JPH0673722B2 - Continuous casting method - Google Patents

Description

The present invention relates to an application of electromagnetic force in continuous casting of steel,
The present invention relates to a method of controlling molten steel flow in a mold for continuous casting.

Conventional technology The continuous casting method is to insert molten steel into a tundish from a container such as a ladle, and inject the molten steel into the mold from a discharge port through a dipping nozzle attached to the tundish. It is the one that is continuously drawn out as a cast piece.

At this time, the molten steel flow in the mold formed by the molten steel jet flow from the nozzle, powder entrainment and inclusion floatability,
Ultimately, the quality of the produced slab is greatly affected.In particular, in a curved continuous casting machine, when inclusions are brought into the mold, it is difficult for them to float up, and they are trapped and accumulated on the inner surface of the arc of the slab However, it is known to cause deterioration of product quality.

Therefore, in order to prevent the inclusion of powder in the conventional technique and to promote the floating of the inclusions in the mold so that the inclusions are not captured by the solidified shell, the method disclosed in Japanese Patent Laid-Open No.
As shown in Japanese Laid-Open Patent Publication No. 137153, it is common to use an inverted Y2 hole type immersion nozzle having a shape suitable for the operating conditions of each continuous casting machine.

However, from the viewpoint of improving productivity in recent years, under the condition that the casting speed is higher, the flow rate of the molten steel flow 3 from the discharge port of the immersion nozzle 2 is increased as shown in FIG. It becomes very large, and the ascending flow 7 and the descending flow 8 formed after the short-side collision also become large, which is disadvantageous in terms of powder entrainment and floating of inclusions, resulting in poor product quality level. Become. Further, it is very difficult to select a dipping nozzle shape that can both prevent powder entrapment and secure the floating property of inclusions.

As a countermeasure against this, as shown in FIG.
Is placed and electromagnetic force is applied to exert a braking force 6 on the molten steel flow 3 from the dipping nozzle 2 in the mold to attenuate the molten steel flow itself, thereby preventing powder entrapment and promoting floating of inclusions. Is disclosed in JP-A-57-17356.

However, when applying the technique, if the applied electromagnetic force is too weak, the expected molten steel flow damping effect cannot be obtained. On the other hand, if it is too strong, an excessive braking force 6 acts on the molten steel flow as shown in FIG. 3 (c), so that local strong upflow 10 and downflows 11 and 13 near the nozzle are generated. As it forms, it causes new inclusion of powder 12 and hinders the floating of inclusions, so the expected effect is not always obtained.

Therefore, when the electromagnetic force is applied to produce high-cleanliness steel under high-bundle casting, an electromagnetic force suitable for the molten steel discharge flow rate from the immersion nozzle, that is, the molten steel flow rate (ton / min), is applied. Must be applied. However, until now, this proper electromagnetic force was unclear.

The present invention is to solve the above problems of the prior art, in order to control the molten steel flow in the mold, in the method of applying an electromagnetic force from the outside of the mold, casting conditions, that is, the molten steel flow rate By controlling the electromagnetic force applied in conformity with the range within a certain specific range, powder entrapment is prevented under any casting conditions, and the floatability of inclusions is promoted, resulting in high cleanliness with few inclusions. The purpose is to manufacture steel stably and with good yield.

Means for Solving the Problems The present invention has been made in order to advantageously solve the above-mentioned problems, and its constitution is to arrange an electromagnetic force applying means in a continuous casting mold, to a molten steel flow from a dipping nozzle, and vice versa. This is a continuous casting method characterized by adjusting and applying the electromagnetic force of the electromagnetic force applying means within a range satisfying the following conditions when the electromagnetic force is applied in a direction to perform casting.

1200 × Q−2100 ≦ B ≦ 2000 × Q−1000 (where B is the proper electromagnetic force to be applied (Gauss / discharge jet flow) and Q is the melt flow rate (ton / min, discharge port)).

In order to prevent powder entrapment, improve the floatability of inclusions, and stably produce high-cleanliness steel, the inventors of the present invention applied electromagnetic force to the molten steel flow from the immersion nozzle under any conditions. Various tests were carried out as to whether or not the addition depth should be increased, and the results were analyzed and arranged in detail to obtain FIG.

According to Fig. 1, molten steel flow rate during casting (ton / min, discharge port)
It was found that there is a clear relationship between the applied electromagnetic force and the applied electromagnetic force (Gauss / discharge jet flow), and the range of the appropriate added electromagnetic force can be specified by the following equation.

1200 × Q−2100 ≦ B ≦ 2000 × Q−1000 However, B: Appropriate electromagnetic force to be applied (Gauss / Discharge jet) Q: Molten steel flow rate (ton / min, discharge port) Here, electromagnetic force B is 1200 × Q If it is less than −2100, the additional electromagnetic force is too weak to obtain the molten steel basin damping effect, and the quality level of inclusions deteriorates. On the other hand, when a strong electromagnetic force exceeding 2000 × Q-1000 is applied, as shown in FIG. 3 (c), strong local upflow 10 and downflow 11, 13 are locally generated near the nozzle.
As a result, powder entrainment, inclusion floating inhibition, etc. occur, and the quality level of inclusions deteriorates.

However, when the electromagnetic force is applied by adjusting the range of the above formula limited by the present invention, the molten steel flow velocity from the immersion nozzle discharge hole is weakened to an appropriate level as shown in FIG. 3 (b). As a result, a nearly uniform flow velocity distribution is obtained for both the upflow and downflow, and the floatability of inclusions can be secured while preventing powder entrapment, ensuring high-quality inclusion levels even during high-speed casting. it can.

Example 1 Casting slab width 1570 mm, slab thickness 245 mm, casting speed 2.0 m
(Dip nozzle Nozzle flow rate Q = 3 ton / min, discharge port) When casting with 400 mm outside the long side mold as shown in Fig. 4.
An electromagnetic force adding device consisting of four electromagnets having a cross-sectional area of × 400 mm and a yoke 5 connecting the two coils 4 and 4 is provided, and a current is passed through the coil 4 to add a magnetic field of maximum 3000 Gauss / jet jet. The relationship between the electromagnetic force and the quality level of inclusions in the product is shown in FIG. 2 (a). In this case, the stronger the electromagnetic force applied, the more stable the inclusion-level product was obtained.

Example 2 Using the same electromagnetic force applying device as in Example 1, the width is 1050 mm,
The relationship between the applied electromagnetic force and the quality level of product inclusions was investigated when casting a 245 mm thick slab at a casting speed of 1.0 m / min (immersion nozzle discharge molten steel flow rate Q = 1 ton / min, discharge port). It is shown in Fig. 2 (b).

In this case, the inclusion level tends to deteriorate as the electromagnetic force is applied, and it has been found that it is more advantageous not to apply the electromagnetic force when casting at low ton / min.

Example 3 Using the same apparatus as in Example 1, a slab width of 1000 mm and a thickness of 24
When a 5 mm slab was cast at a casting speed of 1.85 m / min (immersion nozzle outlet molten steel flow rate Q = 1.75 ton / min, outlet),
As shown in Figure (c), by applying an electromagnetic force of 1000 to 2000 Gauss / ejection jet, a product with a very good inclusion quality level was obtained.

As described above, according to the present invention, in order to control the molten steel flow in the mold, in the method of applying an electromagnetic force from the outside of the mold, the casting conditions, that is, the molten steel flow rate, the By controlling the force within the range of 1200 × Q−2100 ≦ B ≦ 2000 × Q−1000, it is possible to prevent the inclusion of powder under any casting conditions and to promote the floating property of inclusions, thereby reducing inclusions. High-cleanliness steel can be stably manufactured with good yield.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the relationship between the molten steel flow rate and the appropriately applied electromagnetic force according to the present invention, and FIGS. 2 (a), (b), and (c) show the embodiment of the present invention, in which the applied electromagnetic force is different for each molten steel flow rate. And FIG. 3 (a), (b), which is an explanatory view showing the relationship between the inclusion quality level and
(C) is an explanatory view showing a state of molten steel flow in a mold obtained by the magnitude of an electromagnetic force to be applied, and FIG. 4 is an explanatory view showing an apparatus for applying an electromagnetic force to a molten steel flow discharged from a dipping nozzle in a continuous casting mold. is there. 1 ... Long side of mold, 2 ... Immersion nozzle, 3 ... Discharged molten steel flow, 4 ... Electromagnet, 5 ... Yoke, 6 ... Braking force, 7 ...
… Upflow, 8 …… Downflow, 9 …… Mold, 10 …… Upflow,
11 …… Downflow, 12 …… Powder, 13 …… Downflow.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Wada 5-3 Tokai-cho, Tokai-shi, Aichi Nippon Steel Co., Ltd. Inside the Nippon Steel Works (56) References JP-A-63-260652 (JP, A) JP 63-165052 (JP, A)

Claims (1)

[Claims] 1. An electromagnetic force applying means is arranged in a continuous casting mold,
When casting by applying an electromagnetic force in the opposite direction to the molten steel flow from the immersion nozzle, the electromagnetic force of the electromagnetic force applying means is adjusted within a range satisfying the following conditions and applied. Casting method. 1200 × Q−2100 ≦ B ≦ 2000 × Q−1000 (where B is the proper electromagnetic force (Gauss / jet jet) to be applied, and Q is the molten metal flow rate (ton / min, jet)).