JP2548640B2 - Quality guarantee method for seam slab of different steel types - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quality guarantee method for different steel grade seam slabs, which minimizes seams of different steel grades in continuous casting of different steel grades in continuous casting.

[0002]

2. Description of the Related Art In continuous casting, it is desirable that the casting speed be maintained at a constant casting speed, but due to the change of the ladle and other conditions, it is inevitable that the casting speed varies in continuous casting of different steel types.

[0003]

Conventionally, there is no effective means for the fluctuation of the casting speed, and the manufacturing process conditions are set in consideration of the quality variation of the cast piece including the fluctuation.

For example, in the continuous casting method for different steel types using a conventional mixed-prevention iron plate, since the cut-off length of the seam portion is constant, if the aim is to prevent internal defects due to the pipe, the yield will be reduced, and the yield will be increased. If it is aimed at improvement, internal defects will occur due to the pipe, and effective quality assurance has been a problem.

The present invention provides an effective quality assurance method that solves the above-mentioned problems in a continuous casting method of different steel types using an anti-mixing iron plate in continuous casting of steel.

[0006]

Means for Solving the Problems The present invention is a continuous casting method of different steel types using a mixing prevention iron plate in a continuous casting method of a steel, which is poured from a tundish into a mold through a dipping nozzle, and a slab is pulled out by a pinch roll, This is a quality assurance method for seam slabs of different steel types, in which the pipe length is calculated from the following formula 1 from the stop time of the pinch rolls and the cut-off length of the seam is determined.

[0007]

## EQU00001 ## h = 3 Cbv²t / 4K²  However, h: pipe length (m) C: effective reduction gradient b: slab height (m) v: casting speed (m / min.) K: solidification coefficient (m / min)^1/2) T:Pinch roll stop time (Min)

[0008]

EXAMPLES Examples of the present invention will be described below together with their functions.

FIG. 4 is a drawing showing an example of a continuous casting method of different steel types using a mixing prevention iron plate. 1 is a tundish, a container for injecting the molten metal into the mold, 2 is an immersion nozzle, which is a nozzle for injecting the molten metal into the mold,
3 is a mold.

Reference numeral 4 denotes a mixing prevention iron plate, which is used for the purpose of preventing mixing of the cast pieces 5a and 5b of different steel types. Further, the cast slabs 5a and 5b are slabs having different components. 6
Is a pinch roll for pulling out the slabs 5a, 5b.

From diversification of product needs and securing of productivity,
The continuous casting ratio of different steel types tends to increase, and effective quality assurance of joint pieces is a major issue.

Molten steel is poured from a tundish 1 through a dipping nozzle 2 into a mold 3, and a slab is pulled out by a pinch roll 6, which is a different steel type of a slab 5a, 5b using an iron plate 4 for preventing mixing in a continuous steel casting method. In continuous casting, it is important to estimate the length of the pipe generated at the seam.

FIG. 1 shows an example of a measurement result of a pipe generated at a seam.

In FIG. 1, 11 is a mixing prevention iron plate, 12 is a pipe, and 13 is a cavity, and both the pipe 12 and the cavity 13 are internal defects generated by solidification shrinkage of a cast piece.

The pipe 12 is generated just below the mixing prevention iron plate 11, and a fine cavity 13 exists at the tip thereof. The results of the ultrasonic probe test and the results of the inspection of the cut surface are in good agreement, and here, the cavity 1 farthest from the iron plate 11
The distance to 3 was defined as the pipe length.

In FIG. 1, the horizontal axis indicates the length direction of the slab, and the pipe length is about 1.6 m. The length of the pipe is not always constant and changes depending on the pinch roll stop time, and the present invention is that the pipe length can be easily estimated by managing the pinch roll stop time.

FIG. 2 shows the relationship between the pipe length and the pinch roll stop time when the iron plate is inserted.

In FIG. 2, the horizontal axis represents the pinch roll stop time (minutes) and the vertical axis represents the pipe length (m). The pinch roll stop cannot be avoided due to the insertion of the iron plate in the continuous casting method of different steel types using the mixing prevention iron plate, and this pipe length increases with the pinch roll stop time. This is considered to occur because the solidification shrinkage of the slab is not compensated by the light reduction when the pinch roll is stopped.

The volume change ΔV due to the slight pressure reduction during the time t is expressed by the equation 2.

[0020]

(2) ΔV = vCwLt

Assuming that this is in equilibrium with the solidification contraction, the pipe volume ΔV 'at time t and when the pinch roll is stopped is expressed by equation 3 assuming that the pipe is a quadrangular pyramid.

[0022]

## EQU3 ## ΔV '= wbh / 3

Equations 2 and 3 are equally placed and L to (b / 2K) ²
Considering v, the pipe length h is expressed by the equation 4.

[0024]

## EQU4 ## h = 3 Cbv ² t / 4K ²

In equations 2 to 4, v is the casting speed, C is the effective light reduction gradient, w is the slab width, K is the solidification coefficient, L is the effective light reduction distance, and b is the slab height.

Next, an example of estimating the pipe length of the seam slab in continuous casting of different steel types will be described.

In the explanatory views of FIGS. 3A and 3B, the length of the pipe 12 adjacent to the mixing prevention iron plate 11 increases with the stop time of the pinch roll 6. It is considered that this is because the solidification shrinkage of the slab 5b is not compensated by the light reduction when the pinch roll is stopped.

In the figure, L is the effective light rolling distance, C
Is the effective light reduction gradient, and v is the casting speed.

For the sake of simplicity, the effective light pressure reduction gradient C (m
/ M) between the rolls of the slab 5b at a constant casting speed V, the indentation amount .delta.
Becomes

[0030]

(5) δ = C · v · t

Next, consider the inspection surface 14 shown by the dotted line in FIG. The volume change ΔV due to the deformation of the cast slab 5b in the inspection surface 14 during the time t is represented by the formula 6.

[0032]

(Equation 6)

Next, the pipe volume ΔV 'is expressed by the equation 7 assuming that the pipe is a quadrangular pyramid.

[0034]

## EQU7 ## ΔV '= wbh / 3

Here, h is the pipe length, and b is the slab thickness (height).

When the pipe is stopped for a period of time t, it is caused by solidification shrinkage, but if it is assumed that the solidification shrinkage volume is completely replenished by deformation under light pressure during normal casting, equations (6) and (7) are placed equally. It is represented as the number 8.

[0037]

(Equation 8)

On the other hand, from L = v · t _S , b / 2 = K√t _S

[0039]

[Formula 9] L = v (b / 2K) ²

Substituting equation 9 into equation 8 yields equation 10.

[0041]

[Equation 10]

If the actual pipe length is calculated under the following conditions using the equation 10, the equation 11 is obtained. C = 1.0 × 10 ⁻³ (m / m) b = 0.3 (m) v = 0.8 (m / min) K = 25 × 10 ⁻³ (m / min ^1/2 )

[0043]

[Equation 11]

[0044]

As shown in the examples of the present invention, the formula 4 is applied to calculate the conditions of the present experiment, and the results are shown in FIG. 2 (shown by the dotted line). It turns out that it agrees well with. Therefore, based on these results, by calculating the pipe length from the stop time of the pinch roll to determine the cut-off length of the joint, it is possible to easily minimize the dissimilar steel type joint and reduce the joint waste. Preventing defects and establishing quality assurance of the seam,
The yield of the slab can be improved.

[Brief description of drawings]

FIG. 1 is a drawing showing an example of a pipe measurement result in continuous casting of different steel types using a mixing prevention iron plate.

FIG. 2 is a drawing showing a relationship between a pinch roll stop time and a pipe length at a joint portion of different steel types.

3A and 3B are explanatory views for estimating a pipe length, FIG. 3A is a schematic side sectional view, and FIG. 3B is an explanatory view of a reduction gradient.

FIG. 4 is a schematic side view showing an example of continuous casting of different steel types using a mixing prevention iron plate.

[Explanation of symbols]

 1 Tundish 2 Immersion Nozzle 3 Mold 4, 11 Mixing Prevention Iron Plate 5a, 5b Cast Piece 6 Pinch Roll 12 Pipe 13 Cavity 14 Inspection Surface

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiko Kubo 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corp. Kimitsu Works (56) Reference JP 63-174769 (JP, A) JP Sho 58-53359 (JP, A)

Claims (1)

(57) [Claims] 1. A casting from a tundish through a dipping nozzle.
Of the steel which is poured into the mold and the slab is pulled out by the pinch roll 6.
Continuous casting of dissimilar steels using mixing prevention iron plate in continuous casting method
Method, the pipe length is calculated from the stop time of the pinch roll.
Different steel that is calculated from the following formula 1 and determines the cut-off length of the seam
Seed seam slab quality assurance method. ## EQU00001 ## h = 3 Cbv²t / 4K²  However, h: pipe length (m) C: effective reduction gradient b: slab height (m) v: casting speed (m / min.) K: solidification coefficient (m / min)^1/2) T:Pinch roll stop time (Min)