A method for quickly determining the length of seed use in directional solidification of castings

Abstract

The application discloses a method for rapidly determining the length of seed crystals used in directional solidification of a casting, and the method comprises the following steps: preparing a wax mold, then performing slurry dipping and sand spraying on the wax mold to obtain a preliminary ceramic mold shell, then performing dewaxing and baking on the preliminary ceramic mold shell to obtain an experimental mold shell, matching experimental seed crystals into each seed crystal cavity of the experimental mold shell, the lengths of the experimental seed crystals matched into each seed crystal cavity being different, and the side portions of the experimental seed crystals being subjected to a size reduction treatment, so that channels for metal liquid flowing are formed between the seed crystal cavities, then placing the experimental mold shell in a solidification furnace to simulate the actual pouring process of the casting, removing the shell after the directional solidification experiment is completed, axially cutting the seed crystals with alloy liquid flowing through the seams on the size-reduced surfaces, and observing the metallographic structure of the cut surfaces by polishing and etching, so that the remelting interface of the experimental seed crystals is determined, and the shortest length of the seed crystals required for effectively inducing crystals in the directional solidification of the casting is rapidly determined.

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 crystal with the selected primary and secondary crystal orientations in the seed crystal cavity at the bottom of the mold shell in advance, and make the upper part of the seed crystal melt back 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, thereby obtaining 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 melt back. This ensures that the seed crystal can be smoothly seeded, and there will be no waste of material 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 will 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 seeding 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 to effectively seed the casting during directional solidification.

[0005] To this end, the present invention provides a method for quickly determining the shortest length of a seed crystal required for effective seeding, comprising the following steps:

[0006] Determine the seed crystal diameter to be used for directional solidification of castings according to the casting mold assembly plan;

[0007] Prepare wax molds, each wax mold including a base, 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 crystals to be used for directional solidification of the casting;

[0008] Then the wax mold is dipped in slurry and sanded to obtain a preliminary ceramic shell;

[0009] Afterwards, the preliminary ceramic shell is dewaxed and fired to obtain the experimental shell, and the cavity formed after the wax rod is dewaxed constitutes the seed crystal cavity;

[0010] Experimental seed crystals are inserted into each seed crystal cavity of the experimental mold. The lengths of the experimental seed crystals inserted into each seed crystal cavity are different. The lower ends of the experimental seed crystals are flush with the mold bottom plate. The sides of the experimental seed crystals are deburred to form channels for the flow of molten metal between the seed crystal cavities. The material of the experimental seed crystals is the same as that of the seed crystals to be used in the directional solidification of the casting.

[0011] The experimental mold shell was then placed in a solidification furnace to simulate the actual pouring process of the casting;

[0012] 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 3-4 mm was used to prepare castings.

[0013] Specifically, the length of each experimental seed crystal is gradually reduced in a gradient of 1-2 mm.

[0014] 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.

[0015] Specifically, the wax stick has a diameter of 5-8 mm and a length of 10-60 mm.

[0016] Specifically, the holding temperature is 1500-1550° C., and the pulling speed is 3-5 mm / min.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. By preparing a high-throughput experimental mold, multiple sets of seed crystal meltback data at different heights can be obtained through a single directional solidification experiment. Subsequently, by sectioning the experimental seed crystal and polishing and etching the cross-section to observe the metallographic structure, the meltback interface of the experimental seed crystal can be determined, thereby quickly determining the minimum length required for effective seed crystal seeding. Furthermore, by changing the wax rod size of the wax mold and the alloy type of the seed crystal, and repeating the mold and experimental process, multiple sets of seed crystal meltback data at different heights, diameters, and alloy types can be obtained.

[0019] 2. When preparing the experimental mold shell, the wax mold does not require a pouring system, which reduces the difficulty of mold assembly. In addition, 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 experimental process saves the time of heating, melting and pouring the master alloy, and the short pulling distance shortens the pouring time.

[0020] 3. By removing the amount of metal 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 seed crystal cross section to observe the metallographic structure to judge the remelting situation. By simply comparing the surface conditions of the removed surfaces of seed crystals at different heights, it is possible to quickly determine 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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.

[0022] Figure 1 This is a front view of the wax model of the present invention;

[0023] Figure 2 1. It is a top view of the wax model of the present invention;

[0024] Figure 3 It is the experimental shell diagram of the present invention;

[0025] Figure 4 Surface morphology of DD419 seed crystals at different heights after directional solidification experiments;

[0026] Figure 5 This is the metallographic structure of the longitudinal section of the 30mm high seed crystal of the present invention. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] In the description of the present invention, it should 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" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0030] A method for quickly determining the shortest length of a seed crystal required for effective seeding comprises the following steps:

[0031] Determine the seed crystal diameter to be used for directional solidification of castings according to the casting mold assembly plan;

[0032] 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 number of wax rods of the same size. 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.

[0033] Then the wax mold is dipped in slurry and sanded to obtain a preliminary ceramic shell;

[0034] 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 rod is dewaxed constitutes the seed crystal cavity;

[0035] Experimental seed crystals are inserted into each seed crystal cavity of the experimental mold. The lengths of the experimental seed crystals inserted into each seed crystal cavity are different. The lower ends of the experimental seed crystals are flush with the mold bottom plate. The sides of the experimental seed crystals are deburred to form channels for the flow of molten metal between the seed crystal cavities. The material of the experimental seed crystals is the same as that of the seed crystals to be used in the directional solidification of the casting.

[0036] The experimental mold shell was then placed in a solidification furnace to simulate the actual pouring process of the casting;

[0037] 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 undergoing a heat treatment. If the temperature at the top of the seed crystal reaches above the liquidus temperature, the seed crystal begins to melt back from the top, and the top surface is uneven. 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 a clear seam layer. Therefore, it is possible to infer and predict whether there will be remelting 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 remelting interface of the experimental seed crystal will be determined. Then, the length L from the remelting 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 remelting section. The shortest length required for effective seeding of the seed crystal is determined by comparing the remelting conditions of seed crystals at different heights. The experimental seed crystal with a seed crystal remelting section length of 3-4mm (that is, the seed crystal with the shortest length required for effective seeding) is used to prepare castings.

[0038] The present invention prepares a high-throughput experimental mold shell and obtains multiple sets of seed crystal meltback 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 meltback interface of the experimental seed crystal can be determined, and the shortest length required for effective seed crystal induction can be quickly determined.

[0039] When preparing the experimental mold shell, the wax mold does not require a pouring system, which reduces the difficulty of mold assembly. It also eliminates the need to prepare a master alloy before the experiment, reducing pouring costs. Furthermore, compared to conventional pouring, the experimental process saves time for heating, melting, and pouring the master alloy, and the short withdrawal distance shortens the experimental time. By removing the side of the seed crystal to form a flow surface for the molten metal to flow, there is no need to grind and corrode the seed crystal cross-section to observe the metallographic structure to determine the remelting situation. Simply by comparing the surface conditions of the removed surfaces of seed crystals at different heights, the presence of remelting can be quickly determined. Once the seed crystal remelting length is determined, the number of experimental seed crystal sections can be significantly reduced.

[0040] 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.

[0041] Specifically, the length of each experimental seed crystal gradually decreases by 1-2 mm, the diameter of the wax rod is 5-8 mm, the length is 10-60 mm, the holding temperature is 1500-1550° C., and the pulling speed is 3-5 mm / min.

[0042] Specific cases

[0043] A wax stick with a diameter of 6 mm and a height of 50 mm was used to assemble the mold. DD419 seed crystals with lengths of 20 mm, 22 mm, 24 mm, 26 mm, 28 mm, 30 mm, 32 mm, 34 mm, 36 mm, 38 mm, 40 mm, 42 mm, 44 mm, 46 mm, 48 mm, and 50 mm were selected, and the cross section of the seed crystals was all reduced by 1.5 mm. Figure 4 These are some seed crystals that have been shelled and cleaned after the experiment. From left to right, they are 24mm, 30mm, 36mm, 40mm, 46mm, and 50mm in length. The top surface of the 24mm seed crystal is flat, and no molten alloy is observed flowing and solidifying on the degassed surface. Starting from the 30mm seed crystal, the top surface is uneven. Due to the melting of the alloy at the top, the top has shown varying degrees of necking, and the degassed surface can be seen covered by the molten alloy flowing down from above. Therefore, it can be determined that under these casting conditions, meltback begins with the 30mm seed crystal.

[0044] Then the seed crystal that has melted back is axially sectioned, and the section surface is polished and etched to observe the metallographic structure, such as Figure 5 As 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. 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 by comparing 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 length of the seed crystal required for effective seeding is 34mm. Therefore, it was finally determined that a 34mm long seed crystal was selected as the seed crystal for casting under this casting condition.

[0045] Unless otherwise stated, for any of the technical solutions disclosed in the present invention, if a numerical range is disclosed, the disclosed numerical range is a preferred numerical range. Any person skilled in the art should understand that the preferred numerical range is merely a numerical range that is representative or has a more obvious technical effect among many feasible numerical values. Due to the large number of numerical values, it is impossible to enumerate them exhaustively. Therefore, the present invention discloses some numerical values ​​to illustrate the technical solutions of the present invention. Moreover, the numerical values ​​listed above should not be construed as limiting the scope of protection of the present invention.

[0046] 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, using bolts or screws to connect), 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 a casting process) (except where it is obviously impossible to use an integrated forming process).

[0047] In addition, unless otherwise stated, terms used in any of the technical solutions disclosed herein to represent positional relationships or shapes include states or shapes that are similar, analogous, or approximate. Any component provided by the present invention may be assembled from multiple separate components or may be a single component manufactured using an integral molding process.

[0048] The above embodiments are merely examples to clearly illustrate the present invention and are not intended to limit its implementation. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to provide an exhaustive list of all embodiments. Obvious variations or modifications arising therefrom remain 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 for directional solidification of castings according to the casting mold assembly plan; Prepare wax molds, each wax mold including a base, 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 crystals 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 the experimental shell, and the cavity formed after the wax rod is dewaxed constitutes the seed crystal cavity; Experimental seed crystals are inserted into each seed crystal cavity of the experimental mold. The lengths of the experimental seed crystals inserted into each seed crystal cavity are different. The lower ends of the experimental seed crystals are flush with the mold bottom plate. The sides of the experimental seed crystals are deburred to form channels for the flow of molten metal between the seed crystal cavities. The material of the experimental seed crystals is the same as that of the seed crystals to be used in the directional solidification of the casting. The experimental mold shell was 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 3-4 mm was used to prepare castings.

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

3. The method according to claim 1, wherein: 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, diameters, and alloy types can be simulated.

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

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

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