JP3335616B2 - Powder for continuous casting for B-containing steel and method for producing B-containing steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder for continuous casting for B-containing steel, and more particularly to a method for producing a powder having a surface property or a casting defect by vitrification of molten powder during casting and vitrification of a powder film. The present invention relates to a powder for continuous casting, which is effective for preventing instability of operation, and a method for producing a B-containing steel by subjecting it to continuous rolling using the powder, followed by hot rolling and, if necessary, cold rolling. It is.

[0002]

2. Description of the Related Art In continuous casting of steel, powder for continuous casting is supplied into a mold in order to maintain lubricity between the mold and the slab and maintain good surface properties of the slab. In general, the operation is performed while the powder in the molten state (molten powder) flows between the mold and the slab. At this time, the molten powder flowing between the mold and the slab solidifies on the side in contact with the mold (low temperature part) to form a film (powder film), but melts on the side in contact with the slab (high temperature part). Demonstrate lubricity while maintaining the condition. As a powder for continuous casting used for such a purpose, conventionally, a powder containing F and Na in addition to CaO and SiO ₂ as main components has been used.

However, when attempting to continuously cast B-containing steel (mainly, B-containing stainless steel) using this continuous casting powder, the SiO ₂ in the molten powder is replaced by B in the molten steel and (1) A chemical reaction as shown in the equation occurs, the B ₂ O ₃ concentration in the molten powder increases, and the SiO ₂ concentration decreases accordingly. 4 [B] +3 (SiO ₂ ) = 2 (B ₂ O ₃ ) +3 [Si] (1) In the formula: [B]: B content in molten steel (wt %) (SiO ₂ ): SiO ₂ content in powder (wt%) (B ₂ O ₃ ): B ₂ O ₃ content in powder (wt%) [Si]: Si content in molten steel (wt %)

[0004] As a result of the above chemical reaction, the melting point and viscosity of the molten powder are reduced, so that the molten powder flows unevenly and excessively between the mold and the slab during continuous casting, resulting in a deep oscillation mark on the slab surface. And dent defects are caused. In addition, the increase in the concentration of B ₂ O ₃ in the molten powder leads to vitrification of the powder film, which further promotes excessive inflow of the molten powder and reduces the thermal resistance of the powder film. There is a problem that the heat removal increases (rapid cooling) and vertical cracks are generated on the surface of the slab. Further, these problems may lead to operational troubles such as breakouts, which may lead to a problem of reducing productivity.

Heretofore, there have been several proposals for the above-mentioned problems in continuous casting of B-containing steel. For example, JP-A-2-155547 and JP 8-141712, the powder for continuous casting mainly comprising CaO and SiO _2, or a B ₂ O ₃ is added in advance to about 5-30 wt% , JP 11
JP-309548 discloses that, for a powder for continuous casting containing CaO and Al ₂ O ₃ as main components, the SiO ₂ concentration is set to 15 wt% or less to suppress the reaction of the above formula (1), A technique for reducing the change in the melting point and viscosity of the molten powder has been proposed. Further, in JP-A-8-309483, the melting point of continuous casting powder, casting temperature, casting speed,
There is disclosed a technique for preventing non-uniform excessive inflow of molten powder by defining oscillation conditions and the like, thereby improving the surface quality and castability of a slab.

[0006]

However, although the prior art described above has been able to reduce the deterioration of the surface quality of slabs of B-containing steel and the operational troubles to some extent, it has not yet been said to be perfect. For example, in a conventional continuous casting powder containing CaO and SiO ₂ as main components, changes in the viscosity and melting point of the molten powder due to the reaction of the above formula (1) can be reduced by including B ₂ O ₃ in advance. However, it could not be completely suppressed. Furthermore, B ₂ O up to the equilibrium value of equation (1)
_{When 3} is added, there is a problem that the vitrification of the powder film is rather accelerated and the powder film is strongly cooled, which causes a crack. On the other hand, with the powder for continuous casting in which CaO and Al ₂ O ₃ are the main components, the above problems could be overcome, but because of the high melting point, it did not easily melt in the mold, and as a powder for continuous casting. There is a problem that the function of is not fulfilled. In the case of each of the above prior arts,
In the first place, it occurs during continuous casting operation, and it is actually very difficult to judge instantaneously the progress of the reaction on the spot, and therefore, the melting point of the powder for continuous casting changes every moment during the operation of continuous casting. It is originally difficult to appropriately set the optimum casting temperature, casting speed, oscillation conditions, and the like for the above.

A main object of the present invention is to propose a technique for solving the above-mentioned problems of the prior art, which causes operational troubles such as surface defects and breakouts in continuous cast slabs. A powder for continuous casting of B-containing steel and a continuous casting using the powder, and then hot-rolled, so that a slab having excellent surface properties can be stably manufactured throughout the entire casting operation without any need. To provide a method for producing a B-containing steel by cold rolling in accordance with the following. Another object of the present invention is to develop and propose a powder for continuous casting in which the characteristic values of the powder, particularly the viscosity and melting point, hardly change over the entire period of the continuous casting operation, and can prevent the vitrification of the powder film. Is to do.

[0008]

Means for Solving the Problems As a result of earnest studies to realize the above-mentioned objects, the inventors have obtained the following knowledge on powder for continuous casting. That is, B is 0.1 wt%
The reason that the castability of the molten steel containing it is difficult is that SiO ₂ in the molten powder causes a chemical reaction with B in the molten steel as in the above formula (1), and increases the B ₂ O ₃ concentration in the molten powder. At the same time, lowering the SiO ₂ concentration, which reduces the melting point and viscosity of the molten powder during continuous casting,
It was found that the increase in the concentration of B ₂ O ₃ in the molten powder promoted the vitrification of the powder film, which adversely affected the lubrication and cooling of the slab.

[0009] In order to prevent these problems, the inventors of the present invention have investigated the change in physical properties (melting point and viscosity) of molten powder when continuously casting a B-containing steel over the entire period from the start to the end of continuous casting. The relationship with the components of the powder for continuous casting was observed in detail. As a result, it has been found that when using a powder mainly composed of CaO, Li ₂ O and F, which has not been tried before, particularly good casting can be performed, and the surface properties of the slab also become good. The gist configuration of the present invention completed based on such knowledge is as follows.

That is, the present invention relates to a powder for continuous casting for molten steel containing 0.1 wt% or more of B, wherein the main components are CaO: 20 to 40 wt%, Li ₂ O: 5 to 20 wt%, and F: contains 5 to 25 wt%, and CaO and Li ₂ O are CaO / Li ₂ O
In addition, it is adjusted so as to be within 1.0-4.0, and also contains 5-40% by weight of Al ₂ O ₃ as a component for controlling physical properties of molten powder and 1-4% by weight of C as an aggregate component. ,
Further oxides such as SiO ₂ , Fe ₂ O ₃ , MnO, MgO, B
20% by weight of at least one of ₂ O ₃ and Na
It is a powder for continuous casting for B-containing steel, characterized by containing the following. In the present invention, the powder for continuous casting has a melting point of 950 ° C. to 1200 ° C.
Viscosity at 300 ° C .: It is preferable to exhibit a characteristic of 0.3 poise to 1.3 poise and to crystallize at the time of solidification of molten powder.

Ni: 7 to 11 wt%, Cr: 17 to 21
wt%, B: 0.1 to 2.2 wt%, and the balance is mainly F
In the continuous casting of B-containing steel consisting of e and unavoidable impurities, casting is performed using the powder for continuous casting according to claim 1 or 2, followed by hot rolling and, if necessary, cold rolling. A method for producing a B-containing steel is proposed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The construction of the powder for continuous casting according to the present invention will be described below. As a main _{component, CaO: 20~40wt%, Li 2} O: 5~20wt
%, F: 5 to 25 wt%, and CaO and Li ₂ O are CaO /
The reason why the Li ₂ O ratio is adjusted within the range of 1.0 to 4.0 will be described. First, if each content of CaO, Li ₂ O, and F is less than the lower limit of the above range, the powder has a high melting point and a high viscosity, so that melting becomes difficult, and the inflow of the molten powder is drastically reduced. Adversely affects the lubrication between the steel and the slab. On the other hand, when the content of these components is larger than the upper limit of the above range, the melting point and the viscosity are unnecessarily low, the inflow of the molten powder is increased, and the cooling is adversely affected, resulting in strong cooling. This leads to the formation of vertical cracks and dents.

The reason that the ratio of CaO / Li ₂ O is limited to the range of 1.0 to 4.0 is that if the ratio is less than 1.0, the melting point and viscosity become too low, and the inflow of molten powder increases. It becomes strong cooling. As a result, surface defects such as vertical cracks and dents of the slab are generated. On the other hand, when the ratio exceeds 4.0, the powder has a high melting point and a high viscosity and becomes difficult to melt, so that the inflow of the molten powder is drastically reduced, and the lubrication between the mold and the slab is adversely affected. Become. Also, Ca
When the ratio of O / Li ₂ O is in the range of 1.0 to 4.0, the molten powder is easily crystallized when solidified, so that the cooling at the meniscus portion of the mold becomes slow cooling and uniform cooling. The source of CaO may be added from CaCO ₃ or calcium aluminate, and Li ₂ O or F may be added in the form of CaF ₂ , LiCO ₃ , LiF or the like.

Al ₂ O ₃ is added in an amount of 5 to 40% by weight for adjusting physical properties of the molten powder such as viscosity and melting point. This Al
_{If the amount of 2} O ₃ is outside the above range, the melting powder will have a high melting point and a high viscosity, both high and low, and will adversely affect lubrication.

In addition, C is contained as an aggregate.
A carbon material is used as the C supply source, but the amount added is 1
Preferably, the content is about 4 wt%. The reason is 1wt
%, The melting of the powder becomes too fast, resulting in excessive inflow and strong cooling. On the other hand, if it exceeds 4 wt%, melting of the powder becomes too slow and carburization of the slab occurs. In addition, as oxides, SiO ₂ , Fe ₂ O ₃ , MnO, MgO, B
Any one or more of ₂ O ₃ and Na may be contained in a total of 20 wt% or less. Of these, SiO ₂ , Fe ₂ O ₃ , MnO, Mg
O is mixed from the raw material and is limited to a range (≦ 15 wt%) that does not significantly affect the viscosity and the melting point. B ₂ O ₃
And Na are added for adjusting viscosity and melting point, and Na is
Na ₂ O, it is added in the form of such Na ₂ CO _3, NaF, and SiO _2, F
Since e ₂ O ₃ and MnO are elements that react with B contained in the molten steel, it is preferable to contain 4 wt% or less of each. As described above, B ₂ O ₃ is an element that promotes vitrification of the molten powder, and therefore may contain 5 wt% as an upper limit.

The above-mentioned molten powder conforming to the present invention should be adjusted within the above composition range so as to exhibit the following physical properties: melting point: 950 ° C. to 1200 ° C., viscosity at 1300 ° C .: 0.3 to 1.3 poise. Is preferred. Of the above physical property values, the reason for adjusting the melting point to 950 to 1200 ° C is that if the temperature is higher than 1200 ° C, it is difficult to melt the powder, so that the powder inflow becomes too small and adversely affects the lubrication between the mold and the slab. On the other hand, if the temperature is lower than 950 ° C., on the other hand, the flow becomes excessive and the cooling becomes too strong, which leads to the formation of a vertically cracked dent. In addition, the viscosity at 1300 ° C is 0.3
The reason for adjusting to ~ 1.3 poise is that if it is higher than 1.3 poise, the flow of the molten powder will deteriorate and the inflow will be too low,
This is because it adversely affects the lubrication between the mold and the slab.
If it is lower than 0.3 poise, the flow is excessively increased and cooling becomes too strong, which leads to the formation of vertical cracks and dents, which is limited.

When the molten powder flows between the mold surface and the solidified shell and is solidified, if the powder is vitrified, the cooling of the slab at the meniscus portion becomes too strong and tends to become uneven. The slab surface is dented or cracked. Therefore, when the molten powder flows between the mold and the solidified shell and solidifies, it is important to adjust the molten powder to crystallize. That is, when the powder that has flowed and solidified between the mold surface and the solidified shell crystallizes, the powder is cooled slowly and uniformly as compared with the case of vitrification. The reason for this is that if the powder is vitreous, the difference between the good and bad portions of the solidified powder in contact with the mold surface becomes large, and the growth of the solidified shell tends to be uneven. This is considered to be because the glass is easily deformed in the high temperature state during casting and comes into contact with or dissociates from the mold. Further, in the case of vitreous, since heat transfer by radiation increases, it is easy to perform strong cooling compared to crystalline. In contrast, the crystallized powder comes into more uniform contact with the mold,
The growth of the solidified shell becomes uniform.

Since the above-described powder for continuous casting according to the present invention does not cause a chemical reaction with the B-containing molten steel as in the above formula (1), there is no change in composition throughout the continuous casting operation, and an appropriate There is a feature that the powder physical property value can be maintained.

Next, the present invention uses the powder for continuous casting according to the above-mentioned constitution, and particularly, Ni: 7 to 11 wt%, Cr:
17 to 21 wt%, B: 0.1 to 2.2 wt%, with the balance being Fe
When producing a B-containing steel comprising unavoidable impurities, for example, a B-containing stainless steel used in a rack for storing used nuclear fuel, it is preferable to use it particularly in continuous casting. Of course, besides this, B is 0.1 ~ 2.2wt
Even if it is applied to the continuous casting of a B-containing steel containing about 0.1% and the balance being mainly Fe, the effect is sufficiently exhibited, and therefore, it should not be applied only to the steel for the above-mentioned applications.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Continuous casting powders having different compositions and physical properties
Conducted continuous casting experiments under various casting conditions using powder
Was. Furthermore, the surface of the continuous casting slab is ground and
Rolled, if necessary, cold-rolled to a thickness of 1 to 70 mm
Produced products of various thicknesses. Table 1 shows the composition of molten steel
3 shows a powder component composition for continuous casting. The oxidation in the table
The total of the components is 90.1-99.7%, but the rest is
Fe mixed in from raw materials _TwoO_Three, MnO and MgO. Also,
Table 2 and FIG. 1 show the powder physical property values before and after continuous casting.
To remove casting defects and surface defects
Yield is also shown. FIG. 1 shows the pow in this experiment.
This is a comparison between the invention example and the comparative example regarding the
is there. All component analysis was performed by chemical analysis.
Was. In this experiment, the viscosity was determined by the coaxial double rotation cylinder method.
Is a value obtained by measuring the viscosity at 1300 ° C. Melting point is coaxial
Repeat the measurement of viscosity at each temperature by the double rotating cylinder method,
The major departure from the Arrhenius-type temperature dependence
Points.

[0021]

[Table 1]

[0022]

[Table 2]

As is apparent from the results shown in the table supra, Comparative Example 1-7, CaO and SiO ₂ is a main component conventional continuous casting powder which is the main component or CaO and SiO _2,, In addition, the case where a conventional continuous casting powder containing B ₂ O ₃ is used. These are during operation
The change in viscosity and melting point of the molten powder due to the reaction of the formula (1) could not be completely suppressed. In particular, in Comparative Examples 1 and 5, the powder physical properties were largely out of the applicable range of the present invention, and as a result, the maintenance yield of the slab was reduced. In Comparative Examples 4, 3, and 6, the powder physical properties were within the applicable range of the present invention due to changes in the viscosity and the melting point of the molten powder during the operation, but the powder physical properties could not be maintained over the entire period. This is an example in which the care yield has decreased. In Comparative Example 7, changes in the viscosity and melting point of the molten powder could be substantially suppressed despite the use of a conventional continuous casting powder containing CaO and SiO ₂ as main components and containing B ₂ O ₃ . It is an example, because the viscosity at 1300 ℃ is too high,
Breakout occurred due to poor lubrication. In Comparative Example 2, the melting point was excessively low, resulting in an extremely non-uniform inflow, a breakout from a portion where the solidification of the steel was delayed, and the casting was stopped. As described above, in the conventional powder for continuous casting, the degree of change in the viscosity and the melting point of the molten powder during casting cannot be predicted, and it has been found that it is extremely difficult to appropriately control the inflow amount of the molten powder.

In contrast, when the powder according to the present invention was continuously cast to produce a B-containing steel, the changes in the viscosity and melting point of the molten powder could be almost completely suppressed, as shown in Table 2. Also, the care yield of the slab was 98% or more, which was good. This is because during the casting, the powder physical properties conforming to the present invention could be maintained from beginning to end, and the slab surface had no defects such as dents and vertical cracks, and had extremely good surface properties.

[0025]

As described above, according to the present invention,
In the continuous casting of B-containing steel, the rise of B ₂ O _{3 in} the molten powder, the fluctuation of the melting point and viscosity of the molten powder due to the decrease of SiO ₂ can be almost completely prevented, and the vitrification of the powder film can be prevented. Therefore, it is possible to appropriately control the inflow amount of the molten powder, and it is possible to completely prevent excessive inflow and insufficient inflow of the powder. Therefore, in continuous casting, it is possible to prevent the occurrence of slab surface defects due to deterioration of the molten powder, improve the maintenance yield, and to prevent operation troubles such as breakout due to poor lubrication of the molten powder. And B-containing steel can be advantageously produced.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between a post-casting powder property value and a slab care yield when continuous casting of a B-containing steel is performed. Arrows in the figure indicate changes in physical properties due to changes in the powder composition during the casting operation.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Atsushi Hongo 4-2 Kojimacho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Nippon Yakin Kogyo Co., Ltd. Kawasaki Works (56) References JP-A-2002-103008 (JP, A) JP 2001-191153 (JP, A) JP-A-11-309548 (JP, A) JP-A 8-141712 (JP, A) JP-A 2-155547 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) B22D 11/108 B22D 11/00 C22C 38/00 302 C22C 38/54

Claims (3)

(57) [Claims] 1. A continuous casting powder for molten steel containing 0.1% by weight or more of B, wherein the main component is CaO: 20.
_{~40wt%, Li 2 O: 5~20wt} %, and F: 5 to 25
comprises wt%, and the CaO and Li ₂ O in the CaO / Li ₂ O ratio of 1.
0-4.0 and are adjusted so that, in addition, the Al ₂ O ₃ as the molten powder physical properties adjusting component contains 5 to 40 wt%, the C as the aggregate component contains 1～4Wt%, Still other oxides include SiO ₂ , Fe ₂ O ₃ , MnO, MgO, B ₂ O
20% by weight of at least one of ₃ and Na
A powder for continuous casting for B-containing steel, comprising: 2. The powder for continuous casting according to claim 1,
Melting point: 950-1200 ° C, and viscosity at 1300 ° C: 0.3
A powder for continuous casting for a B-containing steel, which exhibits characteristics of poise to 1.3 poise and crystallizes upon solidification of a molten powder. 3. Ni: 7 to 11 wt%, Cr: 17 to 21 wt%,
B: The continuous casting of a B-containing steel containing 0.1 to 2.2 wt% and the balance mainly consisting of Fe and unavoidable impurities is cast using the powder for continuous casting according to claim 1 or 2. And then hot rolling or further cold rolling.