JPH089729B2 - Method for suppressing CaO-based inclusions in Fe-Ni-based alloy - 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 controlling non-metallic inclusions, especially CaO-based inclusions, which influence the properties of Fe-Ni alloys. Further, the present invention is a Fe-Ni used for applications such as lead frame materials and shadow mask materials.
This is a proposal for a technique that is advantageously applicable to the production of a base alloy material.

[0002]

2. Description of the Related Art In general, non-metallic inclusions in alloys are classified according to their sources, that is, deoxidation products formed during deoxidation, reoxidation inclusions formed by being contaminated by the atmosphere, slag and It can be roughly divided into foreign inclusions that enter from refractory materials. Among these inclusions, the reoxidized inclusions have been taken measures such as refining in a non-oxidizing atmosphere and inert gas sealing in a continuous casting apparatus. Regarding foreign inclusions, measures such as selection of refractory material and improvement of tundish shape have been adopted to prevent slag from entering the mold. With these various measures, the presence ratio of reoxidized inclusions and exogenous inclusions in the non-metallic inclusions can be extremely reduced.

On the other hand, regarding the deoxidation product,
It was inevitably generated during deoxidation treatment, and now mainly forms non-metallic inclusions in the alloy. Of course, the composition of this deoxidation product differs depending on the type of deoxidation material, such as Al
In the case of deoxidation, it is Al ₂ O ₃ , and in the case of Si, it is SiO ₂ . In addition, complex deoxidation is often performed, and in the case of Si-Mn deoxidation, FeO is used.
-MnO-SiO ₂ based oxide, FeO in the case of Si-Mn-Al-deoxidized
The -MnO-SiO ₂ -Al ₂ O ₃ based oxide.

Under such a background, various compositions of non-metallic inclusions have heretofore been attempted to be controlled depending on the use of the alloy and the manufacturing conditions. For example, although for the cleanliness of the prevention and the molten metal in the continuous casting nozzle clogging improvement must be suppressed Al ₂ O _3, by adding Ca to the, the Al ₂ O ₃ inclusions Al Techniques such as changing to ₂ O ₃ -CaO inclusions and changing MnS to CaS have been established. In this way, conventionally, preventing nozzle clogging during continuous casting,
The CaO-containing slag is usually used for the purpose of improving the ductility and toughness of the alloy material. Therefore, the final non-metallic inclusion composition remaining in the alloy has a deoxidation product composition and a slag composition. It is usually a mixed composition, that is, an inclusion composition containing CaO.

[0005]

However, the presence of CaO-containing non-metallic inclusions generated for controlling such inclusions, on the other hand, deteriorates the punching property in the Fe--Ni lead frame material, and In the amber shadow mask material, since the etching property is deteriorated, it is desired to prevent the formation of CaO inclusions.

However, in the conventional melting process of the alloy, it is necessary to deoxidize to the order of several tens of ppm.
It is essential to use a basic slag mainly composed of CaO together with the deoxidizer. From an equilibrium point of view, the composition of the non-metallic inclusion must be the same as the slag composition, so that the CaO component is inevitably included in the composition of the non-metallic inclusion. There is currently no report on how to suppress this. On the other hand, CaO
Other slags, such as Li ₂ O and Na ₂ O-based slag, will not mix CaO, but Li ₂ O and Na ₂ O are expensive and are not practical to use as slag. .

In order to solve such problems in the technical field of the art, conventionally, as disclosed in Japanese Patent Laid-Open No. 3-146624, refining by a vacuum induction furnace that does not require refining slag is performed. Has been done. Certainly, if you use a vacuum induction furnace, you can obtain a product with good quality,
It has a drawback that the melting cost is high and the productivity is poor.

An object of the present invention is to propose a technique for suppressing CaO-based inclusions in Fe-Ni-based alloys without using a vacuum induction furnace.

[0009]

[Means for Solving the Problems] As a result of earnest research toward the achievement of the above-mentioned object, when the Fe-Ni alloy used for the lead frame and the shadow mask material in the oxygen-blown refining furnace was melted, the Fe- In the refining in the deoxidizing stage after deoxidizing and slagging the Ni-based alloy molten metal with the basic slag, first of all, the oxygen content after deoxidizing was 500 to 850 ppm as shown in Table 1 .
Perform preliminary deoxidation with strong stirring until the oxygen level is reached,
After that it becomes equal to the target amount of oxygen or in 2Nl / min · t the following conditions
The present invention has been completed based on the finding that it is effective to carry out finishing deoxidation by weak stirring.

[0010]

In general, the punching property of the lead frame material made of Fe-Ni alloy is that the punching surface is not disturbed. By the way, if many nonmetallic inclusions are present on the surface of the material, the punching surface is disturbed due to the hardness difference between the nonmetallic inclusions and the matrix. Therefore, as the lead frame material, it is necessary to melt a material having high cleanliness without non-metallic inclusions.

By the way, the CaO-based inclusions are
Like MnS, it exhibits ductility at the hot working temperature, so it is in a state of being extended in the hot rolling direction. This means that the surface area is increased and the cleanliness in the product stage is deteriorated. On the other hand, with respect to the etching property, since water is used at the time of etching, if CaO-based inclusions are present, they are preferentially eluted and the etching pattern is disturbed. Therefore, control of CaO-based inclusions is extremely important in refining Fe-Ni alloys.

In the refining of the molten Fe-Ni alloy, an AOD furnace and a top-bottom blowing converter are used. However, in the refining furnace with strong stirring, the slag-metal reaction reaches a near equilibrium immediately. It is well known that the composition of inclusions after the completion of deoxidation is close to the slag composition. Therefore, it can be easily imagined that if the amount of CaO in the slag is suppressed, the amount of CaO in the non-metallic inclusions in the alloy is also suppressed. However, since the slag composition plays an important role in adjusting the oxygen level and the sulfur level after deoxidation, it is not possible to easily control the CaO-based inclusions in response to the above-mentioned requirements. .

Therefore, in order to solve this, the inventors investigated the behavior of non-metallic inclusions after oxygen decarburization. As a result, it was found that the composition of the non-metallic inclusions was FeO-MnO system even in the presence of slag having a basicity of 1.0 or more, and CaO was not present. From this, the present inventors considered that it would be possible to change the amount of CaO by changing the oxygen level in the molten alloy.

Based on such knowledge, the inventors of the present invention again conducted an experiment in which the addition amount of the deoxidizing agent was changed in the presence of a slag having a basicity of 3 using a 70 ton AOD furnace and Fe-36% Ni alloy. About. As a result, as shown in FIG. 1, it was discovered that the amount of CaO in the non-metallic inclusions increased as the oxygen level in the molten alloy decreased. For example, the amount of oxygen after deoxidation is 50
Although it was confirmed that the CaO-based inclusions can be completely prevented from being formed when the content is 0 ppm or more, the oxygen level required for the Fe-Ni alloy is several tens of ppm, which is not practically useful.

Therefore, the present inventors have made further detailed studies and found that the amount of CaO in the non-metallic inclusions varies depending on the stirring force of the molten alloy even at the same deoxidizing level. That is, FIG. 2 shows the findings of the experiment conducted using the same molten metal as in FIG. 1, and as can be seen from this FIG. 2, weak agitation of 2 Nl / min · t or less of Ar sparging is performed. Then, substantially no increase in the amount of CaO in the non-metallic inclusions is observed. This is considered to be due to the difference in the speed at which the slag-metal reaction reaches equilibrium.

That is, the molten Fe-Ni alloy is decarburized with oxygen,
Then skimming, and in the presence of a basic slag containing CaO, for example, when subjected to Al deoxidation, the slag metal interface, 3CaO + 2 Al → 3 Ca + Al 2 O 3 ... (1) into the molten alloy by reacting It is considered that after entering and reacting with, for example, FeO in the molten alloy, it becomes FeO + Ca → Fe + CaO ... (2) and becomes CaO inclusions. However, when the oxygen level in the molten alloy is as high as 500 ppm or more, CaO is generated near the slag-metal interface and is easily absorbed in the slag.
When it is lower than 0 ppm, the chance of contact with oxygen decreases, CaO is generated after entering the molten alloy by strong stirring, and remains as CaO inclusions. In addition, CaO-based slag is apt to be mixed due to strong stirring.

On the other hand, in the case of weak agitation, the same as in the case of strong agitation, but the movement of Ca generated in the reaction of the equation (1) is slow, so that the reaction rate of the equation (1) becomes very slow. But (2)
Considering that the movement of Ca is slow in the reaction of the formula, it is considered that the generated CaO is easily absorbed in the slag because it occurs near the metal-slag interface. Therefore, as shown in FIG.
In the strong stirring bubbling with Ar gas of 2 Nl / min · t or more, the movement of Ca becomes active, and the active deoxidation reaction occurs, so that Ca easily enters the molten alloy. The CaO-based inclusions once trapped in the alloy can be effectively removed.

[0018]

[Example] In the case of refining 70 tons of molten Fe-42% Ni alloy melt deoxidized and smelted in a dolomite-clad AOD furnace, the base is used in the deoxidation phase after decarbonization, dephosphorization and slag discharge. Adjusting CaO-containing basic slag of 3 degrees, Si, Al
The preliminary deoxidation according to Table 1 was carried out under the conditions shown in Table 1. afterwards,
Pour hot water into a MgO-C ladle, change the amount of Ar gas blown from a porous plug, and again perform final deoxidation with Al , containing the same CaO.
It was carried out with the presence of basic slag . In addition, the comparative example is the above.
Deoxidized oxygen content, deoxidized under the same basic slag
An example in which the amount of agent added was changed is shown for reference. Na
Contact, Table 1 refining conditions and the results in this example
Summarized in.

[0019]

[Table 1]

[0020]

As described above, according to the present invention, it is possible to use an inexpensive raw material such as scrap, by using a low-cost raw material such as scrap, in the Fe-Ni alloy by changing the conventional melting process. The formation of CaO-based inclusions can be reliably prevented, and the cleanliness of the ingot can be improved. Therefore, the present invention is effective for producing a lead frame material and a shadow mask material of excellent quality.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of oxygen in molten alloy and the amount of CaO in non-metallic inclusions.

FIG. 2 is a graph showing the relationship between the amount of Ar sprayed in a ladle and the amount of CaO in non-metallic inclusions.

Claims (1)

[Claims] 1. When smelting an Fe-Ni alloy in an oxygen-blown refining furnace, the molten Fe-Ni alloy in the furnace is deoxidized through a basic slag and slag is removed. in, first, to <br/> amount of oxygen after deoxidation is oxygen levels of 500 to 850 ppm is subjected to preliminary deoxidation by vigorous stirring, then the deoxidation finish by comprising or in weak stirring the target oxygen amount A method for suppressing CaO-based inclusions in a Fe-Ni alloy, which is characterized by being performed.