JPH04274845A - Continuous casting method for multilayer cast billet and casting mold - Google Patents

Abstract

PURPOSE:To offer a casting method and a casting mold for preventing a molten metal from being mixed by a magnetostatic field in a mold at the time of continuous casting of a multilayer cast billet, and changing easily the thickness of an outer layer, while securing a stable operating state. CONSTITUTION:Injection nozzles having the different height of a molten metal injection part are inserted into a casting mold, the magnetostatic field zone is formed in the casting mold concerned, and the casting mold provided with an induction heating coil 18 which can be subjected to electric conduction control at every stage in the upper side casting mold of the magnetostatic field zone, and a cooling groove 17 which can be subjected to water passing control at every stage in parallel to the induction heating coil on the inside of the induction heating coil is used. In such a manner, the installation cost and the maintenance cost, and also, the refractory cost are curtailed, the flaw of the cast billet is decreased and a good ingot quality is obtained, and moreover, a steel delivery schedule is ensured by a stable operation.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a continuous casting method and a continuous casting mold for multi-layer slabs, in which mixing of molten metals is prevented by a static magnetic field within the mold, and the thickness of the outer layer can be easily changed. .

0002

[Prior Art] Conventional methods for casting multi-layer slabs include, for example, Japanese Patent Application Laid-open No. 108947/1983 and Japanese Patent Application No. 13/1999.
No. 0185 proposes a technique for producing a multilayer slab using a combination of an electromagnetic braking force and two nozzles, or a combination of an electromagnetic braking force and an additive material.

FIG. 5 shows a schematic diagram of casting a multilayer slab using the two-nozzle method.

In the figure, separately produced molten steel with different compositions is transferred from an outer layer pot 1a and an inner layer pot 1b to an outer layer tundish 2a, an inner layer tundish 2b, an outer layer injection nozzle 3a, and an inner layer injection nozzle 3a, respectively. It is injected into the mold 30 through the injection nozzle 3b.

Each of the injected molten steel receives the molten steel braking force of the electromagnet 8, is separated into upper and lower parts in the mold, and begins to solidify. The primary meniscus 4 is the surface of the melt in contact with the atmosphere in normal continuous casting, and the secondary meniscus 5 corresponds to the separation position between the outer layer and the inner layer, that is, the solidification start point of the inner layer. Therefore, the outer layer thickness 14b of the slab is determined by the solidified shell thickness that grows between these two menisci. In the figure, 6a is an outer molten steel pool, and 6b is an inner molten steel pool.

FIG. 6 shows a schematic diagram of casting a multi-layer slab using one injection nozzle and additive material.

First, molten steel is poured into a mold 30 from a molten steel ladle 1 through a tundish 2 and an injection nozzle 3.
Next, an additive material 21 is introduced above or below the electromagnet 8 of the molten steel to produce multilayer slabs having different microcomponents.

[0008] On the other hand, as a method for obtaining a multi-layer slab having a clear boundary between the inner and outer layers, a technique for controlling the initial solidification position using subsurface solidification has been reported in Japanese Patent Laid-Open No. 2-55641. There is. However, no technology has been reported so far regarding a method for appropriately changing the outer layer thickness during casting.

[Problem to be solved by the invention]

Problems encountered when trying to change the thickness of the outer layer using the above process will be explained below.

First, FIG. 7 schematically shows a method of changing the outer layer thickness by changing the primary meniscus level. The broken line in the figure indicates the outer layer molten steel ladle 1a, the outer layer tundish 2a, the injection nozzle 3a, and the molten steel ladle 1a when the primary meniscus is at level 4a, and the solid line indicates the outer layer molten steel ladle 1a, outer layer tundish 2a, injection nozzle 3a, and molten steel when the primary meniscus is at level 4a. The respective formation curves 7a-1 and 7a-2 of solidified shells are shown.

[0011] Here, the level 4a of the primary meniscus is set to 4.
If the outer layer is raised to the position of , the outer layer thickness becomes thicker, and if it is lowered to the position of , the outer layer becomes thinner, but the variation of the solidification thickness relative to the variation of the primary meniscus 4 is at most a few percent in the case of steel. For example, at a casting speed of 0.8 m/min, the primary meniscus level is set to 1
Even if the thickness is changed by 00 mm, the solidified thickness will only change by about 1 to 2 mm.

Therefore, if we try to change the outer layer thickness by several mm, not only will the refractory cost increase due to the lengthening of the injection nozzle 3a, but also the specifications of the surrounding equipment will change, such as an increase in the lifting stroke of the tundish 2a and the pot 1a. The impact on equipment increases, especially in the case of equipment modification.

[0013] Also, it is not preferable to greatly change the primary meniscus level from the viewpoint of operational stability, ensuring slab quality, followability of the molten metal level sensor, etc.

Next, as a method of changing the casting speed, the outer layer thickness can be made thinner by increasing the casting speed, and thicker by slowing it down, but if you try to have a difference in the outer layer thickness of several mm as described above, This requires a speed ratio of about 1:2, which causes problems such as affecting the tapping schedule of the ladle and lowering the temperature of molten steel, which significantly impairs the stability of the operation.

Next, as a method of changing the secondary meniscus level, the thickness of the outer layer can be changed by keeping the primary meniscus level constant and changing the secondary meniscus level, that is, the position of the electromagnet that generates the static magnetic field band. be.

However, in this case, it is necessary to support the mold and the electromagnet separately, but the electromagnet that separates the two types of molten metal usually requires a magnetic flux density of 3000 to 5000 gauss, so the magnet body is large. However, installation space is limited due to interference with peripheral equipment such as a tundish car, a mold vibration device, etc., and it is difficult to incorporate a mechanism for remotely changing the height of the electromagnet body.

The present invention solves the above-mentioned problems and provides a continuous casting method and a casting mold for multi-layer slabs, which make it possible to change the outer layer thickness while ensuring stable operating conditions.

[0018]

[Means for Solving the Problems] The gist of the present invention is as follows.

The first method is to insert two injection nozzles with different heights of molten metal spouting parts into a continuous casting mold with a rectangular cross section, and to insert a nozzle on the long side of the mold that is approximately equal to the width of this long side. A method of continuously casting a multilayer slab by arranging magnetic pole surfaces of electromagnets having a width to face each other to form a static magnetic field zone between the molten metal spouting parts, and supplying metals with different compositions above and below the static magnetic field zone. In this method, a plurality of heating means and cooling means whose temperature can be controlled in each stage are provided in parallel so as to surround the mold on the upper side of the static magnetic field zone, and the heating means and cooling means are controlled to reduce the static magnetic field. This continuous casting method for multilayer slabs is characterized by controlling the cooling rate of the molten metal in the upper part of the band and adjusting the production of a solidified shell formed on the inner surface of the mold to obtain an outer layer of a predetermined thickness.

[0020] Part 2 is to insert two injection nozzles with different heights of molten metal spouting parts into a continuous casting mold with a rectangular cross section, and to insert a mold on the long side of the mold that is approximately equal to the width of this long side. Continuous casting of multi-layer slabs by arranging the magnetic pole faces of electromagnets having widths to face each other to form a static magnetic field zone between the molten metal spouting parts, and supplying metals with different compositions above and below the static magnetic field zone. A continuous casting mold for multilayer slabs, characterized in that the casting mold is provided with a plurality of induction heating coils that can be controlled to supply electricity to each stage so as to surround the mold on the upper side of the static magnetic field zone. .

[0021] Furthermore, the continuous casting mold has a structure in which a plurality of cooling grooves are provided on the inner side of the induction heating coil in contact with the mold, in parallel with the induction heating coil, and in which water flow can be controlled for each stage. It is something to do.

[0022]

[Operation] In the present invention, two injection nozzles are inserted into a continuous casting mold having a rectangular cross section, with the heights of the molten metal spouting portions being different, and the length of the injection nozzle is approximately equal to the width of the long side of the mold. Continuous casting of multi-layer slabs by arranging the magnetic pole faces of electromagnets having widths to face each other to form a static magnetic field zone between the molten metal spouting parts, and supplying metals with different compositions above and below the static magnetic field zone. In the casting mold, a multi-stage induction heating coil that can be controlled with electricity for each stage is provided so as to surround the mold on the upper side of the static magnetic field zone, or on the inner surface of the induction heating coil in contact with the mold,
A continuous casting mold of a multi-layered slab is used, which is provided with a plurality of cooling grooves in which water flow can be controlled in each stage in parallel with the induction heating coil.

In the continuous casting mold described above, the cooling rate of the molten metal in the mold above the static magnetic field zone is controlled by heating control by the induction heating coil and cooling control by the cooling groove, and the solidification shell formed on the inner surface of the mold is started to solidify. An outer solidified shell having a predetermined thickness is obtained by adjusting the number of dots and formation.

[0024] In this way, the thickness of the outer layer of the multilayer slab can be easily changed by applying the subsurface solidification technology without changing the primary meniscus, secondary meniscus, or casting speed. be.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a longitudinal cross-sectional view showing the main parts of a continuous casting mold for multilayer slabs, and a cross-sectional view taken along the line A-A in FIG. 2 below, and FIG. 2 is a perspective view showing the overall structure of the continuous casting mold. It is a diagram.

The upper part of the mold has a lining material 13 made of graphite or the like and a cooling plate 1 having cooling grooves 16 (to be described later) formed from the inner side.
4 and a heat insulating material 15 are laminated, and a copper plate cooling hole 17 is formed between the lining material 13 and the copper plate 11 in the lower part, and these are firmly fixed by the mold frame 12 and the mold fixing frame 20. The mold is formed.

On the outside of the copper plate 11 at the bottom of the mold, magnetic poles 9 of an electromagnet having a width approximately equal to the width of the long side are provided facing each other on the long side of the mold to form a secondary meniscus 5 in the mold. Generates a static magnetic field. Note that 8 is a yoke surrounding the mold, and 9 is an electromagnetic coil.

The structure of this electromagnet includes a single yoke type shown in FIG. 8 and an annular yoke type shown in FIG. 9, which may be selected as appropriate depending on the surrounding situation.

Furthermore, in the embodiment of the present invention, a plurality of induction heating coils 18 (18
-1 to 18-5), and the cooling plate 14 has a plurality of cooling grooves 16 (16-1 to 16-6) in parallel with the induction heating coil 18, in which water flow can be controlled for each stage. is drilled. Note that 19a and 19b are the respective cooling water inlets and outlets that flow into the cooling groove 16, and 22 is the induction heating coil 1 of each stage.
8 terminal box.

FIG. 3 is a drawing showing an example of the cooling system of the cooling groove 16, in which the cooling water is branched off via the cutoff valve 26,
The flow rate is adjusted by the flow rate control valve 23 for each cooling groove 16 attached to each branch pipe, and the cooling grooves 16-1 to 16
A predetermined amount of cooling water is supplied to each of -6 and 6. In this way, each of the cooling grooves 16-1 to 16-6 can be independently controlled for cooling. In addition, in the figure, 25
a, 25b are thermometers attached to the inlet and outlet;
24 is a flow meter for each cooling groove, and 27 is a check valve. Further, 14a and 14b are cooling plates on the long side and the short side, respectively.

FIGS. 4(a) and 4(b) show examples of control wiring diagrams for the induction heating coil 18, in which (a) shows a series circuit, and (b) shows an example of a control connection diagram for the induction heating coil 18.
) indicates a parallel circuit. Reference numeral 29 indicates a power supply device, and 28 indicates a circuit switching device. In the case of a series circuit, fine temperature control is possible, and in the case of a parallel circuit, it is possible to strongly heat locally or the whole. In either case, by operating the circuit switching device 28, heating of the mold can be appropriately controlled in the vertical direction.

In the continuous casting mold configured as above,
Outer layer injection nozzle 3a and inner layer injection nozzle 3b from above
If the height of the molten metal ejecting part is set at the upper and lower parts of the secondary meniscus 5 formed by the static magnetic field band, and metals with different compositions are supplied, each metal will be is separated into upper and lower parts and begins to coagulate. The molten metal supplied from the outer layer injection nozzle 3a is cooled on the upper wall of the mold to form a solidified shell of the outer layer, and is pulled downward to cast a multilayer slab.

In this case, the induction heating coil 18 and the cooling groove 1
By controlling 6 and setting the temperature of the inner wall of the mold above the secondary meniscus 5 to an appropriate temperature, the heat removed from the inner wall of the mold can be changed and the formation of the outer solidified shell can be controlled. In other words, if the heat removal is small, the formation of solidified shell is slow;
Therefore, a thin outer layer is formed, and the greater the heat removal, the faster the formation of the solidified shell, and therefore the formation of a thicker outer layer.

Furthermore, the induction heating coil 18 and the cooling groove 1
By controlling 6 separately for the upper and lower stages, it is possible to control the temperature in the vertical direction of the inner wall of the mold, and by this control, the solidification start point of the outer layer can be appropriately set in the vertical direction, and the formation The thickness of the solidified shell can be adjusted by raising or lowering the solidification start point.

An example is shown in FIG. That is, the solidified shell formation curve 7a-1 is the solidified shell formation curve when the induction heating coils 18-1 to 5 are not energized and water is passed through all the cooling grooves 16-1 to 6. The heat removal increases, solidification starts from the level of the primary meniscus 4, the solidification is accelerated, and a thick outer layer t1 is formed.

Furthermore, the generation curve 7a-2 corresponds to the induction heating coil 1.
This is the solidification shell generation curve when electricity is applied to 8-1 to 3, and water is passed only to cooling grooves 16-4 to 5. In this case, the upper part of the inner wall of the mold is heated more and less heat is removed. The starting point of solidification moves downward from the primary meniscus 4, so that solidification slows down and a thin outer layer t2 is formed.

As described above, the present invention provides the induction heating coil 18
By controlling the temperature of the inner wall of the mold using the cooling grooves 16, the solidification start point of the outer layer and the thickness of the outer layer solidified shell can be changed as appropriate.

The present invention is applicable not only to a continuous casting mold having two injection nozzles, but also to a continuous casting mold having one injection nozzle as shown in FIG.

[0040]

[Effects of the Invention] The present invention constructed as described above has the following effects.

[0041] With the same mold, it is possible to change the outer layer thickness of a multi-layer slab to a greater extent than before, and when changing the outer layer thickness, there is no need to have molds with different electromagnet positions, thus reducing equipment costs. This makes it possible to reduce maintenance costs.

[0042] The injection nozzle for the outer layer may be made longer, or the pot,
Eliminates the need to extend the lifting stroke of the tundish.
Refractory costs and equipment modification costs can be reduced.

[0043] Since there is no change in casting time, etc., the effects of nozzle clogging due to a drop in the temperature of molten steel and changes in the ladle tapping schedule are alleviated.

Since fluctuations in the primary meniscus and casting speed can be minimized, stable operating conditions and good slab quality can be obtained.

[0045] The time required to change the outer layer thickness is shortened, and the yield is improved when continuously producing a wide variety of steel types in small quantities.

[0046] Since the sub-molten metal solidification method can be applied, slab defects caused by fluctuations in the liquid level, entrainment of inclusions, etc. are reduced.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing the main parts of a continuous casting mold for a multilayer slab according to an embodiment of the present invention.

FIG. 2 is a partially cross-sectional perspective view illustrating the overall structure of a continuous casting mold for multilayer slabs.

FIG. 3 is a drawing showing an example of a cooling system of cooling grooves.

FIG. 4 is a drawing showing an example of control connections of an induction heating coil.

FIG. 5 is a schematic diagram showing casting of a multi-layer slab using a conventional two-nozzle method.

FIG. 6 is a schematic diagram showing casting of a multi-layer slab using a conventional single nozzle and additive materials.

FIG. 7 is a schematic diagram of a conventional method of changing the outer layer thickness by changing the primary meniscus level.

FIG. 8 is a drawing showing an example of the structure of an electromagnet that generates a static magnetic field band.

FIG. 9 is a drawing showing another example of the structure of an electromagnet that generates a static magnetic field band.

[Explanation of symbols]

4 Primary meniscus 5 Secondary meniscus 6a Outer molten steel pool 6b Inner molten steel pool 7a　Outer layer solidified shell 7b Inner layer solidified shell 8 York 9 Electromagnet magnetic pole 10 Coil 11 Copper plate 12 Mold frame 13 Lining material 14 Cooling plate 15 Insulation material 16 Cooling groove 17 Copper plate cooling hole 18 Induction heating coil 19a Cooling water inlet 19b Cooling water outlet 20 Mold fixing frame 22 Terminal box 30 Mold

Claims (3)

[Claims] Claim 1: Two injection nozzles are inserted into a continuous casting mold having a rectangular cross section, with the heights of the molten metal spouting parts being different, and a width approximately equal to the width of the long side is formed on the long side of the mold. In a method of continuously casting a multilayer slab by arranging the magnetic pole surfaces of electromagnets facing each other to form a static magnetic field zone between the molten metal spouting parts, and supplying metals with different compositions above and below the static magnetic field zone, A plurality of stages of heating means and cooling means whose temperature can be controlled at each stage are provided in parallel so as to surround the mold on the upper side of the static magnetic field zone, and the heating means and cooling means are controlled to control the temperature of the static magnetic field zone. A continuous casting method for multi-layer slabs characterized by controlling the cooling rate of the upper molten metal and controlling the generation of a solidified shell formed on the inner surface of the mold to obtain an outer layer of a predetermined thickness. 2. Two injection nozzles with different heights of molten metal spouting parts are inserted into a continuous casting mold having a rectangular cross section, and a width approximately equal to the width of the long side is formed on the long side of the mold. A continuous casting mold for continuously casting a multilayer slab by forming a static magnetic field zone between the molten metal spouting portions by arranging the magnetic pole surfaces of electromagnets having the magnetic poles facing each other, and supplying metals with different compositions above and below the static magnetic field zone. A continuous casting mold for a multi-layer slab, characterized in that a plurality of induction heating coils each of which can be controlled to supply electricity to each stage are provided so as to surround the mold on the upper side of the static magnetic field zone. 3. The multilayer structure according to claim 2, wherein a plurality of cooling grooves are provided on the inner side of the induction heating coil in contact with the mold in parallel with the induction heating coil, the water flow being controllable at each stage. Continuous casting mold for slabs.