JPH02303660A - Method for continuously casting steel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a continuous casting method for steel aimed at reducing center segregation.

[Prior Art] Conventionally, methods for reducing center segregation of steel materials produced by continuous casting methods include: (1) increasing the equiaxed product ratio;

Specifically, (a) the casting temperature is kept low, as close to the solidification temperature as possible, and the melt is tapped.

(b) Apply electromagnetic stirring or ultrasonic vibration in the mold or cooling zone to suppress the growth of columnar crystals, multiply crystal nuclei, and increase the equiaxed crystal ratio. (c) Tanditshu,
Alternatively, a cold material such as a metal piece or powder is introduced into the mold to lower the temperature of the molten steel and increase the growth of crystal nuclei.

■Apply pressure to the billet at the final stage of solidification to control the flow of the molten metal to reduce center deviation.

Each of these methods may be used alone or in combination with other methods.

As a method and apparatus that meet the above viewpoints, (1)
Utility Model Publication No. Sho Go-46941i, “Continuous Casting Apparatus J
(2) Japanese Patent Application No. 100481/1983 ``Method for continuous casting of steel''.

What is disclosed in the publication (1) is that a rod-shaped part that has a built-in cooling means and can be rotated at a predetermined circumferential speed by a drive device is immersed in the molten steel in the tundish above the tapping nozzle of the tundish. (2)
What is described in the application is that a part of the molten steel being cast in the tundish is sprayed and turned into droplets by an inert gas jet, and after solidifying part or all during flight, the molten steel is poured into the tundish. The aim is to suspend the solidified particles in the molten steel inside the steel, and use the solidified particles as nuclei during solidification to increase the equiaxed crystallinity and obtain a steel material with less central segregation.

[Problems to be Solved by the Invention] In the apparatus of (1) above, in order to create a solidified shell, a rod-shaped member for cooling the molten steel that can rotate in the molten steel and a cooling system for cooling are required. An apparatus for carrying out method 2) requires means for atomizing a portion of the molten steel using an inert gas jet to form droplets, which actually results in high-cost equipment.

[Structure of the Invention] The present invention has been made for the purpose of solving the above-mentioned problems, but it involves turning a part of molten steel into droplets without performing gas blowing, etc., and solidifying the droplets while they are being scattered. The purpose is to uniformly inject and disperse the coagulated particles into the mold.

Therefore, in the present invention, a plurality of hot water tap nozzles are installed at the bottom of the ladle so that the hot water level of the tundish is at least 0.
The molten steel is placed evenly on the molten metal surface at a ratio of 1 or more per 15 m", and the molten steel is allowed to flow down into the tundish and the molten metal surface is uniformly stirred. In this way, a portion of the molten steel in the tundish is liquefied. After turning into droplets and solidifying them while scattering,
This is a method in which the solidified particles are suspended in molten steel and poured into a mold.

That is, in the method of the present invention, the molten metal can be drawn evenly without blowing gas, etc. by arranging the tapping nozzles of the ladle evenly with respect to the tundish molten metal surface and at least one or more per 0.15 m'' of molten metal surface. A portion of the liquid can be made into sufficiently fine droplets and can be converted into solidified particles.

FIG. 1 is a concrete explanatory diagram of implementing the continuous casting method of the present invention.

In the figure, 1 is a ladle, 2 is a tundish, and 3 is a mold. Molten 84 is transferred from the ladle 1 through the tundish 2 to the mold 3, and is continuously cast.

As shown in the figure, there are a plurality of i hot water tap nozzles q at the bottom of the ladle 1, and seven of them have a hot water level of 0.15 m in the tundish 2.
”, one or more of them are arranged evenly with respect to the hot water surface.
When the tapping nozzle 5 is provided with an area larger than 15 m'', the stirring action of the surface of the hot water, which will be described later, will not be sufficient.

In this case, the tapping nozzle S does not come into contact with the molten metal surface of the tundish 2, and an appropriate molten steel flow distance is maintained between the molten metal surface and the end of the tapping nozzle 5.

The molten steel passes through a plurality of tapping nozzles 5 from the ladle 1 and flows down to the tundish 2, and the flowing molten steel flow 6 stirs the surface of the tundish L2.

At this time, a portion of the molten steel is turned into droplets, and further solidified during the scattering to generate solidified particles 7. This solidified particle 7
Returns to the molten steel 8, suspends it therein, and injects it into the mold 3 located below the nozzle 9 provided at the bottom of the tundish 2.

[Function] According to the continuous casting method of the present invention, molten steel is caused to flow down from a plurality of tapping nozzles so as to stir the molten metal surface of the tundish, so that a part of the molten steel becomes droplets due to this stirring, and further scatters. During the process, the particles are cooled mainly by radiation cooling, and part or most of them solidify to become solidified particles.

These solidified particles are added to the molten steel in the tandish. death,
These solidified particles become crystal nuclei of the equiaxed product, and solidification starts from these, thereby significantly improving the solidified structure, increasing the isotransportation number, and reducing center segregation. Of course, some of the solidified particles generated by stirring are remelted in the molten metal, so
Not all of them are effective crystal nuclei, though! As an eleventh-order effect, these solidified particles take away the latent heat of melting when remelted, so they have a cooling effect.

Furthermore, since stirring is performed within the tundish, there is no problem of slag being caught in the mold.

[Example] 13 tons of high carbon of 0.8% G - 0.25% Sl - 0.5% Mn (all weight %) was melted, and a diameter of 9.5
Cabinet ■φ, ? , (6 from a ladle equipped with 2, 4, and 6 tap nozzles of 1 mmφ and 5.5 mmφ, respectively.
The water was allowed to flow down into a tundish with an area of 90cm x 90cm.

The degree of dissolved Mm in the tundish was adjusted within the range of 1485 to 1495°C.

And the diameter 13.5cm provided at the bottom of the tanditshu.
■Through a φ nozzle, the hot water was poured into a mold that grew a cross section of 0 mm φ.

The macrocorrosion of the cross section and the unevenness of the center of the billet cast by this method were investigated.

For comparison, the same investigation as described above was also carried out on a billet produced by a conventional casting method in which a ladle and a tundish were cast using a single immersion nozzle to prevent droplets from being thrown up.

The results are shown in Table 1.

For the ladle with four and six tapping nozzles, the equiaxed product rate is improved and the center segregation rate of carbon is also reduced. However, there is no noticeable difference between the number of nozzles, 4 and 6, and it is clear that the number of nozzles should be at least 1 per 0.15 2 of the tundish area.

On the other hand, when the number of nozzles was two, there was no significant difference from the conventional method, and neither the improvement in the equiaxed crystallinity nor the reduction in the carbon center segregation rate was sufficiently observed.

Note that the center segregation rate is the ratio of the carbon content in the 5×5 ■■ 2 area at the center of the billet to the carbon content by ladle analysis.

Table 1 [Effects of the Invention] According to the present invention, the equipment cost can be lowered than by the method described in the above-mentioned publication and specification, and a billet having a solidified structure with low center segregation can be produced. I can do it. Therefore, rolled products and secondary processed products using billets that are homogeneous and have excellent workability can be obtained.

[Brief explanation of drawings]

FIG. 1 shows an example of an apparatus for carrying out the invention. 1...Ladle, 2...Tanditshu, 3...
Mold, 4... Molten steel of the dollar, 5... Tapping nozzle of the dollar, 6... Molten steel flow, 7... Solidified particles, 8
...Tanditshu's molten steel, 9...Tanditshu's tapping nozzle.

Claims (1)

[Claims] (1) In a continuous steel casting method in which molten steel is transferred and cast through a ladle, tundish, and mold, a plurality of tap nozzles that are not immersed in the molten metal in the tundish are placed at least at a level of 0.15 m^2 in the tundish. The molten steel flows down into the tundish from one or more ladles arranged evenly on the molten metal surface, stirs the molten steel surface, thereby liquefying a part of the molten steel, and further dispersing it while scattering. A method for continuous casting of steel, characterized in that after solidification, the solidified particles are suspended in molten metal in a tundish and poured into a mold.