Method for rapidly determining using length of seed crystal in directional solidification process of casting

Abstract

The invention discloses a method for rapidly determining the use length of seed crystals in the directional solidification process of a casting, which comprises the following steps: preparing a wax mold, dipping slurry and spraying sand on the wax mold to obtain a primary ceramic shell, dewaxing and roasting the primary ceramic shell to obtain an experimental mold shell, plugging experimental seed crystals into each seed crystal cavity of the experimental mold shell in a matched manner, and finally, carrying out secondary solidification on the experimental mold shell. The lengths of the experimental seed crystals stuffed into the seed crystal cavities are different, the side parts of the experimental seed crystals are subjected to quantity removal treatment, so that channels for molten metal to flow are formed among the seed crystal cavities, then the experimental mold shell is placed in a solidification furnace to simulate the actual pouring process of a casting, and the shell is removed after the directional solidification experiment is completed; the method comprises the following steps: axially sectioning the seed crystal with the alloy liquid flowing fins on the removal surface, polishing and corroding the sectioning surface to observe a metallographic structure, and determining a reflow interface of the experimental seed crystal so as to quickly determine the shortest length required by effective seeding of the seed crystal during directional solidification of a casting.

Description

Technical Field

[0001] The invention belongs to the technical field of directional solidification, and in particular relates to a method for quickly determining the use length of a seed crystal in a casting directional solidification process. Background Art

[0002] The preparation technology of high-temperature alloy single crystal castings can be divided into crystal selection method and seed crystal method. Among them, the seed crystal method is to place the seed crystals with selected primary and secondary crystal orientations in the seed crystal cavity at the bottom of the mold shell in advance, and melt the upper part of the seed crystal during heating and heat preservation, and then pour the molten metal. During the solidification process, the melt grows epitaxially according to the original crystal orientation of the seed crystal, so as to obtain a single crystal casting with the same crystal orientation. In the casting preparation process, for seed crystals of different diameters, it is usually required that 3-4mm of the top of the seed crystal melts back, so as to ensure that the seed crystal can be smoothly seeded, and there will be no waste of materials and limited space of the wax mold. This is because if the seed crystal inserted into the bottom of the mold shell is too short, it will not melt back during heat preservation, and only remain in a solid state, and the crystal phase transfer cannot be achieved. When the inserted seed crystal is too long, although it can ensure that the top of the seed crystal melts back, there will be problems of limiting the space of the wax mold and wasting materials.

[0003] In summary, how to determine the shortest length required for seed crystal induction is a technical problem that needs to be solved urgently. Summary of the invention

[0004] To this end, the main purpose of the present invention is to provide a method for quickly determining the length of a seed crystal used during directional solidification of a casting, aiming to quickly determine the shortest length of a seed crystal required for effective seeding during directional solidification of a casting.

[0005] To this end, the method provided by the present invention for quickly determining the shortest length of a seed crystal required for effective seeding comprises the following steps: Determine the seed crystal diameter to be used in directional solidification of the casting according to the casting mold assembly plan; Prepare wax molds, each wax mold includes a base plate, a center column tube and a number of wax rods of the same size, the diameter of the wax rods being the same as the diameter of the seed crystal to be used for directional solidification of the casting; Then the wax mold is dipped in slurry and sanded to obtain a preliminary ceramic shell; Afterwards, the preliminary ceramic shell is dewaxed and fired to obtain an experimental shell, and the cavity formed after the wax rod is dewaxed constitutes the seed crystal cavity; An experimental seed crystal is matched and inserted into each seed crystal cavity of the experimental mold shell. The length of the experimental seed crystal inserted into each seed crystal cavity is inconsistent. The lower end of each experimental seed crystal is flush with the bottom plate of the mold shell. The side of each experimental seed crystal is degassed to form a channel for the flow of molten metal between the seed crystal cavities. The material of the experimental seed crystal is the same as the seed crystal material to be used in the directional solidification of the casting. The experimental mold shell is then placed in a solidification furnace to simulate the actual pouring process of the casting; After the experiment, the shell was removed, the experimental seed crystal was cleaned, and the surface state of the experimental seed crystal was observed and recorded. The seed crystal with alloy liquid flowing on the measured surface was axially sectioned, and the section surface was polished and corroded to observe the metallographic structure, and the remelting interface of the experimental seed crystal was determined. Then, the length from the remelting interface to the bottom of the experimental seed crystal was measured, and the original length of the seed crystal was subtracted from this length to obtain the length of the seed crystal remelting section. The experimental seed crystal with a seed crystal remelting section length of 3-4mm was used to prepare castings.

[0006] Specifically, the length of each experimental seed crystal is gradually reduced in a gradient of 1-2 mm.

[0007] Specifically, by changing the wax rod size of the wax mold and the alloy type of the seed crystal and repeating the above process, the actual pouring process of seed crystals of different heights, different diameters and different alloy types can be simulated.

[0008] Specifically, the wax stick has a diameter of 5-8 mm and a length of 10-60 mm.

[0009] Specifically, the insulation temperature is 1500-1550° C., and the pulling speed is 3-5 mm / min.

[0010] Compared with the prior art, the present invention has the following beneficial effects: 1. By preparing a high-throughput experimental mold shell and performing a directional solidification experiment, multiple sets of seed crystal remelting data at different heights can be obtained. After that, by sectioning the experimental seed crystal and polishing and corroding the section surface to observe the metallographic structure, the remelting interface of the experimental seed crystal can be determined, and the shortest length required for effective seed crystal seeding can be quickly determined. In addition, by changing the wax rod size of the wax mold and the alloy type of the seed crystal, and repeating the shell and experimental process, multiple sets of seed crystal remelting data at different heights, diameters, and alloy types can be obtained.

[0011] 2. When preparing the experimental mold shell, the wax mold does not require a pouring system, which reduces the difficulty of mold assembly, and there is no need to prepare the master alloy before the experiment, which reduces the pouring cost. At the same time, compared with the usual pouring, the experiment saves the time of heating, melting and pouring the master alloy, and the pulling distance is short, which shortens the pouring time.

[0012] 3. By removing the amount from the side of the seed crystal, a flow surface is formed for the molten metal to flow, so there is no need to grind and corrode the cross section of the seed crystal to observe the metallographic structure to judge the remelting situation. Only by comparing the surface conditions of the removed surfaces of seed crystals at different heights, it can be quickly determined whether the seed crystal has remelted. When the seed crystal remelting length is determined, the number of experimental seed crystal sectioning can be greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0014] Figure 1 It is the front view of the wax model of the present invention; Figure 2 is a top view of the wax model of the present invention; Figure 3 It is the experimental shell diagram of the present invention; Figure 4 The surface morphology of DD419 seed crystals at different heights after directional solidification experiments of the present invention; Figure 5 This is the metallographic structure of the longitudinal section of the seed crystal with a height of 30 mm according to the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0017] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0018] A method for quickly determining the shortest length of a seed crystal required for effective seeding comprises the following steps: Determine the seed crystal diameter to be used in directional solidification of the casting according to the casting mold assembly plan; Prepare wax models, such as Figure 1 and Figure 2 As shown, each wax mold includes a base plate, a center column tube and a plurality of wax rods of the same size, and the diameter of the wax rods is the same as the diameter of the seed crystal to be used for directional solidification of the casting; Then the wax mold is dipped in slurry and sanded to obtain a preliminary ceramic shell; After that, the preliminary ceramic shell is dewaxed and fired to obtain the experimental shell, such as Figure 3 As shown, the cavity formed after the wax stick is dewaxed constitutes the seed crystal cavity; An experimental seed crystal is matched and inserted into each seed crystal cavity of the experimental mold shell. The length of the experimental seed crystal inserted into each seed crystal cavity is inconsistent. The lower end of each experimental seed crystal is flush with the bottom plate of the mold shell. The side of each experimental seed crystal is degassed to form a channel for the flow of molten metal between the seed crystal cavities. The material of the experimental seed crystal is the same as the seed crystal material to be used in the directional solidification of the casting. The experimental mold shell is then placed in a solidification furnace to simulate the actual pouring process of the casting; After the experiment, the shell is removed, the experimental seed crystal is cleaned, and the surface state of the experimental seed crystal is observed and recorded. If the temperature at the top of the seed crystal reaches below the liquidus temperature, the top surface and the degassed surface of the seed crystal are flat, which is equivalent to a heat treatment. If the temperature at the top of the seed crystal reaches above the liquidus temperature, the seed crystal starts to melt back from the top, the top surface is uneven, and the molten alloy liquid will flow along the gap between the seed crystal cavity and the degassed surface of the seed crystal, and solidify on the degassed surface of the seed crystal during subsequent pulling, forming an obvious seam layer. Therefore, it is possible to infer and predict whether there will be any meltback during mold casting based on the surface state of the seed crystal. Then, the seed crystal with alloy liquid flowing on the measuring surface will be axially sectioned, and the section surface will be polished and corroded to observe the metallographic structure, and the meltback interface of the experimental seed crystal will be determined. Then, the length L from the meltback interface to the bottom of the experimental seed crystal will be measured, and the length L will be subtracted from the original length of the seed crystal to obtain the length of the seed crystal meltback section. The shortest length required for effective seeding is determined by comparing the meltback conditions of seed crystals at different heights, and the experimental seed crystal with a seed crystal meltback section length of 3-4mm (that is, the shortest length seed crystal required for effective seeding) is used to prepare castings.

[0019] The present invention prepares a high-throughput experimental mold shell and obtains multiple groups of seed crystal melt-back data at different heights through a single directional solidification experiment. Then, by sectioning the experimental seed crystal and polishing and corroding the section surface to observe the metallographic structure, the melt-back interface of the experimental seed crystal can be determined, and the shortest length required for effective seed crystal induction can be quickly determined.

[0020] When preparing the experimental mold shell, the wax mold does not require a pouring system, which reduces the difficulty of mold assembly, and does not need to prepare the master alloy before the experiment, which reduces the pouring cost. At the same time, compared with the usual pouring, the experiment saves the time of heating, melting and pouring the master alloy, and the pulling distance is short, which shortens the experimental time. By removing the amount from the side of the seed crystal, a flow surface for the molten metal to flow is formed, so there is no need to grind and corrode the cross section of the seed crystal to observe the metallographic structure to judge the remelting situation. Only by comparing the surface state of the removed surface of the seed crystal at different heights, it can be quickly determined whether the seed crystal has remelted. When the seed crystal remelting length is determined, the number of experimental seed crystal sections can be greatly reduced.

[0021] Specifically, by changing the wax rod size of the wax mold and the alloy type of the seed crystal and repeating the above process, the actual pouring process of seed crystals of different heights, different diameters and different alloy types can be simulated.

[0022] Specifically, the length of each experimental seed crystal is gradually reduced by 1-2 mm, the diameter of the wax rod is 5-8 mm, the length is 10-60 mm, the insulation temperature is 1500-1550° C., and the pulling speed is 3-5 mm / min.

[0023] Specific examples Use wax sticks with a diameter of 6mm and a height of 50mm to assemble the mold. Select DD419 seed crystals with lengths of 20mm, 22mm, 24mm, 26mm, 28mm, 30mm, 32mm, 34mm, 36mm, 38mm, 40mm, 42mm, 44mm, 46mm, 48mm, and 50mm, and remove 1.5mm from the cross section of the seed crystal. Figure 4 These are some seed crystals that have been shelled and cleaned after the experiment. From left to right, they are seed crystals with lengths of 24mm, 30mm, 36mm, 40mm, 46mm, and 50mm. The top surface of the 24mm seed crystal is flat, and no molten alloy liquid is found to flow and solidify on the measured surface. Starting from the seed crystal with a height of 30mm, the top surface is uneven. As the top alloy begins to melt, the top has different degrees of necking, and it can be seen that the measured surface is covered by the alloy liquid flowing down from the upper part. Therefore, it can be determined that under this casting condition, remelting begins from the seed crystal with a length of 30mm.

[0024] Then, the melted seed crystal was axially sectioned, and the section surface was polished and etched to observe the metallographic structure. Figure 5As shown, the metallographic structure shows that there is a remelting interface, the matrix dendrite structure near the remelting interface becomes blunt and blurred, and the seed crystal is partially melted. Then the length L from the remelting interface to the bottom of the experimental seed crystal is measured, and the length L is subtracted from the original length of the seed crystal to obtain the length of the seed crystal remelting section. The shortest length required for effective seed crystal induction is determined based on the comparison of the remelting conditions of seed crystals at different heights. By statistically analyzing the seed crystal remelting section length data of each seed crystal, it is found that the remelting section length of a 34mm long seed crystal is approximately 3.2mm, which is within the remelting length range required by the seed crystal method, that is, the shortest seed crystal length required for effective induction is 34mm. Therefore, it is finally determined that a 34mm long seed crystal is selected as the seed crystal for casting under this casting condition.

[0025] Unless otherwise stated, any technical solution disclosed in the present invention disclosed above, if it discloses a numerical range, then the disclosed numerical range is a preferred numerical range, and any technician in the field should understand that the preferred numerical range is only a numerical value with a more obvious technical effect or representative value among many implementable numerical values. Since there are too many numerical values ​​to be exhaustive, the present invention discloses some numerical values ​​to illustrate the technical solution of the present invention, and the numerical values ​​listed above should not constitute a limitation on the scope of protection of the present invention.

[0026] At the same time, if the above-mentioned invention discloses or involves components or structural parts that are fixedly connected to each other, then, unless otherwise stated, the fixed connection can be understood as: a detachable fixed connection (for example, connected by bolts or screws), and can also be understood as: a non-detachable fixed connection (for example, riveting, welding). Of course, the mutual fixed connection can also be replaced by an integrated structure (for example, manufactured by one-piece molding using a casting process) (except when it is obviously impossible to use an one-piece molding process).

[0027] In addition, the terms used in any technical solution disclosed in the present invention to indicate positional relationships or shapes include states or shapes that are similar, similar or close to them unless otherwise stated. Any component provided by the present invention may be assembled from multiple separate components or may be a separate component manufactured by an integrated molding process.

[0028] The above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for quickly determining the length of seed crystal used in the directional solidification process of a casting, characterized in that: The steps include: Determine the seed crystal diameter to be used in directional solidification of the casting according to the casting mold assembly plan; Prepare wax molds, each wax mold includes a base plate, a center column tube and a number of wax rods of the same size, the diameter of the wax rods being the same as the diameter of the seed crystal to be used for directional solidification of the casting; Then the wax mold is dipped in slurry and sanded to obtain a preliminary ceramic shell; Afterwards, the preliminary ceramic shell is dewaxed and fired to obtain an experimental shell, and the cavity formed after the wax rod is dewaxed constitutes the seed crystal cavity; An experimental seed crystal is matched and inserted into each seed crystal cavity of the experimental mold shell. The length of the experimental seed crystal inserted into each seed crystal cavity is inconsistent. The lower end of each experimental seed crystal is flush with the bottom plate of the mold shell. The side of each experimental seed crystal is degassed to form a channel for the flow of molten metal between the seed crystal cavities. The material of the experimental seed crystal is the same as the seed crystal material to be used in the directional solidification of the casting. The experimental mold shell is then placed in a solidification furnace to simulate the actual pouring process of the casting; After the experiment, the shell was removed, the experimental seed crystal was cleaned, and the surface state of the experimental seed crystal was observed and recorded. The seed crystal with alloy liquid flowing on the measured surface was axially sectioned, and the section surface was polished and corroded to observe the metallographic structure, and the remelting interface of the experimental seed crystal was determined. Then, the length from the remelting interface to the bottom of the experimental seed crystal was measured, and the original length of the seed crystal was subtracted from this length to obtain the length of the seed crystal remelting section. The experimental seed crystal with a seed crystal remelting section length of 3-4mm was used to prepare castings.

2. The method according to claim 1, characterized in that: The length of each experimental seed crystal gradually decreases in a gradient of 1-2 mm.

3. The method according to claim 1, characterized in that: By changing the wax rod size of the wax mold and the alloy type of the seed crystal and repeating the above process, the actual pouring process of seed crystals of different heights, different diameters and different alloy types can be simulated.

4. The method according to claim 1, characterized in that: The wax stick has a diameter of 5-8 mm and a length of 10-60 mm.

5. The method according to claim 1, characterized in that: The holding temperature is 1500-1550℃ and the pulling speed is 3-5mm / min.

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