JP2011183424A - Powder for casting boron-containing stainless steel and method of continuously casting boron-containing stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powder for continuous casting which is suitable to continuous casting of a boron-containing stainless steel, and a method of continuously casting a boron-containing stainless steel slab free from surface defects. <P>SOLUTION: The powder for casting contains, by mass, 0.30 to 35% CaO, 20 to 30% SiO<SB>2</SB>, 0.10 to 16% Na<SB>2</SB>O, 8 to 11% Al<SB>2</SB>O<SB>3</SB>, 3 to <5% B<SB>2</SB>O<SB>3</SB>, 4 to 10% F and 1 to 3% aggregate C, and has a basicity of 1.0≤C/S<1.3, a viscosity of 0.5 to 2 poises at 1,300°C, a solidification temperature of 900 to 1,200°C, and allows a powder film having a thickness of 0.5 to 3 mm to be formed when it is made to flow into a space between a mold and a solidified shell, The method of continuously casting a boron-containing stainless steel uses the powder. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a casting powder used when continuously casting a boron-containing stainless steel, particularly a boron-containing stainless steel having a low liquidus temperature (1320 to 1380 ° C.), and boron with less surface defects using this powder. It is a proposal about the method of continuously casting the slab of containing stainless steel.

Boron-containing stainless steel is one of materials used as a storage container material or a shielding material for spent nuclear fuel in nuclear power plants because it has high neutron absorption capability and excellent corrosion resistance. The gold phase characteristic of this boron-containing stainless steel is that it is an eutectic type of austenite and boride, the liquidus temperature is low, and the solidification speed during solidification is slow. For this reason, this steel has a drawback that it tends to cause solidification cracking during casting. Furthermore, this type of steel is known to cause a reaction represented by the following formula between B in molten steel and SiO _{2 in} molten powder during continuous casting, and B ₂ O ₃ is picked up in the powder.

3 (SiO ₂ ) +4 B = 2 (B ₂ O ₃ ) +3 Si (1)
() Indicates the component in the molten powder, and the underline indicates the component in the molten steel.

When B ₂ O _{3 in} the powder increases, the viscosity and solidification temperature of the powder decrease, which not only increases the amount of molten powder flowing into the mold / solidified shell during continuous casting, but also the powder film generated at this time Tends to vitrify. When the powder film becomes vitreous, non-uniform cooling is caused at the meniscus portion in the mold, and vertical cracking and depletion are promoted.

In view of such a phenomenon, conventionally (Patent Documents 1, 2, and 3), the change in physical properties of the powder is suppressed by adding in advance an amount of B ₂ O ₃ corresponding to the reaction end point in the powder. There are suggestions on how to do that. However, the fact is that it is difficult to say that the crystallization behavior can be properly led by these methods alone. That is, these known techniques have a problem that crystals are not formed at all, or the growth is extremely slow even if formed.

On the other hand, CaO—Al ₂ O ₃ -based powder in which SiO ₂ in the powder is reduced as much as possible and Al ₂ O ₃ is added instead has been developed (Patent Documents 4 and 5). According to this powder, changes in physical properties due to reaction can be suppressed. However, this CaO—Al ₂ O ₃ -based powder originally has a drawback of poor hatchability, and thus has a problem that it is easy to bite the powder into the slab surface.

In addition, Patent Document 6 proposes a casting method using powder to which Li ₂ O is added in order to promote crystallization. However, in the case of this technique, the crystallization rate is as high as 15% to 75%, but there is a tendency that the cooling becomes too slow in the mold, and there is a problem that the shell growth is weak and bulging is likely to occur. .

Japanese Patent Laid-Open No. 02-155547 Japanese Patent Laid-Open No. 08-141712 JP 2001-191153 A JP 11-309548 A JP 2002-205153 A JP 2007-61846 A

  As described above, the conventional powder that has been used for continuous casting of boron-containing stainless steel has a problem that the solidification temperature is too high or the melting is too slow, and the crystal phase is difficult to form, or the crystal There was a problem that the phase developed too much. If there is such a problem, non-uniform cooling is likely to occur in the mold, and vertical cracking, depletion or seizure is not likely to occur. In the worst case, the mold may break out and stop casting.

  Therefore, an object of the present invention is to provide a powder for continuous casting used for continuous casting of boron-containing stainless steel, and to propose a method for continuously casting a boron-containing stainless steel slab having no surface defects.

  The inventors first examined a preferable physical property of the powder for continuous casting necessary for continuously casting the boron-containing stainless steel by performing a solidification test. As a result, the boron-containing stainless steel to be treated in the present invention has a low liquidus temperature (1320 to 1380 ° C.) in the first place, and a significantly lower temperature than ordinary stainless steel cast in a continuous casting machine. It is a steel type having In general, the characteristics of powder for continuous casting is that it melts due to the heat of molten steel, so it must melt reliably even in contact with low-temperature molten steel and flow smoothly between the mold and the solidified shell. Don't be. For example, the properties of powder for casting boron-containing stainless steel include a solidification temperature of 900 to 1200 ° C. (which is lower than conventional powder) and a viscosity at 1300 ° C. of about 0.5 to 2 poise. Something is required. Otherwise, in the case of low-temperature boron-containing stainless steel, an appropriate amount of molten powder cannot flow between the mold and the solidified shell.

Therefore, the inventors made about 30 kinds of powder samples (CaO—SiO ₂ —Na ₂ O—Al ₂ O ₃ —B ₂ O ₃ —F system) showing the above physical properties by changing the composition, and these The crystallization behavior and melting rate of the powder samples were investigated. Usually, the powder flowing between the mold and the solidified shell is cooled by the mold to become a solid to form a film. When this film is vitrified without forming a crystalline phase on the mold side, the solidified shell tends to be strongly and non-uniformly cooled, which causes depletion, vertical cracking, bleeding, etc., and breaks out in the worst case. The casting may be stopped. The reason for this is considered to be that when vitrified, the radiant heat transfer becomes high and the contact with the mold tends to be uneven. On the other hand, when crystallization progresses too much, the growth of the shell is delayed, and there is a problem that sufficient shell strength cannot be secured and bulging occurs. Therefore, as the powder for continuous casting, a powder showing an appropriate crystallization behavior is required.

As described above, the crystallization behavior of the casting powder is the most important point in considering the present invention. Therefore, the inventors used a copper plate or the like to melt the molten powder that flowed between the mold and the solidified shell for the purpose of developing a powder that can be surely crystallized even when B ₂ O ₃ is picked up by about 10 mass%. An experiment was conducted to simulate the state of. As a result, it was found that when the molten steel temperature is low, it becomes easy to vitrify and it is difficult to crystallize. The reason is that the molten powder cooled by the copper plate is vitrified at first, but then receives heat from the molten metal side and eventually crystallizes. At this time, if the liquidus temperature of the alloy is low and therefore the casting temperature is low, sufficient heat is not transmitted to the vitrified powder, and it is considered that crystallization is difficult.

Next, the inventors tried to compare the boron-containing stainless steel (liquidus temperature is 1320 to 1380 ° C.) with SUS304 stainless steel (liquidus temperature is 1463 ° C.). That is, paying attention to the difference between the liquidus temperatures of about 100 ° C., it was verified what happens to the pickup of B ₂ O ₃ between molten steel / powder. Specifically, each steel was melted in a magnesia crucible using a high frequency induction furnace, and reaction experiments were repeated between molten steel / powder. As a result, in the boron-containing stainless steel having a liquidus temperature of 1320 to 1380 ° C., it was found that the B ₂ O ₃ pickup stopped at about 1%. This means that even if B ₂ O ₃ is contained in advance, vitrification can be suppressed and a predetermined crystal phase can be generated as long as the amount of pickup can be suppressed.

As a method therefor, in the present invention, attention is paid to the basicity of the powder (CaO / SiO ₂ , hereinafter abbreviated as “C / S”), and this is adjusted to 1.0 ≦ C / S <1.3. , B ₂ O ₃ content of 3 to 5 (less than) mass% designed powder was prepared, and when this powder was applied to a small-scale continuous casting test of 18 tons class, it was found that continuous casting can be performed without problems. .

Further, in this experiment, the powder film formed by flowing between the mold / shell has a thickness of 0.5 to 3 mm, of which the crystal phase is more than 3% and less than 15% on the mold side. (The% occupied by the crystal phase is the ratio of the thickness. See the SEM image in FIG. 1). According to the knowledge of the inventors, it was found that when the proportion of the crystal phase is within this range, it is effective for preferable shell growth. That is, sufficient shell strength can be ensured, bulging does not occur, and, of course, continuous casting can be performed without problems such as vertical cracks, depletion, and seizure. When this crystal phase was analyzed by EDS or X-ray diffraction, it was also found that the crystal phase was caspodyne (3CaO · 2SiO2 · CaF ₂ ) as shown in FIG.

Next, one of the characteristics of the powder according to the present invention is to add C as an aggregate. This aggregate C is interposed between oxides such as CaO.SiO ₂ and Al ₂ O ₃ and fluoride particles such as CaF ₂ and NaF constituting the powder for continuous casting, and functions to adjust the melting rate. Have. In the stage where this C reacts with oxygen in the atmosphere and burns, C prevents contact with oxide and fluoride particles and suppresses melting. However, it finally has the effect of promoting melting by promoting the contact of oxide and fluoride particles. Therefore, the amount of aggregate C in the powder is an important component in order to ensure that the powder is melted even in low-temperature molten steel and to optimize the melting rate of the powder.

  Therefore, the inventors conducted an experiment to measure the melting rate by changing the amount of aggregate C within a range of 0 to 5 mass%. In this measurement experiment, the above-mentioned stainless steel was melted in a high-frequency induction furnace, and the molten steel was continuously cast on the molten steel under the condition that the degree of superheat (difference between the liquidus temperature and molten steel temperature) was kept constant at 40 ° C. The time until the powder was completely melted was measured. The target melting rate is based on the combination of SUS304 stainless steel with a liquidus temperature of 1463 ° C and the continuous casting powder used for it. From the result, it was found that it was necessary to be 1 to 3 mass%.

  Next, a powder having physical properties suitable for the present invention was subjected to an actual machine test, and cast under various conditions to obtain a cast slab. As a result, in order to smoothly and continuously cast boron-containing stainless steel, it has been found that it is effective to appropriately control the superheat degree of the molten steel and the casting speed in addition to the selection of the powder for casting described above. That is, when the molten steel superheat degree is less than 5 ° C., the melting rate is lowered even if the casting powder is used, and sufficient molten powder cannot be obtained. There was a case. On the other hand, when the superheat degree of the molten steel exceeds 50 ° C., solidification is not completed in the continuous casting machine, and a center crack may occur. Therefore, it was found that the superheat degree of the molten steel is preferably 5 to 50 ° C.

  Furthermore, in the present invention, when the slab drawing speed (casting speed) during continuous casting is less than 550 mm / min, the quality of the slab surface deteriorates, and when the slab drawing speed exceeds 900 mm / min, the solidified shell does not grow sufficiently. -Induced quat. Therefore, it was found that the casting speed is preferably 550 to 900 mm / min.

The present invention has been developed on the basis of novel findings obtained from the above-described experimental results. That is, boron-containing stainless steel casting powder according to the present _{invention, Ca0: 30~35mass%, SiO 2} : 20~30mass%, Na 2 O: 10~16mass%, Al 2 O 3: 8~11mass%, B ₂ O ₃ : 3 to 5 (less than) mass%, F: 4 to 10 mass%, aggregate C: 1 to 3 mass%, and basicity is 1.0 ≦ C / S < 1.3 When a viscosity at 1300 ° C. is 0.5-2 poise, a solidification temperature is 900-1200 ° C., and flows between the mold and the solidified shell, a powder film having a thickness of 0.5-3 mm is formed. It is necessary to have characteristics.

  Moreover, this invention is C <= 0.2 mass%, Si <= 3 mass%, Mn <= 5 mass%, Cr: 15-25 mass%, Ni: 3-20 mass%, B: 0.8-1.5 mass%, remainder is A continuous casting method for boron-containing stainless steel, characterized by continuously casting a molten steel of boron-containing stainless steel made of Fe and inevitable impurities using the continuous casting powder, is proposed.

In the present invention configured as described above,
(1) The powder film has, on the mold side, a portion of more than 3% to less than 15% of the thickness of the film has a crystal phase,
(2) The crystalline phase in the powder film is caspidine.
(3) Continuous casting of boron-containing stainless steel having a liquidus temperature of 1320 to 1380 ° C.
(4) Continuous casting under conditions where the molten steel superheat degree is 5 to 50 ° C. and the continuous casting speed is 550 to 900 mm / min,
Is a more preferred embodiment.

  According to the casting powder according to the present invention configured as described above, in continuous casting of boron-containing stainless steel, not only does vertical cracking, depletion or seizure disappear, but there is no accident such as breakout and stable continuous operation. Casting becomes possible. In addition, since the slab continuously cast using the casting powder according to the present invention has excellent surface properties, cutting and grinding yields are improved, productivity is improved, and manufacturing cost is reduced. Can do.

It is a photograph which shows the cross section of a powder film. It is a photograph which shows the crystal | crystallization layer in a powder film.

The casting powder according to the present invention was developed based on the knowledge based on the various experiments described above, and is a CaO—SiO ₂ —Na ₂ O—Al ₂ O ₃ —B ₂ O ₃ —F based powder. When the basicity is 1.0 ≦ C / S <1.3, the viscosity at 1300 ° C. is 0.5-2 poise, the solidification temperature is 900-1200 ° C., and it flows between the mold and the solidified shell, It has the characteristic of forming a powder film having a thickness of 5 to 3 mm. If it is a casting powder having such components and physical properties, it is surely melted even when casting boron-containing stainless steel having a liquidus temperature as low as 1320 to 1380 ° C. and flows between the mold and the solidified shell. When this is done, an appropriate amount of crystal phase can be formed on the mold side. The reason why the physical properties and component composition of the casting powder according to the present invention are limited as described above will be described below.

a. Viscosity at 1300 ° C .: 0.5-2 poise
If the powder viscosity is less than 0.5 poise, excessive flow into the mold / solidified shell will cause deep oscillation and become the starting point of depletion. On the other hand, if the viscosity is higher than 2 poise, the inflow is insufficient and sticking is likely to occur. In either case, breakout may occur. For this reason, the viscosity at 1300 ° C. is set to 0.5 to 2 poise. Preferably, it is 0.6 to 1.6 poise, more preferably 0.7 to 1.5 poise.

b. Solidification temperature: 900-1200 ° C
If the solidification temperature of the powder is less than 900 ° C., excessive flow into the mold / solidification shell will cause deep oscillation, which will be the starting point of depletion. On the other hand, when it exceeds 1200 ° C., the melting rate is lowered, the inflow is insufficient, and sticking may be caused. In either case, the worst is a breakout. Therefore, the solidification temperature is set to 900 to 1200 ° C. Preferably, it is 950-1180 degreeC, More preferably, it is 1000-1150 degreeC.

c. Crystallization behavior In general, a mixed melt of oxide and fluoride has the property of vitrifying when cooled on a copper plate. Therefore, it is estimated that the molten powder flows into the mold / solidified shell due to the heat of the molten steel, and immediately after that, it is vitrified. And it flows in and forms a film, but it is thought that a crystal phase is formed on the mold side by receiving heat of molten steel before long. In this respect, when the crystal phase is formed, uniform contact between the film / mold is realized, and a slab of sound surface quality is obtained. In the present invention, it is necessary to obtain a sufficient crystal phase with heat from a relatively low temperature molten steel, and the crystallization behavior is extremely important. As is apparent from the photograph shown in FIG. 2, the composition of the crystal phase is basically confirmed to be caspodyne (3CaO.2SiO ₂ .CaF ₂ ) by EDS analysis. Optionally, it may be included nepheline _{(Na 2 O · Al 2 O} 3 · 2SiO 2) and CaF _2.

d. The film described above has a thickness of about 0.5 to 3 mm, of which over 3% on the side in contact with the mold and less than 15% occupy the crystal phase as shown in FIG. 1 (the remaining glass layer) To do. The reason for this is that when the thickness of the crystal phase is 3% or less of the total thickness of the film, the glass behaves almost as a glass. Cooling becomes too much, and sufficient shell strength cannot be secured. In these cases, not only does it cause slab surface defects, but there is also a risk of causing breakout. Therefore, the proportion of the crystal phase in the powder film is such that the thickness exceeding 3% and less than 15% is composed of the crystal phase as shown in FIG. This crystallization characteristic can be controlled by optimizing the contents of CaO, SiO ₂ , Na ₂ O, Al ₂ O ₃ , B ₂ O ₃ , and F, which are constituent components of the powder.

e. Next, the reason why the powder composition is limited as described above will be described.
_{CaO: 30~35mass%, SiO 2:} 20~30mass%, Na 2 O: 10~16mass%, Al 2 O 3: 8~11mass%, B 2 O 3: 3~5 ( below) mass%, F: 4-10mass%
All of these are component compositions necessary for achieving the physical property values and crystallization behavior described above. That is, in the present invention, for CaO, SiO ₂ , Na ₂ O, Al ₂ O ₃ , B ₂ O ₃ , and F, in order to make the solidification temperature, viscosity, and crystallization behavior of the powder appropriate, Within the range.

Among the above components, CaO, SiO ₂ , and F are constituent elements of caspodyne, which is a crystalline phase. Therefore, if any component falls below the above lower limit, the above-mentioned crystal phase generation rate is insufficient (≦ 3 On the other hand, if it is higher than the upper limit value, the proportion of the crystal phase is too large (≧ 15%). Further, if SiO ₂ is too high, the viscosity becomes too high, and if CaO is too high, the solidification temperature becomes high, and if it is too low, the solidification temperature becomes low. Na ₂ O is a component that promotes crystallization. If it is low, the generation rate of the crystal phase is low, and if it is too high, it is excessively increased. Al ₂ O ₃ basically affects crystallization behavior and viscosity. When the upper limit is exceeded, the viscosity increases, and the proportion of the crystal phase also decreases. On the other hand, when Al ₂ O ₃ is too lower than the lower limit, the viscosity is lowered and the ratio of the crystal phase is also increased. If B ₂ O ₃ is too low (less than ₃ mass%), the proportion of the crystal phase is increased. On the other hand, if it is too high (5 mass% or more), the proportion of the crystal phase is insufficient. A preferable range of B ₂ O ₃ is 3.1 mass% or more and 4.9 mass% or less.

f. Basicity: 1.0 ≦ C / S <1.3
When the basicity is less than 1.0, vitrification tends to occur and the solidification temperature and viscosity tend to increase, making it difficult to control physical properties. On the other hand, in the case of 1.3 or more, both the solidification temperature and the viscosity tend to be high, and it becomes difficult to control the physical property values. Therefore, the basicity range is 1.0 or more and less than 1.3. Preferably, it is 1.1 or more and 1.25 or less, More preferably, it is 1.15 or more and 1.24 or less.

g. Aggregate C: 1 to 3 mass% or less C is added to control the melting rate of the powder, and is an extremely important component in the present invention. If the amount of C is less than 1 mass%, melting is too fast and excessive inflow occurs. On the other hand, if it exceeds 3 mass%, the melting rate is too slow and the inflow cannot catch up. In either case, there is a risk of causing depletion, vertical cracking, and bleeding, and in the worst case, breaks out. Therefore, it was set to 1 to 3 mass%. Preferably, they are 1 mass% or more and less than 3 mass%, More preferably, it is more than 1.4 mass% and 2.8 mass% or less.

  The present invention also proposes a method for continuously casting boron-containing stainless steel using the above-described casting powder. This method will be described below.

(1) Cast material The boron-containing stainless steel applied to the method of the present invention is C ≦ 0.2 mass%, Si ≦ 3 mass%, Mn ≦ mass 5%, Cr: 15 to 25 mass%, Ni: 3 to 20 mass%, B : 0.8 to 1.5 mass%, the balance being molten steel composed of Fe and inevitable impurities, and boron-containing stainless steel having this component composition is cast using the above powder. Although not particularly limited, the boron-containing stainless steel may be steel containing either one or both of Mo: 5 mass% or less and Co: 1 mass% or less.

  In the above component composition of the boron-containing stainless steel, C is contained for maintaining strength, and Si and Mn are elements useful for deoxidation. Cr is an element useful for corrosion resistance and heat resistance, and Ni is an element useful for maintaining the structure in austenite. B is the most important element because it has the ability to absorb neutrons. Mo improves corrosion resistance, and Co is an element that stabilizes austenite, and is added as necessary.

(2) Casting conditions a. Casting speed (drawing speed): 550 to 900 mm / min When the drawing speed is less than 550 mm / min, the surface quality of the slab deteriorates. On the other hand, when it exceeds 900 mm / min, the solidified shell does not grow sufficiently. -Causes queuing. Therefore, the drawing speed is set to 550 to 900 mm / min. Preferably, it is 600 to 880 mm / min, more preferably 650 to 800 mm / min.
b. Molten steel superheat degree: 5-50 ° C
If the superheat degree of the molten steel (defined as the difference between the liquidus temperature of the molten steel and the molten steel temperature in the tundish) is less than 5 ° C, the melting rate of the powder for continuous casting is reduced and sufficient molten powder cannot be obtained. In addition, the base metal may solidify in the immersion nozzle, resulting in nozzle clogging. On the other hand, when this temperature exceeds 50 degreeC, solidification may not be completed within a continuous casting machine, and it may become a center crack. Therefore, the superheat degree of molten steel shall be 5-50 degreeC. The temperature is preferably 10 to 45 ° C, more preferably 15 to 43 ° C.

  In addition, in order to stabilize casting at the initial stage of casting and to keep the initial slab surface quality sound, it is also effective to use a heat-generating start powder that quickly melts and forms a powder film at an early stage.

  Iron scrap, stainless steel scrap, nickel, ferrochrome, ferroboron, and chromium were melted in an electric furnace and refined using one or both of AOD and VOD to obtain boron-containing stainless steel having the composition shown in Table 1. The scale of casting is 60 tons, and the shape of the slab is 154 mm thick × 800 to 1300 mm wide. The length of one slab was cut to approximately 7-10 m. In Table 1, the component composition of the powder for continuous casting, its physical properties, and the conditions for continuous casting are also shown. The molten steel component, powder component and physical property values were evaluated by the following methods.

(1) Molten steel component: Quantitative analysis was performed using a fluorescent X-ray analyzer. The balance shown in Table 1 mainly contains Fe, and additionally contains P, S, Cu, O, N, etc. as unavoidable impurities. Furthermore, when Al is used for deoxidation, about 0.4 mass% or less of Al is contained.
(2) Powder component for continuous casting: Except for C, quantitative analysis was performed by chemical analysis. The reason why the total of each component shown in Table 1 is less than 100 mass% is because it contains inevitable impurities such as MgO and Fe ₂ O _{3 in} addition to these components. The C content was determined from the added weight ratio.
(3) Viscosity: measured by the rotating cylinder method. That is, powder was put into an iron crucible and melted in a vertical resistance furnace, and then the viscosity was measured by inserting and rotating an iron rotor.
(4) Solidification temperature: When the viscosity is measured, the point at which the viscosity value suddenly rises as the temperature is lowered is determined. This inflection point was taken as the solidification temperature.
(5) Thickness of powder film: The powder film after casting was sampled and the thickness was measured.
(6) Ratio of crystal phase: The powder film after casting was embedded and polished, and observed by SEM. From the observation, the thickness of the crystal phase was measured. An example is shown in FIGS.
(7) Slab surface or internal defects: Surface defects were identified by appearance observation. Internal defects were cut through slabs, and the presence or absence of cracks was confirmed by PT (penetration inspection) inspection of the cross section.
(8) Grinding and cutting yield: Calculated by measuring the weight before and after cutting and grinding of the defective part.

  The liquidus temperature of the boron-containing stainless steel shown in Tables 1 and 2 is the lowest, the B content is 1.41 mass% (Comparative Example 12) at 1321 ° C., the highest, and the B content is 0. It is 1375 degreeC of .82 mass% (Comparative Example 6). In addition, the liquidus temperature of about 1.1% of middle steel is 1350 degreeC.

  Next, continuous casting was performed using the powder for continuous casting shown in Table 1. As a result, in Invention Examples 1 to 4, it was possible to complete casting without any problem. Moreover, both the grinding and cutting yield of the obtained slab were as good as 94% or more.

  On the other hand, in the comparative examples (No. 5 to No. 12), since any of the powder components, powder physical properties, casting conditions, and the crystallinity of the powder film is out of the scope of the present invention, vertical cracks, depletion, This resulted in sticking. Moreover, the grinding yield was also less than 90%, leading to an increase in manufacturing cost. Hereinafter, the comparative example will be described in more detail.

(1) Comparative Examples 5 to 9 show examples in which powders in which each component is out of the scope of the present invention are applied to continuous casting.
a. Comparative Example 5: These _Ca0 in powder, _SiO 2, Na 2 O, _Al 2 _{O 3} content are outside the scope of the present invention, the values of basicity C / S Correspondingly low, further, B _This is an example using powder to which ₂ O ₃ is not added. Therefore, the viscosity was as high as 6.2 poise and the coagulation temperature was as high as 1210 ° C. For this reason, powder flowed in too much, and the film thickness was as thick as 6.5 mm, and it became completely glassy. As a result, the slab was depleted and cracked.
b. Comparative Example 6: Since the amount of B ₂ O ₃ added in the powder was small, the film thickness was as thick as 3.6 mm, and the proportion of the crystal phase was as low as 1%. This caused depression.
c. Comparative Example 7: Since the content of B ₂ O ₃ in the powder was as high as 8.3%, the solidification temperature was too low at 870 ° C. Therefore, the film thickness was as thick as 6.1 mm, and it was completely glassy. Depression and vertical cracking occurred in the slab.
d. Comparative Example 8: The content of CaO, SiO ₂ , Na ₂ O, and Al ₂ O _{3 in} the powder is out of the range of the present invention, and the basicity C / S is accordingly low. The viscosity was as low as 0.35 poise and the coagulation temperature was as low as 725 ° C. Therefore, the film thickness was as thick as 5.6 mm, and it became completely vitreous, and the slab was depleted and vertical cracks occurred.
e. Comparative Example 9: In this example, a large amount of aggregate C was added to the powder. The melting of the powder was delayed, and the film thickness was as thin as 0.3 mm. As a result, it caused sticking.

(2) Next, Comparative Examples 10 to 12 show examples in which the powder suitable for the present invention was used but the casting conditions were not suitable.
a. Comparative Example 10: Since the drawing speed was as fast as 1200 mm / min, the solidified shell did not grow sufficiently, causing breakout and complete casting.
b. Comparative Example 11: Since the degree of superheated molten steel was as low as 2 ° C., melting of the powder was slow, and the thickness of the powder film was as thin as 0.2 mm. Moreover, since the drawing speed was as slow as 500 mm / min, sticking occurred.
c. Comparative Example 12: Since the degree of superheating of the molten steel was as high as 80 ° C., the molten steel was not sufficiently solidified in the continuous casting machine, causing a center crack of the slab. The grinding yield was not so bad, but due to internal cracks, it was not crimped even after rolling and did not become a product.

  The present invention can also be used as a continuous casting of alloy / steel having a low liquidus temperature, such as boron-containing stainless steel or Ni—Cu alloy, and as a powder for that purpose.

Claims (6)

_{Ca0: 30~35mass%, SiO 2:} 20~30mass%, Na 2 O: 10~16mass%, Al 2 O 3: 8~11mass%, B 2 O 3: 3~5 ( below) mass%, F: 4-10 mass%, Aggregate C: having a component composition containing 1-3 mass%, and having a basicity of 1.0 ≦ C / S <1.3, a viscosity at 1300 ° C. of 0.5-2 poise, Continuous for boron-containing stainless steel characterized by having a characteristic of forming a powder film with a thickness of 0.5 to 3 mm when the solidification temperature is 900 to 1200 ° C. and it flows between the mold and the solidified shell. Powder for casting. 2. The powder for casting boron-containing stainless steel according to claim 1, wherein the powder film has a crystal phase in a portion of more than 3% to less than 15% of the thickness of the film on the mold side. . The boron-containing stainless steel building powder according to claim 1 or 2, wherein the crystalline phase in the powder film is caspidine. C ≦ 0.2 mass%, Si ≦ 3 mass%, Mn ≦ 5 mass%, Cr: 15 to 25 mass%, Ni: 3 to 20 mass%, B: 0.8 to 1.5 mass%, the balance from Fe and inevitable impurities A continuous casting method for boron-containing stainless steel, comprising continuously casting a molten steel of boron-containing stainless steel using the continuous casting powder according to any one of claims 1 to 3. The method for continuous casting of boron-containing stainless steel according to claim 4, wherein the boron-containing stainless steel having a liquidus temperature of 1320 to 1380 ° C is continuously cast. The continuous casting method for boron-containing stainless steel according to claim 4 or 5, wherein continuous casting is performed under conditions where the superheat degree of the molten steel is 5 to 50 ° C and the continuous casting speed is 550 to 900 mm / min.

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