JPH09225612A - Continuous casting method - Google Patents

Abstract

(57) [PROBLEMS] To provide a continuous casting method for producing a slab close to a product shape without segregation by a simple method in a continuous casting method for continuously casting and casting a slab. Provide the law. SOLUTION: Under the internal pressure of a machine for producing a slab 10 having a shape close to a product by pulling out a slab from directly below a mold 1, a set of reduction rolls 3 and 7 made up of two or more multi-rolls is formed, and inside the machine. A continuous casting method characterized in that a slab having a shape close to a product shape free from center segregation or V segregation is produced by setting the end time of reduction within the range of 0.3 to 0.6 in terms of center solid fraction. Is. [Effect] A slab having no segregation defect and a shape close to the product shape can be produced by a simple method, the rolling step can be omitted, and a slab of good quality can be produced.

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 reducing a center segregation and producing a slab having a shape as close to a product as possible in a continuous casting method in which a pressure is reduced from directly under a mold.

[0002]

2. Description of the Related Art In recent years, demands for material characteristics of offshore structures, storage tanks, steel pipes for transporting oil and gas, high-strength wire rods, etc. have become more severe, and at the same time, establishment of a method for manufacturing these at lower cost is an important issue It has become.

When the quality of the slab for realizing these is examined first, it is ideal that the slab is homogeneous in the cross section, however, the slab has inclusions, segregation,
Porosity is generated, which affects the properties of steel materials.

Among these defects, segregation is caused by impurity elements such as sulfur, phosphorus and manganese contained in molten steel being partially concentrated in the casting process, and the most serious segregation is central segregation. In the central part of the slab obtained by continuous casting, central segregation or V segregation in which impurity elements and the like are concentrated is observed.

This is because the present inventors have previously described [Materials and Processes] vol. 2 (1989), 1269], bridging that occurs at the center of the slab at the end of solidification and unevenness of the solid-liquid interface, etc., partially increases the liquid passage resistance at the center and The concentrated molten steel between dendrite trees is:
By coagulation contraction suction force, it is sucked and accumulated in the central part.

The reason why the liquid passing resistance at the center of the cast slab increases is that the solid fraction in the central portion locally increases due to bridging or unevenness of the solid-liquid interface, and the dendrite in the central portion having a large solid fraction is increased. Concentrated molten steel with a low melting point such as trees is sucked by downward solidification contraction, and solutes such as dendrites are not concentrated in the demelted molten steel with a low melting point. This is because molten steel penetrates and locally solidifies.

As a measure for preventing center segregation and V segregation, there is a method of controlling the solidification structure into equiaxed crystals or the like in which tree flow is unlikely to occur due to electromagnetic stirring, and solidification shrinkage which causes flow of concentrated molten steel or the like. In recent years, a method of compensating the surface of a slab by means of light reduction has been developed and applied.

[0008]

On the other hand, in consideration of further measures for process saving, a method of increasing the casting speed and omitting the rolling process can be considered. In order to omit the rolling step, as is well known, a method such as a twin roll method that realizes a shape close to a product shape at the casting stage, and an internal machine rolling method that reduces the shape in the solidification step have been proposed.

The occurrence of center segregation and V segregation is also recognized in the above process, and establishment of preventive measures against these is an important issue. Therefore, it is necessary to establish a rolling-down method that rolls down to a shape as close as possible to the product without causing segregation.

The present invention has been made to solve the above problems, and provides a continuous casting method for producing a slab close to a product shape by a simple method while omitting the rolling step.

[0011]

[Means for Solving the Problems] That is, the gist of the present invention is that in a continuous casting method of molten metal in which a slab is drawn out while being pressed, a set of pressing rolls composed of two or more multi-rolls is formed, The central solid fraction of the slab is 0.3 to 0.
The continuous casting method is characterized by producing a slab having a product shape without segregation by rolling down to 6.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the following embodiments.

FIG. 1 shows the influence of the central solid fraction of the cast on the segregation at the end of the reduction in the machine, and FIG. 2 shows the experimental apparatus for experimenting the influence of the reduction in the machine inside the multiple rolls on the segregation. As shown in the figure, a large number of reduction rolls 3 and 7 consisting of two or more are installed just below the mold 1, and a cooling water spray immediately below the mold and a slab temperature adjustment water spray 6 between the reduction rolls are arranged. FIG. 3 is an influence of the central solid fraction at a position 13 immediately after the reduction-finishing roll 7 in the unsolidified reduction on the segregation of 0.1% C steel in the case of the reduction by rolling.

When the central solid fraction immediately after the final roll under the unsolidified pressure by the multiple rolls 3 and 7 is smaller than 0.3, segregation is observed in the slab 10, and the final roll reduction timing of the final roll of the multiple rolls is observed. By setting the central solid fraction to be larger than 0.3, segregation can be prevented.

The reason why the center segregation can be improved is as follows.
As shown schematically in FIG. 2 and further in FIG. 3, by reducing the unsolidified thickness as much as possible under the pressure until the solid fraction f of the central portion of the cast slab becomes 0.1, the curves 11 and 12 are obtained. It is possible to reduce the elapsed time of the central solid phase ratio of 0.1 to 0.4 where the shell thickness of the solid phase ratio of 0.1 to 0.3 shown in the figure instantaneously moves to the center due to rolling and the concentrated molten steel accumulates rapidly. by.

The segregation is observed by macro etching, and the shell thickness and solid fraction of the slab are calculated by calculating the temperature at each position by heat transfer calculation using the cooling water amount, slab thickness and each physical property. The rate was calculated by the following equation (1) using the calculated temperature at each position.

[0017]

## EQU00001 ## Solid phase ratio = (T-Tsl) / (T11-Tsl) ... (1)

In the equation (1), T is the temperature at each position calculated by heat transfer calculation, Tsl is the solidus temperature of the molten metal, and T11 is the liquidus temperature of the molten metal.

[0019]

EXAMPLES Table 1 shows the quality and shape of the slab thus produced. According to the method of the present invention, there is no segregation,
Further, it is possible to manufacture a slab having a shape close to that of the product. The shape of the slab can be further adjusted by cutting the slab after adjusting the temperature of the slab with the water spray 9 shown in FIG. 2 installed after the above-mentioned internal pressure reduction, or continuously supplying the slab to the next step and rolling as it is. Alternatively, it is heated in a heating furnace and then rolled to prepare.

[0020]

[Table 1]

[0021]

As described above, in the continuous casting method of the present invention, the central solid fraction of the cast slab is reduced to 0.3 to 0.6 by the set of reduction rolls consisting of two or more multi-rolls. As a result, a slab having a shape close to the product shape without segregation defects can be manufactured by a simple method, a rolling step can be omitted, and a slab of good quality can be manufactured.

[Brief description of drawings]

FIG. 1 is a drawing showing the influence of the central solid fraction of a slab at the end of internal rolling on segregation.

FIG. 2 is a drawing showing an experimental apparatus for conducting an experiment on the influence of internal pressure reduction of a multi-roll machine on segregation.

FIG. 3 is a drawing showing a state in which segregation of a cast piece is improved by the method of the present invention.

[Explanation of symbols]

 1 Mold 2 Water Spray Nozzle 3 Reduction Roll 4 Molten Metal 5 Immersion Nozzle 6 Water Spray Nozzle for Slab Temperature Adjustment 7 Final Internal Pressure Suppression Roll 8 Shell Thickness of Solid Fraction f 9 Water Spray Nozzle for Slab Temperature Adjustment 10 Slab 11 Solid Shell thickness 12 with a phase ratio of 0.1 12 Shell thickness with a solid phase ratio of 13 13 Center solid phase ratio immediately after the final roll under internal machine pressure

Claims (1)

[Claims] 1. A continuous casting method for molten metal in which a slab is drawn out while being rolled down, a set of rolling rolls consisting of two or more multi-rolls is formed, and the central solid fraction of the slab is 0.3 to 0.
A continuous casting method characterized by producing a slab close to a product shape without segregation by rolling down to 6.