JP2945060B2 - Manufacturing method of continuous cast slab without center porosity - Google Patents

Description

[Detailed Description of the Invention] (Industrial application field) The center porosity present in the continuously cast slab obtained by continuous casting is inevitably caused by volume shrinkage in the solidification process of steel. However, it is difficult to eliminate the slab by rolling, and when the slab is inserted into a heating furnace or the like without solving the problem, the inside of the continuous cast slab may be oxidized, which may cause a serious problem in quality. This invention relates to continuous cast slabs obtained by continuous casting of steel, especially high Cr steel, high Mn
It is intended to effectively prevent remarkable center porosity in high alloy continuous cast slabs such as steel, high Mo steel and the like.

(Prior Art) Conventionally, as an attempt to reduce the center porosity existing in the continuous cast slab, a method of performing low-temperature casting or performing electromagnetic stirring during continuous casting to increase the number of equiaxed crystals (Japanese Unexamined Patent Publication No. 61
Japanese Unexamined Patent Publication (Kokai) No. 229450/1989), a method of lowering the casting speed or a method of applying a light reduction to a continuously cast slab obtained by continuous casting (see Japanese Patent Application Laid-Open No. 49-12738) have been applied.

However, the adoption of low-temperature casting and electromagnetic stirring can reduce the center porosity, but the reduction effect is very small, and the method of lowering the casting speed can reduce the center porosity diameter, but the rate of occurrence In the case of the light reduction method, the reduction in center porosity was very small because the reduction force could not be transmitted to the center of the slab.

(Problems to be Solved by the Invention) In continuous casting of high alloy bloom such as high Cr steel, high Mn steel or high Mo steel, particularly remarkable center porosity is eliminated to obtain continuous cast slab with good internal quality. It is an object of the present invention to propose a new manufacturing method which can be performed.

(Means for Solving the Problems) The present invention relates to an unsolidified thickness of a continuous cast slab extracted from a continuous casting mold in a region where the solid phase ratio at the center of the thickness is 0.9 or more. When the continuous cast slab is a bloom, if the continuous cast slab is a bloom, the area of 20 to 40% of the bloom width in the center area of the bloom width direction A method for producing a continuously cast slab without center porosity, characterized in that the slab is added to a region of 70 to 90% of the slab width in the central region in the width direction of the slab (first method).
Invention), and the present invention provides a method for applying a reduction by forging immediately after the solidification of a continuous cast slab drawn from a continuous casting mold, wherein the continuous cast slab has an internal temperature of 1100 ° C. or more. 5% or more and 15% or less of the thickness of the cast slab is cast, and if the cast slab is a bloom, it is continuously cast in the area of 20 to 40% of the bloom width in the center area in the width direction of the bloom. If the piece is a slab, the slab width is 70
A method for producing a continuously cast slab without center porosity, characterized in that it is added to a region of about 90% (second invention).

Here, the continuous cast slab, particularly a high alloy continuous cast slab, is a high Cr steel with Cr> 1%, a high Mn steel with Mn> 1%, Mn> 0.05%
High carbon steel or medium and high carbon steel of C> 0.7%, and such high alloy continuous cast slabs have remarkable center porosity in ordinary continuous casting.

(Operation) In order to eliminate the center porosity existing in the continuous cast slab, it is effective to apply a reduction to the cast slab and deform the inside of the cast slab. When the cast slab is heated, the temperature distribution in the cross section of the slab is uniform or the outside of the slab becomes hotter than the inside. Since the outer peripheral portion was greatly deformed and the inner deformation was small, the center porosity was not eliminated, and therefore, a very large rolling force was required to eliminate the center porosity.

In the present invention, since the slab is pulled out during the continuous casting, that is, the slab is subjected to the reduction at the stage where the temperature of the center of the slab is high and the temperature of the outer periphery is low, the center porosity can be effectively pressed. It is. Here, the solid phase ratio at the center of the thickness of the continuously cast slab (an index indicating the position between the liquidus temperature and the solidus temperature at which the temperature of the center of the slab is determined by the steel type) is The reason for applying a reduction larger than the unsolidified thickness in a region where 0.9 or more is that this region is in a mixed state of a solid phase and a liquid phase,
At this time, there is no center porosity inside the slab, but here, by applying a pressure larger than the unsolidified thickness (1.5 to 2.0 times the unsolidified thickness) in advance and pressing both solidified parts sandwiching the unsolidified This is because the occurrence of center porosity can be avoided in advance. Further, in the present invention, even after the solidification of the continuous cast slab is completed, a reduction of 15% or less of the thickness of the cast slab is applied immediately thereafter, so that even if center porosity is generated inside, the effect is reduced. Can be eliminated. That is, since the inside of the slab immediately after the completion of solidification is in a high temperature state, the center porosity inside can be pressed by applying a reduction including a thickness reduction. When forging is performed immediately after solidification is completed, the temperature inside the slab depends on the rolling force.
It is good to be above ℃. In order to press the center porosity by pressure, it is necessary to apply a reduction of 5% or more of the thickness of the slab and transmit this reduction force to the inside. In the present invention, the reduction of 15% or less of the thickness of the slab is applied because the compression effect of the center porosity is saturated at a reduction exceeding this, and the pressure required to reduce the solidified slab is reduced. This is because of economic reasons that the reduction means is enlarged due to the increase, and if the reduction at this time is a local reduction, if the reduction exceeds 15%, indentation may occur in rolling in the subsequent process or rolling scratches may occur. Because there is.

As a specific means for applying the reduction to the continuously cast slab, the use of a roll or the like is conceivable. However, in the case of a roll, a crack may occur at the solidification interface inside the slab depending on the amount of reduction. Therefore, as shown in FIGS. 1 (a) and 1 (b),
It is desirable to apply a forging device in which a mold having a flat forging surface is arranged.

In FIGS. 1 (a) and 1 (b), reference numeral 1 denotes a continuous cast slab, 2a and 2b denote dies for vertically sandwiching the continuous cast slab 1, and 3 denotes a die 2b.
Hydraulic cylinder S ₁ for holding and fixing the position of the mold 2b
The frame main body 4 is movable forward and backward along the guide surface of the frame main body 3 and has a hydraulic cylinder S _{2 at} its lower end.
A slider 5 provided with a mold 2a through the shaft 5 is a crankshaft. The frame body 3 and the slider 4 are suspended from the crankshaft 5 via links 6 and 7, respectively.
The slab strand 1 is subjected to forging by moving the molds 2a and 2b toward and away from each other by the rotation of. Numeral 8 denotes a hydraulic cylinder for quickly restoring the frame main body 3 that has moved with the withdrawal of the slab strand 1 at the time of forging, to the initial state. FIG. 1 (a) shows a state in which the molds 2a and 2b are separated from each other and released, and FIG. 1 (b) shows a state in which the molds are brought close to each other to perform forging.

In addition, as the metal mold installed in the apparatus having the above-described configuration, a mold having a flat forging surface can be used, but a crack is not generated at the solidification interface of the slab strand 1 during forging. In addition, as shown in FIG. 2, it is preferable to use a mold having an inclined surface o at a tip end portion of a mold facing the slab strand 1.

It is generally known that the center porosity exists substantially at the center of the slab. Therefore, when the bloom is continuously cast, as shown in FIG. In the case of continuously casting a slab in a region of 20 to 40% of the width, a structure capable of locally reducing the region of 70 to 90% as shown in FIG. 3B reduces the rolling force. It is also advantageous from above.

FIG. 4 shows a situation in which forging is performed on the slab strand 1 by applying the mold having the above-described configuration and repeating the mutual approach and separation.

In the figure, the dashed line indicates the state of the mold in the middle of the reduction of the slab strand, and the solid line indicates the state of the mold after a predetermined forging pressure. In the present invention, even when the center porosity t is generated inside the slab strand 1, it is possible to appropriately transmit the forging effect to the inside in a situation as shown in FIG. Since forging can be performed, defects such as center porosity are effectively eliminated.

(Example) A bloom of a steel type having a thickness of 400 mm and a width of 560 mm as shown in Table 1 was heated at a molten steel heating degree of 20 to 30 ° C. and a drawing speed of 0.4 to 0.5.
While continuously casting under the condition of 5 m / min, from the area of the unsolidified thickness of the bloom of 20 mm to immediately after the solidification is completed,
Forging processing was performed using an apparatus having the form shown in the figure, and the internal quality of each of the obtained continuous cast slabs was examined.
Table 1 shows the results.

When the forging process was performed in accordance with the present invention, the presence of center porosity was not recognized at all, but the cross section of the slab in the continuous cast slab manufactured according to the usual procedure of not applying the forging process during continuous casting. It was confirmed that 5 to 10% of the center porosity was present in the area ratio of.

(Effects of the Invention) Thus, according to the present invention, it is possible to prevent the center porosity, which was difficult to avoid in a slab obtained by continuous casting, without requiring a large rolling force, and to improve the internal quality of the continuously cast slab. Can be improved.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are schematic views of a forging device suitable for use in the present invention. FIG. 2 is a forging die suitable for use in the present invention. FIG. 4 (b) is a sectional view of a main part of a forging die, and FIG. 4 is an explanatory view of a forging procedure according to the present invention. 1 ...... continuous casting slab, 2a, 2b ...... die 3 ...... frame body 4 ...... slider 5 ...... crankshaft, 6,7 ...... link S _1, S ₂ ...... hydraulic cylinders, O ... … Inclined surface

Continuation of the front page (56) References JP-A-63-230262 (JP, A) JP-A-63-268548 (JP, A) JP-A-61-238449 (JP, A) JP-A-63-183765 (JP, A) , A) JP-A-63-108955 (JP, A) JP-A-49-12738 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 11/28 350

Claims (2)

(57) [Claims] (1) In a region where the solid fraction at the center of the thickness of a continuous cast slab drawn from a continuous casting mold is 0.9 or more, forging is performed by 1.5 times or more the unsolidified thickness of the continuous cast slab. When the continuous cast slab is a bloom, the center area in the width direction of the bloom is 20 to 40% of the bloom width when the continuous cast slab is a bloom, and when the continuous cast slab is a slab, the center in the width direction of the slab. A method for producing a continuous cast slab without center porosity, characterized in that the slab width is added to a region of 70 to 90% of the slab width in the region. 2. A continuous casting slab drawn from a continuous casting mold is subjected to a forging process immediately after solidification of the continuous casting slab, and when the internal temperature of the continuous casting slab is 1100.degree. When the continuous cast slab is a bloom, reduce the width of the bloom by 5% or more and 15% or less of the thickness.
If the continuous cast slab is a slab in the area of 20 to 40%, in the center area in the width direction of the slab in the area of 70 to 90% of the slab width,
A method for producing a continuous cast slab without center porosity, characterized by adding.