A fine-grain casting method for high-temperature alloy test rod

Abstract

The invention discloses a fine-grain casting method for a high-temperature alloy test rod, and belongs to the field of precision casting technology. The method mainly reduces the temperature gradient of the liquid phase of the alloy during solidification by means of high shell temperature, low casting temperature, rapid casting, etc., promotes columnar crystal-equiaxed crystal (CET) transformation, and the prepared high-temperature alloy test rod has a fine equiaxed crystal structure and does not have serious loose defects. The present invention does not require the use of other auxiliary equipment or additives, and only realizes the effective refinement of the solidification structure of the high-temperature alloy mechanical test rod through heat control during the casting process, and has the advantages of being simple and convenient, easy to operate, and low cost.

Description

Technical Field

[0001] The invention relates to the technical field of precision casting, and in particular to a fine-grain casting method for a high-temperature alloy test rod. Background Art

[0002] During the design and development of new casting high-temperature alloys, it is necessary to frequently test the mechanical properties of the alloys, and the mechanical properties of casting high-temperature alloys are closely related to their solidification structure state. Compared with coarse columnar crystals, fine equiaxed crystals can enable the alloy to obtain better medium and low temperature strength and toughness matching and fatigue performance.

[0003] Alloy solidification structure refinement is an important topic in the preparation of cast high-temperature alloys. The main methods of structure refinement are physical method, chemical method and thermal control method. The physical method mainly achieves structure refinement by interfering with the alloy solidification process through physical means such as mechanical vibration and electromagnetic stirring, but the required equipment is generally more complex and costly; the chemical method mainly increases the nucleation rate of the alloy during the solidification process by adding nucleating agents, thereby refining the structure, but this method is prone to introduce impurities such as inclusions into the alloy. The thermal control method mainly uses the method of casting heat control to achieve structure control, without the need for other auxiliary equipment or additives, and has the advantages of simplicity, convenience, easy operation and low cost. The present invention achieves effective refinement of the solidification structure of high-temperature alloy mechanical test bars and improves the strength and toughness matching of the alloy only through casting heat control and special casting process design. Summary of the invention

[0004] The object of the present invention is to provide a fine-grain casting method for a high-temperature alloy test bar, which can achieve fine-grain casting of a high-temperature alloy mechanical property test bar simply, conveniently and at low cost by controlling the casting temperature and the shell mold temperature without the aid of other auxiliary equipment and additives.

[0005] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0006] A fine-grain casting method for a high-temperature alloy test bar, the method comprising the following steps:

[0007] (1) Casting shell mold preparation: prepare the investment casting shell mold and preheat it in a muffle furnace;

[0008] (2) Alloy melt preparation: The master alloy is melted and kept warm in a semi-continuous vacuum induction furnace;

[0009] (3) Alloy casting: The shell mold preheated in step (1) is placed into a semi-continuous vacuum induction furnace, and after evacuation, it is moved to the casting position to quickly complete the casting.

[0010] The casting shell mold used in step (1) has a pouring cup, a sprue, an upper pouring plate, a lower pouring plate, and a casting test bar. There are 12 test bars on the shell mold, which are located between the upper and lower plates and are evenly distributed on the outer circumference of the pouring plate. The test bars can be used to process standard round bar mechanical property samples with a thread outer diameter not greater than 14 mm.

[0011] The casting shell mold used in step (1) includes a pouring cup, a sprue, an upper pouring plate, a lower pouring plate and a casting test rod, wherein: the top of the sprue is connected to the pouring cup, the middle is connected to the upper pouring plate, and the bottom is connected to the lower pouring plate. There are 12 casting test rods in total, which are located between the outer circumferences of the upper pouring plate and the lower pouring plate and are evenly distributed; the test rods can be used to process standard round rod mechanical property specimens with a thread outer diameter not greater than 14 mm.

[0012] In step (1), the casting shell is prepared for casting in the form of an empty shell wrapped with cotton. The empty shell wrapped with cotton means that the casting shell is insulated by being entirely coated with 1-2 layers of insulation cotton. The casting shell is coated with aluminum silicate wool of model "1430" and thickness of 10-30 mm.

[0013] In step (1), the shell mold covered with thermal insulation cotton is preheated in a muffle furnace, the preheating temperature is 1050-1150° C., and the insulation time is 4-6 hours.

[0014] In step (2), the high-temperature alloy master alloy ingot is melted in a crucible of a vacuum induction melting furnace and kept warm at a superheat of 15° C. to 40° C. It is prohibited to perform high-temperature overheating treatment on the alloy melt.

[0015] In step (3), the casting shell is taken out of the muffle furnace and quickly placed in the lower chamber of the semi-continuous vacuum induction melting furnace and evacuated. When the vacuum degree of the lower chamber reaches 1-10Pa, the trap door connecting the upper and lower chambers is opened, and the casting shell is raised to the casting position.

[0016] In step (3), casting is carried out immediately after the shell mold is in place, and the casting speed is not less than 1.5 kg / s.

[0017] After the casting shell is cooled to room temperature, the shell is cleaned and cut to complete the casting of the high-temperature alloy mechanical property test bar. After heat treatment and machining, the test bar can be tested for mechanical properties such as tensile strength, endurance, and creep. The high-temperature alloy test bar prepared by the present invention has a fine equiaxed crystal structure, and the grain size of the gauge section is not greater than 0.3 mm.

[0018] The present invention has the following beneficial effects:

[0019] The present invention is aimed at casting high-temperature alloys. The method adopts parameters such as high shell temperature and low casting temperature to control heat, reduce the temperature gradient of the liquid phase during the solidification process of the alloy, promote the columnar crystal-equiaxed crystal (CET) transformation, and ensure that the high-temperature alloy mechanical property test rod will not produce columnar crystals or coarse equiaxed crystals during the casting process. The prepared test rod has a fine equiaxed crystal structure and does not have serious loose defects, and has good medium and low temperature strength and toughness matching and fatigue performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the casting shell structure used in the present invention.

[0021] Figure 2 This is a physical picture of the casting shell mold used in the present invention.

[0022] Figure 3 The present invention provides a comparison of the macroscopic and low-power microstructures of the test rod prepared in the present invention and the ordinary sand-cast K4750 alloy mechanical property test rod; wherein: (a) the test rod of the present invention; (b) the ordinary sand-cast test rod.

[0023] In the figure: 1- pouring cup; 2- sprue; 3- upper pouring plate; 4- casting test rod; 5- lower pouring plate. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with specific embodiments.

[0025] Embodiment 1:

[0026] In a semi-continuous vacuum induction melting furnace, a 10kg coil and a 10kg crucible were used to melt the K4750 high-temperature alloy master alloy and cast the test bars. K4750 is a new type of cast nickel-based high-temperature alloy, and its solidification point is measured at 1354℃ in the furnace. The alloy melt is controlled to maintain a superheat of 20℃.

[0027] The casting shell used is as follows Figure 1-2 As shown, it is a 12-test-bar disc shell mold, specifically including a pouring cup (1), a sprue (2), an upper tundish (3), a lower tundish (5) and a casting test bar (4), wherein: the top of the sprue (2) is connected to the pouring cup (1), the middle is connected to the upper tundish (3), and the bottom is connected to the lower tundish (5), and there are 12 casting test bars in total, which are evenly distributed between the outer circumferences of the upper tundish and the lower tundish. When the alloy melt is cast, the melt first enters the lower tundish (5) through the sprue (2), and then is sequentially injected into the casting test bar (4) and the upper tundish (3).

[0028] Before pouring, double-layer aluminum silicate wool is used for insulation, and the temperature is kept at 1120℃ in the muffle furnace for 4 hours. After the alloy melt reaches the temperature, the shell mold is taken out of the muffle furnace and quickly placed in the lower chamber of the semi-continuous vacuum induction melting furnace to start vacuuming. When the vacuum degree of the lower chamber reaches 5Pa, the upper and lower chamber trap doors are opened, and the shell mold is raised to the casting position. After the shell mold is in place, the alloy melt is cast at 1374℃, and the casting process takes 2-5s. After the casting is completed, the shell mold is taken out from the lower chamber for air cooling.

[0029] Figure 3 The figure is a comparison of the macroscopic and low-power microstructures of the mechanical properties test bars of the present invention and ordinary sand casting K4750 alloy. It can be seen that the test bars prepared by the process of the present invention have fine equiaxed crystal structure, the grain refinement effect of the test bar gauge section is obvious, and the grain size is less than 0.3mm. The grain size of the ordinary sand casting test bar is larger.

[0030] The above embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make modifications to the embodiments without any creative contribution as needed. However, such modifications are protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A fine-grain casting method for a high-temperature alloy test bar, characterized in that: The method comprises the following steps: (1) Casting shell mold preparation: Prepare the investment casting shell mold and preheat it in a muffle furnace at a preheating temperature of 1050-1150°C; (2) Alloy melt preparation: melting and keeping the master alloy in a semi-continuous vacuum induction furnace, wherein the master alloy is a K4750 high temperature alloy master alloy; (3) Alloy casting: The preheated shell mold of step (1) is placed into a semi-continuous vacuum induction furnace, and after evacuation, it is moved to the casting position to quickly complete the casting; In step (2), after the master alloy is melted in the crucible of the vacuum induction melting furnace, it is kept warm at a superheat of 15° C. to 40° C.; high-temperature overheating treatment of the alloy melt is prohibited; In step (3), casting is performed immediately after the shell mold is in place, and the casting speed is not less than 1.5 kg / s; in step (3), the prepared high-temperature alloy test rod has a fine equiaxed crystal structure, and the grain size of the gauge section is not greater than 0.3 mm. The high temperature alloy test rod is a standard round rod with an outer diameter not greater than 14 mm.

2. The fine grain casting method of the high temperature alloy test bar according to claim 1, characterized in that: The casting shell mold used in step (1) includes a pouring cup, a sprue, an upper pouring plate, a lower pouring plate and a casting test rod, wherein: the top of the sprue is connected to the pouring cup, the middle is connected to the upper pouring plate, and the bottom is connected to the lower pouring plate. There are 12 casting test rods in total, which are located between the outer circumferences of the upper pouring plate and the lower pouring plate and are evenly distributed; the test rods can be used to process standard round rod mechanical property specimens with a thread outer diameter not greater than 14 mm.

3. The high temperature alloy test bar fine grain casting method according to claim 1, characterized in that: In step (1), the casting shell is prepared for casting in the form of an empty shell wrapped with cotton, and the empty shell wrapped with cotton means that the casting shell is insulated by being entirely coated with 1-2 layers of thermal insulation cotton.

4. The high temperature alloy test bar fine grain casting method according to claim 3, characterized in that: In step (1), the casting shell is coated with aluminum silicate wool of model "1430" and thickness of 10-30 mm for insulation.

5. The fine-grained casting method for a high-temperature alloy test bar according to claim 3, characterized in that: In step (1), the shell mold covered with thermal insulation cotton is preheated in a muffle furnace, the preheating temperature is 1050-1150° C., and the insulation time is 4-6 hours.

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