JPH08206803A - Method for continuously casting different kinds of steels - Google Patents

Abstract

PURPOSE: To reduce an untreating part of light rolling reduction of a cast slab as little as possible at the time of successively executing continuous castings in the condition of connecting a first kind of steel with a second kind of steel in each cast slab. CONSTITUTION: At the time of continuously casting the first kind of steel, the light rolling reduction treatment is continuously executed for the cast slab 14A at the stationary light rolling reduction position P1 with light rolling reduction rolls 16 and also, the light rolling reduction rolls 18 are positioned at the ascending shifting position P2 in a proper center solid phase rate position of the first kind of steel cast slab 14A displaced during stopping time till starting the continuous casting of the second kind of steel. In this position P2 , together with starting of the continuous casting of the second kind of steel, the remaining light rolling reduction treatment is executed for the first kind of steel cast slab 14A. Thereafter, the light rolling reduction is successively executed for the second kind of steel cast slab 14B at the regular light rolling reductionn position P1 .

Description

Detailed Description of the Invention

[0001]

This invention relates to a continuous casting method,
More specifically, it relates to a continuous casting method characterized by a light reduction treatment when continuously casting different steel types.

[0002]

2. Description of the Related Art The continuous casting method has a great advantage that the yield is good and the productivity is high, and it is widely used as a casting method capable of continuously producing final slabs such as slabs, blooms and billets directly from molten steel. It has been implemented.

By the way, when molten steel is cast by this continuous casting method, there is a problem that C, P, S, etc. are segregated (concentrated) in the center of the slab. Therefore, components that are likely to segregate, especially bearings In the case of steel types such as steel and spring steel containing a large amount of C, there is a problem that it is difficult to adopt the continuous casting method. As a means for suppressing this segregation, a method of performing a light reduction treatment on a cast piece that has come out of a mold is known.

It is considered that the phenomenon in which the components such as C are concentrated and segregated at the center of the slab is caused by the solidification of molten steel progressing from the outer peripheral portion toward the central portion.
In particular, it is considered that a concentrated molten steel flow occurs along with the solidification contraction of the liquid phase remaining in the center portion during the final solidification, which leads to the concentrated segregation of C and the like.

The light reduction treatment suppresses segregation of components during solidification by compressing and deforming the unsolidified portion at the center of the slab by at least the amount of volume reduction during solidification shrinkage.

By the way, in this light reduction treatment, it is important to efficiently perform the reduction treatment on the slab so as to sufficiently change the volume (compressive deformation) of the central unsolidified portion. Under such circumstances, the inventors of the present invention say that, when continuously performing the drawing operation of the cast piece, it is preferable that the cast piece is lightly pressed at a position where the solid fraction of the central portion becomes a predetermined solid fraction. We obtained the knowledge and invented a continuous casting method based on this knowledge, and proposed it in the previous patent application (Japanese Patent Application No. 6-15772).

During continuous casting, the molten steel moves to a complete liquid phase region A, a solid-liquid mixing region B in which a liquid phase and a solid phase are mixed, and a complete solid phase region C, as shown in FIG. The central solid fraction means the weight ratio of the solid phase in the central portion of the cast slab 100 (the complete solid state is 1.0), and thus the central solid fraction is 0.2. When the slab 100 is subjected to the light reduction treatment at the position of 0.8, the unsolidified portion of the slab 100 can be sufficiently changed in volume (compressive deformation),
Segregation of components can be effectively prevented. Therefore, according to this method, continuous casting can be satisfactorily performed even if the C% is 0.5% or more.

By the way, for the purpose of saving casting time, improving productivity, etc., different steel grades, for example, a first steel grade and a second steel grade, are continuously subjected to a casting process in a state in which their slabs are connected. However, the light reduction treatment in this case poses a problem.

For example, continuous casting is performed on the first steel grade, and then a metal for connection is driven into the upper end of the first steel grade slab, and the second steel grade is continuously cast again on the upper side of the first steel grade slab. In this case, immediately before starting the continuous casting of the second steel grade, the casting equipment is temporarily stopped and the work for switching the steel grade is performed, but at this time, it is located a certain distance below the upper end of the first steel grade cast slab. Also, the proper central solid fraction position moves upward as the slab cools during the stop time.

In this case, for the first steel grade, the portion from the position of the light reduction roll to the upper end of the slab becomes incapable of the light reduction treatment, and there is a problem that the slab cannot be used or the quality of the slab deteriorates. Occurs.

[0011]

The invention of the present application has been made to solve such a problem. Thus, the invention of the present application is such that after the first steel type is continuously cast, the casting operation is once stopped for a predetermined short time, and then the second steel type is continuously cast, and the second steel type slab is In continuous casting of the first steel grade in continuous casting of different steel grades in such a manner as to be continuously connected to the steel grade slab, the central solid fraction of the first steel grade slab has a predetermined appropriate solidity. The position that becomes the phase ratio is set as a steady light reduction position, and at the steady light reduction position, the first steel grade slab is continuously light reduced by a light reduction roll, while the continuous casting of the first steel type is stopped. After that, the light reduction roll is positioned at the rising transition position of the proper central solid fraction position in the first steel type slab displaced during the stop time until the continuous casting of the second steel type is started, and the second steel type With the start of continuous casting, the residue for the first steel grade slab at the rising transition position Light reduction treatment is continuously performed until the upper end of the first steel grade cast reaches the rising transition position, and then the light reduction treatment is continued at the steady light reduction position for the second steel grade cast. It is characterized by (claim 1).

According to another invention of the present application, in the method according to claim 1, the light pressure reduction rolls arranged at the steady light pressure reduction position can be moved up or down, or two sets of light pressure reduction rolls are arranged above and below the upper light pressure reduction rolls. It is not possible to move up and down the reduction roll, and the light reduction roll that has been made possible to move up and down is raised to the rising transition position of the proper central solid fraction ratio position in the first steel type cast slab, and by the raised light reduction roll, the second It is characterized in that the remaining light reduction treatment is performed on the first steel type slab after the start of continuous casting of the steel type (claim 2).

Still another invention of the present application is the method according to claim 1, wherein the light reduction roll disposed at the steady light reduction position can be moved up and down, and further, the proper central solidification of the first steel type cast slab is performed during the stop time. The light reduction roll is interlocked with the upward transition of the phase ratio position, and is moved upward to the upward transition position while performing the light reduction treatment on the first steel type cast slab, and after the start of continuous casting of the second steel type. It is characterized in that the remaining light reduction treatment for the first steel grade slab is continuously continued (claim 3).

[0014]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, when the continuous casting of the first steel type is stopped and the continuous casting of the second steel type is started during the stop time, When the proper center solid fraction position moves upward by a distance corresponding to the stop time, a light reduction roll is arranged at the position where the movement has risen, and when the light reduction roll starts continuous casting of the second steel type. At the same time, the remaining light reduction treatment for the first steel type is continued.

According to the present invention, the portion above the steady light reduction position in the first steel grade slab, that is, the portion above the portion where the light reduction roll is located at the time when the continuous casting for the first steel grade is stopped. Of these, at least during the above-mentioned stop time, a portion above the rising transition distance of the proper central solid fraction position can be subjected to the light reduction treatment.

Therefore, the portion to be cut out as the untreated portion under light pressure can be reduced as much as possible, and the yield can be improved. Alternatively, it is possible to reduce the segregated portion as much as possible,
The quality of the slab can be improved.

In the present invention, the term "light reduction" means the reduction of the cross-sectional area of the slab before and after reduction, and the reduction rate is preferably 1.0 to 3.0% in terms of the area reduction rate. It is more preferably in the range of 1.5 to 2.5%.

Further, in the light rolling, in the sense that tensile stress is suppressed to be small at the interface of the unsolidified portion in the center of the slab to prevent cracking and effective rolling is performed, the cross-sectional shape of the slab is It is preferable that the roll has a circular shape, and as the light reduction roll, a roll having a flat portion in the direction perpendicular to the axis of the slab is used, and the slab is lightly reduced at the flat portion. Further, the position where the central solid fraction is 0.2 to 0.8 is preferable as the position to be subjected to the light reduction.

According to the second aspect of the present invention, the light pressure reduction rolls arranged at the steady light pressure reduction position can be moved up or down, or two sets of the light pressure reduction rolls are arranged above and below so that the upper light pressure reduction rolls can be moved up and down. , The light reduction roll that can be raised and lowered is raised to the rising transition position of the proper central solid fraction position of the first steel type cast slab during the above stop time, and the rest of the first steel type cast slab is raised by the vertical light reduction roll. The light pressure reduction process is continued.

When continuously casting different steel types,
The stopping time of the casting equipment for changing the steel type is not precisely determined, and it is possible to avoid variations in the stopping time of 10 minutes, 11 minutes, or 9 minutes. Absent. Along with this, the rising transition distance of the proper central solid fraction position in the first steel type cast slab also varies.

In this case, if the light reduction roll can be moved up and down, the remaining light weight relative to the first steel type cast slab is accurately adjusted to the rising transition distance of the position of the proper central solid fraction in the first steel grade slab. The advantage is that the reduction treatment can be performed. That is, according to the present invention, it is possible to appropriately deal with the variation in the stop time when switching the steel type.

According to the third aspect of the present invention, the light pressure reduction roll arranged at the steady light pressure reduction position can be moved up and down, and further, the light pressure reduction roll is moved in association with the proper central solid fraction position which moves upward during the stop time. The present invention is designed to raise the first steel type cast slab while continuing the light reduction, and according to the present invention, the light reduction untreated portion for the first steel type cast slab can be substantially eliminated. Therefore, according to the present invention, it is not necessary to perform cutting of the light reduction untreated portion in the first steel type cast slab, the manufacturing process can be simplified and the material yield can be improved, and the quality can be improved. .

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, 10 is a water-cooled mold, and 12 is a tundish for injecting molten steel into the mold 10. In the method of this example, first, steel type A (first steel type) is continuously cast. That is, the molten steel in the tundish 12 is poured into the water-cooled mold 10 to solidify the molten steel from the bottom of the mold 10 to form a slab 14A.
As withdrawing continuously.

Then, the position where the central solid fraction of the cast slab 14A becomes a predetermined appropriate solid fraction is set as a steady light pressure reduction position (position P ₁ which is a distance L lower than the upper end in the figure), and the light pressure reduction roll is placed at the same position. (Fixed light pressure roll) 16 is placed in a fixed position,
This fixed light reduction roll 16 is used to cast a steel type A slab 14A.
A light reduction treatment is applied to.

Reference numeral 18 denotes a movable light reduction roll which is arranged above the fixed light reduction roll 16 so as to be able to move up and down. In the method of this example, it is untreated under light reduction when the casting of the first steel type A is stopped. With respect to the portion where the steel type B is continuously cast, a light reduction treatment is performed by the movable light reduction roll 18 when the continuous casting of the steel type B is started.

The light reduction treatment of the slab 14A of the steel type A by the movable light reduction roll 18 is specifically performed by the following procedure. That is, after the continuous casting for the steel type A is stopped, the connecting metal piece 20 is driven into the upper end of the slab 14A and the continuous casting for the steel type B is continuously performed. Thus, from the time when the continuous casting of the steel type A is stopped to the time when the continuous casting of the steel type B is started, the casting apparatus is temporarily stopped and the work for switching the steel type is performed.

At this time, the position of the proper central solid fraction in the cast slab 14A shifts upward with the lapse of time as the cast slab 14A cools. For example, the proper central solid fraction position P ₁
However, if it is a position where 30 minutes have passed after the molten steel was poured into the mold 10, when the casting apparatus was stopped for 10 minutes, this proper central solid fraction position moved up to the P ₂ position which is a position where 20 minutes had elapsed in the figure. (See Fig. 1 (II)).

Therefore, in this example, continuous casting is started for steel type B, and at the same time, the remaining light reduction processing for the slab 14A is started by the movable light reduction roll 18. Then, this light reduction treatment is continued until the upper end of the slab 14A reaches the P ₂ position (III → IV).

Thereafter, the light reduction treatment by the movable light reduction roll 18 is stopped, and as shown in (V), the slab 14B of steel type B is again subjected to the light reduction by the fixed light reduction roll 16 at the position P ₁ . continue processing.

Incidentally, according to this method, SUJ2 material having a C content of 1.0% as steel type A is continuously cast under the conditions that the cross-section of the slab is circular and the thickness is 350 mmφ and the drawing speed is 0.4 m / min. At the same time, at the position where the central solid fraction is 0.4 to 0.5 (P ₁ position), the reduction rate is 2% by the fixed light reduction roll 16.
The light pressure reduction treatment was performed under the conditions of.

Subsequently, after stopping the casting apparatus for 10 minutes, SUP7 having a C content of 0.6% as steel type B was continuously cast (the cross-sectional shape and thickness of the slab are the same as those of steel type A). At this time, at the position P ₂ 4 m above P ₁ , the remaining light reduction treatment for the cast slab 14A was performed by the movable light reduction roll 18.

As a result, slabs 14A and 14B of steel types A and B were obtained by leaving the untreated portion under light pressure reduction 4m and performing light pressure reduction treatment on the other parts.

FIG. 2 shows another embodiment of the present invention. In this example, the light reduction roll 22 arranged at the steady light reduction position P ₁ can be moved up and down, and during the stop time for changing the steel type, the light reduction roll 22 is moved to the proper center solid fraction position in the slab 14A. Slab 1 in conjunction with the rise of
4A while performing a light reduction treatment to raise to P ₂ position, and when the continuous casting of steel type B is started, the position is changed to P ₂ position.
Fixed to the slab 14A, the remaining light reduction treatment for the slab 14A is continued, and after the upper end of the slab 14A reaches the P ₂ position, the light reduction roll is again lowered to the P ₁ position, and the slab 14B is re-formed. The light pressure reduction process is continued. According to this example, the light reduction treatment can be performed without producing an untreated portion under light reduction and leaving the entire cast pieces 14A and 14B.

Although the embodiment of the present invention has been described in detail above, this is merely an example. For example, in the present invention, in the first embodiment, the elevating roll 18 may be raised while performing a light reduction treatment on the cast slab 14A during the casting stop time, or alternatively, it may be vertically stepped. It is also possible to arrange a light reduction roll and select the optimum roll to perform the remaining light reduction treatment on the cast slab 14A according to the variation in the casting stop time. The present invention can be implemented in various modified modes without departing from the scope.

[Brief description of drawings]

FIG. 1 is an explanatory view of a procedure of a continuous casting method which is an embodiment of the present invention.

FIG. 2 is an explanatory view showing a procedure of a continuous casting method which is another embodiment of the present invention.

FIG. 3 is an explanatory diagram for explaining the background of the present invention.

[Explanation of symbols]

14A, 14B Cast slabs 16, 18, 22 Light reduction rolls P ₁ , P ₂ Light reduction position

Claims (3)

[Claims] 1. The continuous casting of the first steel type is followed by once stopping the casting operation for a predetermined period of time, and then the continuous casting of the second steel type is carried out again with the slab of the second steel type being the first steel type. In continuous casting of the first steel grade in continuous casting of different steel grades to be continuously cast so as to be connected to the slab, the central solid fraction of the first steel grade slab has a predetermined appropriate solid fraction. The position is defined as a steady light reduction position, the first steel grade slab is continuously light reduced by a light reduction roll at the steady light reduction position, while the continuous casting of the first steel type is stopped, Positioning the light reduction roll at the rising transition position of the proper central solid fraction position in the first steel type cast slab displaced during the stop time until starting the second steel type continuous casting, the continuous casting of the second steel type Residual light pressure on the No. 1 steel cast at the rising transition position with start Performing the pretreatment continuously until the upper end of the first steel grade cast reaches the rising transition position, and then continuing the light reduction treatment at the steady light reduction position for the second steel grade cast. A method for continuously casting different steel types. 2. The method according to claim 1, wherein the light reduction rolls arranged at the steady light reduction position can be moved up or down, or two sets of light reduction rolls can be arranged vertically to move the upper light reduction rolls up or down. And, the light reduction roll that can be moved up and down is raised to the rising transition position of the appropriate central solid fraction ratio position in the first steel type cast slab, and the raised light reduction roll starts continuous casting of the second steel type. A method for continuously casting different steel grades, characterized in that the rest of the first steel grade cast pieces is subjected to the remaining light reduction treatment. 3. The method according to claim 1, wherein the light reduction roll arranged at the steady light reduction position can be moved up and down, and further, the proper central solid fraction ratio position of the first steel type cast slab is increased during the stop time. Interlocking with, the light reduction roll is moved up to the rising transition position while performing a light reduction treatment for the first steel type cast slab, and continuously after the start of continuous casting of the second steel type A method for continuously casting different steel grades, characterized in that the remaining light reduction treatment for the steel grade slab is continued.