Nickel-based superalloy smelting method

Abstract

The invention relates to the field of high-temperature alloy smelting, in particular to a nickel-based high-temperature alloy smelting method. According to the method, the scandium raw material coated with the nickel base is added in the nickel base alloy smelting process, the corresponding feeding method is designed according to the specific smelting process, the burning loss amount of the scandium element is effectively controlled, and the yield of the scandium element is increased. Specifically, by means of the method, the oxygen content in the system can be reduced to about 10 ppm, and the scandium yield is controlled to be 35%-50%.

Description

Technical Field

[0001] The invention relates to the field of high-temperature alloy smelting, and in particular to a nickel-based high-temperature alloy smelting method. Background Art

[0002] In the field of high-temperature alloy smelting technology, the addition of rare earth elements has become an important means to improve the performance of alloys. Rare earth elements, due to their unique electronic structure and magnetic properties, show excellent stability and performance in high-temperature environments. Specifically, the action mechanisms of rare earth elements such as yttrium (Y), cerium (Ce), lanthanum (La) and scandium (Sc) in high-temperature alloys include purifying alloys, improving oxidation resistance, strengthening grain boundaries, and positively affecting alloy microstructure and mechanical properties. The addition of these elements can not only improve the high-temperature stability and toughness of the alloy, but also enhance its corrosion resistance and thermal conductivity.

[0003] In the actual smelting process, factors such as the amount of rare earth elements added, the method of addition, and the timing of addition have a significant impact on the final properties of the alloy. Therefore, how to accurately control the addition of rare earth elements has become a key technical problem in high-temperature alloy smelting technology.

[0004] Patent CN112538577A discloses a rare earth element control method for high temperature alloy purification smelting. Specifically, in the high temperature alloy smelting process, one or more rare earth master alloys containing rare earth elements, such as Ni-Ce master alloy, Al-Y master alloy and Al-La master alloy, are added.

[0005] Patent CN111004937A discloses a purification smelting process for heat-corrosion-resistant cast nickel-based high-temperature alloys, which reduces the oxygen and nitrogen gas content in the alloy by changing the feeding steps. Specifically, when feeding for the first time, carbon accounting for 1 / 3 of the total carbon content of the high-temperature alloy is added to the vacuum furnace crucible and placed at the bottom of the crucible. All elements in the high-temperature alloy except aluminum, titanium, and rare earth elements are added to the vacuum furnace crucible for smelting; when feeding for the second time, 1 / 3 of the carbon is added; when feeding for the third time, aluminum and carbon components are added to the system; and when feeding for the last time, all the titanium metal is added, and finally a rare earth alloy containing nickel, boron, and rare earth elements is added.

[0006] Research has found that adding scandium to high-temperature alloys can promote the formation of smaller and denser intermetallic compounds Al3Sc in aluminum alloys, increase the solidification nucleation rate, refine the cast structure, reduce segregation, and significantly improve the strength and toughness of the alloy. However, in the actual vacuum smelting process, low vacuum and high temperature environments will promote the volatilization and burning of Sc, making it difficult to control the scandium recovery rate (in most cases, the recovery rate is low, generally fluctuating between 5% and 30%).

[0007] Based on the above situation, a method for adding scandium element and the corresponding smelting control process that can be used in the smelting process of nickel-based high-temperature alloys are proposed. Summary of the invention

[0008] The main purpose of the present invention is to provide a method for smelting a nickel-based high-temperature alloy, and specifically to a feeding method of the rare earth element scandium and a corresponding smelting method.

[0009] The smelting method includes a first feeding step, a first melting step and a second feeding step.

[0010] In the first feeding step, a first batch of raw materials is fed, wherein the first batch of raw materials is at least part of other alloy elements except scandium;

[0011] In a first melting step, a first batch of raw materials is melted into a raw material melt;

[0012] In the second charging step, a second batch of raw materials is added to the raw material melt, wherein the second batch of raw materials includes a scandium composite, wherein the scandium composite is scandium coated with a coating metal different from scandium.

[0013] Furthermore, the density of the coated metal is greater than that of scandium, and the density of the scandium complex is greater than 8.3 g / cm 3 .

[0014] Furthermore, in the second feeding step, a scandium complex is added, wherein the scandium complex is formed by coating scandium with a metal foil as a coating metal.

[0015] Furthermore, the density of the scandium complex is 8.34-8.70 g / cm 3 .

[0016] Furthermore, the metal foil is nickel foil, the scandium complex includes a nickel block, the scandium and the nickel block are coated with the nickel foil, and the weight ratio of the sum of the mass of the nickel foil and the nickel block of the scandium complex to the scandium is 28.2-82.1:1 in terms of mass percentage.

[0017] Furthermore, in the second feeding step, the vacuum degree in the furnace chamber is 0.1-2.0Pa.

[0018] Furthermore, in the second feeding step, the vacuum degree in the furnace chamber is 0.1-0.8Pa.

[0019] Furthermore, after the second feeding step, a second melting step is also included, in which scandium is melted, and the duration of the second melting step is 1-30 minutes.

[0020] Furthermore, the sum of the weights of the first batch of raw materials and the second batch of raw materials is the total feed amount.

[0021] When the total feeding amount is not more than 50 kg, the vacuum degree in the furnace chamber in the second feeding step is 0.3-0.8 Pa, and the duration of the second melting step is 1-5 min.

[0022] Furthermore, the sum of the weights of the first batch of raw materials and the second batch of raw materials is the total feed amount.

[0023] When the total feeding amount is greater than 450 kg, the vacuum degree in the furnace chamber in the second feeding step is 0.1-0.7 Pa, and the duration of the second melting step is 10-20 min.

[0024] Furthermore, when the total feed amount is not more than 50 kg, the first batch of raw materials is all other raw materials except scandium.

[0025] In the first melting step, when the temperature is between 1560 and 1630°C, the heating power is reduced, and further vacuuming is performed to start refining. The refining heating power is 25-35kW, and the refining time is 2-10min. When the vacuum degree is lower than 1.5Pa, the heating is stopped. When the surface of the raw material melt begins to solidify into a film, the heating power is increased to 35-50kW and maintained for 1-6min.

[0026] At the beginning of the second melting step, reducing the heating power to no more than 20 kW;

[0027] After the second melting step, a heating step is also included. The heating power of the heating step is 40-70 kW. When the temperature reaches above 1410° C., the heating power is reduced to no more than 10 kW.

[0028] Furthermore, when the total feed amount is greater than 450 kg, the first batch of raw materials does not include aluminum, titanium, carbon, and scandium.

[0029] In the first melting step, when the temperature is greater than 1570°C, the heating power is reduced to less than 120 kW for refining. The heating power during refining is 55-90 kW, the vacuum degree during the refining period is less than 1.0 Pa, and the heating is stopped after the refining time is 15-40 minutes. When the surface of the raw material melt begins to solidify into a film, the heating power is increased to 220-280 kW and maintained for 1-8 minutes;

[0030] At the beginning of the second melting step, reducing the heating power to less than 100 kW;

[0031] After the second melting step, a heating step is also included. The heating power of the heating step is 210-270 kW. When the temperature reaches above 1450° C., the power is quickly reduced to below 100 kW.

[0032] Furthermore, when the total feed amount is not more than 50 kg, the total smelting time is 35-60 min.

[0033] Furthermore, when the total feed amount is greater than 450 kg, the total smelting time is 4.5-5.5 h.

[0034] Further, after the temperature raising step, the raw material melt is cast into a mold.

[0035] Specifically, the beneficial effects actually produced by the present invention are as follows:

[0036] 1. The present invention can control the recovery rate of scandium to 35-50%, which realizes the utilization of scandium in the high-temperature alloy smelting process and improves the recovery rate of scandium in the high-temperature alloy vacuum smelting process.

[0037] 2. Through the present invention, the oxygen content in the system is reduced from the general 25 ppm to about 10 ppm, and combined with the yield of scandium, the alloy is effectively purified. DETAILED DESCRIPTION

[0038] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0039] The present invention is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0040] The present invention relates to a smelting process of a nickel-based high-temperature alloy containing rare earth elements, through which the traditional Ni3 (Al, Ti) strengthening phase is improved to form a Ni3 (Al, Ti, Nb) strengthening phase containing a higher content of Al and Nb at the same time. Specifically, as a new strengthening mechanism, scandium is added during the smelting process of the above alloy to form a Ni3 (Al, Ti, Nb) composite strengthening phase containing Sc, which is more resistant to high temperatures and more stable than a single traditional strengthening phase Ni3 (Al, Ti) or Ni3 (Al, Ti, Nb), and significantly improves the creep resistance and long-lasting life of the alloy.

[0041] Measured by mass fraction, the components of the above-mentioned high-temperature alloy include: C: 0.04-0.08%, Cr: 18.50-21.50%, Co: 9.00-11.00%, Mo: 8.00-9.00%, Al: 2.00-3.00%, Ti: 1.10-1.49%, Nb: 0.81-2.00%, B: 0.003-0.009%, Sc: 0.001-0.10%, and the remainder includes nickel and unavoidable impurities.

[0042] In other embodiments, nickel-based high-temperature alloys of other components may be selected, which can also effectively exert the strengthening effect of Sc.

[0043] It is known that since the capacity of the crucible of the melting furnace is fixed, when the density of the raw material is low, the loading weight needs to be increased, and when the density of the raw material is high, the loading weight needs to be reduced to ensure that the volume of the melt after melting meets the melting requirements.

[0044] When smelting the above nickel-based alloy, vacuum induction melting furnaces of different specifications can be flexibly selected according to actual smelting requirements. The overall smelting process includes the following steps.

[0045] When a small vacuum induction melting furnace (furnace capacity ≤ 50kg) is selected, the total smelting time is 35-60min, and the smelting process specifically includes the following steps:

[0046] S1: First feeding step: putting all raw materials except scandium, including carbon, chromium, cobalt, molybdenum, aluminum, titanium, neodymium, boron and nickel, into a small vacuum induction melting furnace, closing the furnace body, starting to evacuate and heat up;

[0047] S2 first melting step:

[0048] S2-1 First melting step Stage 1: The power of the vacuum pump is ≤15kW, until the raw material is melted to 50%-70%;

[0049] S2-2 First Melting Step Stage 2: When the raw material is melted to 50-70%, the induction furnace power is increased to more than 40kW until the raw material is completely melted;

[0050] S2-3 refining stage: when the melt temperature is 1560-1630℃, the heating power is reduced and controlled within the range of 25-35kW for alloy refining. The duration of this process is 2-10min.

[0051] During the above S2-3 refining process, the vacuum degree in the furnace chamber is continuously monitored in real time, and the power supply of the melting furnace is turned off to cool down when the vacuum degree is lower than 1.5Pa; when the surface of the raw material melt in the crucible begins to solidify into a film, the furnace power is increased to 35-50kW again, maintained for 1-6 minutes, and finally the vacuum degree in the furnace chamber is stabilized at 0.2-2.0Pa;

[0052] S3: second feeding step: adding nickel blocks and scandium blocks wrapped in nickel foil into the raw material melt;

[0053] S4: Second melting step: Rapidly reduce the power to ≤20kW and maintain it for 1-10min under this condition; after the scandium is completely melted, increase the power to 40-70kW again; when the raw material melt temperature is greater than 1410°C, reduce the power supply of the smelting furnace to ≤10kW.

[0054] After the above steps are completed, the raw material melt is poured into the ingot mold. After the ingot cools and the surface turns black, the furnace cover is opened and the ingot is taken out.

[0055] In a preferred embodiment, when the raw material melt temperature in the above-mentioned S2-3 refining stage is 1570-1610°C, the heating power is reduced.

[0056] In a preferred embodiment, the duration of the above-mentioned S2-3 refining stage is 4-8 minutes.

[0057] In a preferred embodiment, in the above-mentioned S2-3 refining stage, the power supply of the induction furnace is increased again to 35-50 kW and maintained for 1-3 minutes.

[0058] In a preferred embodiment, in the above-mentioned S2-3 refining stage, the vacuum degree in the furnace chamber is finally stabilized at 0.3-0.8Pa.

[0059] In other embodiments, in the second feeding step S3, other forms of scandium complexes may be used, such as using hollow nickel balls or nickel boxes to wrap the scandium to form a scandium complex;

[0060] In a preferred embodiment, in the second melting step S4, the power of the induction furnace is rapidly reduced to ≤20 kW and maintained at this operating condition for 1-5 minutes;

[0061] In a preferred embodiment, in the second melting step S4, after the scandium is completely melted, the induction furnace power is increased again to 45-56 kW.

[0062] When a large vacuum induction melting furnace (furnace capacity > 450kg) is used, the total melting time is 4.5-5.5h, and the smelting process specifically includes the following steps:

[0063] S1: First feeding: several alloy materials including chromium, cobalt, molybdenum, niobium, boron and nickel are loaded into the furnace, and the temperature is raised and vacuum is drawn at the same time;

[0064] S2 first melting step:

[0065] S2-1 First melting step, stage 1: When the vacuum degree in the furnace chamber is less than 100 Pa, power is supplied to increase the temperature;

[0066] S2-2 First Melting Step Phase 2: When the melting degree of the alloy raw material reaches 40-60%, the power of the induction furnace is increased to ≥200kW until the alloy raw material is completely melted;

[0067] S2-3 Refining stage: Measure the temperature of the molten steel. When the temperature is greater than 1570℃, reduce the power to below 120kW and start refining. The refining power of the melting furnace is controlled at 55-90kW, and the vacuum degree is less than 1.0Pa. The duration of this process is 15-40min, followed by power outage and cooling. When the surface of the raw material melt begins to solidify into a film, increase the power of the induction furnace again and increase the power to 220-280kW, maintaining it for 1-8min. At the same time, further evacuate the vacuum, and finally stabilize the vacuum degree in the furnace chamber at 0.1-1.5Pa.

[0068] S3: second feeding step: feeding easily burnable aluminum, titanium, carbon, and nickel blocks and scandium blocks wrapped in nickel foil into the raw material melt;

[0069] S4: Second melting step: reduce the power to <100kW and maintain it for 5-30min under this condition; after the raw materials are completely melted, increase the induction furnace power to 210-270kW again. When the raw material melt temperature reaches >1450℃, quickly reduce the induction furnace power to below 100kW.

[0070] After the above steps are completed, the molten steel is poured into the ingot mold. After the ingot cools and the surface turns black, the ingot mold is taken out of the furnace and continues to cool in the air.

[0071] In a preferred embodiment, in the refining stage of S2-3, the refining power of the induction furnace is controlled at 55-90 kW, the vacuum degree is less than 1.0 Pa, the process lasts for 25-30 minutes, and then the power is turned off for cooling.

[0072] In a preferred embodiment, during the refining stage of S2-3, the induction furnace power is increased to 235-255 kW.

[0073] In a preferred embodiment, in the refining stage of S2-3, the holding time after increasing the power is 1-3 minutes.

[0074] In a preferred embodiment, in the refining stage of S2-3, the vacuum degree in the furnace chamber is finally stabilized at 0.1-0.7 Pa.

[0075] In other embodiments, in the second feeding step S3, other forms of scandium complexes may be used, such as using hollow nickel balls or nickel boxes to wrap the scandium to form a scandium complex.

[0076] In a preferred embodiment, in the second melting step S4, the operating temperature is maintained at <100 kW for 10-20 minutes.

[0077] It is known that in the smelting process of the master alloy of high-temperature alloys, rare earth elements are very easy to burn out when added, and cannot play the role of purifying the alloy, and also weaken their strengthening effect in the alloy. Therefore, the process should be specially designed to ensure that rare earth elements are effectively added to participate in alloy purification. If the specific gravity of rare earth elements is relatively small, they are easy to float on the surface of the alloy liquid when added. Nickel foil with higher density can be used instead of traditional aluminum foil to wrap the rare earth raw materials. Therefore, when using the above two specifications of vacuum induction melting furnaces for smelting, nickel foil is used to wrap the scandium element to form a scandium complex for addition.

[0078] The weight of raw materials of each element required to be charged to the furnace is calculated according to the designed charging point. In terms of mass percentage, the proportion of nickel in general nickel-based alloys is greater than 50%. All nickel raw materials are charged in two parts. Nickel raw materials are mainly charged into the furnace in the first charging step, and the charging weight is the total weight of the required nickel minus the weight of the second charging; in the second charging step, nickel foil is used to wrap the block nickel and scandium and the mass ratio of nickel (nickel foil and nickel block) to scandium in the scandium complex is W 镍箔+镍块 / W 钪 =28.2-82.1:1, the amount of nickel foil used in the scandium complex should be ≤300g. When designing the mass ratio of nickel foil to scandium element, the main consideration is that during the melting process of the raw materials, the scandium complex should have a large enough density so that the scandium complex can sink directly into the molten steel after being added to avoid burning above the molten steel. Depending on the slightly different ratios, the solid density of nickel-based alloys is generally ρ 固 =8.2-8.3g / m 3 Considering that the inevitable gap between the nickel foil and the scandium element will cause the actual volume of the scandium complex to be greater than the theoretical volume and reduce the density of the scandium complex, the lower limit of the specific gravity of the scandium complex is controlled at 8.34 g / m 3 ; The upper limit of the specific gravity of the scandium complex is controlled at 8.70g / m 3 , mainly to prevent the scandium complex from sinking too fast. Therefore, the specific gravity of the scandium complex needs to be controlled at 8.34-8.70g / m 3 In the actual smelting process, as the nickel foil gradually melts, the specific gravity of the scandium complex gradually decreases, causing its sinking speed to gradually decrease. When the nickel foil is completely melted, the scandium raw material is completely submerged in the molten steel. Subsequently, the scandium raw material is fully dispersed in the melt due to the stirring action in the induction furnace.

[0079] Therefore, this specific gravity design enables the scandium complex to sink into the melt during the melting process, ensuring that the scandium raw material is fully melted and effectively avoiding the formation of oxides when the scandium raw material is put into the melt, resulting in an extremely high melting point and being unable to be melted into the molten steel.

[0080] It should be noted that nickel foil is selected as the raw material for wrapping / weighting in the scandium complex because the alloy system is nickel-based and does not introduce elements other than those required. At the same time, the weight of the nickel raw material required for the scandium complex is included in the total weight of the nickel required to be loaded, reducing the amount of nickel loaded during the first feeding, effectively ensuring that the proportion of nickel meets the proportion of the formula design.

[0081] The specific implementation modes of the present invention are further described below in conjunction with examples and comparative examples.

[0082] When a small vacuum induction melting furnace is selected, Examples 1-6 and Comparative Example 1 are as follows:

[0083]

[0084] It can be seen from Examples 1-6 and Comparative Example 1 that the higher the refining power, the longer the smelting time, and the higher the vacuum degree during the smelting process, the more conducive it is to remove oxygen impurities in the molten steel. The higher the vacuum degree, the shorter the insulation time after the scandium is melted, and the shorter the time and opportunity for the scandium to react with oxygen, thereby effectively reducing the probability of scandium burning and improving the scandium recovery rate.

[0085] When a large vacuum induction furnace is selected, Examples 7-12 and Comparative Examples 2-3 are as follows:

[0086]

[0087] It can be seen from Examples 7-12 and Comparative Examples 2-3 that when a large vacuum induction melting furnace is used, the refining power and smelting time of the induction furnace can also have a significant impact on the burnout of scandium. Whether reducing the power of the induction furnace or shortening the refining time, it will have a significant negative impact on the removal effect of oxygen impurities in the system. Failure to fully remove oxygen impurities during the refining stage will directly increase the probability of scandium burnout and reduce the scandium recovery rate. At the same time, a long insulation time will increase the scandium-oxygen reaction time and reduce the recovery rate of anti-.

[0088] In addition, when using a large vacuum induction melting furnace, since the crucible has a larger specific surface area, when the scandium complex is completely melted, the increase in the contact area between the melt and the crucible will cause part of the scandium to be adsorbed on the inner wall of the crucible, resulting in a significant impact on the scandium yield.

[0089] The specific implementation of directly adding scandium into the system without using a packaging method is described below in conjunction with the examples and comparative examples.

[0090]

[0091] The results show that under the same smelting conditions, wrapping scandium with nickel foil can effectively reduce the burnout of scandium and have a significant positive effect on the yield of scandium.

[0092] or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they contradict each other.

[0093] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for smelting a nickel-based high-temperature alloy, wherein the nickel-based high-temperature alloy contains the element scandium, characterized in that: The smelting method comprises a first feeding step, a first melting step and a second feeding step. In the first feeding step, a first batch of raw materials is fed, wherein the first batch of raw materials is at least part of other alloy elements except the scandium; In the first melting step, the first batch of raw materials is melted into a raw material melt; In the second feeding step, a second batch of raw materials is added to the raw material melt, wherein the second batch of raw materials includes a scandium composite, wherein the scandium composite is formed by coating the scandium with a coating metal different from scandium.

2. The smelting method according to claim 1, characterized in that: The density of the coated metal is greater than that of scandium, and the density of the scandium complex is greater than 8.3 g / cm 3 .

3. The smelting method according to claim 2, characterized in that: In the second feeding step, the scandium composite is added, wherein the scandium composite is formed by coating the scandium using a metal foil as the coating metal.

4. The smelting method according to claim 3, characterized in that: The density of the scandium complex is 8.34-8.70 g / cm 3 .

5. The smelting method according to claim 4, characterized in that: The metal foil is a nickel foil, the scandium complex comprises a nickel block, the scandium and the nickel block are coated by the nickel foil, and the weight ratio of the sum of the mass of the nickel foil and the nickel block of the scandium complex to the scandium is 28.2-82.1:1, calculated by mass percentage.

6. The smelting method according to claim 5, characterized in that: In the second feeding step, the vacuum degree is 0.1-2.0Pa.

7. The smelting method according to claim 6, characterized in that: In the second feeding step, the vacuum degree is 0.1-0.8Pa.

8. The smelting method according to claim 7, characterized in that: After the second feeding step, a second melting step is further included, in which the scandium is melted, and the duration of the second melting step is 1-30 minutes.

9. The smelting method according to claim 8, characterized in that: The sum of the weights of the first batch of raw materials and the second batch of raw materials is the total input amount. When the total feeding amount is not more than 50 kg, the vacuum degree in the second feeding step is 0.3-0.8 Pa, and the duration of the second melting step is 1-5 min.

10. The smelting method according to claim 8, characterized in that: The sum of the weights of the first batch of raw materials and the second batch of raw materials is the total input amount. When the total feeding amount is greater than 450 kg, the vacuum degree in the second feeding step is 0.1-0.7 Pa, and the duration of the second melting step is 10-20 min.

11. The smelting method according to claim 9, characterized in that: When the total feed amount is not more than 50 kg, the first batch of raw materials is all other raw materials except the scandium. In the first melting step, when the temperature is between 1560 and 1630° C., the heating power is reduced, and further vacuumization is performed to start refining. The refining heating power is 25-35 kW, and the refining time is 2-10 min. When the vacuum degree is lower than 1.5 Pa, the heating is stopped. When the surface of the raw material melt begins to solidify into a film, the heating power is increased to 35-50 kW and maintained for 1-6 min. At the beginning of the second melting step, reducing the heating power to no more than 20 kW; After the second melting step, a heating step is also included. The heating power of the heating step is 40-70 kW. When the temperature reaches above 1410° C., the heating power is reduced to no more than 10 kW.

12. The smelting method according to claim 10, characterized in that: When the total feed amount is greater than 450 kg, the first batch of raw materials does not include aluminum, titanium, carbon, and scandium. In the first melting step, when the temperature is greater than 1570°C, the heating power is reduced to less than 120 kW for refining, the heating power during refining is 55-90 kW, the vacuum degree during the refining period is less than 1.0 Pa, and the heating is stopped after the refining time is 15-40 minutes. When the surface of the raw material melt begins to solidify into a film, the heating power is increased to 220-280 kW and maintained for 1-8 minutes; At the beginning of the second melting step, reducing the heating power to less than 100 kW; After the second melting step, a heating step is also included. The heating power of the heating step is 210-270 kW. When the temperature reaches above 1450° C., the power is quickly reduced to below 100 kW.

13. The smelting method according to claim 11, characterized in that: When the total feed amount is not more than 50 kg, the total smelting time is 35-60 min.

14. The smelting method according to claim 12, characterized in that: When the total feed amount is greater than 450 kg, the total smelting time is 4.5-5.5 h.

15. The smelting method according to claim 13 or 14, characterized in that: After the temperature raising step, the raw material melt is cast into a mold.

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