JP7157295B2 - Unidirectional solidification apparatus and method - Google Patents

Description

The present invention relates to casting technology, and in particular castings and ingots having a columnar dendrite structure composed of polycrystalline grains (referred to as DS material) and a dendrite structure composed of single grains (referred to as Mono-crystal or SX material). The present invention relates to a unidirectional solidification device and a unidirectional solidification method that are intended to improve the production of.

The Bridgeman method, the Liquid Metal Cooling method, and the Gas Cooling Casting method are conventionally known as typical methods for producing the DS material and the SX material. An outline of this will be described below.

Bridgeman Method A typical Bridgeman method (herein referred to as the Standard Bridgeman method) unidirectional solidification apparatus includes a heating furnace, a cooling chamber, a drawing mechanism for drawing the mold from the heating furnace to the cooling chamber, the heating furnace and a cooling chamber, a cooling chill for initiating solidification (see for example, see also FIG. 1 herein). The mold is preheated to a melting temperature or higher by a resistance heater or induction heating, and after pouring the molten metal, it is pulled out to a cooling chamber at a predetermined speed. The mold is set on the cooling chill and solidification is initiated by heat conduction to the chill, but the cooling effect of the chill is limited to a small range, and large castings are mostly selected (see Fig. 1, the solidification route to obtain the SX structure). ) (see, for example, Konter et al.). The casting solidifies by radiation cooling from the side of the mold in the cooling chamber. The cooling capacity of the radiation is rather small, so there is a drawback that casting defects such as freckles (a type of macro segregation defect that causes early failure of turbine blades) or misoriented grain defects (for example, See p.321 of Non-Patent Document 1).

Liquid Metal Cooling method (hereinafter referred to as LMC method)
In order to eliminate the above-mentioned drawbacks of the standard Bridgman method, a method of cooling by immersion in a molten metal bath with a low melting point material instead of radiative cooling in the cooling area (hereinafter referred to as Liquid Metal Cooling, abbreviated as LMC method) ) was devised. In the LMC method, the mold is gradually immersed in a molten metal bath containing a low-melting-point material such as tin or aluminum in the process of drawing out the mold, thereby cooling the mold while increasing the cooling capacity, thereby unidirectionally solidifying the mold. (Drawings are omitted).

For example, US Patent 6,276,433 B1 (2001) uses an Al eutectic alloy as a medium for a cooling metal bath. Further, Elliott et al. (Non-Patent Document 3) showed that by using molten Sn with a lower melting point as a cooling medium, the cooling rate during solidification can be increased and the quality of Ni-based alloy turbine blades can be improved. In addition, Liu et al. (Non-Patent Document 4 and Non-Patent Document 5) adopted the LMC method, refined the crystal structure, and showed that the high-temperature creep strength of directionally solidified Ni-based superalloys can be increased (for example, , 1050° C. and 160 Mpa, the creep rupture time increased approximately twice from 84 hrs to 131 hrs (see Non-Patent Document 5).

Gas Cooling Casting method (hereinafter referred to as GCC method)
The GCC method is a technology that employs a forced gas cooling method in which inert gas (argon, helium, etc.) is used to cool the mold pulled out in the cooling area (Non-Patent Document 2 and Patent Document 2 reference). That is, in FIG. 1, a cooling gas injection nozzle for blowing cooling gas is arranged immediately below the heat insulation baffle provided for thermally separating the heating region and the cooling region, and during the work period of unidirectional solidification, cooling The mold is cooled by blowing gas onto it (not shown). The cooling gas is circulated and cooled by a cooling gas circulation pump system. According to the above document, it is stated that a cooling capacity equal to or higher than that of the LMC method can be obtained.

However, even in the LMC method or the GCC method, the harmful liquid phase flow (flow turbulence) in the liquid phase and solid-liquid coexisting phase (so-called mushy zone) that inevitably exists cannot be eliminated, and macro segregation such as freckles or It is difficult to completely eliminate misorientation crystal defects. In fact, the casting yield of large single-crystal blades for power generation is extremely low and has not been put to practical use.

US Patent 6,276,433 B1 (2001) US Patent 5921310 (Filed Sep. 26, 1997)

ASM Handbook, Vol. 15, Casting (1988), p. 320, Fig. 3 or p. 321, Fig. 4 M. Konter, et al: "A Novel Casting Process for Single Crystal Gas Turbine Components", Superalloy 2000, TMS 2000, p. 189 A. J. Elliot et al: "Directional Solidification of Large Superalloy Castings with Radiation and Liquid-Metal Cooling", Metallurgical and Materials Transactions A, Vol. 35A, Oct. , 2004, pp3221-3231 Lin Liu, et al: "The Effects of Withdrawal and Melt Overheating Histories on the Microstructure of a Ni-based Single Crystal Superalloy", TMS Superalloy 2008, pp287-293

Lin Liu, et al: "High Thermal Gradient Directional Solidification and its Applications in the Processing of Ni-based Superalloys", J. Am. Materials Processing Technology 210 (2010), pp159-165 Y. Ｅｂｉｓｕ：’Ａ Ｎｕｍｅｒｉｃａｌ Ｍｅｔｈｏｄ ｏｆ Ｍａｃｒｏｓｅｇｒｅｇａｔｉｏｎ Ｕｓｉｎｇ ａ Ｄｅｎｄｒｉｔｉｃ Ｓｏｌｉｄｉｆｉｃａｔｉｏｎ Ｍｏｄｅｌ，ａｎｄ Ｉｔｓ Ａｐｐｌｉｃａｔｉｏｎｓ ｔｏ Ｄｉｒｅｃｔｉｏｎａｌ Ｓｏｌｉｄｉｆｉｃａｔｉｏｎ ｖｉａ ｔｈｅ ｕｓｅ ｏｆ Ｍａｇｎｅｔｉｃ Ｆｉｅｌｄｓ’，Ｍｅｔａｌｌｕｒｇｉｃａｌ ａｎｄ Ｍａｔｅｒｉａｌｓ Ｔｒａｎｓａｃｔｉｏｎｓ Ｂ，ｖｏｌ． 42b (2011), pp341-369 M. C. Flemings: "Solidification Processing", McGraw-Hill, Inc.; , (1974) P. C. Carman: Trans. Inst. Chem. Eng. , Vol. 15 (1937), p. 150 Y. Lian, et al: 'Static Solid Cooling: A new directional solidification technique', J. Am. Alloys and Compounds, Vol. 687 (2016), pp. 674-682

Even if the LMC method or GCC method, which has a higher cooling capacity than the standard Bridgeman method in the production of DS or SX material unidirectionally solidified castings or ingots, is applied, macro segregation such as freckles or casting of anisotropically oriented crystals It is difficult to eliminate defects essentially. In particular, large-sized single crystal blades for power generation have a very low casting yield and are not put to practical use. The reason for this is that, as will be described later in Examples, the transverse temperature gradient that inevitably exists in the liquid phase region causes convection, heat pulses at the solidification interface, and influences the shape of the solid-liquid coexisting phase (mushy zone). It disturbs the flow pattern of the liquid phase in the mushy zone. As a result, macrosegregation occurs. In addition, dendrite branches may separate and seed misorientated crystals.

In order to solve the above problems of the conventional methods, the solid phase region is strongly cooled to reduce the harmful lateral liquid phase flow in the solid-liquid coexisting phase that causes macrosegregation. This finding is a phenomenon theoretically and quantitatively supported for the first time by solidification simulations described later, and is an important point of the present invention. This can reduce macro-segregation or misorientation crystal defects.

As a means for this, a new unidirectional solidification method is proposed herein. The outline is shown in FIG. The apparatus of the present invention comprises a mold 1 filled with molten metal 2, a cooling chiller 3 placed at the bottom of the mold, and a resistance heater serving as the main heater for heating the mold placed at a fixed position surrounding the sides of the mold. It consists of a heater 5 , a mobile sub-heater 10 for heating a relatively small region, and a mobile cooling gas nozzle 15 for blowing cooling gas to the mold 1 .

The sub-heater 10 and the movable cooling gas nozzle 15 are ring-shaped, and are integrally and coaxially movable with respect to the mold 1 from the cooling chill 3 side to the upper end side. The movable cooling gas nozzle 15 is configured to blow the cooling gas obliquely downward to the outer circumference of the mold. A heat insulating baffle 13 is arranged between the sub-heater 10 and the cooling gas nozzles 15 . As shown in FIG. 2(b), the resistance heater 5 is formed by winding a belt-like resistance heating element approximately once in the circumferential direction, raising it, and winding it in the opposite direction approximately once. As a result, a slit-shaped gap is formed, through which the cooling gas introduction pipe 14, the heat insulating baffle 13 and the sub-heater 10 can be moved up and down.

The heater 5 is made of a resistance heating element such as carbon graphite, and is attached inside a tubular heat insulating sleeve 6 . Further, a sliding contact terminal 7 connected to the resistance heating main heater 5 is provided outside the heat insulating sleeve 6, and the sliding contact terminal 7 at the uppermost end and the sliding contact terminal 7 at the current position can be brought into sliding contact with each other. Electric power can be supplied to the heater 5 through the brush 8 configured as above.
In this specification, the above heating method is referred to as sliding resistance heating method.

At the start of operation, the brush 8 is positioned at the lowest end, and the resistance heating main heater 5 heats and retains heat over the entire area from top to bottom. As the operation progresses, the brush 8 is slid upward at a predetermined speed in synchronization with the cooling gas nozzle 15 and the auxiliary heater 10 . As a result, the resistance heating main heater 5 is energized in the section from the current position of the brush 8 to the upper end, and is kept in a heated state, and does not receive power in the section from the current position to the lower end of the brush 8. A cooling zone. That is, the heating/warming area shrinks and the cooling area expands with the lapse of time. Then, the heating area finally disappears, and the entire operation becomes a cooling area, ending the operation.

FIG. 3 is a schematic diagram of the entire device incorporating the device.
A main heater power source 9 supplies power through the upper contact terminal and the brush 8 . The sub-heater copper cable 11 is a power cable for connecting the sub-heater power source 12 and the sub-heater 10 to supply power. 18 is a vacuum pump.

A cooling gas circulation pump system 17 supplies the cooling gas to the cooling gas nozzle 15 through the cooling gas introduction pipe 14, and the suction port 16 is an intake port for circulating the cooling gas blown out into the heating furnace outer cylinder 19. The cooling gas is connected to the cooling gas circulation pump system 17 by a pipe and blown out into the furnace. It is a configuration provided for mold cooling in the cooling zone. The melting chamber containing the induction melting furnace 21 and the mold chamber containing the mold 1 can be separated from each other. not shown).
Hereinafter, the unidirectional solidification method will be referred to as sliding resistance heating-gas cooling casting (SRH_GCC method).

The present invention provides the following effects.
(1) Lateral flow in the solid-liquid phase is reduced during solidification. As a result, macro segregation is improved, and misorientation crystal defects are less likely to occur. [It is well known that macrosegregation does not occur when the liquid phase flow in the mushy zone is rectified in the axial direction (see, for example, p.252 of Non-Patent Document 7, Fig.7-35)]

(2) As will be described later in the examples, the productivity can be increased by increasing the moving speed of the sliding brush corresponding to the pull-out speed.

(3) Since a much larger cooling capacity can be obtained than the standard Bridgman method, it is possible to obtain a fine crystal structure as described in paragraph 0005, and the heating time required for solution treatment of the Ni-based superalloy blade It produces the economic effect of being able to shorten significantly. In addition, it is possible to produce a product with high creep rupture strength (see Non-Patent Document 5 mentioned above).

FIG. 1 is a diagram showing a unidirectional solidification apparatus based on the Bridgman method. FIG. 2 is a diagram showing an outline of a unidirectional solidification apparatus using the sliding resistance heating method of the present invention (referred to as SRH_GCC method). It is a schematic diagram showing an application example of sliding resistance heating method (referred to as SRH_GCC method). A vacuum vessel 22, an induction melting furnace 21, and a cooling gas circulation system 17 are shown. FIG. 4 is a diagram showing the segregation standard deviation of IN718 blades by the standard Bridgman method and the SRH_GCC method (sliding brush moving speed 40 cm / h) (standard deviation of each element (Table 5) is the initial concentration of each element normalized). FIG. 5 is a diagram showing the DAS distribution of an IN718 blade by the standard Bridgman method and the SRH_GCC method (sliding brush moving speed 40 cm/h) (cross-sectional center Z direction). Note: Bottom dummy chill thickness 0.15 cm (from Table 4).

FIG. 6 is a diagram showing the Nb distribution of an IN718 blade by the standard Bridgman method and the SRH_GCC method (sliding brush moving speed 40 cm/h) (in the Z direction of the center of the cross section). Note: Bottom dummy chill thickness 0.15 cm (from Table 4). FIG. 7 is a schematic diagram of the Static Solid Cooling method (see Non-Patent Document 9). FIG. 8 is a schematic diagram of a unidirectional solidification apparatus according to the SRH_GCC method of the present invention employing a mold according to the Static Solid Cooling method (however, heating and cooling means are according to the means of the present invention).

In the present invention, the cooling rate during solidification is increased compared to the standard Bridgman method, thereby refining the solidified structure and reducing casting defects such as macro segregation and crystals with different orientations.
In addition, the present invention is a technique that allows the apparatus to be simplified and miniaturized by making it possible to store the heating area, the strong cooling area, and the heat insulation area in one chamber, and to make it possible to reduce and change the heating area. It is expected that production costs and running costs can be greatly reduced. That is, in the case of the normal Bridgman method (see FIG. 1), the height of the entire apparatus is approximately three times the height of the mold (heating area + cooling area + mold withdrawal device), whereas in the case of the present invention The height of the entire device can be reduced to approximately the height of the mold.

及び温度Ｔの函数として表されることから

で与えられる（表２中の液相密度計算式参照）。A. Mechanism of formation of macrosegregation It is well known that various macrosegregations such as Freckle segregation are caused by liquid phase flow in solid-liquid coexistence phase. External forces such as solidification shrinkage, convection due to the density difference in the interdendritic liquid phase, and electromagnetic force are driving forces that cause this flow.

and as a function of temperature T,

(See liquid phase density calculation formula in Table 2).

An alloy in which _ρL decreases as solidification progresses is called a floating alloy, and an alloy in which _ρL increases is called a sedimentation alloy. It depends on the alloy composition whether it is a floating type alloy, a sedimentation type alloy, or a mixed type alloy (an alloy in which the liquidus density decreases and increases again with the progress of solidification, or vice versa). Ni-10wt%Al is a floating type alloy, and IN718 is a sedimentation type alloy (see Fig. 13 of Non-Patent Document 6). Macro segregation is not limited to the floating type/sedimentation type, but shows various forms depending on the casting conditions.

In addition, a heat pulse caused by convection causes dendrite fusing and separation (referred to as grain multiplication mechanism, see p.154 of Non-Patent Document 7), which breaks the growth of dendrites and easily causes misorientation crystal defects having random orientations. Become.

B. Solidification Analysis Means An outline of a numerical analysis method using a general-purpose solidification simulation system (system name CPRO) developed by the present inventor for analyzing solidification phenomena will be described below.
The physical variables for describing the solidification phenomenon are the temperature, the concentration of elements redistributed in the liquid phase and solid phase during solidification (the number of alloying elements is n), and the liquid It is given by the phase temperature, liquid phase flow rate (three vector components) and pressure in the liquid and solid-liquid phases. 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.

ここに、ベクトルｖはデンドライト間の液相流れ速度、μは液相の粘度、ｇ_Ｌは液相の体積率、Ｋは透過率、Ｐは液相の圧力、Ｘは重力、遠心力等の物体力ベクトルである。Ｋはデンドライトの幾何学的構造によって決まりＫｏｚｎｅｙ－Ｃａｒｍａｎの式（非特許文献８参照）より次式で与えられる。It is known that the flow in the solid-liquid coexistence phase is described by Darcy's equation (2) (see p.234 of Non-Patent Document 7). The Darcy flow phenomenon is included in the equations of motion in Table 1 as a flow resistance term.

Here, vector v is the liquid phase flow velocity between 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, and X is the force of gravity, centrifugal force, etc. is the body force vector. K is determined by the geometrical structure of the dendrite and is given by the following equation from the Kozney-Carman equation (see Non-Patent Document 8).

Ｓ_ｂはデンドライト結晶の単位体積あたりの表面積（比表面積）であり、デンドライトの成長時における形態解析（本明細書において微視的スケールと呼ぶ）により求められる。すなわち、凝固は液相及び固相における一種の拡散律速過程であることからデンドライトを円柱形の枝及び幹と半円球の先端部からなるモデル化を行い固相及び液相における溶質の拡散方程式を解いて求めた。尚、デンドライトの方向によるＫの異方性はないものと仮定した。無次元定数ｆは多孔質媒体中の流動実験により５の値を持つことがわかっている。

_Sb is the surface area (specific surface area) per unit volume of the dendrite crystal, and is determined by morphological analysis during the growth of the dendrite (herein referred to as microscopic scale). Since solidification is a kind of diffusion rate-controlled process in the liquid and solid phases, the dendrite is modeled with a cylindrical branch and trunk and a hemispherical tip, and the solute diffusion equation in the solid and liquid phases is I solved it and asked for it. It is assumed that there is no anisotropy of K due to the direction of dendrites. It is known that the dimensionless constant f has a value of 5 from a flow experiment in a porous medium.

As mentioned above, all the physical variables on the macroscopic scale interact with each other, and furthermore, they are deeply related to the dendrite growth on the microscopic scale (that is, they are coupled). This numerical analysis method is described in detail in the present inventor's paper (Non-Patent Document 6).

Example: IN718 alloy short blade Next, when the standard Bridgman method (R = 15 cm / h) and the sliding resistance heating-GCC method (SRH_GCC method) (R = 40 cm / h) are applied to the IN718 short blade will be described. Table 2 shows the physical properties of IN718, Table 3 shows the casting parameters according to the standard Bridgman method, and Table 4 shows the casting parameters according to the SRH_GCC method of the present invention. Preliminary calculations were performed in preparation for the calculations, and the casting parameters were adjusted so that the mushy zone was at approximately the same horizontal position as the insulating baffle. The withdrawal rate was R=15 cm/h for the standard Bridgman method and R=40 cm/h (and H _GCC =600 W/(m ² ·K)) for the SRH_GCC method.

Calculation Results The calculation results are summarized in Tables 5(a) and (b).

The standard deviation σ (wt %) of each alloy element (the square root of the sum of squares of the difference between the alloy concentration of each element and the average concentration value) was used as an index representing the degree of segregation. A larger σ indicates a greater degree of variation in the alloying elements, that is, macrosegregation.
From Table 5(a), the standard deviation of each alloying element is halved in the SRH_GCC method compared to the standard Bridgman method. It can be seen that the transformation is greatly accelerated.
Table 5(b) shows the minimum, maximum, and average standard deviations. It can be seen that the minimum-maximum width is reduced in the SRH_GCC method.
FIG. 4 shows the effect of the SRH_GCC method on the normalized standard deviation of each alloying element (σ is normalized by C0 to make it easier to see the relative values between elements). As shown in FIG. 4, when the drawing speed is increased from 15 cm/h to 40 cm/h (moving speed of the sliding brush) and strong cooling (Hgcc=600 W/m2/K), the standard deviation is greatly reduced (No. 1→No. 8). That is, macrosegregation is greatly improved.

When the movement speed of the solidification interface is increased from 15 cm/h to 40 cm/h (comparison between No. 1 and No. 8), σ decreases because the disorder of the flow pattern in the mushy zone decreases. However, the thermal flux in front of the solidification interface is on the order of ±20° C. (No. 1) and ±23° C. (No. 8), respectively, and significant convection occurs (1/2 during solidification, at the center in the thickness direction ( Y, Z) cross section).

FIG. 5 shows a comparison of DAS for each process (Z direction distribution at the center position of the XY cross section). No. 1 (standard Bridgman method, 15 cm/h) for DAS≈180 μ, No. 8 (SRH_GCC method, 40 cm/h, H _GCC =600 W/(m ² ·K)), the fineness is reduced to 115 to 120 μm, and the variation width is also reduced from 20 μm to 5 μm.

FIG. 6 shows a comparison of Nb distributions at the positions. No. 1 to No. In No. 8, the range of variation in segregation is improved, and at the same time, the concentration approaches the initial concentration (4.85 wt%), improving homogeneity.

As described in paragraph 0037 regarding the liquid phase flow pattern and macro segregation , in the SRH_GCC method, compared to the standard Bridgman method, although there is thermal fluctuation in front of the solidification interface, the rectification of the liquid flow in the solid-liquid coexistence phase is considerably promoted. It can be seen that That is, the macrosegregation is considerably improved.

Regarding the solidification structure, the refinement and uniformity of the crystal structure improve the creep strength, and the solution treatment performed after casting in the Ni-based alloy (microsegregation in the dendritic arm spacing range or γ' phase (gamma prime), carbides, etc. The heat treatment for dissolving the second phase in the γ phase) and the subsequent aging treatment time (heat treatment for precipitating the γ' phase from the γ phase) can be shortened. For example, the time required for solution treatment is roughly proportional to DAS ² /Ds (Ds is the diffusion coefficient of the alloying element in the solid phase), so if DAS is reduced to 1/2, the required time is reduced to 1/4. (See P.332, Eq.(10-6) of Non-Patent Document 7).

Principle of the Present Invention The flow in the mushy zone is caused by solidification contraction based on the density difference between the liquid phase and the solid phase (treatment of the flow in the mushy zone will be described here focusing on solidification contraction). In other words, the driving force that causes the flow is the suction force associated with solidification contraction, which is transmitted from the root of the dendrite to the tip in order. Therefore, if the cooling capacity of the solid phase region is increased and the movement speed R of the mushy zone is increased, this tendency will become stronger, and as a result, the flow pattern will become stronger in the axial direction. In a simulation of an actual example, the fact that the segregation standard deviation σ becomes smaller as R is increased by strong cooling indicates that the flow pattern tries to be aligned in the axial direction, and the validity of the above mechanism is theoretically and quantitatively confirmed. It proves that [Note: The above principles apply to both floating and sinking types]

Other Matters (1) Static Solid Cooling (SSC)
Recently, Lian et al. (Non-Patent Document 9) proposed a method to enhance the cooling capacity using a Pyrolytic Graphite (PG) mold with high thermal conductivity and high thermal diffusivity. A schematic diagram thereof is shown in FIG. The method encloses the mold with a solid layer of alternating heat transfer layers (PG layers) and thermal insulation layers, inside which the layered solid material is placed to follow up the shape of the blade. The mold itself is coated with an extremely thin coating. Heating and cooling are provided by resistive heaters and water cooling, respectively, disposed around the perimeter of the heat transfer layer. Unidirectional solidification is accomplished by moving the heating-cooling cycle upward layer by layer by means of an electrical network. However, it seems extremely difficult to implement these heating/cooling functions in an actual device.

On the other hand, the SRH_GCC method of the present invention uses a sliding resistance heating method and a gas cooling cooling method, and differs from the SSC method in structure in terms of the heating method and cooling method, respectively. That is, in the SSC method, since the layer is moved upward layer by layer, temperature changes and changes in the flow pattern of the liquid phase that determine macrosegregation are discontinuous. Therefore, temperature changes and liquid phase flow pattern changes are considered to be more continuous (smoother).

A discontinuous change makes the degree of fluctuation in the advancing speed of the solidification interface stronger, so that fluctuation in alloy concentration, that is, banding segregation, is likely to occur (for the mechanism of banding, p.39 of Non-Patent Document 7, Figure 2-6 reference). In contrast, with the SRH_GCC method according to the present application, the change is more continuous (smooth), so it is considered that the banding is alleviated. This mitigation effect can be further enhanced by mounting the sub-heater 10 according to this method.
As described above, the SSC method and the SRH_GCC method differ in heating method and cooling method, and have different effects on solidification.

It is also possible to use a mold according to the SSC method as the strong cooling means according to the present invention. However, the heating and cooling means are according to the means of the present invention. FIG. 8 shows an example of using a template according to the SSC method for the present invention.

(2) The purpose of the sub-heater in the heating means is to prevent the solidification interface temperature of the solid-liquid coexisting phase from dropping, prevent the axial temperature gradient of the solid-liquid coexisting phase from dropping, and make the temperature change smoother.

(3) There is no clear definition of the cooling capacity in unidirectional solidification, but as an example, Non-Patent Document 2 assumes a simple heat transfer model and roughly estimates the heat flux Q for a large blade: Bridgeman Q=86 kW/m ² for the LMC process with molten tin; Q=101 ^{kW/m 2 for} the GCC process. In this specification, cooling by the LMC, GCC, and SSC molds is referred to as intense cooling.

(4) Other factors affecting solidification include the size and shape of the casting (expansion/reduction of the cross section), the thickness of the heat insulating baffle, and the like. Although the shape of the solid-liquid coexisting phase is determined by these casting conditions, it is desirable that it be as flat as possible. For these items, a CPRO simulation may be performed to adjust the moving speed of the solidification interface, heating/cooling conditions, and the like.

Summary The features and merits of the SRH_GCC method according to the present invention are summarized below.
(1) Reduction of macro segregation and misorientation crystal defects : By strongly cooling the solid phase region and increasing the movement speed of the solidification interface, harmful lateral liquid phase flow is suppressed and rectification in the axial direction is achieved. Promoted. This reduces macro-segregation and also makes the solidification more stable, thus reducing the risk of misorientation crystal defects.

(2) Refinement and homogenization of crystal structure: Since the crystal structure can be refined and homogenized by intense cooling of the solid phase region, the solution heat treatment time after casting can be greatly shortened (production performance improvement).

(3) Improvement of economic efficiency and productivity : Productivity can be improved by improving the moving speed of the solidification interface compared to the withdrawal speed of the conventional standard Bridgman method.

(4) Improvement of economic efficiency by downsizing of equipment : The SRH_GCC method of the present invention is a technology in which the equipment is simplified and downsized compared to the standard Bridgman method, and it is expected that production costs and running costs can be greatly reduced. Be expected.

The above features and merits are improvements that have made great progress compared to the conventional standard Bridgman method, and are findings that have been clarified for the first time in the present application.

In this example, the GCC method was used as the strong cooling method, but the same effect can be obtained by using a mold by the static solid cooling method (however, the heating/cooling method of the mold is different) having a higher cooling capacity. is clear in principle.

In the present invention, the IN718 Ni-based superalloy has been described, but the present invention is applicable to alloy systems that form dendrites or cellular structures during the solidification process, such as Ni-based superalloys, titanium alloys, Co-based alloys, Fe-based alloys, and the like. It is clear in principle that the coagulation phenomenon and effect are exhibited. These alloy systems are therefore subject to the application of the present invention.

As described above, the present invention contributes to improving the quality of various turbine blades such as Ni-based superalloy turbine blades and improving the casting yield. It will be possible to greatly contribute to energy saving and global warming countermeasures by increasing the safety and life of these important parts and improving the efficiency of gas turbines.

In particular, in the field of aircraft jet engines, Ni-based superalloy single-crystal turbine blades are in practical use, and by applying the present invention, it is possible to further improve the casting yield, resulting in fuel efficiency and CO2 reduction. It is a contribution.

1 mold 2 casting or ingot (molten metal)
3 Cooling chill (water cooling chill)
4 selector 5 main heater 6 heat insulating sleeve 7 main heater sliding contact terminal 8 main heater brush 9 main heater power source 10 auxiliary heater

11 Sub-heater copper cable 12 Sub-heater power supply 13 Heat insulating baffle 14 Cooling gas introduction pipe 15 Cooling gas nozzle 16 Cooling gas inlet 17 Cooling gas circulation pump system 18 Vacuum pump 19 Outer cylinder 20 Heat insulating upper lid 21 Induction melting furnace 22 Vacuum vessel

Claims (6)

In a directional solidification apparatus for producing castings or ingots having a single crystal structure (called SX material) or a polycrystalline columnar dendrite structure (called DS material) or a crystal structure consisting of a mixed structure of the SX and the DS , a heating area for heating and keeping the mold warm, a strong cooling area for cooling the mold, and a heat insulating area for thermally separating and insulating these areas are housed in one chamber, and in this chamber,
said mold for casting said casting or ingot;
a cooling chill placed at the bottom of said mold to initiate solidification;
a sliding resistance heating main heater for heating and keeping the mold warm;
an insulating sleeve for supporting the main heater and blocking heat radiation to the outside;
a mold cooling gas nozzle as mold cooling means for cooling the mold;
a heat insulating baffle as a heat insulating means arranged close to the upper part of the mold cooling means;
with
The heat insulation baffle and the mold cooling gas nozzle are configured to be able to move up and down synchronously and integrally,
the main heater is attached to and supported by the inner surface of the insulating sleeve;
Further, the main heater is arranged to include the entire mold,
The main heater and the heat insulating sleeve are provided with a cooling gas introduction pipe provided outside the heat insulating sleeve, and connected to the cooling gas introduction pipe for vertically moving the cooling gas nozzle provided inside the main heater. provide the necessary aisles,
Sliding contact terminals connected to the main heater are provided on the outer side of the heat insulating sleeve for each circumference in the vertical direction of the main heater, and sliding brushes are provided for sliding contact with the sliding contact terminals. ,
The energization section is made variable by making the energization section between the upper end of the main heater and the sliding brush, and the sliding brush moves up and down synchronously and integrally with the heat insulation baffle and the mold cooling gas nozzle. It has a configuration that allows movement,
At the start of operation, the sliding brush, the heat insulating baffle and the mold cooling gas nozzle are positioned at the lower end of the mold, and power is supplied to the energizing section to heat and keep the mold to a predetermined temperature above the melting point of the metal material. After melting and casting the metal material, the sliding brush, which can move up and down synchronously and integrally with the heat insulating baffle and the mold cooling gas nozzle, is moved upward at a predetermined speed to reduce the heating and heat retention area. unidirectionally solidifying the casting or the ingot by supplying a cooling gas to the mold cooling gas nozzle positioned immediately below the heat insulating baffle . 2. In claim 1, by heating and retaining heat in the vicinity of the lower end of the heating and retaining region just above the heat insulation baffle, the temperature drop of the solid-liquid coexisting phase solidification interface temperature is prevented and the axial temperature gradient of the solid-liquid coexisting phase is reduced. A unidirectional solidification apparatus characterized by comprising a sub-heater for preventing temperature drop and smoothing temperature changes . 2. A unidirectional solidification apparatus according to claim 1, wherein said mold has a structure in which layers of graphite having high thermal conductivity and layers of heat insulating material having heat insulating properties are alternately laminated in the height direction . In a directional solidification method for producing a casting or an ingot having a crystal structure consisting of a single crystal structure (called SX material) or a polycrystalline columnar dendrite structure (called DS material) or a mixed structure of said SX and said DS , a heating area that heats and retains the mold, a strong cooling area that cools the mold, and an adiabatic area that thermally separates and isolates these areas are housed in one chamber,
In the process of pouring the molten metal into the mold and solidifying it, the method of heating and keeping the mold heats the mold. When resistance heating and heat retention are performed, the energization section is reduced and variable, and the strong cooling region is cooled by injecting inert gas against the side surface of the mold, and at the start of operation, the energization section is Enclosing the entire side surface of the mold, the mold is heated and kept warm to a predetermined temperature, and as time elapses, the lower end side of the energized section is moved toward the upper end at a predetermined speed, thereby reducing the heating area and Unidirectional solidification characterized in that the molten metal cast in the mold is solidified by moving and expanding the cooling region directly under the heat insulation region toward the upper end at the predetermined speed while cooling the cooling region directly under the heat insulation region by the strong cooling. Method. 5. In claim 4, at least one sub-heater is provided directly above the heat insulating region to heat and keep warm the vicinity of the lower end of the heating/warming region , thereby preventing the solid-liquid coexisting phase from lowering the solidification interface temperature. A unidirectional solidification method characterized by preventing a decrease in temperature gradient in the coexisting phase in the axial direction and making the temperature change smoother . 5. A unidirectional solidification method according to claim 4, wherein said mold is a mold in which layers of graphite having high thermal conductivity and layers of heat insulating material having heat insulating properties are alternately laminated in the height direction .

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