JPH11320038A - How to start continuous casting of thin slabs - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To ensure the temperature of a molten metal in a pool at the start of casting, to prevent the formation of sticking shells on side dams and nozzles, and to stabilize slabs with good surface quality. Provided is a method for starting continuous casting of a thin slab that can be cast. SOLUTION: A part of the molten metal in a ladle is supplied to an intermediate container, and then the supplied molten metal is heated in the intermediate container to raise the temperature in a range of 20 ° C or more and 200 ° C or less. The hot water supply from the intermediate container to the water pool is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method for producing thin cast pieces directly from a molten metal such as carbon steel or stainless steel, and more particularly, to a method for producing cast pieces having good surface quality at the start of casting. The present invention relates to a method of starting continuous casting of thin cast pieces that can be stably manufactured.

[0002]

2. Description of the Related Art From a molten metal (hereinafter also referred to as a molten metal), the thickness is about several mm (there is no clear definition, but about 1 to 10 m).
The continuous casting method for directly producing the thin slab of m) is called a strip casting method (SC method), and various methods have been proposed.

[0003] The main method of the SC method is a twin roll top pouring method in which the molten metal is poured from above into a pair of rolls rotating in opposite directions, and a twin roll in which the molten metal is poured between the pair of rolls from the horizontal direction. There are a horizontal pouring method and a single-roll method in which the molten metal is poured into one roll from the horizontal direction. In each case, the roll is used as a mold.

The production of a thin slab by the SC method will be described by taking a twin-roll top pouring system and a twin-roll side pouring system as examples. FIGS. 1A and 1B are conceptual views schematically showing a method of manufacturing a thin cast piece by a twin-roll top-pouring method. FIG. 1A is a longitudinal sectional view, and FIG. 1B is a sectional view taken along the line AA. . As shown in FIG. 1, after the molten metal 2 in the ladle 1 is supplied to the intermediate container 3,
A pair of internally cooled rolls 4 and refractory side dams 5
The hot water is supplied to the hot water pool 6 formed by the above. Reference numeral 7 denotes a stopper for adjusting the amount of molten metal supplied from the intermediate container 3 to the pool 6, which is driven by a stopper elevating device 7 a to control the level of the surface of the pool 6 to be constant.

The molten metal 8 supplied to the pool 6 is cooled on the surface of the roll 4 to form a solidified shell 9. The solidified shell 9 moves downward with the rotation of the roll 4,
The thin slab 10 is cast by pressure bonding in the vicinity of the roll kiss point (the point where two rolls approach each other).

FIGS. 2A and 2B are conceptual views schematically showing a method of manufacturing a thin cast piece by a twin-roll horizontal pouring method. FIG. 2A is a longitudinal sectional view, and FIG. FIG. The same elements as those in FIG. 1 are denoted by the same reference numerals.

As shown in FIG. 2, the molten metal in the ladle (not shown) is cooled by a pair of rolls 4, side weirs 5, nozzles 11 and nozzle fixing containers 12 which are internally cooled through an intermediate container (not shown). Hot water is supplied to the formed hot water pool part 6,
Next, the thin cast piece 10 is cast between the rolls 4 from the horizontal direction, and cast. Usually, the capacity of the hot water pool in the horizontal pouring method is larger than that in the upper pouring method.

The temperature control of the molten metal in the pool is important from the viewpoint of ensuring the quality of the thin slab and improving the stability of operation. Although the temperature of the molten metal varies depending on the temperature of the intermediate container and the pool, or the amount of the molten metal and the moving distance of the molten metal, the temperature drops by about 10 to 100 ° C. every time the ladle is transferred to the intermediate container or from the intermediate container to the pool. I do. Normally, the temperature of the molten metal in the pool is adjusted so that the degree of superheat (= the temperature of the molten metal-the liquidus temperature of the molten metal) is about 35 to 150 ° C.

If the temperature of the molten metal in the pool is too high, the strength of the solidified shell is weak, and the solidified shell tends to break and break out, and the thin slab tends to crack. If the temperature of the molten metal is too low, the molten metal is solidified by the side weir 5 and the nozzle 11 as shown in FIG. 1 (b) or FIGS. 2 (a) and 2 (b), and the fixed shell 13 is formed. This fixed shell 1
The solidified shell 3 grows further, comes into contact with the solidified shell 9 moving in synchronization with the roll 4, and breaks the solidified shell 9 or is united with the solidified shell 9 to form a locally thick thin slab. It becomes 10 and breakout easily occurs. Further, since the end of the thin cast piece 10 comes into contact with the fixing shell 13, there are many undulations and irregularities, and the shape becomes poor.

Therefore, various techniques have been proposed for temperature control of molten metal for the purpose of stabilizing the quality of cast slabs.
For example, Japanese Patent Application Laid-Open No. 63-2442447 discloses a technique in which an electromagnetic induction heating mechanism is provided in an intermediate container and the temperature of the molten metal supplied to the pool is heated by heating the temperature of the molten metal in the intermediate container. Have been.

Japanese Patent Application Laid-Open No. Hei 5-200496 discloses that in order to prevent the molten metal from leaking from both ends of a slab and the occurrence of breakout, a predetermined side weir is provided by a SiC heating element or the like installed inside the side weir. A method for casting by preheating to a temperature has been proposed.

Japanese Patent Application Laid-Open No. Sho 60-21170 discloses that a high-frequency coil is installed in a part of a refractory (casting nozzle) forming a hot-water pool, and a molten metal supplied from an intermediate container is heated to thereby form a hot-water bath. There has been proposed a technique for reducing the degree of superheat of the molten metal in the pool to reduce the variation from the target temperature.

[0013]

The molten metal supplied from the ladle to the pool through the intermediate container at the start of casting has a low temperature at the start of casting, so that operational troubles and the like are likely to occur. The prior arts in the above publications and the like focus on improving the quality of a slab at the time of steady casting, and are insufficient for solving the above-mentioned problems at the start of casting.

That is, Japanese Patent Application Laid-Open No. 63-2442447 describes that "a means for heating the molten metal is provided in the intermediate container", but there is no description suggesting the above problem at the start of casting. There is no description of a method for effectively heating the molten metal at the start of casting in an intermediate container. Therefore,
At the start of casting, the temperature drop of the molten metal supplied to the basin is large, so the degree of superheat of the molten metal in the basin is low, and a sticking shell is formed on the side weirs and nozzles, causing operational troubles, etc. Problem arises.

In the method described in JP-A-5-200496, the heating temperature of the side weir is at most about 1300 ° C., which is lower than that of molten metal such as carbon steel or stainless steel having a liquidus temperature of 1300 ° C. or higher. Furthermore, at the start of hot water supply to the pool, the surface temperature of the side weir drops to 1000 ° C. or lower, so that the same problem occurs at the start of casting.

In the method described in Japanese Patent Application Laid-Open No. Sho 60-21170, the molten metal is heated by a casting nozzle. However, since the molten metal is continuously supplied, particularly, at the start of casting, the molten metal is supplied from an intermediate container. It is not possible to heat the melt at a lower temperature to the required temperature.

In order to optimize the degree of superheat of the molten metal in the pool at the start of casting, a method of raising the temperature of the molten metal in the ladle may be considered. , And as a result, there is a problem that breakout and surface cracking occur.

An object of the present invention is to secure a molten metal temperature in a pool at the start of casting, to prevent the formation of a fixed shell on side dams and nozzles, and to stabilize a slab having good surface quality. It is an object of the present invention to provide a method for starting continuous casting of a thin slab that can be cast by casting.

[0019]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have disclosed a casting method in which a molten metal is heated in an intermediate container, wherein "a part of the molten metal in a ladle is supplied to the intermediate container, Based on the basic idea of "starting hot water supply to the pool after a predetermined temperature increase," various tests were conducted to confirm that the above problem at the start of casting could be solved, and the present invention was reached. did.

The gist of the present invention is as follows. (1) In continuous casting in which molten metal is supplied from a ladle to a pool through an intermediate vessel having a heating function to supply molten metal to a thin cast slab, the molten metal in the ladle is added to the intermediate vessel. And then heating the supplied molten metal in the intermediate container and raising the temperature in a range of 20 ° C. or more and 200 ° C. or less, and then starting hot water supply from the intermediate container to the pool. Characteristic method for starting continuous casting of thin slabs.

(2) The method for starting continuous casting of a thin slab according to the above (1), wherein the liquidus temperature of the molten metal is 1300 ° C. or higher.

[0022]

FIG. 3 is a conceptual diagram schematically showing the method of the present invention by taking a twin-roll top-pouring method as an example. FIG. 3 (a) is a longitudinal sectional view, and FIG. FIG. 2 is a sectional view taken along the line AA in FIG.

In FIG. 3, the same elements as those in FIG. 1 or 2 are denoted by the same reference numerals. As shown in FIG.
The molten metal 2 in the inside is supplied to an intermediate container 3 having a high-frequency coil 14 as a heating means and heated, and then a pool 6 formed by a pair of internally cooled rolls 4 and refractory side weirs 5. Is injected into. Reference numeral 7 denotes a stopper for adjusting the amount of molten metal supplied from the intermediate container 3 to the pool 6.
Driven by the stopper elevating device 7a, the level of the molten metal in the pool 6 is controlled to be constant. Reference numeral 5a denotes an electric heater provided in the side weir 5 to heat the side weir 5.

Next, the molten metal poured into the pool 6 is cooled on the surface of the roll 4 to form a solidified shell 9. The solidified shell 9 moves downward with the rotation of the roll 4 and is pressed in the vicinity of a roll kiss point (a point where two rolls approach each other) to produce a thin cast piece 10.

In the above configuration and casting method, according to the method of the present invention, a part of the molten metal 2 is supplied from the ladle 1 to the intermediate container 3, and then the supplied molten metal is heated in the intermediate container 3 to form the molten metal 2.
After raising the temperature in the range of 0 ° C or more and 200 ° C or less, the intermediate container 3
The hot water supply to the hot water pool section 6 is started from the beginning. Hereinafter, the method of the present invention will be described in detail with reference to FIG.

A. Casting procedure Refractories such as the intermediate container 3 and the side weir 5 are preheated to a predetermined temperature by a gas burner or an electric heater 5a (not shown), and the ladle 1 holding the molten metal 2 is placed in the intermediate container 3.
Installed above The molten metal 2 has a degree of superheat that is higher by about the temperature drop when the molten metal is transferred so that the molten metal temperature in the pool 6 becomes a predetermined temperature during steady casting. If the degree of superheat of the molten metal in the ladle is too small, the degree of superheat of the molten metal in the pool becomes small, and the above-mentioned sticking shell is generated, thereby causing an operation trouble. If the degree of superheat of the molten metal in the ladle is too large, breakouts and surface cracks occur. Preferably, the degree of superheating of the molten metal of the ladle is 70 ° C or more and 200 ° C or less.

Next, the preheating of the intermediate container 3 is stopped, and a part of the molten metal 2 in the ladle 1 is supplied to the intermediate container 3. Here, the hot water supply from the ladle 1 to the intermediate container 3 is temporarily stopped,
Alternatively, a small amount of molten metal is continuously supplied. The molten metal in the intermediate container 3 is not supplied to the pool 6 and is held as it is, and the high-frequency coil 1
Heat at 4. The heating time depends on the amount of the molten metal in the intermediate container 3, the amount of temperature rise of the molten metal, the heating capacity of the intermediate container 3, etc. However, if it is too short, the temperature of the molten metal will not be stable. There is a problem that the hot water supply port is closed and hot water cannot be supplied to the hot water pool portion 6. Preferably, the heating time is between 3 and 30 minutes.

Next, when the temperature of the molten metal in the intermediate container 3 reaches a predetermined temperature, the preheating of the side dam 5 is stopped, and the supply of hot water from the intermediate container 3 to the pool 6 is started. Start casting. Almost simultaneously with the start of the hot water supply, full-scale supply of molten steel from the ladle 1 to the intermediate container 3 is started, and the temperature rise of the molten metal in the intermediate container 3 is reduced or heating is stopped.

B. Heating temperature The temperature of the molten metal in the intermediate container 3 is 20 ° C.
Not less than 200 ° C. For example, if the temperature of the molten metal immediately after the hot water is supplied to the intermediate container 3 is 1500 ° C., heating is performed to a temperature in the range of 1520 ° C. to 1700 ° C.

If the temperature rise amount is less than 20 ° C., the molten metal temperature in the pool 6 is low at the start of hot water supply, and the fixed shell 13 is formed on the side weir 5. When the temperature exceeds 200 ° C., thermal deformation and thermal damage of the refractory on the stopper 7 and the inner wall of the intermediate container 3 are likely to occur. In addition, the temperature of the molten metal in the pool 6 becomes too high, so that the solidified shell 9 breaks and breakout easily occurs.

C. Heating Method, Heating Capability The heating method of the intermediate container 3 is not specified, but a high-frequency induction heating method can be used. In addition. If the capacity of the intermediate container is small, an electric heater or the like may be used. In addition, the heating capacity may be determined so that the heating time is about 30 minutes or less because the heating power becomes expensive if the power is large and the heating time becomes long if the power is small.

D. Capacity of Intermediate Container The capacity of the intermediate container 3 is not particularly limited, but is preferably about 2 to 10 times the capacity of the pool 6 and 20% or less of the capacity of the ladle 1. If the capacity of the intermediate container 3 is small, the temperature rise of the molten metal in the pool 6 becomes large because the temperature rise of the side weirs 5 of the pool 6 is insufficient. If the capacity of the intermediate container 3 is large, a part of the molten metal in the ladle 1 can be supplied to the intermediate container 3 for heating, but the heating efficiency is deteriorated, which is not economical, and the equipment becomes large. It is expensive and not preferred.

E. Preheating of the side weir The preheating of the side weir 5 may be performed in the same manner as in the related art. In particular, it is desirable that the portion of the side weir 5 near the contact between the roll 4 and the molten metal be preheated to 1200 ° C. or more. In a preferred embodiment of the present invention, the molten metal has a liquidus temperature of 1300 ° C. or higher.

In the case of a molten metal having a low liquidus temperature such as aluminum or its alloy, the side weir and the nozzle can be heated to a temperature sufficiently higher than the liquidus temperature by a gas burner or an electric heater. The problem of sticking shell formation described above is small.

On the other hand, in the case of a molten metal having a high liquidus temperature, for example, a molten metal having a liquidus temperature of 1300 ° C. or more, such as stainless steel, carbon steel, or Fe—Ni alloy steel, a side dam is required. And nozzles are difficult to heat up to a temperature sufficiently higher than the liquidus temperature, so that a sticking shell is formed by the conventional method.However, the method of the present invention suppresses the formation of the sticking shell and reduces the surface quality. Good slabs can be cast stably.

The method of the present invention can be applied by a twin-roll lateral pouring method or a single-roll method as in the above-described twin-roll top-pouring method, and the same effect can be obtained.

[0037]

EXAMPLE A stainless steel thin plate of SUS304 was manufactured using a twin-roll top-pour-type thin plate continuous casting apparatus equipped with an intermediate container. Table 1 shows the main specifications of the continuous sheet casting apparatus, and Table 2 shows the manufacturing conditions together with comparative examples.

[0038]

[Table 1]

[0039]

[Table 2]

Table 3 shows the measured values of the temperature of the molten metal in the ladle, the intermediate container and the pool, the operating conditions and the results of the investigation on the surface quality of the slab, together with comparative examples.

FIGS. 4, 5 and 6 are graphs showing the transition of the molten metal temperature (indicated by the degree of superheat) in Example 2 of the present invention, Comparative Example 1 and Comparative Example 3, respectively. 4 to 6
The temperature of the molten metal in the intermediate container has changed since a predetermined amount of molten metal was supplied from the ladle.

[0042]

[Table 3]

In each case of the present invention, after only 2 tons of molten metal was transferred from the ladle to the intermediate container, the supply from the ladle was stopped. The ladle has a superheat of 105 to 1
The range was 36 ° C. Next, heating is performed in the intermediate container for 6 to 20 minutes, and the molten metal supplied to the intermediate container is cooled for 30 minutes.
The temperature was raised in the range of ~ 130 ° C. Due to the heating, the degree of superheating of the molten metal in the intermediate container is reduced from 29 to 60 ° C to 88 to 1 ° C.
The temperature rose to the range of 59 ° C. Next, the preheating of the side weir is stopped, the side weir is pressed against the roll side surface, the hot water is started to be supplied from the intermediate container to the pool, and then the heating is stopped and the hot water is supplied from the ladle to the intermediate container again. Then, thin slabs were continuously cast while controlling with a stopper so that the amount of molten metal in the intermediate container became constant. Five seconds after the start of casting, the degree of superheat of the molten metal in the pool was 40 to 99 ° C, and stable casting was possible without formation of a fixed shell. Also, the superheat degree of the molten metal in the pool is 56
Target superheat degree of molten steel (50-90 ° C)
° C), and the casting was stable. The surface quality of the slab was also good and there was no problem.

In Comparative Example 1, the preheating of the side dam was stopped.
The side weir is pressed against the side of the roll, hot water is supplied from the ladle to the intermediate container, and heating is not performed by the intermediate container. When the molten metal in the intermediate container reaches 1.8 tons, hot water is supplied from the intermediate container to the hot water pool. Started. The superheat degree of the molten metal in the intermediate vessel is 60 ° C, the superheat degree of the molten metal in the pool is 5 ° C 5 seconds after the start of casting, a fixed shell is formed on the side dam, and a breakout occurs 40 seconds after the start of casting. The operation was stopped because of

In Comparative Example 2, the molten metal in the intermediate container was 0.5 to
At the time of n, the amount of hot water supplied from the ladle was reduced by half, and heating of the molten metal in the intermediate container was started. Two minutes after the start of heating, when the amount of molten metal in the intermediate container became 1.8 ton, hot water was supplied from the intermediate container to the pool and casting was started. Heating caused the superheat of the molten metal in the intermediate vessel to rise by 10 ° C from 59 ° C to 69 ° C. However, the superheat of the molten metal in the pool was 24 ° C 5 seconds after the start of casting, and a fixed shell was formed on the side weir. However, the operation was stopped because a breakout occurred 51 seconds after the start of casting.

In Comparative Example 3, the temperature of the molten metal in the ladle was raised (superheat of the molten metal in the ladle: 202 ° C.), and the heating in the intermediate container was not carried out and the molten metal in the intermediate container became 1.8 ton. Then, hot water was supplied from the intermediate container to the pool, and casting was started. The degree of superheat of the molten metal in the intermediate vessel is 124 ° C., and the degree of superheat of the molten metal in the pool is 71 ° 5 seconds after the start of casting.
At 0 ° C, the casting was stable with no formation of a fixed shell.
However, the superheat degree of the molten metal in the pool in the steady state 5 minutes after the start of casting is 154 ° C., and the target superheat degree of the molten steel (50
９０90 ° C.), the number of cracks occurred on the slab surface, and the quality was poor.

[0047]

According to the present invention, at the start of casting,
The temperature of the molten metal in the basin rises to an appropriate value, and the solidified shell does not adhere to refractories such as side dams and nozzles, thereby enabling stable casting. Further, the temperature of the molten metal in the pool in the steady state can be appropriately maintained, and a thin slab of good quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual view schematically showing a method of manufacturing a thin slab by a twin-roll top pouring method, wherein FIG. 1 (a) is a longitudinal sectional view, and FIG. 1 (b) is a sectional view taken along the line AA. .

FIGS. 2A and 2B are conceptual diagrams schematically showing a method of manufacturing a thin cast piece by a twin-roll horizontal pouring method, wherein FIG. 2A is a longitudinal sectional view and FIG. 2B is a sectional view taken along the line AA. .

FIGS. 3A and 3B are conceptual views schematically showing the method of the present invention by taking a twin-roll top-pouring method as an example. FIG. 3A is a longitudinal sectional view, and FIG. It is arrow A sectional drawing.

FIG. 4 is a graph showing a transition of a molten metal temperature in Example 2 of the present invention.

FIG. 5 is a graph showing transition of a molten metal temperature in Comparative Example 1.

FIG. 6 is a graph showing transition of a molten metal temperature in Comparative Example 3.

[Explanation of symbols]

 1: Ladle 2, 8: Molten 3: Intermediate container 4: Roll 5: Side weir 5a: Electric heater 6: Hot water pool 7: Stopper 7a: Stopper elevating device 9: Solidified shell 10: Thin cast piece 11: Nozzle 12 ： Nozzle fixing device 13 ： Fixed shell 14 ： High frequency coil

Claims (2)

[Claims] 1. In continuous casting for producing thin cast slabs by feeding molten metal from a ladle through an intermediate container having a heating function to a pool, and adding molten metal in the ladle to the intermediate container. And then heating the supplied molten metal in the intermediate container to raise the temperature in the range of 20 ° C. or more and 200 ° C. or less, and then start supplying hot water from the intermediate container to the pool. A method for starting continuous casting of thin slabs, characterized in that: 2. The method according to claim 1, wherein the liquidus temperature of the molten metal is 1300 ° C. or higher.