JPS5923902B2 - Electromagnetic stirring method in continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method in which electromagnetic stirring is carried out during the process of continuous casting of steel to make the casting structure equiaxed.

For example, chromium-based stainless steel thin sheets manufactured by continuous casting are usually manufactured using a cast structure because, compared to steel ingots, only the flat surfaces and longitudinal direction are rolled during the process from billet to product, and the reduction rate is small. The columnar crystal structure remains in the product, and when the stainless steel thin plate is pressed, etc., ridging (wrinkle-like undulations with a height of about 20 to 50 μm), which is said to be caused by the columnar crystals, occurs on the surface, which deteriorates the appearance. There is a problem of significant damage.

It is known that one effective way to solve this problem of ridging is to make the columnar crystals of the cast structure equiaxed, and one of the means to obtain equiaxed crystals. It is known that electromagnetic stirring can be applied to cast molten steel during the continuous casting process.

The reason why the cast structure becomes equiaxed due to electromagnetic stirring has been discussed in various ways, but in summary, the stirring flow stirred by electromagnetic action washes the solidified shell, and the flow between the molten steel and the solidified shell 7. Transfer of heat is promoted.

That is, the heat transfer coefficient between the molten steel and the solidified shell increases, the heat of the molten steel is rapidly absorbed by the solidified shell, the cooling of the molten steel is promoted, and the growth of columnar crystals is suppressed.

Due to the effect of this stirring action, the molten steel is uniformly and quickly cooled to a condition where equiaxed crystals are likely to be generated, and then solidified to become equiaxed crystals.

Therefore, in order to obtain equiaxed crystals, it is sufficient to increase the moving speed of the molten steel, and it is particularly effective to concentrate the stirring of the molten steel near the solidified shell.

For this purpose, it is sufficient to install the stirrer at an angle along the solidified shell, but the position of the solidified shell, especially the bottom, varies depending on the slab drawing speed, molten steel injection temperature, slab cooling conditions, etc. Moreover, in this case, many electromagnetic stirring devices are required to be installed along both sides of the slab, which is extremely uneconomical.

The present invention overcomes these problems in generating a concentrated stirring flow along the solidified shell and provides an effective method for obtaining equiaxed crystals using a small number of stirring devices.

The details of the present invention will be explained below with reference to the drawings.

The present inventors measured the direction and stirring thrust of the stirring flow of molten steel in the slab by electromagnetic stirring, and as a result, confirmed that the distribution was as shown in FIG. 1.

In FIG. 1, reference numeral 4 indicates a solidified shell of a slab, 5 indicates an unsolidified molten steel, and 6 indicates an electromagnetic stirring device installed perpendicular to the direction of drawing the slab.

The arrow on the molten steel 5 indicates the direction of the stirring flow when the stirring device 6 is stirred in the direction of arrow A, and the length of the arrow indicates the magnitude of the stirring thrust.

Note that when the stirring device 6 stirs in the direction of the arrow, the direction of the stirring flow is opposite to that in FIG. 1.

As shown in FIG. 1, the stirring flow generated by the stirring device 6 collides with the solidified shell 4, much of the stirring energy is reduced, and the stirring flow is stirred in the order of the arrows below.

The horizontal stirring flow becomes stronger in the latter half (on the right side of the figure).

In the present invention, a stirring device T is additionally provided in the lower part of the stirring device 6 shown in FIG. 1 in the direction of drawing out the slab as shown in FIGS. 2 and 3.

In the figure, 1 shows the Kunditsch nozzle, 2 the mold, and 3 the side surface of the slab.

Then, the stirring device 6 stirs the molten steel in the direction of arrow A, and the stirring device γ stirs the molten steel in the direction of arrow C.

Here, for one point in the molten steel, the molten steel flow rate obtained by the stirring device 6 is 1 person, and the molten steel flow rate obtained by the stirring device γ is 1 person.
B, and when stirring devices 6 and 1 are excited at the same time, stirring flow 1 and 1B are vectorially combined as shown in Fig. 4, and stirring flow 1 is generated.
It becomes C.

That is, in FIG. 2, since each stirring flow can be combined, the stirring flow 2 can be made in a direction substantially parallel to the solidified shell 4, and moreover, it can concentrate the molten steel near the solidified shell over a wide range in the direction of drawing the slab. can be stirred.

Therefore, cooling of the molten steel is promoted over a wide area of the slab during solidification without being influenced by solidification shell fluctuations, and the growth of columnar crystals is suppressed to form equiaxed crystals.

Furthermore, when the molten steel is stirred in the direction of the arrow by the stirring device 6, the stirring flow is in the opposite direction.

Therefore, in actual operation, the stirring device 6 is alternately excited in the directions of arrows A and 2, and the stirring direction is reversed one by one, thereby stirring both sides of the solidified shell to obtain a uniform casting structure.

That is, in the present invention, when electromagnetically stirring molten steel poured into a continuous casting mold, electromagnetic stirring devices are installed in two stages, upper and lower. This electromagnetic stirring method in continuous casting is characterized by stirring alternately toward the side surface of a slab.

Note that the agitation flow generated in the present invention is produced by the agitation device 6 in FIG.
By changing the ratio of the excitation force between 1 and 1, the direction and magnitude can be freely changed.

As described above, according to the present invention, it is possible to stir molten steel in the vicinity of the solidified shell over a wide range in the slab drawing direction, which has a large stirring effect, with a small number of stirring devices, and is an invention with high practical value.

Next, examples of the present invention will be shown.

Figure 5 shows the superheating temperature (△T) of 5US430 stainless steel.
) In the process of continuous casting at 20 to 30°C, the equiaxed crystallinity of each slab subjected to electromagnetic stirring by the method of the present invention (horizontal alternating 10 vertical stirring) and the conventional method (horizontal alternating stirring 2 stages) is shown.

In the case of the conventional method, the equiaxed crystal ratio is low, which has a negative effect on product sagging, whereas according to the method of the present invention, high equiaxed crystals can be obtained with the same stirring thrust as in the conventional method, and a product with less ridging can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the direction of the stirring flow and the distribution state of the stirring thrust, Fig. 2 is an example of an apparatus for explaining the stirring method of the present invention, Fig. 3 is a side view of Fig. 2, and Fig. 4 The figure is a vector composite diagram of stirring flow, and FIG. 5 is a chart showing the relationship between stirring thrust and equiaxed crystallinity. 1...Tanditshu nozzle, 2...
Mold, 3...Slab side, 4...Solidified shell, 5...Unsolidified molten steel, 6,7...
Stirring device.

Claims (1)

[Claims] 1. When electromagnetically stirring the molten steel injected into the continuous casting mold, two electromagnetic stirring devices are installed in the upper and lower stages, the lower electromagnetic stirring device stirs the steel in the opposite direction to the slab drawing direction, and the upper electromagnetic stirring device An electromagnetic stirring method for continuous casting, characterized by stirring alternately toward the sides of the slab.