JP3389367B2 - Nozzle blockage prevention method for Al-less Ti deoxidized steel - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to non-metallic inclusions in steel that lead to defects in thin products, thick plates, strips and other products in the final product in the casting of steel. (Hereinafter abbreviated as inclusions) and a method for preventing nozzle blockage. 2. Description of the Related Art In recent years, there has been an increasing demand for defects in the surface and internal quality of various products such as thin plates for automobiles and home appliances, marine structures, storage tanks, steel pipes for oil and gas transportation, high tension wires, and the like. Is coming. These defects occur due to surface bubbles, internal bubbles, internal cracks, center segregation, inclusions, and the like in the slab. Among these, inclusions are the main causes of surface flaws of a thin plate and internal defects of a thick plate. Inclusions observed in these product defects are due to deoxidation of the molten metal after converter tapping and deoxidization performed in order to remove excess oxygen in the molten metal after decarburization refining in secondary refining. It originates in the reaction products from the deoxidizing material, or foreign inclusions caused by entrainment of refractories and slag. [0003] For example, the 127th Nishiyama Technical Commemorative Lecture (1)
Many studies have been made as shown in (1988). However, in the case of Al deoxidized steel, which must be deoxidized only with Al due to restrictions on product components, although it is very excellent in terms of deoxidation stability, workability, and material, it is difficult to use inclusions. It has not been possible to eradicate the resulting surface defects. Also, fine deoxidation products suspended in the molten metal accumulate on the inner surface of the nozzle and block the nozzle,
Multiple casting becomes difficult, and the deoxidized product in Al deoxidization is a hindrance to efficient production. As a countermeasure for preventing nozzle clogging, the present inventors have conducted various researches and developments, and as a result, by using a nozzle containing CaO.ZrO ₂ particles, CaO
-Generation of a low melting point layer of Al ₂ O ₃ and prevention of nozzle clogging were confirmed by the materials and process Vol. 4 (1991),
p. 219,220. However, even these measures have not led to extinction of product defects caused by inclusions, and further measures are needed. In order to avoid such disadvantages of Al deoxidation, as a result of studying various deoxidation methods, the present inventors found that Ti deoxidation with very low Al content (hereinafter abbreviated as Al-less Ti deoxidation).
Has been found to have the same properties as a thin sheet material as Al deoxidized steel, and to reduce the surface defects of the manufactured thin sheet. However, in the case of Al-less Ti deoxidation, A
In addition to the deoxidation, the ladle nozzle and the immersion nozzle are more likely to be clogged, making mass production of such steel difficult, and mass production of thin sheets of Al-less Ti deoxidized steel with very few surface flaws. In order to realize the above, it is indispensable how to prevent the occurrence of the nozzle blockage, and a preventive measure thereof. Therefore, in order to realize mass production of a thin sheet material by Al-less Ti deoxidation, which can reduce the surface defects of the thin sheet and has good material properties, a method of preventing nozzle blockage is required. Is an important issue to be solved for the time being. SUMMARY OF THE INVENTION The gist of the present invention is as follows. By weight%, Al: 0.01%
Hereinafter, in continuous casting of steel containing Ti: 0.02 to 0.15%, the nozzle clogging of Al-less Ti deoxidized steel characterized by adjusting the Si concentration in the molten metal within the range of the following formula (1). Prevention law. Si> 5.93 · 10 ⁻⁴ · T ^0.49 (1) Where, Si: Si concentration of the product (%) T: Amount of molten metal cast by one nozzle (t) Action and Examples FIG. 1 shows an enlarged view of a part of the actual condition of the deposited metal 2 observed on the inner surface of the nozzle 1 when the molten metal composed of the chemical components shown in Table 1 is continuously cast with an alumina graphite nozzle. Indicated. The adhered metal 2 grew 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 were observed in the metal, forming clusters. . [Table 1] The present inventors have further studied the growth mechanism of the deposited metal 2. As a result, the clusters generated by Al-less Ti deoxidation are not Al ₂ O ₃ , which is well known as a cluster-forming substance, but are shown in FIG. As shown in the result of the X-ray diffraction of No. 2, it was confirmed that Ti ₃ O ₅ contained a little Al. This cluster-containing metal is melted above its melting point (1580 ° C)
As shown in FIG. 3A, when heated to a shape, a shape maintaining portion 3 in which the shape before heating does not collapse and the shape is maintained, and a shape changing portion 4 in which the shape before heating changes are observed. Was. Fine inclusions forming clusters are observed in the shape maintaining part 3 in the same manner as before heating, and the clusters of fine inclusions disappear in the shape changing part 4 and the shape maintaining part 3 and the shape maintaining part 3 are changed. Coarse inclusions 6 were observed in the boundary layer 5 of the part 4. The reason why the shape maintaining portion 3 can maintain the shape at a temperature equal to or higher than the melting point is considered to be that the molten metal is held like water contained in a sponge between fine Al-containing Ti ₃ O ₅ cluster particles. On the other hand, the reason why the shape of the shape changing portion 4 cannot be maintained is that clusters of fine inclusions to be a skeleton disappear. The shape maintaining unit 3 and the shape changing unit 4 in FIG.
FIG. 3B schematically shows the results of microscopic observation of the coarse inclusions 6 observed in the boundary layer of FIG. Table 2 shows the coarse inclusions 6.
2 and a Si-concentrated phase 8 having a composition shown in Table 3 were observed. [Table 2] [Table 3] From the above results, the growth of the deposited metal leading to nozzle blockage is caused by the fine inclusions of Ti ₃ O ₅ growing and solidifying while holding the molten metal between the grains, while the clusters are thus strongly formed. 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. It is presumed that the reason why SiO ₂ is easily absorbed by the Ti oxide is that the activity of SiO ₂ becomes very small in the case of inclusions containing Ti oxide. The present inventors have studied the method of preventing the growth of the deposited metal by utilizing the characteristics of the Ti oxide which causes the growth of the deposited 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 blockage is very large, and the amount of molten metal that can be cast by one nozzle increases as the Si concentration increases, and to prevent the nozzle blockage of Al-less Ti deoxidation , The amount of molten metal T to be cast with the nozzle
With the knowledge that the Si concentration should be controlled within the range of the following equation (1), the present invention has been accomplished. Note that the Si concentration in the molten metal collected from tundish and the S
There is no significant difference from the i concentration. The amount of molten metal that can be cast was determined based on a stopper that causes a product defect and an abnormality in the opening of the sliding nozzle. Si> 5.93 · 10 ⁻⁴ · T ^0.49 (1) Where, Si: Si concentration of product (%) T: amount of molten metal cast by one nozzle (t) 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. As described above, according to the present invention, it is possible to prevent the nozzle clogging of Al-less Ti deoxidized steel, which was conventionally difficult to mass-produce due to the nozzle clogging, and to greatly improve the surface defect of the thin plate. It has enabled mass production of Al-less Ti-deoxidized steel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially enlarged schematic view showing an adhered metal in a nozzle when Al-less Ti deoxidized steel is cast with an alumina graphite nozzle. FIG. 2 Inclusions extracted from the adhered metal Fig. 3 shows the results of X-ray diffraction of Fig. 3 Fig. 3 shows the change in sample shape and inclusion morphology when cluster-containing adhered metal is heated above its melting point Fig. 4 Amount of molten metal that can be cast with one nozzle And S in the molten metal
Diagram showing the relationship of i-concentration [Explanation of symbols] 1 Nozzle 2 Nozzle metal on inner surface of nozzle 3 Shape maintaining part 4 that maintains shape before heating even if heated to above melting point 4 Shape that changes shape when heated to above melting point Changed portion 5 Boundary layer between shape maintaining portion and shape changing portion 6 Coarse inclusions observed in shape maintaining portion and shape changing portion 7 Ti enriched portion observed in coarse inclusion 8 Si concentration observed in coarse inclusion Transformation part

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kenichi Yoshii 1 Kimitsu, Kimitsu City, Chiba Prefecture Inside Nippon Steel Corporation Kimitsu Works (72) Inventor Tetsuji Kadoya 1 Kimitsu, Kimitsu City, Chiba Prefecture New Japan (56) References JP-A-6-299286 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/11 B22D 11/00 B22D 11 /Ten

Claims (1)

(57) [Claims 1] By weight%, Al: 0.01% or less, T
i: In a continuous casting of steel of 0.02 to 0.15%, a method of preventing nozzle clogging of Al-less Ti deoxidized steel, wherein 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 cast by one nozzle (t)