JP2563681B2 - Powder for casting steel containing high aluminum rare earth elements - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to rare earth elements (hereinafter referred to as REM).
(Hereinafter referred to as)) is used for casting a high aluminum content steel.

[0002]

2. Description of the Related Art Generally, in continuous casting of steel, in order to prevent oxidation of molten steel and lubricate between a mold and a solidified shell, Ca
O, SiO ₂ as a main component, and Na ₂ O, K as a solvent agent
₂ O, Al ₂ O ₃ , NaF, KF, AlF _{3 and the} like to which carbon powder is added are used.

However, even if these powders are used, in the casting of high aluminum content steel, a part of Al in the molten steel is oxidized to Al ₂ O ₃ , and since the oxide in the powder is reduced, casting is performed. The powder changes in quality, and the viscosity and melting temperature, which are important physical properties of the powder, rise. As a result, casting accidents such as frequent occurrence of vertical cracks and lateral cracks on the surface of the slab, deterioration of the internal quality of the slab, and breakout due to poor lubrication occur. Further, during casting, white smoke is generated due to powder in the mold, which causes problems such as hindering casting work such as monitoring the molten metal surface and deteriorating the working environment.

Therefore, in the casting of high aluminum content steel, as shown in, for example, Japanese Patent Publication No. 63-56019, Si in powder is used to suppress Al oxidation in molten steel.
O _{2 is set} to 7% by weight or less. In addition, JP-A-61-186
As disclosed in Japanese Patent No. 156, the content of BaO is 8 to 40% by weight, the basicity is 0.3 to 0.6, the melting point is 800 to 900 ° C., and SiO ₂ in the powder is increased to stabilize the physical properties at the time of absorbing Al ₂ O ₃ . A powder containing 1 to 10% by weight of Li ₂ O has been proposed.

[0005]

However, even if these powders are used, for example, if the SiO ₂ in the powder is
Even if the content is less than 10% by weight, the generation of Al ₂ O ₃ can be suppressed, but the viscosity and melting temperature of the powder become unstable, resulting in poor powder inflow. On the other hand, a powder that increases the amount of SiO ₂ in the powder and adds Li ₂ O to stabilize the physical properties when absorbing Al ₂ O ₃ is also used in the powder A due to the SiO _{2 in} the powder.
Oxidation consumption of Al in molten steel is large due to the oxidation reaction of 1
The amount of Al ₂ O ₃ in the molten powder increases, the quality of the powder changes during casting, and the viscosity and melting temperature, which are important physical properties of the powder, rise. As a result, problems such as frequent occurrence of vertical cracks and lateral cracks on the surface of the slab, deterioration of the internal quality of the slab, breakout due to poor lubrication, and the like cannot be solved.

Therefore, in order to solve the problems during casting due to the powder and Al in the molten steel as described above, the inventors of the present invention first conducted a casting method for high aluminum content steel and a casting powder (Japanese Patent Application No. No. 1-209894), which suppresses the increase of Al ₂ O ₃ in the molten powder and has a high melting point of 2Ca.
O. Al ₂ O ₃ . Prevents the precipitation of SiO ₂ and keeps the melting temperature of the powder below 1250 ° C.
Solved casting accidents such as breakout due to poor lubrication. In addition to solving the casting accident, Na ₂ O and NaF
The white smoke caused by the above is prevented, the casting work environment is improved, and a considerable effect is achieved.

However, in addition to high aluminum content, REM
In the continuous casting of steel with added, the melting temperature of the powder rises, the viscosity becomes unstable, and vertical cracks occur on the surface of the slab,
Lateral cracks frequently occur, and the physical properties of the powder deteriorate significantly, causing breakout due to poor lubrication. Further, there is a problem that the white smoke caused by the powder during casting is severe and it becomes difficult to monitor the molten metal surface, which hinders the casting work and deteriorates the working environment including the surroundings.

The present invention prevents and breaks slab surface defects such as vertical cracks and lateral cracks caused by deterioration of melting temperature and viscosity of powder during casting, which are the drawbacks of the conventional casting powders. It is an object of the present invention to provide a powder used for casting high aluminum content steel to which rare earth elements are added, which avoids casting accidents such as out, and has solved the work environment deterioration due to white smoke.

[0009]

Means for Solving the Problems In the continuous casting of high-aluminum content steel, the present inventors have discovered that white smoke causes deterioration of powder properties, deterioration of slab quality, casting accidents such as breakout, and deterioration of working environment. As a new finding, a part of aluminum in the steel is oxidized by SiO ₂ in the powder to form Al ₂ O ₃ and 2Ca having a high melting point in the powder is produced.
O. Al ₂ O ₃ . The formation of SiO ₂ causes the melting temperature and viscosity of the powder to increase, and the Na compound in the powder is reduced by aluminum in the steel, so that Na vaporizes in the powder layer and NaF and Na ₂ CO ₃ It was found that it becomes fine particles and produces white smoke.

Therefore, this finding led to deterioration of the quality of the slab,
For casting accidents such as breakouts and deterioration of working environment, 10 to 20% of powder SiO ₂ and 5 to 10 of Na ₂ O
% And Al ₂ O ₃ is 10% or less, the problem is solved and the effect is enhanced.

Furthermore, as a result of continuous research by the inventors of the present invention on a continuous casting powder of a high aluminum content steel, in the continuous casting of a steel containing a high aluminum content and REM, a part of aluminum in the steel is oxidized. Al ₂ O ₃ and the REM concentration in the steel is extremely low (several pp
Despite its m), REM is Al because it is a highly active element.
Even if / REM is 100 times or more, REM is selectively oxidized in steel and oxidation products such as La ₂ O ₃ , CeO ₂ and Nd are produced.
10 to 15% of ₂ O ₃ etc. is mixed and concentrated in the powder during continuous casting. As a result, the melting temperature and viscosity of the powder during continuous casting are affected by the partial oxidation of aluminum in steel
_It becomes much worse than the concentration of ₂ O ₃ mixed.

That is, REM is different from aluminum in steel because it is a strongly active element, so that the oxidation reaction of REM proceeds even though the oxidation reaction of Al is stable, although the addition amount to molten steel is small. At the same time, the reaction of reducing the oxide (mainly SiO ₂ ) which is the main component of the powder at the interface between the powder and the molten steel is proceeding, and as the concentration of Al ₂ O ₃ increases, L
a ₂ O _3, 10~15% in powder CeO _2, Nd ₂ O ₃ or the like during continuous casting is also mixed concentrated. This contamination concentrated in powder such as an oxide becomes a various troubles on casting cause excessive melting temperature and viscosity of the powder in the continuous casting, in particular, oxides of REM is as shown in FIG. 1 Al ₂ O ₃
Is more conspicuous than the thickening of, and the melting temperature rises by 50 to 100 ° C.

[0013] Therefore, powder itself by reducing to reduce the oxidation-inhibiting and powder of SiO ₂ REM powder properties change the powder SiO ₂ was synergistic by oxides of the steel in the aluminum and steel during REM powder during continuous casting In addition to preventing the physical properties of the powder from changing, the melting temperature of the powder, which is the characteristic of the oxide of REM, was lowered by the addition of Li ₂ O to stabilize the physical properties of the powder as a whole.

The powder of the present invention contains 10 to 20 SiO ₂ .
% By weight and Al ₂ O _{3 up} to 10% by weight, CaO 20 to 40% by weight, Li ₂ O 1 to 10% by weight, Na ₂
O up to 10% by weight, F ⁻ at 5 to 15% by weight, and M
Contains less than 10% by weight of gO, and BaO, TiO
₂ , 1 or 2 or more of MnO, SrO, and B ₂ O ₃ in which the total of each component is 20% by weight or less, and carbon powder as a melting rate adjusting agent is 10% by weight or less. Moreover, this powder is for continuous casting of steel containing 2% by weight or more of aluminum and 0.01% by weight or more of REM.

Further, the physical properties of the powder are further stabilized,
In addition, in order to hinder the casting work due to white smoke during continuous casting and to improve the working environment, 4% by weight or less of Na ₂ O in the above composition, L
More preferably, i ₂ O is 1 to 10% by weight, and the sum of Na ₂ O and Li ₂ O is 10% by weight or less. Further, this powder has a melting temperature in the range of 800 to 1100 ° C. and a viscosity at 1300 ° C. of 1.0 poise or less. 2% by weight or more of aluminum RE
REM of steel containing M in an amount of 0.01% by weight or more may be added either in the tundish or in the mold during continuous casting. The means of addition is RE coated with REM with metal.
Use M wire.

Here, the SiO ₂ content of the powder is 10 to 2
The reason why the content is 0% by weight is that if the initial amount of SiO ₂ in the powder is reduced, it becomes difficult to lower the initial melting temperature, and 10% by weight or more is necessary from the viewpoint of ensuring lubricity. If it exceeds 20% by weight, aluminum in steel and REM in steel have a weak affinity for oxygen and Si in powder.
A large amount of O ₂ is reduced to REM and aluminum oxides, and at the same time as the reduction of SiO _{2 in} the powder, the REM and aluminum oxides are mixed and concentrated in the powder, which causes an increase in melting temperature and an increase in viscosity.

The reason why the content of Na ₂ O is 10% by weight or less is that Na ₂ O is also reduced and vaporized by REM and aluminum as described above, and C, O and CO ₂ in the unmelted powder are used.
Reacts with to generate white smoke due to ultrafine particles such as Na ₂ CO ₃ , which hinders the monitoring of the molten metal level in the mold during continuous casting and the working environment. Further, the rare earth element Li ₂ O is also set to 10% by weight or less for the same reason. However, if the content of Li ₂ O is less than 1% by weight, it becomes difficult to control the melting temperature and viscosity increase of the molten powder with La ₂ O ₃ , CeO ₂ , Nd ₂ O _3, etc., and stable casting becomes impossible.

The reason why the content of Al ₂ O ₃ in the powder is 10% by weight or less is that Al ₂ O is formed by oxidation of aluminum in steel.
It is to suppress the deterioration of physical properties due to the thickening of powder in ₃ . Further, CaO can be blended in an amount of 20 to 40% by weight in order to impart predetermined physical properties to the powder. If it is less than 20% by weight, it becomes impossible to obtain a predetermined viscosity in the physical properties of the powder, and if it exceeds 40% by weight, the glass property of the powder cannot be maintained, resulting in poor lubrication, which is not preferable.

F ⁻ is mixed as a fluoride in an amount of 5 to 15% by weight for the purpose of adjusting the physical properties of the powder, but if it exceeds 15% by weight, gasification of the fluoride and dissolution of refractory materials such as immersion nozzles will be significant. On the other hand, if it is less than 5% by weight, the predetermined viscosity and melting temperature cannot be obtained, resulting in poor lubrication.

[0020] MgO is 10 wt% or less but, Al ₂ O _3, based on generating a spinel MgO · Al ₂ O ₃ refractory material is produced in large amounts during casting it exceeds 10 wt%, reduced lubricity powder To do. In order to adjust the physical properties of the powder, the total content of one or more of BaO, TiO ₂ , MnO, SrO, and B ₂ O ₃ is 20% by weight or less, but if it exceeds 20% by weight, it is the same as SiO _2. In addition, the amount of reduction is increased, the physical properties of the powder are changed during casting and the molten steel is contaminated, the quality of the slab is deteriorated, and the casting operation is hindered. For this reason, it is preferable that the total amount of one or more of BaO, TiO ₂ , MnO, SrO, and B ₂ O ₃ be 20 wt% or less.

Further, although carbon powder is used as a melting rate adjusting agent, if the amount of addition thereof exceeds 10% by weight, the melting rate of the powder becomes slow and molten slag cannot be produced and lubrication by molten powder becomes impossible. Since it will hinder the casting work such as deterioration of slab quality or breakout,
It was made to be less than weight%.

As described above, La ₂ which is an oxide of REM
Unlike the change when Al ₂ O ₃ is concentrated, the deterioration of the powder physical properties due to the concentration and concentration of O ₃ , CeO ₂ , Nd ₂ O _3, etc. is slow, and the melting temperature is extremely high. The formulation of materials for lowering the melting temperature makes it impossible to simultaneously satisfy the important viscosity and melting temperature of the powder, and it cannot be used. However, 1 to ₂ % of Li ₂ O is used as a powder property adjusting agent.
Addition of 10% by weight has an effect on viscosity, which is a peculiar powder property at the time of concentrating Al ₂ O ₃ concentrated REM oxides such as La ₂ O ₃ , CeO ₂ and Nd ₂ O ₃ when concentrated. The melting temperature can be remarkably decreased remarkably.

These effects are due to the presence of SiO ₂ , N in the powder.
a ₂ O and the like, by properly mixing as described above, the melting temperature,
Ideally, the melting rate, viscosity, etc. can be more remarkably exhibited. For this reason, Na ₂ O is 4% by weight or less, Li ₂ O is 1 to 10% by weight, and Na ₂ O and L are included in the powder composition.
By adjusting the sum of i ₂ O to 10% by weight or less, REM
It is more preferable because the white smoke associated with the vaporization of Na due to the reducing action of Na ₂ O due to is surely suppressed and the physical properties of the powder can be further stabilized due to the reduction of Na ₂ O.

Further, the melting temperature of the powder is 800 to 11
Within the range of 00 ° C, the viscosity at 1300 ° C is 1.3.
By controlling the porosity below, the powder physical properties during casting are Al ₂ O ₃ , REM oxides such as La ₂ O ₃ and CeO.
_It is possible to guarantee powder properties that can suppress breakout due to surface defects and poor lubrication of cast slabs when enriched with ₂ , ₂ , Nd ₂ O _3, etc. Moreover, the change in the physical properties of the powder in the molten state in the mold due to continuous casting is the breakout suppression limit due to the surface defects and poor lubrication of the slab, and the melting temperature of the powder is 1280 ° C and the viscosity at 1300 ° C is 1.
Since it can be maintained at 5 poise or less, stable casting is possible.

[0025]

EXAMPLE 250 × 10 of stainless steel containing 0.02 to 0.2% by weight of REM and 2.5 to 5% by weight of Al
A 30 mm slab was continuously cast at 1500 ° C. using a powder having the composition shown in Table 1. For comparison, a powder having the compounding composition of the comparative example in the table was also cast under the above conditions. As a result, the powder of the present invention does not generate white smoke during continuous casting as compared with Comparative Example, and further, it is possible to achieve casting without surface defects and internal defects of the slab without the formation of slag bear, and when casting due to powder physical properties. I was able to suppress the breakouts.

In Examples 4 to 8 of the powder of the present invention, Na ₂ O in the powder is 4% by weight or less, and Li ₂ O is 1 to 1% by weight.
The content of Na ₂ O and Li ₂ O was 10% by weight or less, and as a result, N was due to the reducing action of the molten powder in which the REM strongly active element and aluminum synergized.
The white smoke associated with the vaporization of a is reliably suppressed, and furthermore, it is possible to achieve the casting without the formation of slag bear and the surface and internal defects of the slab and the suppression of the breakout.
From the examples of 3 to 3, preferable results are obtained in terms of work environment, casting stabilization accompanying monitoring of casting work, and the like.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

By using the powder of the present invention,
In casting of high aluminum steel with REM added,
Prevents white smoke during casting, improves the working environment, suppresses the generation of slag bear, enables operation without breakout, and has no vertical cracks or horizontal cracks on the surface of the cast slab and improves the surface properties. In addition, it is possible to produce a slab having a good slab internal quality, and in addition to the operability, the yield is significantly improved as compared with the conventional one.

[Brief description of drawings]

FIG. 1 shows changes in melting temperature with respect to the amount of REM oxide produced, with respect to the content of Al ₂ O _{3 in} molten powder (cast slag).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Japanese Patent Publication Sho 57-2124 (JP, B2)

Claims (2)

(57) [Claims] 1. CaO in an amount of 20 to 40% by weight, SiO _{2 in an amount} of 10 to 20% by weight, Al ₂ O _{3 in an amount} of 10% by weight or less, Na ₂ O in an amount of 10% by weight or less, and F ^{− in an amount} of 5 to 15% by weight. %
And MgO is 10% by weight or less, Li ₂ O is 1 to 10% by weight, and one or more of BaO, TiO ₂ , MnO, SrO, and B ₂ O _{3 is} contained in a total amount of 20% by weight or less, and A high aluminum rare earth element-containing steel casting powderer containing 10% by weight or less of carbon powder as a melting rate adjusting agent. 2. CaO of 20 to 40% by weight, SiO ₂ of 10 to 20% by weight, Al ₂ O ₃ of 10% by weight or less, F ⁻ of 5 to 15% by weight and MgO of 10% by weight or less, _{BaO, TiO 2, MnO, SrO} , B 2 sum of the components one or two or more O ₃ is the Na ₂ O in 20 wt% or less than 4% by weight, Li ₂ O is from 1 to 10 wt% , moreover Na ₂ O and Li ₂ O in the sum 10 wt% or less in the high aluminum containing a rare earth element steel casting powder <br/> over a carbon powder comprising less than 10 wt% as a melting rate adjusting agent.