JP7032600B1 - Mold powder for continuous casting and continuous casting method used for Fe—Ni based alloys or Ni-based alloys. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold powder used for continuous casting of a molten metal of Fe—Ni based alloy or Ni based alloy in order to produce a continuous casting slab of Fe—Ni based alloy or Ni based alloy having excellent surface properties, and for main continuous casting. A continuous casting method using a mold powder is provided. SOLUTION: The mold powder for continuous casting of Fe—Ni based alloy or Ni based alloy containing 30 wt% or more of Ni is CaO—SiO2 based powder, CaO: 30 to 40 wt%, SiO2: 30 to 40 wt%, Al2O3 :. 3 to 10 wt%, Na2O: 8 to 15 wt%, F: 5 to 10 wt%, K2O: 0.01 to 2.00 wt%, S: 0.01 to 0.50 wt%, P: 0.01 to 2.00 wt% % And C: 1.0 to 3.5 wt% component composition, basicity of 0.75 ≦ CaO / SiO2 ≦ 1.33, and viscosity at 1300 ° C. of 1.0 to 4.0 poise. The solidification temperature is 1000 to 1250 ° C. [Selection diagram] Fig. 2

Description

The present invention relates to a mold powder for continuous casting for producing a slab of an Fe—Ni based alloy or a Ni-based alloy having excellent surface properties, and also relates to a continuous casting method using the mold powder.

For Fe-Ni based alloys or Ni-based alloys containing 30% or more of Ni, 36 wt% Ni-Fe alloys, 42 wt% Ni-Fe alloys, 45 wt% Ni-Fe alloys, 50.5 wt% Ni-Fe alloys, 76. There are 5 wt% Ni-15.5 wt% Cr-6.5 wt% Fe alloy, 77 wt% Ni-4 wt% Mo-5 wt% Cu-Fe alloy, 99.5 wt% Ni alloy and the like. Since these alloys have a single-phase austenite structure, impurities such as P and S tend to concentrate between the dendrite trees during solidification, and have the disadvantage of being easily cracked. Such cracks often appear in the form of vertical cracks, horizontal cracks, or bleeding in which unsolidified molten metal oozes out from the cracks on the surface of the slab ingot by a continuous casting machine. , It sometimes broke out and stopped casting.

Therefore, Fe—Ni-based alloys or Ni-based alloys have traditionally been cast by ordinary ingot formation. Even if the surface of the slab is finely cracked, it may cause scratches on the tropical surface and the surface of the plank after hot rolling. Therefore, the surface of the slab before hot rolling is ground, and then a penetration flaw detection test is performed. If there is a crack, it is necessary to remove fine cracks by additional grinding, resulting in a decrease in productivity and an increase in manufacturing cost due to a decrease in yield.

In response to these problems, Patent Document 1 optimizes the viscosity, solidification temperature, and crystal phase of the powder for continuous casting sprayed on the molten metal during continuous casting of an Fe—Ni based alloy or Ni-based alloy during continuous casting. It is disclosed that by preventing non-uniform cooling in the meniscus, vertical cracking, bleeding, and breakout can be prevented, and a grinding yield of 90% or more of the slab can be ensured.

However, 15 of the 24 invention examples of Patent Document 1 have a slab grinding yield of 95 wt% or less, and these 15 examples indicate that the slab surface needs to be ground by 5 wt% or more. That is, in the disclosure content of Patent Document 1, it can be said that the problem of fine cracking on the slab surface of the Fe—Ni based alloy or Ni-based alloy remained.

Further, in Patent Document 2, for a Ni-containing steel slab containing 7.5 to 10% by mass of Ni, a solidification cell is formed by setting the solidification nucleation generation density on the slab surface to 0.6 pieces / mm ² or more. By reducing the size of the solidified cell, the segregation of S and P at the solidified cell interface is reduced, the brittleness at the solidified cell interface is reduced, and the stress acting on the solidified cell interface is also dispersed, whereby the solidified cell is dispersed. It is proposed that solidification cracking at the interface is suppressed and the occurrence of cracking on the surface of the slab is reduced. Further, in order to make the solidification nucleation density of 0.6 pieces / mm ² or more, the components of the Ni alloy, the viscosity of the mold powder at 1300 ° C., and the frequency of the mold are disclosed.

However, since the solidification nucleation density and the stress capable of suppressing solidification cracking depend on the components of the steel and the alloy, the Fe—Ni based alloy or Ni-based alloy containing 30 wt% or more of Ni, which is the subject of the present invention, is a patent document. The disclosure content of 2 cannot be applied, and cracking on the surface of the slab cannot be prevented.

Further, in Patent Document 3, when continuously casting a molten steel containing 5 to 10% by weight of nickel, the molten steel is melted so that phosphorus is 0.006% by weight or less and sulfur is 0.003% by weight or less. In the secondary cooling zone, the temperature range from the liquidus temperature of the slab to 1050 ° C is cooled at a rate of 3.0 ° C / sec or higher, and the surface temperature at the end of passing through the correction point is maintained at 850 ° C or higher. Therefore, a method for completely preventing the occurrence of fine cracks as well as surface cracks and subsurface cracks of continuously cast slabs is disclosed.

However, the content of Patent Document 3 is intended only for continuous casting in which a curved portion is present in the casting process, and surface cracking occurs even in a slab ingot by a vertical continuous casting machine in which a vertical curved portion is not present. According to the disclosure of Patent Document 3, it is not possible to prevent surface cracking of the slab ingot by the vertical continuous casting machine. Further, in Patent Document 3, the slab temperature at the end of straightening is 850 ° C. or higher. Below this temperature is the embrittlement temperature range of the slab, and it is disclosed that surface fine cracks occur. The contents disclosed in Patent Document 3 cannot be applied to Fe—Ni based alloys or Ni-based alloys containing 30 wt% or more of Ni, and cracks on the surface of slabs cannot be prevented.

Japanese Patent No. 3574428 Japanese Unexamined Patent Publication No. 2009-248099 Japanese Unexamined Patent Publication No. 8-10919

As described above, since the conventional technique cannot prevent fine cracks on the slab surface of Fe—Ni based alloys or Ni-based alloys containing 30 wt% or more of Ni, the surface of the slab before hot rolling is ground to be fine. By removing the cracks, scabs on the tropical and plank surfaces were prevented after hot rolling. Therefore, the yield has decreased and the manufacturing process has been added. That is, it can be said that the problem of fine vertical cracking on the slab surface of the Fe—Ni based alloy or Ni-based alloy containing 30 wt% or more of Ni remained.

The present invention provides a mold powder used for continuously casting a slab of an Fe—Ni based alloy or a Ni-based alloy having excellent surface properties, and a continuous casting method using the present mold powder.

In order to solve the above-mentioned problems, the inventors first investigated in detail the cracked portion of the slab surface of the Fe—Ni based alloy or Ni-based alloy. From the etching structure of the cross section of the crack, the cracks existed along the solidified grain boundaries, and the composition of the solidified grain boundaries was analyzed by SEM / EDS and EPMA, and it was confirmed that S and P were concentrated. .. This is consistent with the conventional finding that since the solidification structure of the Fe—Ni based alloy or Ni-based alloy is austenite single phase, impurities such as P and S are likely to be concentrated between the dendrite trees during solidification and are easily cracked.

Subsequently, the inventors prepared a sample in which the vicinity of the surface of the slab of the Fe-36Ni-based alloy was cut out thinly to a thickness of 0.5 mm, and the concentration distribution in the thickness direction of S and P was analyzed by emission spectroscopy and fluorescent X-ray analysis. The analysis was performed, and the results are shown in the graphs of FIGS. 1 (a) and 1 (b). In FIG. 1, the S concentration and the P concentration at the molten metal stage were 0.0005% and 0.0046%. As shown in FIG. 1, it was discovered that the S and P concentrations on the surface layer were high. Moreover, it was found that the S concentration and P concentration of the surface layer were higher than the S concentration and P concentration of the molten metal collected by the tundish during continuous casting. It was considered that the thickening of the S concentration and the P concentration of the slab surface layer promoted the cracking of the slab surface layer.

Furthermore, the inventors continued to investigate the cause of the increase in S concentration and P concentration on the surface layer of the slab. FIG. 2 shows a schematic diagram thereof. Reference numeral 1 is a mold for continuous casting, and the molten metal 3 is poured into the mold 1 from the dipping nozzle 2. A solidified shell 4 is formed on the peripheral edge of the molten metal 3 cooled by the mold 1. Further, the molten powder 5 and the mold powder 6 are sprayed on the upper portion of the molten metal 3. As shown in FIG. 2, the molten metal is instantly pulled up by inserting an iron rod 7 having a diameter of 8 mm into the surface of the molten metal in the mold 1 during continuous casting of a Fe—Ni based alloy or a Ni-based alloy by about 10 mm, adhering the molten metal to the tip, and pulling it up instantly. The molten metal on the surface was collected. The solidified molten metal and the glass-like solidified mold powder adhered to the tip of the iron rod. The glass-like mold powder was crushed with a hammer, and only the solidified molten metal sample portion was collected and analyzed. As shown in FIG. 3, the molten metal was collected at a plurality of locations halved in the width direction of the mold. When the S concentration and P concentration of the collected molten metal sample were analyzed by chemical analysis, as shown in the upper view of FIG. 3, there is a portion higher than the S concentration and P concentration of the molten metal collected by the tundish during continuous casting. It turned out. That is, it was found that the enrichment of the S concentration and the P concentration on the surface layer of the slab did not occur during the solidification process, but occurred at the time of the molten metal in the mold.

Therefore, the inventors melted the Fe-36Ni alloy in a 20 kg high frequency induction furnace in the laboratory, and after raising the temperature at the liquidus line temperature + 50 ° C., turned off the high frequency power supply to eliminate the convection of the molten metal due to high frequency. After that, 100 g of mold powder with adjusted S concentration and P concentration is added on the molten metal, and immediately after the mold powder is melted, a φ8 mm iron rod is inserted into the molten metal by about 10 mm and pulled up instantly to collect a molten metal sample on the surface of the molten metal. did. This test was repeated with various S and P concentration mold powders. When the S concentration and P concentration of the collected molten metal sample were analyzed by chemical analysis, as shown in FIG. 4, the S concentration and P concentration of the added mold powder and the S concentration and P concentration of the molten metal sample collected by the iron rod Found that there was a correlation.

From the above investigation results, the cause of the concentration of S and P on the slab surface layer of the Fe—Ni based alloy or Ni based alloy is the interface between the molten mold powder and the molten metal of the Fe—Ni based alloy or Ni based alloy. This is because S and P are transferred to the molten metal in the reaction shown in 2.
(% S) in molten mold powder → [% S] in molten metal ... (Equation 1)
(% P) in molten mold powder → [% P] in molten metal ... (Equation 2)

As shown in FIG. 5, the molten metal 3 in the mold 1 during continuous casting starts solidification from the meniscus portion indicated by the arrow, and the meniscus portion becomes the surface layer portion of the slab. That is, if there is a portion where S and P are concentrated in the meniscus portion, a portion 8 where S and P are concentrated is present in the surface layer portion of the slab. In the portion where S and P are concentrated, vertical cracks and horizontal cracks are formed on the slab surface due to the non-uniformity of solidification shrinkage caused by the slight shading of the spray water in the secondary cooling zone and the stress of the bulge in the solidification shell between the rolls. Will occur.

Therefore, the inventors further produced mold powders having various S and P concentrations, and produced Fe—Ni alloys or Ni-based alloy slabs by continuous casting under various operating conditions to obtain the composition of the mold powder and the composition of the mold powder. By investigating the relationship between the manufacturing conditions of continuous casting and the number of cracks on the surface of the slab, it was possible to manufacture Fe—Ni based alloys or Ni-based alloy slabs without surface cracks. The present invention has been completed through the above studies, and the contents are as shown below.

The present invention is a mold powder for continuous casting of Fe—Ni based alloy or Ni based alloy containing 30 wt% or more of Ni, and this mold powder is CaO—SiO ₂ based powder, CaO: 30-40 wt%, SiO. ₂ : 30-40 wt%, Al ₂ O ₃ : 3-10 wt%, Na ₂ O: 8-15 wt%, F: 5-10 wt%, K ₂ O: 0.01-2.00 wt%, S: 0. It has a component composition of 01 to 0.50 wt%, P: 0.01 to 2.00 wt% and C: 1.0 to 3.5 wt%, and has a basicity of 0.75 ≤ CaO / SiO ₂ ≤ 1. It is a mold powder for continuous casting of a Fe—Ni based alloy or a Ni-based alloy, which satisfies 33 and has a viscosity at 1300 ° C. of 1.0 to 4.0 poise and a solidification temperature of 1000 to 1250 ° C.

Further, the Fe—Ni based alloy or Ni-based alloy is further characterized in that S: 0.0001 to 0.0050 wt% and P: 0.0001 to 0.0150 wt%.

Further, when the Fe-Ni alloy or Ni-based alloy is cast by a continuous casting machine, the above conditions are such that the drawing speed of the continuous casting slab is 400 to 900 mm / min and the superheating degree of the molten metal is 5 to 50 ° C. It is a continuous casting method of a Fe—Ni based alloy or a Ni-based alloy, which comprises casting using a mold powder for continuous casting.

According to the mold powder and the continuous casting method of the present invention, it is possible to prevent fine cracks generated on the surface of the continuously cast slab of a Fe—Ni based alloy or a Ni-based alloy containing 30 wt% or more of Ni, and as a result. The slab surface grinding before hot rolling can be reduced, the yield is good, and the manufacturing process can be shortened.

From the surface of the alloy slab, (a) is a graph showing the change in the concentration of S, and (b) is a graph showing the change in the concentration of P. It is a schematic diagram of the method of collecting the molten metal sample from the molten metal surface during continuous casting. It is a top view of the mold which shows the molten metal sampling position and the enrichment state of S, P. (A) is a graph showing the relationship between the S concentration in the mold powder and the S concentration in the molten metal sample, and (b) is a graph showing the relationship between the P concentration in the mold powder and the P concentration in the molten metal sample. It is a schematic diagram which shows the mechanism which the S and P concentrated layers are formed on the surface of a solidified shell.

The reasons for limiting the chemical composition and physical properties of the mold powder for continuous casting of Fe—Ni based alloys or Ni-based alloys containing 30 wt% or more of Ni of the present invention will be described below. CaO: 30-40 wt%, SiO ₂ : 30-40 wt%, Al ₂ O ₃ : 3-10 wt%, Na ₂ O: 8-15 wt%, F: 5-10 wt%, K ₂ O: 0.01-2 It has a component composition of .00 wt%, S: 0.01 to 0.50 wt%, P: 0.01 to 2.00 wt% and C: 1 to 3.5 wt%, and has a basicity of 0.75 ≦ CaO. Within the component range of / SiO ₂ ≤ 1.33, the viscosity at 1300 ° C. is 1.0 to 4.0 poise, and the solidification temperature is 1000 to 1250 ° C. Mold powder is a powder that is a mixture of oxides, fluorides, sulfides, charcoal materials, and the like.

CaO: 30-40 wt%
CaO is one of the main components of the mold powder. When CaO is lower than 30 wt%, the basicity CaO / SiO ₂ is smaller than 0.75, and conversely, when CaO is higher than 40 wt%, the basicity CaO / SiO ₂ is larger than 1.33. The CaO-SiO ₂ powder has a low viscosity and solidification temperature in the vicinity of basicity CaO / SiO ₂ = 1, and a high viscosity and solidification temperature when the basicity CaO / SiO ₂ is higher or lower than in the vicinity of 1. The viscosity and solidification temperature are adjusted by adding Na ₂ O, F, and K ₂ O, but the viscosity at 1300 ° C. and the solidification temperature of 1250 ° C., which are within the range of the present invention, are exceeded, the consumption of powder is reduced, and solidification occurs. Lubrication of the shell and mold deteriorates. When seizure occurs between the solidified shell and the mold, the solidified shell is torn off and the molten metal leaks out, causing breakout trouble. Even if the solidified shell is torn off without breaking out, large lateral cracks will occur on the slab surface and the grinding yield will deteriorate. Therefore, it is specified as 30 to 40 wt%. It is preferably 32 to 39 wt%, more preferably 34 to 38 wt%.

SiO ₂ : 30-40 wt%
SiO ₂ is one of the main components of the mold powder. When SiO ₂ is higher than 30 wt%, the basicity CaO / SiO ₂ is smaller than 0.75, and conversely, when SiO ₂ is lower than 40 wt%, the basicity CaO / SiO ₂ is larger than 1.33. The CaO-SiO ₂ powder has a low viscosity and solidification temperature in the vicinity of basicity CaO / SiO ₂ = 1, and a high viscosity and solidification temperature when the basicity CaO / SiO ₂ is higher or lower than in the vicinity of 1. The viscosity and solidification temperature are adjusted by adding Na ₂ O, F, and K ₂ O, but the viscosity at 1300 ° C. and the solidification temperature of 1250 ° C., which are within the range of the present invention, are exceeded, the consumption of powder is reduced, and solidification occurs. Lubrication of the shell and mold deteriorates. When seizure occurs between the solidified shell and the mold, the solidified shell is torn off and the molten metal leaks out, causing breakout trouble. Even if the solidified shell is torn off without breaking out, large lateral cracks will occur on the slab surface and the grinding yield will deteriorate. Therefore, it is specified as 30 to 40 wt%. It is preferably 31 to 38 wt%, more preferably 32 to 36 wt%.

Al ₂ O ₃ : 3 to 10 wt%
Al ₂ O ₃ has an effect of increasing the solidification temperature, an effect of increasing the viscosity, and an effect of producing neferin (Na ₂ O · Al ₂ O _{3.2SiO 2} ) in the crystalline phase. If Al ₂ O ₃ is greater than 3%, the crystalline phase neferin (Na ₂ O · Al ₂ O _{3.2SiO 2} ) is produced when the molten powder hardens between the mold and the solidified shell. During casting, the mold powder melts under the heat of the molten metal, and the melted mold powder flows between the solidified shell and the mold whose back surface is water-cooled, and is rapidly cooled and solidified to form a glassy powder film. Generate. Since the glassy powder film is transparent, the solidified shell is rapidly cooled by radiant heat transfer, but the presence of neferin, which is a crystalline phase, in the powder film reduces the radiant heat transfer and slows the cooling of the solidified shell. This makes it possible to prevent cracking of the slab surface. On the contrary, when Al ₂ O ₃ is more than 10 wt%, the viscosity becomes larger than 4 poise and the solidification temperature exceeds 1250 ° C. Further, when the amount of Al ₂ O ₃ is more than 10 wt%, coarse Al ₂ O ₃ grains are generated in the powder film, a vertically long dent defect is generated on the slab surface, and a vertical crack is generated under the dent. .. Therefore, it is specified as 3 to 10 wt%. It is preferably 4 to 9 wt%, more preferably 5 to 8 wt%.

Na ₂ O: 8 to 15 wt%
Na ₂ O has the effect of lowering the solidification temperature, the effect of lowering the viscosity, and the effect of producing nepheline (Na ₂ O · Al ₂ O _{3.2SiO 2} ) in the crystalline phase. When Na ₂ O is lower than 8 wt%, the viscosity becomes higher than 4 poise and the solidification temperature also exceeds 1250 ° C. In addition, the formation of nepheline (Na ₂ O · Al ₂ O _{3.2SiO 2} ) in the crystal phase is eliminated, and vertical cracking occurs due to quenching of the solidified shell. On the contrary, when Na ₂ O is higher than 15 wt%, the viscosity is lower than 1 poise and the solidification temperature is also lower than 1000 ° C. Further, when Na ₂ O is higher than 15%, the crystal phase in the powder film becomes excessive, the cooling in the mold becomes too weak, the necessary solidification shell is not generated, and the static pressure of the molten steel directly under the mold is used. The solidified shell swells, causing bulging trouble to stop casting. Therefore, it is specified as 8 to 15 wt%. It is preferably 9 to 13 wt%, more preferably 10 to 12 wt%.

F: 5-10 wt%
F has an effect of lowering the solidification temperature, an effect of lowering the viscosity, and an effect of producing caspidyne (3CaO, 2SiO ₂ , CaF ₂ ) in the crystalline phase. When F is lower than 5 wt%, the viscosity becomes higher than 4 poise, and the solidification temperature also exceeds 1250 ° C. In addition, the formation of caspidyne (3CaO, 2SiO ₂ , CaF ₂ ) in the crystalline phase is eliminated, and vertical cracking occurs due to rapid cooling of the solidified shell. On the contrary, when F is higher than 10 wt%, the viscosity becomes lower than 1 poise and the solidification temperature becomes lower than 1000 ° C. Further, when F is higher than 10%, the crystal phase in the powder film becomes excessive, the cooling becomes too weak in the mold, the required solidification shell is not generated, and the solidification shell is formed by the static pressure of the molten steel directly under the mold. Causes casting to be stopped due to bulging trouble. Even bulging deformation that does not stop casting causes vertical cracks and horizontal cracks due to the swelling of the solidified shell. Therefore, it is specified as 5 to 10 wt%. It is preferably 6 to 9 wt%, more preferably 7 to 8 wt%.

K ₂ O: 0.01-2.00 wt%
K ₂ O has the effect of lowering the solidification temperature and the effect of lowering the viscosity. Further, since K ₂ O does not generate a crystal phase in the powder film, the present invention has a viscosity and a solidification temperature while appropriately ensuring the amount of the crystal phase generated by the addition of Al ₂ O ₃ , Na ₂ O and F. It can be precisely controlled in the range of 1.0 to 4.0 pores and 1000 to 1250 ° C. That is, if only the addition of Al ₂ O ₃ , Na ₂ O, and F is increased and the viscosity and solidification temperature are adjusted, the crystal phase in the powder film becomes excessive, the cooling in the mold becomes too weak, and the necessary solidification shell is used. Is not generated, and the solidified shell swells due to the static pressure of the molten steel directly under the mold, causing casting to be stopped due to bulging trouble. Even bulging deformation that does not stop casting causes vertical cracks and horizontal cracks due to the swelling of the solidified shell. Therefore, it is very important to adjust the viscosity and solidification temperature of _K2O , which does not generate a crystal phase. In order to control the viscosity and solidification temperature within the range of the present invention, it is defined as 0.01 to 2.00 wt%. It is preferably 0.05 to 1.80 wt%, more preferably 0.10 to 1.00 wt%.

S: 0.01 to 0.50 wt%
S is an important component for preventing fine cracks on the surface of the slab. If it exceeds 0.50 wt%, fine cracks on the surface of the slab become remarkable, and the yield of slab grinding is lowered. Further, S is also a component that greatly affects the surface tension of the molten mold powder. If it is less than 0.01 wt%, the surface tension of the molten mold powder becomes high, the consumption of the powder decreases, seizure of the solidified shell and the mold occurs, the solidified shell is torn off, and the molten metal leaks out, which causes a breakout trouble. Even if the solidified shell is torn off without breaking out, large lateral cracks will occur on the slab surface and the grinding yield will deteriorate. Furthermore, S is a component that lowers the melting point of the molten oxide, and plays an important role in forming a sintered body by partially melting the molded powder powder after contacting it on the molten metal. If it is less than 0.01 wt%, the mold powder melts slowly, and the unmelted sintered body touches the solidified shell of the meniscus, causing vertical cracks and entrainment of the molded powder sintered body on the slab surface. Therefore, it is specified as 0.01 to 0.5 wt%. It is preferably 0.02 to 0.30 wt%, more preferably 0.03 to 0.15 wt%.

P: 0.01-2.00 wt%
P is an important component for preventing fine cracks on the surface of the slab. If it exceeds 2.00 wt%, fine cracks on the surface of the slab become remarkable, and the yield of slab grinding is lowered. In addition, P is also a component that greatly affects the surface tension of the molten mold powder, and if it is less than 0.01 wt%, the surface tension of the molten mold powder becomes high, the consumption of the powder decreases, and seizure of the solidified shell and the mold occurs. The solidified shell is torn off and the molten metal leaks out, causing breakout trouble. Even if the solidified shell is torn off without breaking out, large lateral cracks will occur on the slab surface and the grinding yield will deteriorate. For the above reasons, it is specified as 0.01 to 2.00 wt%. It is preferably 0.05 to 1.50 wt%, more preferably 0.10 to 1.00 wt%.

C: 1.0-3.5 wt%
The C particles of the carbonaceous material exist between the above-mentioned oxides, fluorides, and sulfides, and have a function of preventing melting due to contact. That is, when C is burned and gasified, the C particles disappear, and oxide, fluoride, and sulfide powders come into contact with each other to form a partially melted sintered body, which is then completely melted. By controlling the amount of C in this way, the melting rate of the powder can be controlled. If it is less than 1.0%, the melting is too fast, the molten powder layer on the molten metal becomes thick, and the solidified product formed by cooling the once melted powder called a bear on the mold surface grows greatly on the inner surface of the mold. Vertical cracks occur due to the unevenness of the bear, which reduces the grinding yield. On the contrary, if it is higher than 3.5 wt%, the melting is too slow, the molten powder does not flow between the mold and the solidified shell, and the sintered body touches the solidified shell of the meniscus. This causes vertical cracks and biting of the molded powder sintered material on the slab surface. There is also a risk of breakout. Therefore, it is specified as 1.0 to 3.5 wt%. It is preferably 1.5 to 3.2 wt%, more preferably 2.0 to 3.0 wt%.

Basicity CaO / SiO ₂ : 0.75 to 1.33
The CaO-SiO ₂ powder has a low viscosity and solidification temperature in the vicinity of basicity CaO / SiO ₂ = 1, and a high viscosity and solidification temperature when the basicity CaO / SiO ₂ is higher or lower than in the vicinity of 1. The viscosity and solidification temperature are adjusted by adding Na ₂ O, F, K ₂ O, but if the basicity CaO / SiO ₂ is less than 0.75 or greater than 1.33, the viscosity 4 at 1300 ° C. within the range of the present invention. The 0.0 Poise and the solidification temperature exceed 1250 ° C., the consumption of powder is reduced, and the lubrication of the solidified shell and the mold is deteriorated. When seizure occurs between the solidified shell and the mold, the solidified shell is torn off and the molten metal leaks out, causing breakout trouble. Even if the solidified shell is torn off without breaking out, large lateral cracks will occur on the slab surface and the grinding yield will deteriorate. Further, when the basicity CaO / SiO ₂ is less than 0.75, S in the molten powder is likely to be transferred to the Fe—Ni alloy and the molten Ni alloy. For the above reason, the basicity CaO / SiO ₂ was set in the range of 0.75 to 1.33. It is preferably 0.84 to 1.26, more preferably 0.94 to 1.19.

Viscosity at 1300 ° C: 1.0-4.0 poise
If the viscosity at 1300 ° C. is less than 1.0 poise, the fluidity of the molten powder is too good, the consumption of the powder increases, and the thickness of the molten powder flowing between the mold and the solidified shell becomes uneven. Cooling in the meniscus becomes uneven and promotes vertical cracking. On the other hand, if the viscosity at 1300 ° C. is higher than 4.0 poise, the fluidity of the molten powder deteriorates, so that the consumption of the powder decreases and the lubrication of the solidified shell and the mold deteriorates. When seizure occurs between the solidified shell and the mold, the solidified shell is torn off and the molten metal leaks out, causing breakout trouble. Even if the solidified shell is torn off without breaking out, large lateral cracks will occur on the slab surface and the grinding yield will deteriorate. Therefore, the viscosity at 1300 ° C. was set to 1.0 to 4.0 poise. It is preferably 1.5 to 3.0 poise, and more preferably 1.7 to 2.5 poise.

Coagulation temperature: 1000-1250 ° C
When the solidification temperature is less than 1000 ° C., the consumption of the molten powder becomes large, the thickness of the molten powder flowing between the mold and the solidification shell becomes uneven, the cooling in the meniscus becomes uneven, and the vertical direction becomes uneven. It promotes cracking. On the other hand, when the solidification temperature is higher than 1250 ° C., the consumption of powder is reduced and the lubrication of the solidification shell and the mold is deteriorated. When seizure occurs between the solidified shell and the mold, the solidified shell is torn off and the molten metal leaks out, causing breakout trouble. Even if the solidified shell is torn off without breaking out, large lateral cracks will occur on the slab surface and the grinding yield will deteriorate. Therefore, the solidification temperature is defined as 1000 to 1250 ° C. It is preferably 1050 to 1230 ° C, more preferably 1100 to 1200 ° C.

The present invention is an invention applied to a Fe—Ni-based alloy or Ni-based alloy containing 30 wt% or more of Ni, and further, the Fe—Ni-based alloy or Ni-based alloy is S: 0.0001 to 0.0050 wt%, P :. It is a desirable invention that the content is 0.0001 to 0.0150 wt%. The reason for limiting the chemical composition of S and P of the Fe—Ni based alloy or Ni-based alloy will be described below.

S: 0.0001 to 0.0050 wt%
S is an element that segregates between dendrite columns and at grain boundaries during the solidification process, and is an element that causes grain boundary embrittlement. Therefore, S is an important element for preventing fine cracks on the slab surface. In order to reduce S in the desulfurization step from 0.0001 wt%, it is necessary to add a large amount of Al and / or Si to strengthen the desulfurization. By strengthening deoxidation, MgO is reduced from refractories and slag, the Mg concentration in the molten metal increases, and a large amount of non-metal inclusions MgO and Al ₂ O ₃ are generated. The non-metal inclusions MgO and Al ₂ O ₃ adhere to the dipping nozzle during continuous casting, coarsen, then fall off, flow into the molten metal, enter the mold, and adhere to the solidified shell. Therefore, the large non-metal inclusions MgO and Al _{2O 3} have a size of about 5 mm, and a large number of fine cracks occur on the surface layer of the slab, which needs to be removed by grinding and the yield deteriorates. Further, when the concentration of S exceeds 0.0050 wt%, the dendrite trunk and grain boundaries become brittle due to the segregation between the dendrite columns and the grain boundaries, and the slab surface cracks become remarkable. Therefore, the upper limit is 0.0050 wt%. did. For the above reason, it is defined as 0.0001 to 0.050 wt%. It is preferably 0.0002 to 0.0040 wt%, more preferably 0.0003 to 0.0030 wt%.

P: 0.0001 to 0.0150 wt%
P is an element that segregates between dendrite columns and at grain boundaries during the solidification process, and is an element that causes grain boundary embrittlement. Therefore, it is an important element for preventing fine cracks on the slab surface. However, since P is mixed as an impurity from raw materials such as scrap, it is necessary to select and use low P raw materials. Further, P needs to be sufficiently removed by dephosphorization refining in the steelmaking process. However, in order to reduce P to 0.0001 wt% or less, the lower limit is set to 0.0001 wt% because the cost increases due to the use of expensive pure metal raw materials and the load of long-term dephosphorization refining. Further, at a concentration exceeding P: 0.0150 wt%, cracking on the slab surface becomes remarkable, so the upper limit is set to 0.0150 wt%. It is preferably 0.0002 to 0.0100 wt%, more preferably 0.0005 to 0.0050 wt%.

Further, the present invention also proposes a method of continuously casting the Fe—Ni based alloy or Ni-based alloy with the mold powder of the present invention. That is, under the conditions of a continuous casting slab drawing speed: 400 to 900 mm / min and a molten metal superheat degree: 5 to 50 ° C., the Fe—Ni alloy or Ni-based alloy is continuously cast with the mold powder of the present invention. It is a casting method.

Extraction speed: 400 to 900 mm / min If the extraction speed is as slow as less than 400 mm / min, the amount of molten metal supplied to the mold decreases, and the heat supply decreases. As a result, the molten layer of the mold powder is reduced, the lubrication between the solidified shell and the mold is deteriorated, and the solidified shell and the mold are seized, the solidified shell is torn off and the molten metal leaks out, which causes a breakout trouble. Fortunately, even if a small amount of molten metal leaks and does not lead to breakout trouble, the torn part of the solidified shell needs to be heavily ground on the surface of the slab, resulting in a decrease in grinding yield. On the other hand, if the speed exceeds 900 mm / min, the heat supply increases and the powder melts faster, so that the solidified shell and the molten mold powder layer flowing into the mold become thicker. The molten mold powder plays a role of heat transfer between the solidified shell and the mold, but the thickening of the molten mold powder reduces the heat removal from the solidified shell to the mold and slows down the development of the solidified shell thickness in the mold. .. Further, when the withdrawal speed is faster than 900 mm / min, the solidification shell stays in the mold for a short time, so that the heat withdrawn from the mold is also reduced. As a result, the thickness of the solidified shell becomes thin, and the slab surface is cracked due to deformation due to bulging due to static pressure of the molten metal between the rolls for secondary cooling after the mold. For the above reasons, the pulling speed was set to 400 to 900 mm / min. It is preferably 450 to 850 mm / min, more preferably 500 to 800 mm / min.

Superheat of molten metal: 5 to 50 ° C
The degree of superheat of the molten metal is defined by the temperature of the molten metal measured by the tundish during continuous casting by the temperature difference from the liquidus temperature of the molten metal. When the degree of superheat is lower than 5 ° C., the viscosity of the molten metal increases, the floating removal of non-metal inclusions in the tundish and the mold is insufficient, and the adhesion of non-metal inclusions to the solidification shell increases. Therefore, a large number of fine cracks caused by non-metal inclusions occur on the surface layer of the slab, which needs to be removed by grinding and the yield deteriorates. On the contrary, when the degree of superheat exceeds 50 ° C., the thickness of the solidified shell becomes thin, and the slab surface is cracked due to deformation due to bulging due to static pressure of the molten metal between the rolls for secondary cooling after the mold. For the above reason, the degree of superheat of the molten metal was set to 5 to 50 ° C. It is preferably 20 to 45 ° C, more preferably 30 to 40 ° C.

Next, examples will be presented to further clarify the configuration and effects of the present invention, but the present invention is not limited to the following examples. In an electric furnace with a capacity of 60 tons, ferronickel, pure nickel, iron scraps, Fe—Ni alloy scraps and the like were melted as raw materials. Then, refining was performed in AOD and / or VOD, and then hot water was discharged to a ladle to adjust the temperature and composition, and a slab was manufactured by a continuous casting machine. The mold size of the continuous casting machine was 200 mm thick × 1000 to 1600 mm width. The cast Fe-Ni alloy or Ni-based alloy is 36 wt% Ni-Fe alloy, 42 wt% Ni-Fe alloy, 45 wt% Ni-Fe alloy, 50.5 wt% Ni-Fe alloy, 76.5 wt% Ni-15. It is a .5 wt% Cr-6.5 wt% Fe alloy, a 77 wt% Ni-4 wt% Mo-5 wt% Cu-Fe alloy, and a 99.5 wt% Ni alloy.

After removing the oxide layer on the surface by grinding 1% of the surface thickness of the cast slab long side surface with a grinder, a penetrant inspection test was performed and the number and total length of cracks with an observed length or width of 1 mm or more. Was counted. Chemical composition of Fe-Ni alloy or Ni-based alloy obtained in Tables 1 to 3, mold powder composition used for continuous casting, physical properties of mold powder, continuous casting conditions, number of cracks measured by penetrant inspection test, total crack length The total crack length per flaw detection area is shown.

Here, the measuring method of each component and the physical property value is described.
Alloy composition:
Quantitative analysis was performed using a fluorescent X-ray analyzer, and the oxygen concentration of the alloy was quantitatively analyzed by the inert gas impulse melting infrared absorption method. The balance shown in Table 1 is Fe and unavoidable impurities such as C, Co, W, V, N, H, and O.

Mold powder component:
The amount of C contained in the mold powder was determined from the weight ratio of the C raw material added as the C source. The composition of other components was quantitatively analyzed by chemical analysis. The total of each component shown in Table 1 is less than 100% because it contains unavoidable impurities such as Fe ₂ O ₃ and Mg O in addition to these components.

Mold powder viscosity and solidification temperature:
The viscosity of the mold powder was measured by the rotary cylinder method. That is, powder was charged into an iron crucible, heated to 1300 ° C. in a vertical resistance furnace to melt it, an iron rotor was inserted, and the viscosity was measured from the load when rotating. Then, after the viscosity measurement, the temperature was lowered, and the temperature at which the viscosity value suddenly increased was defined as the solidification temperature.

Total crack length:
After grinding the surface of the slab with a grinder to remove the oxide film on the surface, a penetrant inspection test is performed to count and evaluate the number and length of cracks with a visually observed length or width of 3 mm or more. did. The total crack length was calculated by summing up all crack lengths. The amount of grinding was uniformly evaluated as 1% of the thickness. The flaw detection area m ² was measured by slab width × slab length 5 m. The slab width was evaluated in three types of 1.0 m, 1.3 m, and 1.6 m. Cracks were measured only on the surface.

Total crack length per flaw detection area:
The total crack length was evaluated by dividing the total crack length by the flaw detection area to calculate the total crack length per flaw detection area. The evaluation criteria are as follows.
◎: No crack 〇: Total crack length: 100 mm / flaw detection area m ² or less △: Total crack length: 100 mm / flaw detection area m longer than ² , 200 mm / flaw detection area m ² or less ×: Total crack length: 200 mm / Longer than the flaw detection area m ² If the total crack length per flaw detection area is 100 mm / flaw detection area m ² or less, the subsequent processing can be partial grinding only for the cracked portion, and 100 mm / flaw detection area m ² If it is longer and 200 mm / flaw detection area m ² or less, it is necessary to additionally require 2% of slab full surface grinding to prevent bending during hot rolling, and if it is 200 mm / scratch detection area m ² or more, the entire slab surface needs to be ground. An additional 5% of grinding must be required, resulting in significant cost and lead time losses due to reduced yield and additional manufacturing processes.

Slab grinding yield:
All vertical cracks and horizontal cracks were removed by grinding, and after confirming no cracks in the penetrant inspection test, the slab weight was measured and the slab yield was also measured.

In the examples of the invention and the reference examples 1 to 14, since the scope of the present invention was satisfied, the surface of the slab had few cracks and the grinding yield was good. In particular, since Invention Examples 1 to 8 were in a preferable range, the number of cracks generated was small, the crack evaluation was good in the ⊚ or ◯ evaluation, and the SLG yield was as good as 97% or more.

In Reference Example 9, S of the alloy component was as high as 0.0084%, and vertical cracks were generated with a length of 144 mm / flaw detection area m ² . The crack evaluation was Δ, and the grinding yield was 96.1%.

In Reference Example 10, P of the alloy component was as high as 0.0190%, and vertical cracks were generated with a length of 152 mm / flaw detection area m ² . The crack evaluation was Δ, and the grinding yield was 96.0%.

In Reference Example 11, the alloy components were as high as S = 0.0072% and P = 0.0188%, and vertical cracks were generated with a length of 168 mm / flaw detection area m ² . The crack evaluation was Δ, and the grinding yield was 95.6%.

In Invention Example 12, since the drawing speed was as fast as 950 mm / min and the overheating temperature of the molten metal was as high as 65 ° C., bulging occurred and vertical cracks and horizontal cracks occurred with a length of 134 mm / flaw detection area m ² . The crack evaluation was Δ, and the grinding yield was 96.3%.

In Invention Example 13, since the superheat temperature of the molten metal is as low as 3 ° C., a large number of fine vertical cracks due to non-metal inclusions occur, and the length is 116 mm / flaw detection area m ² . The crack evaluation was Δ, and the grinding yield was 96.7%.

In Reference Example 14, the S concentration of the Fe—Ni alloy was as low as S = 0.00003% because excessive deoxidation was performed during the refining of the Fe—Ni alloy, and a large amount of non-metal inclusions MgO and Al ₂ O ₃ were generated. However, a large number of fine vertical cracks caused by non-metal inclusions occurred, resulting in a length of 114 mm / flaw detection area m ² . The crack evaluation was Δ, and the grinding yield was 96.6%.

Although the invention examples and the reference examples 9 to 14 are within the scope of the present invention, the components of the Fe—Ni based alloy or the Ni-based alloy and the continuous casting method are not within the preferable range, and therefore cracks are within the permissible range. It was detected and the crack evaluation was Δ evaluation.

On the other hand, Comparative Examples 15 to 22 deviate from the scope of the present invention. Each example will be described below.
In Comparative Example 15, the S concentration of the mold powder was as high as S = 0.72%, many long vertical cracks were generated on the slab surface, and a length of 230 mm / flaw detection area m ² was generated. The crack evaluation was ×, and the entire surface was ground again in order to remove vertical cracks, resulting in a grinding yield of 94.4%.

In Comparative Example 16, the P concentration of the mold powder was as high as S = 2.21%, many long vertical cracks were generated on the surface of the slab, and a length of 210 mm / flaw detection area m ² was generated. The crack evaluation was ×, and the entire surface was ground again in order to remove vertical cracks, resulting in a grinding yield of 94.8%.

In Comparative Example 17, the S concentration of the mold powder was as low as S = 0.002%, and long vertical cracks caused by the sintered body of the powder generated in the meniscus were generated on the slab surface, resulting in 215 mm / flaw detection area m ² . rice field. The crack evaluation was ×, and the entire surface was ground again in order to remove vertical cracks, resulting in a grinding yield of 94.7%.

In Comparative Example 18, the P concentration of the mold powder was as low as S = 0.002%, and long vertical cracks caused by the sintered body of the powder generated in the meniscus were generated on the slab surface, resulting in 216 mm / flaw detection area m ² . rice field. The crack evaluation was ×, and the entire surface was ground again in order to remove vertical cracks, resulting in a grinding yield of 94.6%.

In Comparative Example 19, the basicity CaO / SiO ₂ of the mold powder was as high as 1.35, and Na ₂ O, F, and K ₂ O were low, the viscosity at 1300 ° C. was 4.22 poise, and the solidification temperature was 1275 ° C. And used high mold powder. The solidified shell and the mold were seized, the solidified shell was torn off, and a breakout occurred in which the molten metal leaked out, and the casting was canceled.

In Comparative Example 20, the mold powder has a low basicity CaO / SiO ₂ of 0.73, a high Na _2O and F, a viscosity of 0.92 poise at 1300 ° C., and a low solidification temperature of 982 ° C. It was used. The consumption of the molten powder increased, the cooling with the meniscus became uneven, and many vertical cracks occurred on the slab surface. It was 228 mm / flaw detection area m ² , and the crack evaluation was ×. Since the entire surface was ground again in order to remove vertical cracks, the grinding yield was 94.4%.

In Comparative Example 21, the C of the mold powder was as low as C = 0.3%, the molten powder melted too quickly, a sintered product called a bear was formed on the inner surface of the mold, and the unevenness of the bear caused the surface of the slab. Many long vertical cracks occurred. It was 207 mm / flaw detection area m ² , and the crack evaluation was ×. Since the entire surface was ground again in order to remove vertical cracks, the grinding yield was 94.9%.

In Comparative Example 22, the C of the mold powder was as high as C = 3.8%, the molten powder melted too slowly, and the sintered product of the molten powder touched the solidified shell of the meniscus, resulting in fine vertical on the surface of the slab. Many cracks occurred. It was 237 mm / flaw detection area m ² , and the crack evaluation was ×. Since the entire surface was ground again in order to remove vertical cracks, the grinding yield was 94.3%.

In Comparative Example 23, K ₂ O of the mold powder is as high as 2.23%, Na ₂ O is as low as 7.3%, and the F concentration is also within the range of the present invention but low. Since the viscosity and solidification temperature of the molten powder were adjusted with K ₂ O, the viscosity and solidification temperature were within the range of the present invention, but since Na ₂ O and F were low, the crystalline phase neferin (Na ₂ O · Al ₂ ) was used. O3.2SiO ₂ ) and caspidyne (3CaO ・ 2SiO ₂・ CaF ₂ ) _were produced in small amounts, a vitreous powder film was formed, and the solidified shell was rapidly cooled by heat transfer, resulting in many vertical cracks on the slab surface. .. The total crack length was 218 mm / flaw detection area m ² , and the crack evaluation was ×. Since the entire surface was ground again in order to remove vertical cracks, the grinding yield was 94.5%.

A Fe-Ni alloy having excellent surface properties or a continuous casting method using the mold powder used for continuous casting of Fe-Ni alloy or Ni-based alloy and the mold powder for continuous casting provided by the technique of the present invention. A continuously cast slab of Ni-based alloy can be obtained. Since the cast slab has excellent surface properties, it is expected that the grinding yield will be good, the productivity will be improved, and the manufacturing cost will be reduced.

1: Mold, 2: Immersion nozzle, 3: Molten, 4: Coagulation shell, 5: Molten powder, 6: Mold powder, 7: Sample sampling iron rod, 8: Coagulation shell with concentrated S and P

Claims (2)

A mold powder for continuous casting of Fe-Ni alloy or Ni-based alloy containing 30 wt% or more of Ni. This mold powder is CaO-SiO ₂ powder, CaO: 30-40 wt%, SiO ₂ : 30-. 40 wt%, Al ₂ O ₃ : 3 to 10 wt%, Na ₂ O: 8 to 15 wt%, F: 5 to 10 wt%, K ₂ O: 0.01 to 2.00 wt%, S: 0.01 to 0. It has a component composition of 50 wt%, P: 0.01 to 2.00 wt% and C: 1.0 to 3.5 wt%, and satisfies a basicity of 0.75 ≤ CaO / SiO ₂ ≤ 1.33. The viscosity at 1300 ° C. is 1.0 to 4.0 poise, the solidification temperature is 1000 to 1250 ° C., and the Fe—Ni based alloy or the Ni-based alloy is S: 0.0001 to 0.0050 wt%, P :. A mold powder for continuous casting of a Fe—Ni based alloy or a Ni-based alloy, which is characterized by having a content of 0.0001 to 0.0150 wt% . When the Fe-Ni alloy or Ni-based alloy according to claim 1 is cast by a continuous casting machine, the drawing speed of the continuous casting slab is 400 to 900 mm / min, and the superheating degree of the molten metal is 5 to 50 ° C. , A method for continuously casting an Fe—Ni based alloy or a Ni-based alloy, which comprises casting using the mold powder for continuous casting according to claim 1.

Images