JPH0526589B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention involves injecting molten steel from a master ladle into a tundish, and pouring it into a mold from this tundish.
Concerns the continuous casting method of steel that directly produces billets and slabs.

(Prior art) In the conventional continuous casting method, after continuous casting, the tundish is transported by a crane or the like to a tundish maintenance yard, where it is maintained (hereinafter referred to as cold maintenance) by personnel other than the casting personnel. was.

That is, in this tundish maintenance yard, the remaining steel is first processed.

One method for disposing of this residual steel is to tilt the tundish after continuous casting to dispose of the remaining steel and residue inside the tundish, so-called sloping. The inner surface of the tundish was cleaned by oxygen spraying, and a breaker or the like was used to remove residual metal and slag that had adhered to the inner surface of the tundish during the casting process.

Another method for processing residual steel is to cool the tundish after continuous casting by water cooling, etc., and then use a metal punching machine etc. to push out the metal and slag that adhered to the inner surface of the tundish during the previous casting. The remaining steel was being removed.

After going through this residual steel processing process, maintenance such as replacing the sliding valve installed at the bottom of the tundish and replacing the submerged nozzle is carried out.
Furthermore, after repairing the inner surface of the tundish by spraying amorphous refractories onto locally worn parts of the tundish's inner surface, the tundish is reheated using a burner or the like (hereinafter, this reheating operation will be referred to as preheating). )
Then, they were made to wait until it was their turn to pour in the molten steel.

In such cold maintenance, the process of servicing a series of tundishes takes about eight hours, so conventionally, about 12 tundishes, including spares, were prepared for one continuous facility and used in sequence. .

By the way, cleaning the inner surface of the tundish with oxygen spray cannot completely clean the inner surface of the tundish.
Moreover, it is unavoidable that oxides adhere to the refractory surface of the inner surface of the tundish. Therefore, when casting is performed using this tundish, there is a problem in that a large amount of slag and oxides are mixed into the molten steel, and giant inclusions are generated in the molten steel. For this reason,
After using the tundish, remove the slag and metal attached to the inner surface, then completely cool the tundish and spray new refractory material to prepare the inner surface, or do not clean the inner surface by spraying oxygen. After the tundish was used, it was cooled down, the bare metal was pushed out and removed, and the inner surface was prepared by spraying with new refractory material.The tundish with the inner surface prepared was preheated with a burner, etc. before casting. be.

(Problems to be Solved by the Invention) In recent years, as user needs for steel have become more sophisticated and diversified, it has become necessary to produce in small lots.

However, when producing small lots using the conventional continuous casting method, it is necessary to frequently replace and maintain the tundish in order to prevent the mixing of different steel components. For this reason, conventional continuous casting methods have had problems such as an increase in the cost of refractories and an increase in heat loss wasted in a series of repeated cooling and preheating of the tundish.

In addition, in the conventional continuous casting method, the cost of refractory material attached to the inner surface of the tundish is
It accounts for nearly 40% of operating costs, and reducing this was an extremely important technical issue to be solved. In particular, when producing small-lot materials, it is necessary to frequently maintain the tundish as described above, so reducing the cost of refractories has become an extremely important problem to be solved.

Furthermore, in the conventional continuous casting method, there was a problem in that it was necessary to allocate dedicated personnel to maintain the tundish. Conventionally, approximately the same number of these personnel as casting personnel were required, and reducing the number of these personnel was also an important problem to be solved.

Furthermore, in terms of the quality of the steel produced, in the conventional continuous casting method, at the start of casting, oxidation of the molten steel poured into the tundish from the parent ladle (ladle),
The surface peeling of the refractory on the inner surface of the tundish is unavoidable, resulting in molten steel with many giant inclusions.Moreover, even though the tundish has been preheated, the molten steel that is first poured into the tundish from the master ladle transfers heat to the tundish side. As the temperature of the molten steel decreases,
There was a problem in that the giant inclusions were poured into the mold without being separated.

In addition, low-temperature casting is required to eliminate center segregation, but if low-temperature casting is performed in this way, the molten steel will solidify due to the temperature drop in the initial stage of casting, which will clog the submerged nozzle. However, it was considered impossible to pursue a low-temperature casting method that reached its theoretical limits.

This invention has been made in view of the problems of the prior art described above, and firstly, it is possible to dramatically reduce the cost of tundish refractories, as well as to reduce heat loss and operating personnel. The first object of the present invention is to provide a continuous casting method, and the second object is to provide a continuous casting method that can produce high quality steel without large inclusions and center segregation.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a continuous casting method in which molten steel from a parent ladle is poured into a tundish, and the molten steel is poured from the tundish into a mold. After completion of the casting process, the tundish used for this casting will be hot-maintained without being substantially cooled by discharging the remaining steel and residue, and the technical means of casting will be carried out using this hot-maintained tundish. This is a characteristic feature.

Furthermore, prior to casting, the molten steel in the tundish is heated and stirred, and then the molten steel is poured into a mold.

(Function) According to the present invention, after the completion of casting, the remaining steel and residue are discharged from the tundish used for this casting and hot maintenance is performed without substantially cooling, and the hot maintenance tundish is used for casting. The tendishu is repeatedly used hot.

This causes the temperature inside the tundish to
Since the temperature does not drop to the point at which residual steel and residue adhere to the inner surface of the tundish, the residual steel and residue within the tundish hardly solidify and adhere to the inner surface of the tundish. Therefore, there is no need to strip off this adhesion as in the past, so it is possible to prevent damage to the refractory due to this stripping operation, and to extend the life of the refractory.

Furthermore, in addition to simplifying the work of stripping off this deposit, there is no need to transport the tundish to the tundish maintenance yard using a crane or the like as in the past, which reduces the time required from the end of the previous casting to the current casting. The time can be dramatically shortened and the temperature change of the refractory inside the tundish can be reduced. Therefore, fatigue of the refractory due to temperature changes is reduced, and this also improves the life of the refractory.

In addition, according to the present invention, since the tundish is repeatedly used in a hot state, the number of tundishes required in the past can be reduced to 2.
In fact, it can be reduced to about three. This also reduces the cost of the tundish refractories.

Further, according to the present invention, since the tundish is repeatedly used in a hot state, there is no need to substantially preheat the tundish, so that the heat loss required for preheating can be reduced.

Naturally, according to the present invention, it is possible to simplify the work of removing deposits, and it is possible to omit transporting the tundish to the tundish maintenance yard using a crane or the like, thereby reducing the number of personnel required for tundish maintenance. You can also.

On the other hand, according to the continuous casting method related to another invention,
When pouring molten steel from the parent ladle into the tundish, the molten steel flow can temporarily capture slag and oxides on the inner surface of the tundish into the molten steel, and by heating and stirring this molten steel, slag and oxides can be removed from within the molten steel. Since the separation and flotation of oxides can be promoted, the formation of giant inclusions in the molten steel can be prevented, and since there is no temperature drop until the end of casting, center segregation can be prevented.

Furthermore, in this invention, since the tundish is repeatedly used in hot conditions, the amount of heat input required for heating and stirring can be suppressed compared to the conventional method.

(Example) Hereinafter, the method of the present invention will be explained in detail based on illustrative drawings.

FIG. 1 is a drawing schematically explaining the method of the present invention. In FIG. 1, 1 is a master ladle containing molten steel 4, 2 is a tundish placed directly under the master ladle 1,
3 is a mold disposed directly below the tundish 2, and first, the molten steel A in the master ladle 1 is poured into the tundish 2. At this time, slag and oxides on the inner surface of the tundish 2 are taken into the molten steel A by the molten steel flow caused by the injection of the molten steel A.

Next, the tundish 2 that received the steel as described above is moved from above the mold 3, and is heated by an electric method such as arc, plasma, inductor, etc. (as shown by the two-dot chain line in FIG. (The upper part of the tundish is a torch for plasma heating.) to heat the molten steel A without oxidation (approximately +30°C/30 minutes from the temperature at the time of receiving the steel), and during this heating time, the molten steel A is Stir with a stirrer etc. This makes the temperature distribution of the molten steel A uniform, and the slag and oxides in the molten steel A are separated and floated, thereby preventing the formation of giant inclusions in the molten steel A.

In addition, in parallel to the above-mentioned heating and stirring of molten steel A,
By using a dummy basset, preparation time for casting can be further saved.

Thereafter, the tundish 2 is returned onto the mold 3, and the molten steel A is poured into the mold 3. It passes through section 6 and is finished as a desired billet or slab.

Next, after the continuous casting is completed, the tundish 2 is moved from above the mold 3 as shown by the imaginary line on the right side in FIG. It is something.

This tundish servicing includes tundish servicing that is commonly performed insofar as it is performed hot, ie, without substantial cooling.

For example, by tilting the tundish 2, etc., the slag is turned back and the remaining steel is processed.
After replacing the stopper, replacing the sliding valve and submerged nozzle installed at the bottom of the tundish 2, and, if necessary, spraying refractories locally on the tundish 2 to repair the inner surface, etc. This consists of a series of operations in which the tundish 2 is placed on the mold 3 again, and molten steel for the next casting is poured into the hot-maintained tundish 2.

Since the above-described hot maintenance of the tundish 2 is performed in a hot state immediately after the completion of casting, there is no need to substantially preheat the tundish 2 before the next casting is performed. Normally, preheating is not necessary, but since the temperature does not drop at all during hot maintenance, it is necessary to compensate for this temperature drop, or even if hot maintenance is completed, the main pot etc. If the upstream side is forced to wait until the next casting starts, preheating may be performed for 30 minutes or less.

Here, Figure 2 shows a comparison of the changes in the number of ground scratches caused by the formation of inclusions when a tundish with a capacity of 50 tons was used, and when conventional cold maintenance was performed and when hot maintenance was performed using the casting method of the present invention. show. FIG. 2 is a graph in which the number of ground defects is plotted on the vertical axis and the casting amount is plotted on the horizontal axis.

As shown in Figure 2, compared to the case of conventional cold maintenance in which the tundish is cooled once and then used (the top dotted line in Figure 2), the tundish according to the present invention is used repeatedly during hot maintenance. In the case of hot maintenance (middle dotted line in Figure 2), and in the case of hot maintenance + heating and stirring of molten steel (bottom solid line in Figure 2),
In all cases, it can be seen that high-quality casting was performed with few ground defects due to inclusion formation from the early stages of casting when the casting amount (T) was small.

In summary, the essence of this invention lies in the repeated use of the tundish in a hot state. Therefore, it goes without saying that changes can be made as appropriate without departing from the essence of the invention.

(Effects of the Invention) According to the continuous casting method of the present invention, after the completion of casting, the tundish used for this casting is hot-conditioned, and casting is performed using this hot-conditioned tundish, so that the tundish is not preheated. unnecessary or
It can be done in less than 30 minutes.

Therefore, the life of the refractory on the inner surface of the tundish can be improved and the number of tundishes themselves can be reduced, so the cost of the refractory on the inner surface of the tundish can be held down to 1/10 or less of the conventional cost.

Furthermore, in addition to being able to reduce the number of personnel required to maintain the tundish, it is also possible to shorten casting preparation time.

Furthermore, since the present invention can reduce heat loss, the amount of C gas used for heating the tundish can be reduced.

Also, according to the continuous casting method related to another invention,
At the early stage of casting, slag and oxides are separated and floated from the molten steel in the tundish, and the formation of giant inclusions in the molten steel can be suppressed, so there is no mixing of giant inclusions into the steel billet, and the steady state is maintained from the early stage of casting. It is possible to produce high-quality castings that are no different from other parts.

Further, there is no temperature drop in the initial stage of casting, and low temperature casting is possible, thereby improving center segregation in the cast billet.

Furthermore, the amount of heat input for heating and stirring can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically explaining the method of the present invention, and FIG. 2 is a graph showing the transition of inclusion generation during casting. A...molten steel, 1...master pot, 2...tendishu, 3...
template.

Claims (1)

[Scope of Claims] 1. In a continuous casting method in which molten steel is poured from a parent pot into a tundish and the molten steel is poured from the tundish into a mold, after the completion of casting, residual steel and residue are left as they are in the tundish used for casting. perform hot maintenance without exhausting and substantially cooling;
A continuous casting method characterized by casting using this hot-conditioned tundish. 2. The continuous casting method according to claim 1, characterized in that prior to casting, the molten steel received in a tundish is heated and stirred, and then the molten steel is poured into a mold.