JPH02121760A - Method for continuously squeezing cast slab in continuous casting - Google Patents

Abstract

PURPOSE:To prevent the development of surface flaw on a product by squeezing the last solidified zone of a strand with one pair of anvils having flat squeezing part and sandwiching the cast slab with upper and lower thereof while continuously casting the cast slab strand having the projecting part at center part zone in width direction. CONSTITUTION:The cast slab strand providing the projecting part having width corresponding to the width of molten steel, which is not yet solidified, and thickness (a) at the time of optimum squeezing condition at the center part in the width direction, is cast. This is squeezed with the anvils 2 having flat squeezed working surface at the squeezing part. By this method, in the cast slab strand after squeezing, the recessed part is not formed, and then, even if the projecting part or the recessed part is formed, in the rolling process after that, by rolling this with the rolling reduction rate to be possible to cancel the projecting part and recessed part, the surface flaw can be avoided.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a continuous forging method for a slab strand in continuous casting, and a method for eliminating surface flaws that are likely to occur during the rolling process after forging of the slab strand. This is an attempt at effective avoidance.

(Prior art) As a measure to reduce center segregation that inevitably occurs in slab strands obtained by continuous casting, for example, Japanese Patent Laid-Open No. 62
As disclosed in Japanese Patent No. 81255, attempts have been made to apply partial forging to the unsolidified portions of cast slab strands.

(Problems to be Solved by the Invention) Although the technology disclosed in the above publication has the advantage of being able to effectively reduce center segregation of slab strands without causing internal cracks, etc., on the other hand, when the amount of processing during forging is large, There has been a problem in that surface flaws caused by forging impressions remain on products that have undergone the rolling process.

Here is the reduction amount δ that does not leave surface scratches on the final product after rolling.
Assuming that the forging pressure amount is S, based on past results, δ≧1. IS
However, the reduction amount δ is regulated by the product dimensions and product shape, so if the above conditions are not met, it is necessary to take extra effort such as grinding or scarfing, or to sacrifice center segregation of the slab strands. I guess I should also reduce the forging pressure amount S.
In the former case, the yield was reduced, and in the latter case, the quality was reduced.

It is an object of the present invention to propose a forging method that can advantageously avoid the conventional problems that occurred when forging a slab strand obtained by continuous casting, as well as improving center segregation.

(Means for Solving the Problems) The present invention continuously casts a slab strand having a convex portion in the central region in the width direction, and processes the final solidification region of the slab strand by forging with a flat rolling part. This is a continuous casting pressure method for a slab strand in continuous casting, characterized in that rolling is performed using a pair of anvils having surfaces and sandwiching the pass line of the slab strand above and below. In this invention, the thickness a of the convex portion of the slab strand is preferably set to δ with respect to the required forging pressure amount S and the rolling reduction amount δ after forging.

(Function) In this invention, first, in continuous casting, the width of the unsolidified molten steel under the optimum forging conditions is measured in the central region in the width direction as shown in Fig. 1. A slab strand with a convex portion having a corresponding width and wall thickness a is cast, and this is rolled into a rolled part as shown in FIGS. 2(a)(b) or 3(a)(b), for example. The slab is rolled down using an anvil with a flat forging surface, but at this time, no recesses are formed in the slab strand after forging, and even if recesses or protrusions are formed, subsequent rolling In the process, surface flaws are advantageously avoided because the material is rolled with a reduction amount that can eliminate the recesses and projections.

Here, in this invention, if a≧S, for example, as shown in FIG. 4 (a
) When the pressure is reduced by S in the forging process from the state shown in ), the thickness of the convex portion becomes (a-S)/2 as shown in the same figure et al.). This is then rolled, as shown in Figure (C), in order to eliminate the protrusions, the thickness of the protrusions must be 1.1
Since it is sufficient to apply twice the rolling reduction, the required rolling reduction amount δ is determined as follows.

δ≧1.1(a-s) By solving the above equation for a and providing a convex portion, ag
o, therefore, the thickness a of the convex portion may be within the following range.

δ If a<S, for example, if the state shown in FIG. 5(a) is reduced by S by forging press, a groove of (s−a)/2 on one side is formed as shown in the axis of FIG. 5(a). This is rolled to reduce the amount δ
In order to erase the grooves, it is sufficient to apply a reduction of 1.1 times the groove depth, so δ≧1.1(s-a) Solving the above equation for a and using the condition that a<S, rolling The thickness a of the convex portion capable of erasing the groove may be within the following range.

Figure 6 shows the remaining concavities or convexities caused by forging as a measure to prevent surface flaws caused by forging during continuous casting.
Results of investigating the relationship between C (protrusion amount for convex shape, groove depth for concave shape) and rolling reduction amount δ in rolling after forging using the actual product (S45C) and plasticine. This is a graph showing. From FIG. 6 above, it is clear that at least δ/S≧1.1, that is, δ≧1. With IS, even if concave or convex portions are left on the slab strand during forging, the concave or convex portions can be completely eliminated by subsequent rolling.

If the shape is such that the unsolidified molten steel can be pressed during forging, the convex portion of the slab strand 1 will be, for example, as shown in Fig. 7(a).
As shown in (b) and (c), it may be provided only on one side of the strand 1, or it may be curved.

(Example) In the central area in the width direction, wall thickness a: 20 mm, width L: I50
Between, θ: 45° and wall thickness a: 50 mm, radius L: 1
50 n+m, θ: has a convex portion of 45°, thickness t:
300III11, two types of slab strands with width H: 400 mm (steel type: 345C, see Figure 8 (a)
) at a drawing speed of 0.9 m/min, the final solidification zone of each strand was cast using an anvil with a flat rolling part and a forging surface with a width of 180 ml (see Figure 9). It was pressed down. The obtained slab was then rolled according to formulas (1) and (2) above to eliminate the concavities or convexities caused by the above-mentioned forging process, and then the presence or absence of surface flaws on the slab surface and center segregation were investigated. . The result is a slab with a normal cross-sectional shape (thickness t: 300 m,
Table 1 shows the results of the investigation when casting a width H: 400+nm (see box 8).

Table 1 It was confirmed that when forging according to the present invention was performed, no surface flaws were generated due to the forging, and center segregation could be advantageously reduced.

(Effects of the Invention) According to the present invention, 1) Even when the required forging pressure is large, there are no concave indentations caused by forging on the slab strand, or the amount of indentation can be reduced, so surface flaws occur on products that have undergone the rolling process. There is no risk of it happening.

2) By adding recesses to several pieces, the thickness of the cast slab after forging can be increased, so a product of a larger size can be produced compared to when rectangular cast slabs are forged.

3) Since the short side of the solidified part of the slab strand is not forged, the rolling blade is small and the equipment cost can be reduced.

4) After forging, the cross-sectional shape of the slab strand can be rectangular, or it can be forged to a slab with an unevenness within the range that does not interfere with the rolling process, allowing new measures such as modifying equipment in the rolling process. becomes completely unnecessary.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a slab strand suitable for use in the present invention, FIGS. 2(a), (b) and 3(a), (b) are diagrams showing the procedure for forging the slab strand, Figure 4 (a) (b) (C) and Figure 5 (a) (
b) (C) is an explanatory diagram of the forging procedure of the slab strand and the subsequent rolling procedure, and Figure 6 shows the remaining amount C after forging.
7(a), (b), and (C) are schematic cross-sectional views of other slab strands suitable for use in the present invention. ) is a schematic cross-sectional view of a slab strand, and FIG. 9 is a schematic cross-sectional view of an anvil.

Claims (1)

[Claims] 1. While continuously casting a slab strand having a convex portion in the central region in the width direction, the final solidification region of the slab strand is formed by forming the casting with a forging surface with a flat rolling part. A method for continuous casting of slab strands in continuous casting, characterized by rolling down the pass line of one strand using a pair of anvils that sandwich the pass line above and below. 2. When the thickness a of the convex part of the slab strand is the required forging pressure amount S and the rolling reduction amount δ after forging pressure, {if a≧S: 0
The continuous forging method according to claim 1, wherein <a≦δ/1.1+S a<S: S−δ/1.1≦a<S}.