KR20170026726A - Method of manufacturing ferritic stainless steel improved the equiaxed structure ratio - Google Patents

Method of manufacturing ferritic stainless steel improved the equiaxed structure ratio Download PDF

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Publication number
KR20170026726A
KR20170026726A KR1020150120721A KR20150120721A KR20170026726A KR 20170026726 A KR20170026726 A KR 20170026726A KR 1020150120721 A KR1020150120721 A KR 1020150120721A KR 20150120721 A KR20150120721 A KR 20150120721A KR 20170026726 A KR20170026726 A KR 20170026726A
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South Korea
Prior art keywords
tundish
molten steel
stainless steel
ferritic stainless
equiaxed
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KR1020150120721A
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Korean (ko)
Inventor
김지준
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주식회사 포스코
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Publication of KR20170026726A publication Critical patent/KR20170026726A/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
    • B22D11/002—Stainless steels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/108—Feeding additives, powders, or the like
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D41/00—Casting melt-holding vessels, e.g. ladles, tundishes, cups or the like

Abstract

The present invention relates to a method of manufacturing ferritic stainless steel with an improved equiaxed dendrite ratio, and ferritic stainless steel manufactured in accordance with the method. The method of manufacturing ferritic stainless steel with the improved equiaxed dendrite ratio, which includes a step of continuously casting molten metal, comprises: a step of inputting molten metal to a ladle; a step of inputting the molten metal input to the ladle and to a tundish through an injection nozzle; a step of inputting TiN particles having an average particle size of 5-20 m into the molten metal input to the tundish; and a step of inputting the molten metal input to the tundish, to a continuous casting mold through an immersion nozzle, and performing continuous casting. Accordingly, it is possible to secure an equiaxed dendrite ratio through the addition of TiN and control thereof in a tundish process; thereby being possible to reduce ridging defects in a final product.

Description

TECHNICAL FIELD [0001] The present invention relates to a ferritic stainless steel having improved equiaxed retention,

The present invention relates to a ferritic stainless steel having improved equiaxed retention, and more particularly, to a ferritic stainless steel capable of securing an equiaxed rate by TiN addition in a tundish process in order to reduce ridging defects in high chromium ferritic stainless steels. To a method of manufacturing a steel.

Generally, ferritic stainless steels are widely used as kitchen appliances, electric appliances, and automobile materials because they are relatively inexpensive and have good processability and corrosion resistance.

In the production of the high chromium ferritic stainless steel, the steelmaking process is performed in the form of final slab-type products through an electric furnace, Argon Oxygen Decarburization (AOD), Vacuum Oxygen Decarburization (VOD), Ladle Treatment . The technical field to which the present invention belongs corresponds to a continuous casting (CC) process. A step of decarbonating molten steel decarbonated in the AOD at a very low temperature by blowing oxygen under vacuum in VOD, and a step of charging the chromium oxide generated by the oxygen blowing with an aluminum deoxidizer to reduce the molten steel.

Ferritic stainless steels are less expensive than austenitic stainless steels, have lower thermal expansion rates, have better surface gloss, formability, and oxidation resistance. However, depending on the plastic deformation section of the material during the processing of sheet metal products, ridging A surface defect caused by the processing of the substrate may occur. The main reason for the ridging is due to the coarse ferrite band remaining in the center of the hot rolled plate and it is necessary to improve the equiaxed crystal ratio of the cast steel and to miniaturize the equiaxed crystal and to add titanium (Ti) or niobium (Nb) ) To produce equiaxed crystals.

Conventionally, in order to increase the equilibrium constant, for example, an Al-Ti-based composite inclusion having a size of 0.3 to 0.5 탆 is applied as an equiaxed nucleation seed, or an alloy containing 0.002 to 0.02% Al and 0.0005% generate MgO, MgO-Al 2 O 3 and less than added to the steel having a diameter of 0.3 to 5㎛ to about 30 / ㎥ to have been conducted a study to secure the polygonal information.

However, according to the conventional method, it is not easy to handle nucleation seeds of a specific size or deoxidation working conditions for forming fine MgO nucleation seeds, and there may be many variations depending on conditions. Thus, a high chromium ferrite stainless steel It is necessary to develop a method for securing equipments.

Further, if nucleation seeds produced in such high-chromium ferritic stainless steels are present at a temperature higher than the coagulation temperature, Ti is added to facilitate the equilibrium purification of the solidification structure in the ferrite-based stainless steel by using TiN as the solidification nuclei of the oxides It is known. However, in some cases, the solidification structure may become equiaxed to the columnar phase even under the condition where the content of Ti and N is constant. In order to improve the equiaxed crystal ratio, addition of Ti is required, but excessive Ti addition causes defects such as nozzle clogging and surface flaws . Therefore, it is difficult to control the equilibrium constant of the solidification structure by Ti addition.

In addition, one of the most troublesome problems in the manufacture of Ti-added stainless steels is nozzle clogging. The main cause of nozzle clogging is a large amount of Ti-based oxides having good molten steel and wettability according to the addition of Ti, So as to easily adhere to the wall surface of the nozzle and to adhere and grow. The grown oxide clusters have a good wettability with the molten steel, so that the molten steel easily flows into the clusters, which causes the growth of the nozzle deposits to rapidly increase, resulting in a problem of nozzle clogging.

Japanese Patent Application Laid-Open No. 10-2002-30395

Embodiments of the present invention provide a method of manufacturing a ferritic stainless steel capable of securing an equiaxed constant by adding TiN in a tundish process for reducing ridging defects in high chromium ferritic stainless steels.

A method of manufacturing a ferritic stainless steel including continuously casting molten steel capable of securing an equiaxed constant according to an embodiment of the present invention includes the steps of injecting molten steel into a ladle, injecting molten steel into the ladle through an injection nozzle Introducing TiN particles having an average particle size of 5 to 20 占 퐉 into the molten steel injected into the tundish; and injecting the molten steel injected into the tundish into a continuous casting mold through an immersion nozzle And continuously casting.

According to an embodiment of the present invention, the average residence time of the TiN particles in the tundish may be 400 seconds or more.

According to an embodiment of the present invention, a main dam and a sub dam are disposed between the injection nozzle and the immersion nozzle in the tundish, so that the molten steel injected from the injection nozzle may have an upward flow.

According to an embodiment of the present invention, the main dam is disposed adjacent to the injection nozzle, and the sub dam is disposed adjacent to the immersion nozzle, and one side of the tundish adjacent to the sub dam and the immersion nozzle The TiN particles can be introduced into the space.

Also, according to an embodiment of the present invention, the degree of superheat of the molten steel in the tundish may be 45 ° C or less.

A ferritic stainless steel having an improved equiaxed constant according to an embodiment of the present invention is manufactured by the above manufacturing method.

According to an embodiment of the present invention, the equiaxed constant of the stainless steel may be 80% or more.

In embodiments of the present invention, the equiaxed rate can be ensured through TiN addition and its control in the tundish process in the process for producing high chromium ferritic stainless steels, thereby reducing ridging defects in the final product.

FIG. 1 is a flowchart for explaining a method of manufacturing a ferritic stainless steel capable of securing an equilibrium constant according to an embodiment of the present invention.
2 is a cross-sectional view of a continuous casting facility for explaining a method of manufacturing a ferritic stainless steel capable of securing an equiaxed constant according to an embodiment of the present invention.
3 is a graph showing the correlation between the retention time and the residual fraction of particles in the tundish of TiN particles.
FIG. 4 is a graph showing the correlation between the size of TiN particles and the number of equiaxed crystals such as a cast steel.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided to fully convey the spirit of the present invention to a person having ordinary skill in the art to which the present invention belongs. The present invention is not limited to the embodiments shown herein but may be embodied in other forms. For the sake of clarity, the drawings are not drawn to scale, and the size of the elements may be slightly exaggerated to facilitate understanding.

FIG. 1 is a flowchart for explaining a method of manufacturing a ferritic stainless steel capable of securing an equilibrium constant according to an embodiment of the present invention. 2 is a cross-sectional view of a continuous casting facility for explaining a method of manufacturing a ferritic stainless steel capable of securing an equiaxed constant according to an embodiment of the present invention.

A method of manufacturing a ferritic stainless steel having improved equiaxed constant, comprising continuously casting molten steel according to an embodiment of the present invention.

1 and 2, a step (S200) of injecting TiN particles into molten steel in a tundish via a step (S100) of producing molten steel, and a step (S300) of continuously casting molten steel into which TiN particles are injected A final slab product can be produced.

The molten steel 110 produced according to the above process is introduced into the ladle 100.

The molten steel 110 injected into the ladle 100 is introduced into the tundish 200 through the injection nozzle 120.

TiN particles having an average particle size of 5 to 20 mu m are introduced into the molten steel 210 injected into the tundish 200. [

When the average particle size of the TiN particles is less than 5 占 퐉, the number of TiN particles to be added increases as a whole but the size of the particles is too small to uniformly nucleate the equiaxed crystals and thus it is difficult to increase the equiaxed crystal ratio. When the average particle size of the TiN particles is more than 20 占 퐉, the number of TiN particles per unit area decreases compared to the amount of TiN particles to be injected, thereby reducing the number of particles capable of forming nuclei. .

For example, the average residence time of the TiN particles injected into the tundish 200 in the tundish may be at least 400 seconds. When the average residence time of the TiN particles is less than 400 seconds, the TiN particles are not sufficiently stirred in the tundish, so that it is difficult to control the TiN particles, which makes it difficult to increase the equiaxed retention rate.

The tundish 200 includes a tundish main body, the injection nozzle 120 for injecting the molten steel into the tundish main body, the main dam 220 A sub dam 230 and an immersion nozzle 240 for injecting the molten steel 210 into the continuous casting mold 300.

For example, the main dam 220 and the sub dam 230 may be disposed between the injection nozzle 120 and the immersion nozzle 240 in the tundish 200.

The tundish 200 includes a tundish main body and a tundish cover disposed on and covering the tundish main body. The main dam 220 protrudes from the lower surface of the tundish cover, 210). In other words, after the molten steel 210 is charged into the tundish 200, the main dam 220 is immersed on the molten steel 210 to block the flow of the molten steel 210, Accordingly, the molten steel 210 can move to a lower portion of the main dam 220.

The sub dam 230 is disposed adjacent to the main dam 220. The sub dam 230 may protrude from the upper surface of the tundish main body. The sub dam 230 may block the flow of the molten steel 210 and the molten steel 210 may move to the upper portion of the sub dam 230. [

The molten steel 210 supplied to the tundish 200 through the injection nozzle 120 is discharged from one side of the tundish 200 where the injection nozzle 120 is disposed, The tundish 200 moves to the other side of the tundish 200 and flows through the main dam 220 and the sub dam 230. This flow may have an upward flow, ) Can be sufficiently stirred.

The main dam 220 is disposed adjacent to the injection nozzle 120 and the sub dam 230 is disposed adjacent to the immersion nozzle 240. For example, the sub dam 230 is disposed adjacent to the immersion nozzle 240 in comparison with the main dam 220. Therefore, the molten steel may have an upward flow from the main dam 220 toward the sub dam 230.

The tundish 200 is connected to one side of the tundish 200 adjacent to the injection nozzle 100 and the first region A between the sub dams 230 and the sub dams 230, The second region B is divided into a second region B between the sub dam 230 and the immersion nozzle 240 and a second region B between the other side of the tundish 200 adjacent to the sub- An area B1 and a second -2 region B2 between the immersion nozzle 240 and the other side of the tundish 200. [

At this time, the position where the TiN particles are injected may be the second region B between the sub dam 230 and the other side of the tundish 200.

When the TiN particles are injected into the first region A between one side of the tundish 200 and the sub dam 230, the stirring speed of the molten steel 210 injected from the ladle 100 is too high It is difficult to produce equiaxed nuclei because the TiN particles are dissolved rapidly.

Accordingly, it is preferable that the TiN particles are introduced into the second region (B).

For example, the degree of superheat of the molten steel 210 in the tundish 200 may be 45 ° C or less.

Superheat degree = Tundish temperature - Theoretical solidification temperature (1)

In the formula (1), the superheat degree refers to a temperature at which the molten steel starts to solidify when the continuous casting is performed, and the theoretical solidification temperature means a temperature at which molten steel begins to solidify.

When the superheating degree is higher than 45 ° C, the TiN nucleation is reduced and the equilibrium constant can be rapidly reduced. This is because, when the superheating degree is high, the TiN particles injected into the molten steel are melted to decrease the nucleation of TiN, which is disadvantageous. As a result, the size of the TiN particles becomes smaller and the number of the TiN particles satisfying the effective TiN decreases.

Thereafter, the molten steel 210 injected into the tundish 200 is injected into the continuous casting mold 300 through the immersion nozzle 240 to perform continuous casting. Accordingly, the final slabs 400 can be manufactured by continuous casting.

Accordingly, the ferritic stainless steel produced may have an equilibrium constant of 80% or more.

Hereinafter, the present invention will be described in more detail with reference to Examples.

18.3% Cr-0.17% Si-0.15% Mn-0.1% Ni-60 ppm After finishing refining with 60 ppm N as the target composition, the size of the charged TiN particles was changed as shown in Table 1 below, And the superheating degree of the molten steel in the tundish are controlled, and the examples and the comparative examples are shown in the following Table 1.

Remarks Average particle size (占 퐉) Average residence time (sec) Input location Superheat (℃) Equilibrium constant (%) Minimum Size (mm) DTi (%) Inventory 1 5 423 B1 40 93 0.14 0.11 Inventory 2 10 423 B1 39 100 0.18 0.09 Inventory 3 15 423 B1 38 98 0.20 0.09 Honorable 4 20 423 B1 35 95 0.24 0.07 Inventory 5 5 423 B2 42 96 0.13 0.07 Inventory 6 10 423 B2 38 98 0.17 0.08 Honorable 7 10 423 B1 20 100 0.13 0.09 Honors 8 20 423 B1 10 94 0.24 0.08 Comparative Example 1 3 423 B1 38 32 2.5 0.10 Comparative Example 2 5 423 A 39 36 0.37 0.11 Comparative Example 3 10 423 A 38 42 0.46 0.12 Comparative Example 4 10 387 B1 37 64 0.33 0.11 Comparative Example 5 25 423 B1 41 39 0.48 0.12 Comparative Example 6 5 423 B1 55 24 0.08 0.13 Comparative Example 7 - - - 39 45 2.5 -

FIG. 4 is a graph showing the correlation between the size of TiN particles and the number of equiaxed crystals such as a cast steel.

2, 4 and Table 1, Inventive Example 1 to Inventive Example 4 show that the equilibrium constant rate can be secured when the tundish is charged at the position of the second-first region B1 in which the stirring of the tundish is the strongest under the same casting condition .

In Inventive Example 1, when TiN having an average particle size of 5 탆 was introduced, the equiaxed rate was 100%, and the degree of equiaxedness was very fine. The average particle size of TiN was gradually increased, Of TiN was added, and the average size of equiaxed crystals increased.

In the case of Comparative Example 1 in which the size of the charged TiN particles was 3 탆, the number of charged TiN particles increased but no equiaxed crystals could be formed. In Comparative Example 5 in which the size of charged TiN particles was 25 탆, One effect could not be confirmed.

In Comparative Example 2 and Comparative Example 3, in the first region (A) where molten steel is injected into the tundish at the tundish injection position, the stirring speed of molten steel injected from the ladle is too fast to dissolve the injected TiN, , And at least the TIN injected into the second-1 region (B1) of the second region (B) was partially melted and crystallized in the vicinity of the TiN crystallization temperature to grow as isostatic nuclei.

It was confirmed that when the average residence time was decreased as in Comparative Example 4, no equiaxed crystal was formed.

In Comparative Example 6, the change in equilibrium constant according to the superheating degree of 55 캜 was tested. When the superheat of high chromium steel was 55 ℃, the nucleation of TiN decreased and the equiaxed rate decreased rapidly. As a result of the analysis of the cause, it was confirmed that when the superheat is high, the injected TiN is melted and the nucleation of the recycled TiN becomes small and becomes disadvantageous, and as a result, the size of the TiN becomes small and the number satisfying the effective TiN is also decreased. Therefore, it is understood that at least the superheat degree should be controlled to be less than 45 degrees in order to increase the equilibrium constant rate.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited thereto. Those skilled in the art will readily obviate modifications and variations within the spirit and scope of the appended claims. It will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

100: Ladle 120: injection nozzle
200: tundish 220: main dam
230: Sub-dam 240: Immersion nozzle
300: continuous casting mold 400: slab
110, 210: molten steel A: first region
B: second area B1: second-1 area
B2: Area 2-2

Claims (7)

A method of manufacturing a ferritic stainless steel comprising continuously cast molten steel,
Injecting molten steel into the ladle;
Injecting the molten steel injected into the ladle into a tundish through an injection nozzle;
Introducing TiN particles having an average particle size of 5 to 20 占 퐉 into the molten steel charged in the tundish; And
And continuously casting the molten steel injected into the tundish into a continuous casting mold through an immersion nozzle, thereby improving the equiaxed constant of the ferritic stainless steel. The method according to claim 1,
Wherein the average residence time of the TiN grains in the tundish is at least 400 seconds. The method according to claim 1,
Wherein a main dam and a sub dam are disposed between the injection nozzle and the immersion nozzle in the tundish, and the molten steel injected from the injection nozzle has an ascending flow. The method of claim 3,
The main dam is disposed adjacent to the injection nozzle, the sub dam is disposed adjacent to the immersion nozzle,
And injecting the TiN particles between one side of the tundish adjacent to the sub dam and the immersion nozzle. The method according to claim 1,
Wherein the superheating degree of the molten steel in the tundish is 45 DEG C or less. A ferritic stainless steel produced by any one of claims 1 to 5 with improved equiaxed crystallinity. The ferritic stainless steel according to claim 6, wherein the equiaxed constant of the stainless steel is 80% or more.


KR1020150120721A 2015-08-27 2015-08-27 Method of manufacturing ferritic stainless steel improved the equiaxed structure ratio KR20170026726A (en)

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Citations (1)

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Publication number Priority date Publication date Assignee Title
KR20020030395A (en) 2000-10-17 2002-04-25 허화영 Apparatus and method for ordering browser

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20020030395A (en) 2000-10-17 2002-04-25 허화영 Apparatus and method for ordering browser

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