JP3256146B2 - Melting test method of mold flux and mold for observation sample collection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for testing the melting of a mold flux for evaluating a mold flux to be added to a mold during continuous casting of steel, and a mold for observation sample collection used in the test. .

[0002]

2. Description of the Related Art For example, mold flux added to a mold during continuous casting of steel plays various roles. In other words, to keep the surface of the molten steel to be cast warm, to prevent oxidation of the molten steel surface in the mold and to quickly dissolve the floating inclusions, to control the lubrication between the mold and the slab,
Tasks such as controlling the optimal heat removal from the slab are imposed.

[0003] These effects of the mold flux have the effect of eliminating the surface defects of the slab and forming a beautiful casting surface. In particular, it is necessary to ensure the stability of the casting operation in the continuous casting operation and to improve the slab casting yield. It is indispensable to plan.

The mold flux is usually in the form of powder or granules, and its components are generally composed mainly of CaO and SiO ₂ , as well as Al ₂ O ₃ , compounds of alkaline earth metals and alkali metals (oxides, carbonates, etc.). Salt, fluoride, etc.), and adjusts the melting temperature, viscosity, etc., and further adds carbon to adjust the melting rate to form a flux composition. , Organic,
An inorganic binder or the like is used to keep a certain shape.

[0005] Here, the properties in the form of powder or granules such as the particle size distribution and bulk specific gravity of the mold flux,
Viscosity, melting state, especially the solidification characteristics of the film mold flux between the slab and mold during casting, that is, whether the mold flux is crystalline or amorphous in the solidified state, and whether the crystal is columnar or equiaxed Whether it is crystalline, or even coarse or fine, greatly affects the quality of the surface properties of the slab. Therefore, in actual use, it is necessary to measure each of the above-mentioned characteristics and to grasp them accurately.

Among the above-mentioned properties, the particle size distribution and bulk specific gravity in a powder or granule state can be easily measured, and viscosity, which is an important physical property in a molten state, can be measured relatively easily. On the other hand, as a method for reliably grasping the behavior in the melting process, an accurate method has not yet been established, and conventionally, the powder of the mold flux is formed into a triangular pyramid shape or a cylindrical shape, and this is formed in a heating furnace. A method of heating and observing the state of melting has been adopted.

However, even with such a method, even if the melting rate and the melting amount can be measured, it is difficult to accurately grasp the melting state of the mold flux. That is, there is a considerable difference in the situation between the case where the mold flux is added to the mold during the actual operation, and it has been considered difficult to find the difference in the delicate molten state of the mold flux. In addition, since the sample has a three-dimensional shape of a triangular pyramid or a column, observation in a wide field of view is impossible.

According to Japanese Patent Application Laid-Open No. 53-70040, there is also a method in which a mold flux is placed in a crucible, heated from one direction for a predetermined time and cooled, and then the crucible is cut vertically to observe the molten state of the additive. Are known.

However, in this method, after the surface layer of the mold flux is completely melted, the mold located in the inner layer with respect to the surface layer and supplied with less heat energy than the surface layer (at the same time) is located. Thermal energy is transmitted from the surface layer to the flux, and it is possible to measure whether the mold flux located in the layer is sequentially and uniformly melted, but in the surface layer where the same thermal energy is uniformly supplied, What ratio of the molten portion and the unmelted portion to the surface layer in the initial stage of melting of the surface layer,
It is possible to determine whether they exist with a distribution pattern and whether they are crystalline or amorphous, and to gain insight into the behavior in the melting process of how the surface layer melts. Did not.

Further, Japanese Patent Application Laid-Open No. Hei 7-204810 discloses a method for measuring the crystallization rate in a molten mold flux, which is a simple measurement formula for a mold flux crystallized under specific conditions. It is difficult to say that all the mold fluxes are properly evaluated by measuring the crystallization ratio by the method.

[0011]

As described above, since the molten state of the mold flux cannot be accurately observed by the conventional method, there is a mutual relationship between the observation result of the molten state and the quality of the surface properties of the slab. Could not be found.

Generally, the influence on the quality of the surface properties of the slab differs depending on the difference in the characteristics of the mold flux. This is considered to be due to the molten state of the mold flux, and therefore, in order to specifically obtain appropriate knowledge about what behavior is optimal, how to determine the molten state of the mold flux There has been a strong demand for establishment of an appropriate melt test method from the viewpoint of what should be grasped and what the melt test method should be for that purpose.

[0013] This is because if a melting test method for mold flux is established and an appearance similar to the actual molten state between the mold and the slab can be confirmed, it is necessary to select and use the optimal mold flux for various types of steel to be cast. This is because For the above reasons, it is an object of the present invention to provide a mold flux melting test method capable of simply observing the melting state of a mold flux and a mold used for the melting test.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has the following means. (1) The mold flux is charged into a graphite crucible, and the graphite crucible is heated for a predetermined time to dissolve the mold flux uniformly. Thereafter, the molten mold flux is extracted from the graphite crucible, and the internal shape prepared in advance is reversed. Circle
Injected into a tilted cooling mold with a cone or inverted pyramid ,
A melting test method of a mold flux, comprising preparing a cooled sample of a mold flux, traversing the sample, observing a cross section of the sample, and evaluating the mold flux.

(2) The mold flux is a graphite crucible
, The graphite crucible is heated for a predetermined time,
Dissolve the flux uniformly, then melt
Extract the flux from the graphite crucible and prepare
Note on inclined cooling molds with cylindrical or prismatic parts
To make a cooled sample of the mold flux,
And observe the cross section to evaluate the mold flux.
Of melting flux of mold flux
Test method.

(3) Dissolution of the mold flux of (1) or (2)
In the mold used for the melting test method, the heat capacity of the mold
Having inclined cooling action due to different orientations
A mold, characterized in that: (4) Dissolution of mold flux of (1) or (2)
A mold for use in a melting test method, wherein a cooling device is provided in the mold.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the melting test of a mold flux, the present inventors have found that the crystal precipitation temperature, which is one of the characteristic values of the mold flux when the molten mold flux is solidified, and the number of generated crystals and the particle size are different. We learned that this is a major factor in determining the quality of mold flux. Therefore, when the mold flux added to the actual mold is present in a film form between the mold and the slab, the crystal precipitation temperature, the number of crystals and the grain size are set as a test apparatus capable of realizing the state with good reproducibility. Fig. 2 shows the operation of the mold flux melting test device shown in
(A) and (b).

As a furnace for melting the mold flux, a muffle furnace is generally used, and a fixed amount of mold flux 1 (a flux component excluding Ig.loss) is charged from above the upper graphite crucible 2. At this time, the upper graphite crucible 2 is in a lowered state, the stopper 5 located at the center of the lower graphite crucible 3 is closed, and the loaded flux 1 is in a state where the upper graphite crucible 2 is in a heated state.
A part of it flows down to the lower crucible 3 while being dissolved (see FIG. 2).
-A), the flux in the crucible 3 is uniformly melted. A heating element 9 for heating the lower graphite crucible 3 is provided on the outer periphery of the lower graphite crucible 3.

After a certain uniform melting and holding time, the mold flux 1 rises the upper crucible 2 so that the stopper 5 rises at the same time and instantaneously flows out from the extraction port 4 of the lower graphite crucible 3 (FIG. 2B). ), The molten flux injected into the mold is accurately cooled under certain conditions through the intermediate nozzle 6 into the mold 7 located below. The molten flux is cooled and becomes a solidified sample of the mold flux.

The mold flux that has been cooled and solidified
It is taken out, the sample is cut in the longitudinal direction, the cut surface is observed with the naked eye, the structure is observed, the state of the crystal grains is observed, the state of the mold flux is grasped, and evaluation is performed. Then, it is determined whether or not it is appropriate for the type of cast steel.

Here, the injection into the mold 7 must be performed as quickly as possible in consideration of cooling of the molten mold flux. If this time is different for each mold flux sample, it will affect the state of crystal grains after solidification, causing a large error in the comparison between samples, making the meaning of the comparison thin, variation in evaluation, meaningless if it is strong May be evaluated.

The mold used in the present invention has a very important meaning and influences the proper evaluation of the mold flux. Therefore, the mold flux added to the mold becomes a film between the mold and the billet, and the It must be a sampling mold that is suitable for accurately grasping the state of exerting its effect as an agent.

As described above, in the present invention, it has been found that the molten mold flux is cooled, and the state of crystals generated during the cooling process affects the surface properties of the cast slab. As a mold suitable for measuring the crystallization ratio of the flux, it is necessary to have a shape such that inclined cooling is performed. The present inventors have conducted various studies on a mold suitable for inclined cooling, and as a result, have developed the mold of the present invention.

In view of the shape of the mold of the present invention, a portion to be rapidly cooled and a portion to be gradually cooled are constituted by a continuous and integral mold wall, and the temperature difference (heat capacity difference) of the mold wall is continuously increased. It must be a changing structure. Various structures can be considered as having such a structure. However, the present inventors consider that the sample after cooling accurately represents the target crystallization ratio and that the sample can be easily handled. FIG. 3 shows an example of the shape of the mold.

FIG. 3A shows a cylindrical mold having a shape in which an inverted conical hole is formed in the center of the cylindrical mold. The lower part is quenched by injecting a molten mold flux into the mold.
It is gradually cooled down to the top. A sample obtained from a mold having such a shape is advantageous because the sample can be cut from any position passing through the center of the bottom surface of the cone when cutting the sample to observe the crystal state of the longitudinal section.

FIG. 3B shows a mold having an inverted pyramid-shaped hole. As shown in FIG. When collecting a vertical cross section sample, it may be cut along a line passing through the center on the diagonal of the bottom surface of the cone. Figure 3-
a, In the mold of FIG. 3B , the sample can be easily taken out from the mold by reversing the upper and lower sides of the mold when collecting the sample.

As a modified example, as shown in FIG. 4, a circular (square) hole is formed in the center of a truncated inverted circular (pyramidal) pyramidal mold in order to make the sample into a cylindrical or prismatic shape. It is also conceivable to perform inclined cooling based on the difference in heat capacity in the vertical direction. In this case, it is possible to use the mold as a bottomed mold, but from the point of handling, place the mold on the bottom and place it on the surface plate 11 and inject the molten mold flux to make a sample. When the sample is taken out, there is an advantage that the sample can be easily taken out by pushing down the sample from the upper part of the mold after removing the surface plate 11. The sample may be cut by a line passing through the center of the bottom surface or the top surface in the same manner as described above.

In FIGS. 3 and 4, the shape of the sample is expressed as a pyramid or a prism, which means a polygon other than a triangle, and a square is the most preferable shape from the viewpoint of mold preparation.
As shown in FIG. 5, a water cooling device 10 for cooling the mold itself may be provided in the mold in order to avoid the temperature of the mold from the outside air, which is effective from the viewpoint of reproducibility.

The material of the mold is not particularly limited.
It may be made of metal such as iron, copper, or the like, or may be made of porcelain or porcelain.

[0030]

[Table 1]

In order to confirm the effects of the present invention, a mold flux having the composition and physical properties shown in Table 1 was used.
The molten mold flux was melted by the melting method shown in FIGS. 1 and 2, and poured into a mold shown in FIG. 3B. After cooling, the sample was taken out, the sample was cut vertically, and its cross section was observed. FIG. 6 shows an outline of the solidified structure of the sample sketched. Of course, the melting test conditions are all the same.

(A) to (f) shown in FIG. 6 correspond to mold fluxes A to F in Table 1. As shown in FIG. 6, the mold fluxes (a) and (b) are mold fluxes having a high degree of vitrification and high lubricity, and are easily vitrified regardless of whether the solidification temperature is high or low.

(C) and (d) have high crystallinity and slow cooling, and are excellent in quality, but because of their high crystallinity (columnar crystals), poor lubrication results in restraint. Often, a breakout alarm is generated, the crystallinity is large, the generation of slag bears also increases, and troubles due to poor operability often occur.

Further, (e) and (f) correspond to the above (a) to
This is an improvement over the disadvantage of (d), and its action is (c)
Prevents the columnar crystal or granular crystal from growing as shown in (d) and prevents the crystal from growing significantly when the molten mold flux is solidified. It is possible to obtain the nature.

As is apparent from FIG. 6, there is a large difference in the generation of crystal grains of the solidified structure obtained in the melting test depending on the characteristics of the mold flux, and the mold flux can be evaluated based on this difference. Furthermore, based on this evaluation, various mold fluxes may be used for the steel type suitable for this, and conversely, a mold flux suitable for the steel type can be created by selecting or blending the component composition.

[0036]

As described above, according to the present invention, the melting test of the mold flux can be carried out by a simple method, and by using a mold suitable for the method, accurate observation of the melting state of the mold flux can be performed. Has the effect of being able to perform, and by enabling accurate observation of such a molten state, it is possible to find a correlation between the observation result of the molten state and the quality of the surface properties of the slab, This is a great contribution to the production of good quality cast slabs having a smooth and beautiful casting surface.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a melting test method of a mold flux of the present invention.

FIG. 2 is a diagram showing an operation state of a melting test furnace.

FIG. 3 is a perspective view showing an example of a mold used in the present invention.

FIG. 4 is a perspective view showing another example of a mold used in the present invention.

FIG. 5 is a perspective view showing an example of a cooling mold used in the present invention.

FIG. 6 is a schematic view of a solidified structure of a sample obtained according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold flux 2 Upper graphite crucible 3 Lower graphite crucible 4 Extraction port 5 Stopper 6 Intermediate nozzle 7 Mold 9 Heating element 10 Water cooling device 11 Surface plate

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hidehisa Taniguchi 2544-6 Oya Hachiya, Buzen City, Fukuoka Prefecture Nippon Steel Construction Materials Industry Co., Ltd. Buzen Factory (56) References JP-A 7-204810 (JP, A) JP-A-7-164120 (JP, A) JP-A-10-58104 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/108 B22D 11/07 G01N 33/20 C21C 7/076

Claims (4)

(57) [Claims] The method according to claim 1] mold flux was charged into a graphite crucible, the graphite crucible and heated for a predetermined time, the mold flux allowed uniformly dissolved, then the molten mold flux was extracted from the graphite crucible, the internal shape previously prepared
Is injected into an inclined cooling mold having an inverted conical shape or an inverted pyramid shape to form a cooled sample of the mold flux, cut the sample longitudinally, observe its cross section, and evaluate the mold flux. Flux melting test method. 2. A mold crucible is charged into a graphite crucible, and the graphite crucible is heated for a predetermined time to uniformly dissolve the mold flux. Thereafter, the molten mold flux is extracted from the graphite crucible, and the internal shape prepared in advance is prepared.
Is injected into an inclined cooling mold having a cylindrical or prismatic shape , a cooled sample of the mold flux is prepared, the sample is traversed and its cross section is observed, and the mold flux is evaluated. Melt test method. 3. The mold flux according to claim 1, wherein
In the mold used for the melting test method, the heat capacity of the mold
It has a tilt cooling effect by being different in the vertical direction
A mold, characterized in that: 4. The mold flux according to claim 1, wherein :
The mold used in the melting test method of claim 1, wherein a cooling device is provided in the mold.