JPS6349351A - Continuous casting installation - Google Patents

Abstract

PURPOSE:To obtain a cast slab having fine solidified structure by holding under reducing pressure mixing flow of molten metal with cooling medium at the time of drawing the cast slab by pouring the molten metal into a mold from a nozzle in a molten metal vessel to make the molten metal into fine droplet and producing the cast slab by cooling. CONSTITUTION:A reducing pressure chamber 21 is arranged at the space between the nozzle 14 of a tundish 11 and the mold 16 and at the time of ascending a stopper 22 while supplying the cooling medium 25 from a pipe 26, the cooling medium 25 is injected into the molten metal 12 passing through a discharging hole 13 from the lower end of passing hole 24. The cooling medium 25 mixed in the molted metal 12 is sharply vaporized and expanded in the reducing pressure chamber 21, caused to make the molten metal 12 into the fine droplet 27 and also cool it rapidly. On this result, the molten metal 12 is poured into the mold 16 while becoming to the metallic grain 28 under semi- solidified condition and is become to the cast slab 17 and drawn. In this way, the continuous casting slab having fine solidified structure is obtd. by the simple construction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to continuous casting 6 [that can produce slabs having a fine structure].

[Prior Art] Usually, slabs or ingots, which are intermediate materials for metal products, contain molten metal. c It is manufactured by pouring into a casting mold or an ingot mold and solidifying it.

However, in these techniques, completely molten metal is cast, so the produced slab or ingot has a relatively large crystal grain size in its solidified structure.

For this reason, when applying a reduction to a slab or the like to ensure mechanical properties, if a large reduction is applied, cracks will occur in the slab or the like. Therefore, it is necessary to apply the reduction blade in multiple steps, but this requires a long processing time and also requires a large amount of thermal energy, resulting in high processing costs. The sensitivity to cracking caused by coarsening of the crystal grain size of the solidified structure is particularly noticeable in difficult-to-work materials such as high-alloy steel, and when manufacturing this type of alloy, the manufacturing process is extremely complicated. become. In addition, when producing slabs or ingots using the above-mentioned method, it is inevitable that pores and segregation (center segregation, v-segregation, etc.) will occur in the axial center of the slabs or ingots, especially for high-grade steel. It is difficult to manufacture. In particular, in continuous casting, the yield is extremely reduced due to these disadvantages, and the types of steel to which continuous casting can be applied are significantly limited.

In order to eliminate these shortcomings in general casting technology, VADER (VacuuglArcD or
le E Ielectrode Remelting
A casting technique called the vacuum arc two-electrode melting method has been proposed (Japanese Patent Application Laid-Open No. 165271/1983). This V
The application of the ADER method to continuous casting will be explained with reference to FIG. 4. An arc 2 is formed by appropriate means between a pair of electrodes 1 made of a metal having the same composition as the slab to be manufactured, and the opposing ends of the electrodes 1 are melted. This molten metal droplet 3 is cooled by a mold 4 and solidified. A slab 6 obtained by partially solidifying the molten metal is continuously drawn downward from the mold 4. In this case, droplet 3 of molten metal
In the process of falling from the electrode 1 to the mold 4, it is slightly cooled and becomes a semi-molten state. Therefore, the semi-molten metal 5 in the mold 4 solidifies in a state where the solid-liquid coexistence phase exists uniformly, so that the crystal grain size of the solidified structure of the slab 6 is small. Therefore, even if a large reduction is applied, the slab will not sag. In addition, since the crystal structure is refined, pores and segregation in the axial center of the slab are substantially not generated. For this reason, continuous casting of high-grade steel becomes easier, and yield decreases due to oxidation of pores during slab cutting, and cracks originating from pores during slab processing. There is very little yield loss.

[Problems to be Solved by the Invention] However, in such a conventional device, an electrode made of a metal having the same composition as the slab must be manufactured in advance, and the electrode must be melted by arc discharge. At this time, it is necessary to provide the electrode with a rotating Hid so as to uniformly dissolve the N pole. Therefore, there is a problem in that the process and the configuration of the device are extremely complicated.

This invention was made in view of such circumstances, and
A slab with a fine crystal grain size in the solidified structure and virtually no defects in the core can be obtained directly from molten metal without the need to prepare an electrode in advance, and the a-pole configuration is relatively simple. The purpose of this invention is to provide a 3I VT&IF manufacturing device.

[Means for Solving the Problems] A continuous casting apparatus according to the present invention includes a container for storing molten metal, a nozzle provided in the bottom mold of the container through which the molten metal in the container can flow, and a mixing means for blowing a coolant into the molten metal to form a mixed flow thereof; a mold having a cylindrical shape with open upper and lower surfaces into which the mixed flow flowing out from the nozzle is cast; and reducing pressure between the nozzle and the mold. It has a pressure reducing means for holding the molten metal at the bottom and a drawing means for continuously pulling downward the slab obtained by solidifying the molten metal in the mold, and the mixed flow of the molten metal and the cooling medium is reduced in pressure by the pressure reducing means. The method is characterized in that the molten metal is turned into fine droplets and cooled to produce slabs. In this case, it is preferable that the nozzle has a heating means for heating the molten metal.

[Operation] In this invention, the molten metal is injected into the mold from a container containing the molten metal through a nozzle, and the slab solidified in the mold is pulled out downward by the pulling means. In this case, a cooling medium is blown into the clearing medium flowing through the nozzle to form a mixed flow thereof, and the space between the nozzle and the mold is maintained under reduced pressure. As a result, the coolant in the mixed flow rapidly evaporates when it reaches the mold.

The metal expands, turns the melt into droplets, and is cooled to a semi-molten state. In the mold, the semi-molten metal solidifies in a state where a solid-liquid coexistence phase is uniformly present; Can be made smaller. In this way, a cast slab with a fine structure can be obtained directly from molten metal by straight casting, which is relatively easy to produce, without preparing an N pole in advance.

[Actual Flow Example] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 is an f% sectional view showing a continuous casting apparatus according to a first embodiment of the present invention. A molten metal 12 is supplied into the tundish 11 from a ladle (not shown), and a molten metal outlet hole 13 is formed in the bottom wall of the tundish 11. Further, a pouring nozzle 14 is attached to the bottom wall of the tundish 11 so as to be continuous with the hole 13. A heating device 15 is embedded in this nozzle 14, and by heating the molten metal 12 flowing through the nozzle 14, the molten metal 12 is prevented from solidifying and clogging the nozzle 14. Below the nozzle 14,
A mold 16 is installed.

This mold 16 has a cylindrical shape with an open top and bottom, into which the molten metal 12 is poured. A slab 17, which is produced by solidifying the molten metal 12 by cooling it in the mold 16, is pulled downward by rotation of pinch rolls (not shown). Moreover, this mold 16 is stroked so as to be driven up and down by a drive device 18, thereby reducing the friction between the inner wall of the mold 16 and the slab 17.

The lower end of the nozzle 14 is fitted into a support plate 19, and the support plate 19 and mold 16 are sealed by bellows 20. Mold 16, support plate 19 and bellows 2
#4 area surrounded by 0 is evacuated by an exhaust means (not shown) and maintained under reduced pressure, and the area #4 is kept under reduced pressure.
1. Moreover, in this decompression chamber 21, y/le
Argon gas is supplied to maintain the interior of the vacuum 21 in an inert atmosphere. In this case, the pressure inside the decompression chamber 21 is 0.1 to 300
It is held at Torr.

A cylindrical stopper 22 made of a refractory material is installed in the tundish 711 so as to be RRable, and this stopper 22 is driven up and down by a lift ¥*1t23. Is the stopper 22 caused by an emergency? 17 Block the lagoon outflow hole 13 to prevent the molten metal 12 from flowing out, and then rise to open the molten metal outflow hole 13 and direct the molten metal 12 to the nozzle 14.
It is designed to be injected into the decompression chamber 21 via. By adjusting the position of the stopper 22, the melt 112 is
The injection amount is adjusted. The stopper 22 has a coolant passage hole 24 extending in the longitudinal direction approximately at the center of its cross section. A refrigerant supply source (not shown) is connected to the refrigerant flow hole 24 via a via 26 .

The molten metal 12 flows through the nozzle 14 from this refrigerant supply source.
The cooling medium 25 is blown into the injection flow of the molten metal 12.
It is supposed to be mixed. The molten metal 12 mixed with the refrigerant 25 is supplied to the decompression chamber 21, and is cooled by the heat of evaporation or sensible heat of the refrigerant 25 to r! The resulting droplets 27 are supplied to the mold 16. As the cooling medium 25, an inert gas such as argon gas or helium gas, or liquefied argon, helium, or the like can be used. In this way, the refrigerant may be anything that can cool down the liquid W427 with its heat of vaporization or sensible heat, such as liquefied hydrocarbons (toluene, propane, methane, etc.).
, alcohol, etc. can also be used, but these are not preferred in the case of materials that will adversely affect the slab by being decomposed and absorbed into the molten metal.

In the continuous casting apparatus configured in this way, first,
When the stopper 22 is raised while the refrigerant 25 is supplied from the refrigerant supply source through the pipe 26, the molten metal 12 in the tundish 11 is injected into the decompression chamber 21 through the nozzle 14. In this case, the coolant 25 is blown into the molten metal 12 flowing through the nozzle 14 from the lower end of the coolant passage hole 24 and mixed with the molten metal 12 . And this cooling medium 25
The molten metal 12 is supplied to the vacuum chamber 21 together with the molten metal 12, and rapidly expands (evaporates and expands in the case of liquid) in the vacuum chamber 21, thereby turning the molten metal 12 into fine droplets 27. The fine droplets 27 are rapidly cooled by the latent heat of vaporization and sensible heat of the cooling medium 24, and are cast into the mold 16 as metal grains 28 in a state where the degree of superheat is close to zero or in a semi-solid state. Therefore, the metal particles 28 are cooled and solidified by the mold 16 in a state where the solid-liquid coexisting phase exists uniformly within the mold 16. Therefore,
The crystal grain size of the solidified structure of the obtained slab 17 is small, and pores and segregation in the axial core portion are substantially free.

Next, a second embodiment of the invention will be described with reference to FIG. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals, and their explanations will be omitted.

Nozzle 2 that connects the tandish 11 and the decompression chamber 21
9 has a heating device 30 embedded therein, and is further provided with a plurality of coolant flow holes 31 penetrating from the outer periphery to the inner periphery. The nozzle 29 is surrounded by a housing 32 , and a vibrator 33 connected to a coolant supply 8 (not shown) communicates within the housing 32 . Therefore, the coolant 25 can be blown into the molten metal 12 flowing through the nozzle 29 through the coolant passage hole 31, and the coolant 25 can be mixed with the molten metal 12. In this embodiment as well, similarly to the first embodiment, the molten metal 12 becomes fine droplets 27 and is cast into the mold 16 as metal grains 28 in a state where the degree of superheat is close to zero or in a semi-solid state. .

As described above, a slab with a fine structure can be obtained directly from molten metal scraps using an apparatus with a relatively simple configuration without preparing electrodes in advance.

Next, an example of a manufacturing test result when a slab was manufactured by continuous casting using the apparatus of the present invention will be explained. Stainless steel tN (SUS316) melted in an electric furnace was heated to a diameter of 370 II 1 m using the apparatus of the first embodiment described above.
' billet! ! Continuously manufactured. The manufacturing conditions were as follows: the amount of molten metal was 20 tons, the diameter of the molten I injection nozzle was 15 mm,
Argon gas was used as the cooling medium. Gas flow rate 4
Continuous casting was carried out for about 2 hours with a gas pressure of 200 torr before depressurization and a drawing speed of about 0.2 m/min. The total length of the produced slab was about 25 m.

It was confirmed that the crystal grain size of the solidified structure of the slab manufactured by FIJ under these conditions was fine, and when the porosity and segregation degree of the axial core were investigated, it was found that it was different from that of the conventional continuous slab as shown in Figure 3. These defects were reduced to about 115 compared to the casting equipment.

Although a tundish was used as the molten metal container in this embodiment, the molten metal can also be poured directly into the mold from the surroundings or the like.

Further, as a method for blowing the coolant into the injection stream, a method may be used in which a refractory lance is immersed in the molten metal in the container and the coolant is blown through the lance.

In addition, in the apparatus of this invention, the nozzle diameter is smaller than that of the conventional continuous casting apparatus (the diameter of the conventional nozzle is 7 mm).
QIm, whereas the diameter of the nozzle of the device according to the invention is between 20 and 3 Qim. )! The waiting time for construction is long.

For this reason, nozzle clogging is likely to occur due to a drop in the temperature of the melt in the melt container. Therefore, in the case of the apparatus of the present invention, a heating means for heating the molten metal injection nozzle is more necessary than in the conventional apparatus.

[Effects of the invention] According to this invention, it is not necessary to manufacture electrodes having the same composition as the slab to be manufactured in advance, and an apparatus having a simple structure can be used without generating an arc between the electrodes. It is possible to produce a continuous cast slab with a fine texture and extremely few pores and segregation in the shaft core with a simple operation.

Therefore, this invention has extremely high practicality.

[Brief explanation of the drawing]

1 is a sectional view showing a continuous casting apparatus according to a first embodiment of the present invention, FIG. 2 is a sectional view showing a continuous casting apparatus according to a second embodiment, and FIG. 3 is a sectional view showing a continuous casting apparatus according to a second embodiment of the present invention. FIG. 4 is a graph showing the internal defects of the slab manufactured by the apparatus according to the example in comparison with a conventional slab, and FIG. 4 is a sectional view showing the conventional apparatus. 11; tundish, 12; molten metal, 13: molten metal outflow hole, 14, 29: nozzle, 15, 30; heating device, 16;
Mold, 17; slab, 21; pressure reduction, 22; stopper, 2
4.31: Refrigerant passage hole, 25; Refrigerant, 26.33
: Vibrator, 27; Droplet, 28; Metal particle Applicant's representative Patent attorney Takehiko Suzue Figure 1 fs 2 Figure

Claims (2)

[Claims] (1) A container containing molten metal, a nozzle provided on the bottom wall of the container through which the molten metal in the container can flow, and a mixing method in which a cooling medium is blown into the molten metal flowing through the nozzle to form a mixed flow of these. means, a mold having a cylindrical shape with open upper and lower surfaces and into which the mixed flow flowing out from the nozzle is cast; a depressurizing means for maintaining a space between the nozzle and the mold under reduced pressure; and a drawing means for continuously pulling the obtained slab downward, and the mixed flow of the molten metal and the cooling medium is reduced in pressure by the pressure reducing means to reduce the pressure of the molten metal into fine droplets and cool it to produce a slab. A continuous casting device characterized by: (2) The continuous casting apparatus according to claim 1, wherein the nozzle has a heating means for heating the molten metal.