JPH05123829A - Treatment of molten steel - Google Patents

Abstract

PURPOSE:To absorb and remove nucleation site in molten steel by repeating cooling and heating operations, between the temp. at lower than the solidus of a steel and the temp. exceeding the liquidus and injecting glassy silicon dioxide together with inert gas into the molten steel. CONSTITUTION:The molten steel 8 is charged into a vessel 1 for molten metal coating the inner surface with glassy silicon dioxide 4 and the glassy silicon dioxide powder is injected together with the stream of inert gas from a nozzle 6. After this molten steel 8 is cooled at the lower temp. than the solidus, the molten steel is heated to the temp. exceeding the liquidus. After there coolings and heatings are repeated to become the aimed degree of undercooling, a stopper 2 is lifted to cast the molten steel 8 into a mold. The injected silicon dioxide powder is dispersed into the molten steel 8 and the nucleation site is absorbed and removed to obtain a casting having little micro segregation.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for supercooling molten steel.

[0002]

2. Description of the Related Art It is known that molten steel solidified under supercooling is rapidly solidified, so that microsegregation is reduced and a solidified structure becomes a fine ingot.

There is a method for producing good molten steel by such treatment. For example, Japanese Patent Application Laid-Open No. 1-127147 proposes the following method.

FIG. 3 is an explanatory view of an apparatus used in this method. Reference numeral 1 is a refractory container for molten metal, 2 is a stopper for closing the discharge hole of the container 1 for molten metal, 3 is a mold, 10 is molten steel, and 11 is an ingot. The inner surface of the molten metal container 1 and the outer surface of the stopper 2 are coated with vitreous silicon dioxide 4. Further, a high frequency induction heating coil 5 is provided on the outer periphery of the molten metal container 1 so that the molten steel 10 in the molten metal container 1 can be heated.

When the molten steel is treated by using the apparatus as described above, after the molten steel 10 is put in the molten metal container 1, glassy silicon dioxide powder is added to cover the molten metal surface for cooling and heating. Repeat the operation. When this cooling and heating operation is repeated, the inclusions (hereinafter referred to as nucleation sites) that are the starting points of solidification nucleation are removed from the molten steel, and the degree to which the molten steel is supercooled (the degree of supercooling of molten steel) is growing. By casting the sufficiently supercooled molten steel 10 in the mold 3, a good ingot 11 with very little microsegregation can be obtained.

At this time, since the vitreous silicon dioxide 4 is coated on the inner surface of the molten metal container 1 and the outer surface of the stopper 2, the molten steel 10 is treated without coming into contact with the refractory material such as the molten metal container 1. It For this reason, the nucleation site is not brought in from the refractory, so that the molten steel 10
Is easily overcooled. Further, the vitreous silicon dioxide 4 also has a function of absorbing inclusions in the molten steel 10 and makes the molten steel 10 more easily overcooled.

[0007]

However, the above-mentioned conventional method has a problem that it is difficult to apply it to a large-scale apparatus for treating a large amount of molten steel.

As described above, the vitreous silicon dioxide 4 coated on the inner surface of the molten metal container 1 has the function of preventing the nucleation site from being mixed into the molten steel. As the scale increases, the action of absorbing inclusions in the molten steel 10 becomes insufficient. That is, when the scale of the molten metal container 1 becomes large, the above glassy silicon dioxide 4
The degree of contact between the molten steel and molten steel becomes very small, and the inclusions are adsorbed only gradually.

Therefore, in order to increase the degree of supercooling and obtain good molten steel, it is necessary to repeatedly perform the cooling and heating operations of the molten steel, and it takes a long time for the treatment.

An object of the present invention is to provide a method for treating molten steel which can reduce the number of repetitions of cooling and heating operations for increasing the degree of supercooling of molten steel and can be applied to a large-sized treatment apparatus. To do.

[0011]

In order to achieve the above object, in the first invention, molten steel is placed in a vessel for molten metal whose inner surface is coated with vitreous silicon dioxide, and the molten steel is cooled. In the method for treating molten steel, which comprises repeating cooling and heating operations to make molten steel at a temperature lower than the solidus line of the steel, and then heating the cooled molten steel to make it at a temperature above the liquidus line of the steel, The vitreous silicon dioxide powder is blown into the molten steel in the container together with the inert gas.

Further, in the second invention, a steel ingot is placed in a molten metal container whose inner surface is coated with glassy silicon dioxide, and the steel ingot is heated to have a temperature above the liquidus line of the molten steel. Then, the heating operation and the cooling operation of cooling the molten steel to a molten steel at a temperature lower than the solidus of the steel are repeated, and the vitreous silicon dioxide powder is mixed with the inert gas into the molten steel in the molten metal container. Blow in.

[0013]

FIG. 6 is a diagram showing the relationship between the peak value of microsegregation of the ingot and the degree of supercooling of the molten steel before casting. In this figure, the solid line shows the value of P and the dotted line shows the value of C. As shown in this figure, if the degree of supercooling of the molten steel is increased, a good cast product with less microsegregation can be obtained. Therefore, the present invention has established a treatment method for easily obtaining molten steel capable of forming a cast product with less microsegregation.

When glassy silicon dioxide powder is blown into the molten steel, the silicon dioxide powder is dispersed in the molten steel, and the contact area between them is dramatically increased. Further, since the above-mentioned silicon dioxide powder is blown together with the inert gas, the molten steel is agitated and the contact between the two becomes even better. And
The blown silicon dioxide powder efficiently adsorbs and removes nucleation sites in the molten steel, so that it is possible to increase the degree of supercooling of the molten steel without repeating the heating operation and the cooling operation many times. it can.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an illustration of an embodiment of an apparatus for carrying out the present invention. In FIG. 1, parts that are the same as the description of the molten metal container in FIG. 3 are given the same reference numerals and description thereof is omitted. In this embodiment, a gas injection nozzle 6 is provided at the bottom of the molten metal container 1. The gas blowing nozzle 6 is connected to a pipe 7 for air-flowing the vitreous silicon dioxide powder by an inert gas such as argon, and the gas blowing nozzle 6 is introduced into the molten steel 10 together with the inert gas. A high quality silicon dioxide powder 8 is blown in. 9 is a molten steel temperature measuring instrument.

FIG. 2 is an explanatory view of a state in which molten steel treated according to the present invention is cast. 2, FIG. 1 and FIG.
The same components as those in FIG.

The processing operation for obtaining a good molten steel by the method of the present invention will be described. When molten steel is used as the starting material, it is processed as follows. Molten steel is put in the container 1 for molten metal, glassy silicon dioxide powder is added to cover the surface of the molten metal, and then the glassy silicon dioxide powder is blown from the gas blowing nozzle 6 onto an inert gas stream. This molten steel is allowed to cool and cooled as it is to be supercooled to a temperature lower than the solidus. Next, the high-frequency induction heating coil 5 is energized to heat the supercooled molten steel to make it a temperature higher than the liquidus. Further, the molten steel is allowed to cool again and cooled, and is supercooled to a temperature lower than the solidus. Then, the above cooling / heating operation is repeated until the molten steel reaches the target degree of supercooling.

When the starting raw material is a steel ingot, the following treatment is performed. A steel ingot is placed in the molten metal container 1 and the high frequency induction heating coil 5 is energized to heat it to obtain molten steel having a temperature higher than the liquidus line. After the glassy silicon dioxide powder is added to this molten steel to cover the surface of the molten metal, the glassy silicon dioxide powder is blown from the gas blowing nozzle 6 while being put on the stream of the inert gas. Then, this molten steel is allowed to cool and cooled,
The molten steel is supercooled to a temperature lower than the solidus. After that, the same operation as in the case of using the molten steel as a starting material is performed.

In any of the above cases, when the molten steel reaches the target degree of supercooling, the stopper 2 is raised and the molten steel is cast into the mold 3.

In addition, the blowing of the above-mentioned silicon dioxide powder is
The following three methods are appropriately adopted. It is blown only at the stage where molten steel is put into the molten metal container 1 or the stage where molten steel is produced.

Bubbling is continuously performed from the stage where molten steel is placed in the molten metal container 1 or the stage where molten steel is produced until the last supercooling is performed.

The molten steel is poured into the molten metal container 1 at the stage where the molten steel is put in or at the stage where the molten steel is produced, and then only the inert gas is blown to stir the molten steel.

(Example 1) 1000 kg of chromium steel having the components shown in Table 1 was placed in a molten metal container 1 having the structure shown in FIG. 1, and a high frequency induction heating coil 5 was energized and melted. Next, 80 kg of glassy silicon dioxide powder having a size of about 25 μm or less was blown into this molten steel for 5 minutes together with argon gas. Thereafter, the cooling-heating-cooling operation (totally two heating / cooling operations) was performed as described above to obtain molten steel having a degree of supercooling of about 140 ° C. Then, this molten steel was cast into a mold to form an ingot. The course of temperature change due to heating / cooling of the molten steel is shown in FIG.

[0024]

[Table 1]

(Prior Art Example 1) Heating and cooling operations were carried out in the same manner as in Example 1 except that glassy silicon dioxide powder was not blown in. The heating / cooling operation was performed for 4 cycles to obtain molten steel having a supercooling degree of about 140 ° C. The change in temperature due to heating / cooling of the molten steel is also shown in FIG.

(Embodiment 2) In a molten metal container 1 having the structure shown in FIG.
After adding g, the molten steel was allowed to cool and cooled.
Next, when the temperature of the molten steel reached about 1500 ° C., 80 kg of vitreous silicon dioxide powder having a size of about 25 μm or less was blown into the molten steel together with argon gas for 5 minutes.
After that, in the same manner as in Example 1, cooling-heating-cooling operation (1.5 cycles of heating / cooling operation) was performed,
A molten steel having a supercooling degree of 140 ° C. was obtained. The course of the temperature change of the molten steel due to this heating / cooling is shown in FIG.

(Conventional Example 2) The heating and cooling operations were performed in the same manner as in Example 1 except that the vitreous silicon dioxide powder was not blown in. The heating / cooling operation was performed for 3.5 cycles to obtain molten steel having a supercooling degree of about 140 ° C. The change in temperature due to heating / cooling of the molten steel is also shown in FIG.

Referring to FIGS. 4 and 5 showing the changes in temperature of molten steel in each of the examples and the comparative examples, the solid line A shows the result of the example and the dotted line B shows the result of the conventional example. Further, c ₁ is a point where molten steel is cast in the embodiment, c ₂
Is the point where molten steel was cast in the conventional example. And T
_L is the liquidus of this steel (1494 ° C), T _S is the solidus (1
473 ° C.) and ΔT indicates the degree of supercooling of molten steel.

Based on the results of FIG. 4 and FIG. 5, the processes of reaching the target degree of supercooling will be compared with each of the above embodiments and each of the conventional examples. The final degree of supercooling ΔT is about 140 ° C., but in order to obtain molten steel having the degree of supercooling ΔT, heating and cooling operations of 2 cycles and 1.5 cycles are performed in Examples 1 and 2, respectively. In contrast, in Conventional Examples 1 and 2, it was necessary to carry out 4 cycles and 3.5 cycles, respectively.

[0030]

INDUSTRIAL APPLICABILITY According to the present invention, a glassy silicon dioxide powder is blown together with an inert gas into molten steel in a molten metal container whose inner surface is coated with glassy silicon dioxide, and heating and cooling operations are repeated. This is a treatment method, and the blown silicon dioxide powder is dispersed in the molten steel and the contact area between them is dramatically increased, so that the nucleation sites in the molten steel can be efficiently absorbed and removed.

Therefore, according to the present invention, heating and
The degree of supercooling of the molten steel can be increased without repeating the cooling operation, a molten steel capable of forming a good cast product with less microsegregation can be obtained, and can be processed in a short time even with a large apparatus.

[Brief description of drawings]

FIG. 1 is an illustration of an embodiment of an apparatus for carrying out the present invention.

FIG. 2 is an explanatory view of a state in which molten steel treated according to the present invention is cast.

FIG. 3 is an explanatory diagram of an apparatus used in a conventional method.

FIG. 4 is a diagram showing changes in temperature of molten steel due to heating / cooling in Examples and Conventional Examples in the case of using molten ingot as a starting material.

FIG. 5 is a diagram showing changes in temperature of molten steel due to heating / cooling in Examples and Conventional Examples when molten steel is used as a starting material.

FIG. 6 is a diagram showing a relationship between a peak value of microsegregation of an ingot and a supercooling degree of molten steel before casting.

[Explanation of symbols]

 1 Molten Metal Container 2 Stopper 3 Template 4 Coated Glassy Silicon Dioxide 5 High Frequency Induction Heating Coil 6 Gas Blowing Nozzle 8 Blown Silicon Dioxide Powder 10 Molten Steel 11 Ingot

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B22D 41/01 7819-4E 41/02 A 7819-4E

Claims (2)

[Claims] 1. A molten steel having an inner surface coated with vitreous silicon dioxide, is charged with molten steel, the molten steel is cooled to a temperature lower than the solidus of the steel, and the cooled molten steel is then cooled. In the method for treating molten steel, in which cooling and heating operations are repeated to heat the molten steel to a temperature above the liquidus of the steel, a glassy silicon dioxide powder is blown into the molten steel in the molten metal container together with an inert gas. A method for treating molten steel, characterized in that 2. A steel ingot is placed in a molten metal vessel having an inner surface coated with glassy silicon dioxide, the steel ingot is heated to a molten steel having a temperature above the liquidus line of the steel, and then the molten steel is cooled. Then, the heating operation and the cooling operation for making molten steel at a temperature lower than the solidus of the steel are repeated, and a glassy silicon dioxide powder is blown into the molten steel in the molten metal container together with an inert gas. Method for processing molten steel.