JP3025088B2 - Continuous casting of steel - 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 preventing vertical cracks on the surface of a slab in continuous casting of steel.

[0002]

2. Description of the Related Art As shown in FIG. 3, in a medium carbon steel slab manufactured by continuous casting, a vertical surface crack may be generated near the center in the width direction. Such a slab defect causes a reduction in yield and a serious quality defect as a product, and thus it is necessary to prevent its occurrence beforehand.

[0003] As a technique for preventing vertical cracks, there are Japanese Patent Application Laid-open No. Hei 3-114466 and Japanese Patent Publication No. 2-23260. In the former, during continuous casting of steel, the shell thickness in the mold width direction is controlled by controlling the shell washing rate to a specific value or less by optimizing the molten steel temperature, the shape of the molten steel injection nozzle, and the casting speed to specific conditions. The latter is a technology that prevents the formation of air gaps by optimizing the mold length and prevents vertical cracks on the surface of the continuous cast slab due to insufficient cooling. No consideration has been given to the cooling situation of the device.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a technique for optimizing cooling in a mold to prevent the occurrence of vertical cracks on the surface of a slab during continuous casting of medium carbon steel.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object advantageously, and its gist is to continuously cast steel containing 0.07 to 0.17% of carbon. A continuous casting method of steel, wherein the casting is performed at a heat release per unit volume of molten steel in the mold calculated by the following formula (1) of 2.4 × 10 ⁵ KJ / m ³ or less. (TV × 4.18) / (V _c・ H ・ W) (1) T: mold cooling water supply / drain temperature difference (° C.) V: mold cooling water flow (l / min) V _c : casting speed ( m / min) H: Casting thickness (m) W: Casting width (m)

[0006]

[Function] As an evaluation index of the cooling condition in the mold, the heat removal per unit area and unit time of the mold copper plate (Kcal / m ³ · Hr)
Is generally used, but merely indicates that as the casting speed increases, the amount of heat received by the mold itself increases as the amount of molten steel passing through the mold increases. In this evaluation method, the amount of heat received by the mold copper plate per unit volume and unit area can be evaluated, and the amount of heat received by the mold itself due to a change in the design of the mold can be evaluated and examined.
However, the relationship between the above-mentioned evaluation index and the vertical crack is not found, and a new evaluation index is required for preventing the vertical crack.

[0007] For this reason, the present inventor has conducted extensive and detailed data analysis based on a large number of casting results in actual operation. As a result, the heat removal per unit volume of molten steel in the mold derived from the following equation (1) has a correlation with the vertical crack, and as shown in FIG. 1, the heat removal is 2.4 × 10 ⁵ KJ / m.
It was found that vertical cracking can be reliably prevented by setting it to ³ or less.

(T · V × 4.18) / (V _c · H · W) (1) where T: mold cooling water supply / drain temperature difference (° C.) V: mold cooling water amount (l / min) V _c : Casting speed (m / min) H: Casting thickness (m) W: Casting width (m)

Thus, it can be seen that the amount of heat removal per unit volume of molten steel can be reduced by increasing the denominator of equation (1) or by reducing the numerator. Regarding the denominator, if the casting size is constant, an action to increase the casting speed is required.

On the other hand, in order to reduce the number of molecules, T: mold cooling water supply / drain temperature difference (° C.) or V: mold cooling water amount (l / min) may be reduced. Here, in order to reduce T, a break point is appropriately selected from the physical properties of the mold powder, the heat insulation is increased, the inside of the mold is slowly cooled, and the heat removal per unit volume of the molten steel calculated by the above equation (1) is calculated. It may be set to 2.4 × 10 ⁵ KJ / m ³ or less. Here, the upper limit of the heat removal per unit volume of molten steel is as described above, but as the lower limit, an optimum value may be appropriately selected so as to secure a shell thickness that does not cause breakout.

In the present invention, the reason for limiting the carbon content of the target steel is as follows. FIG. 2 shows the relationship between the carbon content in steel and vertical cracks. Vertical cracking occurs only in steels containing 0.07 to 0.17% carbon, and none in steels having a carbon content outside this range. Therefore, the carbon content of the target steel targeted in the present invention is set to 0.01 to 0.17%.

[0012]

EXAMPLES Examples of the present invention will be described together with comparative examples. still,
The casting machine used was a curved continuous caster having a radius of R10.5 m, and was cast under the casting conditions shown in Table 1. The control of the heat removal per unit volume of molten steel was performed by changing the breakpoint (BP) of the mold powder and thereby changing the temperature difference (T) between the supply and discharge temperatures of the mold cooling water. Table 1 also shows the state of occurrence of vertical cracks.

[0013]

[Table 1]

Thus, in the case of the method of the present invention, no vertical cracks occurred in any of the examples, but in the case of the comparative example, the heat removal per unit volume of molten steel was over 2.4 × 10 ⁵ KJ / m ^3. Because of the large size, vertical cracks occurred in all cases, and the surface had to be cut and cut.

[0015]

As described above, according to the present invention, it is possible to effectively suppress the occurrence of vertical cracks, and to avoid a decrease in the yield due to the maintenance of the slab surface by cutting.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the heat removal per unit volume of molten steel and the rate of occurrence of vertical cracks.

FIG. 2 is a graph showing the relationship between the carbon content in steel and the rate of occurrence of vertical cracks.

FIG. 3 is an explanatory view showing a vertical crack generated on a slab surface.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B22D 11/055 B22D 11/124

Claims (1)

(57) [Claims] When a steel containing 0.07 to 0.17% of carbon is continuously cast, the heat removal per unit volume of molten steel in a mold calculated by the following equation (1) is 2.4 × 10 ⁵ KJ
/ M ³ or less, a continuous casting method for steel. (TV × 4.18) / (V _c・ H ・ W) (1) T: mold cooling water supply / drain temperature difference (° C.) V: mold cooling water flow (l / min) V _c : casting speed ( m / min) H: Casting thickness (m) W: Casting width (m)