JPWO2007126114A1 - Casting method and apparatus - Google Patents

Abstract

The present invention pays attention to the flow phenomenon of the liquid phase in the solid-liquid coexisting phase during solidification in the production of an ingot by unidirectional solidification casting or remelting method such as ESR, VAR, etc. It has been clarified that the application of can suppress the very low-speed liquid phase flow between dendrites, which causes the formation of macrosegregation, thereby suppressing the macrosegregation defects such as fleckle. The present invention seeks to provide a casting technique for producing a high-quality cast product free from such macro-segregation defects.

Description

  The present invention belongs to the field of casting technology, and is a unidirectionally solidified casting having a columnar dendrite structure (referred to as a DS material) composed of polycrystalline grains and a dendrite structure composed of a single grain (referred to as a Mono-crystal or SX material), and electro The present invention relates to a casting technique mainly for improving macro segregation defects in ingot production by remelting methods such as slag remelting (ESR) and vacuum arc remelting (VAR).

[Unidirectional solidified casting]
Typical examples of the unidirectionally solidified casting, which is the technical field of the present invention, include turbine blade materials used in aircraft jet engines, power generation gas turbines, and the like. FIG. 1 (a) shows an outline of a typical unidirectional solidification apparatus currently used. After casting the molten metal into a ceramic mold (actual mold is a complicated three-dimensional shape) set on the bottom of the cooling chill, the mold is drawn from the furnace maintained at high temperature in the direction of gravity and solidified sequentially. By doing so, a casting having a polycrystalline columnar dendrite structure (referred to as DS material) or a single dendrite structure (referred to as SX material) is obtained. The figure shows the liquid phase in the middle of drawing, the solid-liquid coexisting phase, and the solid phase. Details of the actual apparatus such as the casting apparatus and the vacuum vessel are not shown. Since the turbine blade is used under severe conditions, a Ni-base superalloy excellent in heat resistance such as high-temperature strength is used as a main material. However, in these turbine blades, casting segregation such as channel segregation, misaligned grain defects, microporosity, and the like called freckle is caused, and this is a factor that lowers the product yield (see, for example, page 321 of Document 1). .
The origin of Fleckle is currently considered qualitatively as follows. One of the characteristics of the Ni-base superalloy is that it has a γ ′ phase (intermetallic compound based on Ni3 (Al, Ti) called gamma prime) that precipitates consistently with the γ phase that is the alloy base. Generally, the higher the volume fraction of γ ′, the higher the high temperature strength. However, in an alloy containing Al, Ti, W, etc. that is lighter than Ni, the density of the liquid phase between dendrites where these elements are concentrated decreases as the solidification progresses. Therefore, when solidifying such an alloy in the direction opposite to the direction of gravity, the density of the liquid phase at the bottom of the solid-liquid coexisting phase, that is, the dendritic root, is the density of the liquid phase at the boundary between the solid-liquid coexisting phase and the liquid phase, that is, the tip of the dendrite. It becomes relatively small compared. [Such alloys are referred to herein as 'solute instability' with respect to convection. On the other hand, the temperature distribution does not cause convection because the dendritic root is lower than the tip and therefore has a higher density. That is, it is “thermally stable”. When the solute instability is higher than the thermal stability, a density inversion layer is formed, and the liquid phase in the solid-liquid coexisting phase tends to cause an upward flow due to this density difference, and easily causes channel segregation called freckle. In addition, the dendrite growth is broken and an irregularly oriented crystal is likely to be formed. [Such alloys are referred to herein as 'floating alloys'. It is understood that the freckle generated in the Ni-base superalloy blade is caused by the upward flow based on such a density difference.
At present, in order to reduce these casting defects, a great amount of trial and error improvement efforts such as improvement of casting conditions such as heating and holding temperature, drawing speed, radiation cooling ability, etc. or addition of elements such as Ta heavier than Ni are carried out. It has been paid, but it is still insufficient. Accordingly, there is a strong demand for a technique for eliminating such casting defects.
[Ingot production by remelting method]
In ingot production by remelting methods such as electroslag remelting (ESR) and vacuum arc remelting (VAR), the depth of the liquid phase pool and the solid-liquid coexisting phase is relatively shallow. In the unidirectional solidification method, solidification from the side surface is suppressed, but in these remelting methods, solidification proceeds from the side surface due to heat removal from the mold (usually a water-cooled copper mold is used). It is well known that macrosegregation such as freckle (channel segregation) occurs in the production of Ni-base superalloys by ESR or VAR (see, for example, Reference 2). In these remelting methods, the above-mentioned segregation defects are generated not only in the above-mentioned floating type alloy but also in the opposite sedimentary type alloy (that is, an alloy in which the density of the solute-rich liquid phase between dendrites increases with the progress of solidification). In order to reduce these casting defects, the casting conditions such as cooling conditions, melting speeds, etc. are set or chemistry that makes the liquid phase pool depth as shallow as possible (especially effective for precipitated alloys) or increases the cooling rate. Although component adjustment is performed, the generation of the segregation defect is inevitable when the cross-sectional area of the ingot increases. Therefore, there is a strong demand for a technique for stably producing an ingot having a diameter as large as possible and having little segregation in producing an ingot used for the Ni-base superalloy turbine disk, the Fe-base alloy power generation turbine rotor, and the like.

The present invention manufactures high-quality castings that are free from macrosegregation defects such as fleckle and the like caused by the flow of the liquid phase in the solid-liquid coexisting phase in the ingot casting process by re-melting methods such as unidirectionally solidified castings and ESR and VAR. It intends to provide a casting technique for doing this.
The present invention focuses on the flow phenomenon of the liquid phase in the solid-liquid coexisting phase, particularly in the casting process, and applies a strong magnetic field to the entire solid-liquid coexisting phase, thereby causing an extremely low-speed liquid phase flow between dendrites in the phase. It is clarified for the first time that macro segregation such as freckle is eliminated.

FIG. 1 is a diagram showing an outline of a unidirectional solidification method in Example 1, FIG. 1 (a) shows an outline of a conventional production method, and FIG. 1 (b) shows an outline of the production method according to the present invention.
FIG. 2 shows the relationship between the temperature during solidification of the Ni-10 wt% Al alloy and the IN718 alloy and the volume fraction of the solid phase (see FIG. 1 of Reference 10 for IN718).
FIG. 3 is a diagram showing a change in liquid phase solute concentration during solidification of a Ni-10 wt% Al alloy.
FIG. 4 is a diagram showing a change in liquid phase solute concentration during solidification of the IN718 alloy (see FIG. 2 in Reference 10).
FIG. 5 is a graph showing changes in liquid phase density during solidification of Ni-10 wt% Al alloy and IN718 alloy.
FIG. 6 is an Al concentration contour map showing the effect of an axially applied magnetic field Bz on the freckle segregation of a Ni-10 wt% Al alloy round unidirectionally solidified ingot in Example 1. Fig. (A) shows the case of Bz = 0, Fig. (B) shows Bz = 5 (Tesla), and Fig. (C) shows the case of Bz = 10 (Tesla), and Fig. (D) shows the RR 'cross section (bottom surface) of these ingots. The effect of Bz at 91.9 mm) is shown.
FIG. 7 is a view showing a solid phase ratio distribution during solidification (after 18 minutes) of the same ingot as in FIG. The figure (a) shows the whole cross section, and the figure (b) shows an enlarged view of the outer periphery.
FIG. 8 is a view showing a liquid phase flow during solidification (after 18 minutes) of the same ingot as in FIG. The figure (a) is a case where Bz = 0 and the figure (b) is a case where Bz = 10 (Tesla).
FIG. 9 is an Al concentration contour diagram showing the freckle segregation of a Ni-10 wt% Al alloy unidirectionally solidified ingot in Example 2. The figure (a) shows the freckle in a cross section (86.6 mm from the bottom face) and the figure (b) in a vertical section (Y direction end face).
FIG. 10 shows (a) fleckle segregation and solid phase distribution of Al after 20 minutes in the Y-direction end longitudinal section of the same ingot as in FIG. 9, (b) flow field and solid phase in solid-liquid coexistence phase and liquid phase. The rate distribution is shown. Contour lines in the figure represent solid phase ratios of 0.2, 0.4, 0.6, and 0.8. The upper gray in the background represents the liquid phase, the light gray represents the solid-liquid coexisting phase, and the dark gray in the lower portion represents the solid phase. The velocity vector is normalized.
FIG. 11 is an Al concentration contour diagram showing the effect of the axial magnetic field Bz on the freckle segregation of a Ni-10 wt% Al alloy unidirectionally solidified ingot in Example 2. The figure (a) shows the case of Bz = 0, the figure (b) shows the case of Bz = 3 Tesla, and the figure (c) shows the case of Bz = 5 Tesla. The figure (d) shows the segregation suppressing effect in the XX ′ cross section (91.9 mm from the bottom surface, end face in the Y direction).
FIG. 12 is an Al concentration contour map showing the effect of a Y-direction magnetic field (By = 3 Tesla) on the freckle segregation of a Ni-10 wt% Al alloy unidirectionally solidified ingot in Example 2. The figure (a) shows XX 'cross section (91.9 mm from the bottom face), and the figure (b) shows segregation at the end face in the Y direction.
FIG. 13 is an Al concentration contour map showing the effect of a longitudinal magnetic field on the freckle segregation of a Ni-10 wt% Al alloy sheet unidirectionally solidified casting in Example 3. The figure (a) is a case where Bz = 0, the figure (b) is a case where Bz = 1 Tesla, and the figure (c) is a case where Bz = 2 Tesla. In each figure, the longitudinal section shows the end face in the Y direction, and the transverse section shows the XX ′ transverse section (91.9 mm from the bottom).
FIG. 14 is an Nb concentration contour diagram showing the effect of the axial magnetic field Bz on the center freckle segregation of the IN718 alloy remelting process ingot in Example 4. The figure (a) is a case where Bz = 0, the figure (b) is a case where Bz = 5 Tesla, and the figure (c) is a case where Bz = 10 Tesla.
FIG. 15 is a diagram showing the segregation distribution of each alloy element in the RR ′ cross section (1068.8 mm from the bottom surface) when there is no magnetic field in FIG.
FIG. 16 is a view showing the effect of suppressing segregation of Nb in the cross section of FIG. 14 RR ′ (1068.8 mm from the bottom).
FIG. 17 is a diagram showing an application example of the present invention in the remelting process. Fig. (A) shows an application example to the ESR process, and Fig. (B) shows an application example in which VAR, slag refining, and a static magnetic field are combined.
FIG. 18 is a diagram showing some examples of the DC coil 5 according to the present invention. Fig. (A) shows a solenoid type, Fig. (B) shows a 1 unit coil, and Fig. (C) shows a 2 unit coil (Helmholtz type or a similar type). Fig. (D) shows a racetrack type 1 unit coil when a magnetic field is applied in a direction crossing the direction of gravity, and Fig. (E) shows a racetrack type 2 unit coil.
FIG. 19 shows the Al concentration distribution when no magnetic field is applied in unidirectional solidification of a Ni-10 wt% Al alloy thin plate in Example 3. Figure (a) is straight, 126 mm long, figure (b) is 126 mm long with taper, and figure (c) is straight, 252 mm long.
FIG. 20 shows the flow field and the solid phase ratio in the mushy zone after 1005 sec (45 mm from the bottom) from the start of drawing of the tapered thin ingot in FIG. 19 (b) (0.2 kneading from 0.2 to 1.0) Show the distribution. The legend at the right end indicates the speed range.
FIG. 21 (b) shows the macrosegregation suppressing effect when an axial magnetic field is applied to the thin-walled ingot unidirectionally solidified in FIG. 19 (b). The figure (a) is a case where Bz = 0.5 Tesla, the figure (b) is 3 Tesla, and the figure (c) is 5 Tesla. The cross section is a distribution diagram at the position XX ′.

Explanation of symbols

1. Electrode (consumable electrode)
2. Molten slag 2. Insulating refractory sleeve 4. 4. Heater 5. DC coil for applying axial or transverse static magnetic field Water-cooled mold Ingot 8. Water-cooled base 9 Receiving base 10. 10. Vacuum or inert gas atmosphere Magnetic shield A. About the mechanism of macrosegregation formation It is well known that various macrosegregations such as Freckle segregation are caused by liquid phase flow in a solid-liquid coexisting phase. The driving force that causes this flow includes solidification shrinkage, convection due to the density difference between the dendritic liquid phases, external force such as electromagnetic force, etc. In the present invention, convection due to the density difference is particularly important. Whether it is a floating type alloy or a sedimentary type alloy as defined above or a mixed type alloy (an alloy whose liquid phase density decreases and increases again as solidification progresses or vice versa) is an alloy component And a unique macrosegregation is produced by the casting process.
B. Flow suppression effect by magnetic field The principle of flow suppression by a static magnetic field is briefly described below.
According to Ohm's law for electromagnetic fluid,
σ is the conductivity of the conductive molten metal (1 / Ωm), v is the flow velocity vector (m / s) of the molten metal, B is the externally applied magnetic flux density vector (Tesla), E is the strength vector (V / m) and J are induced current density vectors (A / m ² ). From continuous conditions for current fields
If the potential is φ (V)
The electromagnetic force (Lorentz force) f (N / m ³ ) generated by J and B is given by the following equation.
All of the above formulas are well known.
Substituting Equations (1) and (3) into Equation (2) yields Equation (5).
Equation (5) is solved to obtain φ, J is obtained from equations (1) and (3), and then Lorentz force f, that is, electromagnetic braking force, can be calculated from equation (4). However, it is necessary to calculate v by a numerical analysis described later including an equation of motion, and the flow field and the electromagnetic field have a highly coupled relationship.
C. Solidification analysis means An outline of a numerical analysis method by a general solidification simulation system (system name CPRO) developed by the present inventor in order to analyze a solidification phenomenon will be described below.
The physical variables for describing the solidification phenomenon are the temperature, the liquid phase during solidification, the concentration of the elements redistributed in the solid phase (the number of alloy elements is n), and the liquid that gives the relationship between the temperature and the solid fraction. It is given by the liquid phase flow rate (three vector components) and pressure in the phase temperature, liquid phase and solid-liquid coexisting phase. These are referred to herein as physical variables on a macroscopic scale. Table 1 shows the governing equations corresponding to these n + 6 physical variables.
It is known that the flow in the solid-liquid coexisting phase is described by Darcy's equation (6) (see p.234 of Document 3). The Darcy flow phenomenon is included as a flow resistance term in the equation of motion of Table 1.
Where v is the liquid phase flow velocity between the dendrites, μ is the viscosity of the liquid phase, g _L is the volume fraction of the liquid phase, K is the permeability, P is the pressure of the liquid phase, X is the gravity, centrifugal force, etc. It is an object force vector. Note that X includes the electromagnetic braking force introduced in the present invention. K is determined by the geometric structure of the dendrite and is given by the following equation from the Kozney-Carman equation (see Reference 4).
S _b is the surface area per unit volume of the dendrite crystals (specific surface area), the dimensionless constants f are found to have a value of 5 by the flow experiments in a porous medium. The transmittance K is determined by morphological analysis (referred to herein as a microscopic scale) during dendrite growth. Since solidification is a kind of diffusion-controlled process in liquid and solid phases, dendrites are modeled by cylindrical branches and trunks and hemispherical tips to solve solute diffusion equations in solid and liquid phases. I asked. It was assumed that there was no anisotropy of K due to the direction of dendrite.
As described above, all the physical variables on the macroscopic scale have an interaction, and are also deeply related to the dendrite growth on the microscopic scale. This numerical analysis method is described in detail in Document 5: Japanese Patent No. 3747216 and US Patent 624004B1 filed by the present inventor. Furthermore, the influence of the electromagnetic braking force by the magnetic field was incorporated into the numerical solution. This makes it possible to completely describe the solidification phenomenon taking into account the effect of the electromagnetic braking force. However, the solid phase in the solid-liquid coexisting phase was assumed not to move.

  A. Example 1: Macro segregation in unidirectional solidification of Ni-10 wt% Al alloy round ingot
  FIG. 1 (a) shows a schematic view of a general unidirectional solidification apparatus. While the susceptor is heated by an induction coil and the ceramic mold is heated and kept warm by radiant heat, it is solidified in one direction by pulling down the mold while cooling the ingot with a water-cooled chill (or even if the mold is fixed and the heating furnace is raised) Good). Giamei and Kear (see reference 6) show that in a floating Ni-based superalloy mono-crystal round ingot, channel segregation called “freckle” occurs in the outer periphery (see FIG. 1 to 4 of the same document). It has been clarified that as the diameter of the ingot becomes larger, more freckle occurs, that is, there is a size effect (see Table II in the same document). Further, it was also shown that a freckle is generated in the outer peripheral portion of a 1.5 inch (38.1 mm) diameter mono-crystal ingot of a floating type Ni-10 wt% Al alloy. With reference to these data, the size and casting conditions of the ingot used for the calculation were set as shown in Table 2. In addition, Table 3 shows chemical components and physical property values. It should be noted that the dendrite specific surface area S so that a fleck is generated on the outer periphery of the ingot in light of the same document._bThe correction coefficient α was adjusted to 0.4.
  FIG. 2 shows a graph in which the relationship between the temperature of Ni-10 wt% Al alloy and the solid phase volume fraction is calculated under the assumption of non-equilibrium solidification (no diffusion in the solid phase, complete diffusion in the liquid phase). This alloy forms a eutectic at 1385 ° C. from the equilibrium diagram. As the Al element is discharged from the solid-liquid interface to the liquid phase as the solidification progresses, the Al liquid phase concentration between dendrites increases. This is shown in FIG.
  Here, the liquid phase density between dendrites is the alloy concentration C in the liquid phase.₁ ^L, C₂ ^L, ..., and as a function of temperature T (ρ in Table 3)_LSee formula)
(8) ρ of Ni-10 wt% Al during solidification using the formula_LFIG. 5 shows the result of calculating. The figure shows that the alloy is “floating”.
  The number of elements of the ingot used for the calculation is radial direction 29x axial direction 71 = 2059. The calculation results are shown in FIGS. FIGS. 6 (a) to 6 (c) are graphs showing the distribution state of macrosegregation in contour lines, and FIG. 6 (d) shows the radial distribution at the RR 'position (91.9 mm from the bottom surface). As shown in FIG. 6 (a), in an ordinary ingot to which a magnetic field is not applied, a fleck is generated on the outer peripheral portion. The degree of macrosegregation is evaluated by C / Co (C is the calculated concentration (wt%) and Co is the initial concentration (wt%)). C / Co> 1 indicates positive segregation, and C / Co <1 indicates negative segregation (Co = 10 wt%). Positive segregation of C / Co maximum value = 1.14 occurs in the freckle part. Further, a decrease in density is observed in the vicinity of the freckle (see FIG. 6 (d)). A magnetic field having a uniform strength was applied in the axial direction. From these figures, there is no segregation reducing effect at Bz = 3 (Tesla) or less (results not shown), C / Co maximum value = 1.08 at 5 (Tesla), and about C / Co at 10 (Tsla). Co maximum value = 1.015 and segregation substantially disappeared.
  The flecks generated in the ingot to which the magnetic field is not applied are based on the flow pattern of the liquid phase in the solid-liquid coexisting phase. FIG. 8 (a) shows the flow pattern in the liquid phase and the solid-liquid coexisting phase (mushy zone) after 18 minutes (the solidification time is 29.2 minutes). It can be seen that the shape of the mushy zone is affected by heat removal from the outer surface. The flow in the mushy zone is influenced by the “buoyancy” of the low-density liquid phase on the high solid fraction side (lower side) as a whole from the center to the outer periphery, and an upward flow is generated at the outer periphery. That is, at the outer periphery, the liquid phase having a high solute concentration at a low temperature flows to the higher temperature, low solute concentration portion on the upper side, and as a result, solidification is delayed (even if it does not reach re-dissolution), and the liquid phase easily passes (permeation). The rate K becomes smaller (see equation (7)). That is, a liquid phase passage or channel is formed. This is the reason why the solid phase ratio is lower than the inner side in the outer peripheral portion of FIG. [Regarding the mechanism of channel segregation formation, p. 249).] In such a channel portion, the unidirectional dendrite structure breaks down to become equiaxed crystals, and solidification is delayed more than the inside, which is accompanied by porosity due to solidification shrinkage.
  As the strength of the axial magnetic field is increased, the radial flow is suppressed and the channel flow in the outer peripheral portion is eliminated, so that segregation does not occur. The flow pattern of Bz = 10 (Tesla) is shown in FIG. 8 (b). A slight upward flow is recognized on the outer periphery, but the flow is very weak, the flow in the radial direction is almost completely suppressed, and the flow is only in the axial direction (solidification contraction flow). Thus, the phenomenon that only the flow (convection or locally turbulent flow) other than the gravity direction that forms the channel segregation is suppressed while the liquid phase replenishment by the coagulation shrinkage is maintained is interesting. Although not shown here to save space, this phenomenon was also observed in the case of horizontal unidirectional solidification perpendicular to the direction of gravity or unidirectional solidification (solidification from top to bottom) in the same direction as the direction of gravity. In addition, as a result of suppressing the remarkable convection seen in the liquid phase, the width of the Mushy zone is widened. These features due to the application of a static magnetic field favor the production of DS materials, and in particular SX materials. That is, the effect of suppressing the generation of dendrite irregular orientation crystal defects is produced, and the stable growth is promoted.
  B. Specific Example 2: Macro segregation in unidirectional solidification of Ni-10 wt% Al alloy square ingot
  In order to investigate the effect of the direction of the applied magnetic field on the freckle generation, a square ingot was calculated. The dimension of the square cross section was a 60 mm square having a cross sectional area equivalent to that of Example 1. All other casting parameters are the same as for the round ingot (see Table 2). The calculation was performed for a ¼ section in consideration of symmetry. The number of elements of the ingot is X direction 18xY direction 18xZ direction 71 = 23044.
  Macro segregation of a normal ingot without applying a magnetic field is shown in FIGS. As shown in FIGS. 9 (a) and 9 (b), the flecks are generated in the vertical direction at the outer peripheral portion and are arranged at almost equal intervals. The maximum C / Co value is about 1.18. The segregation formation situation after 20 minutes during solidification is shown in FIGS. 10 (a) and 10 (b) (solidification time is 28.5 minutes). As in Example 1, the liquid phase in the vicinity of the freckle flows in the mushy zone and rises along the channel (see FIG. 10 (b)), causing a delay in coagulation (equal solid fraction line in the figure). reference). This upward flow causes freckle (see FIG. 10 (a)). FIG. 11 shows the effect of suppressing segregation by the axial magnetic field. FIGS. 11 (a), (b) and (c) show the longitudinal cross-sectional macrosegregation at the end face in the Y direction, and FIG. 11 (d) shows the Al concentration along XX '(91.9mm from the bottom) in FIG. Show the distribution. From these figures, the effect is small at Bz = 1 (Tesla), and segregation is substantially eliminated at Bz = 3 (Tesla) or more. As for the flow pattern in the mushy zone, the flow in the horizontal direction was suppressed as in the first specific example, and all were downward in the axial direction (not shown for simplicity).
  Next, an example when a uniform magnetic field is applied in the Y direction (horizontal direction) is shown in FIG. 12 (By = 3 Tesla). Although it is slightly effective compared with Bz = 3 (Tesla), it may be said that it is substantially the same. From this, it was found that the flow suppression behavior in the mushy zone is substantially the same regardless of the direction of the magnetic field. However, the electrical boundary condition between the ingot and the mold boundary was insulation.
  C. Example 3: Macro segregation in unidirectional solidification of Ni-10 wt% Al thin plate ingot
  The turbine blade described in the background art has a complicated shape having a thin wall portion (see, for example, p.320, FIG.1 and p.321, FIG.5 of Document 1). Considering this point, in this specific example, the effect of a magnetic field was examined on the unidirectional solidification of a thin plate having a thickness of 6 mm, a width of 60 mm, and a length of 126 mm. Table 2 shows the casting conditions. In order to prevent solidification from the side surface, the same conditions were set except that the heat removal rate from the side surface was reduced to 1/10 compared to the round and square ingots.
The calculation was performed on a ¼ cross section in consideration of symmetry. The number of ingot elements is X direction 18 × Y direction 5 × Z direction 71 = 6390. FIG. 13 shows the calculation results. In the case of a normal ingot to which a magnetic field is not applied, a fleck is generated at the end face in the width direction, particularly at the corner (see FIG. 13 (a)). When an axial magnetic field was applied 1, 2 and 3 (Tesla), segregation substantially disappeared at 2 (Tesla) (see FIGS. 13B and 13C). From the figure, when Bz = 0, C / Co maximum value = 1.13, 1 (Tesla), C / Co maximum value = 1.22, and 1 (Tesla) is sufficiently effective.
  Further, when a uniform magnetic field was applied in each of the width direction (X direction) and the thickness direction (Y direction), there was almost no difference from the axial direction application (not shown for simplicity).
  Next, these influences were investigated by changing the casting conditions and the shape of the blade.
As for casting conditions, the drawing speed was lowered from 5 mm / min in Table 2 to 1.667 mm / min, and the susceptor temperature = 1773 K so that the temperature gradient in the solidification speed temperature section was about 45 ° C./cm (intermediate position of the blade length). ε (emissivity) = 0.05, ε (emissivity) of the radiation cooling region = 0.02, h (heat transfer coefficient) of the bottom surface = 0.001 (the above casting conditions were actually performed) This is set for convenience of calculation). When drawn at the above-mentioned constant speed, the temperature gradient decreases to about 50 ° C./cm in the first half of solidification and to about 25 ° C./cm in the second half. Note that a selector unit and the like necessary for manufacturing the SX material are omitted.
  The actual cross-sectional shape of the blade is a curved surface, and the cross-section is tapered in consideration of the fact that the thickness is not uniform, including the core inside the blade thickness (hereinafter referred to as taper material. Called material). However, here, for the purpose of roughly examining the influence of the change in thickness, the thickness is 6 mm at the center of the cross section, 3 mm at both ends, and a 1/4 symmetric cross section is used as the calculation region. Therefore, it differs from the actual blade cross-sectional shape. I ignored him. Moreover, it calculated also about the case where a blade length was doubled (252 mm length). For the above three types of blades, the above casting conditions are applied to straight, 126 mm long blade (element number 6390) and taper, 126 mm long blade (element number 5751), while straight, 252 mm long blade (element number 12780) The other conditions were set to the same value except that ε = 0.01 for radiation cooling.
  The calculation results are shown in FIGS. FIG. 19 shows the Al concentration distribution after completion of solidification in normal unidirectional solidification without applying a magnetic field. The vertical cross-sectional view is a distribution diagram at the central portion of the thickness, and the horizontal cross-sectional view is a distribution diagram at the position XX ′. In any of the ingots, a fleck is generated in the inside of the ingot rather than the outer peripheral portion seen in the specific example 1 (round ingot, see FIG. 6) and the specific example 2 (square ingot, see FIG. 9). This is presumably because the temperature difference between the surface and the inside of the ingot almost disappeared due to heating from the susceptor (the outer peripheral portion was slightly higher). Moreover, in the specific examples 1 and 2, the fleckle is considerably shorter than that extending to the upper end. In the taper and 126 mm ingot, a fleckle is remarkably generated due to the inside, particularly the thick part. FIG. 20 shows the shape of the mushy zone and the flow between dendrites at the center of the longitudinal section 1005 sec after the start of drawing (only the flow pattern in the mushy zone is shown). The horizontal lines in the figure are equal solid phase rate lines with 0.2 intervals from the solid phase rate of 0.2 to 1.0. The flow velocity at the position where the freckle is generated (45 mm from the bottom) is 3 x 10^-2cm / s, lateral flow rate is 10^-3The order is cm / s. It is recognized that the mushy zone is slightly inclined from the central thick part toward the thin end face, and that the interdendritic liquid phase flow is directed from the end face toward the center, and a strong upward flow is generated at the part where the freckle is generated. Further, it can be seen from the equisolid phase ratio distribution that the solidification is delayed from the surroundings in the freckle portion. In a straight and 252 mm ingot with double the blade length, the freckle appears more prominently (FIG. 19 (c)). The fleckle also becomes longer.
  When a magnetic field of Bz = 0.5, 1.0, 3.0, and 5.0 (Tesla) is applied in the axial direction to the above three types of ingots, 0.5 (Tesla) is obtained in any ingot. The fleckle disappears and the macro segregation of the product part excluding the upper end of the ingot that causes a contraction at 3 (Tesla) and the lower end connected to the selector or seed crystal is substantially a problem of Al = 9.95 to 10.04 (wt%). Improved to no level. FIG. 21 shows the effect when a magnetic field of Bz = 0.5, 3 and 5T is applied to a tapered, 126 mm ingot. In any of the ingots, no flecks are generated, and it can be seen that the negative segregation on the thin wall side (right end) decreases as the magnetic field increases. This is because the lateral extremely low speed flow as shown in FIG. 20 is suppressed.
  As described above, the place and form in which the freckle is generated varies depending on the heating / cooling conditions, the casting conditions such as the drawing speed, the shape of the blade, etc., but in any case, it can be eliminated by applying a strong magnetic field.
  D. Example 4: Macrosegregation in remelting process of IN718Ni-base superalloy
  Table 3 shows the chemical composition and physical properties of the alloy used in the calculation. For the relationship between the chemical components and the temperature-liquid phase and solid phase concentrations in the multi-component equilibrium state, see FIG. Reproduced from 1-3. Therefore, the calculation results of the relationship between the temperature and the solid fraction (see FIG. 2) and the change in the concentration of the liquid phase solute during solidification (FIG. 4) are the same as in the literature 10. FIG. 5 shows the change in liquid phase density according to the equation (8). FIG. 5 shows that the alloy is a “sedimentation type” alloy.
  Van Den Avey et al. Reported in reference 2 above that in the remelting process of IN718 and similar Alloy 625 Ni-base superalloys, respectively, a freckle in the middle in the radial direction and a “central” freckle segregation in the center are reported. . In these remelting processes, the shape of the mushy zone becomes deeper toward the center due to heat removal from the side surface, so that channel segregation occurs even in the case of a sedimentation type such as IN718. The chemical component of IN718 used herein is approximately regarded as Alloy 625, rather than IN718 of the same document. With reference to the literature 2, the ingot size and casting parameters were set as shown in Table 2. The casting method was a method of casting at a constant dissolution rate on a stationary mold. In actual operation, the heat transfer at the boundary between the ingot and the water-cooled copper mold is greatly affected by the formation of an air gap, etc., so it is difficult to set the thermal boundary condition with high accuracy. Therefore, for convenience of calculation, hypothetical hot plates and hot sleeves are provided on the bottom and side surfaces of the ingot (assuming that the thermophysical property values are the same as those of the ingot). The heat transfer coefficients from the outer surfaces of these molds were adjusted so as to approach the solidification state of the mold. Also, the dendrite specific surface area S with reference to the flecking state in the literature 2_bThe correction coefficient α was set to 0.6. The number of elements of the ingot is 40 in the radial direction and 120 in the axial direction = 4800.
  The calculation results are shown in FIGS. 14 and 16 show the Nb concentration contours, and FIG. 15 shows the radial concentration distribution of each element when a magnetic field is not applied (at a position of 1068.8 mm from the bottom). As shown in FIG. 14 (a), the central freckle generated in the Alloy 620 of the above-mentioned document 2 is generated. In addition, in IN718 of this specific example, a normal freckle in the middle in the radial direction did not occur. These results are in good agreement with the view of the literature 2 and show the validity of the numerical solution described in this specification. From FIG. 15, Al, Ti, Nb having an equilibrium distribution coefficient smaller than 1 and Cr and Fe having a distribution coefficient larger than 1 cause positive and negative segregation, respectively. As a result of calculation by changing the axial magnetic field to Bz = 3 to 10 (Tesla), it can be seen that segregation can be suppressed to a level where there is no problem at Bz = 10 (Tesla) (FIGS. 14 and 16).
  In the above specific examples 1 to 4, the macrosegregation is caused by the liquid phase flow between dendrites in the solid-liquid coexisting phase, and it is specifically shown that the flow pattern is the most important. Furthermore, the present inventor has shown for the first time that by applying a strong magnetic field to the entire solid-liquid coexisting phase, extremely low-speed liquid phase flow between dendrites, which causes macrosegregation formation, can be suppressed. It was clarified that segregation can be suppressed. Thus, although the electromagnetic braking phenomenon with respect to the molten metal has been known for a long time, no example has been found as far as the present inventor knows that macro segregation can be eliminated.
  Hereinafter, consideration of the electromagnetic brake effect according to the present invention and the main points of the present invention will be described.
(1) Consider an electromagnetic fluid that flows at a uniform velocity v in a lateral direction (X direction) perpendicular to the direction of gravity. In this state, when a magnetic field B perpendicular to the direction of v and gravity is applied, the electromagnetic braking force is f_χ= -ΣB²It is given by ν. However, in the case of metal, since electric conductivity σ is large, E = 0 in the above formula (1) was considered. At this time, the equation of motion is expressed by the following equation.
When the above equation is integrated and time t = 0, initial speed v = v₀Then, the following equation is obtained.
Here, the unit system is v (m / s), σ (1 / Qm), B (Tesla), ρ (Kg / m³) And t (sec). From the equation (10), it can be seen that the exponential curve decays with the passage of time t, and v becomes larger as the alloy has a larger σ and a smaller ρ. As an example, for 10Al-Ni alloy herein, σ = 10⁶, Ρ = 7300 and B = 0.1, v / v₀= Exp (-0.14t).
  V / v after t = 2.15 seconds₀= 0.5, and v / v after t = 4.3 seconds₀= Decelerate to 0.25. Also, for Al alloy, σ = 5 × 10⁶, Ρ = 2700, and B = 0.1, v / v₀= Exp (-1.9t) and v / v after t = 0.15 seconds₀= 0.5, v / v after another 0.3 seconds₀= Decelerate to 0.25. From the above estimation, it can be seen that a magnetic field as low as about B = 0.1 (Tesla) has an effect sufficient to suppress the flow velocity in the liquid phase pool.
  Next, in Equation (6), X is the electromagnetic braking force f, and the Darcy flow resistance force v μg_L/ K (both sides of equation (6) are K / μg_LDefined as π,
Here, π is a dimensionless number representing the braking effect on the inter-dendritic liquid phase flow in the mushy zone. f is given by f = σ (− ▽ φ + vxB) × B from the equations (1) and (4). For convenience of consideration, as in the case described above, considering the case where the electromagnetic braking force is applied to the uniform horizontal flow in the mushy zone, equation (6) results in the following equation.
From the above equation, the electromagnetic braking force (-σB for the flow of v> 0²v) acts in the opposite direction to the flow (volume force acting on the liquid phase due to the pressure gradient-opposite to ∂P / ∂χ (> 0)), that is, it acts as a braking force (when v <0 As well as braking). Solving for v from equation (12) yields:
From the above equation, the speed when B is not applied is v₀V and v₀Using the π defined in equation (11)
The flow velocity decays hyperbola as π increases. K and g in the actual casting process_LTable 4 shows the result of calculating π with respect to the value of B when segregation such as fckle is suppressed, using roughly average values in the specific examples 1 to 4. σB²Unit conversion of 1T²/ Ωm = 10^-3dyn · sec / cm⁴Note).
In the case of specific example 1, π = 0.05B²From
When Bz = 5 (Tesla), π = 1.25 and v / v₀= 0.44, and
When Bz = 10 (Tesla), π = 5.0 and v / v₀= 0.17.
From Table 4, there is a gap in the value of π that suppresses segregation, and as described in the next section (2), the form and degree of segregation vary depending on the individual case, so the value of the dimensionless number π necessary for suppressing segregation is determined. This is a difficult but meaningful guide. In the case of a magnetic field of 1 (Tesla) or less, π << 1, and it can be understood that there is almost no segregation suppressing effect.
(2) In the actual casting process, there are the following three main factors that determine the flow pattern of the liquid phase in the mushy zone.
  I. density difference of liquid phase in mushy zone_LBuoyancy due to (△ ρ_Lg_r, G_rIs the acceleration of gravity)
  II. the shape of the mushy zone (especially the gradient and extent to the direction of gravity)
  III. Transmittance K determined by dendritic form (see equation (7))
△ ρ_Lg_rIs a driving force that causes convection in the mushy zone and is determined by the alloy composition. These include a floating type, a sinking type, or a mixed type thereof. Factors II and III depend on cooling conditions in various casting processes. There are many different cases. To give a few examples, the most important factor for the occurrence of fleckle in unidirectional solidification of a floating alloy turbine blade is Δρ._Lg_r△ ρ_LOr △ ρ_L/ Ρ_LOccurs when exceeds a certain value. Compared with this, the contribution of factors II and III is small. In addition, in the production of an ingot by a remelting method of a sedimentation type alloy, if the shape of the mushy zone is flat (no depression), no segregation occurs regardless of the factors I and III. That is, the segregation at the center of Example 4 is caused by the fact that the shape of the mushy zone has a gradient with respect to the direction of gravity, and the factor I (Δρ_LCaused by the action of sedimentation). Even in this case, segregation does not occur when the diameter of the ingot decreases and K decreases. [K decreases as the dendrite arm spacing (DAS) decreases. In general, when the cooling rate is high and the DAS is small, convection due to the factor I does not occur, and channel segregation such as freckle does not occur. ]
From the above, it is meaningful to take the ratio of braking force to buoyancy as another dimensionless number for evaluating the effect of electromagnetic braking force. Ie
The results of calculating φ with respect to the average approximate value v and the required magnetic field B are shown in Table 4 (σB²Note the unit conversion).
  From the consideration of the above items (1) and (2), in order to suppress high-speed flow in the liquid phase region (generally on the order of about 10 cm / s in the remelting process), it is 1 Tesla or less (for example, 0.1 Tesla). A magnetic field is sufficient, but very slow flow in a mushy zone (about 10^-2-10^-4It can be seen that a strong magnetic field is required to suppress (order of cm / s). As a guideline for roughly evaluating the strength of the strong magnetic field, the dimensionless number π or φ according to the equation (14) or (15) is significant. In other words, the limit value π necessary to suppress segregation empirically in accordance with the individual alloy system and solidification process._COr φ_CΠ ≧ π_COr φ ≧ φ_CB should be determined so as to satisfy π_COr φ_CIt is more economical to decide on a scaled-down small-scale experiment, and the numerical analysis method described in this specification is an extremely effective tool. In the case of a turbine blade having a relatively small size and having a thin wall portion as compared with the above specific example, it is effective in reducing defects such as flackles and irregularly oriented crystals with a magnetic field of about 0.5 (Tesla) or more. [It is well known that the form of the solidification interface changes from a smooth interface to a cell and then to a dendrite as the value of G / R (G is the temperature gradient of the liquid phase at the interface, R is the rate of progress of the interface) decreases. In the case of the SX material, it is considered that the single crystal growth is broken when it becomes a certain value or less, and a different crystal, that is, an irregularly oriented crystal is generated therefrom (see, for example, Reference 15). On the other hand, it is generally known that crystal grains become coarse when a magnetic field is applied during solidification. That is, irregularly oriented crystals are less likely to occur. This is presumably because the flow of the liquid phase is suppressed by applying a magnetic field and stable single crystal growth is promoted. For large remelt process ingots, a magnetic field of at least about 1 (Tesla) or more will be required. However, these lower limits are rough guidelines when optimizing the casting conditions, and have already been changed according to individual cases. Moreover, it depends on the degree of demand for quality.
(3) The liquid phase flow suppression effect in the mushy zone does not depend on the direction of the magnetic field. Therefore, an optimum application method for the casting process may be employed. However, in all the specific examples, the ingot and the mold were insulated as electrical boundary conditions. Although a uniform magnetic field was applied in the calculation, it need not be strictly uniform.
(4) FIG. 1 (b) shows a schematic diagram when a static magnetic field is applied to unidirectional solidification. As described in the background art section, a typical unidirectional solidification apparatus includes basic elements such as a chill cooling apparatus, a mold heating furnace, a drawing apparatus, and a vacuum apparatus, but there are various variations besides these. For example, it is possible to apply a zone melting method (for example, refer to page 2 of Document 3) in which a small amount of an ingot that has been solidified is first melted and then the molten zone is slowly moved from one end to the other end. . In short, the present invention is directed to a method and apparatus for forming a solid phase, a solid-liquid coexisting phase, and a liquid phase region in a casting or ingot and unidirectionally controlling and solidifying these regions from one end to the other end. It is clear in principle that it applies to all these unidirectional solidification processes. An actual unidirectionally solidified turbine blade has a complex shape. Reference 11 describes a technique in which the blade part is a single dendrite structure (SX) and the base part is a polycrystalline columnar dendrite structure (DS), but the present invention can also be applied to such a mixed structure. . As described above, the present invention can also be applied to the case of horizontal unidirectional solidification perpendicular to the direction of gravity or unidirectional solidification (solidification from top to bottom) in the same direction as the direction of gravity. FIG. 18 shows some examples of the DC coil 5 used in the present invention. When a magnetic field is generated in a direction perpendicular to the solid-liquid coexisting phase, there are a solenoid type (Fig. A), a 1 unit coil (Fig. B), a 2 unit coil (Fig. C, Helmholtz type or a similar type), etc. . When applied in a direction crossing the direction of gravity, there are a racetrack type 1 unit coil (FIG. D), a racetrack type 2 unit coil (FIG. E), and the like. It is recommended to use superconducting coils for these coils. Actually, various coil designs are possible, and an optimum design may be performed for the shape of the casting, the direction of solidification, the strength of the required magnetic field, and the like.
(5) In remelting processes such as VAR (vacuum arc remelting method) and ESR (electroslag remelting method), a strong current generally flows through the mushy zone, and electromagnetic force is generated by the interaction with a strong applied magnetic field from the outside. Is not preferable. Therefore, it is necessary to adopt a method that does not energize the ingot. One most desirable example of such a scheme is shown in FIG. FIG. 17 (a) shows a case where a strong magnetic field according to the present invention is applied to the ESR process. Reference numeral 5 denotes a DC coil for generating a strong magnetic field, which is configured to be applied in the horizontal direction or the vertical direction. The coil mechanism is as described in the above section (4), and it is recommended to use a superconducting coil. The electrode 1 is arranged away from the coil so as not to be affected by the magnetic field. The molten slag phase is heated by the Joule heat generated by the current flowing between the electrodes, thereby melting the electrodes. The molten slag phase is heated and kept warm by a heater 4 disposed on the outer periphery of the heat-insulating refractory sleeve 3. The molten droplets generated from the electrodes fall through the slag phase to the water-cooled copper mold 6 and solidify. The ingot 7 is drawn downward by a base 9 that can be extended and contracted while being cooled from the bottom by a bottom made of a water-cooled copper mold. Since the molten slag 3 is interposed at the boundary between the mold 6 and the ingot 7 and an air gap is usually generated (not shown), the cooling ability from the side surface is relatively small. FIG. 17 (b) shows a most desirable example in which VAR, slag refining, and a strong magnetic field according to the present invention are combined. The space 10 is a vacuum or an inert gas atmosphere. Electrode 1 is melted by a high current arc (usually DC). By adding a strong magnetic field according to the present invention to the merits of both VAR and slag refining (not described since well known), it is possible to produce a high-quality ingot that is highly clean and free from segregation. In these processes, the magnetic shield 11 is applied to isolate the current field near the electrode electrode portion from the magnetic field. As is apparent from the example of FIG. 17, various combinations are possible.
That is,
ESR + strong magnetic field
VAR + strong magnetic field
VAR + slag refining + strong magnetic field
Etc. are possible.
(6) It is well known that the shape of the solid-liquid interface during solidification of the alloy is determined by the aforementioned parameter G / R based on the compositional supercooling theory (G is the liquid phase temperature gradient at the interface, R is the interface temperature) Progress speed). In the production of a true single crystal (for example, semiconductor Si) (whether the Bridgeman method or Czochralski method), G and R are controlled independently to increase G and decrease R (that is, increase G / R). This realizes smooth interface (stable interface) solidification. [In general, the amount of alloys contained in these single crystals is extremely small, there is no solid-liquid coexisting phase (and it must not be generated), and the dendrite structure (DS Material or SX material). ]
  It is known that the alloy concentration distribution in the growth direction of the single crystal varies greatly depending on the convection state of the liquid phase in front of the smooth interface (see, for example, p. 42 of FIG. 3, FIG. 2-9). Reference 12 prepares raw materials with different compositions in advance in order to reduce large changes in solute concentration in the longitudinal direction (growth direction) of the single crystal due to the influence of liquid phase convection that is unavoidable in the process of growing a semiconductor single crystal. However, it is intended to reduce the concentration change by unidirectional growth using this raw material. Further, the crystal once grown and solidified is once again grown in the opposite direction, or a magnetic field (about 0.2 Tesla) is applied to suppress convection and to produce a single crystal having a more uniform composition. That is, the technique in the literature is different from the present invention because it tries to suppress the convection of the liquid phase in front of the smooth interface in the process of growing a single crystal without a mushy zone.
  Reference 13 describes a material in which the amount of change in magnetic susceptibility at the melting point accompanying the liquid-solid phase change is positive (that is, the magnetic susceptibility of the solid phase is greater than that of the liquid phase) in the production of a single crystal by the Bridgeman method. Single crystal growth technology to improve the single crystallization rate by increasing the energy barrier for crystal nucleation by applying a magnetic field during crystal growth and to make good single crystals with as few crystals as possible And different from the technology of the present invention.
  When G / R is decreased, stable interface type growth is broken, and a solid phase begins to protrude from the interface, and a cell structure is formed. When G / R is further decreased, a dendrite structure is formed. In the case of cell type growth, the principle of the present invention can be applied to the solid-liquid coexisting phase because the cell crystal and the liquid phase coexist. That is, by applying a strong magnetic field, the liquid phase flow between cells can be suppressed and a stable cell crystal structure free from segregation can be obtained.
(7) In the field of continuous casting, Document 14 discloses a technique for reducing macro segregation by applying a maximum static magnetic field of 0.15 Tesla to the liquid phase pool during continuous casting of an Al alloy. [In continuous casting, the flow velocity in the liquid phase pool is on the order of 10 to 100 cm / s, and as described in (1) and (2) above, for such a high-speed flow, about 0.1 Tesla. Although there is a sufficient braking effect at low magnetic fields, there is no braking effect for very low velocity flows in the mushy zone. The document 14 does not mention a mechanism for reducing macrosegregation, and in the examples of the document, a crystal grain refining agent is added. This point is noteworthy. The present inventor infers the segregation suppressing effect in the case of Document 14 as follows. It is considered that the effect of suppressing the flow in the liquid phase pool by the static magnetic field increased the refining effect compared to the case without a magnetic field, resulting in a finer granular crystal structure and less segregation in the central region. [In general, the reason for adding a crystal refining agent is to reduce segregation by forming a finer grain structure. However, active convection in the liquid phase pool increases the frequency of agglomeration, coalescence, and coarsening of the grain refiner and reduces the refinement effect. Therefore, it is presumed that when a magnetic field is applied, convection in the liquid phase pool is suppressed, and the frequency of agglomeration and coalescence of the crystal grain refining agent is reduced, so that the refinement effect is not hindered. That is, it is inferred that the technique of the reference 14 requires the use of a crystal grain refiner, which increases the refinement effect by applying a magnetic field and, as a result, indirectly reduces segregation. The Applying a magnetic field with a half-pitch strength compared to the case where no crystal refining agent is added results in the suppression of flow in the liquid phase pool, resulting in the tendency for coarse columnar crystals to develop and conversely increase the segregation in the central region. There is.
On the other hand, the essence of the present invention is to cause macro segregation such as fleckle to the entire mushy zone in the unidirectional solidification (for the original purpose, do not use the crystal refiner) or the remelting process. The macrosegregation is intended to be suppressed by applying a magnetic field having a strength necessary for suppressing the extremely low-speed liquid phase flow in the mushy zone. The magnetic field application region and the magnetic field strength are different.

As is clear from the above specific examples 1 to 3, the application of the strong magnetic field according to the present invention can eliminate segregation such as freckle generated in DS or SX casting of the floating Ni-base superalloy currently in practical use. it can. Furthermore, the present invention is also effective for an alloy that becomes more buoyant (Δρ _L g _r due to the liquid phase density difference in the mushy phase) and cannot be cast. This means that the degree of freedom in alloy selection is increased, or the possibility of developing an alloy having higher high-temperature strength is opened (for example, the γ ′ volume fraction can be increased to the limit).
In the remelting process of Example 4, it was shown that the present invention is effective for a sedimentation type alloy (IN718), but it is clear from Examples 1 to 3 that it is also effective for a general floating type alloy. It is. Therefore, by applying the present invention, it becomes possible to manufacture a floating type alloy ingot having a larger diameter than the conventional casting impossible by a remelting process.
As described above, the effects of the present invention are summarized as follows.
Regarding the production of unidirectionally solidified castings such as Ni-base superalloy turbine blades,
1. Macrosegregation such as fleckle can be completely eliminated.
2. It is possible to eliminate fusing / separation of dendrites due to convection, thereby obtaining a complete mono-crystal having no misoriented crystal defects.
3. By completely eliminating macrosegregation such as fleckle, new alloys can be developed to increase the volume fraction of γ 'to the limit.
In addition, regarding the manufacture of ingots by a remelting process, it is possible to cast a floating type alloy (generally having a lower density than the settled type), which is conventionally impossible to cast, as well as a settled type alloy.
As described above, according to the present invention, it is possible to manufacture a unidirectionally solidified casting such as a high-quality turbine blade or a remelted ingot, and the practical application greatly contributes to the safety of important parts and the energy saving by improving the efficiency of the gas turbine. is there. Considering the situation where a strong magnetic field can be obtained relatively inexpensively due to recent advances in superconducting technology, there are no factors impeding the realization of the present invention, and the industrial value is extremely high. In this specification, specific examples of two types of Ni-based alloy ingots have been shown. However, not only all Ni-based alloys but also TiAl alloy unidirectionally solidified blades and low-alloy steels that are expected to develop in the future. However, it is apparent in principle that the same effect can be obtained.
Reference (1) ASM Handbook Vol. 15 Casting (1988)
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(7) T.W. Iida and R.I. I. L. Guthrie: The Physical Properties of Liquid Metals, Clarendon Press, Oxford, United Kingdom (1993), pp. 199-111. 70-73
(8) P.I. N. Quested and M.M. MacLean: “Solidification Morphologies in Directionally Solidified Superalloys”, Materials Science and Engineering, Vol. 65 (1984), pp. 171-184
(9) M.M. C. Schneider, J. et al. P. Gu, C.I. Beckermann, W.M. J. et al. Boettinger and U.S. R. Kattner: “Modeling of Micro- and Macrosegregulation and Freckle Formation in Single-Crystal Nickel-Base Superalidative Liquidation Amplifications”, Metallurgic. 28A (1997), pp. 1517-1531
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Claims (28)

In a method for producing a single crystal structure (referred to as SX material) casting such as a casting or ingot made of a floating Ni-base alloy, a solid phase, a solid-liquid coexisting phase and a liquid phase region are formed, and these regions are formed at one end. To the other end to solidify unidirectionally, and during the unidirectional solidification, an extremely slow liquid phase flow between dendrites that causes freckle in the solid-liquid coexisting phase (channel flow) or macrosegregation A method for producing a cast product, comprising applying a static magnetic field having a strength required to suppress at least one of the phases to the entire solid-liquid coexisting phase. In a method for producing a cast cast or ingot of a polycrystalline columnar dendrite structure (referred to as DS material) such as a floating Ni-base alloy, a solid phase, a solid-liquid coexisting phase, and a liquid phase region are formed, and these regions are An extremely low-speed liquid phase between dendrites that moves from one end to the other end and solidifies in one direction, and at the time of the one-way solidification, generates an upward flow (channel flow) or macrosegregation in the solid-liquid coexistence phase. A method for producing a cast product, comprising applying a static magnetic field having a strength necessary for suppressing at least one of the flows to the entire solid-liquid coexisting phase. Solid and solid-liquid coexistence phases in the manufacturing method of mixed structure castings of single crystal structure (referred to as SX material) and polycrystalline columnar dendrite structure (referred to as DS material) such as castings or ingots by floating Ni-base alloy And a liquid phase region, and these regions are moved from one end to the other end to solidify in one direction, and at the time of the one-way solidification, an upward flow (channel) A static magnetic field having a strength necessary to suppress at least one of the ultra-low-speed liquid phase flows between the dendrites that cause macrosegregation is applied to the entire solid-liquid coexisting phase. Production method. In a method for producing a single crystal structure (referred to as SX material) casting such as a casting or ingot made of a Ni-based alloy, a solid phase, a solid-liquid coexisting phase and a liquid phase region are formed, and these regions are formed from one end to the other. At least one of the flow of the channel that causes flecks in the solid-liquid coexisting phase and the flow of micro-segregation between the dendrites that causes the macrosegregation during the unidirectional solidification. A method for producing a cast product, comprising applying a static magnetic field having a strength required for suppressing the solid to the entire solid-liquid coexisting phase. In a method for producing a cast product of a Ni-based alloy or a polycrystalline columnar dendrite structure (referred to as a DS material) such as an ingot, a solid phase, a solid-liquid coexisting phase, and a liquid phase region are formed, and these regions are formed from one end. And moving toward the other end to solidify unidirectionally, and at the time of the unidirectional solidification, at least one of a channel flow causing freckle in the solid-liquid coexisting phase or a very low-speed liquid phase flow between dendrites causing macrosegregation. A method for producing a cast product, comprising applying a static magnetic field having a strength necessary for suppressing flow to the entire solid-liquid coexisting phase. In a method for producing a mixed structure cast product of a single crystal structure (referred to as SX material) and a polycrystalline columnar dendrite structure (referred to as DS material) such as a cast or ingot made of a Ni-base alloy, a solid phase, a solid-liquid coexisting phase and a liquid Phase regions are formed, and these regions are moved from one end to the other end to solidify in one direction, and at the time of the one-way solidification, channel flow or macrosegregation that causes freckle in the solid-liquid coexisting phase is generated. A method for producing a cast product, comprising applying a static magnetic field having a strength necessary to suppress at least one of the extremely low-speed liquid phase flows between dendrites to the entire solid-liquid coexisting phase. In the manufacturing method of cell crystal structure castings such as castings or ingots of Ni-based alloys, solid phase, solid-liquid coexisting phase and liquid phase region are formed, and these regions are moved from one end to the other end. In addition to solidifying unidirectionally, at the time of the unidirectional solidification, a strong force necessary to suppress at least one of the flow of channels that causes freckle in the solid-liquid coexisting phase or the extremely low-speed liquid phase flow between dendrites that causes macrosegregation. A method for producing a cast product, comprising applying a static magnetic field to the entire solid-liquid coexisting phase. 8. The method for manufacturing a cast product according to claim 1, further comprising an irregular orientation defect in addition to any one of the freckle and the macrosegregation. 9. 9. The method for manufacturing a cast product according to claim 1, wherein the static magnetic field has a strength of at least 0.5 Tesla or more. In the production method of unidirectionally solidified castings such as castings or ingots made of TiAl based alloys, solid phase, solid-liquid coexisting phase and liquid phase region are formed, and these regions are moved from one end to the other end. During the unidirectional solidification, a static magnetic field having a strength required to suppress at least one casting defect of macrosegregation or irregularly oriented crystals in the solid-liquid coexisting phase is applied to the entire solid-liquid coexisting phase. A method for producing a cast product, characterized by applying the method. A cooling chill table, a mold placed in contact with the cooling chill table, a means for casting molten metal into the mold, and a heating furnace that holds the mold at a high temperature, and the mold is relative to the heating furnace. In the casting manufacturing apparatus by the unidirectional solidification method in which the molten metal is sequentially solidified, the flow of the dendrites that cause the channel flow or the macro segregation in the solid-liquid coexisting phase during the unidirectional solidification. Manufacture of a cast product characterized by comprising a static magnetic field applying means for applying a static magnetic field of at least 0.5 Tesla or more to the entire solid-liquid coexisting phase in order to suppress at least one of the extremely low speed liquid phase flows. apparatus. An ingot by electroslag remelting method (ESR) in which at least two electrodes are arranged, and the molten slag phase is heated by energizing between the electrodes, and the electrodes are melted and cast into a mold. In this manufacturing apparatus, a solid phase, a solid-liquid coexisting phase, and a liquid phase region are formed, these regions are moved from one end toward the other end to be solidified, and a freckle is generated in the solid-liquid coexisting phase. A static magnetic field applying means for applying a magnetic field having a strength required to suppress at least one of the extremely low-speed liquid phase flows between dendrites causing channel flow or macrosegregation to the entire solid-liquid coexisting phase of the ingot. An ingot manufacturing apparatus characterized by being provided. 13. The ingot production apparatus according to claim 12, further comprising heating means for heating and keeping the molten slag phase. 14. The manufacturing apparatus according to claim 12, further comprising a magnetic shield that shields the magnetic field generated by the static magnetic field applying unit from the electrodes. An ingot manufacturing apparatus using a vacuum arc remelting method (VAR), in which a plurality of electrodes are arranged, the electrodes are heated and melted by a current flowing between the electrodes, and supplied to a mold to manufacture the ingot. In the ingot manufacturing apparatus, a solid phase, a solid-liquid coexisting phase, and a liquid phase region are formed, and these regions are moved from one end to the other end to be solidified. Application of a static magnetic field that applies a magnetic field having the strength necessary to suppress at least one of the very slow liquid phase flow between dendrites and the channel flow causing macrosegregation to the solid-liquid coexisting phase of the ingot. An ingot manufacturing apparatus characterized by comprising means. The manufacturing apparatus according to claim 15, wherein a molten slag phase for receiving the melt of the electrode is provided on an upper portion of the mold. 17. The ingot manufacturing apparatus according to claim 16, further comprising heating means for heating and keeping the molten slag phase. The manufacturing apparatus according to claim 15, further comprising a magnetic shield that shields a magnetic field generated by an application unit that applies the static magnetic field to the electrodes. 19. The manufacturing apparatus according to claim 15, wherein the applying unit generates a static magnetic field of at least about 1 Tesla or more. 20. The manufacturing apparatus according to claim 15, wherein the applying unit applies a static magnetic field in a direction along the direction of gravity or in a direction intersecting with the direction of gravity to the entire solid-liquid coexisting phase of the molten metal. An ingot manufacturing apparatus characterized by being a thing. An electroslag remelting method in which an ingot is produced by arranging at least two electrodes and heating the molten slag phase by energizing between these electrodes, thereby melting the above-mentioned electrodes and casting them in a mold ( In the ingot production method by ESR), a solid phase, a solid-liquid coexisting phase, and a liquid phase region are formed, and these regions are moved from one end to the other end to be solidified. A static magnetic field is applied to the entire solid-liquid coexisting phase of the ingot to suppress the flow of at least one of the channel flow causing freckle or the very slow liquid phase flow between dendrites causing macrosegregation. An ingot manufacturing method comprising a magnetic field applying means. The method for producing an ingot according to claim 21, wherein the molten slag phase is heated and kept warm. 23. The manufacturing method according to claim 21, wherein the static magnetic field is shielded against the electrodes. A method for producing an ingot by a vacuum arc remelting method (VAR), wherein a plurality of electrodes are arranged, and an electrode is heated and melted by a current flowing between the electrodes to produce a cast ingot. In the ingot manufacturing method, a solid phase, a solid-liquid coexisting phase, and a liquid phase region are formed, and these regions are moved from one end to the other end to be solidified. A static magnetic field is applied to the entire solid-liquid coexisting phase of the ingot to suppress the flow of at least one of the dendrite flow and the very slow liquid phase flow between dendrites causing macro segregation. An ingot manufacturing method comprising an applying means. 25. The method of manufacturing an ingot according to claim 24, wherein a molten slag phase is provided on an upper portion of the mold, and molten droplets generated from the electrodes are refined and supplied to the mold. 26. The method for producing an ingot according to claim 25, wherein the molten slag phase is heated and kept warm. 27. The method of manufacturing an ingot according to claim 24, wherein the static magnetic field is shielded against the electrodes. 28. The method of manufacturing an ingot according to any one of claims 24 to 27, wherein the static magnetic field is a static magnetic field of at least about 1 Tesla.