed crystal ratio) in the continuous casting process of steel bath, that is, the percentage that the formed equiaxed crystals occupy in all the crystals after the crystals solidify. Axis ratio is the percentage of the center equiaxed section diameter with respect to the billet diameter.) Reaches 60%, controls the inclusion components well, prevents clogging of the intermediate tundish nozzle in the casting process, and finally steel The total oxygen content of the hot water is also maintained at a low level. However, in this patent, the alkalinity of the soot is controlled to 1.2-2.4, the oxygen activity of the slag is still high, and it is difficult to reduce the oxygen content of the steel bath to a low level.

  In the Chinese patent CN101058837 of the patent name “Ultrapure Ferritic Stainless Steel Decarburization and Denitrification Method”, a smelting method of ultrapure ferritic stainless steel is disclosed. After decarburizing the steel bath by vacuum treatment, the vacuum conditions (vacuum degree ≤ 5 mbar), first deoxygenation by adding ferrosilicon, deep deoxygenation in 5-10 minutes by adding aluminum, Tweaked. Since the treatment time of this deoxidation method is short and the effect of deoxygenation is good, it is widely used.

  However, JP2002030324 (A) and CN101058837 do not specifically teach how to add aluminum to steel bath, and the density of aluminum lump or aluminum fine particles is much lower than that of steel bath, so when added directly to VOD vacuum conditions It drifts in the upper part of the steel bath, directly contacts and reacts with the slag, releases a large amount of heat, enters the steel bath and is hard to precipitate and deoxygenate. The content is difficult to control, and the precipitation deoxygenation effect cannot be guaranteed.

  At the same time, the final content of silicon and aluminum elements related to the adoption of silicon-aluminum composite deoxygenation has a certain effect on the deoxygenation effect of steel, post-process treatment and steel structure performance. Mainly 1) If the aluminum content in the steel is low, the deoxidation effect is not significant, that is, the oxygen content in the steel is higher, and if the subsequent titanium supply treatment is performed, a large amount of titanium oxide inclusions 2), according to recent research, ferritic stainless steel with high silicon content (generally higher than 0.3%) has been pickled in the subsequent process Difficult, affects the smoothness of the surface of stainless steel products. Therefore, in order to further improve the mass of the product and the smoothness of production, for most varieties of ultra-pure ferritic stainless steel, control over the content of deoxygenated elements has developed in the direction of low silicon and high aluminum, Specifically, a silicon content of less than 0.3% or lower is required and the lower limit of the silicon content is determined according to other requirements of the steel. When the aluminum content is controlled to be in the range of 0.01 to 0.1%, the total oxygen content can be efficiently reduced, and oxidation of titanium in the subsequent titanium alloying process can be prevented.

Regarding the smelting of low silicon, high aluminum ultra pure ferritic stainless steel, as mentioned above, the aluminum content in the steel is raised to the target content range in the process of VOD treatment by such patent and ordinary method. At the same time, if the aluminum content is improved, once the control of billet slag alkalinity is inconvenient, the silicon content in the steel cannot be controlled within an appropriate range. If the aluminum content in steel is improved by imitating the aluminum deoxidation method in the carbon steel smelting process, that is, by supplying the aluminum wire, the difficulty of supplying the wire under vacuum conditions is great. Aluminum wire can only be supplied under vacuum conditions. This can certainly improve the aluminum content in the steel, but the stainless steel hot water cannot be vigorously stirred after feeding the aluminum wire, and the generated Al ₂ O ₃ inclusions are difficult to grow quickly and difficult to eliminate, and non-vacuum Conditioned aluminum wire supply increases the risk of nitrogen absorption in the hot water and extends the processing time. Therefore, the supply of aluminum wire under non-vacuum conditions is not a scientific method. If aluminum powder is blown under vacuum conditions, the aluminum content in the steel can be improved, but the vacuum blowing equipment is complicated and the control is difficult.

  Thus, the prior art and normal operations cannot efficiently solve the technical problem of improving the aluminum content in steel and controlling the silicon content under vacuum conditions.

In order to solve the above-mentioned problems, the present invention improves the reduction process of the VOD vacuum process, thereby adding high-density ferroaluminum to control the slag alkalinity of the billet, and then the wire supply process. The aim is to provide a method for smelting high aluminum low silicon ultra-pure ferritic stainless steel that employs measures such as protective casting during the continuous casting process. High aluminum low silicon ultra pure ferritic stainless steel can be smelted from VOD to continuous casting process, improving the pickling performance of ultra pure ferritic stainless steel, and the purity of steel bath and casting in continuous casting process Improves performance and at the same time efficiently suppresses the formation of harmful inclusions such as magnalium spinel, effectively removes Al ₂ O ₃ inclusions, suppresses titanium oxidation in titanium steel, and continuously casts Avoid clogging the intermediate tundish nozzle in the process.

  In order to achieve the above object, the present invention adopts the following technical scheme.

In the present invention, (1) the ferritic stainless steel hot water is vacuum-oxygen blown decarburized and free decarburized in a VOD furnace, and the main components of the treated ferritic stainless steel hot water are as follows: A content content of 10 to 23%, a carbon mass percentage content of less than 0.01%, a nitrogen mass percentage content of less than 0.01%,
(2) Preliminary deoxygenation: Ferrite silicon and / or aluminum lump is added to the ferritic stainless steel hot water obtained by the treatment in step (1), preliminarily deoxygenated, lime and fluorite are added to make slag, Then, a step of processing for 5 to 10 minutes under conditions of high vacuum and vigorous stirring,
(3) Final deoxygenation: Ferroaluminum is added to the ferritic stainless steel hot water obtained in step (2) and subjected to final deoxygenation treatment. The mass percentage content of aluminum in the ferroaluminum is 20-60%, and further lime and fluorite are added to make slag, then stirred under vacuum for 2-5 min at medium strength, then treated under high vacuum, vigorous stirring for 12-18 min And steps to
(4) Vacuum breaking step,
(5) After the above-mentioned ferritic stainless steel hot water is softly stirred for 8 to 10 minutes under normal pressure conditions, the calcium wire is supplied to the ferritic stainless steel hot water under normal pressure conditions, After the supply is completed, a step of stirring for 5 to 10 minutes in software;
(6) Subsequently, after gently stirring for 15 to 30 minutes, performing continuous casting of the ferritic stainless steel hot water in a protective atmosphere, and finally obtaining a high aluminum low silicon ultrapure ferritic stainless steel,
A method for smelting high-aluminum low-silicon ultra-pure ferritic stainless steel.

  In step (2), the total addition amount of the ferrosilicon and / or aluminum mass is 4 to 9 kg / t, the mass percentage content of silicon in the ferrosilicon is 70 to 80%, As the addition mass of lime, a large numerical value is selected from two ranges consisting of 4 to 6 times the addition mass of ferrosilicon and 2 to 3 times the addition mass of aluminum lump. The addition mass of fluorite is the addition mass of lime. After being treated in step (2), the mass content of silicon in the ferritic stainless steel hot water is less than 0.1%, exceeding 0, and the mass content of oxygen. Smelting method of high aluminum low silicon ultra-pure ferritic stainless steel.

  In step (3), the addition amount of pure aluminum in the ferroaluminum is 2 to 6 kg / t, the addition amount of lime is 2 to 3 times the addition amount of pure aluminum in ferroaluminum, and fluorite addition The amount is 0.05 to 0.3 times the amount of lime added, and after being treated in step (3), the mass content of silicon in the ferritic stainless steel hot water is less than 0.3% and more than 0 The smelting method of high aluminum low silicon ultrapure ferritic stainless steel, wherein the mass content of aluminum is 0.01 to 0.1% and the mass content of oxygen is less than 0.003%.

  In step (5), the calcium wire supply refers to supplying pure calcium wire to ferritic stainless steel hot water. The pure calcium wire supply amount is 0.1 to 0.3 kg / t, After the treatment in (5), the mass content of calcium in the ferritic stainless steel hot water is 15 to 30 ppm.

  In step (5), calcium wire is supplied and softly stirred, then titanium wire is supplied to ferritic stainless steel hot water, and the pure titanium content in the titanium wire is 1 to 3 kg / t. Smelting method of silicon ultra-pure ferritic stainless steel.

  In the finally obtained high aluminum low silicon ultrapure ferritic stainless steel, the silicon mass percentage content is less than 0.3%, and the aluminum mass percentage content is 0.01-0.1%. , Smelting method of high aluminum low silicon ultra pure ferritic stainless steel.

In step (2)
Add only ferrosilicon if you require that the upper limit of silicon mass content in the final high aluminum low silicon ultra pure ferritic stainless steel is 0.3%;
When it is required that the upper limit of the silicon mass content in the finally obtained high aluminum low silicon ultrapure ferritic stainless steel is 0.2% or less, only an aluminum block is added;
When it is required that the upper limit value of the silicon mass content in the finally obtained high aluminum low silicon ultrapure ferritic stainless steel is 0.2 to 0.3%, ferrosilicon and aluminum lump are added, and the above ferro Addition ratio of silicon and aluminum lump = (upper limit value of silicon mass content in high aluminum low silicon ultra-pure ferritic stainless steel finally obtained-0.2%) / (0.3%-finally obtained high A method for smelting high aluminum low silicon ultrapure ferritic stainless steel, which is the upper limit of silicon mass content in aluminum low silicon ultrapure ferritic stainless steel.

In step (3), the shape of the ferroaluminum was massive or spherical, the density was 4.5 to 6.5 g / cm ³ , the diameter was ³ to 6 cm, and was processed in step (3) Then, the mass ratio of CaO and SiO _{2 in} the billet exceeds 2.8, and the mass ratio of CaO and Al ₂ O ₃ in the billet exceeds 1, The method for smelting high aluminum low silicon ultrapure ferritic stainless steel.

The conditions of vigorous stirring in the high vacuum are as follows. The vacuum pressure is controlled to 800 Pa or less, and the flow rate of argon blowing at the bottom of the VOD furnace is controlled to a range of 4 to 8 L / (min · t). ;
The conditions for the above-mentioned medium-strength agitation are as follows: the vacuum pressure is controlled to 2000 Pa or less, and the flow rate of the VOD furnace bottom argon blowing is controlled in the range of 1 to 4 L / (min · t);
The above-mentioned soft stirring conditions are as follows: high aluminum low silicon ultra-pure ferritic stainless steel that controls the flow rate of argon blowing at the bottom of the VOD furnace to the range of 1-5 L / (min · t) under normal pressure conditions Smelting method.

The excellent effect of the smelting method of the high aluminum low silicon ultrapure ferritic stainless steel provided in the present invention is as follows:
1. In the VOD smelting process, the aluminum precipitation deoxygenation efficiency can be improved efficiently, the aluminum content in steel can be improved efficiently, and the silicon content in the slag can be controlled to a low level. Prevents return to steel hot water and realizes smelting of high aluminum low silicon content ultra pure ferritic stainless steel;
2. Adopting protective casting measures in continuous casting process, can prevent secondary oxidation of high aluminum content steel bath, and avoid clogging of intermediate tundish nozzle by combining calcium treatment; Since the control of the oxygen effect and the aluminum content target has already been realized, the generated Al ₂ O ₃ inclusions can sufficiently grow in the vigorous stirring process of VOD, float efficiently after breaking the vacuum, and the purity of the steel bath Improve;
3. Since the added high-density ferroaluminum aluminum enters the steel bath sufficiently, the rate of reaction of MgO in the slag directly with MgO to produce magnalium spinel is significantly reduced, and the formation of magnalium spinel, a harmful inclusion, is formed. Effective removal of Al ₂ O ₃ inclusions and suppression of magnalium spinel formation can also avoid clogging of the intermediate tundish nozzle;
4. If the alloying of titanium is required by improving the aluminum content, titanium oxidation can be greatly suppressed during the titanium supply process, and the titanium yield can be improved. Has a positive effect on clogging;
5. The method of the present invention is safe and reliable, strong in operability, and can greatly improve the stability of smelting and the mass of products.

  The principle of the process of the present invention is as follows.

  1. In the present invention, the target silicon and aluminum content of the ultrapure ferritic stainless steel are respectively less than 0.3% by mass of silicon and less than 0.3% by mass of aluminum. Require smelting to be in the range of%. The purpose is as follows.

  The reason why the silicon content is less than 0.3% is to improve the pickling performance of this stainless steel. If the silicon content exceeds 0.3%, the difficulty of pickling the steel increases, which affects the smoothness of the steel. In addition, silicon in this content range can secure the toughness of the steel and improve its processing performance. it can. The reason why the aluminum mass is required to be in the range of 0.01 to 0.1% is mainly due to the deoxidation effect. By calculation of thermodynamics, the range of dissolved oxygen corresponding to 0.01% Al content is 0.002 to 0.0025% (ie, for ferritic stainless steel liquids with different Cr contents at 1550 ° C. (ie 20-25 ppm). Since inclusions are further included in the total oxygen, when the total oxygen in the billet is required to be less than 30 ppm, the aluminum content of the present application is required to exceed 0.01%. At the same time, the upper limit of the aluminum content is set to 0.1% mainly for steel containing titanium, and it is necessary to ensure that the ratio of aluminum-titanium content exceeds 0.15. If the upper limit of the aluminum content is 0.1%, it can be guaranteed that the upper limit of the titanium content is 0.7%. Naturally, if the aluminum content exceeds 0.1%, the smelting cost increases and is not necessary.

2. Pre-deoxygenation and final deoxygenation:
For the smelting of ferritic stainless steel in the above silicon aluminum content range, the present invention first performs pre-deoxygenation with ferrosilicon and an aluminum block, as shown in steps (2) and (3), In addition, final deoxygenation is performed. The present invention further requires deoxygenation by adding ferrosilicon, aluminum lumps and ferroaluminum. The reason for this is as follows. If only ferroaluminum is added to the entire deoxygenation process, the cost of ferroaluminum is higher than that of ferrosilicon, so that the overall smelting cost is improved and the recovery of coal is worsened. If only ferrosilicon and aluminum lumps are added, the aluminum lumps are light, so they cannot be put into steel hot water efficiently, and the purpose of improving the aluminum content in the steel cannot be achieved. When ferrosilicon, aluminum lump, and ferroaluminum are added together to achieve final deoxygenation, the binding capacity of aluminum and oxygen is much larger than that of silicon and oxygen, so Cr ₂ O _{3 in} slag is basically reduced. The aluminum reacts violently with SiO _2, and the silicon content in the steel is rapidly improved and it is likely not to meet the requirement that the endpoint silicon content be less than 0.3%. Therefore, the present invention first employs a system in which ferrosilicon and a part of aluminum lump are added to perform preliminary deoxygenation. During the preliminary deoxygenation process, the oxygen content in the steel cannot be lowered very low. The thermodynamic formula of silicon and oxygen equilibrium can guarantee that the silicon content in the steel is in a low range during the treatment process because silicon element can react with oxygen in a large amount during the pre-deoxygenation process. After preliminary deoxygenation treatment, ferroaluminum is added to perform final deoxygenation. Since the density of ferroaluminum is much higher than the density of pure aluminum lump, it can be guaranteed that most of the ferroaluminum will settle on the bottom of the hot water after entering the hot water melting tank. First, steel hot water is entered, effective precipitation deoxygenation can be realized, and the aluminum content in the steel is also efficiently improved. Of course, some molten aluminum directly enters the slag and reacts, but this does not interfere with the rapid increase in aluminum content in the steel.

1) Preliminary deoxygenation In the preliminary deoxygenation of step (2) of the present invention, ferrosilicon and / or aluminum lump having a silicon content mass percentage of 70 to 80% is added to perform predeoxygenation treatment, and ferrosilicon and / The total addition amount of aluminum lump is 4-9kg / t, and further lime and fluorite are added to make slag, and the addition mass of lime is 4-6 times the ferrosilicon addition mass and the aluminum lump addition amount Choose larger value from 2-3 times group, fluorite added mass is 0.05-0.3 times lime added mass, processed under high vacuum, vigorous stirring conditions for 5-10 min Later, it is required that the silicon mass content is less than 0.1% and the oxygen mass content exceeds 0.01%.

Before this step, the hot water has just undergone oxygen decarburization treatment, so there is a large amount of dissolved oxygenated chromium oxide in the melting tank, and the purpose of pre-deoxygenation by adding ferrosilicon and aluminum lump is in steel This is because chromium in chromium oxide is reduced using ferrosilicon or aluminum lump without lowering the oxygen content. The aluminum mass has a strong reducing ability and can react directly with Cr ₂ O ₃ in the slag. Here, the reducing ability of silicon is mainly examined, and the process of the silicon reduction reaction is as follows.
1.5 [Si] + (Cr ₂ O ₃ ) = 2 [Cr] +1.5 (SiO ₂ )

According to the thermodynamic calculation, the thermodynamic activities as pure substance standards of the oxides (Cr ₂ O ₃ ) and (SiO ₂ ) are all 1, and according to the calculation, the stainless steel having a chromium content of 18% As long as the silicon content exceeds 0.6%, the reaction can be promoted to proceed in the positive direction. This is because the density of the ferrosilicon should not be too high, the ferrosilicon drifts above the hot water, reacts directly with (Cr ₂ O ₃ ) in the slag, and the local silicon content of the hot water in contact with the slag is 0 It must be guaranteed that it exceeds 6%. Therefore, this application selects the ferrosilicon used frequently, the silicon content is 70 to 80%, and satisfies the requirement that the density of ferrosilicon is not so high. Of course, as the lime melts, the SiO ₂ activity in the slag decreases and pre-deoxygenation of silicon is promoted. The present invention further selects aluminum and preliminarily deoxygenates mainly for steels that require a lower target silicon content, as further described below. The amount of deoxygenation of 75% silicon-containing ferrosilicon and the same weight of aluminum lumps is close to 1, so the range of ferrosilicon and aluminum lumps added is low in chromium and at the same time the initial carbon content is low. , Requiring less total addition of ferrosilicon and aluminum mass. Conversely, if the steel has a high chromium content and at the same time a high initial carbon content, it requires a higher total amount of ferrosilicon and aluminum mass. In the following, two extreme situations that may appear during production will be analyzed as an example, and based on this, the range of the total amount of ferrosilicon and aluminum mass added will be determined. According to the calculation, for the smelting of ferritic stainless steel with low chromium content, in the case of steel with a chromium content of 11.6%, the condition that the initial carbon is 0.3% before the steel bath enters VOD, The amount of oxygen blown per ton of steel is about 7 Nm ³ / t, and carbon can be removed under vacuum conditions. By previous experience, the oxygen of approximately 30-40% oxidizes chromium _Cr 2 _{O 3,} requires pure aluminum pure silicon or 3.5~4.6kg about 2.6～3.45Kg. In consideration of the silicon content in ferrosilicon, the present invention sets the lower limit of the required total amount of ferrosilicon and aluminum mass to 4 kg / t. For high-chromium steel smelting, for example, for steel with a chromium content of 22.6%, before entering VOD, if the initial carbon is 0.6%, the oxygen blow rate per ton of steel is It is about 13 Nm ³ / t, and carbon can be removed under vacuum conditions. By previous experience, the oxygen of approximately 35-45% oxidizes chromium _Cr 2 _{O 3,} requires pure aluminum pure silicon or 7.5~9.7kg about 5.6～7.24Kg. In consideration of the silicon content in ferrosilicon, the present invention sets the upper limit of the required total amount of ferrosilicon and aluminum ingot to 9 kg / t. The amount of lime added is determined by the amount of SiO ₂ produced and must meet the range of alkalinity requirements. In the present invention, as the lime addition mass, a large value is selected from the group consisting of 4 to 6 times the ferrosilicon addition mass and 2 to 3 times the aluminum lump addition amount, and the billet slag alkalinity is 2.8 or more. The mass ratio of CaO and Al ₂ O ₃ in the billet slag is controlled to exceed 1, and is satisfied. The main purpose of adding fluorite is to promote dissolution and melting of lime, and the amount added is determined by the degree of difficulty in melting lime itself. Depending on production experience, the addition mass of fluorite is 0.05 to 0.3 times the addition mass of lime. The ferrosilicon and aluminum ingot added to step (2) does not significantly reduce the dissolved oxygen content in the steel and requires the oxygen content to exceed 0.01%, so the silicon content in the reacted steel It can be guaranteed that the amount is less than 0.1%. In this step, the range of total addition amount of ferrosilicon and aluminum lump is specified, but in the actual execution process, oxygen gas blown in the decarburization process of smelting process is decarburized, secondary combustion, loss, melting tank The amount of oxygen to be removed from the ferrosilicon and aluminum block is determined by the specific distribution ratio. Since the amount of decarburization is known, the secondary combustion rate is obtained by analysis on the composition of the furnace gas, and the loss is also obtained by regression analysis on historical data, so the ratio of oxygen gas entering the melting tank is obtained by calculation. Based on this, it is possible to calculate a specific value of the total amount of ferrosilicon and aluminum lump, and this value is within the scope of the present invention.

In the present invention, it is also required to determine the addition ratio of such ferrosilicon and / or aluminum lump for step (2).
a, add ferrosilicon only if the final high aluminum low silicon ultrapure ferritic stainless steel is required to have an upper limit of silicon mass content (ie target silicon content) of 0.3% ;
b, when the upper limit of the silicon mass content in the finally obtained high aluminum low silicon ultra-pure ferritic stainless steel is low, that is, when the upper limit is required to be 0.2% or less, only an aluminum block is added. ;
c, when the upper limit of the silicon mass content in the finally obtained high aluminum low silicon ultrapure ferritic stainless steel is required to be between 0.2 and 0.3%, the addition ratio of ferrosilicon and aluminum lump = (Upper limit value of silicon mass content in high aluminum low silicon ultrapure ferrite stainless steel finally obtained -0.2%) / (0.3% -high aluminum low silicon ultrapure ferrite stainless steel finally obtained Upper limit of silicon mass content in steel).

  Among them, the upper limit value of the silicon mass content in the high aluminum low silicon ultrapure ferritic stainless steel finally obtained refers to a value that the silicon content must not exceed.

  The reason why the present invention further selects aluminum and performs pre-deoxygenation is mainly due to the lower demands on the target silicon content. If the target silicon content is required to be less than 0.3%, this target can be achieved by adding only ferrosilicon and subsequent alkalinity control. However, when the target silicon content is required to be less than 0.2%, it is considered that the final deoxygenation process forms a silicon increase of about 0.1 to 0.2%. In this case, it is required to add only aluminum, since adding ferrosilicon does not satisfy the condition that a silicon increase is formed and the final silicon content is less than 0.2%. When the upper limit value of the target silicon mass content is between 0.2 and 0.3%, the ferrosilicon and the aluminum lump are mixed and added to the present invention, and the specific ratio is the upper limit of the target silicon content. Once determined by a value request, such a request can be satisfied.

2) Final deoxygenation Ferroaluminum is added to the final deoxygenation process of step (3) of the present invention to perform a final deoxygenation treatment, and the aluminum mass content of ferroaluminum is 20 to 60%. The mass content is less than 0.1%, and the remaining amount is iron and other trace impurity elements. The amount of pure aluminum added to ferroaluminum is 2 to 6 kg / t, lime and fluorite are added, the amount of lime added is 2 to 3 times the amount of pure aluminum in ferroaluminum, and the added mass of fluorite is lime 0.05 to 0.3 times the added mass, and after adding the material, first stir for 2-5 min at medium strength under vacuum conditions, then treat for 12-18 min under vigorous stirring conditions under high vacuum, treatment Is finished, 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%. Can guarantee.

When ferroaluminum having a higher density is used as a deoxidizer for final deoxidation, as described above, if ferroaluminum is added, a large amount of oxide and slag in slag can be added if added in a large amount like pure steel. The aluminum contained does not enter the steel bath melting tank. Production practices already proved the above facts. The reason why the aluminum mass percentage content in ferroaluminum is 20 to 60% is that the iron content becomes too high if the aluminum content is less than 20%, besides satisfying the density requirement range. . Since there is a certain requirement for the amount of pure aluminum added in the present invention, if the amount of ferroaluminum added is too large, not only will the amount of carbon increase increase, but the temperature drop in the melting tank will increase. It also leads to things. According to calculations, when 1 kg of aluminum participates in the reaction, the released energy can heat about 4 kg of iron from room temperature to 1700 ° C. in hot water. Therefore, the aluminum content in ferroaluminum should be higher than 20%. The requirement for the aluminum content in ferroaluminum to be less than 60% is mainly due to the demand for density control. The aluminum content corresponding to a ferroaluminum density higher than 4.5 g / cm ³ is 60%. The reason why the carbon content in ferroaluminum is less than 0.01% is mainly considered from the viewpoint of control of carbon increase. Since the steel to be smelted is an ultra-low carbon steel, the smaller the increase in carbon after adding ferroaluminum, the better. When the carbon content of ferroaluminum is 0.1%, when 10 kg of ferroaluminum is added to the steel per ton, the amount of carbon increase in the steel bath is 10 ppm, which is basically recognized. Therefore, it is required that the carbon content in ferroaluminum is less than 0.1%, which is also the carbon content range that can be realized for the production of ferroaluminum. The amount of ferroaluminum added is calculated by the pure aluminum in it. The present invention requires that the amount of pure aluminum added is 2 to 6 kg / t. The addition of aluminum is not only for removing dissolved oxygen in the steel, but also for reducing Cr ₂ O _{3 in the} slag where ferrosilicon cannot be removed in the preliminary deoxidation process. About 0.5 to 2.4 kg / t of pure aluminum is consumed. Since there is a possibility of further reaction with SiO _{2 in the} slag, a silicon recovery amount of 0.1% to 0.2% is derived, and pure aluminum is consumed by about 1.4 to 2.6 kg / t. In addition, in order to satisfy the final target of aluminum content of 0.01 to 0.1%, pure aluminum is consumed by about 0.1 to 1 kg / t. By adding the above lower limit value and adding the above upper limit value, it is possible to obtain a range of addition amount of pure aluminum of 2 to 6 kg / t. Ferroaluminum addition was obtained by dividing the pure aluminum addition by the aluminum content. The purpose of adding lime is to continue to guarantee the mass ratio of CaO to Al ₂ O _{3 in} the billet. The present invention requires that the material be added to this step and then stirred at medium strength for 2-5 min under vacuum conditions. The purpose is to stir the steel hot water at a certain strength to promote the aluminum entering the steel hot water. On the other hand, if the stirring strength is too high, the ferroaluminum is sprayed on the surface of the slag. Here, medium strength agitation is adopted because it leads to aluminum not being able to enter the steel bath. The reason for requiring a high vacuum and a vigorous stirring time of 12 to 18 min for this step is to ensure a sufficient time to grow Al ₂ O ₃ inclusions. In this way, it will be sufficiently lifted and removed during the subsequent soft agitation process under atmospheric conditions. In addition, the following should be pointed out in particular, since aluminum in ferroaluminum sufficiently enters the steel bath, when deoxidizing to a certain extent, it is avoided that aluminum directly enters the slag and reduces MgO in the slag, Suppresses the formation of magnalium spinel well. Compared to stainless steel, magnalium spinel is a very harmful inclusion, leading to product defects. By adopting ferroaluminum, aluminum control and silicon control are realized, so after the treatment is finished, silicon mass content of less than 0.3%, aluminum mass content of 0.01-0.1% and 0.003% An oxygen mass content of less than can be guaranteed.

This application requires the shape and density of ferroaluminum to be added to step (3), but for the ferroaluminum according to step (3), a lump or spherical shape, a density of 4.5 to 6.5 g / cm ³ , 3 to A diameter of 6 cm is required.

The lump or spherical shape is for convenience in manufacturing and addition. When the diameter is less than 3 cm, the collision depth is insufficient when ferroaluminum enters the steel bath from the raw material warehouse. The reason why the diameter is less than 6 cm is to consider that it is inconvenient to add the raw material when the size is mainly too large. The reason why the density is required to be in the range of 4.5 to 6.5 g / cm ³ is that, when ferroaluminum is added, 2/3 of the steel must be infiltrated into the steel bath. The density of the steel hot water is about 6.9~7.2g / cm ^3, it is necessary for the density exceeds 4.5 g / cm ^3. At the same time, the aluminum content should not be lower than 20%, so the upper limit of the density is 6.5 g / cm ³ .

In the smelting step (3) of the present application, after the final deoxidation, the alkalinity of the billet, that is, the mass ratio of CaO and SiO ₂ in the slag is higher than 2.8 and the mass ratio of CaO and Al ₂ O _{3 in} the billet is Control to be higher than 1.

The reason why the alkalinity of the billet is made higher than 2.8 after the final deoxygenation is mainly considered in terms of controlling the activity of SiO ₂ . According to the ternary activity diagram of CaO—SiO ₂ —Al ₂ O ₃ , the activity coefficient of pure substance as standard SiO ₂ is about 0.028 under the conditions of this alkalinity value. Taking smelting of ultra-pure ferritic stainless steel with a content of 22.6% as an example, the equilibrium SiO ₂ activity of the slag for the aluminum content of 0.01% and the silicon content of 0.3% is 0 .009. Under this alkalinity condition, it is calculated that the mole fraction occupied in the slag of SiO ₂ is 0.32. Since the alkalinity is already set higher than 2.8, the percentage content of SiO ₂ is always less than 26%. From this range, it is obtained that the molar fraction can generally be controlled within 0.32. From this, it can be seen that this alkalinity range can guarantee that Al does not reduce SiO ₂ in the slag under the above-mentioned conditions of silicon and aluminum content. For other chromium-containing steels, if the chromium content is less than 22.6%, chromium is an element that lowers the activity of silicon and improves the activity of aluminum. In this case, the activity of silicon is increased, the activity of aluminum is lowered, and the Al element cannot reduce SiO ₂ in the slag. Conversely, Al elements can reduce SiO ₂ in the slag. There are not many steels with a chromium content higher than 22.6%, the ability to suppress Al from reducing SiO ₂ in the slag by adjusting the content of SiO _{2 in} the slag, and the lower limit of alkalinity is too small In view of the fact that setting it high leads to an increase in the amount of slag, the present invention finally determines the slag alkalinity of the billet to exceed 2.8, which is the lowest requirement for the slag alkalinity value of the billet. There is no particular limitation on the upper limit of billet slag alkalinity. Higher aluminum content may increase Al ₂ O ₃ in the slag and increase the slag alkalinity of the billet, and finally the billet becomes an aluminum calcium slag with a very low SiO ₂ content, ie billet This slag is a slag mainly composed of CaO—Al ₂ O ₃ , and this is allowed in the present invention. The present invention requires that the mass ratio of CaO and Al ₂ O _{3 in} the billet is higher than 1 mainly for the case where the SiO ₂ content in the billet slag is lower and changes to aluminum calcium slag. When the mass ratio of CaO to Al ₂ O ₃ is higher than 1, it is possible to guarantee a good absorption capacity of billet slag with respect to Al ₂ O ₃ . For calcium aluminum slag, when the mass ratio of CaO and _Al 2 _{O 3} is 1.1 to 1.4, it has the ability to absorb billet slag good inclusions having good fluidity. In the present invention, the upper limit of the ratio of CaO and Al ₂ O ₃ is not particularly limited to the case of non-aluminum calcium slag, and it is recognized that the content range of Al ₂ O ₃ is low. About control of CaO content in billet slag, it describes in the setting of the amount of lime addition of step (2) and (3).

_3. About Step (5) 1) Soft stirring before supplying the pure stirring pure calcium wire is made to enter the inclusion Al ₂ O ₃ floating slag that has already grown under vacuum conditions and supplying the pure calcium wire. The soft agitation of the material promotes the entry of low melting point calcium aluminate inclusions generated after supplying calcium into the slag.
2) Wire supply A), Calcium wire supply (ie, calcium treatment process)
A calcium treatment process is supplying a pure calcium wire to steel hot water at a normal pressure with a wire feeder. The supply amount of pure calcium is 0.1 to 0.3 kg / t. After supplying the calcium wire, soft stirring is performed on the steel bath by blowing argon into the bottom under normal pressure conditions, the time of soft stirring is 5 to 10 min, and the mass content of calcium in the steel after the treatment is finished. Control to 15-30 ppm.

Since high aluminum steel is smelted in the present invention, the amount of aluminum added during the deoxidation process is very large. Various measures are taken to remove the generated Al ₂ O ₃ inclusions from the hot water and prevent secondary oxidation, but production practices still risk Al ₂ O ₃ blocking the intermediate tundish nozzle . As the cause, when the aluminum content is high, aluminum may reduce MgO in the slag, and the produced magnalium spinel inclusions are difficult to eliminate and cause clogging. In addition, Al ₂ O ₃ inclusions that cannot be removed cleanly also pose a risk of blocking the tundish nozzle. Although the present application has already lowered the above risk to various levels by various measures, in order to ensure high stability of high aluminum steel production, the present invention further adopts calcium treatment technology so as not to clog the tundish nozzle. . The calcium treatment is mainly to change the Al ₂ O ₃ inclusions into low melting point inclusions of 12CaO · 7Al ₂ O ₃ . In general, the maximum content of Al ₂ O _{3 in} steel is 0.01%. In order to change this amount of Al ₂ O ₃ to 12CaO · 7Al ₂ O ₃ , the required calcium content is 67 ppm. At the same time, after the calcium treatment is completed, the dissolved content of calcium element itself is required to be 0.09 to 0.15 times the aluminum content. When the aluminum content is 0.03%, the dissolved calcium content is required to be about 30 ppm. Thus, the amount of pure calcium necessary to enter the steel bath is 100 ppm, that is, 0.01%. Considering that the yield of calcium is higher than 30% in the calcium supply process of high aluminum steel, finally the supply amount of pure calcium is 0.1 to 0.3 kg / t, and finally the calcium content is 15 to Control within the range of 30 ppm. This range satisfies the calcium treatment within the aluminum content range of the present invention, and can realize effective modification of inclusions. If the final calcium content exceeds 30 ppm, the intermediate tundish nozzle may be eroded.

B), Titanium Wire Supply For smelting of titanium-containing steel, a titanium wire can be further supplied to the ferritic stainless steel liquid. The amount of pure titanium in the titanium wire is 1 to 3 kg / t, and titanium alloying is realized. Among them, the pure titanium amount is a value obtained by multiplying the titanium wire supply amount by the titanium content in the titanium wire.

4. Step (6) 1) Soft stirring for 15 to 30 minutes Such soft stirring time can sufficiently guarantee further floating of inclusions and further improve the purity of the hot water.
2) Continuous casting of hot water in a protective atmosphere

  Continuous casting in a protective atmosphere includes argon gas protection for large tundish nozzles, argon gas protection for intermediate tundish nozzles and argon gas protection above the intermediate tundish nozzle, the purpose is to prevent secondary oxidation of steel Because. This protection is necessary even for high-aluminum steel smelting, and since these are skilled continuous casting techniques that can be realized, they are omitted here.

5. About the above moderate strength stirring, high vacuum vigorous stirring and soft stirring The above-mentioned conditions of the medium strength stirring are that the vacuum pressure is controlled to 2000 Pa or less and the flow rate of argon is 1 to 4 L / (min at the bottom of the VOD furnace. Refers to controlling during t);
The high vacuum vigorous stirring conditions refer to controlling the vacuum pressure to 800 Pa or less and controlling the flow rate of the VOD furnace bottom blown argon between 4 to 8 L / (min · t);

  The soft agitation conditions refer to controlling the argon flow rate at the bottom of the VOD furnace between 1 and 5 L / (min · t) under normal pressure conditions.

  Among them, the setting of such parameters is determined by production practices, and it is necessary to ensure that the surface of the slag does not vigorously reversely roll as a moderate intensity stirring under vacuum conditions. For vigorous stirring in high vacuum, it is necessary to ensure that the spout of steel hot water does not affect production. For soft agitation, it is necessary to ensure that the slag surface is not blown away. The range of the bottom blowing flow rate was determined while searching for the above conditions during production.

  In the units relating to the present invention, the symbol “t” is ton steel hot water, “L” is liter, “min” is minute, “kg / t” is the number of kilograms added to steel hot water per ton, “L / “(Min · t)” refers to the amount of argon gas blown per minute to steel bath per ton.

  Hereinafter, an embodiment in which the low silicon high aluminum ferritic stainless steel of the present invention is produced by combining examples and the obtained effect will be described in detail. As an example, description will be given of ultrapure ferritic stainless steels of three steels 409, 443 and 445, respectively.

Example 1
In this embodiment, the requirements for the smelting equipment VOD furnace are as follows. As the equipment, 120 t of steel hot water can be processed, the extreme vacuum is less than 300 Pa, the total blowing capacity of bottom argon exceeds 60 Nm ³ / h, and the fireproof material of the steel hot water tank is magnesium calcium brick. Steel is 409, the amount of hot water is 116000 kg or 116 t, and the initial components of the hot water before VOD smelting are as follows:
C: 0.3%, Si: 0.25%, Cr: 11.6%, S: 0.010%, N: 0.025%, Mn: 0.56%, P: 0.015%, all O: 0.02%, Ti: 0.01%, Al: 0.001%, remaining Fe and trace impurity elements.
The initial temperature of the steel bath is 1580 ° C.

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

1) The steel bath was subjected to oxygen blowing decarburization and free decarburization. The consumption amount of oxygen gas is 885 Nm ³ , the free decarburization time is 15 min, the temperature of the steel hot water is 1630 ° C. after the treatment is completed, and the components are as follows:
C: 0.003%, Si: 0.01%, Cr: 11.1%, S: 0.008%, N: 0.007%, Mn: 0.14%, P: 0.015%, all O: 0.04%, Ti: 0.01%, Al: 0.001%, remaining Fe and trace impurity elements.

  2) preliminary deoxygenation, 400 kg of ferrosilicon containing 77% silicon (ie 3.45 kg / min) in accordance with the upper limit of 0.27% of silicon mass content in the high aluminum low silicon ultrapure ferritic stainless steel finally obtained t, conversion method: 400 kg ÷ steel amount 116 t, within the range of Example 1, except for the mass of lime and fluorite, the conversion method is the same below) and aluminum lump 200 kg (ie 1.71 kg / t), total 600 kg (ie 5.16kg / t) is added, preliminary deoxygenation is performed, 1.6t of lime and 200kg of fluorite are added, slag is made, materials are added, the vacuum pressure is controlled to 800Pa or less, and argon is added to the bottom. Gas is blown, the stirring intensity is 600 L / min (that is, 5.17 L / (min · t), conversion method: 600 L / min ÷ steel amount 116 t, within the range of Example 1. The conversion method is the same below), and the processing time is 8 min so as to guarantee the initial melting of lime. After the treatment is completed, the silicon content is 0.08% and the oxygen content is 0.015%.

3) The final deoxidation, 650 kg added aluminum content of 40% ferro aluminum, the diameter of the ferro aluminum is 5 cm, density of 5.4 g / cm ^3, comprising 0.008% or carbon, 260 kg of pure aluminum (Ie 2.24 kg / t), 600 kg of lime and 50 kg of fluorite are further added, the final deoxygenation is performed, and after adding the material, the flow rate of the bottom stirring argon blow reaches 150 L / min. After stirring for 3 minutes, high-intensity stirring is performed, the gas flow rate of bottom argon blowing reaches 800 L / min (that is, 6.90 L / (min · t)), and the processing time is 15 min. When the treatment is finished, the silicon content is 0.19%, the aluminum content is 0.054%, and the oxygen content is 7.8 ppm. The main components of billet slag are: CaO 60%, SiO ₂ 12%, Al ₂ O ₃ 17%, MgO 3%, and the alkalinity requirement of billet slag and the ratio of CaO to Al ₂ O ₃ exceeds 1. Satisfy the request. When the treatment is finished, the temperature is 1570 ° C.

  4) Vacuum break.

  5) Soft stirring for 10 minutes, blowing argon gas at the bottom, and stirring intensity is 200 L / min (ie 1.72 L / (min · t)). After calcium treatment, 20 kg of pure calcium wire (i.e., 0.17 kg / t) is added using a wire feeder, soft stirring is performed for 10 minutes after the supply of the wire is completed, argon gas is blown to the bottom, and the stirring strength is 200 L / min (i.e., 1 .72 L / (min · t)). This steel needs to be titanium alloyed by supplying titanium wire. The amount of pure titanium in the titanium wire is 150 kg (that is, 1.38 kg / t), and the end point titanium is 0.1%.

  6) Subsequently, the mixture is softly stirred for 20 minutes, and argon gas is blown to the bottom, and the stirring strength is 180 L / min (that is, 1.55 L / (min · t)). Continuous casting in a protective atmosphere, both large tundish nozzles and intermediate tundish nozzles are protected with argon blowing.

  The opening degree of the intermediate tundish nozzle was very stable during the casting process, there was no intense vibration, the vibration range was generally within 3%, and the tundish nozzle was not clogged or eroded.

Finally, the steel bath is cast into billets and the ingredients are as follows:
C: 0.006%, Si: 0.20%, Cr: 11.7%, S: 0.001%, N: 0.008%, Mn: 0.23%, P: 0.015%, all O: 0.0020%, Ti: 0.09%, Al: 0.044%, remaining Fe and trace impurity elements.

Among them, the silicon content slightly increased after breaking the vacuum, which is a result of a small amount of SiO _{2 in the} slag being reduced to aluminum. The aluminum content drops slightly, the cause of which is to promote the contact between aluminum and oxygen according to temperature drop, time advance and secondary oxidation, leading to a slight drop in its components. Since a certain amount of carbon is contained in the ferroaluminum added during the deoxygenation process, it leads to a certain increase in the carbon content relative to that before the treatment, but it is still in the ultrapure range.

The amount of magnalium spinel inclusions in the billet is significantly reduced from that in the normal process. The inclusions are mainly TiN or Ti (CN) inclusions having a size of 5 μm or less and spherical plastic CaO—Al ₂ O having a size of 10 μm or less. ₃ -SiO ₂ are inclusions (including a slight MgO to a portion), the performance of the steel, there is no adverse effect on particular surface properties.

Example 2
As the equipment, 120 t of steel hot water can be processed, the extreme vacuum is less than 300 Pa, the total blowing capacity of bottom argon exceeds 60 Nm ³ / h, and the fireproof material of the steel hot water tank is magnesium calcium brick. The steel is 443, the amount of hot water is 108400 kg, ie 108.4 t, and the initial components of the hot water before VOD smelting are as follows:
C: 0.36%, Si: 0.018%, Cr: 20.8%, S: 0.005%, N: 0.015%, Mn: 0.3%, P: 0.010%, all O: 0.02%, Ti: 0.01%, Al: 0.001%, remaining Fe and trace impurity elements.
The initial temperature of the steel bath is 1600 ° C.

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

1) The steel bath was subjected to oxygen blowing decarburization and free decarburization. The consumption amount of oxygen gas is 1266 Nm ³ , the free decarburization time is 20 min, and after the treatment is completed, the temperature of the hot water is 1670 ° C., and the components are as follows:
C: 0.005%, Si: 0.01%, Cr: 19.7%, S: 0.004%, N: 0.004%, Mn: 0.14%, P: 0.015%, all O: 0.05%, Ti: 0.01%, Al: 0.001%, remaining Fe and trace impurity elements.

  2) Pre-deoxygenation, Ferro-ferrous so as to avoid the increase of silicon by adding only aluminum lump in accordance with the upper limit of 0.2% of silicon mass content in high aluminum low silicon ultra-pure ferritic stainless steel finally obtained No silicon was added. Add 780 kg of aluminum lump (ie, 7.20 kg / t, conversion method: 780 kg divided by 108.4 t of hot water, conversion method is the same except for the mass of lime and fluorite within the range of Example 2). Oxygen is added, 1.6t of lime and 100kg of fluorite are added, slag is made, materials are added, the vacuum pressure is controlled to 800Pa or less, argon gas is blown to the bottom, and the stirring strength is 700L / min. (Ie, 6.46 L / (min · t), conversion method: 700 L / min ÷ steel amount 108.4 t, within the range of Example 2, the conversion method is the same below), and guarantees the initial melting of lime. Thus, the processing time is 6 min. After the treatment is finished, the silicon content is 0.04% and the oxygen content is 0.02%.

3) Final deoxygenation, 500 kg of ferroaluminum with an aluminum content of 40% (ie 4.61 kg / t) is added, the diameter of ferroaluminum is 5 cm, the density is 5.4 g / cm ³ and the carbon is 0 0.01%, 200 kg of pure aluminum (ie 1.85 kg / t), 400 kg of lime and 50 kg of fluorite are added, the final deoxygenation is performed, the materials are added, and the flow rate of bottom stirring argon blowing is increased. Adjust to 200 L / min (ie 1.85 L / (min · t)), stir for 4 min at medium strength, then stir at high strength, and the argon gas blowing flow at the bottom is 800 L / min (ie 7.38 L). / (Min · t)), and the processing time is 18 min. After the treatment is finished, the silicon content becomes 0.20%, the aluminum content becomes 0.018%, and the oxygen content becomes 10 ppm. The main components of billet slag are CaO 55%, SiO ₂ 2%, Al ₂ O ₃ 37%, and MgO 5%. The alkalinity requirement of billet slag and the ratio of CaO and Al ₂ O ₃ exceeds 1. Satisfy the request. When the treatment is finished, the temperature is 1605 ° C.

  4) Vacuum break.

  5) Soft stirring for 9 minutes, blowing argon gas to the bottom, and stirring strength is 200 L / min (that is, 1.85 L / (min · t)). After calcium treatment, 12.8 kg of pure calcium wire (that is, 0.12 kg / t) was added with a wire feeder, and after 10 minutes of soft feeding, the argon gas was blown into the bottom and the stirring strength was 200 L / min ( That is, 1.85 L / (min · t)). This steel needs to be titanium alloyed by supplying titanium wire. The amount of pure titanium in the titanium wire is 300 kg (ie 2.77 kg / t), and the end point titanium is 0.2%.

  6) Subsequently, the mixture is softly stirred for 25 minutes, and argon gas is blown to the bottom, and the stirring strength is 160 L / min (that is, 1.48 L / (min · t)). Continuous casting in a protective atmosphere, both large tundish nozzle and intermediate tundish nozzle have argon blowing protection.

  The opening degree of the intermediate tundish nozzle was very stable during the casting process, there was no intense vibration, the vibration range was generally within 3%, and the tundish nozzle was not clogged or eroded.

Finally, the steel bath is cast into billets and the ingredients are as follows:
C: 0.008%, Si: 0.20%, Cr: 20.8%, S: 0.001%, N: 0.006%, Mn: 0.21%, P: 0.015%, all O: 0.0018%, Ti: 0.15%, Al: 0.019%, remaining Fe and trace impurity elements.
Over time, the aluminum content increased slightly because the titanium supply decreased the oxygen potential of the steel bath. The silicon content remains the same because the SiO ₂ content in the slag is very low and aluminum or titanium avoided reducing the silicon in the slag. Since a certain amount of carbon is contained in the ferroaluminum added during the deoxygenation process, it leads to a certain increase in the carbon content with respect to that before the treatment, but it is still in the ultrapure range.

The amount of magnalium spinel inclusions in the billet is remarkably reduced from that of the ordinary process. The inclusions are mainly TiN or Ti (CN) inclusions having a size of 5 μm or less and spherical plastic CaO—Al ₂ O having a size of 10 μm or less. _{It was a 3-} SiO ₂ inclusion (containing a small amount of MgO in a part) and had no adverse effect on the performance of the steel, particularly the surface performance.

Example 3
In this embodiment, the requirements for the smelting equipment VOD furnace are as follows. As the equipment, 120 t of steel hot water can be processed, the extreme vacuum is less than 300 Pa, the total blowing capacity of bottom argon exceeds 60 Nm ³ / h, and the fireproof material of the steel hot water tank is magnesium calcium brick. Steel is 444, the amount of hot water is 110000 kg or 110 t, and the initial components of the hot water before VOD smelting are as follows:
C: 0.40%, Si: 0.06%, Cr: 18.8%, S: 0.005%, N: 0.012%, Mn: 0.3%, P: 0.010%, all O: 0.02%, Ti: 0.01%, Al: 0.001%, remaining Fe and trace impurity elements.
The initial temperature of the steel bath is 1620 ° C.

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

1) The steel bath was subjected to oxygen blowing decarburization and free decarburization. The consumption of oxygen gas is 1440 Nm ³ , the free decarburization time is 20 min, the temperature of the steel bath is 1700 ° C. after the treatment is complete, and the components are as follows:
C: 0.006%, Si: 0.20%, Cr: 17.4%, S: 0.005%, N: 0.005%, Mn: 0.14%, P: 0.015%, all O: 0.05%, Ti: 0.01%, Al: 0.001%, remaining Fe and trace impurity elements.

  2) Pre-deoxygenation, in accordance with the upper limit of 0.3% of silicon mass content in the high aluminum low silicon ultrapure ferritic stainless steel finally obtained, add only ferrosilicon without adding aluminum lump, silicon Add 900 kg of ferrosilicon containing 77% (that is, 8.12 kg / t, conversion method: 900 kg ÷ 110 t of molten steel, conversion method is the same except for the mass of lime and fluorite within the range of Example 3), aluminum Perform preliminary deoxygenation without adding lump, add 3.6t of lime and 200kg of fluorite, make slag, add material, control the vacuum pressure to 400Pa or less, blow argon gas to the bottom The stirring strength is 800 L / min (that is, 7.27 L / (min · t), conversion method: 800 L / min ÷ steel amount 110 t, within the range of Example 3 and conversion method. Is the same below), to ensure the initial melting of the lime, the processing time to 10min. After the treatment, the silicon content is 0.1% and the oxygen content is 0.013%.

3) Final deoxygenation, 750 kg of ferroaluminum with an aluminum content of 47% (ie 6.82 kg / t) is added, the diameter of ferroaluminum is 5 cm, the density is 5.1 g / cm ³ and the carbon is 0 0.007%, pure aluminum 350 kg (ie 3.18 kg / t), lime 700 kg and fluorite 200 kg are added, the final deoxygenation is performed, the material is added, and the bottom stirring argon flow rate is increased. It is adjusted to 200 L / min (that is, 1.82 L / (min · t)), stirred for 5 minutes at medium strength, and then stirred with high strength, and the argon gas blowing flow rate at the bottom is 750 L / min (that is, 6.L). 82 L / (min · t)), and the processing time is 18 min. After the treatment is finished, the silicon content becomes 0.27%, the aluminum content becomes 0.035%, and the oxygen content becomes 10 ppm. The main components of billet slag are CaO 65%, SiO ₂ 18%, Al ₂ O ₃ 10%, MgO 5%, and the alkalinity requirement of billet slag and the ratio of CaO and Al ₂ O ₃ exceeds 1. Satisfy the request. When the treatment is finished, the temperature is 1642 ° C.

  4) Vacuum break.

  5) Soft stirring for 10 minutes, blowing argon gas at the bottom, and stirring intensity is 200 L / min (that is, 1.82 L / (min · t)). After calcium treatment, 25 kg of pure calcium wire (that is, 0.23 kg / t) is added by a wire feeder, soft stirring is performed for 10 minutes after the supply of the wire is finished, argon gas is blown to the bottom, and the stirring strength is 180 L / min (that is, 1 .64L / (min · t)). Since this steel does not need to be titanium alloyed, it is not necessary to supply titanium wire.

  6) Subsequently, the mixture is softly stirred for 15 minutes, and argon gas is blown to the bottom, and the stirring strength is 180 L / min (that is, 1.64 L / (min · t)). Continuous casting in a protective atmosphere, both large tundish nozzles and intermediate tundish nozzles are protected with argon blowing.

  In the casting process, the opening degree of the intermediate tundish nozzle was very stable, there was no intense vibration, the vibration range was generally within 5%, and the tundish nozzle was not clogged or eroded.

Finally, the steel bath is cast into billets and the ingredients are as follows:
C: 0.01%, Si: 0.29%, Cr: 18.6%, S: 0.001%, N: 0.007%, Mn: 0.21%, P: 0.015%, all O: 0.0017%, Ti: <0.01%, Al: 0.030%, remaining Fe and trace impurity elements.

The aluminum content dropped slightly and the silicon content increased slightly. The cause is that the SiO ₂ content in the slag is higher, which leads to the aluminum further reducing the silicon in the slag. Since a certain amount of carbon is contained in the ferroaluminum added during the deoxygenation process, it leads to a certain increase in the carbon content with respect to that before the treatment, but it is still in the ultrapure range.

The amount of magnalium spinel inclusions in the billet is remarkably reduced from that in the normal process, and the inclusions are mainly spherical plastic CaO—Al ₂ O ₃ —SiO ₂ inclusions with a size of 10 μm or less (some MgO in part). There is no adverse effect on the performance of the steel, particularly the surface performance.

By the smelting method of high aluminum low silicon ultrapure ferritic stainless steel provided in the present invention, low silicon high aluminum ultrapure with silicon content of less than 0.3% and aluminum content of 0.01-0.1% Can smelt ferritic stainless steel. The total oxygen content in the billet is less than 30 ppm, improving the pickling performance of the product. The present invention can further effectively suppress the formation of harmful inclusions such as magnalium spinel, can efficiently remove Al ₂ O ₃ inclusions, can suppress titanium oxidation in titanium-containing steel, Avoid clogging the tundish nozzle.
The present invention includes the following aspects.
・ Mode 1
(1) Ferritic stainless steel hot water is subjected to vacuum oxygen blowing decarburization and free decarburization treatment in a VOD furnace, and the main components of the treated ferritic stainless steel hot water are as follows: Chromium mass percentage content 10 -23%, carbon mass percentage content less than 0.01%, nitrogen mass percentage content less than 0.01%;
(2) Preliminary deoxygenation: Ferrite silicon and / or aluminum lump is added to the ferritic stainless steel hot water obtained by the treatment in step (1), preliminarily deoxygenated, lime and fluorite are added to make slag, Then, a step of processing for 5 to 10 minutes under conditions of vigorous stirring in high vacuum,
(3) Final deoxygenation: Ferroaluminum is added to the ferritic stainless steel hot water obtained in step (2) and subjected to final deoxygenation treatment. The mass percentage content of aluminum in the ferroaluminum is 20-60%, and further add lime and fluorite to make slag, then stir for 2-5 min at medium strength with vacuum, then 12-18 min for vigorous stirring under high vacuum Processing steps;
(4) Vacuum breaking step,
(5) After stirring the ferritic stainless steel hot water for 8 to 10 minutes under normal pressure conditions, supplying calcium wire to the ferritic stainless steel hot water under normal pressure conditions; After the supply is completed, a step of stirring for 5 to 10 minutes in software;
(6) Subsequently, after stirring gently for 15 to 30 minutes, performing continuous casting of the ferritic stainless steel hot water in a protective atmosphere, and finally obtaining a high aluminum low silicon ultrapure ferritic stainless steel,
A method for smelting high-aluminum low-silicon ultra-pure ferritic stainless steel.
・ Aspect 2
In step (2), the total addition amount of the ferrosilicon and / or aluminum mass is 4 to 9 kg / t, the mass percentage content of silicon in the ferrosilicon is 70 to 80%, As the lime addition mass, a large numerical value is selected from two ranges consisting of 4 to 6 times the ferrosilicon addition mass and 2 to 3 times the aluminum lump addition mass, and the fluorite addition mass is 0. 0 of the lime addition mass. After being treated in step (2), the mass content of silicon in the ferritic stainless steel hot water is less than 0.1% and exceeds 0, and the mass content of oxygen is 0. The method for smelting high aluminum low silicon ultra-pure ferritic stainless steel according to aspect 1, characterized by exceeding 0.01%.
・ Aspect 3
In step (3), the addition amount of pure aluminum in the ferroaluminum is 2 to 6 kg / t, the addition amount of lime is 2 to 3 times the addition amount of pure aluminum in ferroaluminum, After the addition amount is 0.05 to 0.3 times the addition amount of lime and treated in step (3), the mass content of silicon in the ferritic stainless steel steel bath is less than 0.3%, 0 The high aluminum low silicon ultrapure according to aspect 1, characterized in that the mass content of aluminum is 0.01 to 0.1% and the mass content of oxygen is less than 0.003%. A method for smelting ferritic stainless steel.
・ Aspect 4
In step (5), the supply of calcium wire refers to supplying pure calcium wire to ferritic stainless steel hot water, and the supply amount of pure calcium wire is 0.1 to 0.3 kg / t, After the processing in (5), the mass content of calcium in the ferritic stainless steel hot water is 15 to 30 ppm. Alchemy method.
・ Aspect 5
In step (5), a calcium wire is supplied and softly stirred, and then a titanium wire is supplied to ferritic stainless steel hot water, and the amount of pure titanium in the titanium wire is 1 to 3 kg / t. The smelting method of the high aluminum low silicon ultrapure ferritic stainless steel according to aspect 1.
・ Aspect 6
In the finally obtained high aluminum low silicon ultra pure ferritic stainless steel, the silicon mass percentage content is less than 0.3%, and the aluminum mass percentage content is 0.01-0.1%. The smelting method of the high aluminum low silicon ultrapure ferritic stainless steel according to aspect 1,
・ Aspect 7
In step (2)
Add only ferrosilicon if you require that the upper limit of silicon mass content in the final high aluminum low silicon ultra pure ferritic stainless steel is 0.3%;
When it is required that the upper limit of the silicon mass content in the finally obtained high aluminum low silicon ultrapure ferritic stainless steel is 0.2% or less, only an aluminum block is added;
When it is required that the upper limit value of the silicon mass content in the finally obtained high aluminum low silicon ultrapure ferritic stainless steel is 0.2 to 0.3%, ferrosilicon and aluminum lump are added, and the above ferro Addition ratio of silicon and aluminum lump = (upper limit value of silicon mass content in final aluminum low silicon ultrapure ferritic stainless steel−0.2%) / (0.3% −high aluminum finally obtained The high aluminum low silicon ultrapure ferritic stainless steel smelting method according to the aspect 1 or 2, characterized in that the upper limit of the silicon mass content in the low silicon ultrapure ferritic stainless steel.
・ Aspect 8
In step (3), the shape of the ferroaluminum was massive or spherical, the density was 4.5 to 6.5 g / cm ³ , the diameter was ³ to 6 cm, and was processed in step (3) After that, the mass ratio of CaO and SiO _{2 in} the billet slag exceeds 2.8, and the mass ratio of CaO and Al ₂ O ₃ in the billet slag exceeds 1, The high aluminum according to aspect 1 or 3, A method for smelting low silicon ultra-pure ferritic stainless steel.
・ Mode 9
The conditions for vigorous stirring in the high vacuum are to control the vacuum pressure to 800 Pa or less and to control the flow rate of argon blown to the bottom of the VOD furnace in the range of 4 to 8 L / (min · t). ;
The condition of the medium-strength stirring is to control the vacuum pressure to 2000 Pa or less and to control the flow rate of the VOD furnace bottom argon blow to a range of 1 to 4 L / (min · t);
In the aspect 1, the soft stirring is performed under the condition of normal pressure, and the flow rate of argon blowing at the bottom of the VOD furnace is controlled in the range of 1 to 5 L / (min · t). The smelting method of the described high aluminum low silicon ultra-pure ferritic stainless steel.

Claims (7)

(1) Ferritic stainless steel hot water is subjected to vacuum oxygen blowing decarburization and free decarburization treatment in a VOD furnace, and the main components of the treated ferritic stainless steel hot water are as follows: Chromium mass percentage content 10 -23%, carbon mass percentage content less than 0.01%, nitrogen mass percentage content less than 0.01%;
(2) Preliminary deoxygenation: Ferrite silicon and / or aluminum lump is added to the ferritic stainless steel hot water obtained by the treatment in step (1), preliminarily deoxygenated, lime and fluorite are added to make slag, then, under vigorous stirring conditions at high vacuum, comprising the steps of 5~10min process,
(3) Final deoxygenation: Ferroaluminum is added to the ferritic stainless steel hot water obtained in step (2) and subjected to final deoxygenation treatment. The mass percentage content of aluminum in the ferroaluminum is 20-60%, and further add lime and fluorite to make slag, then stir for 2-5 min at medium strength under vacuum conditions , and 12-18 min under vigorous stirring conditions at high vacuum Processing steps;
(4) Vacuum breaking step,
(5) After stirring the ferritic stainless steel hot water for 8 to 10 minutes under normal pressure conditions, supplying calcium wire to the ferritic stainless steel hot water under normal pressure conditions; After the supply is completed, a step of stirring for 5 to 10 minutes in software;
(6) Subsequently, after stirring gently for 15 to 30 minutes, performing continuous casting of the ferritic stainless steel hot water in a protective atmosphere, and finally obtaining a high aluminum low silicon ultrapure ferritic stainless steel ,
The condition of the vigorous stirring in the high vacuum is that the vacuum pressure is controlled to 800 Pa or less, and the flow rate of argon blown to the bottom of the VOD furnace is controlled in the range of 4 to 8 L / (min · t). Yes;
The condition of the medium strength stirring is to control the vacuum pressure to 2000 Pa or lower and to control the flow rate of the VOD furnace bottom argon blow to a range of 1 to 4 L / (min · t);
The condition of the soft stirring is to control the flow rate of argon blowing at the bottom of the VOD furnace to a range of 1 to 5 L / (min · t) under normal pressure conditions.
The high aluminum low silicon ultra-pure ferritic stainless steel has a silicon mass percentage content of less than 0.3% and an aluminum mass percentage content of 0.01 to 0.1%. To smelt high aluminum low silicon ultra pure ferritic stainless steel.   In step (2), the total addition amount of the ferrosilicon and / or aluminum mass is 4 to 9 kg / t, the mass percentage content of silicon in the ferrosilicon is 70 to 80%, As the lime addition mass, a large numerical value is selected from two ranges consisting of 4 to 6 times the ferrosilicon addition mass and 2 to 3 times the aluminum lump addition mass, and the fluorite addition mass is 0. 0 of the lime addition mass. After being treated in step (2), the mass content of silicon in the ferritic stainless steel hot water is less than 0.1% and exceeds 0, and the mass content of oxygen is 0. The method for smelting high aluminum low silicon ultrapure ferritic stainless steel according to claim 1, characterized by exceeding 0.01%.   In step (3), the addition amount of pure aluminum in the ferroaluminum is 2 to 6 kg / t, the addition amount of lime is 2 to 3 times the addition amount of pure aluminum in ferroaluminum, After the addition amount is 0.05 to 0.3 times the addition amount of lime and treated in step (3), the mass content of silicon in the ferritic stainless steel steel bath is less than 0.3%, 0 The high-aluminum-low-silicon superoxide according to claim 1, characterized in that the mass content of aluminum is 0.01 to 0.1% and the mass content of oxygen is less than 0.003%. Smelting method of pure ferritic stainless steel.   In step (5), the supply of calcium wire refers to supplying pure calcium wire to ferritic stainless steel hot water, and the supply amount of pure calcium wire is 0.1 to 0.3 kg / t, The high-aluminum low-silicon ultra-pure ferrite stainless steel according to claim 1, wherein after the treatment in (5), the mass content of calcium in the ferritic stainless steel hot water is 15 to 30 ppm. Smelting method.   In step (5), a calcium wire is supplied and softly stirred, and then a titanium wire is supplied to ferritic stainless steel hot water, and the amount of pure titanium in the titanium wire is 1 to 3 kg / t. The smelting method of the high aluminum low silicon ultrapure ferritic stainless steel according to claim 1. In step (2)
Add only ferrosilicon if you require that the upper limit of silicon mass content in the final high aluminum low silicon ultra pure ferritic stainless steel is 0.3%;
When it is required that the upper limit of the silicon mass content in the finally obtained high aluminum low silicon ultrapure ferritic stainless steel is 0.2% or less, only an aluminum block is added;
When it is required that the upper limit value of the silicon mass content in the finally obtained high aluminum low silicon ultrapure ferritic stainless steel is 0.2 to 0.3%, ferrosilicon and aluminum lump are added, and the above ferro Addition ratio of silicon and aluminum lump = (upper limit value of silicon mass content in final aluminum low silicon ultrapure ferritic stainless steel−0.2%) / (0.3% −high aluminum finally obtained 3. The smelting method of high aluminum low silicon ultrapure ferritic stainless steel according to claim 1 or 2, characterized in that the upper limit of the silicon mass content in the low silicon ultrapure ferritic stainless steel. In step (3), the shape of the ferroaluminum was massive or spherical, the density was 4.5 to 6.5 g / cm ³ , the diameter was ³ to 6 cm, and was processed in step (3) 4. The high ratio according to claim 1, wherein the mass ratio of CaO and SiO _{2 in} the billet slag exceeds 2.8 and the mass ratio of CaO and Al ₂ O ₃ in the billet slag exceeds 1. Smelting method of aluminum low silicon ultra pure ferritic stainless steel.