JPS61276751A - Twin roll casting method for thin metallic sheet - Google Patents

Abstract

PURPOSE:To stabilize a casting operation and to obtain an ingot having an excellent characteristic without internal defects by controlling casting conditions in such a manner that the ingot drawn out between twin rolls completes the solidification near the line connecting the axial centers of the casting rolls. CONSTITUTION:The casting conditions of the twin roll casting method for casting continuously a thin metallic sheet by pouring a molten metal 2 between a pair of the horizontal casting rolls 1 and 1 rotating in an arrow direction and drawing drawing out the ingot 3 obtd. by cooling and solidifying the molten metal toward the arrow direction are so controlled that the ingot 3 solidifies on the line connecting the axial centers of the rolls 1, 1 or near the same by joining of the solidified shells formed on the surfaces of the rolls 1, 1. The generation of the internal and surface cracks and bulging, etc. is thus prevented and the ingot 3 having good quality is stably cast.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for continuously casting a thin metal plate by supplying molten metal between a pair of horizontal casting rolls (twin rolls), and in particular, a method that enables stable casting. The present invention also relates to a twin-roll casting method that allows slabs with excellent properties to be obtained.

(Prior Art) In the twin roll casting method, a pair of water-cooled rotatable casting rolls are arranged at a predetermined interval, and molten metal such as molten steel is supplied between these rolls.

This is a technology that continuously casts thin metal sheets by pulling out solidified thin sheet slabs downward while rotating rolls.

In this twin-roll casting method, the most important point is how to efficiently cast slabs with excellent properties and no defects. In order to achieve this purpose, conventional casting techniques have taken various measures, but none of them have been effective at present.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a twin-roll casting method that focuses on controlling the solidification completion position and that can obtain slabs with excellent properties. be. Note that, in the past, no proposals have been made regarding controlling the solidification completion position in order to improve the properties of the slab.

(Structure and operation of the invention) That is, the structure of the twin-roll casting method of the present invention is that in a method of continuously casting a thin metal plate by injecting molten metal between a pair of horizontal casting rolls, The solidification completion position of the piece is shown.

The method is characterized in that the casting conditions are controlled so that the casting conditions are on or near a line connecting the axes of the pair of casting rolls.

One of the casting conditions to be controlled is, for example, the casting speed.

Possible factors include the height of the hot water level, the contact arc length) or the distance between the rolls. In this way, if the solidification completion position of the slab is on or near the line connecting the axes of the pair of casting rolls, the casting operation itself will be stabilized, and the solidified shells formed on the roll surfaces will be mutually This results in good contact and a defect-free slab is cast.

The present invention will be explained in detail below with reference to the drawings.

First, the circumstances that led to the completion of the present invention will be explained using Fig. 1. In Fig. 0, 1 is a pair of horizontal casting rolls;
It is rotatable in the direction of the arrow, and has a water-cooled interior (not shown). 2 is a molten metal such as molten steel that is supplied between the rolls by a pouring nozzle from a tundish, and 3 is a slab that is solidified from between the rolls and drawn downward.

Therefore, three solidification completion points were selected in the figure: a position above the roll axis (■), an axis position (■), and a position below the axis (■), and the properties of the slab were investigated. The solidification completion point refers to the position where the respective solidified shells formed on the surfaces of a pair of casting rolls collide with each other.

At the position marked ■ in Figure 1, the solidification completion point is above the roll axis, so the extremely brittle slab (in the embrittlement region due to high temperature) immediately after solidification passes between the rolls. During this passage, the slab is rolled by rolls, which causes cracks in the slab. In addition, the molten metal is severely squeezed where the solidified shells collide, which is undesirable as it causes negative segregation.

Therefore, the position (2) causes the problem that internal cracks and surface cracks occur in the slab, and furthermore, it promotes segregation of the slab.

Next, in the case of position ■ below the axis center line position.

Even after passing through the roll axis, the slab still contains unsolidified molten metal, and as a result, the shell is remelted by the static pressure of the molten metal and the latent heat of solidification when the unsolidified portion solidifies. This has the disadvantage that bulging and breakout of the slab may occur.

Therefore, when the solidification completion point is set at the axial center line position (2), all of the problems described above that occur when the solidification is completed at the above-mentioned positions (2) and (2) are solved.

The present invention thus controls casting so that the solidification completion point is located on and near the roll axis, and for this purpose uses the following solidification formula as one means.

In the twin-roll casting method for thin sheets, when contact thermal resistance exists and the temperature distribution between the - rolls and the solidified shell is as shown in FIG. 2, the solidification equation is expressed as follows.

Here, ds is the solidified shell thickness, h is the overall heat transfer coefficient between the roll and shell, t is the contact time between the molten metal and the roll, )('
f is the latent heat of fusion considering superheat, and ρl,
′ and C′P are the density and thermal conductivity of the solidified shell, respectively.
When equation (1) expressing specific heat is solved for tis, the following relationship is obtained. The solidification equation obtained from this equation by considering the contact thermal resistance is that ds changes curvedly with respect to J in the range where t is small, and ds changes linearly with respect to π when t is sufficiently large. I understand that.

Figure 3 shows the 5n-Pb obtained by the inventors' experiments.
The relationship between d c/2 (d g) and t in an alloy was actually measured and shown. In addition, when calculating equation (3), the value of the overall heat transfer coefficient is required, but this is calculated from an arbitrary point of the actual measurement value (specifically, π = 0.04m1n4, ds
=0.8mm) h was determined by substituting the f) value into equation (3). The h obtained in this way is L#I'7v
lI'14/bA-17-2---dat-1+++
(A), and by substituting this into equation (3) to find the relationship between ds and t, the results of comparison with actual measured values are shown in FIG. In addition, when calculating, p'= 1.05X
10'kg/la", k'= 34.07kcal
/m・hr-deg, C'p = 3.58X
1O-2kcal/kg-deg, Hf =
9.58kcal/kg, TM=200”
0. Each value of T,=20°C was used. Furthermore, as can be seen from Figure 1, which also shows the relationship in the case of no thermal resistance, the relationship expressed by equation (3) agrees very well with the measured values over a wide range. therefore,
It can be said that the relationships of equations (1) and (3) above are extremely useful as solidification equations for twin roll casting.

Next, in Figure 4, the relationship between dc/2 and E in molten steel obtained through experiments by the present inventors is actually measured and indicated by a white circle. Let's examine whether it matches the calculation result obtained using the coagulation equation. First, from Figure 4, we can see that the measured value is relatively large, K = 0.02.
When the value of h in the case of molten steel is determined using the value of ds (=0.3 mm) of 9m1n"t', the following equation is obtained.

h = 1.4 x 10' (kcal/m”-hr
-deg) -(5) In FIG. 4, the results obtained using equations (3) and (5) are shown as a solid line, and the results when there is no thermal resistance are shown as a dotted line. It can be seen that this calculation result and the actual measurement value are relatively in agreement with each other by l,%.

As mentioned above, since the solidification equation (3) is in good agreement with the actual measurement value in the twin roll casting method, this is used to determine the contact time between the molten metal and the rolls so that the solidification completion point coincides with the axial center position of the twin rolls. In other words, it is sufficient to control the casting speed, etc.

Note that in the present invention, the solidification completion position does not need to be strictly on the roll axis, and there is a certain tolerance range there. That is, FIG. 5(a) shows the case where the solidification completion point is located above the roll axis, and in this case, if the tolerance range is 2a/view<1.3, slab cracking will be drastically reduced. Here, a is the shell thickness in the normal direction of the rolls, and ``a'' is the initial set roll spacing at the roll neutral point.

On the other hand, Figure 5 (0) shows the case where the solidification completion point is below the roll axis, and in this case, the allowable range is 2b/sentence>0.7 to suppress the occurrence of breakout. can do. However, b is the shell thickness at the neutral point of the roll.

Therefore, in the present invention, it is optimal to control the solidification completion position to the roll neutral point, but even if the solidification completion position deviates from the roll neutral point, as long as the above conditions are satisfied, the slab can be stably cast. Is possible.

(Effects of the Invention) According to the casting method of the present invention, it is possible to easily obtain slabs with good properties without cracks or blisters, and it is also possible to carry out stable casting operations. Therefore, the industrial value of the twin roll casting method of the present invention is extremely high.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of twin roll casting equipment for explaining the method of the present invention, Fig. 2 is an explanatory diagram showing the temperature distribution of each part between the rolls and the coagulation plate, and Fig. 3 is a 5n-pb Graph showing the relationship between ds and L in gold alloys, Figure 4 is a graph showing the relationship between cls and t in molten steel, Figure 5 (A) (0)
is a schematic diagram for explaining the permissible range of the present invention.

Claims (1)

[Claims] In a method of continuously casting thin metal sheets by injecting molten metal between a pair of horizontal casting rolls, the solidification completion position of the slab pulled out between the rolls is on or on a line connecting the axes of the pair of casting rolls. A twin-roll casting method for thin metal sheets, characterized by controlling casting conditions so that they are close to each other.