JPH08281390A - Method for preventing clogging of nozzle of al-less ti deoxidized steel - Google Patents

Abstract

PURPOSE: To prevent the surface defects, etc., of an extra-low carbon steel by preventing the clogging of the nozzle made of the Al-less Ti deoxidized steel as the Al-less Ti deoxidized steel is extremely little in the defects of the product but the clogging of the nozzles occurs therein. CONSTITUTION: The components of Ti3 O5 inclusions which are the skeleton of the deposited base metal are changed to the compsn. of Ti3 O5 -SiO2 -X inclusions by setting the concn. of Si in molten metal at an adequate value in continuous casting of the At-less Ti deoxidized steel, by which the growth of the deposited base metal is prevented, the clogging of the nozzle made of the Al-less Ti deoxidized steel is prevented and mass production is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-metallic inclusion (hereinafter abbreviated as inclusion) and a nozzle in steel, which leads to defects in each product such as a thin plate, a thick plate and a bar steel in a final product in casting of steel. The present invention relates to a method for preventing the blockage of

[0002]

2. Description of the Related Art In recent years, demands for surface and internal defects of various products such as thin plate materials and marine structures for automobiles and home appliances, storage tanks, steel pipes for carrying oil and gas, and high-strength wire rods have become more severe. . These defects occur due to surface bubbles, internal bubbles, internal cracks, center segregation, inclusions, etc. in the cast slab. Among these, inclusions are the main cause of surface defects of thin plates and internal defects of thick plates, and in wire rods, they are the cause of disconnection during wire rod rolling. The inclusions observed in these product defects are the deoxidation of the molten metal after tapping of the converter and the deoxidation of the molten metal after decarburization in the secondary refining to remove excess oxygen. It originates in the reaction products from the deoxidizers, or foreign inclusions caused by the inclusion of refractories and slag.

The molten metal cleaning method for preventing such a product defect is, for example, the 127th Nishiyama Memorial Memorial Course (1
(1988), many studies have been conducted. However, in the case of Al deoxidized steel, which must be deoxidized only with Al due to restrictions on product components, it is extremely excellent in terms of stability of deoxidation, workability, and material, The surface defects caused by this have not been eliminated. In addition, the fine deoxidized product suspended in the molten metal is deposited on the inner surface of the nozzle and blocks the nozzle,
Multi-casting becomes difficult, and the deoxidation product in Al deoxidation is an obstacle to efficient production.

As a measure for preventing these nozzle blockages, the inventors of the present invention have conducted various researches and developments, and as a result, by using a nozzle containing CaO.ZrO ₂ particles, the CaO can be used on the operating surface.
Generates a low melting point layer of -al ₂ O _3, that nozzle clogging can be prevented, materials and processes Vol. 4 (1991),
p. 219, 220. However, even with these measures, it has not been possible to eliminate the product defects caused by inclusions, and further measures are needed. In order to avoid such a drawback of Al deoxidation, as a result of research on various deoxidation methods, the present inventors have found that Ti deoxidation with a very small amount of Al (hereinafter abbreviated as Al-less Ti deoxidation).
The ultra low carbon steel according to the above has obtained the knowledge that it has the same characteristics as Al deoxidized steel as a thin plate material, and that the surface defects of the manufactured thin plate can be reduced.

However, in the case of Al-less Ti deoxidation, A
l More than deoxidation, ladle nozzles and dipping nozzles are more likely to be clogged, making it difficult to mass-produce such steel, and mass-producing thin plates of Al-less Ti deoxidized steel with very few surface defects. In order to realize the above, it was indispensable to prevent the nozzle blockage from occurring.

[0006]

Therefore, in order to realize the mass production of thin plate material by Al-less Ti deoxidation, which is capable of reducing the surface defects of the thin plate and has good material characteristics, a method for preventing nozzle clogging is established. Is an important issue to be solved for the time being.

[0007]

The gist of the present invention is as follows. % By weight, Al: 0.01%
Hereinafter, in continuous casting of steel consisting of Ti: 0.02 to 0.15%, the nozzle concentration of Al-less Ti deoxidized steel is characterized by adjusting the Si concentration in the molten metal within the range of the following formula (1). Prevention method. Si> 5.93 · 10 ⁻⁴ · T ^0.49 (1) where Si: Si concentration of product (%) T: Amount of molten metal that can be cast with one nozzle (t)

[0008]

[Operation and Example] FIG. 1 is an enlarged view of a part of the actual state of deposit metal 2 observed on the inner surface of the nozzle 1 when a molten metal having the chemical composition shown in Table 1 is continuously cast with an alumina graphite nozzle. The outline was shown. The adhered metal 2 grows on the inner surface of the nozzle 1. As a result of further microscopic observation of the adhered metal 2, a large amount of fine inclusions are observed in the metal, forming clusters. .

[0009]

[Table 1]

As a result of further research on the growth mechanism of the deposited metal 2, the present inventors found that the cluster generated by Al-less Ti deoxidation is not Al ₂ O ₃ , which is well known as a cluster-forming substance, but As shown in the result of X-ray diffraction of No. 2, it was confirmed to be Ti ₃ O ₅ containing a small amount of Al. This cluster-containing metal is above the melting point (1580 ° C)
When heated to the shape shown in FIG. 3 (a), the shape-preserving portion 3 in which the shape before the heating is not collapsed and the shape is maintained and the shape-changing portion 4 in which the shape before the heating is changed are observed. It was

Fine inclusions forming clusters are observed in the shape maintaining portion 3 in the same manner as before heating, and clusters of fine inclusions disappear in the shape changing portion 4 to change shape with the shape maintaining portion 3. Coarse inclusions 6 were observed in the boundary layer 5 of the part 4. It is considered that the shape maintaining portion 3 can maintain the shape at a temperature equal to or higher than the melting point because the molten metal is retained between the grains of the fine Al-containing Ti ₃ O ₅ clusters like water contained in the sponge.

On the other hand, the reason why the shape of the shape-changing portion 4 cannot be maintained is that the clusters of fine inclusions that should form the skeleton disappear. The shape maintaining unit 3 and the shape changing unit 4 in FIG.
The outline of the result of the microscopic observation of the coarse inclusions 6 observed in the boundary layer of is shown in FIG. Table 2 for coarse inclusions 6
A Ti-enriched phase 7 having the composition shown in Table 1 and a Si-enriched phase 8 having the composition shown in Table 3 were observed.

[0013]

[Table 2]

[0014]

[Table 3]

From the above results, in the growth of the adhered metal which leads to the nozzle clogging, the fine inclusions of Ti ₃ O ₅ grow and solidify while holding the molten metal between the grains, and on the other hand, such strong cluster formation is achieved. easily forming Ti oxide has a characteristic that tends to absorb SiO _2, by absorption of SiO _2, easily cluster came to knowledge that collapse. The reason why SiO ₂ is easily absorbed by the Ti oxide is presumably because the activity of SiO ₂ is extremely small in the case of inclusions containing Ti oxide.

The present inventors have studied the method of preventing the growth of the adhered metal by utilizing the characteristics of the Ti oxide which is the cause of the growth of the adhered metal. FIG. 4 shows the effect of the Si concentration in the molten metal on the amount of molten metal that can be cast with one nozzle. The influence of the Si concentration in the molten metal on the nozzle clogging is very large, and the molten amount that can be cast with one nozzle increases as the Si concentration increases, and in order to prevent the nozzle clogging of Al-less Ti deoxidation, the following ( The present invention has been accomplished with the knowledge that the Si concentration should be controlled within the range of the formula (1). There is no significant difference between the Si concentration in the molten metal sampled from the tundish and the Si concentration of the product. Also, the amount of melt that can be cast was determined by the stopper that causes product defects and the opening of the sliding nozzle.

Si> 1.85 · 10 ⁻⁵ · T ^1.21 (1) where Si: Si concentration of product (%) T: Amount of molten metal that can be cast by one nozzle (t) or more According to the present invention The occurrence of nozzle blockage when casting ultra-low carbon steel by Al-less Ti deoxidation can be avoided by limiting the Si concentration of the molten metal.

[0018]

As described above, according to the present invention, it is possible to prevent the nozzle clogging of Al-less Ti deoxidized steel, which was difficult to mass-produce due to the conventional nozzle clogging, and to significantly improve the surface defects of the thin plate. Enables mass production of Ti deoxidized steel.

[Brief description of drawings]

FIG. 1 is a partially enlarged schematic view showing a metal adhered in a nozzle when Al-less Ti deoxidized steel is cast by an alumina graphite nozzle.

FIG. 2 is a diagram showing an X-ray diffraction result of inclusions extracted from deposited metal.

FIG. 3 is a diagram showing changes in sample shape and inclusion morphology when a cluster-containing deposited metal is heated to a melting point or higher.

FIG. 4 Amount of molten metal that can be cast with one nozzle and S in the molten metal
The figure which shows the relationship of i density

[Explanation of symbols]

1 Nozzle 2 Metal attached to the inner surface of the nozzle 3 Shape-maintaining part where the shape before heating is maintained even if heated above the melting point 4 Shape-changing part where the shape changes when heated above the melting point 5 Boundary between shape-maintaining part and shape-changing part Layer 6 Coarse inclusions observed in shape maintaining part and shape change part 7 Ti enriched part observed in coarse inclusion 8 Si enriched part observed in coarse inclusion

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenichi Yoshii, 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Co., Ltd. Inside the Kimitsu Works (72) Inventor, Tetsuji Kadoya, Kimitsu, Chiba Shin Nippon Steel Stock Company Kimitsu Works

Claims (1)

[Claims] 1. By weight%, Al: 0.01% or less, T
i: A nozzle clogging prevention method for Al-less Ti deoxidized steel, characterized in that, in continuous casting of steel consisting of 0.02 to 0.15%, the Si concentration in the molten metal is adjusted within the range of the following formula (1). . Si> 5.93 · 10 ⁻⁴ · T ^0.49 (1) where Si: Si concentration of product (%) T: Amount of molten metal that can be cast with one nozzle (t)