JP2915544B2 - Continuous forging method of slab strand in continuous casting. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is intended to effectively reduce the internal quality of a continuous cast slab obtained by continuous casting, in particular, center segregation.

(Prior Art) The segregation of the center of a continuous cast slab of steel is caused by the C in the center of the thickness of the final solidification zone of the slab strand drawn from the continuous casting mold.
It appears as positive segregation due to the concentration of molten steel components such as P, S, and so on, which causes deterioration of mechanical properties in the thickness direction of thick plate products and the occurrence of lamination. It was one of the quality defects.

As a countermeasure for reducing the center segregation, for example, electromagnetic stirring in the secondary cooling zone has been attempted, but the effect cannot be said to be sufficient because it does not reduce the degree to the semi-macro segregation.
Attempts have also been made to apply an inline reduction method (iron and steel: 1974, No. 7, pp. 875-884) in which a pair of rolls is used to greatly reduce the pressure of the slab strand at the end of solidification of the molten steel. However, in the case of such a method, cracking occurs at the solidification interface when the reduction in the large region of the unsolidified layer is insufficient, and when the reduction amount is large, a strong negative force is applied to the center of the thickness of the slab. There were problems such as segregation.

As an attempt to improve the above-mentioned problems, for example, Japanese Patent Application Laid-Open No. 63-183765 discloses a pair of forging pressures sandwiching the slab strand drawn from a continuous casting mold on both sides in the vicinity of the solidification completion point. A method of performing forging with a mold is disclosed.

However, in the case of such an approach, fluctuations in operating conditions,
For example, when the drawing speed of the slab strand fluctuates, since the unsolidified thickness of the slab strand at the forging point changes, a complicated operation that requires appropriate adjustment of the rolling reduction by the forging die was required. .

(Problems to be Solved by the Invention) Even if the operating conditions in continuous casting fluctuate, a new cast slab with a sound internal quality can be stably obtained without any extra operation. It is an object of the present invention to propose a forging method.

(Means for Solving the Problems) According to the present invention, a slab strand drawn from a continuous casting mold is continuously connected to a region near the solidification completion point of the slab strand by a pair of forging molds sandwiching the slab strand. A method for continuous forging of slab strands in continuous casting, characterized in that prior to forging of slab strands, rolling is performed to make the unsolidified thickness of the slab strands uniform during forging.

FIG. 1 shows an example of an apparatus suitable for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a slab strand drawn from a continuous casting mold (not shown), and reference numeral 2 denotes a slab strand 1. Are formed on both sides (in this example, up and down in this example) of a pair of forging dies. The dies 2 are connected to a reciprocating drive mechanism (not shown), respectively, in a region near the solidification completion point of the slab strand 1. A predetermined amount of forging is performed by repeating the opening and closing operations of the mutually approaching and separating spaces. A rolling roll 3 is arranged on the entry side of the forging die 2, and a rolling roll for equalizing the unsolidified thickness of the slab strand 1 until reaching the forging die 2. This is a measuring device for measuring the thickness of the solidified portion 1a. Based on the unsolidified thickness of the slab strand 1 measured by the measuring device 4, the thickness is adapted to a predetermined amount of reduction of the forging die 2. The roll opening degree of the pressing roll 3 is set so as to have the adjusted thickness.

Here, as the above-mentioned measuring device 4, an ultrasonic wave transmitted from a transmitter arranged above or below the slab strand 1 is received by a receiver arranged below or above the strand 1 and the ultrasonic wave is received. Slab strand 1 with sound wave intensity
It is advantageously suitable to measure the solidified thickness of the sample and to detect the unsolidified thickness from the entire thickness.

(Function) When forging is performed on the slab strand 1 drawn from the continuous casting mold, the unsolidified thickness 1 of the internal molten steel at the forging point fluctuates depending on fluctuations in operating conditions such as a cooling speed and a casting speed. Even if the forging amount of the die at the processing point was set appropriately in advance, the rolling reduction was insufficient or conversely too large to obtain a satisfactory result.

According to the present invention, even if the operating conditions during continuous casting are changed, the unsolidified thickness at the forging point becomes a predetermined thickness before reaching the forging point, for example, such as the roll 3 described above. In this case, cracking does not occur in the slab strand due to forging, and negative segregation does not occur due to excessive reduction.

As a means for keeping the unsolidified thickness of the slab strand 1 constant, it is also possible to apply a flat rolling surface such as the forging die 2 shown in FIG. Is not particularly limited. In the rolling process using the rolling roll, if the rolling amount is too large, there is a possibility that a crack occurs at the solidification interface of the internal molten steel of the slab strand. For this reason, when a reduction roll is applied, the reduction amount is preferably limited to a maximum of about 20 mm.

(Embodiment) The apparatus having the structure shown in FIG.
Continuous casting of a slab with a thickness of 0 mm and a thickness of 400 mm, and then forging processing in which the reduction amount on one side is 30 mm in the area near the solidification completion point of the slab (21 m from the exit side of the continuous casting mold) And the internal quality of the obtained continuous cast slab was investigated. In the forging process in this embodiment, a reduction roll was installed at a position 1 m on the entry side of the forging machine, and an ultrasonic thickness measuring device was installed 1 m upstream of the rolling roll, and the casting speed was adjusted to the forging point of the forging device. Was adjusted so that the unsolidified thickness was 60 mm.

Drill from the center of the cross section of the obtained cast slab (3mmφ)
As a result of investigating the state of center segregation by C analysis by sampling 10 chip samples at, as shown in Table 1,
When forging was performed without performing the rolling process to maintain the unsolidified thickness of the slab upstream of the forging point, the internal quality deteriorated. It was confirmed that when the forging process was performed with the solidified thickness kept constant, a product having good internal quality was obtained.

(Effects of the Invention) Thus, according to the present invention, internal defects such as center segregation, which were difficult to reduce in continuous cast slabs obtained by continuous casting, can be easily reduced without requiring an extra operation. . Further, according to the present invention, since the cross-sectional dimension of the slab strand can be reduced before forging, there is an advantage that the working amount in forging can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus suitable for use in the practice of the present invention. DESCRIPTION OF SYMBOLS 1 ... Cast strand, 1a ... Solidified shell 1b ... Unsolidified part, 2 ... Forging die 3 ... Roll-down roll, 4 ... Detecting device for unsolidified thickness l ... Unsolidified thickness

Continuation of the front page (56) References JP-A-4-118162 (JP, A) JP-A-3-275259 (JP, A) JP-A-2-224856 (JP, A) JP-A-2-155550 (JP) JP-A-63-183765 (JP, A) JP-A-62-286653 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 11/128 350 B22D 11/20

Claims (1)

(57) [Claims] 1. A slab strand drawn from a continuous casting mold is subjected to continuous forging in a region near a solidification completion point of the slab strand by opening and closing a pair of forging dies sandwiching the slab strand on both sides. A method for continuous forging of slab strands in continuous casting, characterized in that prior to forging of the casting agency strands, a reduction process is performed to make the unsolidified thickness of the slab strands uniform.