JPS5847260B2 - Renzokuchiyuuzou Niokeru Denjikakuhanhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of making the cast structure equiaxed by applying electromagnetic stirring during continuous casting of steel.

Normally, thin sheets of chromium-based stainless steel, especially those produced by continuous casting, are rolled only in the flat face button and longitudinal direction during the process from slab to product 1, and the rolling reduction ratio is small compared to steel ingots. The columnar crystal structure is product 1.
It is said that when the thin stainless steel plate is subjected to press working, 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 significantly impairs the appearance. There's a problem.

It is known that making the columnar crystals of the cast structure into equiaxed crystals is one of the effective means of solving the problem of occurrence of richness. It is known that electromagnetic stirring can be applied to cast molten steel during continuous casting.

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

In other words, the heat transfer coefficient between the molten steel and the solidified shell increases, the amount of heat in the molten steel is rapidly transferred to the solidified shell, and the cooling of the molten steel is accelerated.The temperature of the molten steel in the unsolidified part becomes uniform due to the button and stirring. It is to be cooled down.

Due to the effects of these two stirring actions, the molten steel is cooled uniformly and quickly under condition 1, which facilitates the generation of equiaxed crystals, and solidifies to become equiaxed crystals.

Therefore, in order to obtain equiaxed crystals, it is only necessary to increase the moving speed of the molten steel, and for this purpose, for example, if the molten steel flow is concentrated or circulated, the stirring resistance will be reduced, and the thrust force will be less attenuated and more effective. .

On the other hand, however, there is a problem in that drifting of the molten steel occurs, impeding uniform stirring and uniform cooling, making it impossible to obtain a homogeneous product.

Conventionally, as an electromagnetic stirring method for uniformly stirring, an electromagnetic stirring device is installed in a direction perpendicular to the slab drawing direction, and the stirring direction is alternated.

However, in this case, the molten steel flow collided with the short side of the slab from the right angle direction, which weakened the stirring flow and reduced the equiaxed crystal effect.

The present invention utilizes a method of electromagnetic stirring to make a continuously cast steel slab into an equiaxed crystal, which uniformly stirs the inside of the slab, minimizes the attenuation of the molten steel flow velocity, and uniformly achieves excellent equiaxed crystal action. We have discovered a method of electromagnetic stirring that achieves this effect.

1 and 2 show an example in which the electromagnetic stirring method of the present invention is applied to continuous slab casting. 1 is an immersion nozzle for injecting molten steel into a mold from a tundish (not shown); 2 is a mold; 3 is solidified shell, 4 is powder, 5
Reference numeral a15b denotes an electromagnetic stirring device, and each electromagnetic stirring device 5 is installed so as to be inclined toward the wide side of the slab, and intersectingly intersect with the slab at opposing positions.

However, when performing electromagnetic stirring, the electromagnetic stirring devices 5a and 5
(b) are alternately stirred diagonally downward.

When stirred in this way, the molten steel flow collides with the solidified shell 3 from diagonally above, which improves the disadvantage of the conventional method in that the molten steel flow collides with the solidified shell and is weakened. Since the molten steel is stirred alternately, the molten steel inside the slab is uniformly stirred, so that it uniformly cools and solidifies, forming equiaxed crystals evenly within the slab.

This situation will be explained in detail with reference to FIG. 1 as follows.

The molten steel flow stirred by the electromagnetic stirrers 5a and 5b collides with the solidified shells 3 and 3', forming a strong downward flow in the direction of the arrows C and 2.

This strong downward flow stirs the molten steel just before solidification at the bottom of the slab, where the effect of the equiaxed crystal action is particularly large, where it would not have been shattered and stirred in the conventional method, promoting the exchange of heat between the molten steel and the solidified shell. is rapidly cooled and solidified, creating very favorable conditions in which equiaxed crystals are likely to occur.

Moreover, since the molten steel flow is stirred obliquely downward, the molten steel flow is generated over a wide range in the direction of drawing the slab in the mold, and since the molten steel flow is alternately stirred, the molten steel is uniformly stirred and a homogeneous product can be obtained.

The installation angle of the electromagnetic stirring device may be set to an appropriate angle depending on the width of the slab, the width of the electromagnetic stirring, etc.

As described above, the method of the present invention is an extremely useful invention that maximizes the equiaxed crystal effect of electromagnetic stirring and makes the cast structure uniformly equiaxed.

Next, examples of the present invention will be shown.

Figure 3 shows the superheating temperature (J
T) In the process of continuous casting at 20 to 30°C, the average segregation score of each slab (5 pieces) subjected to electromagnetic stirring by the method of the present invention (alternate tilted stirring) and the conventional method (alternate horizontal stirring) is shown. .

In the case of the conventional method, the segregation score was 4.4, which resulted in very high segregation.
While this had a negative effect on the bendability of the product, the slab produced by the method of the present invention had a segregation score of 1.3, resulting in a product with very little segregation and excellent bendability.

FIG. 4 shows the equiaxed crystallinity of a slab with respect to the stirring thrust, the casting temperature (superheating temperature IT) j, and the installation angle of the electromagnetic stirring device in the same electromagnetic stirring as in FIG. 3.

In the case of the conventional method, the equiaxed crystal ratio is low and has a negative effect on the product paste zinc, whereas with the method of the present invention, a high equiaxed crystal ratio was obtained with the same stirring thrust as the conventional method, and a product with less ridging was obtained. .

[Brief explanation of the drawing]

Figure 1 shows an example in which the method of the present invention is applied to continuous casting of slabs, Figure 2 shows the situation in which Figure 1 is rotated 90 degrees around the vertical axis, and Figure 3 shows the method of the present invention and the conventional method. Figure 4 also shows the equiaxed crystallinity. In the figure, 1 is the immersion nozzle, 2 is the mold, 3 is the solidified shell, 4 is the powder, 5 is the electromagnetic stirring device, arrow A, the mouth,
C, 2 shows the molten steel flow stirred by the electromagnetic stirring devices 5a and 5b.

Claims (1)

[Claims] 1. When performing electromagnetic stirring on molten steel to be cast by the continuous casting method, electromagnetic stirring devices are arranged on opposite sides of the broad side of the slab so as to cross each other, and the molten steel is directed diagonally downward and alternately An electromagnetic stirring method in continuous casting characterized by stirring.