JP2937625B2 - Continuous casting method of slab by unsolidified large pressure reduction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously reducing the unsolidified end of a slab drawn from a continuous casting mold by using a forging device so that a concentrated steel of an impurity solute is formed in a diffusion region. The present invention relates to an improvement in a continuous casting method of cast slabs under unsolidified large pressure for preventing the center segregation of impurity solute elements by diffusing into molten steel.

[0002]

2. Description of the Related Art In the slab obtained by continuous casting of steel, so-called center segregation is inevitably generated. To reduce or avoid adverse effects, the steel is drawn from a continuous casting mold through a secondary cooling zone and moved. It is known that it is effective to apply a reduction in the thickness direction of the slab to the slab near the unsolidified end (crater end). For example,
JP-132247 discloses that in continuous casting of steel, an electromagnetic stirring action is applied to the unsolidified portion before the solidification complete point of the slab to make the unsolidified portion near the solidification complete point an equiaxed crystal, thereby solidifying the slab. A continuous casting method is disclosed in which the end portion is locally reduced by a roll to forcibly form a solidification completion point.

Further, Japanese Patent Publication No. 3-66057 discloses that the unsolidified end of a slab drawn from a mold is pressed down by a pair of upper and lower dies, and is brought close to each other in the process of expansion and contraction of a hydraulic cylinder for driving down via a lever. A slab forging device for continuously performing forging by applying a reduction in the thickness direction at the center in the width direction of the slab by repeating the separation is disclosed. According to this forging device, impurity solute elements (P, S) segregated at the unsolidified end of the slab
, Etc.), the central part in the width direction is locally greatly reduced by the forging force with a reduction exceeding the thickness of the unsolidified layer, whereby the impurity solute element segregated in the central part is diffused into the molten steel in the diffusion region. Therefore, center segregation can be reduced.

[0004]

In the prior art, in which the roll is reduced at the unsolidified end of the slab, a local load occurs in which the roll comes into contact with the slab in a state close to linear contact. There is a risk that the amount of reduction cannot be increased because there is a risk of causing internal cracks in the slab due to solidification shrinkage and bulging of the slab, and there is a problem that center segregation cannot be prevented under light pressure.

[0005] In the case of using the latter mold, in which the unsolidified end of the slab is greatly reduced, the impurity solute element segregated in the center is diffused into the diffusion region, so that the center segregation can be prevented. When a large pressure is continuously applied to the non-solidified terminal portion, the impurity solute element of the concentrated molten steel that has been forcibly discharged without solidifying at the non-solidified terminal portion gradually accumulates in the diffusion region.

[0006] As the length of the slab, which greatly reduces the unsolidified end portion by using such a mold, increases, the impurity solute concentration in the diffusion region gradually increases. As a result, it becomes difficult to produce slabs of stable quality,
In particular, since the impurity solute element having a small equilibrium dispersion coefficient such as P and S has a more prominent tendency to be concentrated, P and
There is a problem that internal cracks are easily generated only by minute bulging of the slab due to an increase in the concentration of S.

[0007] The present invention solves the problems of the prior art,
When reducing the unsolidified end of the slab using a mold,
It is an object of the present invention to provide a continuous casting method of cast slabs under unsolidified large pressure, which can prevent impurity solute elements from accumulating in a diffusion region and adversely affecting cast slab quality.

[0008]

In order to prevent accumulation by diffusion of impurity solutes into a diffusion region when a non-solidified end portion of a slab is largely reduced by forging, the present inventors have proposed a method in which a diffusion region is formed at an appropriate timing. The inventors of the present invention have made intensive studies focusing on the fact that they are separated from each other to separate them from other parts, and as a result, have reached the present invention. The gist of the present invention is as follows.

According to the present invention, an unsolidified end portion of a slab drawn from a continuous casting mold is continuously subjected to a large pressure reduction using a forging device so that a concentrated molten steel of an impurity solute element is introduced into a molten steel in a diffusion region. In a continuous casting method of cast slabs under unsolidified large pressure that diffuses to prevent center segregation of impurity solute elements, impurity solute elements are diffused and accumulated in molten steel in the diffusion region, and the concentration limit of impurity solute elements is increased. Set the length of continuous forging slab until immediately before reaching the value, the slab length under large pressure by continuous forging, when the set length reaches the set length, stop forging and stop the impurity solute element concentrated molten steel accumulated in the diffusion region Through the forging of the slab, and then consolidate the concentrated molten steel in which impurity solute elements accumulated in the diffusion region in the slab have reached near the permissible limit by restarting the large reduction by forging pressure of the slab. Characterized by Coagulation is a continuous casting method of the slab by a large pressure.

In the above method for continuous casting of cast slabs by unsolidified large reduction, the length of the cast slab which is not reduced by forging is set to be longer than the length of the diffusion region of the impurity solute element-concentrated molten steel. It is preferable that the length of the slab, which is safe and is greatly reduced by the forging pressure, is determined so that the impurity solute element which has a remarkable tendency to concentrate is below the allowable limit.

[0011]

The present invention will be described below in detail with reference to the drawings. FIG. 1 schematically shows a continuous casting facility provided with a continuous forging device. The slab 2 is supported on a support roll 3 from a mold 1 and pulled out using a pinch roll 5 and disposed in the continuous forging device. Cast slab 2 with a pair of upper and lower molds 4
In the state where the unsolidified end portion (crater end) is continuously subjected to forging work, the concentrated molten steel A in which impurity solute elements such as P and S, which adversely affect the center segregation, are formed by the mold 4 Due to the large pressure, the solidified shell of the slab 2 is continuously pressed to the sound slab with reduced center segregation.

However, such a slab 2 is
When the unsolidified end portion large pressure reduction is continuously performed, the concentrated molten steel of the impurity solute element discharged without solidification is accumulated in the diffusion region B due to the forging pressure, and the continuous reduction length of the slab 2 is increased. As described above, the concentration increases accordingly.

Therefore, in the present invention, the impurity solute elements such as P and S are diffused and accumulated in the molten steel in the diffusion region B, and the continuous forging pressure of the slab 2 immediately before reaching the concentration limit value of the impurity solute element is reached. Set L _M. Then Mejaroru 6 depending on whether pressure is reached in the continuous rolling length L _M against the slab 2 with a die 4 while measuring the length, or once passing at discontinue forged with a die 4 non forging just before. In other words, the forging pressure is stopped until the non-forging length _{LN including} the diffusion region (length 1), which has been concentrated to near the allowable concentration limit due to the accumulation of the impurity solute element, passes through the mold 4.

After the slab having the non-forging pressure length L _N has passed, large pressure reduction by forging of the slab is resumed by using the mold 4 to increase the concentration of the diffusion region B in which the impurity solute element is close to the allowable concentration limit. The molten steel can be contained in the slab 2 having a non-forging length _LN . Therefore, the impurity solute element concentration in the diffusion region B at the time of resuming a large reduction by forging the slab 2 by a die 4 is lowered, a large reduction by continuous forging until again reaching the continuous forging length L _M It can be carried out.

When the slab is continuously reduced by forging using a metal mold under constant casting conditions, the length of the slab by forging and the segregation of P and S in the center of the slab after forging are reduced. The degrees are shown in FIG. 2 and FIG. 2 and 3
As shown in the figure, within the range of the reduction length shown in both figures,
The degree of segregation of P and S increases almost linearly with the reduction length. 2 and 3, the allowable limit value of the segregation degree of the slab is C / Co (P) for P and C / C for S.
o (S), and the reduction lengths required to keep it below this allowable limit are L _P and L _S , respectively.
The shows a ratio L / L _S and L _p or L _S.

Therefore, when L _p ≧ L _S , L _S , L _{S
When p} ≧ L _S , the maximum length L that continuously reduces L _{p
As the M} , the reduction length reaches this maximum length (L _M ), or immediately before the reduction, the reduction is temporarily stopped, and the non-reduction length L _N that is not reduced beyond the length 1 of the diffusion region B of the concentrated molten steel is measured. As described above, a slab portion is formed and re-reduction by forging is started again.

The slab 2 is cut to a predetermined length by a cutting torch 7, and a continuous rolling length L _M of the slab 2 from the start of forging by the die 4 on the slab using the measuring roll 6. And the non-rolling length _LN is measured, and the slab 2 is cut by the cutting torch 7 so as to have the non-rolling length _{LN including the} diffusion region B, and this portion is treated as scrap or as a rejected product. I do.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The thickness used as a material for carbon steel S53C for machine structure is obtained by using a continuous casting equipment of a curved one-point straightening system shown in FIG.
Production of a continuous cast slab having a size of 400 mm and a width of 560 mm was carried out in accordance with the method of the present invention, and the conventional method was carried out for comparison.

The casting conditions of the present invention are as follows. Casting speed: 0.51 m / min forging die installation position: 26m reduction amount from the meniscus of the mold: 110 mm Casting _{Length: 80m L p = 80m: C} / Co (P) = 1.0 L S = 90m: C / Co ( S) = 1.0 Set rolling length L _M for continuous forging pressure: 40 m Set length for non-rolling L _N : 2.5 m Degree of segregation of P and S at the center of cast slab obtained by continuous casting performed under the above conditions Are shown in Table 1.

[0020]

[Table 1]

As shown in Table 1, in the conventional method, the impurity solute elements P and S continue to accumulate in the diffusion region, so that the segregation degree of P and S at the center of the slab increases as the reduction length of the slab increases. When the distance from the bottom of the slab is 70 m, the degree of segregation of both P and S is 1.1, exceeding the allowable limit.

On the other hand, in the present invention, when the set reduction length L _M = 40 m by continuous forging is reached, the set non-roll reduction length L _N
= 2.5, the concentrated molten steel of the impurity elements P and S is sealed and shut off, so that the segregation degree of P and S is stabilized and the allowable concentration limits C / Co (P) and C / Co (S) are set to 1.0. It is possible to produce a cast slab of good quality with less center segregation which can be suppressed as follows.

[0023]

As described above, according to the present invention, the concentrated molten steel in which the impurity solute element accumulated in the diffusion region in the slab is close to the permissible limit value is sealed off in the slab and cut off. At the stage where the reduction is resumed, it is possible to restart without being affected by the reduction, and it is possible to stably produce a high quality cast slab with little center segregation.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a continuous casting facility provided with a continuous forging device.

FIG. 2 is a diagram showing the relationship between the reduction length (L / L _p ) of a slab and the degree of segregation of P.

FIG. 3 is a diagram showing a relationship between a reduction length (L / L _s ) of a slab and a segregation degree of S.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Slab 3 Support roll 4 Die 5 Pinch roll 6 Measure roll 7 Cutting torch

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshinori Matsukawa 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref. Kawasaki Steel Corporation Mizushima Works (56) References JP-A-63-49353 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B22D 11/128 B22D 11/20

Claims (3)

(57) [Claims] An unsolidified end portion of a slab drawn from a continuous casting mold is continuously subjected to large pressure reduction using a forging device.
In a continuous casting method of casting slabs under unsolidified large pressure for preventing concentrated segregation of impurity solute elements into molten steel in a diffusion region to prevent central segregation of impurity solute elements, the impurity solute element is contained in the molten steel in the diffusion region. Diffusion and accumulation, set the continuous forging slab length immediately before reaching the permissible limit value of the concentration of impurity solute elements, stop the forging pressure when the slab length under continuous forging under large pressure reaches the set length The impurity solute element accumulated in the diffusion region is passed through the molten steel without reduction, and thereafter, the large reduction by the forging pressure of the slab is restarted to thereby reduce the impurity solute element accumulated in the diffusion region in the slab. A continuous casting method of slabs by unsolidified large pressure, wherein a concentrated molten steel having a temperature close to an allowable limit value is contained. 2. The casting under unsolidified large reduction according to claim 1, wherein the length of the slab which is not reduced after forging is stopped is longer than the length of the diffusion region of the molten steel enriched with impurity solute elements. Continuous casting of pieces. 3. The slab according to claim 1, wherein the length of the slab which is greatly reduced by forging is determined so that the impurity solute element having a remarkable concentration tendency is equal to or less than an allowable limit value. Continuous casting method.