A method for improving the performance of a melting crucible for gas atomization powder making

Abstract

This invention belongs to the field of powder metallurgy and metal additive manufacturing technology, and relates to a method for improving the performance of melting crucibles used in gas atomization powder production. First, a graphite core is baked: the graphite core is placed inside an alumina prefabricated crucible in a vacuum induction melting furnace using a suspension rod. The crucible is heated using a medium-frequency power supply, ensuring uniform heating inside the crucible and gradually removing moisture to prevent cracking. Then, a staged heating method is used to bake the crucible to ensure complete removal of moisture, maintaining structural stability during high-temperature melting and preventing cracking. The baking environment is controlled so that the entire baking process takes place within a vacuum induction melting furnace to prevent the crucible from absorbing new moisture during heating, ensuring thorough drying. This invention can be used to improve the performance of melting crucibles used in gas atomization powder production, providing a reliable technical means for the preparation of high-quality metal powders.

Description

Technical Field

[0001] This invention belongs to the field of metal powder preparation technology, and in particular relates to a method for improving the performance of melting crucibles used in gas atomization powder preparation. Background Technology

[0002] Argon atomization is the mainstream preparation process for high-temperature alloy powders. High-quality, pure high-temperature alloy powders are the foundation and key to high-performance powder metallurgy components. The purity control of raw materials for powder metallurgy mainly focuses on powder preparation. Inclusions in powder metallurgy are primarily non-metallic ceramic particles, containing Al, Si, Mg, Zr, etc., mainly derived from refractory materials such as crucibles used in atomization powder preparation, as well as deoxidation products from the smelting process. The inclusions and the matrix material have different coefficients of thermal expansion and elastic moduli, causing asynchronous deformation under heat and applied stress, leading to stress concentration at the inclusion-metal interface and surrounding areas. During hot working, the difference in deformation rates between inclusions and the matrix material makes it easy for microcracks to initiate in the inclusions themselves or at the inclusion-matrix interface, gradually developing into fatigue crack initiations. These crack initiations propagate along the inclusion-matrix interface under operating conditions, ultimately leading to unstable fracture of the matrix material, significantly impacting fatigue performance.

[0003] In the gas atomization preparation of high-temperature alloy powders, the melting crucible is a crucial component for supporting and melting the metal. The melting crucible used for atomization powder preparation is an isostatically pressed alumina prefabricated crucible. The prefabricated crucible has excellent internal refractory material density, good overall performance stability, and a clean, smooth inner surface. It is also easy to mass-produce, offering advantages in convenience, stability, cleanliness, and flexibility compared to traditional knotted crucibles. During atomization powder preparation, the purification of the alloy material through vacuum induction remelting mainly depends on the vacuum impurity removal effect; the higher the vacuum level, the more significant the impurity removal effect. However, in actual production, the alumina prefabricated crucible absorbs moisture from the air during storage, leading to moisture accumulation on the surface and inside the crucible. During the initial melting, the high temperature can cause rapid evaporation of moisture, increasing the risk of crucible cracking. Meanwhile, during the initial smelting, the large amount of gas released from the crucible leads to an increase in the oxide film of the alloy melt and poor smelting vacuum. Crucible spalling and oxide products can easily cause non-metallic inclusions and excessive oxygen content in the powder, resulting in unqualified powder that is scrapped, which seriously affects the powder quality.

[0004] Therefore, there is an urgent need for an improved pretreatment method for precast crucibles to ensure that they are fully dried before first use, to avoid cracking, to improve the melting vacuum level, and to reduce the impurity content in the powder, thereby improving the quality of the powder. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the performance of melting crucibles used in gas atomization powder production. Specifically, for pre-made crucibles before the first atomization powder production and melting, the method aims to remove moisture from the pre-made crucibles through a specific baking process, prevent the crucibles from cracking during the first use, improve the melting vacuum and powder purity, and thus improve powder quality.

[0006] To solve this technical problem, the technical solution of the present invention is as follows:

[0007] A method for improving the performance of melting crucibles used in gas atomization powder production involves first baking a graphite core: the graphite core is placed inside a prefabricated crucible in a vacuum induction melting furnace using a suspension rod, and the crucible is heated using a medium-frequency power supply. The graphite core has excellent thermal conductivity, which ensures uniform heating inside the crucible, gradually removes moisture from the crucible, and prevents cracking.

[0008] The crucible is then baked using a staged heating method to ensure complete removal of moisture from the inside, maintaining structural stability during high-temperature melting and preventing cracking. The power of the intermediate frequency power supply is gradually adjusted from 20KW to 60KW.

[0009] The method specifically includes the following steps:

[0010] Step 1: Place the graphite core into the pre-made crucible of the vacuum induction melting furnace using a hanging rod, turn on the medium frequency power supply for heating and baking, set the power of the medium frequency power supply to 30±2KW, and the baking time to 1h to 3h, in order to initially remove the moisture on the surface of the crucible and prevent surface cracking.

[0011] Step 2: Adjust the power of the medium frequency power supply to 40±2KW and continue to heat and bake the crucible for 2 to 4 hours to further remove the moisture adsorbed inside the crucible and ensure that the internal temperature of the crucible gradually increases to prevent stress cracking caused by internal moisture in subsequent melting.

[0012] Step 3: Adjust the power of the medium frequency power supply to 50±2KW and continue to heat and bake the crucible for 1 to 3 hours to ensure that the moisture inside the crucible is completely removed, so that the crucible can maintain structural stability during high-temperature melting and avoid cracking.

[0013] Step 4: After baking, turn off the intermediate frequency power supply and cover the crucible with insulation cotton to keep it from being affected by external moisture during the cooling process and prevent it from absorbing moisture from the air and becoming damp.

[0014] The baking times in steps one, two, and three should be adjusted according to the size of the crucible to achieve the best moisture removal effect. The baking time t of the crucible at each power level should meet the following conditions:

[0015] The inner wall thickness of the crucible is d < 10 mm, and the stepped baking time t is 1 h ≤ t < 1.5 h, 2 h ≤ t < 2.5 h, and 1 h ≤ t < 1.5 h respectively.

[0016] The inner wall thickness of the crucible is 10mm≤d<20mm, and the step baking times are 1.5h≤t<2h, 2.5h≤t<3h, and 1.5h≤t<2h respectively.

[0017] The inner wall thickness of the crucible is 20mm≤d<30mm, and the stepped baking times are 2h≤t<2.5h, 3h≤t<3.5h, and 2h≤t<2.5h respectively.

[0018] The inner wall thickness of the crucible is 30mm to 40mm, and the stepped baking times are 2.5h to 3h, 3.5h to 4h, and 2.5h to 3h respectively. The shape and size of the graphite core match the inner cavity of the prefabricated crucible, and the distance between the graphite core and the inner wall of the crucible is 8mm to 20mm to ensure that the crucible is heated evenly during the baking process and to prevent local cracking caused by uneven heating.

[0019] The entire baking process is carried out in a vacuum induction melting furnace to prevent the crucible from absorbing new moisture during heating and to ensure it is thoroughly dried. The heating and baking process is conducted in a vacuum or inert gas environment to prevent the crucible from absorbing new moisture or undergoing oxidation at high temperatures, ensuring complete removal of moisture from the inside of the crucible and improving the melting vacuum level of the crucible.

[0020] The insulating cotton can fully cover the entire outer surface of the crucible when covering it, so as to prevent external moisture from entering the inner cavity of the crucible and ensure that the crucible remains dry after cooling, providing ideal conditions for subsequent melting.

[0021] The alumina crucible treated by the aforementioned method can achieve a vacuum level below 10^-1 Pa during the first melting process, effectively reducing the oxygen content of the metal powder, decreasing non-metallic inclusions, and improving powder purity. Crucible baking removes gas from the crucible, reducing gas release during melting. The vacuum level reflects the effectiveness of the baking process, as the crucible releases gas during heating, affecting the vacuum level. A higher vacuum level indicates better moisture removal during crucible baking.

[0022] The process parameters described above are applicable to the baking and heat pretreatment of alumina crucibles, magnesium oxide crucibles, and calcium oxide crucibles to improve their performance and service life during high-temperature melting. This method is particularly suitable for alumina crucibles, ensuring thorough removal of moisture while also providing uniform heating and preventing localized cracking.

[0023] The beneficial effects of this invention are:

[0024] This invention employs a graphite core to bake a prefabricated crucible using a staged heating method. This effectively removes moisture absorbed from the crucible's surface and interior, thereby reducing crucible cracking, improving the vacuum level and powder purity during the initial melting process, preventing the powder from being scrapped due to excessive oxygen content and inclusions, improving crucible performance, and enhancing powder quality. Specifically, it offers the following technical advantages:

[0025] 1. Improve crucible performance: By using a graphite core in conjunction with a medium-frequency power supply for staged heating and baking, moisture on the surface and inside of the crucible can be effectively removed, reducing cracking during high-temperature melting and extending the service life of the crucible.

[0026] 2. Increase the vacuum level of melting: A fully dried crucible helps to increase the vacuum level of the first melting, reduce the contact between the molten metal and oxygen, reduce the oxygen content of the powder, and ensure the purity of the powder.

[0027] 3. Improve powder quality: Avoid impurities caused by crucible cracking, improve the purity of metal powder, and thus improve powder quality.

[0028] 4. Simple process: Using a conventional vacuum induction melting furnace and medium frequency power supply, combined with graphite core baking, the process is simple, easy to operate, and suitable for industrial production. Attached Figure Description

[0029] To more clearly illustrate the technical solutions implemented in this invention, the accompanying drawings used in the embodiments of this invention will be briefly explained below. Obviously, the drawings described below are merely some embodiments of this invention. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0030] Figure 1 This describes the condition after the prefabricated crucible is used for the first melting process in the method of this invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The features of various aspects of the embodiments of the present invention will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can also be practiced without these specific details. The following description of the embodiments is merely intended to provide a better understanding of the invention by illustrating examples. The invention is not limited to any specific setups and methods provided below, but covers all improvements, substitutions, etc., to product structures and methods without departing from the spirit of the invention.

[0033] In the various accompanying drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the invention.

[0034] Example 1:

[0035] 1. Using a pre-fabricated alumina crucible with dimensions of Φ360x500mm and a wall thickness of 20mm, place the graphite core inside the pre-fabricated alumina crucible using a lifting rod, and then place the crucible in a vacuum induction melting furnace. The graphite core has dimensions of Φ300x700mm.

[0036] 2. Turn on the intermediate frequency power supply and set the power to 30KW. Bake the crucible for 2 hours as required in step one to initially remove the moisture on the surface of the crucible.

[0037] 3. Adjust the power of the medium frequency power supply to 40KW, and continue to bake the crucible for 3 hours as required in step two to further remove the adsorbed moisture inside the crucible.

[0038] 4. Adjust the power of the medium frequency power supply to 50KW, and continue baking for 2 hours as required in step 3 to completely remove the moisture inside the crucible.

[0039] 5. Turn off the intermediate frequency power supply, cover the crucible with insulating cotton to prevent it from getting damp, and ensure that the crucible remains dry after cooling to provide good conditions for subsequent melting.

[0040] 6. During the first melting process, the vacuum degree of the prefabricated crucible after baking reached 0.08 Pa, and no cracks appeared on the surface of the crucible after melting. Figure 1 The prepared metal powder showed satisfactory oxygen content and non-metallic inclusions, meeting the technical requirements. In contrast, the vacuum level during the first melting of the pre-fabricated alumina crucible in the prior art is around 1 Pa, and the vacuum level is measured using a vacuum gauge.

[0041] Example 2:

[0042] 1. Using a pre-fabricated magnesium oxide crucible with dimensions of Φ400x650mm and a wall thickness of 12mm, place the graphite core inside the pre-fabricated alumina crucible using a lifting rod, and then place the crucible in a vacuum induction melting furnace. The graphite core has dimensions of Φ340x800mm.

[0043] 2. Turn on the intermediate frequency power supply and set the power to 30KW. Bake the crucible for 1.5 hours as required in step one to initially remove the moisture on the surface of the crucible.

[0044] 3. Adjust the power of the medium frequency power supply to 40KW, and continue to bake the crucible for 2.5 hours as required in step two to further remove the adsorbed moisture inside the crucible.

[0045] 4. Adjust the power of the medium frequency power supply to 50KW, and continue baking for 1.5 hours as required in step 3 to ensure that the moisture inside the crucible is completely removed.

[0046] 5. Turn off the intermediate frequency power supply, cover the crucible with insulating cotton to prevent it from getting damp, and ensure that the crucible remains dry after cooling to provide good conditions for subsequent melting.

[0047] 6. During the first melting of the prefabricated crucible after baking, the vacuum degree reached 0.05 Pa, and the oxygen content and non-metallic inclusions of the prepared metal powder both met the technical requirements. In contrast, the vacuum degree of the prefabricated alumina crucible in the prior art during the first melting is around 1.2 Pa.

[0048] Example 3:

[0049] 1. Using a pre-fabricated alumina crucible with dimensions of Φ450x750mm and a wall thickness of 30mm, place the graphite core inside the pre-fabricated alumina crucible using a lifting rod, and then place the crucible in a vacuum induction melting furnace. The graphite core has dimensions of Φ360x900mm.

[0050] 2. Turn on the intermediate frequency power supply and set the power to 30KW. Bake the crucible for 2.5 hours as required in step one to initially remove the moisture on the surface of the crucible.

[0051] 3. Adjust the power of the medium frequency power supply to 40KW, and continue to bake the crucible for 3.5 hours as required in step two to further remove the adsorbed moisture inside the crucible.

[0052] 4. Adjust the power of the medium frequency power supply to 50KW, and continue baking for 2.5 hours as required in step three to ensure that the moisture inside the crucible is completely removed.

[0053] 5. Turn off the intermediate frequency power supply, cover the crucible with insulating cotton to prevent it from getting damp, and ensure that the crucible remains dry after cooling to provide good conditions for subsequent melting.

[0054] 6. During the first melting of the precast crucible after baking, the vacuum degree reached 0.06 Pa. The oxygen content and non-metallic inclusions of the prepared metal powder both met the technical requirements. The vacuum degree of conventional precast alumina crucible during the first melting is about 1.4 Pa.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A method for improving the performance of a melting crucible used in gas atomization powder production, characterized in that: The method first uses a graphite core for baking: the graphite core is placed in a prefabricated crucible in a vacuum induction melting furnace by means of a hanging rod, and the crucible is heated by a medium frequency power supply; Then, the crucible is baked using a staged heating method to ensure that the moisture inside the crucible is completely removed, so that the crucible maintains structural stability during high-temperature melting and avoids cracking; specifically, the following steps are included: Step 1: Place the graphite core into the pre-made crucible of the vacuum induction melting furnace using a hanging rod, turn on the medium frequency power supply for heating and baking, set the power of the medium frequency power supply to 30±2KW, and the baking time to 1h to 3h, in order to initially remove the moisture on the surface of the crucible and prevent surface cracking. Step 2: Adjust the power of the medium frequency power supply to 40±2 KW and continue to heat and bake the crucible for 2 to 4 hours to further remove the moisture adsorbed inside the crucible and ensure that the internal temperature of the crucible gradually increases to prevent stress cracking caused by internal moisture in subsequent melting. Step 3: Adjust the power of the medium frequency power supply to 50±2 KW and continue to heat and bake the crucible for 1 to 3 hours to ensure that the moisture inside the crucible is completely removed, so that the crucible can maintain structural stability during high-temperature melting and avoid cracking. Step 4: After baking, turn off the medium frequency power supply and cover the crucible with insulation cotton to keep it from being affected by external moisture during the cooling process and prevent it from absorbing moisture from the air and becoming damp. The baking times in steps one, two, and three should be adjusted according to the size of the crucible to achieve the best moisture removal effect. The baking time t of the crucible at each power level should meet the following conditions: The inner wall thickness of the crucible is d < 10 mm, and the stepped baking time t is 1 h ≤ t < 1.5 h, 2 h ≤ t < 2.5 h, and 1 h ≤ t < 1.5 h respectively. The inner wall thickness of the crucible is 10mm≤d<20mm, and the step baking times are 1.5h≤t<2h, 2.5h≤t<3h, and 1.5h≤t<2h respectively. The inner wall thickness of the crucible is 20mm≤d<30mm, and the stepped baking times are 2h≤t<2.5h, 3h≤t<3.5h, and 2h≤t<2.5h respectively. The inner wall thickness of the crucible is 30mm to 40mm, and the step baking times are 2.5h to 3h, 3.5h to 4h, and 2.5h to 3h respectively. The shape and size of the graphite core are matched with the inner cavity of the prefabricated crucible. The distance between the graphite core and the inner wall of the crucible is 8mm to 20mm to ensure that the crucible is heated evenly during the baking process and to prevent local cracking caused by uneven heating.

2. The method according to claim 1, characterized in that: The heating and baking process is carried out in a vacuum or inert gas environment to prevent the crucible from absorbing new moisture or undergoing oxidation at high temperatures, ensuring the complete removal of moisture inside the crucible and improving the melting vacuum level of the crucible.

3. The method according to claim 1, characterized in that: The insulating cotton can fully cover the entire outer surface of the crucible when covering it, so as to prevent external moisture from entering the inner cavity of the crucible and ensure that the crucible remains dry after cooling, providing ideal conditions for subsequent melting.

4. The method according to claim 1, characterized in that: The crucible is an alumina crucible.

5. The method according to claim 1, characterized in that: The crucible treated by the method achieved a vacuum level of 10 during the first melting process. -1 To improve powder purity, Pa is below 1.

6. The method according to claim 1, characterized in that: The crucible used in the method is a magnesium oxide crucible.

7. The method according to claim 1, characterized in that: The crucible used in the method is a calcium oxide crucible.

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