JPH05285596A - Continuous casting method for double-layer metallic material - Google Patents

Abstract

PURPOSE:To uniformalize the thickness of a front layer by measuring the temps. of the metals in a casting mild and improving the component sepn. of a front layer and an inside layer at the time of continuously producing the double layer metallic material varying in the chemical components of the front layer part and the inside layer part from molten metals. CONSTITUTION:The DC magnetic flux in the direction crossing the thickness of a slab is applied in a continuous casting mold and molten metals of the compsn. varying from each other are supplied above and below the static magnetic field band formed in the casting direction of the casting mold by the DC magnetic flux as a boundary. The temps. of the metals within the casting mold are measured and the boundary of two kinds of the metals is estimated. The supply rates per unit time of two kinds of the metals are so controlled that the boundary position coincides with a target value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously producing a multi-layer metal material having different compositions of surface layer portion and inner layer portion, that is, chemical compositions, from molten metal.

[0002]

2. Description of the Related Art As shown in FIG. 2, a DC magnetic flux across the entire width of a cast piece 2 is applied to a continuous casting mold 1 over its entire width, and a static magnetic field formed in the vertical direction of the mold by the DC magnetic flux. A continuous casting method for a composite metal material, in which metals having different compositions are supplied above and below the band 3 as a boundary, is disclosed in Japanese Patent Laid-Open No. 63-10894.
No. 7, etc.

[0003]

The above-mentioned conventional technique shows the basic concept of a continuous casting method for a composite metal material using a static magnetic field band formed by a DC magnetic flux.

However, since the method for detecting the boundary position of the two kinds of metals in the mold is not specifically disclosed, the component separation between the surface layer and the inner layer of the obtained multi-layer metal material becomes insufficient, or the surface layer There was a problem in quality assurance because the thickness became unstable and the product quality characteristics became uneven.

[0005]

SUMMARY OF THE INVENTION The gist of the present invention is to apply a direct current magnetic flux in the direction across the thickness of a slab in the continuous casting mold over the entire width, and to form in the casting direction of the mold by the direct current magnetic flux. In a continuous casting method of a multi-layer metal material in which two kinds of molten metals having different compositions are supplied above and below the static magnetic field band as a boundary, the temperature of the metal in the mold is measured to estimate the boundary between the two kinds of metal, A continuous casting method for a multi-layer metal material, characterized in that the supply amounts of two kinds of metals per unit time are controlled so that the boundary position coincides with a target value. In particular, it is effective to measure the temperature at the center of the mold. Specifically, it is preferable in actual operation to install a thermocouple on the side surface of the inner layer molten metal injection nozzle near the center of the mold.

[0006]

The function of the present invention will be described in detail below.

In the continuous casting method of a multi-layer metal material for supplying two kinds of molten metals having different compositions, a temperature difference occurs depending on the surface metal temperature immediately before casting into the mold and the inner layer metal temperature in the casting direction in the mold. Therefore, 2 corresponding to the surface and inner layers
The estimation of the boundary position in the mold from the temperature of the molten metal was investigated.

FIG. 1 shows the results obtained by immersing a thermocouple in molten steel at the center of the mold every 50 mm in the casting (depth) direction about 2 minutes after the start of casting and measuring the temperature. It can be seen that the temperature is almost constant in the vicinity of the meniscus, which corresponds to the surface layer metal, but when it gets deeper, the temperature rises rapidly and then becomes almost constant. That is, it is estimated that the position where the temperature changes abruptly corresponds to the boundary position, and the width of the transition region corresponds to the mixing region.

As a method of measuring the temperature in this way,
The method of immersing the thermocouple in the casting mold is generally considered. At that time, the temperature measurement position on the mold cross-section is such that the stagnation of the molten steel flow easily occurs on the inner surface of the mold and its vicinity, especially on the mold short side of the nozzle immersion part, and the difference in the molten steel temperature between the surface layer and the inner layer due to heat removal from the mold surface. Can be difficult to detect. Therefore, it is effective to measure the temperature in the central portion, which is less susceptible to heat removal from the mold surface.
Specifically, it is preferable to provide a thermocouple on the side surface of the immersion nozzle for the inner layer near the center of the mold to continuously measure the temperature.

From the thus obtained measurement results of the molten steel temperature in the casting direction in the mold, the actual boundary position of the two kinds of molten metal is estimated, and the two kinds of boundary positions are aligned so that they coincide with the target position, for example, the center of the static magnetic field band. The amount of metal supplied per unit time (injection rate) is controlled. This eliminates the problems that the boundary position deviates from the static magnetic field band due to operational fluctuations, the surface layer and inner layer components are not sufficiently separated, the surface layer thickness is not stable, and the product quality characteristics are non-uniform. ..

[0011]

EXAMPLE 18-8 stainless steel as shown in Table 1,
Two types of molten steel of general low-carbon steel were held in different tundishes, and molten steel was injected into the upper part of the static magnetic field zone 3 and molten steel into the lower part by using different immersion nozzles 4 and 4a as shown in FIG. .

[0012]

[Table 1]

The inner surface shape of the continuous casting mold 1 is 250 mm (thickness)
× 1200 mm (width), the casting speed was 1.0 m / min. The position of the static magnetic field band 3 is 4 from the meniscus 6 in the mold 1.
The height was 50 to 700 mm below and the intensity of the DC magnetic flux was 0.5 Tesla.

Comparative Example 1 is a case in which the temperature was not measured and the injection rate of the type 2 molten steel was controlled to be constant irrespective of the operational fluctuation. Comparative Example 2 is a case where a protective tube equipped with a thermocouple was inserted into the dipping nozzle for the inner layer in the mold on the short side of the mold during casting, and the temperature was measured. In Invention Example 1, when the temperature in the casting direction was measured by inserting a protective tube equipped with a thermocouple into the center of the mold during casting, the Invention Example 2 showed that the inner surface of the nozzle for injecting the inner surface of the mold was thermoelectrically charged. This is when the pair is attached. In Comparative Example 2 and Inventive Examples 1 and 2, the temperature distribution in the depth direction in the mold is obtained, and the boundary position of the two kinds of metals is estimated from the result, and the boundary position is the center of the static magnetic field band (below 575 mm from the meniscus 6) The injection rate of the two kinds of metals was controlled so that That is, when the boundary position estimated from the temperature distribution is above the static magnetic field band, the injection rate of the surface layer metal was increased and the injection rate of the inner layer metal was decreased. When the estimated boundary position is below the static magnetic field band, the reverse operation was performed, and the total injection speed of the surface layer and the inner layer was constant in each case.

Table 2 shows the results of summarizing the condition of component separation of the inner surface layer and the variation in surface layer thickness under each condition. According to the present invention, the separation of components in the inner surface layer is improved, and the variation in surface thickness is reduced.

[0016]

[Table 2] Note 1) Separation Index = (C1-C2) / ( C1 0 -C2 0) C1: slab solute concentration of the surface layer C2: slab inner layer of solute concentration C1 ^0: solute concentration C2 ⁰ of the supply molten steel to the surface : Solute concentration of molten steel supplied to the inner layer 2) Surface layer thickness fluctuation: Deviation from average thickness

[0017]

According to the present invention, in continuous casting of a multi-layered metal material, it is possible to produce a multi-layered metal material having excellent separation of components in the inner and outer layers and a uniform surface layer thickness.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a temperature distribution of molten metal in a casting direction in a mold.

FIG. 2 is a schematic diagram showing mold injection.

[Explanation of symbols]

 1 Continuous casting mold 2 Cast piece 3 Static magnetic field band 4 Surface layer immersion nozzle 4a Inner layer immersion nozzle 5 Surface layer solidified shell 5a Inner layer solidified shell 6 Meniscus 7 Surface metal and inner layer metal boundary

Claims (3)

[Claims] 1. A continuous magnetic flux is applied with a direct current magnetic flux in a direction transverse to the thickness of the slab over its entire width, and a composition is formed above and below a static magnetic field band formed by the direct current magnetic flux in the mold casting direction as a boundary. In the continuous casting method of a multi-layer metal material for supplying two kinds of molten metals having different temperatures, the temperature of the metal in the mold is measured to
A continuous casting method for a multi-layer metal material, which comprises estimating a boundary between two kinds of metals and controlling a supply amount of the two kinds of metals per unit time so that the boundary position coincides with a target value. 2. The continuous casting method for a multi-layer metal material according to claim 1, wherein the temperature measurement is performed at the center of the mold. 3. The continuous casting method for a multi-layer metal material according to claim 1, wherein the temperature is measured by installing a thermocouple on the side surface of the inner layer molten metal injection nozzle near the center of the mold.