KR0122342B1 - Method of measuring solid fraction of continuous casting strip shell - Google Patents

Abstract

A method of measuring solid fraction of solid shell of main piece through continuous casting by inserting pin which coated by metal which the melting point and density is lower than liquid pool, characterized in that the metal coated layer on the pin is within the limit of 0.3mm-1.0mm. Thereby, it is possible to provide a method of measuring the situation of 0.7 and 0.3 of the solid fraction among the solid shell of main piece through continuous casting at the same time by controlling thickness of the coated layer of the pin inserting in the main piece.

Description

How to measure solidification cell solidification cell

1 is a schematic diagram showing the area and the boundary of the solid and liquid phase during solidification of the cast cast.

Figure 2 is a photograph showing the Sulfur print of the cast slab with internal cracks generated during the performance.

3 is a layout view of an electronic stirrer (EMS) in the instrument.

FIG. 4 is a photograph showing a sulfur print of a cast steel in which white bands are generated by electrostirring.

5 is a magnified view of the position where the coated pin is inserted into the cast piece in the instrument.

6 is a macro etching picture showing the behavior of the Al coating layer according to the present invention and the comparative example and the positions of the solid phase ratios of 0.3 and 0.7.

＊ Explanation of symbols on main parts of drawing

1: Mold, 2: cast steel, 2a: solid shell, 2b: liquid pool, 3: 1st electronic stirring device (No. 1 EMS), 4: 2nd electronic stirring device (No. 2EMS), 5: fin, 6: Al coating layer.

The present invention relates to a method for measuring the solidity rate of the casting slag solidification cell (Shell) during casting in a continuous casting machine, and more particularly, the position of the solidification rate of the solidification cell layer of the casting slab is 0,7 and 0.3 It is about a method which can measure.

When casting is produced by continuous casting method, it is very important to know the formation behavior of cast solidification cell and solid fraction of cast solidification cell, for the following reasons.

In general, in the case of producing casting pieces by continuously casting molten steel, due to mechanical stress or bulging (swelling phenomenon of the cast pieces) caused by the change in the interval between the rolls of the players, the casting pieces have internal cracks or center segregation (solute elements at the center of the thickness of the cast pieces). Phosphorus carbon, phosphorus, sulfur, etc. ubiquitous phenomenon) occurs. These defects inside the cast steel will cause a major disruption to product quality as well as productivity.

Therefore, the electronic stirring method and the non-solidified cast reduction method are used as methods for reducing such internal cracks and central segregation. In order to derive the appropriate application conditions for the application of these methods, the cast steel solidification cell is described above. The formation behavior and the identification of solid state must be preceded.

The solid and liquid phases and their boundaries when the cast piece solidifies are shown in FIG. In FIG. 1, P layer is a region in which residual molten steel is impossible to flow, q1 layer is a region in which residual molten steel can be restricted, and q2 layer is a region in which residual molten steel is not affected by solid phase. And the solid phase rate of the boundary part (a) of q layer and q1 layer is 0.7, and the solidity rate of the boundary part (b) of q1 layer and q2 layer is 0.3. In addition, the position where the internal crack is generated is the boundary between the q1 layer and the p layer, and the central segregation is formed by collecting the solutes collected in the q1 layer in the central porosity generated by coagulation shrinkage.

The above-mentioned solid phase ratios 0.7 and 0.3 have an important meaning because control of the solid phase ratio 0.7 is necessary for the control of the internal crack, and control of the solid phase ratio 0.3-0.7 interval is necessary for the control of the central segregation. to be.

During continuous casting, the internal crack of the cast piece is caused by a gap between the q1 layer and the p layer (a), which is the boundary between the q1 layer and the p1 layer, due to the solidification of the dendrite of the q1 layer. The size of the inner crack once formed increases with the growth of dendrites.

The Sulfur print around which the internal crack is formed is illustrated in FIG. 2. As can be seen in FIG. 2, it can be seen that the solidification cell grows without any internal cracks, and then internal cracks are formed at a predetermined depth from the surface of the cast steel. In order to prevent the occurrence of such internal cracks, when molten steel flows through electronic stirring, the growth of dendrites is hindered when the cast steel is solidified, thereby reducing or preventing internal cracks.

FIG. 3 shows a schematic diagram of the instrument and the arrangement of the electronic stirrer, and is formed in the white bands (white, band, a and b) in the cast steel 2 to which the electronic stirrer 3, 4 of FIG. 3 is applied. It can be seen that. As described above, the position where the white band is formed in the boundary layer between the solid phase and the liquid phase by battery stirring is a point at which the solid phase ratio is 0.3 ((b) in FIG. 1).

As a result, when the white band is formed around the solidification cell in which the internal crack starts to be formed in consideration of the thickness of the q1 layer of FIG. 1, the internal crack can be more effectively reduced or prevented. Therefore, if the position of the white band formed by the electron agitation can be predicted before directly applying the electron agitation, an appropriate installation position of the electronic agitator for reducing the internal crack can be easily derived.

As described above, central segregation occurs when the solute of the q1 layer of FIG. 1 moves to the contraction hole. Therefore, by identifying the starting point (Fig. 1 (a)) and the finished part (b) in Fig. 1, the pores inside the playing piece are removed to prevent the central segregation caused by the movement of the solute. It is possible to effectively set the non-coagulated cast reduction section.

As described above, the conventional technique for measuring the solidification rate of the cast slab solidification cell for effectively setting the proper installation position of the electronic stirrer and the application section of the unsolidified slab reduction method is as follows.

A limit position where the molten steel can be molten from the distribution of A1 (the position at which the flow of A1 starts) by inserting a pin coated with 0.1 mm of A1 into the cast steel during casting (solid phase ratio 0.7 (Fig. 1)). After the bay was measured, the position where the center segregation was started (solid phase 0.3, (B) in FIG. 1) was inferred for computer calculation.

However, this method has a problem in that it is difficult to accurately measure the position of solidification ratios of the solidification cells of the cast steels 0.7 and 0.3 because the width of the q1 layer shown in FIG. 1 varies with the steel grade, the cooling rate, and the molten steel injection rate.

Thus, the present inventors have conducted research and experiments to solve the problems of the conventional method described above, and proposed the present invention based on the results, and the present invention adjusts the thickness of the coating layer of the pin inserted into the cast steel casting pieces It is an object of the present invention to provide a method for simultaneously measuring a position having a solid phase of 0.7 and a position of a solid phase of 0.3 in a solidification cell.

Hereinafter, the present invention will be described.

In the present invention, in the continuous casting, the method of measuring the solid phase rate of the solidification cell of the cast steel by inserting a pin coated with a metal having a lower melting point and density than the molten steel in the cast steel, wherein the metal coating layer of the pin is 0.3 ~ The present invention relates to a method for measuring the solid state rate of a solidified cell of a cast steel so as to be within a 1.0 mm thickness range.

Hereinafter, the present invention will be described in more detail.

In the present invention, in order to achieve the above object, when the continuous casting of molten steel, the melting point and density is lower than that of molten steel, the pin is coated in the thickness range of 0.3 ~ 1.0㎜ in the inside of the casting cast solid solid of the cast steel It is preferable to measure a rate, for the following reason.

If the thickness of the metal coating layer is less than 0.3 mm, the supply of A1 cannot be sufficiently observed when the coated metal rises due to the specific gravity difference in molten steel. Therefore, the linear distribution of the metal in the casting cast cell cannot be sufficiently observed, 1.0 In the case of mm or more, the thickness of the pin is so thick that it is difficult to insert the pin into the cast piece. In the present invention, the thickness of the metal coating layer is preferably limited to 0.3 to 1.0 mm.

In the present invention, the material coated in the above thickness range may be any material as long as the material has a sufficiently low melting point and a sufficiently low specific gravity than molten steel.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

When continuously casting molten steel using a continuous casting machine as shown in FIG. 5, A1 is 0.1 mm in the casting bow part installed with the electronic stirrer with the electronic stirrer (EMS: 3,4) off. 0.24 mm, 0.31 mm and 0.39 mm coated pins 5 were inserted into the slab 2 during casting at the positions shown in FIG.

After the cast was completely solidified, the specimen of the pin insertion part was taken, and the behavior of A1 was examined with a microetching structure. The results are shown in FIG.

As can be seen in Figure 6, in the case of Inventive Examples (1,2) satisfying the coating layer thickness range of the present invention A1 than in the case of Comparative Examples (a, b) that do not satisfy the coating layer thickness range of the present invention This restricted flow portion (A) and the portion (B) in which A1 flowed linearly are clearly shown, whereby the solidification ratio of the solidification cell of the cast steel piece is 0.7 (A) and 0.3 (B). .

The cause of the distribution of A1 as described above will be described in more detail with reference to FIG. 5. 5 is an enlarged view of a fin coated with A1 in the caster casting part, where a is a q2 layer, that is, a liquid region with a solid phase of 0.3 or less, and b is a p layer, that is, a solid phase of 0.7 or more. And c is a q1 layer, that is, an area ranging from 0.3 to 0.7 in solid phase.

When the pin 5 coated with A1 is inserted into the cast steel 2, A1 having a melting point of 660 ° C exists as a liquid phase inside the cast steel. Therefore, A1 in FIG. 5A is instantaneously diffused into the surrounding liquid phase, but A1 in FIG. 5B is moved to molten steel through the C in FIG. 5C. At this time, if the movement of the residual molten steel is limited by the surrounding dendrite, that is, in the c region, A1 moves only a limited distance (Fig. 6A), and is not interfered at all by the dentrite. That is, in the site a, A1 increases due to the specific gravity difference between A1 and molten steel. Further, A1 of the b part in the liquid phase on the surface of the cast steel continuously moves to the c part of FIG. As a result, a linear A1 distribution as in FIG. 6B is formed. From the above, it can be seen that the solid phase rate at position A of FIG. 6 is 0.7 and the solid state rate at position B of FIG. 6 is 0.3.

Further, as can be seen in FIGS. 4 and 6, the No. 5 in FIG. The depth of the white band (Fig. 4B) formed by the influence of 2EMS (4) coincides well with the depth of the linear distribution (Fig. 6B) of A1. From this, the linear distribution position of A1 (Fig. 6B) It was confirmed that the solid phase ratio of 0.3.

As described above, the present invention has the effect of simultaneously measuring the position of the solid phase ratio of 0.7 and 0.3 of the solidified cell of the cast slab by adjusting the thickness of the coating layer of the pin inserted into the cast.

Claims (1)

In the continuous casting, the method of measuring the solid phase rate of the solidification cell of the cast steel by inserting a metal coated pin having a lower melting point and density than the molten steel inside the cast steel, the metal coating layer of the pin is 0.3 ~ 1.0㎜ thickness The solid cast cell solidification measurement method of the cast steel, characterized in that the range.