JPS606254A - Continuous casting method - Google Patents

Abstract

PURPOSE:To prevent generation of central segregation in a continuous casting billet in the stage of casting continuously a steel by changing the spacing between the rolls that contact with the continuous casting billet drawn from a mold according to the position of the billet to act bulging force to a part existing an unsolidified base. CONSTITUTION:The inter-roll spacing between the bottom end of a mold 3 for a continuous casting billet 1 and the crater end point A of a liquidus line is stepwise increased successively for each one roll and the rolls in the solid-liquid coexisting section 4 between the point A and the crater end point B of a solidus line are maintained at the specified spacing in the stage of pouring a molten steel into the mold 3 and performing continuous casting. The inter-roll spacing is stepwise narrowed for each one roll after the point B. Bulging force is thus acted to the solidified shell between the bottom end of the mold and the point A which is the cause for generation of central segregation thereby preventing the generation of the central segregation in the continuous casting billet 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting method aimed at reducing center segregation.

Conventionally, in order to reduce center segregation, low-temperature casting methods and methods of electromagnetic stirring of molten steel in a mold have been adopted. That is, by these methods, the structure near the center of the slab is equiaxed crystallized to reduce center segregation.

However, according to the above method, although it is possible to reduce the huge central segregation, it is not possible to reduce the relatively large V-shaped segregation or island-shaped segregation.

None of the above methods can serve as a measure to essentially reduce center segregation.

As shown in Figure 1 (a), the rolls used in the above method are arranged between the rolls of a plurality of rolls installed between the mold and the solidus crater end. (distance between a pair of rolls) from the upstream side by an amount corresponding to the heat shrinkage caused by the temperature drop of the slab after casting.
0-roll by step narrowing (0.3 to 0 per liter roll)
．． 5 myn) was installed.

On the other hand, as another method for reducing center segregation,
Some of these are disclosed in Japanese Patent Publication No. 1'738 and Japanese Patent Publication No. 54-22777. These methods are.

As shown in FIG. 1 (b), at the final stage of solidification of the unsolidified layer within the slab, the narrowing of the roll spacing is significantly increased.

In other words, the distance between the rolls of the plurality of rolls installed between the liquidus crater end and the inphase crater end of the slab is gradually narrowed for each roll as the slab is pulled out]. .

This is to reduce center segregation by applying a reduction to the slab at the final stage of solidification to prevent movement of concentrated molten steel due to contraction of the 91 slabs.

However, it is extremely difficult to make the thickness of the unsolidified layer within the slab at the final stage of solidification uniform across the width of the slab. The thickness of the unsolidified layer is non-uniform.

As shown in FIG. 2, unsolidified layers 2 are scattered within the slab due to the large reduction of the slab.

As a result, surrounding concentrated molten steel is sucked into the closed unsolidified layer 2 due to solidification shrinkage as solidification progresses, so segregation occurs in the unsolidified layer 2.

This invention was made to solve the above-mentioned problems.

When casting slabs using the continuous casting method.

3- Actively apply a bulging force to the solidified shell between the mold and the liquidus crater end of the slab to increase the thickness of the unsolidified layer within the slab, and then The present invention is characterized in that a reduction is applied to the slab between the line crater end and the solidus line crater end of the slab, thereby reducing the occurrence of center segregation.

The method of this invention will be further explained.

Figure 3 shows the progress of solidification of continuously cast slabs.
FIGS. 4(a) to 4(c) show longitudinal cross-sections of the slab at each part in FIG. 3. In Figures 3 and 4, l is the slab, 2
is the unsolidified layer in the slab l, 3 is the mold, 4 is the solid-liquid coexistence layer in the slab l, and 5 is the solidified shell, and point A is the point where the center of the slab l starts solidifying. , that is, the liquidus crater end, and point B indicates the point at which the slab 1 completes solidification, that is, the solidus crater end.

When continuously casting steel, it is desirable to reduce the bulging force acting on the solidified shell 5 as much as possible since it causes internal cracks in the slab and center segregation. However, upstream from the liquidus crater end point A, the molten steel at the initial concentration in the unsolidified layer 2 flows easily, so the bulging force upstream from the point A does not cause center segregation.

Therefore, in the present invention, a bulging force is actively applied to the slab in a region where center segregation is not likely to occur, thereby increasing the thickness of the unsolidified layer within the slab in the region.

Next, in the present invention, a reduction is applied to the slab 1 whose unsolidified layer has become thick due to the bulging force until it is completely solidified.

As in the case shown in FIG. 1(b), center segregation is prevented from occurring. When applying a reduction to the slab 1.

As mentioned above, the thickness of the unsolidified layer 2 in the slab l has increased due to the bulging force.

It is possible to prevent the unsolidified layer 2 from clogging, which has conventionally occurred, and as a result, the occurrence of center segregation can be significantly reduced. This point is a feature of the present invention.

On the upstream side from the liquidus crater end point A.

5- In order to increase the thickness of the unsolidified layer 2 by actively applying a bulging force to the slab l, the roll of the roll installed between the mold 3 and the liquidus crater end point A is used. The spacing is gradually widened every 10 l from the upstream side toward the point A. In this case, the amount of increase in the distance between the rolls per 10 mm is preferably less than 1.5 rnyn; if the distance between the rolls is increased more than this, the amount of deformation of the solidified shell 5 will become too large.

Cracks occur at the solidification interface of the solidified shell.

On the other hand, in order to apply a reduction to the slab 1 between the liquidus crater end point A and the solidus crater end point 8, the distance between the rolls installed between the points A and B is of,
It is decreased stepwise in steps of 10 lbs from point A to point B. In this case, the amount of reduction of the slab by each roll is preferably such that the thickness of the slab is reduced by 0.2 to 2.0% per meter of slab.

Next, embodiments of the invention will be described.

As shown in Figure 1 (C), the thickness at the bottom of the mold is approximately 22 mm.
For an 8 mm slab, the meniscus (roll (7) installed between mold 6 and 10771)
0 step interval from the flow side to - stepwise widen for each roll (referred to as reverse taper), 10 to 10 steps from the meniscus. 2
The roll spacing of the rolls installed between 2 and 20 meters is kept constant, and the roll spacing of the rolls installed between 2 and 20 meters from the meniscus is gradually narrowed every 10 rolls from the upstream side (referred to as a positive taper). , Tono': Casting of slabs was carried out.

Table 1 shows the results of other casting cases and the center segregation level of the 01 piece in comparison with the results of the conventional example.

−7= According to the present invention, as is clear from Table 1.

Compared to the conventional method, the area ratio of center segregation to the cross-sectional area of the slab (center segregation area ratio) and the number of center segregation grains are dramatically reduced.

As explained above, the present invention brings about the useful effect of being able to significantly reduce center segregation.

[Brief explanation of the drawing]

FIG. 19 is a diagram showing the relationship between the distance from the meniscus and the roll interval, FIG. 2 is a longitudinal cross-sectional view of a slab with unsolidified layers scattered, and FIG. 3 is a diagram showing the progress of solidification. 4(a)-(C) are longitudinal sectional views of the piece. FIG. 3 is a longitudinal cross-sectional view of a slab on which a bulging force is applied. In the drawings: 1... Slab 2... Unsolidified layer 3... Mold 4... Solid-liquid coexistence layer 5... Solidified shell 19'- 8- Procedural amendment (method) 1981 January 14, 2016 Kazuo Wakasugi, Commissioner of the Japan Patent Office1, Indication of the case, Patent Application No. 113642/1982, Name of the invention, Continuous casting method, 3, Person making the amendment, Relationship with the case Patent applicant address: Chiyoda-ku, Tokyo Marunouchi-chome 1-2 record (name A)
Representative of Nippon Kokan Co., Ltd. Minoru Kaneo 4, Detailed description of the invention column in the agent's specification and UArm 7, Contents of the amendment As attached (1) Specification, page 4, Detailed description of the invention column , 10
~11th line, "Figures 4 (a) to (C) ...... are shown." (b
) shows a sectional view between TI and JT in FIG. 3, and (C) shows a sectional view between m and ■ in FIG. ” is corrected. (2) Figure 4 will be corrected in the attached document. 8 List of attached documents (1) One or more corrected drawings

Claims (1)

[Claims] When casting slabs using the continuous casting method, a bulging force is actively applied to the solidified shell between the mold and the liquidus crater end of the slab to reduce the thickness of the unsolidified layer within the slab. 1, and then applying a reduction to the slab between the liquidus crater end and the solidus crater end of the slab, thus reducing the occurrence of center segregation. .