JPS63268548A - Production of continuously cast slab - Google Patents

Abstract

PURPOSE:To produce a continuously cast slab having only little development of cavity or porosity by eliminating center segregation, by executing plastic deformation to the cast slab at cooling process of the cast slab continuously cast under pressing reduction by pressing device. CONSTITUTION:The cast slab 4 drawn from a mold 3 in the continuous casting apparatus is cooled by injecting cooling water, to make progress of solidification of the liquid phase 4a at center part of the cast slab 4. The pressing device 20 of hydraulic type, etc., is arranged between straightening rolls 8 and guide rolls 6 or 7 in a strand, where the solidification of the liquid phase 4a at center part of the cast slab 4 is not completed, and the pressing reduction is applied to upper/lower direction of the cast slab 4. By this pressing reduction, the center segregation of carbon in the cast slab 4 substantially becomes zero and cavity is crushed. A pressing device 30 is arranged between the straightening rolls 8 and cutting machine 10 together with the above pressing device 20 or instead of the pressing device 20 and by applying the pressing reduction to the cast slab 4, the development of cavity and porosity is extremely reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a continuously cast slab, and particularly to a method for producing a continuous cast slab with less segregation and cavities in the center of the slab.

(Prior art and its problems) Continuous slabs such as billets, blooms, and slabs that are continuously cast by a continuous casting machine are cut into appropriate lengths by a cutting machine after the center of the slab is completely solidified. It is then cut into pieces and transported to the next process, the rolling process.

In the rolling process, a steel billet is first heated to a predetermined temperature in a heating furnace, and then rolled into a finished product or into a base material for the next process of rolling into small bars, wire rods, etc.

Manufacturing slabs using continuous casting equipment is not only more productive than manufacturing steel ingots using ingot cases, but also has superior center segregation of steel materials. The proportion of steel products obtained from continuous slabs is increasing.

However, the requirements for the quality of steel materials have become more stringent in recent years. It is desired to improve the center segregation of

In order to meet this demand, efforts have been made to reduce the center cavity (including porosity) through the development of electromagnetic stirring technology in the mold and in the strand. Unlike in the production of steel ingots, the final solidification zone accompanied by solidification shrinkage occurs continuously at the center of the slab cross-section, so it is difficult to completely eliminate cavities in the center. When a steel material is heated with cavities present, air enters the steel through the cavities exposed at the end face of the slab, and internal oxidation progresses along the length of the slab. Add steel? The degree of progression varies depending on the A degree, the size of cavities and porosity, the density of occurrence, etc.
The end face portion where internal oxidation has progressed needs to be cut off after rolling, and the larger the cut off portion, the worse the yield.

A conventional method for preventing the above-mentioned internal oxidation is to weld cavities and porosity-generating areas on the end faces of steel materials, but this method has poor workability, creates a poor working environment, and is labor-intensive. It takes.

The present invention has been made in order to solve such problems, and provides a method for manufacturing continuous cast slabs that has less center segregation, prevents the progress of internal oxidation during heating of steel materials, and improves yield. With the goal.

(Means for Solving the Problems) In order to achieve the above-mentioned object, according to the present invention, in the cooling process of the slab continuously cast by the continuous casting device, the slab is subjected to reduction by a press device. Provided is a method for manufacturing a continuously cast piece, characterized in that the continuous cast piece is plastically deformed.

(Function) When a slab that has just been pulled out of the mold of a continuous casting machine and is in the cooling process is subjected to a reduction using a press device without being heated, if this reduction is performed before the center of the slab has solidified, , center segregation is eliminated at the same time as the center cavity is crushed, and if this is done after the center of the slab has solidified, almost no effect on center segregation can be expected, but the center cavity is crushed and disappears.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a conceptual diagram showing the configuration of a continuous casting apparatus for carrying out the method of the present invention. This continuous casting apparatus continuously casts slabs such as billets, plumes, and slabs. It is a tongue push method, and molten steel is injected from a ladle (not shown). An immersion nozzle 2 is attached to the lower surface of the tundish 1, and the molten steel stored in the tundish 1 is passed from the immersion nozzle 2 to a mold 3 that is cooled with cooling water.
is injected into. Below the mold 3 is a slab 4 in the solidification process.
A support roller apron 5 consisting of a large number of sets of rolls 5a, which restrains the outer surface of the apron to prevent free deformation, and a guide roller apron 6.7 and a drawing and straightening roll 8 are arranged in this order, and these rolls 5. 6. 7. 8
As a result, the slab 4 is pulled out below the roller apron at a predetermined speed.

A large number of cooling water injection devices (not shown) are arranged on the upper part of the support roller apron 5, and the slab 4 pulled out from the mold 3 is cooled by the cooling water sprayed from the cooling water injection devices, and the central part of the slab 4 is cooled. Solidification of the liquid phase 4a progresses gradually.

The drawing and straightening roll 8 corrects the downwardly drawn slab from being curved into a straight line and sends it out in the horizontal direction. Cutting machine 1
At the time when the slab 4 is conveyed to zero, the center of the slab 4 has completely solidified. Then, it is cut into a suitable length by cutting a10, and is transferred to the next process by a transfer roll (not shown).

The above configuration is the same as the conventional continuous casting apparatus, but the continuous casting apparatus to which the method of the present invention is applied has a liquid phase 4a in the center of the slab 4 between the straightening roll 8 and the guide roll 6 or 7. A pressing device 20 is disposed within the strand which has not yet completed solidification.

The press device 20 is a hydraulic press and has a press capacity necessary for a predetermined reduction. The press device 20 consists of an anvil 21 and a head 22 facing the anvil 21 with the slab 4 in between. It is formed.

This press device 20 presses the slab 4 in the vertical direction (the slab 4
(in the direction perpendicular to the drawing direction of , when the slab becomes 4, (Ha-II) X100
/He is represented. As a result of this reduction, the center segregation of carbon in the slab 4 becomes substantially zero, and the cavities are also crushed and their occurrence is no longer observed.

FIG. 2 shows a cross-sectional shape 370 at the exit of the kite roll 6.
A slab 4 of m5 x 480m has a cross-sectional shape of 3555m.
The graph shows the carbon content distribution state when the slab is rolled down to x 480 mm, and shows that the center segregation of carbon content is significantly improved when rolling is applied by the method of the present invention, compared to the case where the slab is not rolled by the press device 20. ing. In addition, in Figure 2, carbon! CO is the carbon content analysis value of the molten steel sampled in the ladle, and carbon content C is the analysis value obtained by cutting the slab and collecting chips with a drill from each position along the cross-sectional center line.
The vertical axis of the graph shown in the figure shows the C/Co ratio, and the horizontal axis shows the distance from the center of the slab cross section.

In addition to or in place of the press device 20, a press device 30 may be disposed between the straightening roll 8 and the cutting machine IO. If30 is installed at a position where the slab 4 has just been pulled out of the mold 3 of the continuous casting device and is in the cooling process, more specifically, when the central liquid phase 4a of the slab 4 has completely solidified. The surface temperature of slab 4 is 600-12
It is placed in a cooled position in the range of 00°C. The press device 30 is also a hydraulic press and has the press capacity necessary for rolling. The press device 30 consists of an anvil 31 and a head 32 facing the anvil 31 with the slab 4 in between, and the opposing end surfaces of the anvil 31 and the head 32 are not curved but flat.

The reduction amount of the slab 4 by the press device 30 is also 0.5.
It is sufficient to reduce (light reduction) to about 6%, and although reduction cannot be expected to improve center segregation of carbon, cavities and porosity may occur due to crushing of cavities in the center. problem is solved.

Cross-sectional shape 370III11×48 by press device 30
0111+1 slab with cross-sectional shape 360auw x 48
When the slab was rolled down to 0 mm, no cavities or porosity were found as a result of cutting the slab after rolling down and visually observing it after pickling with a 20% + 1 (J! hot solution).

In the case of slabs with small dimensions (150 mm square or less), the degree of center segregation is lower than that of large cross-section slabs, so instead of using the press device 20 described above, press after the center of the slab has completely solidified. The method of rolling down using only the device 30 is particularly effective in preventing the occurrence of cavities and porosity. Note that, of course, in addition to the press device 20, a press device 30 may be used in combination.

(Effects of the Invention) As described in detail above, according to the continuous cast slab manufacturing method of the present invention, the cooling process of the slab continuously cast by the continuous casting device, that is, before the solidification of the slab is completed; /Or after the slab has solidified, the slab is pressed down by a press machine to cause plastic deformation, so that the center segregation of the slab is significantly improved, and the occurrence of cavities and porosity is extremely reduced. The method of the invention has the excellent effect of significantly improving the product yield of steel rods rolled from continuous slabs.

[Brief explanation of the drawing]

FIG. 1 is a conceptual configuration diagram showing a schematic configuration of a continuous casting apparatus for carrying out the method for producing continuous cast slabs according to the present invention, and FIG. 2 shows changes in carbon content along the cross-sectional center line of continuous cast slabs. It is a graph. ! ...Tandish, 3...Mold, 4...Slab,
4a...Central liquid phase, 5...Support roll, 6,
7... Guide roll, 8... Pull-out straightening roll, 10
... Cutting machine, 20 ... Press device, 30 ... Press device.

Claims (3)

[Claims] (1) A method for producing a continuous slab, which comprises applying pressure to the slab by a press device to plastically deform it during the cooling process of the slab continuously cast by a continuous casting device. (2) The method for manufacturing a continuous slab according to claim 1, characterized in that the slab is subjected to a reduction before the solidification of the central part of the slab is completed. (3) The method for manufacturing a continuous slab according to claim 1, wherein the slab is subjected to a reduction after solidification of the central part of the slab is completed.