JPH01113164A - Method and apparatus for producting unidirectionally solidified ingot - Google Patents

Abstract

PURPOSE:To radically eliminate problem of air gap caused by strain of lower face of shell and to improve cooling speed by water-cooling as directly hitting cooling water to the exposed shell. CONSTITUTION:Molten steel 1A is poured into a mold 2 on a water cooled base plate 31. Then, the molten metal poured is cooled with the water cooled base plate 31 and then the shell 1B comes to so thick that thickness thereof can support the molten metal 1A at the upper part, it is shifted to water cooling part 4. At there, by directly bringing the cooling water 5 into contact with the shell 1B without the base plate 31, it is cooled. In this result, as the unidirectional solidification is perfectly developed and rapidly progressed, an ingot without any segregation can be obtd.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a metal ingot in which solidification progresses in one direction throughout the ingot, and also includes an apparatus for carrying out the method. [Prior art] Taking steel as an example, metal casting generally involves pouring molten steel into a cylindrical ingot case placed on a surface plate using a top pouring method or a bottom pouring method. death,
This is done by solidifying using a riser if necessary. Solidification of molten steel progresses from the lateral direction toward the center, and although there are differences in degree, it is inevitable that segregation, so-called pipe, and looseness will occur in the center. Regarding inclusions, they solidify before they can fully float through the molten steel, so they become trapped in the steel ingot. These drawbacks are due to the relatively high C content (over 0.30%), and although it is necessary to prevent C segregation and coarsening of carbides, bearing steel, tool steel, and rough This problem is particularly serious when it comes to clean steel, where inclusions must be reduced as much as possible. As a method for obtaining ingots with virtually no segregation, the so-called unidirectional solidification method, in which molten steel is solidified from the bottom to the surface, has gained attention as being effective. The applicant has developed the technology and has already proposed it (Patent Application No. 1986-1)
No. 15747, Japanese Patent Application No. 137967/1982). These methods maintain conditions that strengthen the directionality of molten steel solidification by insulating or actively heating the surface of the molten steel, while allowing the solid-liquid interface to slowly rise. be. Through these efforts, we were able to reduce the segregation of the ingot to a level that does not pose a practical problem. However, because the bottom of the molten steel is cooled while the surface is kept warm or heated, it takes a long time to solidify the entire ingot. In addition, there is a problem that energy consumption is large. In addition, we experienced that it is difficult to obtain a thick unidirectional solidified mass in the solidification direction when cooling on a surface plate. This difficulty is due to the fact that the thicker the ingot, the less the after-heat from the molten metal will proceed to the extent expected from the thermal conductivity of the surface plate (made of copper). [Problems to be Solved by the Invention] An object of the present invention is to provide a method for producing a unidirectionally solidified ingot, which can perform unidirectional solidification completely and quickly and can easily cast even thick ingots. It is also within the object of the invention to provide an apparatus for carrying out the method. Feeling of distance

[Means to solve the problem]

The method for producing a unidirectionally solidified ingot of the present invention involves injecting molten metal, typically molten steel, into a mold set on a water-cooled surface plate, forming a solidified metal shell at the bottom of the molten metal, and then molding the molten metal into a mold. The shell is separated from the water-cooled surface plate, and cooling water is applied directly to the exposed shell to cool it, thereby promoting unidirectional solidification. The apparatus for carrying out this method is as shown in the drawings:
It is equipped with an indirect water cooling section 3 provided with a water cooling surface plate 31 that is cooled by cooling water 5 flowing on the lower surface, and a direct water cooling section 4 adjacent to the indirect water cooling section 3 having an open top and through which the cooling water flows, and includes a fireproof heat insulating material 21.
A bottomless mold 2 lined with , 22B, and while the mold 2 is in the indirect water cooling part 3, the skirt plate 22A covers the top of the direct water cooling part 4 and the cooling water 5
It is characterized by being configured to form a flow path. [Function] The molten steel 1A injected into the mold 2 is cooled in contact with the surface plate 31 in the indirect water cooling section 3, and the lower part of the molten steel solidifies to form the shell 1B. The shell becomes thicker as cooling progresses, slowing down the cooling rate. The degree of this is greater than expected from the thermal conductivity of the surface plate and solidified metal as described above, because as the shell becomes thicker, the surface in contact with the surface plate becomes distorted, and there is a gap between the surface plate and the shell. It turned out that this was due to the formation of an air gap.
It will be easily understood that if an air gap occurs, no matter how much the surface plate is cooled with water, the surface plate cannot be cooled effectively. Therefore, in the present invention, cooling is performed on a water-cooled surface plate at the initial stage of cooling, and once the shell becomes thick enough to support the molten metal on the upper part, cooling water is brought into direct contact with the shell without using a surface plate to cool the shell. I took it. By bringing the cooling water into direct contact with the shell, it is possible to essentially eliminate the problem of air gaps caused by distortion of the lower surface of the shell, and to improve the cooling rate. [Example] Using the apparatus shown in Figures 1 to 4, the length and width are 30 cm.
, an ingot with a height of 40CIIt was produced. At first, as shown in Figure 1, the mold 2 is placed on the water-cooled surface plate 31 @tl1250! J was injected, and after one minute had elapsed, the mold 2 was moved to the position shown in FIG. 3, that is, directly to the water cooling section 4, and the molten steel was cooled. During cooling, the cooling water flow rate is 8m/
The water was circulated at sec. In the obtained ingot, columnar crystals were well developed in the vertical direction throughout, and no segregation was observed. For comparison, the same equipment was used to solidify molten steel with only indirect cooling, that is, with the mold placed on a water-cooled surface plate.
An ingot was produced. This ingot had columnar crystals and no segregation up to a height of about 3 cm from the bottom, but above that the directionality became weak and segregation of C was observed. According to the method for producing an ingot of the present invention, unidirectional solidification occurs thoroughly and proceeds rapidly, so that an ingot substantially free of segregation can be obtained. In this way, it is also possible to produce thick unidirectionally solidified ingots, which has been difficult in the past. Therefore, the present invention applies not only to steel types that require uniform dispersion of fine carbide particles, such as low-speed steel and stainless steel for cutlery, but also to steels for extra-thick high-grade plates used in boilers and pressure vessels, etc. Suitable for producing ingots of steel types that are required to be homogeneous and free of defects. The apparatus of the present invention can easily carry out the above-described method for producing a unidirectionally solidified ingot.

[Brief explanation of the drawing]

The drawings are for explaining the present invention in detail, and FIG. 1 is a plan view of the apparatus. Figures 2 and 3
The figures are side views, partially in cross section, with the former showing the mold placed in the indirect water cooling section, and the latter showing the mold being moved to the direct water cooling section. Figure 4 shows the third
FIG. 2 is a longitudinal cross-sectional view taken along the line I-I in the figure. 1A... Molten metal IB... Solidified metal shell 2... Mold 21... Fireproof insulation material 3...
・Indirect water cooling section 31... Surface plate 4... Direct water cooling section 5... Cooling water 6... Mold drive means patent applicant Daido Steel Co., Ltd. Agent Patent attorney Souo Suga Figure 4

Claims (2)

[Claims] (1) After pouring molten metal into a mold set on a water-cooled surface plate and forming a shell of solidified metal at the bottom of the molten metal, the mold is separated from the water-cooled surface plate and cooling water is directly applied to the exposed shell. 1. A method for producing a unidirectionally solidified ingot, characterized in that unidirectional solidification is progressed by cooling with water. (2) Equipped with an indirect water cooling section equipped with a water cooling surface plate that is cooled by cooling water flowing on the bottom surface, and an adjacent direct water cooling section with an open top and through which cooling water flows, the bottom is lined with fireproof insulation material. and a drive means for reciprocating the mold between the indirect water cooling section and the direct water cooling section, the mold having a skirt plate extending laterally from the lower end, and while the mold is in the indirect water cooling section. 1. An apparatus for producing a unidirectional solidified ingot, characterized in that a skirt plate is configured to directly cover a water cooling part to form a cooling water flow path.