Method for improving use performance of smelting crucible for gas atomization powder preparation

Abstract

The invention belongs to the technical field of powder metallurgy and metal additive manufacturing, and relates to a method for improving the usability of a smelting crucible for gas atomization powder.The method comprises the steps that firstly, a graphite core is used for baking, specifically, the graphite core is placed in an aluminum oxide prefabricated crucible of a vacuum induction smelting furnace through a hanging rod, and the crucible is heated through a medium-frequency power source; the inside of the crucible can be uniformly heated, moisture in the crucible is gradually removed, and the crucible is prevented from cracking. And then the crucible is baked in a staged heating mode, so that moisture in the crucible is thoroughly removed, the structure of the crucible is kept stable during high-temperature smelting, and cracking is avoided. And the baking environment is controlled, so that the whole baking process is carried out in the vacuum induction melting furnace, the crucible is prevented from adsorbing new moisture in the heating process, and sufficient drying of the crucible is ensured. The method can be used for improving the use performance of the smelting crucible for gas atomization powder preparation, and a reliable technical means is provided for preparation of high-quality metal powder.

Description

Technical Field

[0001] The invention belongs to the technical field of metal powder preparation, and in particular relates to a method for improving the performance of a smelting crucible for gas atomization powder preparation. Background Art

[0002] Argon atomization is the mainstream preparation process for high-temperature alloy powder. High-quality pure high-temperature alloy powder is the basis and key to high-performance powder high-temperature alloy components. The purity control of powder high-temperature alloy raw materials is mainly concentrated in powder preparation. The inclusions in powder high-temperature alloys are mainly non-metallic ceramic particles, whose components include A1, Si, Mg, Zr, etc., which mainly come from refractory materials such as crucibles for atomization powder making, and deoxidation products during the smelting process. The inclusions and the material matrix have different thermal expansion coefficients and elastic moduli, so that the deformation of the two under heat and external stress cannot be synchronized, causing stress concentration at the interface between these inclusions and the metal and the surrounding area. During the hot processing of the material, due to the difference in deformation rate between the inclusions and the matrix material, microcracks are easily initiated in the inclusions themselves or between the inclusions and the matrix interface, and gradually develop into fatigue crack sources. Under the working conditions, this crack source extends along the interface between the inclusions and the matrix, eventually leading to the instability fracture of the matrix material, which has a significant impact on the fatigue performance.

[0003] In the gas atomization preparation process of high-temperature alloy powder, the melting crucible is an important component for carrying and melting metal. The melting crucible for atomization powder making adopts an isostatically pressed alumina prefabricated crucible. The internal refractory material of the prefabricated crucible has excellent density, good overall performance stability, and a clean and smooth inner surface. It is also easy to mass-produce. Compared with traditional knotted crucibles, it has the advantages of better convenience, stability, cleanliness and flexibility. In the atomization powder making process, the purification of the alloy material by vacuum induction remelting mainly depends on the vacuum impurity removal effect. The higher the vacuum degree, the more obvious the impurity removal effect. However, in actual production, the alumina prefabricated crucible absorbs moisture from the air during the storage process, resulting in moisture enrichment on the surface and inside of the crucible. When the crucible is first smelted, it is easy to cause rapid evaporation of moisture due to high-temperature heating, increasing the risk of cracking the crucible. At the same time, during the first smelting, due to the large amount of gas released from the crucible, the alloy melt oxide film increases and the smelting vacuum is poor. The crucible peeling and oxide products can easily cause non-metallic inclusions and oxygen content in the powder to exceed the standard, resulting in the powder being unqualified and scrapped, seriously affecting the powder quality.

[0004] Therefore, an improved pre-crucible pretreatment method is urgently needed to ensure that the pre-crucible can be fully dried before the first use to avoid cracking, improve the smelting vacuum level, reduce the impurity content in the powder, and thus improve the quality of the powder. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the performance of a melting crucible for gas atomization powder making, targeting a prefabricated crucible before the first atomization powder making melting, aiming to remove moisture in the prefabricated crucible through a specific baking process, prevent the crucible from cracking during the first use, improve the melting vacuum and powder purity, and thus improve the powder quality.

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

[0007] A method for improving the performance of a melting crucible for gas atomization powder making, the method first uses a graphite core for baking: the graphite core is placed in a prefabricated crucible of a vacuum induction melting furnace through a suspension rod, and the crucible is heated by a medium frequency power supply. The graphite core has excellent thermal conductivity, which can make the inside of the crucible evenly heated, gradually remove moisture in the crucible, and prevent the crucible from cracking.

[0008] Then the crucible is baked by heating up in stages to ensure that the moisture inside the crucible is completely removed, so that the crucible maintains a stable structure during high-temperature smelting to avoid cracking. The power of the medium-frequency power supply is gradually adjusted from 20KW to 60KW.

[0009] The method specifically comprises the following steps:

[0010] Step 1: Place the graphite core in a prefabricated crucible of a vacuum induction melting furnace through a suspension rod, turn on the medium frequency power supply for heating and baking, set the medium frequency power supply power to 30±2KW, and the baking time to 1h to 3h to preliminarily remove moisture from the crucible surface to 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 2h to 4h to further remove the moisture adsorbed inside the crucible, ensure that the temperature inside the crucible gradually increases, and prevent the internal moisture from causing stress cracking in subsequent smelting;

[0012] Step 3: Adjust the power of the medium frequency power supply to 50±2KW, and continue to heat and bake the crucible for 1h to 3h to ensure that the moisture inside the crucible is completely removed, so that the crucible maintains a stable structure during high-temperature smelting to avoid cracking;

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

[0014] The selection of baking time in step 1, step 2 and step 3 is adjusted according to the size of the crucible to achieve the best water removal effect. The baking time t of the crucible at each power should meet the following conditions:

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

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

[0017] The inner wall thickness of the crucible is 20mm≤d<30mm, and the step baking time is 2h≤t<2.5h, 3h≤t<3.5h, and 2h≤t<2.5h;

[0018] The thickness of the inner wall of the crucible is 30mm to 40mm, and the step baking time is 2.5h to 3h, 3.5h to 4h, and 2.5h to 3h. 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 evenly heated during the baking process and 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 the heating process and ensure that it is fully dried. The heating baking process is carried out in a vacuum or inert gas environment to prevent the crucible from absorbing new moisture or oxidation reaction at high temperature, ensure the complete removal of moisture inside the crucible, and improve the melting vacuum level of the crucible.

[0020] When covering the crucible, the heat-insulating cotton can fully wrap the entire outer surface of the crucible to prevent external moisture from entering the inner cavity of the crucible, ensure that the crucible remains in a dry state after cooling, and provide ideal conditions for subsequent smelting.

[0021] The vacuum degree of the alumina crucible treated by the method can reach below 10^-1Pa during the first smelting, thereby effectively reducing the oxygen content of the metal powder, reducing the non-metallic inclusions in the powder, and improving the purity of the powder. Crucible baking is to remove the gas in the crucible and reduce the outgassing during the smelting process. The vacuum degree is a reflection of the effect of crucible baking, because the crucible will release gas when heated during smelting, affecting the vacuum level. The better the vacuum degree, the better the removal of moisture in the crucible baking.

[0022] The process parameters in the above steps are applicable to the baking heat pretreatment of alumina crucibles, magnesium oxide crucibles, and calcium oxide crucibles to improve their performance and service life in high-temperature smelting. It is particularly suitable for alumina crucibles. The method can ensure that the moisture inside the alumina crucible is completely removed, and it can also be heated evenly to prevent local cracking.

[0023] The beneficial effects of the present invention are:

[0024] The present invention uses a graphite core to bake the prefabricated crucible in a staged heating manner, fully removing the moisture absorbed on the surface and inside of the crucible, thereby reducing the cracking of the crucible, improving the vacuum level and powder purity of the first smelting, avoiding the problem of powder oxygen content and inclusions exceeding the standard and being scrapped, improving the performance of the crucible, and improving the quality of the powder. The specific technical effects are as follows:

[0025] 1. Improve the performance of the crucible: By using the graphite core and the medium frequency power supply to heat up and bake in stages, the moisture on the surface and inside of the crucible can be effectively removed, the cracking of the crucible during high-temperature smelting can be reduced, and the service life of the crucible can be extended.

[0026] 2. Improve the vacuum degree of melting: A fully dried crucible helps to improve the vacuum degree 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 help improve powder quality.

[0028] 4. Simple process: using conventional vacuum induction melting furnace and medium frequency power supply, combined with graphite core for baking, the process is simple, easy to operate, and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions implemented in the present invention, the following is a brief explanation of the drawings required to be used in the examples of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 This is the condition of the prefabricated crucible after first melting and use in the method of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 making creative work are within the scope of protection of the present invention.

[0032] The features of various aspects of the embodiments of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to fully understand the present invention. However, it is obvious to those skilled in the art that the present invention can also be implemented without these specific details. The following description of the embodiments is only for a better understanding of the present invention by illustrating examples of the present invention. The present invention is not limited to any specific settings and methods provided below, but covers all product structures, any improvements, replacements, etc. of methods covered without departing from the spirit of the present invention.

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

[0034] Embodiment 1:

[0035] 1. Use an alumina prefabricated crucible with a size of Φ360x500mm and a wall thickness of 20mm, place the graphite core in the prefabricated alumina crucible through a hanger, and place the crucible in a vacuum induction melting furnace. The size of the graphite core is Φ300x700mm.

[0036] 2. Turn on the medium frequency power supply, set the power to 30KW, and bake the crucible for 2 hours according to the requirements of step 1 to initially remove moisture from the surface of the crucible.

[0037] 3. Adjust the medium frequency power supply to 40KW, and continue to bake the crucible for 3 hours according to the requirements of step 2 to further remove the adsorbed moisture inside the crucible.

[0038] 4. Adjust 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 medium frequency power supply, cover the crucible with insulation cotton to prevent it from getting wet, and ensure that the crucible remains dry after cooling, providing good conditions for subsequent smelting.

[0040] 6. During the first melting of the prefabricated crucible after baking, the vacuum degree reached 0.08Pa, and no cracks appeared on the surface of the crucible after melting ( Figure 1 ), the oxygen content and non-metallic inclusions of the prepared metal powder meet the technical index requirements. In contrast, the vacuum degree of the prefabricated alumina crucible in the prior art during the first smelting is about 1Pa, and the vacuum degree is measured by a vacuum gauge.

[0041] Embodiment 2:

[0042] 1. Use a magnesium oxide prefabricated crucible with a size of Φ400x650mm and a wall thickness of 12mm, place the graphite core in the prefabricated alumina crucible through a suspension rod, and place the crucible in a vacuum induction melting furnace. The size of the graphite core is Φ340x800mm.

[0043] 2. Turn on the medium frequency power supply, set the power to 30KW, and bake the crucible for 1.5 hours according to the requirements of step 1 to initially remove moisture from the surface of the crucible.

[0044] 3. Adjust the medium frequency power supply to 40KW, and continue to bake the crucible for 2.5 hours according to the requirements of step 2 to further remove the adsorbed moisture inside the crucible.

[0045] 4. Adjust 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 medium frequency power supply, cover the crucible with insulation cotton to prevent it from getting wet, and ensure that the crucible remains dry after cooling, providing good conditions for subsequent smelting.

[0047] 6. The vacuum degree of the prefabricated crucible after baking treatment reaches 0.05Pa during the first melting, and the oxygen content and non-metallic inclusions of the prepared metal powder meet the technical index requirements. In contrast, the vacuum degree of the prefabricated alumina crucible in the prior art during the first melting is about 1.2Pa.

[0048] Embodiment 3:

[0049] 1. Use an alumina prefabricated crucible with a size of Φ450x750mm and a wall thickness of 30mm, place the graphite core in the prefabricated alumina crucible through a hanger, and place the crucible in a vacuum induction melting furnace. The size of the graphite core is Φ360x900mm.

[0050] 2. Turn on the medium frequency power supply, set the power to 30KW, and bake the crucible for 2.5 hours according to the requirements of step 1 to initially remove moisture from the surface of the crucible.

[0051] 3. Adjust the medium frequency power supply to 40KW, and continue to bake the crucible for 3.5 hours according to the requirements of step 2 to further remove the adsorbed moisture inside the crucible.

[0052] 4. Adjust the medium frequency power supply to 50KW and continue baking for 2.5 hours as required in step 3 to ensure that the moisture inside the crucible is completely removed.

[0053] 5. Turn off the medium frequency power supply, cover the crucible with insulation cotton to prevent it from getting wet, and ensure that the crucible remains dry after cooling, providing good conditions for subsequent smelting.

[0054] 6. The vacuum degree of the prefabricated crucible after baking treatment reaches 0.06Pa during the first melting. The oxygen content and non-metallic inclusions of the prepared metal powder meet the technical index requirements. The vacuum degree of the conventional prefabricated alumina crucible during the first melting is about 1.4Pa.

[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 technician familiar with the field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A method for improving the performance of a melting crucible for gas atomization powder making, characterized in that: The method first uses a graphite core for baking: the graphite core is placed in a prefabricated crucible of a vacuum induction melting furnace through a suspension rod, and the crucible is heated by a medium frequency power supply; Then, the crucible is baked by heating up in stages to ensure that the moisture inside the crucible is completely removed, so that the crucible maintains a stable structure during high-temperature smelting to avoid cracking; the power of the medium-frequency power supply is gradually adjusted from 20KW to 60KW.

2. The method according to claim 1, characterized in that: The specific steps include: Step 1: Place the graphite core in a prefabricated crucible of a vacuum induction melting furnace through a suspension rod, turn on the medium frequency power supply for heating and baking, set the medium frequency power supply power to 30±2KW, and the baking time to 1h to 3h to preliminarily remove moisture from the crucible surface to prevent surface cracking; Step 2: Adjust the power of the medium frequency power supply to 40±2KW, and continue to heat and bake the crucible for 2h to 4h to further remove the moisture adsorbed inside the crucible, ensure that the temperature inside the crucible gradually increases, and prevent the internal moisture from causing stress cracking in subsequent smelting; Step 3: Adjust the power of the medium frequency power supply to 50±2KW, and continue to heat and bake the crucible for 1h to 3h to ensure that the moisture inside the crucible is completely removed, so that the crucible maintains a stable structure during high-temperature smelting to avoid cracking; Step 4: After baking, turn off the medium frequency power supply and cover the crucible with insulation cotton to keep the crucible from being affected by external moisture during the cooling process to prevent it from absorbing moisture in the air and getting damp during the cooling process.

3. The method according to claim 1, characterized in that: The selection of baking time in step 1, step 2 and step 3 is adjusted according to the size of the crucible to achieve the best water removal effect. The baking time t of the crucible at each power should meet the following conditions: The thickness of the inner wall of the crucible is d<10mm, and the step baking time t is 1h≤t<1.5h, 2h≤t<2.5h, 1h≤t<1.5h; The thickness of the inner wall of the crucible is 10mm≤d<20mm, and the step baking time is 1.5h≤t<2h, 2.5h≤t<3h, and 1.5h≤t<2h; The inner wall thickness of the crucible is 20mm≤d<30mm, and the step baking time is 2h≤t<2.5h, 3h≤t<3.5h, and 2h≤t<2.5h; The thickness of the inner wall of the crucible is 30mm~40mm, and the step baking time is 2.5h~3h, 3.5h~4h, and 2.5h~3h respectively.

4. The method according to claim 1, characterized in that: 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-20mm to ensure that the crucible is evenly heated during the baking process and prevent local cracking caused by uneven heating.

5. 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 reaction at high temperature, thereby ensuring that moisture inside the crucible is completely removed and improving the melting vacuum level of the crucible.

6. The method according to claim 2, characterized in that: When covering the crucible, the heat-insulating cotton can fully wrap the entire outer surface of the crucible to prevent external moisture from entering the inner cavity of the crucible, ensure that the crucible remains in a dry state after cooling, and provide ideal conditions for subsequent smelting.

7. The method according to claim 2, characterized in that: The crucible is an alumina crucible.

8. The method according to claim 2, characterized in that: The crucible treated by the method can achieve a vacuum degree of less than 10^-1Pa during the first smelting, thereby improving the purity of the powder.

9. The method according to claim 2, characterized in that: In the method, the crucible is a magnesium oxide crucible.

10. The method according to claim 2, characterized in that: In the method, the crucible is a calcium oxide crucible.

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