JPS62179855A - Solidified structure controlling method for casting slab - Google Patents

Abstract

PURPOSE:To break dendrite arm, to obtain equi-axed crystal for solidified structure and to prevent segregation by discharging electric capacitor for a short time and shifting non-solidifying liquid phase in casting slab by Lorentz force generated under interaction between a static magnetic field pre-supplied. CONSTITUTION:Under supplying the static magnetic field in the casting slab 4, in which the inner part is non-solidifying state, by a magnetic field generator 2, an electric charge of the capacitor 6 is discharged by using electrode rolls 5a, 5b for a short time, as pulsation in the casting slab. Lorentz force is obtd. by relative action between the discharge and the magnetic field, and molten metal, which is non-solidifying part in the casting slab 4, is shifted under large flow speed only by a little length. In this way, this force breaks the dendrite structure under growing and the broken dendrite structure causes generation of equi-axed crystal as the nucleus in the solidified part. Therefore, interruption of the casting operation and generation of inverse segregation is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for obtaining an equiaxed crystal structure during metal solidification.

[Conventional technology]

In continuous casting of steel, it is necessary to make the solidified structure equiaxed to prevent center segregation in the final solidified part. Conventionally, low-temperature casting and electromagnetic stirring have been used as methods for modifying solidified structures into equiaxed crystals.

The former method facilitates heterogeneous nucleation by minimizing the degree of superheating of the molten metal during liquid metal casting, thereby obtaining granular equiaxed crystals.
The conventional amount is also known as a simple coagulation structure modification method. The latter method uses electromagnetic stirring, such as a linear motor type, rotation type, or static magnetic field energization type, to forcibly generate molten metal flow near the solidification interface, thereby dividing the dendrite arms and obtaining uniaxial crystals. For the linear motor type and rotating type, a moving magnetic field is applied to the molten metal, and the eddy current generated in the molten metal interacts with the added magnetic field to generate forced flow of the molten metal. In this method, a static magnetic field is applied to the molten metal, and a direct current is constantly supplied in this state to obtain the Lorentz force.

[Problem that the invention seeks to solve]

However, these conventional methods have a problem in that center segregation that occurs in the final solidification part of continuously cast slabs cannot be completely prevented. Also.

The low-temperature casting method has a problem in that base metal tends to adhere to the inside of the nozzle for supplying the molten metal, and therefore the casting operation is often interrupted. on the other hand.

In the electromagnetic stirring method, molten steel is strongly stirred in one direction for a certain period of time, so that the liquid phase within the solid-liquid coexistence phase is strongly stirred in one direction, which tends to cause so-called negative segregation zones. In addition, with linear motor type or rotation type methods, if electromagnetic stirring is applied just before the end of solidification, the solidified shell has already developed thickly, so in order to supply electromagnetic force to the center, extremely large-capacity oscillation is required. In addition, in the case of the static magnetic field energization method, it is necessary to constantly supply a large direct current. The purpose of the present invention is to provide a method that can appropriately obtain equiaxed muscles without causing any damage.

[Means to solve the problem]

For this reason, the present invention provides a method for discharging the electric charge stored in a capacitor in the slab within a short time while supplying a static magnetic field within the slab.
The basic feature is that the unsolidified liquid phase of the slab is moved by the Lorentz force caused by the static magnetic field supply and electric discharge, thereby dividing the growing dendrite arms and obtaining fine crystals.

Hereinafter, the present invention will be explained based on the drawings.

Figures 1 and 2 show an example of the structure when the present invention is applied to a continuous cast slab of steel, where (1) shows a guide roll;
(2) is a magnetic field generator a, <3 is a discharge device, (April is a continuously cast slab (hereinafter simply referred to as slab), and the slab (
4) has a completely solidified phase on the outside (41) and an unsolidified phase on the inside (41).
42).

The magnetic field generator (2) has an N pole and an S pole facing each other on both sides of the slab (4). Also, the discharge device (31) has a magnetic field generator ff ( 2
The electrode roll (
5a) (5b), and electricity is applied between the upper and lower electrode rolls (5a) and (5b) on each side of the slab. In addition, (6) is a capacitor that constitutes a discharge device, (
7) is a switch.

The present invention uses the above-described device to generate a static magnetic field (a static magnetic field due to the N and S poles on both sides of the slab) by the magnetic field generator (2) to the slab (4) whose inside is in an unsolidified state. is supplied, and in this state, the electric charge stored in the capacitor (6) is discharged into the slab (4) in a pulsed manner within a short time using the electrode rolls (5a) (5b). Due to the interaction between the electric discharge and the magnetic field supply, a Lorentz force is obtained, and the unsolidified molten metal of the slab (4) moves by a small length at a large flow velocity, thereby destroying the growing dendrites.
Equiaxed muscles are generated using this as a nucleus.

The time required for discharging the capacitor (6) depends on the inductance of the circuit, but by making the inductance sufficiently small, the discharging can be completed in an extremely short time. In other words, by reducing the inductance, it is possible to supply a large current to the slab, albeit for a short time.

For example, if a 500 μF capacitor is charged with 25 KJ and the inductance of the %@ path is 10 mH, the discharge time will be on the order of 50 μsee. At this time, the Lorentz force generated by the static magnetic field and discharge current supplied from the outside also acts within the slab for a time equal to the discharge time, thereby moving the liquid phase at the solidification front. In the method of the present invention, even if the Lorentz force F=JXB (F=Lorentz force, J=current density, B=magnetic flux density) is small compared to conventional electromagnetic stirring, the discharge time is extremely short, so The acceleration of the dendrite arm becomes extremely large, and therefore the amount of change over time in the shear stress exerted on the dendrite arm becomes large. For this reason, the strain rate within the dendrite arm becomes extremely high, albeit for a short time, and grain boundaries are likely to occur within the arm. Conventionally, it has been believed that the melting point of grain boundaries is much lower than that inside grains (due to interfacial tension), and if a grain boundary exists within an arm in a solid-liquid coexistence state, the grain boundary will remelt and the arm will It will be divided. Thus.

Nuclei for equiaxed myogenesis are released into the liquid phase.

This accumulates and becomes fine granular equiaxed streaks. As described above, in the present invention, since the amount of time change in the Lorentz force is extremely large, even if the Lorentz force itself is small, the rate of strain generated in the dendrite arm is extremely large compared to normal electromagnetic stirring, and the arm is divided. This is based on the principle that it becomes easier.

Furthermore, in the method of the present invention, the liquid phase is not constantly moved but only instantaneously accelerated.

It has the advantage that the so-called white band generated by electromagnetic stirring is not generated at all.

〔Example〕

Figure 3 shows the solidification structure when the method of the present invention is applied to continuously cast slabs, in comparison with that of continuously cast slabs produced by low-temperature casting. In the method of the present invention, a steel type containing 0.45 H in C was used.

A device similar to that shown in FIGS. 1 and 2 was used, in which a 25 KJ charge was carried out using a 500 μF capacitor.

Discharge was performed at a frequency of 15 seconds each under a circuit inductance of 10 mH. In addition, as other conditions, the distance between the electrode rolls of e and e is 4005 m, and the magnetic flux density is 1
/2 is 1000 Gaus@ with the air center at the corresponding position,
The slab size was 1000 vum" x 250 m, and the casting speed was 1 m/min.

Furthermore, the coagulation rate at the location where the electromagnetic pulse discharge was performed was approximately 30%.

As is clear from the figure, the solidified structure obtained by the method of the present invention has stable equiaxed striations in the center, and C = 0.45%, which was difficult to form equiaxed striations even at low temperature casting. It can be seen that the coagulation structure is effectively improved even with carbon concentration.

〔Effect of the invention〕

According to the present invention described above, by discharging a capacitor in a short time and obtaining a Lorentz force by interaction with a static magnetic field supplied in advance, an extremely large amount of time change in the liquid phase transfer rate can be achieved by discharging an unsolidified liquid. The phase can be moved for a short time,
This effectively breaks one dendrite arm,
The coagulated tissue can be appropriately made into equiaxed muscle. and,
By applying the present invention to the manufacturing process of continuously cast slabs, it is possible to reliably prevent center segregation from occurring in the final solidified part of the slab. Furthermore, according to the method of the present invention, continuous casting can be carried out without causing problems such as interruption of casting operations as in conventional low-temperature casting methods. It also has the advantage of being able to effectively suppress it. Furthermore, in terms of equipment, there is no need for a large-capacity oscillator, and there is no need to constantly flow a large current, so it can be implemented at a lower cost than conventional methods.

[Brief explanation of drawings]

Figures 1 and 2 show an implementation situation when the method of the present invention is applied to continuous casting of steel. Figure 1 is a front view,
The figure is a sectional view taken along the - line in Figure 1. FIG. 3 shows a comparison of the solidified structure of a slab in an embodiment of the present invention with that of a slab cast by low temperature casting. Patent applicant Nippon Kokan Co., Ltd. Inventor Middle 1) Positive 2 Same
Hide Takasugi Tatami volume
Akira Ozeki, Patent Attorney
Yoshihara Ministry Ball amount same high school
Bridge consumption lawyer Hiroko Yoshihara Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] While supplying a static magnetic field into the slab, Removes the charge stored in the capacitor within a short time discharge, and this static magnetic field supply and discharge - Moves the unsolidified liquid phase of the slab by Lenz force This allows Dendra to grow. To divide the light arm and obtain fine crystals. Solidification structure control of cast slabs characterized by Method.