JP3056582B2 - Slab rolling method in continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method of steel for obtaining a slab of excellent quality.

[0002]

2. Description of the Related Art By rolling a continuous cast slab including an unsolidified portion, it is possible to obtain a high-quality slab without segregation and porosity.
P137-146.

[0003] However, if the rolling conditions are not appropriate under the unsolidified rolling, internal cracks are generated at the solidification interface, which deteriorates the internal quality. Therefore, it is necessary to find appropriate rolling conditions. The above-mentioned literature indicates that internal cracks can be prevented by pressing the upper and lower solidified shells by pressing, and for that purpose, a rolling reduction of 30% or more is required. It is thought that factors other than the rolling reduction also affect the compression of the solidified shell, but the deformation behavior of the solidified shell is complicated, and no factors other than the rolling reduction have been clarified.

[0004]

In the prior art, it has been shown that the reduction ratio is set to 30% or more as a condition for pressing the solidified shell. However, when trying to obtain slabs of different sizes using the same continuous casting machine, it is necessary to change the rolling reduction of the rolling mill installed at the rear end of the continuous casting machine,
% Or more cannot be secured. That is,
The prior art has a problem in that it cannot be applied to a process of manufacturing slabs of a plurality of sizes due to a change in the draft.

[0005] The present invention solves the above-mentioned problems, changes the rolling reduction of the rolling mill at the rear end of the continuous casting machine, and compresses the solidified shell in the process of manufacturing slabs of a plurality of sizes by pressing the solidified shell. The purpose is to obtain high quality slabs.

[0006]

The gist of the present invention is to provide a method of installing a rolling mill at the rear end of a continuous casting machine and rolling down a slab including an unsolidified portion, in which a non-solidification ratio f ₀ immediately before rolling is reduced.
And the cooling rate of the slab is adjusted so that the rolling reduction r satisfies f ₀ ≦ 1.32r-21.0. However,
f ₀ is the unsolidified rate (%) immediately before rolling f ₀ = d ₀ / H ₀ × 1
00, d ₀ are the unsolidified thickness (mm) immediately before rolling, H ₀ is the slab height (mm) before rolling, and r is the slab draft (%) r = (H ₀
−h) / H ₀ × 100, where h is the slab height after rolling (mm)

Hereinafter, the present invention will be described in detail. The inventors studied the crimping conditions of the solidified shell by simulation using the rigid-plastic finite element method. First, the inventors examined the effect of the initial unsolidified rate on the pressure bonding of the solidified shell. Table 1 shows the simulation conditions. 220
A simulation was performed on a case where a slab of × 220 mm was rolled down with a flat roll having a diameter of 700 mm.

[0008]

[Table 1]

FIG. 3 shows a case where a slab of 220 × 220 mm is rolled by flat rolls,
2 shows the relationship between the unsolidified rate and the compression of a solidified shell. As is clear from FIG. 3, even when the rolling reduction is less than 30%, if the unsolidified ratio is small, the solidified shell is pressed. That is, by setting the unsolidified rate to an appropriate value, the solidified shell can be pressed.

Therefore, the present inventors conducted a more detailed simulation and examined the effect of the unsolidified rate on the compression bonding of the solidified shell. FIG. 1 shows the relationship between the rolling reduction and the unsolidified rate at which the solidified shell compresses. As is clear from FIG. 1, the unsolidified rate at which the solidified shell compresses can be expressed by a linear expression of the rolling reduction shown below. f ₀ = 1.32r-21.0 (1) From the above facts, the inventors found that the unsolidification rate immediately before rolling was expressed by the equation (1) with respect to the reduction rate. It has been found that by adjusting the cooling rate of the slab so as to be less than the estimated unsolidified rate, it is possible to produce a slab with excellent internal quality.

The execution method of the present invention will be specifically described. FIG. 4 shows an example of an implementation method of the present invention. The molten metal 4 is poured into the mold 5 from the tundish 3 and cooled from the inner surface of the mold 5 to form the solidified shell 1. The solidified shell 1 is bent by the guide roll group 6 and guided to the pinch roll 7. The slab is guided horizontally after the pinch roll 7 and pressed down by the rolling roll 2. During this time, the slab is cooled and the thickness of the solidified shell increases.

In this cooling process, the cooling rate can be controlled so that the unsolidified rate immediately before rolling satisfies the expression (1). That is, when the thickness of the slab after rolling is reduced , the speed of the pinch roll 7 is increased and the drawing speed is increased in order to increase the unsolidified ratio at the rolling position. Alternatively, the water cooling flow rate of the cooling device 8 is increased. When increasing the thickness of the slab after rolling, the speed of the pinch roll 7 is reduced and the drawing speed is reduced in order to reduce the unsolidified ratio at the rolling position. Alternatively, the water cooling flow rate of the cooling device 8 is reduced. An appropriate pinch roll speed and cooling water amount for each rolling reduction can be determined in advance based on a solidification calculation.

[0013]

EXAMPLE A flat roll having a diameter of 700 mm was placed at the rear end of a continuous casting machine, and in the process of rolling down a 220 × 220 mm slab, an attempt was made to change the slab thickness after rolling. In addition, 35% was the maximum rolling reduction rate due to the restriction of the rolling load.

Uncooled rate is 18% without changing cooling conditions
(When the unsolidified thickness is 40 mm), the rolling reduction is 30 ~
The internal quality was improved only by crimping of the solidified shell in a narrow range of 35% (thickness of slab after rolling: 143 to 154 mm). The uncoagulated ratio was determined for each rolling reduction using the equation (1), and the uncoagulated ratio was changed from 5 to 18% by adjusting the water cooling flow rate. As a result, the effect of improving the inner quality by the compression bonding of the solidified shell was observed over a wide range of a reduction ratio of 20 to 35% (a slab thickness of 143 to 176 mm after rolling).

[0015]

According to the present invention, various reduction ratios can be
Since it is possible to perform rolling by pressing the solidified shell, it is possible to obtain slabs of various sizes with excellent internal quality.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between a reduction ratio of a slab and a critical initial unsolidification ratio required for pressure bonding of a solidified shell.

FIG. 2 is a schematic diagram showing definitions of an initial unsolidified rate and a reduction rate.

FIG. 3 is a diagram showing the relationship between the reduction ratio of a slab, the initial unsolidified ratio, and the pressure bonding of a solidified shell.

FIG. 4 is an explanatory view showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solidification shell 2 Rolling roll 3 Tundish 4 Melt 5 Mold 6 Guide roll group 7 Pinch roll 8 Cooling device

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenji Yamada 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (56) References JP-A-50-55529 (JP, A) Kaihei 3-281048 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 11/20 B22D 11/124 B22D 11/128

Claims (1)

(57) [Claims] 1. A method of installing a rolling mill at the rear end of a continuous casting machine and rolling down a slab including an unsolidified portion, wherein the unsolidification ratio f ₀ and the reduction ratio r immediately before rolling are f ₀ ≦ 1.32r− 2
A method for rolling a slab in continuous casting, wherein the cooling rate of the slab is adjusted so as to satisfy a relationship of 1.0. Here, f ₀ is the unsolidified rate (%) immediately before rolling f ₀ = d
₀ / H ₀ × 100, d ₀ is the unsolidified thickness (mm) immediately before rolling,
H ₀ is pre-rolling of the slab height (mm), the rolling reduction of r is cast piece _{(%) r = (H 0} -h) / H 0 × 100, h is the slab height after rolling (mm)