JPS5997746A - Construction in tundish nozzle part for continuous casting of horizontal type - Google Patents

Abstract

PURPOSE:To obviate the generation of the damage and failure in the nozzle part having a double-stepped construction and the defect on the surface of a billet and to perform stably casting by forming a dense and smooth refractory material layer on at least the perpendicular surface of a tundish nozzle of said nozzle part of the respective perpendicular surfaces of the tundish nozzle and refractories for connection. CONSTITUTION:A tundish nozzle 1 is formed of zircon refractories and refractories 2 for connection are formed of a simple substance of borone nitride. The void volume of the refractories 2 is made about <=5%. Zirconia is deposited by plasma melt spraying on the perpendicular surface 1a of the nozzle 1 to about 200mu thickness whereby a refractory material layer 4 is formed. The nozzle 1 and the refractories 2 as well as the refractories 2 and a casting mold 3 are joined by a known means. If the nozzle part is constructed in such a way, the layer 4 remains nearly in the defect-free state after casting, by which the damage on the nozzle 1 is prevented and a cast billet is produced satisfactorily.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nozzle structure for horizontal continuous casting in which a connecting refractory is interposed between a tundish nozzle and #iI type. Horizontal continuous casting that allows casting to be carried out without damage to the nozzle even if a drop in temperature or temporary interruption of casting occurs, and also to prevent surface defects from occurring in the cast piece. This is related to the nozzle A/parts for.

The horizontal continuous casting method is a method in which the entire process from pouring molten steel into the mold and solidifying it to shining and cutting the slab is performed in a nearly horizontal straight line. Compared to the continuous casting method, the machine height is low, making operation and maintenance easy, and the weight of the machine is small, resulting in low construction costs. Because they are connected through the mold, the melting pressure inside the mold is large and the precision of the slab shape is high.Also, secondary oxidation of the molten steel in the atmosphere is prevented, so the cleanliness of the slab is good. Due to its unique properties, it has recently attracted particular attention, and efforts are being actively made to industrialize it.

However, although it has the above-mentioned advantages, it also has some specific disadvantages, and one of these disadvantages is that the conditions required for the nozzle structure are extremely strict.

In other words, tundish nozzles are required to have properties such as (1) thermal shock resistance against large temperature changes during injection of molten steel, and (1) melting resistance that can withstand long-term continuous contact with various types of molten steel. Since the cooling effect of the refractory is relatively small, it is not expected that a solidified shell will occur in this area, and since the structure is quite large, relatively inexpensive inorganic oxide-based porous refractories are used. There is. On the other hand, the connection refractory material has ■good workability that ensures high dimensional accuracy for accurate joining with the mold;
■Thermal shock resistance against large temperature changes during temperature-controlled injection; ■Erosion resistance that can withstand long-term contact with molten steel in each building.
Abrasion resistance, ■The formation of a solidified shell on the surface of the connecting refractory due to the cooling effect from the mold, and the formation of a dense and smooth surface to reduce the frictional resistance with the solidified shell, as well as the formation of molten steel. Low wettability and low porosity are required to prevent entry into the pores, and B is a material that meets these requirements.
Expensive ceramics such as N-based or Si3N4-based are used.

FIG. 1 is an explanatory cross-sectional view showing an example of a nozzle structure 5 made of such a material, in which 1 is a tundish nozzle;
2 is a connecting refractory, 8 is a mold, and the molten steel moves in the direction of the arrow, contacts the inner surface of the mold 8, forms a solidified shell, and is drawn out as a slab. In addition, at the joint between the tundish nozzle l and the connecting refractory 2, and between the connecting refractory 2 and the connecting mold 8, there are planes l& and 2a that are oriented in the mold pulling direction and perpendicular to the mold pulling direction. is formed, forming a double-step structure. This is because when the inner diameter of each of the joints is made quiet, the inner surface of the tundish nozzle l is exposed to the melt m, and the diameter of that part is enlarged, resulting in an undercut at the joint between the tundish nozzle l and the connecting refractory 2. This is to avoid a situation in which, if the cut is made sharply, the connecting refractory will be damaged due to the pulling out of the solidified shell when the solidified shell reaches the undercut. A similar situation can also occur at the joint between the connecting refractory and the mold, so the nozzle part is formed from the beginning with a double-step structure as described above to prevent damage to the connecting refractory, etc. .

However, depending on the mm, especially in the case of SUS, the damage to the vertical surface 1a in the double-step att structure may be large and the connecting refractory may be damaged.

That is, since the vertical plane 1a formed of the oxide refractory is porous as described above, molten steel easily penetrates (on the other hand, since the vertical plane 1a is easily affected by the cooling effect from the mold, the refractory The molten steel that has entered the interior of the product forms a solidified layer that seems to take root in the porous parts.When the temperature of the molten steel drops or when casting is temporarily interrupted, a solidified Vwell is formed in the runner. If these are integrated and the slab is pulled out at that stage, mechanical damage such as peeling will occur on the vertical plane 1a and its vicinity. Considering that, if the nozzle is made of a similar porous material, the same mechanical damage as above will occur on the vertical plane '2a side.If such a situation occurs, the entire nozzle structure will be destroyed and a breakout will occur. Therefore, it is absolutely necessary to avoid causing the above-mentioned problems.Even if it does not lead to mechanical damage as described above, it is possible that surface defects of uneven sieves may remain on the surface of the casting. Furthermore, since these may cause scratches on the inner surface of the mold, it is desired that some kind of improvement measures be taken.

The present invention has been made with attention to these circumstances.
Horizontal continuous casting equipment, especially the 119 parts from the tundish nozzle to the mold, will not be damaged or destroyed.
Stable continuous casting without interruption of continuous casting and without defects on the surface of the slab U)
The purpose of this invention is to provide a nozzle structure for horizontal continuous casting.

The nozzle structure of the present invention that achieves the above object is as follows:
A horizontal series If in which a Km-shaped connecting refractory is interposed between the tundish nozzle and the mold, and a surface perpendicular to the mold pulling direction is formed on the mold pulling side of each of the tundish nozzle and the connecting refractory. ;'? This is a nozzle part structure for &j e, and its main feature is that a fa-tight and flattened refractory material layer is formed on at least the vertical surface of the tundish nose.

In other words, one of the main reasons why damage occurs in the nozzle M section tt1m from the tundish nozzle to the mold, especially on the vertical surface, is because the vertical surface is made of porous refractory material. Because the holes are porous, it is thought that molten steel will penetrate and cause damage or destruction.

Therefore, the inventors of the present invention sought to prevent molten steel from penetrating in the vertical plane while satisfying the various conditions required for the nozzle structure.
We ended up adopting the configuration described above. As a result, even if the cooling effect from the mold side is applied to the vertical surface, the molten steel will only solidify in contact with the vertical surface, and the roots of the solidified shell will remain in the porous refractory underlying the vertical surface. Even if a pull-out force due to casting acts on the solidified shell without being formed, the pull-out force will hardly reach the porous refractory. In addition, since the surface refractory material layer is minutely dense and smooth, the solidified shell does not penetrate into the refractory material layer, and the contact resistance given to the solidified shell is small, so that drawing by casting is performed smoothly. There was no damage to the nozzle portion, and as a result, no damage or breakage occurred on the vertical surface.

For example, zirconia or alumina can be used as a means for forming a surface fireproof material layer that exhibits such effects.

Examples include plasma spraying of titania, etc., powder coating of alumina, electrified boron, zirconia, electrified silicon, silicone, etc., and impregnation with electrified silicon, etc., or further treatment after impregnation. Examples of methods include applying heat treatment and sintering. The thickness of the refractory material layer is preferably 100 to 700 μIn, especially 200 to 800 μIn.
μm is optimal.

Incidentally, if the thickness of the refractory material layer is less than 100 μm, there is a risk that the refractory layer will be worn away during the life cycle, making it impossible to achieve the purpose, while if it exceeds 700 μm, the spalling resistance will deteriorate.

Hontsutoaki is constructed as outlined above, and even if there is a drop in molten steel temperature or a temporary interruption in casting, it is possible to perform casting without damaging or destroying the nozzle part.
Furthermore, it is possible to produce cast pieces without surface defects.

The following examples will further clarify the structure and effects of the present invention.

That is, FIG. 2 is a cross-sectional explanatory view showing an example of the nozzle structure of the present invention, and is a tundish nozzle l.

Connection refractory 2. The shape of the mold 8 is as shown in FIG. 1. The tundish nozzle 1 in this example is zircon 11
The connecting refractory 2 is made of borosilicate. In this case, the porosity of the fireproof material for the connection shall be 5 or less. On the vertical surface 1a of the tamp nozzle l, zirconia is plasma-welded to a thickness of 200 μm to form a layer of human resources.

The connection between the ceramic tundish nozzle 1 and the connecting refractory 2 and between the connecting refractory 2 and the mold 8 may be performed using a heat-resistant adhesive or a known means dedicated to flange bonding.

In the nozzle structure as described above, the casting temperature is 1560℃.
When we cast 4.5 tons of stainless steel (SUS804) under the conditions of a slab diameter of 110 mm, a drawing speed of 1 inch, and a speed of 5 m/min, we were able to successfully complete a cast piece of approximately 64 m. (At the time of casting) I also inspected the inner surface of the nozzle part after casting: The refractory material layer 4 remained in an almost complete state, and the vertical surface No damage was observed in a certain Tandate Schnoz A/l. # When casting was carried out under the same conditions on a nozzle 1v Narisukuri in which no refractory material layer was formed on the vertical surface 1a, as the operating time progressed, 1, wave resistance increased and casting became impossible after 10 m.Also, when the inner surface of the nozzle part was investigated after casting in the same way as above, □' □Rollers and vertical surfaces 1 & The melt 1 and steel had penetrated into the boundary between the tush nozzle 1 and the connecting refractory 2, and clicks had also occurred in the connecting refractory 2.

□ Fig. 8 is an explanatory cross-sectional view showing another embodiment of the present invention. In the nozzle part 5 having the same shape as the example in Fig. 2, the tongue nozzle A/1 is made of zircon refractory material, and The refractory 2 is made of Si3N4 (90% by weight) and BN (10 quadrillion 1%).The porosity of the connecting refractory 2 is 20 in this case. Alumina is plasma sprayed onto the vertical surface [ff11B and the vertical surface 2a of the connecting refractory 2 to a thickness of 800 μm, respectively, to form a refractory material 4.4.

In the above nozzle structure, casting of sub-element copper (C: 0.6) 4.5) was carried out under the following conditions: casting temperature 1570°C, slab diameter 150 mm, drawing speed it, am/=. As a result, approximately 84 m of slab was successfully cast. (
(casting time approximately 26 minutes). In a casting experiment using the same conventional nozzle part structure, casting was interrupted at a length of 15 m, and the vertical surface 1a after casting.

When I looked at 2a, I saw that it had sustained significant damage. In particular, the penetration of molten steel was severe, causing scratches on the inside of the mold.

[Brief explanation of the drawing]

FIG. 1 is an explanatory sectional view showing the nozzle structure of a conventional Yokoya continuous casting machine, and FIG. 2.8 is an explanatory sectional view showing the nozzle structure according to the present invention. l...Tundish nozzle la, 2a...Vertical surface 2...Connecting refractory 8...Mold 4, 4 &... Refractory material layer Applicant Kobe Steel, Ltd. 1/piece y

Claims (1)

[Claims] 111 An annular connecting refractory between the tundish nozzle and the fishing part is interposed, and a surface perpendicular to the elongated direction is formed on the mold pulling side of each of the tundish nozzle and the connecting refractory. A tundish nozzle structure for horizontal continuous casting, characterized in that the vertical surface of the tundish nozzle is smoothly coated with a fine refractory material. Construction.