JPH0245939B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention aims to prevent macro/semi-macro segregation and center porosity that occur at the center of a slab cross section in continuous casting of molten steel, and to obtain a healthy core structure with high precision. That is. (Prior art) In conventional continuous casting machines, elements with high segregation coefficients such as C, S, and P are segregated in the center of the slab cross section, and when this slab is rolled, elements with high segregation coefficients are segregated in the center of the slab cross section. However, there are segregation lines, and when used in sour gas line pipes, defects such as damage to the material occur along these segregation lines. These segregations are called macrosegregation and semi-macrosegregation, and the common origin is the flow of unsolidified molten steel. Produced by bulging. In order to solve this problem, it is necessary to completely stop the flow of molten steel. However, simply stopping the flow cannot compensate for the volumetric contraction, so center porosity is generated. In order to eliminate this phenomenon, there is a method of rolling down the vicinity of the solidification tip with rolls (Japanese Patent Publication No. 54-38978, Japanese Patent Publication No. 54-39215), but these methods support the slab with a wire, In practice, the practical effect is unsatisfactory because it inevitably exceeds approximately 50 mm, which is considered to be a harmless spacing. As described in Japanese Patent Publication No. Sho 59-16541, the taper reduction method using a surface involves the process of drawing out and guiding a continuously cast slab by removing the solidification completion point (unsolidified tip) and the upper and lower surfaces of the vicinity thereof. There is a method of preventing center segregation of continuously cast slabs by alternately repeating clamping and releasing with a walking bar device depending on the volume to be solidified and shrunk, while supporting and guiding the continuous casting slab. (Problems to be Solved by the Invention) This method can prevent the flow of unsolidified molten steel in the longitudinal direction of the rolling support area, but the slab is supported and guided while being alternately clamped and released by the walking bar device. Sometimes, in the support guide region, bulging occurs between the walking bars in the slab width direction on the side of the mold from the solidification completion point [unsolidified tip], resulting in uneven segregation improvement in the slab width direction. (Means for Solving the Problems) The present invention is configured as follows in order to solve the above problems. That is, the gist of the present invention is that, in the process of drawing and guiding a continuously cast slab, the solidification completion point (unsolidified tip) of the slab and the upper and lower surfaces of the vicinity thereof are held by a walking bar device according to the volume to be solidified and shrunk. In the method of preventing center segregation of a continuously cast slab by alternately repeating opening and rolling support and guiding, the surface temperature of the rolling support area of the continuous casting slab is controlled by the walking bar device in a range of 600 to 900°C for 1 to 7 minutes. A method for preventing center segregation of a continuously cast slab characterized by maintaining and guiding the slab. (Function) In the process of drawing and guiding a continuously cast slab, the solidification completion point (unsolidified tip) of the slab and the upper and lower surfaces of the vicinity thereof are held and opened by a walking bar device according to the solidified and contracted volume. The present invention is not to prevent the center segregation of a continuously cast slab by alternately repeating the steps of rolling down and supporting and guiding the slab. The technical conditions have been found to effectively solve the unique problem of non-uniform segregation improvement in the width direction of the slab. By maintaining and guiding the temperature in the range of 600 to 900℃ for 1 to 7 minutes, the rigidity of the surface layer of the slab is increased and the rolling support pressure of the walking bar device is spread evenly over the entire surface layer of the slab. By suppressing the amount of bulging between walking bars in the slab longitudinal direction as well as in the slab width direction to 0.05 mm or less, the flow of unsolidified molten steel in the slab width direction is prevented, and the segregation of components in the width direction in the solidified part is evenly improved to a high level. This prevents the occurrence of segregation and semi-macro segregation. The surface layer portion of the slab that has passed through the rolling support region is reliably heated, thereby advantageously improving the diffusion of minutely segregated portions. (Example) Occurrence status of slab defects

【table】

[Table] Note 1: A sketch of the standard photograph for scoring is shown in Figure 1.
Note 2: A sketch of the standard photograph for scoring is shown in Figure 2.
Note 3: The 10mm thick central portion was investigated by X-ray flaw detection and evaluated by area ratio.
As is clear from the table, the example of the present invention has no macro segregation or center porosity, and has no semi-macro segregation (P _nax /P).

Claims (1)

[Claims] 1. In the process of drawing and guiding a continuously cast slab, the solidification completion point (unsolidified tip) of the slab and the upper and lower surfaces of its vicinity are clamped and released by a walking bar device according to the volume to be solidified and contracted. In the method of preventing center segregation of a continuously cast slab by alternately repeating rolling support and guiding, the surface temperature of the rolling support area of the continuous casting slab is maintained in the range of 600 to 900°C for 1 to 7 minutes by the walking bar device. A method for preventing center segregation of a continuously cast slab, characterized by guiding the slab by