JPS63108952A - Electromagnetic stirring method for molten metal in continuous casting - Google Patents

Abstract

PURPOSE:To avoid over-stirring in a final solidified area and to prevent segregation in inner part of a cast slab by reducing the intensity of magnetic field in accordance with the falling of molten metal pressure in the above area at the time of electromagnetic stirring in the final solidified area of the molten metal in a continuous casting. CONSTITUTION:The prescribed quantity of molten steel 12 is poured in a water cooled mold 10 and the cast slab forming solidified shell 14 is drawn at the prescribed velocity. Then, the magnetic field is impressed on the molten steel 12 of non-solidifying area 16 and the molten steel 12 in the vicinity of crater end 18 is stirred, to avoid the enclosure of the molten steel 12 with low melting point. At the time of once stopping the drawing at the end stage of casting, the cast slab becomes to over-cooling state and the crater end 18 position is risen and the molten steel 12 pressure in this range is fallen. Then, after reopening the drawing in accordance with the molten steel 12 pressure at the crater end 18, the impressed intensity of magnetic field is reduced. In this way, the over-stirring in the finish solidified range is avoided, and the segregation in the inner part of cast slab is prevented.

Description

Detailed Description of the Invention "Field of Industrial Application" This invention is applicable to continuous casting in which the molten metal is stirred by applying a rotating magnetic field or the like to the final solidification region of the molten metal to prevent segregation of slabs. This invention relates to a method for electromagnetic stirring of molten metal.

[Prior Art] Normally, in continuous casting, a rotating magnetic field or a shifting magnetic field is generated in the final solidification region (crater end) of poured molten steel using an electromagnetic stirring device, and by stirring the molten steel at the crater end, the inside of the slab is stirred. Prevents segregation.

[Problem to be Solved by the Invention 1] However, when the injection of molten steel into the mold is stopped during the connection of continuous casting, the drawing of the slab is temporarily stopped, and when the casting is restarted, the drawing of the slab is restarted. There is. In this case, the continuous cast slab is in a subcooled state compared to when it is used in a steady state.

On the other hand, at the final stage of casting, the drawing of the slab is similarly stopped and a thin solidified layer covering the rear end surface is formed at the rear end. In this case as well, the slab is in a supercooled state.

However, in the conventional 1iVifi stirring method, the stirring intensity is constant regardless of the cooling state of the slab, so segregation (so-called white band) due to excessive stirring occurs at the joint of continuous casting and at the rear end of the slab R. Occur. There is a problem in that the yield of slabs is low due to the occurrence of such white bands.

This invention was made in view of such circumstances, and
At the joint of continuous casting and at the rear end of the slab, segregation can be prevented up to the rear end of the slab without excessively stirring the final solidification region of the molten metal, and the yield of slab can be improved. The purpose of this invention is to provide a method for electromagnetic stirring of molten metal for continuous casting.

[Means for Solving the Problems] The method for electromagnetic stirring of molten steel in continuous casting according to the present invention involves applying a magnetic field to the final solidification region of the molten metal in continuous casting to stir the molten metal. The method is characterized in that the intensity of the magnetic field is reduced as the molten steel pressure in the final solidification region is reduced.

[Function] In the method for electromagnetic stirring of molten steel in continuous casting according to the present invention, once the slab drawing is stopped, the slab is in a supercooled state compared to during steady drawing, and the final solidification region of the molten metal rises. do. Therefore, the molten metal pressure in the final solidification region is lower than in the steady state. Then, when the slab drawing is restarted, the strength of the magnetic field applied to the final solidification region is lower than in the steady state in accordance with the decrease in the molten metal pressure. As a result, the force for stirring the molten metal in the final solidification region is weakened, and excessive stirring of the molten metal in the final solidification region is avoided.
Segregation inside the slab can be prevented.

(Embodiments) Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram illustrating a method for electromagnetically stirring molten metal in continuous casting according to an embodiment of the present invention. A tundish (not shown) is disposed above the mold 10 of the vertical continuous casting machine, and a predetermined amount of molten w is poured into the mold 10 through an immersion nozzle (not shown) attached to the tundish.
7/412 were injected. The mold 10 is made of copper and has many passages (not shown) through which cooling water flows.
is formed. This cooling water passage is connected to a 1 liter cooling water supply (not shown) with a flow rate adjustment function,
By supplying a predetermined amount of cooling water to the passage, the mold 10 is cooled at a predetermined cooling rate. Also,
A solidified shell 14 is formed in the mold 10 along the contour, and when the initial solidified shell 14 grows to a predetermined thickness, the slab is pulled apart by pinch rolls (not shown). An unsolidified region 16 in which molten tA 12 remains in an unsolidified state is formed inside the solidified shell 14, and a crater end 18 is formed at the end of this unsolidified region 16. An electromagnetic stirring device (not shown) is disposed at a height where the crater end 18 is located in a steady state. N
The magnetic field generating section of the magnetic stirrer has three pairs of solenoid coils, and these coils are arranged so as to surround the slab. Further, the three pairs of solenoid coils are connected to a three-phase AC power source, and the magnetic poles generated between each pair of solenoid coils are exchanged at a predetermined period. Also,!
The Ia It stirring device has a current control circuit that can increase or decrease the input current to the solenoid coil.

Next, the operation of this embodiment will be explained. V! While supplying a predetermined amount of cooling water to the mold 10, the mold 1 is removed from the tandish.
When a predetermined amount of molten steel 12 is injected into the molten steel 12 and the slab is pulled out at a predetermined drawing speed, the thickness of the solidified @I crotch 14 becomes approximately constant;
The position where the crater end 18 is generated also becomes approximately constant. The crater end 18 in this steady state is the initial solidified shell 1
The position is approximately h (1) downward from the position where 4 is formed.

On the other hand, when current 7 is applied to the solenoid coil of the electromagnetic stirring device, a rotating magnetic field approximately centered on the longitudinal axis of the slab is generated. When this rotating magnetic field acts on the slab, a current is induced in the molten tJA 12 in the unsolidified region 16 inside the slab. When the N current flows through the molten steel 12, a force is generated in a direction perpendicular to the direction of the current, and this force causes the crater end 1
The molten steel 12 in the vicinity of 8 is stirred. Then, in the crater end 18, the low melting point molten tA12 in which solute elements such as carbon are concentrated and the molten tA12 (molten II, a part of which has started to solidify) immediately above it are stirred, and the low melting point molten steel 12 is stirred. is prevented from being trapped in the crater end 18, and segregation inside the slab is prevented.

By the way, at the final stage of casting, mold 1 was removed from Tanditshu.
When the injection of molten IJA 12 into 0 is stopped and the slab drawing is also temporarily stopped, the slab that is not being pulled becomes supercooled and solidification of the molten steel 12 progresses, so that the position of the crater end 18 changes. It rises to the position shown by the broken line in the figure. That is, in a steady state, the crater end 18 exists at a position HA downward from the position where the initial solidified shell 14 is formed, but after stopping the slab drawing and immediately before restarting handling, the initial solidified shell 14 is formed. The crater end 18 rises downward to a position h away from the position where the crater end 14 is formed. In this way, at the final stage of casting, the position of the crater end 18 rises and the molten steel pressure at the crater end 18 decreases, so if a magnetic field of the same strength as in the steady state is applied to the molten steel, the molten steel 1412 will be stirred excessively. However, the electricity tittIj after restarting the slab drawing! Since it reduces the current supplied to the solenoid coil of the stirring device,
The strength of the rotating magnetic field applied to the molten steel 12 decreases, and the molten steel 1
The stirring intensity in step 2 is weakened. That is, crater end 18
The molten steel pressure at the time of the molten steel 12 is quickly determined from the molten steel pressure (the length of the molten steel 12), the molten steel withdrawal speed, and the amount of cooling water. Stir under conditions.

FIG. 2 shows the electromagnetic stirring method for molten metal in continuous casting according to the embodiment of this invention and the conventional l1i
It is a graph diagram comparing the tilff stirring method. In the figure,
The solid line shows the results of this invention, and the dashed line shows the conventional results. As is clear from the figure, after restarting slab drawing, conventionally the molten steel is stirred excessively and the white band index increases significantly, but according to the above example, the increase in the white band index can be suppressed. , it is possible to obtain a slab that is sound all the way to the end.

[Effects of the Invention] According to the present invention, since the strength of the magnetic field is reduced as the molten metal pressure in the final solidification region decreases, it is possible to avoid excessive stirring of the molten steel. Therefore, segregation at the joint of continuous casting and at the rear end of the slab R can be prevented, and the yield of the slab can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating a method of electromagnetic stirring of layer temperature in continuous casting according to an embodiment of the present invention, and FIG. 2 is a graph diagram comparing the present invention with the conventional method. Applicant's agent Patent attorney Takehiko Suzue -○ () Day+-:
stomach! Two ha! Stylish≦

Claims (1)

[Claims] A method for electromagnetic stirring of molten metal in which a magnetic field is applied to the final solidification region of the molten metal in continuous casting to stir the molten metal, characterized in that the intensity of the magnetic field is reduced as the molten metal pressure in the final solidification region decreases. Electromagnetic stirring method for molten metal.