KR102175364B1 - Manufacturing method of ferritic stainless steel with improved surface quality - Google Patents

Abstract

The present invention discloses a method of manufacturing a ferritic stainless steel with improved surface quality by adding a nucleating material to the center of a cast steel during continuous casting. A method of manufacturing a ferritic stainless steel having improved surface quality according to an embodiment of the present invention includes a molten steel refining step; Component adjustment step for the refined molten steel; Continuous casting step of injecting molten steel that has undergone the component adjustment step into the tundish and moving it to the mold through the immersion nozzle to cast it; And adding a nucleating material containing CaTiO ₃ oxide to the molten steel in the mold; Including, the nucleating material is added at a position corresponding to 40 to 50% of the thickness of the total cast steel coagulation cell thickness To do.

Description

Ferritic stainless steel manufacturing method with improved surface quality{MANUFACTURING METHOD OF FERRITIC STAINLESS STEEL WITH IMPROVED SURFACE QUALITY}

The present invention relates to a method of manufacturing a ferritic stainless steel, and more particularly, to a method of manufacturing a ferritic stainless steel having fine core grains by adding a nucleating material to the central portion of a cast steel during continuous casting.

In general, in manufacturing ferritic stainless steel, the initially formed casting structure is maintained at room temperature because it does not undergo transformation during the cooling process, and even after the rolling and annealing process, the properties of the casting structure affect the final product. It is very important to control the initial casting structure. In particular, in the case of ferritic stainless steel, where surface quality is important, the cast steel that does not secure more than 40% of the equiaxed structure ratio of the cast steel remains coarse band structure in the hot-rolled coil, resulting in deep drawing of the cold-rolled steel sheet or During the forming process, the coil surface is liable to be parallel to the cold rolling direction called ridging or roping, and fine irregularities are likely to occur. In addition, even if the equiaxed crystal ratio is more than 40%, when the size of the equiaxed crystal is coarse, the driving force required for recrystallization is lowered, and the coarse band structure remains, making it difficult to manufacture a product with excellent reasing properties.

In the past, cold-rolling re-rolling and hot-rolling depressurization have been performed to prevent such leasing defects, but this has a problem that causes a decrease in productivity as well as an increase in manufacturing cost when manufacturing ferritic stainless steel.

Accordingly, recently, as a technique for improving the equiaxed crystallization rate of ferritic stainless steel casts, a low-temperature casting method, a method of adding powdered iron or steel, a method of adding rare earth elements, and an electromagnetic stirring device (Electro Magnetic Stirring) have been used.

For example, Patent Document 1 discloses that an Al-Ti-based composite inclusion having a size of 0.3 to 0.5 μm acts as an equiaxed crystal nucleation seed, and in Patent Document 2, the basicity composition is set to 0.5 to 3.0 and overheated. It is disclosed that the equiaxed crystal can be improved by setting the degree to 20 to 70°C. In addition, in Patent Document 3, by including 0.002 to 0.02% by weight of Al and less than 0.0005% by weight of Mg, MgO and MgO-Al ₂ O ₃ having a diameter of 0.3 to 5 μm were produced by 30 pieces/m ³ It is disclosed that an equiaxed well can be secured.

However, these methods utilize oxides formed in the steelmaking industry, and the problem remains quite difficult to control uniform oxides due to the steelmaking operations with large operational fluctuations. As a result, there are many equiaxed correction rates depending on the working conditions or surrounding conditions. There is a risk of deviation.

In addition, since Ti is added to ferritic stainless steel, it is known that when TiN precipitated in molten steel is used as ferrite solidification nuclei, the solidification structure is easily equiaxed, and sufficient addition of Ti is required to improve the equiaxed crystallization rate. .

However, since excessive Ti addition causes defects such as nozzle clogging and surface flaws, improvement of the equiaxed crystal rate simply by adding Ti is not a preferable method. In addition, when the amount of Ti added is 0.2% by weight or less, the crystallization temperature of TiN is low, making it difficult to purify the equiaxed axis. In the case of steel without Ti, it is impossible to secure and refine the equiaxed crystal.

In addition, the size of the cast iron equiaxed rate is also recognized as an important factor in leasing quality. In general, the casting structure of the surface layer of the cast steel is subjected to severe shear stress during the rolling process, so that the casting structure is easily destroyed and recrystallization is facilitated, so it is not a big problem.

However, in the case of the central part of the cast steel where the shear stress does not act during the hot rolling process, in more detail, the plane stress acts at a point corresponding to 40 to 50% of the total thickness of the cast, so deformation is not easy. Since recrystallization does not occur easily due to poor concentration, coarse casting structures tend to remain.

In particular, when the crystal grains at the point of transition from shear deformation to planar deformation among the cast structure are coarse, for example, columnar crystals or coarse equiaxed crystals, there is a problem that the surface quality characteristics of the final product are significantly deteriorated.

Accordingly, there is a need to establish a manufacturing method capable of improving the surface quality by miniaturizing the casting structure in the center of the ferritic stainless steel while securing a high equiaxed crystallization rate.

Japanese Laid-Open Patent Publication No. 1999-323502 (published on November 26, 1999) Japanese Patent Laid-Open Publication No. 2001-049322 (published on 20 February 2001) Japanese Unexamined Patent Publication No. 2002-030395 (published on Jan. 31, 2002)

An object of the present invention is to provide a method of manufacturing ferritic stainless steel with improved surface quality by adding a nucleating material to a central part of a cast iron during continuous casting to ensure equiaxed crystallization and refinement of the central casting structure.

A method of manufacturing a ferritic stainless steel having improved surface quality according to an embodiment of the present invention includes a molten steel refining step; Component adjustment step for the refined molten steel; A continuous casting step of injecting the molten steel that has undergone the component adjustment step into the tundish and moving it into a mold through an immersion nozzle to cast it; And adding a nucleating material containing CaTiO ₃ oxide to the molten steel in the mold, wherein the nucleating material is added at a position where the solidification cell thickness of the molten steel corresponds to 40 to 50% of the total thickness of the cast steel. It features.

In addition, according to an embodiment of the present invention, the nucleating material may be uniformly distributed in the base metal and added to the molten steel in the form of a wire.

In addition, according to an embodiment of the present invention, determining the input speed of the wire, when the position corresponding to 40 to 50% of the total thickness of the cast steel exceeds the melting position of the wire, the input speed of the wire Increase; When the position corresponding to 40 to 50% of the total thickness of the cast is less than the melting position of the wire, reducing the input speed of the wire; may include.

In addition, according to an embodiment of the present invention, the nucleation material may have a size of 0.5 to 15㎛.

In addition, according to an embodiment of the present invention, the nucleation material may satisfy the following equations (1) to (3).

(1) %(TiO ₂ )+%(CaO)+%(Al ₂ O ₃ ) ≥ 85%

(2) %(CaO)+%(TiO2) ≥ 40%

(3) 0.3 ≤ %(CaO)/[%(TiO2)+%(CaO)] ≤ 0.8

Here, %(TiO ₂ ), %(CaO), and %(Al ₂ O ₃ ) mean the weight% of TiO ₂ , CaO, and Al ₂ O ₃ .

In addition, according to an embodiment of the present invention, the nucleation material may have a melting point lower than that of the base metal by 10 to 100°C.

In addition, according to an embodiment of the present invention, the step of stirring the molten steel at the position where the planetary material is added; may further include.

In addition, according to an embodiment of the present invention, the molten steel may be stirred with a 　 electromagnetic 　 stirring device (Electromagnetic Stirrer).

In addition, according to an embodiment of the present invention, the average grain size of the center cast structure may be 1.5mm or less.

According to the disclosed embodiment, it is possible to provide a ferritic stainless steel with improved surface quality by securing an equiaxed crystallinity and minimizing the average grain size of the central casting structure to 1.5 mm or less.

1 is a flowchart schematically showing a method of manufacturing a ferritic stainless steel according to the present invention.
2 is a view showing the shear stress distribution in the thickness direction of the cast steel during the rolling process of ferritic stainless steel.
3 is a view showing a continuous casting equipment for explaining the manufacturing method of the ferritic stainless steel according to the present invention.
4 is a diagram schematically illustrating a method of controlling a melting position of an alloy wire for nucleation including a nucleation material injected from a mold.
Figure 5 is an optical microscope photograph showing the cast structure of the comparative example and the example of the present invention.
6 is a graph showing the average grain size for each thickness of a cast piece in Comparative Examples and Examples of the present invention.
7 is a graph analyzing the size and number of oxides including CaTiO ₃ phase in a cast iron according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are presented in order to sufficiently convey the spirit of the present invention to those of ordinary skill in the art to which the present invention pertains. The present invention is not limited only to the embodiments presented herein, but may be embodied in other forms. In the drawings, in order to clarify the present invention, portions not related to the description may be omitted, and sizes of components may be somewhat exaggerated to help understanding.

1 is a flowchart schematically showing a method of manufacturing a ferritic stainless steel according to the present invention.

The method of manufacturing a ferritic stainless steel with improved surface quality according to the present invention includes a molten steel refining step; Component adjustment step for the refined molten steel; A continuous casting step of injecting the molten steel that has undergone the component adjustment step into the tundish and moving it into a mold through an immersion nozzle to cast it; And adding a nucleating material containing CaTiO ₃ oxide to molten steel in the mold.

The step of refining and component adjustment of molten ferritic stainless steel may be performed by a conventional method.

Thereafter, the molten steel that has undergone the above-described component adjustment step is injected into the tundish, and is transferred to a mold through an immersion nozzle to undergo a continuous casting step.

The present inventors experimented by preparing various types of oxides, nitrides and boron compounds to obtain a fine equiaxed crystal structure. As a result, it was concluded that when the composition range and size range were as follows, it could act as a nucleation site of an equiaxed crystal, and a ferritic stainless steel having a fine equiaxed crystal could be manufactured.

The present inventors have derived the fact that it can function as an equiaxed crystal nucleation site by controlling the oxide composition and size distribution of ferritic stainless steel in Korean Patent Application Publication No. 10-2018-0064758. When the oxide composition of molten steel is controlled under the conditions disclosed in the above publication, CaTiO ₃ oxide and Al ₂ O ₃ -MgOTiO ₂ oxide are crystallized during the cooling process, and CaTiO ₃ oxide is more effective in the formation of equiaxed crystal nuclei in these crystal phases. Was revealed.

The nucleation material includes CaTiO ₃ and may be uniformly distributed in the base metal in the form of a powder. In order to uniformly distribute the nucleation material in the molten steel, the role of the base metal, which is the base material, is important, and in the present invention, a wire-type nucleation alloy in which the nucleation material in the base metal is uniformly distributed was used.

The nucleating material may include oxides in molten steel, including CaTiO ₃ . CaTiO ₃ is also effective in its pure form, but it is also possible to lower the melting point to improve wettability with molten steel. That is, it can be used by adjusting the components in the form of an Al-Ti-Ca-Mg-O-based complex oxide, and at this time, the chemical composition of each oxide contained in the nucleating material is prepared to satisfy the following equations (1) to (3). Can be used.

(1) %(TiO ₂ )+%(CaO)+%(Al ₂ O ₃ ) ≥ 85%

(2) %(CaO)+%(TiO2) ≥ 40%

(3) 0.3 ≤ %(CaO)/[%(TiO2)+%(CaO)] ≤ 0.8

Here, %(TiO ₂ ), %(CaO), and %(Al ₂ O ₃ ) mean the weight% of TiO ₂ , CaO, and Al ₂ O ₃ .

The size of the nucleation material acting as nucleation of the primary ferrite phase in molten steel satisfies 0.5 to 15 μm. When the diameter of the oxide is less than 0.5 μm, the activation energy barrier required for nucleation is large due to the interfacial curvature energy, making it difficult to nucleate the ferrite phase. On the other hand, oxides of more than 15 μm are easy to float and remain difficult to remain in molten steel, so they do not help in nucleation.

In the actual operation, when the nucleation alloy is introduced into the molten steel, the base metal is preferentially dissolved and the nucleating material distributed inside is dispersed into the molten steel, and in particular, the melting occurs sequentially from the surface of the nucleation alloy. As the nucleation material is dispersed, it is possible to prevent coarsening and coarsening.

For smooth dissolution of the nucleating alloy, the powder containing the nucleating material should be a material having a higher melting point than that of the base metal. Preferably, the material may be selected to have a melting point higher than that of the base metal by 10 to 100°C.

The base metal should be a material with a melting point lower than the molten steel temperature during continuous casting. Preferably, the material should be selected so as to have a melting point lower than the molten steel temperature by 10°C or more, and it can be made of carbon steel or stainless steel depending on the application.

The nucleation alloy may be added to molten steel by mechanical mixing. For example, the nucleation alloy may be manufactured in a wire form and added by a wire feeding method using a steel tube tube.

2 is a view showing the shear stress distribution in the thickness direction of the cast steel during the rolling process of ferritic stainless steel.

Referring to FIG. 2, it can be seen that in the hot rolling process, shear deformation occurs from the surface of the cast steel to about 40 to 50% of the section due to the pressure and rotational force of the roll, but plane deformation occurs in the center. Accordingly, it is difficult to cause recrystallization due to low strain accumulation energy and low strain in the center.

Therefore, the casting structure or coarse texture tends to remain easily in the center, which causes surface quality problems such as leasing during molding of the final product.

Accordingly, it was attempted to refine the casting structure of the central portion of the ferritic stainless steel while securing a high equiaxed crystal rate.

On the other hand, many studies have been conducted on the method of directly introducing oxide powder among the methods of forming equiaxed crystals using oxide, but it is quite difficult to see the actual effect. The typical reason is that the difference in specific gravity between oxide and molten steel is large, making it difficult to uniformly disperse in molten steel, and dispersed oxides are also easily floated and separated, making it difficult to act as a nucleation site.

Therefore, in the present invention, CaTiO ₃ is advantageous for the nucleation site of primary ferrite. A method of minimizing the central grain of ferritic stainless steel was developed by not forming a phase in molten steel in the tundish, but directly injecting it into the central part of the cast steel during continuous casting in the mold.

In the method of manufacturing a ferritic stainless steel having a fine casting structure according to an embodiment of the present invention, in continuous casting of a cast steel by supplying molten steel in a tundish to a mold, a nucleating material containing CaTiO ₃ is continuously cast in the mold. It is injected directly into the center of the cast iron. The nucleating material can form a fine equiaxed crystal structure by acting as a primary ferrite nucleation site when the cast is solidified.

In addition, in order to evenly disperse the nucleation material in molten steel, methods of injecting fine particles in a component adjustment step or tundish have been proposed. If fine particles are added in the component adjustment stage, a waiting time is required in most continuous casting processes, so there is a disadvantage that it cannot act as a nucleus during solidification and is dissolved. When a nucleating material is added to the molten steel in the tundish, the fine particles It can be a method to increase the fine equiaxed crystallization rate over the entire cast steel by being uniformly dispersed in the molten steel. However, if the injected fine particles are distributed on the surface of the coagulation cell during the initial solidification process during the continuous casting process, there is a risk that it may cause inclusion defects in post-processing such as rolling, and is easily recrystallized by shear deformation in the rolling process. There is a disadvantage in that the manufacturing cost increases due to the addition of an excessive amount of ferroalloy that occurs due to the excessive refinement of the cast structure that is refined to the surface layer region of the cast steel.

In consideration of the above, the present invention fundamentally blocks the occurrence of inclusion defects in the cast iron surface layer due to additionally added microparticles, and at the same time, only for areas where there is little shear deformation in the rolling process, which may cause problems for recrystallization. As a method of minimizing unnecessary addition of excessive ferroalloy by miniaturization, a nucleation material containing CaTiO ₃ oxide is placed in the center of the cast steel during continuous casting in the mold, specifically at a position corresponding to 40 to 50% of the thickness of the cast steel from the cast surface. Intended to be added.

3 is a view showing a continuous casting equipment for explaining the manufacturing method of the ferritic stainless steel according to the present invention. Referring to FIG. 3, the continuous casting facility of ferritic stainless steel according to the disclosed embodiment is composed of a secondary cooling zone after mold cooling, and has an EMS (electromagnetic stirrer) installed on the strand.

The molten steel discharged from the immersion nozzle collides with the inner wall of the mold and vortex and starts to solidify gradually from the inner wall of the mold. The solidification cell is a part where the molten steel is solidified, and the flow of molten steel occurs in the area except for the solidification cell.

As shown in Fig. 3, as the molten steel 　 coagulation cell is formed on the inner wall of the top of the mold and casting proceeds, the thickness of the coagulation cell gradually increases. The thickness of the coagulation cell can be predicted by the following equation (4).

(4) Coagulation cell thickness = k * t ^1/2

Where k is the solidification constant and t is the solidification time.

The solidification time t can be represented by the following formula (5).

(5) t = distance from the hot water surface / casting speed

From the above equations (4) and (5), the thickness of the ferritic stainless steel solidification cell according to the distance from the hot water surface can be calculated. From this, it is possible to predict the position corresponding to the 40 to 50% section from the surface of the cast steel, that is, the distance from the surface of the cast steel, and refine the core cast structure of the ferritic stainless steel by injecting the aforementioned nucleating agent at the predicted position. can do.

The present inventors derived a process by which the ferroalloy wire surrounding the nucleation material flows into the molten steel and melts through computational simulation.

Based on this, a method for introducing the alloy for nucleation into a desired position, that is, a position corresponding to the 40 to 50% section from the surface of the cast steel among the thickness of the ferritic stainless steel cast is proposed.

For example, in the method of manufacturing ferritic stainless steel with improved surface quality according to the present invention, the position of the alloy wire for nucleation and the position of the coagulation cell thickness corresponding to 40% of the total thickness of the cast plate are compared with each other to obtain the alloy wire for nucleation. The melting position of can be controlled.

4 is a diagram schematically illustrating a method of controlling a melting position of an alloy wire for nucleation including a nucleation material injected from a mold.

Using the molten steel temperature, casting speed, secondary cooling water amount, and steel type properties as input variables, the thickness of the solidification cell according to the distance from the hot water surface was calculated through heat/flow analysis, and from the calculated result, the solidification cell thickness was 40 Derive the position (S) corresponding to the %.

Separately, by using the wire properties, wire thickness, wire diameter, and heat/flow analysis as input variables, the melting position (L) of the nucleation alloy wire flowing into the molten steel, and more specifically, the nucleation alloy shell It is possible to derive the location where the internal nucleation material is dispersed into the molten steel by melting.

Referring to Figure 4, if the position (S) corresponding to 40% of the total thickness of the cast steel is the same as the melting position (L) of the alloy wire for nucleation inflow, it is possible to maintain the input speed of the wire injected in the molten steel. That is, the melting position of the alloy wire for nucleation is maintained.

On the other hand, when the position (S) corresponding to 40% of the total thickness of the cast steel exceeds the melting position (L) of the inflowing alloy wire for nucleation, it is possible to increase the input speed of the wire injected in the molten steel. For example, in FIG. 3, the melting position of the alloy wire for nucleation may be adjusted downward.

On the other hand, when the position (S) corresponding to 40% of the total thickness of the cast steel is less than the melting position (L) of the inflowing alloy wire for nucleation, the input speed of the wire injected in the molten steel can be reduced. For example, in FIG. 3, the melting position of the alloy wire for nucleation can be adjusted upward.

In addition, the method of manufacturing a ferritic stainless steel having improved surface quality according to the disclosed embodiment may further include agitating the molten steel at a position where the alloy for nucleation is added.

The molten steel can be stirred to uniformly disperse the nucleating material in the molten steel. For example, when molten steel is stirred by applying an electromagnetic stirrer (EMS) current of appropriate strength to a location where the nucleation alloy is dispersed, the injected nucleation material can be uniformly dispersed.

As described above, by controlling the injection speed of the nucleating alloy according to the change of the operating parameters in the actual operation, that is, the molten steel temperature and the casting speed, the position where the nucleating material is injected is controlled to refine the core casting structure of the ferritic stainless steel. I can.

Hereinafter, the present invention will be described in detail through examples, but the following examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

In wt%, C: 0.02% or less, N: 0.015% or less, Si: 0.5% or less, S: 0.01% or less, Cr: 16-18%, Mn: 2.0% or less, Si: 2.0% or less, Ti: 0.1 % Or less, Nb: 0.6% or less, for ferritic stainless steel containing the balance Fe and inevitable impurities, the electric furnace-refining furnace (AOD)-component adjustment (LT)-tundish-continuous casting process Then, a cast iron was produced.

Molten steel of 80 ton ladles was produced three times in total, and the first charge was cast without inputting an alloy wire for nucleation, which will be described as a comparative example below. For the remaining two charges, an alloy wire for nucleation was introduced, and at the point when the ladle residual water became 60 tons after the ladle was replaced, the alloy wire for nucleation was injected through the wire input device installed on the column and cast. It is described as

For the nucleation alloy, 0.02% carbon steel powder is used as a base metal, and a nucleation material containing 35% TiO ₂ -20% CaO-35% Al ₂ O ₃ -10% MgO with an average composition is prepared, and then crushed. After the powder was prepared, only powder of 15 μm or less was separated through a sieve and used. Then, 5% of the nucleating material and 95% of carbon steel powder were weighed by weight, mechanically mixed, and pressed to produce a solid powder, and then prepared in the form of a wire coated with iron skin.

The nucleation alloy was injected at a constant speed in synchronization with the casting speed so that the injection speed was adjusted to target 0.05% by mass. At this time, the molten steel temperature in the tundish was adjusted to an average of 1,545°C, and the casting speed was continuously cast at a rate of 1.0 m/min.

The produced cast slab was cut in full width at every 10 m in the longitudinal direction, and 4 sheets per charge, a total of 12 slabs were produced, and 100 mm of cast slabs in the length direction from the tail of each cast slab were spread over the entire width. It was collected, which was again divided into five sections in the width direction to observe the casting structure.

The produced cast slab was cut and polished in a width direction, and then macro-etched with aqua regia. Thereafter, an image was obtained through photographing with an optical microscope, and the average diameter of the equiaxed crystal was measured through an image analysis method, and is shown in Table 1 below.

Here, the equiaxed crystal was defined as a grain with a ratio of the long side to the short side of 2 or less, and was converted to circular diameter and expressed as the average equiaxed crystal diameter. The measurement range of the equiaxed crystal diameter was evaluated by limiting the range from 45% of the total thickness on the surface of the cast to the center in the direction of the thickness of the cast.

division Equiaxed rate (%) Equiaxed diameter (mm) Number of analysis pieces Average Deviation Average Deviation Comparative example 52 3 2.85 1.11 4 Example 54 2 1.05 0.31 8

Referring to Table 1, in the case of the comparative example, the average equiaxed crystal ratio was at the level of 52%, and the equiaxed crystal diameter was analyzed to be 2.85 mm. On the other hand, in the case of the Example, the average equiaxed crystal rate was 54%, which was similar to that of the comparative example, but it was confirmed that the equiaxed crystal diameter was approximately 2 to 3 times finer to about 1 mm.

Then, the cast steels of Examples and Comparative Examples were subjected to the same hot rolling, annealing pickling, cold rolling, and annealing pickling processes, and then a coil having a thickness of 0.6 mm was manufactured. Table 2 shows the results of evaluating the height of the leasing by collecting five specimens in the width direction from the top and tail of each coil.

division Average leasing height (㎛) Maximum leasing height (㎛) Number of analysis specimens Number of analysis coils Average Deviation Average Deviation Comparative example 14 4 18 3 40 4 Example 10 2 13 One 80 8

Referring to Table 2, in the case of the Example, it was confirmed that the average leasing height was about 4 μm lower than that of the comparative example, and the deviation of the average leasing height was also reduced. In addition, in the case of the Example, the maximum leasing height was 13 μm, and the result was improved by more than 30% compared to the Comparative Example.

Figure 5 is an optical microscope photograph showing the cast structure of the comparative example and the example of the present invention.

6 is a graph showing an average grain size for each thickness of a cast piece in Comparative Examples and Examples of the present invention.

In the case of a conventional ferritic stainless steel, it grows into a coarse columnar crystal at the initial solidification, and a transition occurs to an equiaxed crystal at 40 to 50% of the thickness of the cast steel. Referring to FIG. 6, it can be seen that the average equiaxed crystal size at the transition point is 2.1 mm in the case of the comparative example, and 1.1 mm, which is half the level of the comparative example in the case of the example. Further, referring to FIG. 5, it can be seen that the central crystal grains were finely derived in the Example compared to the Comparative Example.

7 is a graph analyzing the size and number of oxides including CaTiO ₃ phase in a cast iron according to an embodiment of the present invention. 7 is a graph analyzing the size and number of oxides including a CaTiO ₃ phase in a cast iron according to an embodiment. The size of the oxide was evaluated as the maximum diameter, and the size was distributed in the range of 0.5 to 10 μm. About 60% of the nucleating material contained in the nucleation alloy remained in the final cast iron, and it could be estimated that ferrite was formed by non-uniform nucleation by the residual nucleating material. That is, the formation of fine equiaxed crystals in the examples could be determined by the effect of the nucleation material in the nucleation alloy proposed in the present invention.

As described above, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the protection scope of the present invention should be interpreted by the following claims, and all within the scope equivalent thereto. The technical idea should be interpreted as being included in the scope of the present invention.

Claims (9)

Molten steel refining step;
Component adjustment step for the refined molten steel;
A continuous casting step of injecting the molten steel that has undergone the component adjustment step into the tundish and moving it into a mold through an immersion nozzle to cast it; And
Including; adding a nucleating material containing CaTiO3 oxide to the molten steel in the mold,
The nucleating material is added at a location where the thickness of the solidification cell of the molten steel corresponds to 40 to 50% of the total thickness of the cast steel,
The nucleating material is uniformly distributed in the base metal and added to the molten steel in the form of a wire,
Determining the input speed of the wire,
When the position corresponding to 40 to 50% of the total thickness of the cast steel exceeds the melting position of the wire, increasing the input speed of the wire;
When the position corresponding to 40 to 50% of the total thickness of the cast steel is less than the melting position of the wire, reducing the input speed of the wire; the method of manufacturing a ferritic stainless steel with improved surface quality comprising. delete delete The method of claim 1,
The method for producing a ferritic stainless steel with improved surface quality of the nucleating material having a size of 0.5 to 15㎛. The method of claim 1,
The nucleating material is a method for producing a ferritic stainless steel with improved surface quality satisfying the following formulas (1) to (3).
(1) %(TiO ₂ )+%(CaO)+%(Al ₂ O ₃ ) ≥ 85%
(2) %(CaO)+%(TiO2) ≥ 40%
(3) 0.3 ≤ %(CaO)/[%(TiO2)+%(CaO)] ≤ 0.8
(Here, %(TiO ₂ ), %(CaO), %(Al ₂ O ₃ ) means the weight% of TiO ₂ , CaO, Al ₂ O ₃ .) The method of claim 1,
The method for producing a ferritic stainless steel with improved surface quality, wherein the nucleating material has a melting point higher than that of the base metal by 10 to 100°C. The method of claim 1,
Stirring the molten steel at the position where the nucleating material is added; the method of manufacturing ferritic stainless steel with improved surface quality further comprising. The method of claim 7,
A method for producing ferritic stainless steel with improved surface quality, characterized in that stirring the molten steel with an electromagnetic stirrer. The method of claim 1,
A method of manufacturing ferritic stainless steel with improved surface quality with an average grain size of 1.5mm or less in the core casting structure.

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