A smelting and casting method of ultra-high purity copper

Abstract

The present application relates to a kind of ultra-high purity copper smelting casting method, the smelting casting method includes: the copper material is carried out vacuum smelting, when the vacuum degree becomes 280-310 times of the vacuum degree when vacuum smelting starts in process, vacuumizing is carried out, then in turn, heat preservation and casting are carried out;The casting speed is gradient change in the casting.This smelting casting method provided by the present application realizes the preparation of ultra-high purity copper ingot by the design of vacuum degree in vacuum smelting and the combination of specific casting process, the purity of the obtained ultra-high purity copper is ≥99.9999%, and there is no inclusion and no casting defects such as internal or surface hole.

Description

Technical Field

[0001] This invention relates to the field of ultra-high purity metal materials, specifically to a method for smelting and casting ultra-high purity copper. Background Technology

[0002] Currently, ultra-high purity copper is the raw material for manufacturing ultra-high purity copper sputtering targets for semiconductors. It is mainly used for integrated circuit wiring and is an indispensable raw material in the production of high-quality chips.

[0003] For example, CN111001921A discloses a diffusion welding method for ultra-high purity copper targets. The welding method includes the following steps: (1) preparing an ultra-high purity copper target and a threaded back plate, adding copper powder to the threads on the back plate, and then assembling it with the ultra-high purity copper target; (2) placing the assembled ultra-high purity copper target and back plate into a sleeve, then welding the sleeve and evacuating it; (3) subjecting the evacuated sleeve to hot isostatic pressing, then cooling and removing the sleeve to complete the welding; wherein, the thread spacing is 0.35-0.45mm; and the thread depth is 0.2-0.3mm. In this invention, by reasonably setting the thread size and configuring the overall process conditions, the target can still maintain good electrical and thermal conductivity and welding strength during the welding process of ultra-high purity copper targets, thereby ensuring the uniformity of the target sputtering rate. In addition, it can also avoid abnormal phenomena such as particulate, peeling, and arcing of the target during the sputtering process.

[0004] However, the ultra-high purity copper currently produced still has problems such as many impurities, low purity, inclusions, and casting defects. Summary of the Invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a smelting and casting method for ultra-high purity copper, so as to solve the problems that the ultra-high purity copper obtained by current smelting and casting still has many impurities, low purity, inclusions and casting defects.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a method for smelting and casting ultra-high purity copper. The smelting and casting method includes: smelting copper material under vacuum, and when the vacuum degree becomes 280-310 times the vacuum degree at the beginning of the vacuum smelting, vacuuming is performed, followed by heat preservation and casting.

[0008] The casting speed in the casting process varies in a gradient.

[0009] The smelting and casting method provided by this invention, through the design of the vacuum degree in vacuum smelting and the combination of a specific casting process, realizes the preparation of ultra-high purity copper ingots. The resulting ultra-high purity copper has a purity of ≥99.9999% and is free of inclusions and casting defects such as internal or surface pores.

[0010] As a preferred technical solution of the present invention, the copper material includes one or a combination of at least two of 4N copper, 5N copper or 6N copper.

[0011] As a preferred technical solution of the present invention, the absolute vacuum degree at the start of the vacuum melting is ≤0.067Pa.

[0012] As a preferred technical solution of the present invention, the temperature of the vacuum melting is 1050-1080℃.

[0013] As a preferred technical solution of the present invention, the temperature of the melt is maintained at 1050-1080℃ during the vacuuming process.

[0014] As a preferred technical solution of the present invention, the endpoint of the vacuuming is an absolute vacuum degree ≤ 0.67 Pa.

[0015] As a preferred technical solution of the present invention, the temperature of the heat preservation and static setting is 1180-1280℃.

[0016] Preferably, the heat preservation and static setting time is 5-30 minutes.

[0017] As a preferred technical solution of the present invention, the absolute vacuum degree is controlled to be 1-3 Pa at the beginning of the casting process.

[0018] As a preferred technical solution of the present invention, the casting speed in the casting process is a gradient change: the casting speed in the early stage of casting is 1-7 mm / min, the casting speed in the middle stage of casting is 10-20 mm / min, and the casting speed in the later stage of casting is 1-5 mm / min.

[0019] As a preferred technical solution of the present invention, the flow rate of molten metal in the early stage of casting is 1-8 kg / min.

[0020] Preferably, the flow rate of molten metal during the intermediate stage of casting is 10-20 kg / min.

[0021] Preferably, the flow rate of molten metal in the later stage of casting is 1-5 kg / min.

[0022] Compared with existing technical solutions, the present invention has the following beneficial effects:

[0023] The smelting and casting method for ultra-high purity copper provided by this invention improves the yield of the ingots, reduces internal impurities and defects, and reduces the depth of the liquid cavity and shrinkage cavities in the ingot during the process, which is conducive to the floating of impurities. Furthermore, the as-cast microstructure of the ingot is uniform and refined, which is beneficial to subsequent processing and deformation. Detailed Implementation

[0024] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0025] This embodiment provides a method for smelting and casting ultra-high purity copper. The smelting and casting method includes: smelting copper material under vacuum, and when the vacuum degree becomes 280-310 times the vacuum degree at the beginning of the vacuum smelting, vacuuming is performed, followed by heat preservation and casting.

[0026] The casting speed in the casting process varies in a gradient.

[0027] During the vacuum melting process, vacuuming is performed when the vacuum level becomes 280-310 times the initial vacuum level. For example, the values ​​could be 280, 282, 284, 286, 288, 290, 292, 294, 296, 298, 300, 302, 304, 306, 308, or 310 times, but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] For example, if the absolute vacuum degree at the start of vacuum melting is A, then when the absolute vacuum during the melting process becomes A*(250-310), a vacuuming operation is performed to control the absolute vacuum degree to the required value.

[0029] In this invention, the ultra-high purity is 99.9999% or higher.

[0030] Specifically, the copper material includes one or a combination of at least two of 4N copper, 5N copper, or 6N copper.

[0031] In this invention, the raw materials used in the smelting process can be selected from 4N copper, 5N copper, or 6N copper. Specifically, the purpose of this invention is to prepare high-purity copper using low-purity copper. Based on this, it can be reasonably inferred that when using 6N copper, ultra-high-purity copper can be prepared even more effectively. The raw copper used can be industrially produced or commercially available copper ingots, or copper waste generated during production operations, such as waste generated during turning and milling in the preparation of target materials.

[0032] Among them, 4N copper has a copper purity of ≥99.99%.

[0033] Among them, 5N copper has a copper purity of ≥99.999%.

[0034] Among them, 6N copper has a copper purity of ≥99.9999%.

[0035] Specifically, the absolute vacuum degree at the start of the vacuum melting is ≤0.067 Pa, for example, it can be 0.067 Pa, 0.066 Pa, 0.065 Pa, 0.06 Pa, 0.05 Pa, 0.04 Pa, 0.03 Pa, 0.02 Pa, 0.01 Pa, 0.005 Pa or 0.001 Pa, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Specifically, the vacuum melting temperature is 1050-1080℃, for example, it can be 1050℃, 1052℃, 1054℃, 1056℃, 1058℃, 1060℃, 1062℃, 1064℃, 1066℃, 1068℃, 1070℃, 1072℃, 1074℃, 1076℃, 1078℃ or 1080℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0037] Specifically, during the vacuuming process, the temperature of the melt is maintained at 1050-1080℃, for example, it can be 1050℃, 1052℃, 1054℃, 1056℃, 1058℃, 1060℃, 1062℃, 1064℃, 1066℃, 1068℃, 1070℃, 1072℃, 1074℃, 1076℃, 1078℃ or 1080℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0038] Specifically, the endpoint of the vacuuming is an absolute vacuum degree ≤ 0.67 Pa, which can be, for example, 0.67 Pa, 0.66 Pa, 0.65 Pa, 0.64 Pa, 0.63 Pa, 0.62 Pa, 0.61 Pa, 0.6 Pa, 0.5 Pa, 0.4 Pa, 0.3 Pa, 0.2 Pa, 0.1 Pa, 0.05 Pa, 0.01 Pa, 0.005 Pa, or 0.001 Pa, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Specifically, the temperature for heat preservation and static setting is 1180-1280℃, for example, it can be 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, 1260℃, 1270℃ or 1280℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the heat preservation and standing time is 5-30 minutes, for example, it can be 5 minutes, 6 minutes, 8 minutes, 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes or 30 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] Specifically, the absolute vacuum degree is controlled at the beginning of the casting process to be 1-3 Pa, for example, it can be 1 Pa, 1.2 Pa, 1.4 Pa, 1.6 Pa, 1.8 Pa, 2 Pa, 2.2 Pa, 2.4 Pa, 2.6 Pa, 2.8 Pa or 3 Pa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Specifically, the casting speed in the casting process varies in a gradient: 1-7 mm / min in the early stage of casting, 10-20 mm / min in the middle stage of casting, and 1-5 mm / min in the later stage of casting.

[0043] In this invention, the early stage, middle stage, and late stage of casting are distinguished by the amount of molten metal used in casting. At the beginning of casting, when the amount of molten metal used is ≤17-18% of the total liquid volume, it is the early stage of casting; when the amount of molten metal used is >17-18% of the total liquid volume and ≤70-71% of the total liquid volume, it is the middle stage of casting; when the amount of molten metal used is >70-71% of the total liquid volume, it is the late stage of casting.

[0044] The casting speed in the casting process is a gradient change, with the casting speed in the early stage of casting being 1-7 mm / min. For example, it can be 1 mm / min, 2 mm / min, 3 mm / min, 4 mm / min, 5 mm / min, 6 mm / min or 7 mm / min, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] The casting speed during the casting process is a gradient change, with the casting speed in the middle stage of casting being 10-20 mm / min. For example, it can be 10 mm / min, 11 mm / min, 12 mm / min, 13 mm / min, 14 mm / min, 15 mm / min, 16 mm / min, 17 mm / min, 18 mm / min, 19 mm / min, or 20 mm / min, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] The casting speed in the casting process is a gradient change, with the casting speed in the later stage of casting being 1-5 mm / min. For example, it can be 1 mm / min, 2 mm / min, 3 mm / min, 4 mm / min or 5 mm / min, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] Specifically, the flow rate of the molten metal in the early stage of casting is 1-8 kg / min, for example, it can be 1 kg / min, 2 kg / min, 3 kg / min, 4 kg / min, 5 kg / min, 6 kg / min, 7 kg / min or 8 kg / min, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Specifically, the flow rate of molten metal during the middle stage of casting is 10-20 kg / min, for example, it can be 10 kg / min, 11 kg / min, 12 kg / min, 13 kg / min, 14 kg / min, 15 kg / min, 16 kg / min, 17 kg / min, 18 kg / min, 19 kg / min or 20 kg / min, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Specifically, the flow rate of the molten metal in the later stage of casting is 1-5 kg / min, for example, it can be 1 kg / min, 2 kg / min, 3 kg / min, 4 kg / min or 5 kg / min, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] In this invention, cooling is performed under a protective atmosphere after casting, such as furnace cooling. The protective atmosphere is a commonly used protective atmosphere in the art, such as argon or helium.

[0051] Furthermore, in order to obtain ingots with even better performance, vibration can be applied to the mold during casting, with a vibration frequency of 0-2000Hz.

[0052] To further illustrate the advantages of the ultra-high purity copper smelting and casting method provided by this invention, the following specific embodiments are provided for explanation:

[0053] Example 1

[0054] This embodiment provides a method for smelting and casting ultra-high purity copper. The smelting and casting method includes: smelting copper material under vacuum, and when the vacuum degree becomes 300 times the vacuum degree at the beginning of the vacuum smelting, vacuuming is performed, followed by heat preservation and casting.

[0055] The copper material is composed of 80% 4N copper, 10% 6N copper and 10% 5N copper;

[0056] The absolute vacuum degree at the start of the vacuum melting is 0.067 Pa; the temperature of the vacuum melting is 1070℃;

[0057] The temperature of the melt is maintained at 1070℃ during the vacuuming process; the endpoint of the vacuuming process is an absolute vacuum of 0.67 Pa.

[0058] The temperature for heat preservation and static setting is 1200℃; the time for heat preservation and static setting is 20 minutes.

[0059] The casting process begins with an absolute vacuum of 2 Pa.

[0060] The casting speed in the casting process is a gradient change; the casting speed is 5 mm / min in the early stage of casting, 16 mm / min in the middle stage of casting, and 4 mm / min in the later stage of casting; the flow rate of the molten metal in the early stage of casting is 6 kg / min; the flow rate of the molten metal in the middle stage of casting is 14 kg / min; and the flow rate of the molten metal in the later stage of casting is 2 kg / min.

[0061] In this embodiment, the early, middle, and late stages of casting are distinguished by the amount of molten metal used during casting. At the beginning of casting, when the amount of molten metal used is ≤17% of the total liquid volume, it is the early stage of casting; when the amount of molten metal used is >17% of the total liquid volume but ≤70% of the total liquid volume, it is the middle stage of casting; and when the amount of molten metal used is >70% of the total liquid volume, it is the late stage of casting.

[0062] The performance parameters of the cast copper ingots are detailed in Table 1.

[0063] Example 2

[0064] This embodiment provides a method for smelting and casting ultra-high purity copper. The smelting and casting method includes: smelting copper material under vacuum, and when the vacuum degree becomes 280 times the vacuum degree at the beginning of the vacuum smelting, vacuuming is performed, followed by heat preservation and casting.

[0065] The copper material is 50% 4N copper and 50% 5N copper;

[0066] The absolute vacuum degree at the start of the vacuum melting is 0.017 Pa; the temperature of the vacuum melting is 1060℃;

[0067] The temperature of the melt is maintained at 1060℃ during the vacuuming process; the endpoint of the vacuuming process is an absolute vacuum of 0.067 Pa.

[0068] The temperature for heat preservation and static setting is 1190℃; the time for heat preservation and static setting is 15 minutes.

[0069] The casting process begins with an absolute vacuum of 2.5 Pa.

[0070] The casting speed in the casting process is a gradient change; the casting speed in the early stage of casting is 6 mm / min, the casting speed in the middle stage of casting is 14 mm / min, and the casting speed in the later stage of casting is 2 mm / min; the flow rate of the molten metal in the early stage of casting is 3 kg / min; the flow rate of the molten metal in the middle stage of casting is 17 kg / min; and the flow rate of the molten metal in the later stage of casting is 3 kg / min.

[0071] The performance parameters of the cast copper ingots are detailed in Table 1.

[0072] Example 3

[0073] This embodiment provides a method for smelting and casting ultra-high purity copper. The smelting and casting method includes: smelting copper material under vacuum, and evacuating the vacuum when the vacuum degree becomes 310 times the vacuum degree at the beginning of the vacuum smelting, followed by heat preservation and casting.

[0074] The copper material is 4N copper;

[0075] The absolute vacuum degree at the start of the vacuum melting is 0.0067 Pa; the temperature of the vacuum melting is 1050℃;

[0076] The temperature of the melt is maintained at 1050℃ during the vacuuming process; the endpoint of the vacuuming process is an absolute vacuum of 0.0067 Pa.

[0077] The temperature for heat preservation and static setting is 1280℃; the time for heat preservation and static setting is 5 minutes.

[0078] The casting process begins with an absolute vacuum of 1 Pa.

[0079] The casting speed in the casting process is a gradient change; the casting speed in the early stage of casting is 7 mm / min, the casting speed in the middle stage of casting is 10 mm / min, and the casting speed in the later stage of casting is 1 mm / min; the flow rate of the molten metal in the early stage of casting is 1 kg / min; the flow rate of the molten metal in the middle stage of casting is 10 kg / min; and the flow rate of the molten metal in the later stage of casting is 5 kg / min.

[0080] The performance parameters of the cast copper ingots are detailed in Table 1.

[0081] Example 4

[0082] This embodiment provides a method for smelting and casting ultra-high purity copper. The smelting and casting method includes: smelting copper material under vacuum, and when the vacuum degree becomes 290 times the vacuum degree at the beginning of the vacuum smelting, vacuuming is performed, followed by heat preservation and casting.

[0083] The copper material is 5N copper;

[0084] The absolute vacuum degree at the start of the vacuum melting is 0.037 Pa; the temperature of the vacuum melting is 1080℃.

[0085] The temperature of the melt is maintained at 1080℃ during the vacuuming process; the endpoint of the vacuuming process is an absolute vacuum of 0.17 Pa.

[0086] The temperature for heat preservation and static setting is 1180℃; the time for heat preservation and static setting is 30 minutes.

[0087] The casting process begins with an absolute vacuum of 3 Pa.

[0088] The casting speed in the casting process is a gradient change; the casting speed in the early stage of casting is 1 mm / min, the casting speed in the middle stage of casting is 20 mm / min, and the casting speed in the later stage of casting is 5 mm / min; the flow rate of the molten metal in the early stage of casting is 8 kg / min; the flow rate of the molten metal in the middle stage of casting is 10 kg / min; and the flow rate of the molten metal in the later stage of casting is 1 kg / min.

[0089] The performance parameters of the cast copper ingots are detailed in Table 1.

[0090] Example 5

[0091] The only difference from Example 1 is that during the vacuum melting process, when the vacuum degree becomes 300 times the vacuum degree at the beginning of the vacuum melting, no vacuuming is performed, and after the same time is reached, heat preservation and casting are performed in sequence.

[0092] The performance parameters of the cast copper ingots are detailed in Table 1.

[0093] Example 6

[0094] The only difference from Example 1 is that during the vacuum melting process, vacuuming is performed when the vacuum level becomes 220 times the vacuum level at the start of vacuum melting.

[0095] The performance parameters of the cast copper ingots are detailed in Table 1.

[0096] Example 7

[0097] The only difference from Example 1 is that during the vacuum melting process, vacuuming is performed when the vacuum level becomes 380 times the vacuum level at the start of vacuum melting.

[0098] The performance parameters of the cast copper ingots are detailed in Table 1.

[0099] Example 8

[0100] The only difference from Example 1 is that the vacuum degree at the start of vacuum melting is 0.67 Pa.

[0101] The performance parameters of the cast copper ingots are detailed in Table 1.

[0102] Example 9

[0103] The only difference from Example 1 is that the end point of the vacuuming is an absolute vacuum of 10 Pa.

[0104] The performance parameters of the cast copper ingots are detailed in Table 1.

[0105] Example 10

[0106] The only difference from Example 1 is that the absolute vacuum is controlled at 8 Pa at the beginning of the casting process.

[0107] The performance parameters of the cast copper ingots are detailed in Table 1.

[0108] Example 11

[0109] The only difference from Example 1 is that the absolute vacuum is controlled at 0.5 Pa at the beginning of the casting process.

[0110] The performance parameters of the cast copper ingots are detailed in Table 1.

[0111] Example 12

[0112] The only difference from Example 1 is that the casting speed is maintained at 16 mm / min during the casting process.

[0113] The performance parameters of the cast copper ingots are detailed in Table 1.

[0114] Example 13

[0115] The only difference from Example 1 is that the casting speed is maintained at 5 mm / min during the casting process.

[0116] The performance parameters of the cast copper ingots are detailed in Table 1.

[0117] Example 14

[0118] The only difference from Example 1 is that the casting speed in the casting process is a gradient change, with the casting speed in the early stage of casting being 16 mm / min.

[0119] The performance parameters of the cast copper ingots are detailed in Table 1.

[0120] Example 15

[0121] The only difference from Example 1 is that the casting speed in the casting process is a gradient change, with the casting speed in the later stage of casting being 16 mm / min.

[0122] The performance parameters of the cast copper ingots are detailed in Table 1.

[0123] Example 16

[0124] The only difference from Example 1 is that the casting speed in the casting process is a gradient change, with the casting speed in the middle stage of casting being 30 mm / min.

[0125] The performance parameters of the cast copper ingots are detailed in Table 1.

[0126] In the above embodiments, the early casting stage, middle casting stage, and late casting stage are distinguished by the amount of molten metal used in casting. At the beginning of casting, when the amount of molten metal used is ≤17% of the total liquid volume, it is the early casting stage; when the amount of molten metal used is >17% of the total liquid volume but ≤70% of the total liquid volume, it is the middle casting stage; and when the amount of molten metal used is >70% of the total liquid volume, it is the late casting stage.

[0127] The detection process for insoluble particles in the above embodiments is as follows:

[0128] Weigh 10 grams of sample and dissolve it in 100 ml of nitric acid and copper nitrate solution. After complete dissolution, vacuum filter the solution. Insoluble particles remain on filter paper. Immerse the filter paper in 500 ml of test solution and use an LPC 500 liquid particle counter to count the number of particles corresponding to 1.3 μm, 5 μm, 10 μm, and 20 μm. Defect detection is performed using a combination of microscopy and ultrasonic defect detection to confirm whether the surface of the copper material has depressions or internal pores.

[0129] Table 1

[0130]

[0131] As can be seen from the results of the above embodiments, the smelting and casting method provided by the present invention, through the design of the vacuum degree in vacuum smelting and the combination of a specific casting process, realizes the preparation of ultra-high purity copper ingots. The purity of the obtained ultra-high purity copper is ≥99.9999%, and there are no inclusions or casting defects such as internal or surface pores.

[0132] The present invention is described in detail through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0133] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0134] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0135] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for smelting and casting ultra-high purity copper that reduces ingot cavitation depth and shrinkage cavities, characterized in that, The smelting and casting method includes: vacuum smelting copper material, and when the vacuum degree becomes 280-310 times the vacuum degree at the beginning of vacuum smelting, vacuuming is performed, followed by heat preservation and casting. The casting speed in the casting process is a gradient change; the casting speed in the early stage of casting is 1-7 mm / min, the casting speed in the middle stage of casting is 10-20 mm / min, and the casting speed in the later stage of casting is 1-5 mm / min.

2. The smelting and casting method as described in claim 1, characterized in that, The copper material includes one or a combination of at least two of 4N copper, 5N copper, or 6N copper.

3. The smelting and casting method as described in claim 1, characterized in that, The absolute vacuum degree at the start of the vacuum melting is ≤0.067 Pa.

4. The smelting and casting method as described in claim 1, characterized in that, The vacuum melting temperature is 1050-1080℃.

5. The smelting and casting method as described in claim 1, characterized in that, The temperature of the melt is maintained at 1050-1080℃ during the vacuuming process.

6. The smelting and casting method as described in claim 1, characterized in that, The endpoint of the vacuuming process is an absolute vacuum degree ≤ 0.67 Pa.

7. The smelting and casting method as described in claim 1, characterized in that, The temperature for heat preservation and static setting is 1180-1280℃.

8. The smelting and casting method as described in claim 1, characterized in that, The heat preservation and static setting time is 5-30 minutes.

9. The smelting and casting method as described in claim 1, characterized in that, The casting process begins with an absolute vacuum of 1-3 Pa.

10. The smelting and casting method as described in claim 1, characterized in that, The flow rate of molten metal during the early stage of casting is 1-8 kg / min.

11. The smelting and casting method as described in claim 1, characterized in that, The flow rate of molten metal during the middle stage of casting is 10-20 kg / min.

12. The smelting and casting method as described in claim 1, characterized in that, The flow rate of molten metal during the later stage of casting is 1-5 kg / min.

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