JPH0243576B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for integrally connecting an intermediate container with a mold,
This relates to a subsurface solidification continuous casting method that starts solidification at a certain level of the mold. [Prior Art] The minimum dimension of the cross section of a slab in a continuous casting method is limited to the outer diameter of the immersion nozzle. Therefore, as a method for casting slabs having a diameter smaller than the minimum diameter of the immersion nozzle, a so-called submerged solidification casting method is known, in which casting is performed by connecting a tundish (hereinafter referred to as TD) and a mold. In such a casting method as well, lubrication between the mold and the slab is required as in normal methods. However, it is not possible with the submerged solidification casting method to reduce the friction between the mold and the slab by utilizing powder lubrication, as in the commonly applied powder casting method. On the other hand, static casting without lubrication between the mold and the slab is impossible because breakage of the outer shell, that is, a breakout accident will definitely occur. In addition, in the intermittent pultrusion casting method, which repeats constant drawing and stopping, not only does the mechanism of the drawing device that controls and drives the drawing and stopping become complicated, but it also causes cracks on the surface of the slab in response to the drawing and stopping cycles. There is a drawback that this occurs. For example, as a submerged solidification casting method,
There are methods described in Japanese Patent Publication No. 27028 and Japanese Patent Publication No. 53-37043. The former method involves casting by vertically vibrating the TD and the mold together, but in this method, the solidification start position varies depending on the uneven flow of molten steel into the mold and the degree of contact between the mold and the shell. There is a high risk of breakout due to rupture. The latter method involves inserting a graphite mold into the TD and casting without vibrating the mold in order to maintain a constant solidification start position.
For example, when casting low carbon stainless steel,
Graphite molds cause surface carburization of slabs, which requires surface removal. Therefore, the actual situation is that a method of casting by connecting a TD and a mold has not been put to practical use to date. [Problems to be Solved by the Invention] An object of the present invention is to keep the solidification start position constant and to prevent the occurrence of shell rupture, breakout, etc. in the submerged solidification casting method. [Means and effects for solving the problems] FIG. 1 shows an example of an apparatus for carrying out the present invention. An intermediate container 2 having an area larger than the cross-sectional area of the mold is placed above the water-cooled mold 1 to integrally communicate the water-cooled mold 1 and the intermediate container 2, and a heat insulating ring (described later) is placed at the boundary between the mold and the intermediate container. Install 3. The molten steel is fed from a TD (not shown) through a submerged nozzle 4 into the intermediate vessel 2, and solidification of the molten steel begins under the insulating ring 3. The outer shell slab 5 solidified in the water-cooled mold 1 is moved to pinch rolls (not shown) while the friction with the mold 1 is reduced by vibration in the casting direction of the mold 1 integrated with the intermediate container. It is continuously drawn and cast by The configuration and operation of this device will be explained in more detail. The mold is essentially the same as the water-cooled copper mold used in conventional continuous casting machines, but in order to further reduce the friction between the water-cooled mold (hereinafter simply referred to as the mold) and the slab, the length of the mold has been increased. It is also possible to shorten the length and connect a carbon graphite mold to the lower part. The heat insulating ring 3 is installed for the purpose of controlling the solidification start positions so that they are all on the same line in the circumferential direction.
The heat insulating ring 3 can be installed at the boundary between the mold 1 and the intermediate container 2, from the upper part of the mold 1 (Fig. 4) to the lower part of the intermediate container 2 (Fig. 5), and from the inner wall surface of the mold. Either the same position or a structure that protrudes inward. It is desirable that the material of the heat insulating ring 3 has low thermal conductivity, and it is necessary to control the material so that the progress of solidification of the molten steel at the position of the heat insulating ring is extremely small. In addition, it is necessary to select a material that has high high-temperature heat resistance against molten steel and has low chemical and mechanical erosion loss. BN, Si ₃ N ₄ and the like are suitable as materials having these characteristics. It is desirable that the intermediate container 2 is fixed to the mold 1 to have an integral structure and has an area larger than the cross-sectional area of the mold, and that a heating device 6 is added for the purpose of compensating the temperature within the container. FIGS. 6 and 7 show other examples of devices for implementing the present invention. FIG. 6 shows an example of an apparatus for casting small cross-section blooms using two strands.
In this case, blooms with even smaller cross-sections can be cast with multiple strands. FIG. 7 shows an example of an apparatus for casting a hollow round bloom by continuously feeding a steel pipe 7 into a mold 1. In this case, there are restrictions on the diameter of the immersion nozzle 4 and the cross-sectional size of the mold 1. It can be cast without any problems. Next, the casting method will be explained. In Fig. 1, when the mold 1 and the intermediate vessel 2 are combined into an integral mold and solidified under the surface of the metal in the mold for casting, the solidification within the mold may occur due to uneven inflow of molten steel into the mold or Depending on the degree of contact with the outer shell, it becomes non-uniform in the circumferential direction and the solidification start position varies. Further, when molten steel enters the joint between the mold 1 and the intermediate vessel 2 and solidifies, the shell ruptures and a breakout occurs. Therefore, in order to perform stable casting, it is necessary to start solidification uniformly in the circumferential direction below the joint between the mold 1 and the intermediate container 2. By installing the heat insulating ring 3 at the joint portion, it is possible to stop solidification from progressing above the ring and to solidify uniformly in the circumferential direction of the mold. However, even if solidified in this manner, as mentioned above, breakout accidents occur in stationary casting, so it is necessary to vibrate the mold in the casting direction. Note that if the mold is vibrated in the usual way, microcracks will occur on the surface of the slab, which will require maintenance. The first aspect of the present invention as a method for solving such problems is a continuous casting method that causes fewer surface cracks in slabs. Figure 2 shows the relationship between mold vibration speed and casting speed (Figure 2a) and slab in the mold vibration method in which the mold is vibrated in a sine curve and there is a region where the maximum descending speed of the mold is greater than the casting speed. The displacement situation between the mold and the mold (Fig. 2b) is shown. The feature of this casting method is that, as shown in Fig. 2a, there is a region (negative strip region shown with diagonal lines) in which the descending speed of the mold is higher than the casting speed of the slab. By compressing the cracks by pressing in the same direction, slabs with fewer surface cracks can be obtained. The ratio of the pressing length to the casting length per unit time corresponds to the negative strip speed rate expressed by the following equation. 0<2sf-V/V×100<5% where V=casting speed (mm/min) s=vibration stroke (mm) f=vibration cycle (c/min) If the mold vibration stroke s is less than 3mm, the mold The friction between the solidified shell and the solidified shell increases rapidly, causing surface cracks and breakouts in the slab. Moreover, if the stroke s exceeds 10 mm, the solidified shell will be pulled up and broken while the mold is rising. For this reason, the stroke s needs to be in the range of 3 mm or more and 10 mm or less. Moreover, when 2sf-V/V×100 exceeds 5%, the heat insulating ring pushes down the solidified shell and dents occur in the slab. Therefore, it is necessary to keep 2sf-V/V×100 below 5%. In this case, a shallow dent is formed on the surface of the slab in the circumferential direction corresponding to the area where the descending speed of the mold is greater than the casting speed once during one cycle, and shallow micro-cracks may occur in this dent. be. The second aspect of the present invention is a method in which no blemishes occur in the circumferential direction of the slab. Figure 3 shows the relationship between the mold vibration speed and the casting speed (Figure 3a) and the slab in the mold vibration method, in which the mold is reciprocated approximating a sine curve and the casting speed is always greater than the maximum descending speed of the mold. The displacement situation between the mold and the mold (Fig. 3b) is shown. In this method, since there is no region (negative strip region) in which the descending speed of the mold is always faster than the casting speed, the dent that occurs once during one cycle of casting as described above is not observed at all. However, this method tends to cause greater friction between the slab and the mold than the previous method, and to reduce friction it is desirable to select a mold taper or mold length that matches the amount of shrinkage in the mold of the cast steel type. [Examples] Examples of the present invention are shown in Table 1. 50 of SUS304
A 30T slab with a cross section of ×700mm is 1000mm/
It was cast at a casting speed of min. By installing an insulating ring made of BN or Si ₃ N ₄ on the top of the mold, casting can be performed without any breakout of the slab. Furthermore, as shown in Nos. 3 to 5 in Table 1, the range 0<2sf-V/ satisfies the condition that the pressing length to the casting length per unit time is 5% or less in the stroke range of 3 to 10 mm. When f was selected to be V×100<5%, the surface crack occurrence index was reduced to about half compared to Nos. 1 and 2. Next, as shown in Nos. 6 to 8 in Table 1, if f is selected in the range V > πsf in which the casting speed is always greater than the descending speed of the mold in the same stroke range of 3 to 10 mm, the surface crack occurrence index further decreased, becoming No.1
It decreased to less than 1/4 compared to ~2. [Effects of the Invention] By carrying out the present invention, it becomes possible to cast small sections, especially thin slabs, which were impossible to cast using the conventional immersion nozzle powder casting method, and there is no contamination due to air oxidation. In addition, it has become possible to produce a good slab without surface defects such as slag, which tend to occur due to the small cross section. Furthermore, by selecting the casting vibration conditions, the number of minute cracks that had occurred on the slab surface was reduced by half, and the grinder maintenance yield was also improved. 【table】

[Brief explanation of drawings]

1, 4, 5, 6, and 7 are explanatory diagrams showing examples of apparatus for carrying out the present invention, and
The figure shows the relationship a between mold vibration speed and casting speed in the region where the maximum descending speed of the mold is greater than the casting speed.
Figure 3 shows the relationship a between the mold vibration speed and the casting speed in the mold vibration method in which the casting speed is always greater than the descending speed of the mold, and the displacement situation b of the mold relative to the slab and the slab. FIG. 3 is a diagram showing the displacement situation b of the mold with respect to the slab. 1: Water cooling mold, 2: Intermediate container, 3: Heat insulating ring, 4: Immersion nozzle, 5: Outer shell, 6: Heating device,
7: Steel pipe.

Claims (1)

[Scope of Claims] 1. A continuous steel casting method in which an integral combination mold is used in which an intermediate container is placed above a water-cooled mold, and a heat insulating ring is attached to the boundary between the water-cooled mold and the intermediate container. The above-mentioned integrated combination mold is vibrated in the casting direction approximating a sine curve, and the maximum descending speed of the mold during vibration is faster than the casting speed, and the following conditions are satisfied: Solidification continuous casting method. 3≦s≦10 0<2sf-V/V×100≦5% where V=casting speed (mm/min) s=vibration stroke (mm) f=motion cycle (c/min) 2 At the top of water-cooled casting In a continuous steel casting method in which an integral combination mold in which an intermediate container is arranged is used, and a heat insulating ring is attached to the boundary between the water-cooled mold and the intermediate container for casting, the integral combination mold is approximated to a sine curve. At the same time, the casting speed is always faster than the vibration speed of the mold, and the vibration stroke of the mold is set to 3 mm or more and 10 mm.
A subsurface solidification continuous casting method characterized by the following: