JPH01289552A - Forging press apparatus for round shaped continuously cast billet - Google Patents

Abstract

PURPOSE:To improve the quality of a product by arranging plural steps of two-divided metallic mold to casting direction, setting rolling reduction direction of each metallic mold so as to differ by 90 deg. angle and further regulating radius of curvature in pressed surface of each metallic mold with the specific condition. CONSTITUTION:A forging press apparatus 1 composed of plural metallic molds K1-K5 is arranged in the finishing solidified range of a round shaped continuously cast billet 2, and the metallic molds K1-K5 are set so that rolling reduction direction of each metallic mold mutually becomes 90 deg. angle. Further, the radius ri of curvature in the pressed surface of each metallic mold K1-K4 is set so as to satisfy the inequality. The round cast billet 2 having the radius R0 of curvature is pressed with the first metallic mold K1 and successively, by changing the rolling reduction direction by 90 deg. angle, pressing is executed in order with the metallic mold K2-K4. As stress and strain generated at the previous step are relaxed in order with pressing work at each step, the development of center segregation, crack, etc., is prevented, and the circular cast billet of the desired radius R5 of curvature is obtd. with the finished metallic mold K5. By this method, the quality of the cast slab is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a forging device for a round continuously cast slab having an unsolidified portion inside.

(Prior Art) Center segregation inevitably occurs in slabs manufactured by continuous casting. This is the final solidification region of the slab c, s
, P and other molten steel components become concentrated and appear as positive segregation, and at the same time porosity (small blowholes)
The presence of center segregation and porosity, which often occur, causes a decrease in tensile strength or the occurrence of cracks due to concentrated hydrogen.

In recent years, various measures have been taken to improve these problems. For example, ■ performing electromagnetic stirring or low-temperature casting during casting to disperse segregation, ■ adding a promoting substance that generates unrestricted solidified shells to increase the equiaxed crystal rate and preventing segregation, and ■ high-purity refining. Measures were taken to reduce the components that are likely to segregate, and to prevent bulging that induces center segregation.
That's it.

It has a positive effect. However, it has not yet been possible to prevent the occurrence of porosity and segregation caused by the flow of molten steel at the final stage of solidification. Many methods have been proposed to eliminate porosity and porosity.For example, -61766 Publication), ■ A method of suppressing the movement of the solid-liquid coexisting phase by intermittently pressing the slab with a forging die at a reduction ratio of 0.1 to 0.6 (Tetsu to Hagane Vol. 1.60 (1974) No.
, 5209-S211), (2) The slab is rolled at a rolling ratio of 1.
A method of squeezing out the solid-liquid coexistence phase by reducing the pressure at about 0 (iron and steel V
o, 60 (1974) No.

P857-P884) The gist of these techniques is to reduce the two parallel sides of the slab, prevent center segregation, and flatten the cross section of the slab, improving the internal quality of the slab. This is an excellent product, as it can reduce the load on the subsequent rolling process by improving the rolling process and flattening the rolling process.

However, the techniques described in (1) to (2) above are related to continuous casting of rectangular shapes such as slabs and blooms, and cannot be used for continuous casting of round slabs. Unsolidified part 2b inside by mold l
When the round slab 2 having the shape is pressed in the direction of the white arrow, the round slab 2 deforms into an oval shape as shown in the figure, and loses its purpose as a round slab. Furthermore, strain due to tensile stress is generated in the solidified portion on the short axis side of the elliptical slab 2, and compressive stress C is generated on the long sleeve side. This is because this strain accumulates and causes internal cracks W.

(Problem to be solved by the invention!) The purpose of this invention is to reliably prevent center segregation, porosity, internal cracks, etc. that inevitably occur in round continuously cast slabs, while not impairing roundness. An object of the present invention is to provide a forging device for round slabs.

(Means for Solving the Problems) As a result of repeated studies on prevention of center segregation and porosity in round continuously cast slabs, the present inventors have determined that round slabs having an internal unsolidified part are The present invention has been completed based on the knowledge that if appropriate reduction is performed using a mold having a pressing surface, it is possible to produce a cast slab free from center segregation and porosity.

In other words, the gist of the present invention is "a forging device for pressing the final solidification zone of a round continuous cast slab, which is equipped with a plurality of two-part molds in a plurality of stages in the direction of casting the slab, and The molds are arranged so that they roll in directions that are 90 degrees different from each other.
The radius of curvature r of the pressing surface of each mold is 1.005 Ri≦
A forging device for a round cast slab, characterized in that it is formed to satisfy r1≦1.03Rt (where Ri is the radius of curvature of the round slab to be pressed).

(Function) Hereinafter, the forging press apparatus of the present invention will be explained in detail. FIG. 1 (al is a diagram showing the forging device of the present invention.
In the figure (al), l is a forging device placed in the final solidification zone of a round continuous cast slab, 2 is a round slab having an unsolidified part 2a inside, and 3 is a pinch roll. ,
It is equipped with a mold (kl to ks) consisting of five stages, and these molds are arranged in multiple stages in the casting direction of the round slab 2, and the molds in the former stage and the latter stage are arranged so that the rolling direction differs by 90 degrees. ing. These molds (k, to ks) are moved forward and backward in the directions indicated by arrows in the figure by a pressure device (not shown). The radius of curvature of the slab pressing surface of each mold is as follows (
1) It is formed to satisfy the formula.

1.005R+≦ri≦1.03RI (1) In the formula, Ri is the radius of curvature (m+i) of the slab to be pressed.

In the present invention, the reason why the radius of curvature of the mold is limited to satisfy Equation 11 is that when ri is less than 1.005Rt,
This is because it requires a large number of mold stages, which is not efficient, and causes bite during pressing, resulting in poor roundness, and the ri is 1.03.
This is because when R+ is exceeded, the amount of distortion increases, causing cracks in the slab and causing it to become distorted, resulting in poor roundness. Although the forging press shown in Fig. 1 is an example equipped with a five-stage mold, the number of stages is not limited to this, and the number of stages is determined based on the internal quality improvement target of the round slab and the final slab size. It should be determined by

Next, a method of forging a round slab 2 using such a forging device 1 will be described. Figure 1 et al.) are shown in Figure 1 (
It is a diagram showing the X-X cross section of a), and this diagram shows a round slab 2 having a radius of curvature R0, which is cast in a continuous casting facility and has an unsolidified part 2a inside, and a pressing surface having a radius of curvature r1. 1st
The state after being pressed into the stepped mold in step 1 is shown. This first
The positive pressing surface curvature radius rl of the stepped mold is determined by the above formula (1), that is, 1.00SR, ≦rt≦1.03R, (however, Ro
is the radius of curvature of the round slab 2), so after pressing, the cross section of the round slab 2 has a radius of curvature R on the long sleeve side, a radius of curvature r on the short axis side, as shown in the figure. becomes an oval shape.

Strain due to compressive stress c1 occurs at the molten steel interface point A1 of the unsolidified portion 2a of this elliptical slab 2, and tensile stress also occurs at point 81.
However, since this forging press 1 has molds arranged in multiple stages, by reducing the amount of reduction in each stage, it is possible to prevent the occurrence of internal cracks due to distortion.

FIG. 1(C) is a diagram showing the Y-Y cross section of FIG.
This shows a state in which the second stage mold is pressed with a different angle of 0 degrees. The radius of curvature r2 of the pressing surface 8 on the second stage mold is also the same as (
1) Since it is formed based on the formula, it can be used as a mold! As shown in the figure, strain occurs at point A8 due to tensile stress L8, and strain occurs at point 81 due to compressive stress c2. The strain caused by the tensile stress at point A2 caused by pressing 2 in the second stage mold [,] is the strain caused by A1 caused in the first stage mold by 1.
It acts to offset the strain caused by the compressive stress c1 at the point, and also
The strain caused by the compressive stress c2 at two points relieves the strain caused by the tensile stress t1 at 81 points caused by the previous mold. One of the major features of the present invention is that the strain that causes internal cracks in the slab can be offset and eliminated in this way.

The third and fourth stages are also sequentially pressed using molds ks and ka having radii of curvature formed based on the above-mentioned formula (1).

FIG. 1(d) is a cross-sectional view taken along line 2-2 in FIG. 1(a), and shows the state of the slab after being pressed into the fifth stage mold. This fifth stage mold is a mold for forming a slab, and a perfectly circular slab having a target slab size (radius R) is manufactured using this mold. Note that, due to the reduction in cross section due to mold pressing, a metal flow is generated and the slab 2 is elongated in the casting direction, so it is preferable to pull it backward with the pinch rolls 3 so as to synchronize with this elongation.

(Example 1) Molten steel of 545G carbon steel was poured into a round mold with a length of 900 m at a casting speed of 2.4 m/win, and the initial slab diameter was 2.
A round slab of 00III11 was manufactured. Then, a position approximately 5 mm away from the outlet of the mold (with a central solid phase ratio of 0.2 to
0.67), a forging device equipped with a five-stage die as shown in Figure 1 was installed, and forging was performed at various reduction rates to examine the internal quality and roundness of the slab. . The results are shown in Table 1. The radius of curvature of the pressing surface of the mold at each stage is r +
: lol, 5mm, r g;99.5m-1r,;9
7.5+*m, r 4; 95.51111% r s
; 93.5 mm, and the slab surface temperature during forging was 100
The temperature was 0 to 1100°C.

In Table 1, test 1 is a case in which the apparatus of the present invention was not used, and center segregation, porosity, and internal cracks occurred. Tests 2 to 9 are cases in which the rolling reduction ratio is varied from 4 to 10% using the apparatus of the present invention. From this, it can be seen that the center segregation is improved as the rolling reduction rate increases, and that the addition of rolling reduction can also prevent the occurrence of porosity and internal cracks. On the other hand, although the roundness deteriorated slightly due to rolling reduction, a roundness of 98% or more was obtained, which is within the permissible size range for a continuously cast product.

The table excludes cases where the rolling reduction is less than 4% and more than 10%, but if it is less than 4%, porosity cannot be completely eliminated, and if it exceeds 10%, internal cracks may occur. , the quality of the slab deteriorated due to the occurrence of surface defects. In Table 1, the reduction ratio is the value obtained by dividing the amount of radius reduction due to all stages of pressing by the radius of the initial Xll slab, 100 + am, and the center segregation index is a comparison based on the segregation amount when no reduction is applied as 1. , the roundness is the value obtained by dividing the minimum radius of the slab by the maximum radius after pressing with a five-stage mold.

(Comparative Example 1) Initial diameter 2001 manufactured under the same casting conditions as Example 1
The slab is forged using a mold having a radius of curvature smaller than the range defined by the present invention (rt<1.005 Rt),
The internal quality and roundness of the slab were investigated. The radius of curvature of the mold used is
rt; 100.3 amSrg; 97.8+amSr*
;95.3s+m, r a;92.8mmSr s
; It was 90.3 mm.

The results after forging are shown in Table 2. Tests 10 to 13 in the same table
As can be seen, no porosity or internal cracks occurred, but there was some bulging, and the roundness was 94.5.
It was as low as ~96.3%, which did not meet the dimensional tolerance required for round slabs.

(Comparative Example 2) Initial diameter 200m manufactured under the same casting conditions as Actual Example 1
The internal quality and roundness of the slab were evaluated by forging the slab with a mold having a radius of curvature exceeding the range defined by the present invention (rt>1.03Rt). The radius of curvature of the mold used is r
t;104. oa+m, rz; 101.5mm, r
x;99. Oa+mSr n; 96.5m+m, r
s:94. It was omm.

The results after forging are shown in Table 3. Test 1 in Table 3
According to Nos. 4 to 17, porosity did not occur in any case, but internal cracks did occur. Also, the roundness is 98%
was not achieved and was not within the allowable tolerances.

Table 2 Table 3 (Effects of the Invention) As explained above, if the forging press of the present invention is used, it is possible to produce a round shape with good quality, with improved center segregation, porosity, internal cracks, etc., without impairing roundness. Shaped slabs can be manufactured.

[Brief explanation of the drawing]

FIG. 1(a) is a front view of the main parts of the device of the present invention, first view (b)
is a diagram showing the XX cross section of FIG. 1(a), FIG. 1(C) is a diagram showing the y-y cross section of FIG. 1(a), and FIG. 1(d) is a diagram showing the XX cross section of FIG. ), and FIG. 2 is a schematic cross-sectional view showing a state in which a round slab is pressed by a conventional device. 1 is a forging device, 2 is a round slab, and 3 is a pinch roll.

Claims (1)

[Scope of Claims] A forging device for pressing the final solidification zone of a round continuously cast slab, the device being equipped with a plurality of stages of two-part molds in the direction of casting the slab, and the molds of each stage are in contact with each other. 1. A forging device for a round continuously cast slab, characterized in that the molds are arranged so as to press down in directions different by 90 degrees, and the radii of curvature of the pressing surfaces of the respective molds satisfy the following formula. 1.005R_i≦r_i≦1.03R_ir_i; Radius of curvature of mold pressing surface (mm) R_i; Radius of curvature of pressed slab (mm)