JPS6153145B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for horizontal continuous casting of steel.

In the cross-sectional structure of a slab cast by the horizontal continuous casting method, columnar crystals and branched columnar crystals are developed up to the axial center of the slab. As a result, as shown in Fig. 1, the columnar crystals 1 and branched columnar crystals 2 that have grown relative to each other collide with each other at the axial center of the slab in the final solidification zone. , bridging 3 is likely to occur, and further discontinuous bridging occurs due to the movement force of the solidified front concentrated bath steel in the casting direction caused by the interaction between the solidification shrinkage of the molten steel and the static pressure of the molten steel. The bridging portion is deformed and fractured, and the enriched bath steel solidifies while moving discontinuously in the casting direction, resulting in discontinuous segregation with a V-shaped flow pattern, a so-called central positive and negative segregation zone, and a coarse Center porosity tends to occur. If such defects remain in the axial center of the slab, they not only cause a so-called end face oxidation phenomenon in the subsequent heating processing stage, causing a decrease in yield, but also remain as voids in the axial center of the slab even at the finished product stage. or increase variations in material properties, such as hardness. Furthermore, during secondary and tertiary processing, it causes various material and quality deterioration such as cutlet breakage and surface opening flaws, and there is a need to prevent such deterioration.

For this purpose, as shown in Fig. 2, in normal vertical continuous casting, an electromagnetic stirring device 4 is installed inside the mold or in the secondary cooling zone under the mold to control the solidification form of the axial center of the slab. to convert it into an equiaxed crystal structure,
This prevents the occurrence of bridging and
A technique has been implemented to ensure that the equiaxed crystal pieces 5 and the enriched bath steel move continuously and integrally in the casting direction, and to disperse and reduce the defects. In other words, in conventional vertical continuous casting, the casting direction and the direction of gravity coincide or are relatively close to each other until the final stage of solidification, so the equiaxed crystal pieces generated at the front of solidification due to electromagnetic stirring are shown in Figure 2. As shown, there is a strong tendency to easily settle and grow and accumulate up to the part corresponding to the casting axis, which is the final solidification position, and for this reason, the electromagnetic stirring effect can be easily obtained.

However, in horizontal continuous casting, the direction of gravity acts at an angle of 90° with the casting direction from the start to the end of solidification, so as shown in Figure 3, the electromagnetic stirring device 4 is used to stir the solidifying slab. Even if the limited solidification front is locally stirred and oscillated to generate equiaxed crystal pieces 5 at that position, the equiaxed crystal pieces 5 will quickly settle to the lower solidification interface, and the desired casting will not be achieved. It has been impossible to maintain equiaxed crystal pieces floating in molten steel until the final solidification position, ie, the crater end position, where the uniaxial core structure can be controlled, is reached.

This invention has been made to solve the above-mentioned problems, and includes installing at least two electromagnetic stirring devices in the secondary cooling zone where unsolidified slabs are retained during horizontal continuous casting of steel. A rotating flow is applied to the molten steel inside the unsolidified slab in the casting direction by a composite type electromagnetic stirring device installed in the former stage and installed on the mold side, and this causes the formation of The feature is that the equiaxed crystal slab is moved to the crater end side by a linear electromagnetic stirrer installed at the latter stage, and thus a sound slab without center segregation or macroporosity is cast. .

The present invention will be described by way of examples with reference to the drawings.

FIG. 4 is an explanatory diagram of an embodiment of the invention.

In FIG. 4, 6 is an injection nozzle connected to the tundish, 7 is a mold horizontally attached to the injection nozzle 6 via a break ring 8, and 9 is a mold.
was installed on the slab exit side of the mold 7. A composite electromagnetic stirring device that applies a rotational flow around the casting direction that advances in the casting direction to the molten steel inside the unsolidified slab, and
10 is a linear electromagnetic stirring device installed on the side of the crater end 11 for imparting a flow in the casting direction to the molten steel inside the unsolidified slab.

The molten steel inside the unsolidified slab in the secondary cooling zone is rotated and stirred around the casting direction by the composite electromagnetic stirring device 9 in the previous stage, and a large amount of equiaxed crystal slabs 12 are formed. This equiaxed crystal piece 12 is a composite electromagnetic stirring device 9
crater end 1 without settling due to the action of
Although it moves in one direction, this movement is further promoted by the linear electromagnetic stirring device 10 at the rear stage. As a result, the solidified structure of the axial center of the slab becomes finer, and a healthy slab without center segregation or macroporosity is obtained.

In the embodiment shown in FIG. 4, one linear electromagnetic stirring device 10 is installed at the bottom of the slab.
This may be installed on the upper and lower sides of the slab as shown by the dotted lines in Figure 4. In this case, if the stirring directions of the upper and lower stirring devices are reversed, the equiaxed slab will be more efficient. can be caused to occur and move.

In the above embodiment, a composite electromagnetic stirring device and a linear electromagnetic stirring device are installed in two stages, one in the front stage and the other in the latter stage, but it goes without saying that these devices may be installed in two or more stages.

Next, the installation position of the front-stage composite type electromagnetic stirring device 9, the installation interval between this and the rear-stage linear type electromagnetic stirring device 10, and the stirring flow rate of molten steel by these electromagnetic stirring devices in the case of FIG. 4 will be explained.

The composite electromagnetic stirring device 9 is installed at a position of 50% or less of the distance from the slab outlet end of the mold 7 to the crater end 11, and the distance from the linear electromagnetic stirring device 10 is similarly set to 55% or less. On the other hand, the stirring flow rate of molten steel is 20 cm/sec with the composite electromagnetic stirring device 9.
The above is 10 cm/sec or more using the linear electromagnetic stirring device 10. This allows stable formation and movement of equiaxed crystal pieces.

In addition, in order to prevent the occurrence of white bands, better results can be obtained by setting the stirring flow rate to a maximum of 70 cm/sec or less for the composite type electromagnetic stirring device 9 and a maximum of 45 cm/sec or less for the linear type electromagnetic stirring device 10. . Alternatively, a so-called alternating method may be adopted in which the stirring directions are changed at regular intervals.

As explained above, according to the present invention, the electromagnetic stirring device in the first stage stirs the molten steel to promote the formation of equiaxed crystal flakes, and the electromagnetic stirring device in the latter stage creates a crater without causing the equiaxed crystal flakes to settle. Since it can be moved to the end side, the solidified structure at the axial center of the slab can be made finer, resulting in useful effects such as casting of a healthy slab without center segregation or macroporosity.

[Brief explanation of the drawing]

Figure 1 shows the solidification form of a slab, Figure 2 shows the state of equiaxed crystal pieces in molten steel when magnetically stirred in vertical continuous casting, and Figure 3 shows the state of equiaxed crystal pieces in horizontal continuous casting. FIG. 4, a diagram showing the state of equiaxed crystal pieces in molten steel when stirred, is an explanatory diagram showing an embodiment of the method of the present invention. In the drawings, 1... Columnar crystal, 2... Branched columnar crystal, 3... Bridging, 4... Electromagnetic stirring device, 5... Equiaxed crystal piece, 6... Tundish, 7... Mold, 8
... Break ring, 9 ... Composite electromagnetic stirring device, 10 ... Linear type electromagnetic stirring device, 11 ... Crater end, 12 ... Equiaxed crystal piece.

Claims (1)

[Claims] 1. When performing horizontal continuous casting of steel, at least two stages of electromagnetic stirring devices are installed in the part of the secondary cooling zone where unsolidified slabs accumulate, and the combined electromagnetic stirring device in the previous stage installed on the mold side The molten steel inside the unsolidified slab is given a rotational flow around the casting direction that advances in the casting direction, and the equiaxed crystal pieces formed thereby are sent to a subsequent linear type electromagnetic stirring device installed on the crater end side. A horizontal continuous casting method for steel, which is characterized by moving the steel slab to the crater end side, thereby casting a sound slab without center segregation or macroporosity.