METHOD FOR REMOVING SLAG DURING REMELTING OF NI-BASED SUPERALLOY

Abstract

The invention discloses a method for removing the slag during the remelting of Ni-based superalloy, including: the master Ni-based superalloy is placed in a crucible located in a vacuum induction melting furnace; under the condition of maintaining a predetermined vacuum degree, the furnace cavity is heated to melt the master Ni-based superalloy, during the melting process, the metallic element Ca is thrown into the alloy melt, when the temperature in the furnace cavity rises to a predetermined degree, the master Ni-based superalloy is completely melted, at this time, the slag is formed on the surface of the alloy melt. When the master Ni-based superalloy is completely melted and enters the smelting stage, the metallic elements Ca, Ba, and Sr are put into the alloy melt in turn and the electromagnetic stirring is performed to rapidly remove the slag on the surface of the alloy melt.

Claims

1. A method for removing slag during a remelting of Ni-based superalloy, wherein the removal method comprises the following steps in order: Step 1: placing the master Ni-based superalloy in a crucible located in a vacuum induction melting furnace, closing the vacuum induction melting furnace, and pumping a furnace chamber to a predetermined degree of vacuum; Step 2: heating the furnace chamber under a predetermined degree of vacuum to melt the master Ni-based superalloy; during a melting process, adding a metallic element Ca to the alloy melt by a feeder and performing an electromagnetic stirring; wherein, when a temperature in the furnace chamber rises to a predetermined degree, the master Ni-based superalloy is completely melted, and a layer of slag is formed on a surface of the alloy melt; Step 3: when the master Ni-based superalloy is completely melted and enters a smelting stage, putting the metallic elements Ca, Ba, and Sr into the alloy melt in turn by the feeder in the smelting stage, and performing a process of electromagnetic stirring; wherein, in the process of electromagnetic stirring, the slag on the surface of the alloy melt rapidly accumulates to the circumferential position of the contact between the surface of the alloy melt and a crucible wall, and the slag on the surface of the alloy melt is rapidly removed; Step 4: using a Ni-based superalloy to cast a product after removing the slag; wherein in Step 1, a vacuum degree in the furnace chamber does not exceed 20 Pa; wherein in Step 2, the vacuum degree in the furnace chamber should not exceed 20 Pa, and the temperature should be raised from room temperature to 850 C. at a heating rate of 80-100 C./min, wherein heat preservation is performed for 30-60 s, wherein after the heat preservation, argon is introduced into the furnace chamber, and the argon flow rate is 0.1-0.15 MPa/min, and then the metallic element Ca is added to the alloy melt within 10 s, the temperature continues to rise from 850 C. to 1430-1550 C. at a heating rate of 100-150 C./min, and wherein heat preservation is again performed for 30-60 s, and the master Ni-based superalloy is completely melted at this time; wherein in Step 3, in the smelting stage, argon is kept in the furnace chamber, and the argon flow rate is 0.15-0.25 MPa/min, the metallic elements Ca, Ba, and Sr are successively put into the alloy melt, and a time interval of the three metal elements is not more than 10 s; after the three metal elements are put into the alloy melt, the electromagnetic stirring is performed for 1-2 min, and then the furnace chamber is vacuum pumped until the vacuum degree does not exceed 20 Pa; wherein in Step 2 and Step 3, a total mass of metallic elements Ca, Ba, and Sr added to the alloy melt is 1-4 wt % of the mass of the master Ni-based superalloy, the mass of metallic elements Ca, Ba, and Sr added to the alloy melt accounts for 20-30 wt %, 10-20 wt % and 50-70 wt % of the total mass of metallic elements Ca, Ba, and Sr, respectively; wherein in Step 2, the mass of the metallic element Ca added to the alloy melt is 30-50% of the total mass of the metallic element Ca; in Step 3, the mass of the metallic element Ca added to the alloy melt is 50-70% of the total mass of the metallic element Ca.

2. The method for removing the slag during the remelting of Ni-based superalloy according to claim 1, wherein an oxygen content in the master Ni-based superalloy does not exceed 10 ppm and a sulfur content does not exceed 5 ppm; a material of the crucible is oxide refractory, and the oxide is any one of magnesium oxide, alumina, silicon oxide, mixture of magnesium oxide and alumina, mixture of alumina and silicon oxide, zirconia and barium zirconate.

3. The method for removing the slag during the remelting of Ni-based superalloy according to claim 2, wherein in Step 2 and Step 3, the metallic elements Ca, Ba, and Sr placed in the alloy melt are blocky or filamentous.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a flow chart of a preferred embodiment according to the method for removing the slag during the remelting of Ni-based superalloy for the invention;

[0031] FIG. 2 is a photograph of the slag film-forming during the slag-removing process of the embodiment in FIG. 1 for the invention;

[0032] FIG. 3 is a photograph of the gradual removal of the slag during the slag-removing process of the embodiment in FIG. 1 for the invention;

[0033] FIG. 4 is a photograph of the clearing phenomenon of the slag film during the slag-removing process of the embodiment in FIG. 1 for the invention;

[0034] FIG. 5 is a photograph of the slag removal process in another preferred embodiment according to the method for removing the slag during the Ni-based superalloy remelting for the invention;

[0035] FIG. 6 is a photograph of the gradual removal of the slag during the slag- removing process of the embodiment in FIG. 5 for the invention;

[0036] FIG. 7 is a photograph of the clearing phenomenon of the slag film during the slag-removing process of the embodiment in FIG. 5 cthe invention;

[0037] FIG. 8 is a photograph of the slag removal process in another preferred embodiment according to the method for the slag removal during Ni-based superalloy remelting for the invention;

[0038] FIG. 9 is a photograph of the gradual removal of the slag during the slag-removing process of the embodiment in FIG. 8 for the invention;

[0039] FIG. 10 is a photograph of the slag film clearing during the slag-removing process of the embodiment in FIG. 8 for the invention;

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] In order to further understand the invention content of the invention, the following will elaborate on the invention in detail with specific implementation examples.

Example 1

[0041] As shown in FIG. 1, according to a preferred embodiment of the method for the removing slag during the remelting of Ni-based superalloy in the invention, the removal method includes the following steps in order: [0042] Step 1: the master Ni-based superalloy was placed in a crucible located in a vacuum induction melting furnace, the vacuum induction melting furnace was closed, and the furnace chamber was pumped to a predetermined degree of vacuum; [0043] Step 2: the furnace chamber was heated under a predetermined degree of vacuum to melt the master Ni-based superalloy, during the melting process, the metallic element Ca was added to the alloy melt by a feeder and an electromagnetic stirring was performed, when the temperature in the furnace chamber rose to a predetermined temperature, the master Ni-based superalloy was completely melted, and a layer of the slag was formed on the surface of the alloy melt at this time. [0044] Step 3: when the master Ni-based superalloy was completely melted and entered a smelting stage, in the melting stage, the metallic elements Ca, Ba, and Sr were put into the alloy melt in turn by the feeder and the electromagnetic stirring was performed; in a process of electromagnetic stirring, the slag on the surface of the alloy melt could be rapidly removed, at this time, the slag on the surface of the alloy melt rapidly accumulated to the circumferential position of the contact between the surface of the alloy melt and the crucible wall; [0045] Step 4: the Ni-based superalloy was used to cast a product after removing the slag.

[0046] In Step 1, the grade of Ni-based superalloy was DD419, the oxygen content in the master superalloy was not more than 10 ppm, and the sulfur content was not more than 5 ppm; the material of the crucible was an oxide refractory, and the oxide was a mixture of magnesium oxide and alumina, the vacuum degree in the furnace was 20 Pa.

[0047] In Step 2, the vacuum degree in the furnace chamber was kept at 20 Pa, the heating rate was increased from room temperature to 850 C. at a heating rate of 90 C./min, and the heat preservation was performed for 45 s, after the heat preservation was completed, argon was introduced into the furnace chamber, the argon flow rate was 0.12 MPa/min, and then the metallic element Ca was thrown into the alloy melt within 10 s, with the heating rate of 125 C./min increasing from 850 C. to 1490 C. and heat preservation was performed for 45 s, the Ni-based superalloy was completely melted.

[0048] In Step 3, in the smelting stage, argon was introduced into the furnace chamber, and the argon flow rate was 0.2 MPa/min, the metallic elements Ca, Ba, and Sr were successively thrown into the alloy melt, and the time interval of the three metal elements was 10 s. After the three metal elements were put into the end, the electromagnetic stirring was 1.5 min, and then the furnace chamber was vacuumed to 20 Pa.

[0049] In Step 2 and Step 3, the total mass of metallic elements Ca, Ba, and Sr added to the alloy melt was 2.5 wt % of the mass of the master Ni-based superalloy, the mass of metallic elements Ca, Ba, and Sr added to the alloy melt accounted for 25 wt %, 15 wt% and 60 wt % of the total mass of metallic elements Ca, Ba, and Sr respectively. The metallic elements Ca, Ba, and Sr put into the alloy melt are all blocky.

[0050] In Step 2, the mass of the metallic element Ca added to the alloy melt was 40% of the total mass of the metallic element Ca.

[0051] In Step 3, the mass of the metallic element Ca added to the alloy melt was 60% of the total mass of the metallic element Ca.

[0052] The vacuum induction melting furnace, vacuum pump, crucible, etc. used in this implementation case could be selected according to the actual use, the existing equipment may be selected according to the actual use. There is no special requirement for the equipment model, the pouring equipment and pouring process used in the subsequent pouring can be used by the traditional technology. In this embodiment, the addition timing, addition amount, and addition sequence of metallic elements Ca, Ba, and Sr were very important, combined with the synergistic effect of other process parameters, the efficient and rapid removal of slag in the remelting process of Ni-based superalloy was finally realized.

[0053] In Step 2, when the temperature in the furnace chamber reaches 850 C., a part of metallic element Ca needs to be put in, because the melting point of Ca is 842 C., a part of metallic element Ca was added at 850 C. in advance, the melted Ca could be used to form a liquid, covering the contact area between the alloy and the crucible, which could effectively control the contact between the alloy and the crucible matrix at the moment of melting in advance. Ca would instantly participate in the reaction between the melt and the crucible, thereby inhibiting the reaction between the melt and the crucible. In addition, since the metallic element Ca had a strong volatility under vacuum, before the metallic element Ca was put into the furnace chamber, argon gas needed to be introduced into the furnace chamber first. The introduction of argon gas was beneficial in inhibiting the volatilization of the Ca element and promoting the participation of the Ca element in the interaction between the alloy melt and the crucible.

[0054] In Step 3, in the melting stage, the metallic elements Ca, Ba, and Sr needed to be added to the alloy melt. The reaction between the alloy melt and the crucible was mainly based on the physical dissolution of the crucible, and the dissolved O would rapidly react with Ca, Ba, and Sr to form oxides. These oxides reacted with the impurity phase Al.sub.2O.sub.3 in the alloy to form a low melting point slag phase, which made the impurities float on the liquid surface rapidly. At the same time, under the electromagnetic stirring, it attached to the inner wall of the crucible and played a role in rapidly removing the slag.

[0055] The process of removing slag in this example was shown in FIG. 2, where (a) was a picture of the slag film, (b) was a picture of the gradual removal of the slag, and (c) was a picture of the cleaning phenomenon of the slag film. It could be clearly seen from FIG. 2 that a layer of slag was initially formed on the surface of the melt. With the addition of metallic elements Ca, Ba, and Sr, the slag gradually moved in the direction of the crucible wall, and finally gathered at the circumferential position of the melt surface in contact with the crucible wall, and the melt surface was clear.

[0056] The method for removing slag during the remelting of Ni-based superalloy in this implementation case has the following beneficial effects: (1) Three alkaline earth metals Ca, Ba, and Sr are added to the superalloy melt, these three alkaline earth metals have a low vapor pressure, and volatilize rapidly on the surface of the liquid alloy, which destroys the surface metal slag film. At the same time, these three alkaline earth metals have the strong oxygen absorption capacity. Under the melt stirring, they form composite oxides with the inclusions in the melt, which are adsorbed on the inner wall of the melting crucible of the superalloy. Or by stirring, the formed composite oxides are adsorbed to the edge of the contact between the crucible and the melt to form a slag line. So as to reduce the amount of the slag in the alloy melt and the inclusion in the alloy melt. (2) There is no introduction of the new slag removal equipment and means, which reduces the introduction of solid phase and gas phase impurities, at the same time, it can rapidly remove the slag and reduce the possibility of generated slag entering the alloy melt to cause the contamination. It offers the advantages of reduced processing time and lower slag contamination. (3) The addition of metallic elements Ca, Ba, and Sr is used to improve the amount of the slag in the melting process of Ni-based superalloy, and the purity of the molten alloy is improved, so that the produced superalloy meets the performance requirements for use in demanding or extreme service environments.

Example 2

[0057] According to another preferred implementation example of the method for removing slag during the remelting of Ni-based superalloy for the invention, the process steps, the equipment used, the technical principle, and the beneficial effect were basically the same as Example 1. The difference was as follows:

[0058] In Step 1, the grade of Ni-based superalloy was DD419, the oxygen content in the master Ni-based superalloy was not more than 10 ppm, and the sulfur content was not more than 5 ppm; the material of the crucible was an oxide refractory, and the oxide was a mixture of alumina and silica, the vacuum degree in the furnace was 20 Pa.

[0059] In Step 2, the vacuum degree in the furnace chamber was kept at 20 Pa, and the temperature was increased from room temperature to 850 C. at a heating rate of 80 C./min for 60 s, after the heat preservation was completed, argon was introduced into the furnace chamber, the argon flow rate was 0.1 MPa/min, and then the metallic element Ca was put into the alloy melt within 10 s. The temperature continued to rise from 850 C. to 1550 C. at a heating rate of 100 C./min, and heat preservation was performed for 30 s. At this time, the master Ni-based superalloy was completely melted.

[0060] In Step 3, in the smelting stage, argon was introduced into the furnace chamber, and the argon flow rate was 0.15 MPa/min, the metallic elements Ca, Ba, and Sr were successively thrown into the alloy melt, and the time interval of the three metal elements was 10 s, after the three metal elements were put into the furnace, the electromagnetic stirring was performed for 1 min, and then the vacuum degree in the furnace chamber was 20 Pa.

[0061] In Step 2 and Step 3, the total mass of metallic elements Ca, Ba, and Sr added to the alloy melt was 1 wt % of the mass of the master Ni-based superalloy. The mass of metallic elements Ca, Ba, and Sr added to the alloy melt accounted for 20 wt %, 10 wt %, and 70 wt % of the total mass of metallic elements Ca, Ba, and Sr respectively. The metallic elements Ca, Ba, and Sr put into the alloy melt were all blocky.

[0062] In Step 2, the mass of the metallic element Ca added to the alloy melt was 30% of the total mass of the metallic element Ca.

[0063] In step 3, the mass of the metallic element Ca added to the alloy melt was 70% of the total mass of the metallic element Ca.

[0064] The process of removing slag in this example is shown in FIG. 3, where: (a) is a picture of the slag film, (b) is a picture of the gradual removal of the slag, and (c) is a picture of the cleaning phenomenon of the slag film. It can be clearly seen from FIG. 3 that a layer of slag is initially formed on the surface of the melt, with the addition of metallic elements Ca, Ba, and Sr, the slag gradually moves towards the crucible wall, and finally gathers at the circumferential position where the melt surface is in contact with the crucible wall, and the melt surface is cleaned.

Example 3

[0065] According to another preferred implementation example of the method for removing slag during the remelting of Ni-based superalloy for the invention, the process steps, the equipment used, the technical principle, and the beneficial effect are basically the same as Example 1, the difference is:

[0066] In Step 1, the grade of Ni-based superalloy was DD419, the oxygen content in the master Ni-based superalloy was not more than 10 ppm, and the sulfur content was not more than 5 ppm; the material of the crucible is an oxide refractory, and the oxide is a mixture of alumina and silica, the vacuum degree in the furnace was 20 Pa.

[0067] In Step 2, the vacuum degree in the furnace chamber was kept at 20 Pa, and the temperature was increased from room temperature to 850 C. at a heating rate of 100 C./min for 30 s. After the heat preservation was completed, argon was introduced into the furnace chamber, the argon flow rate was 0.15 MPa/min, and then the metallic element Ca was added to the alloy melt within 10 s, the temperature continued to rise from 850 C. to 1430 C. at a heating rate of 150 C./min, and heat preservation is performed for 60 s, at this time, the master Ni-based superalloy is completely melted.

[0068] In Step 3, in the smelting stage, argon was introduced into the furnace chamber, and the argon flow rate was 0.25 MPa/min, the metallic elements Ca, Ba, and Sr were successively thrown into the alloy melt, and the time interval of the three metal elements was 10 s, after the three metal elements were put into the furnace, the electromagnetic stirring was performed for 2 min, and then the vacuum degree in the furnace chamber was 20 Pa.

[0069] In Step 2 and Step 3, the total mass of metallic elements Ca, Ba, and Sr added to the alloy melt was 4 wt % of the mass of the Ni-based superalloy master alloy ingot. The mass of metallic elements Ca, Ba, and Sr added to the alloy melt accounted for 30 wt %, 20 wt%, and 50 wt % of the total mass of metallic elements Ca, Ba, and Sr respectively. The metallic elements Ca, Ba, and Sr put into the alloy melt were all blocky.

[0070] In Step 2, the mass of the metallic element Ca added to the alloy melt was 50% of the total mass of the metallic element Ca.

[0071] In Step 3, the mass of the metallic element Ca added to the alloy melt was 50% of the total mass of the metallic element Ca.

[0072] The process of removing slag in this example is shown in FIG. 4, where: (a) is a picture of the slag film, (b) is a picture of the gradual removal of the slag, and (c) is a picture of the cleaning phenomenon of the slag film. It can be clearly seen from FIG. 4 that a layer of slag is initially formed on the surface of the melt, with the addition of metallic elements Ca, Ba, and Sr, the slag gradually moves towards the crucible wall, and finally gathers at the circumferential position where the melt surface is in contact with the crucible wall, and the melt surface is cleaned.

Comparison Case 1

[0073] The master Ni-based superalloy was placed in a crucible; located in a vacuum induction melting furnace for the melting, the alloy grade was DD419, the oxygen content in the master alloy ingot was no more than 10 ppm and the sulfur content was no more than 5 ppm, the crucible material was a mixture of alumina and silicon oxide, the vacuum in the furnace chamber was 20Pa and the melting temperature was 1490 C. Since no metallic elements Ca, Ba, and Sr were added during the smelting process, a layer of the slag was generated on the surface of the melt. After the electromagnetic stirring, the slag entered the alloy melt again, leading to a serious contamination in the alloy melt. The OTS automatic steel non-metallic inclusion analysis system was used to test the inclusions of the samples of the above three examples and the comparison case (mainly test oxides), the test environment, and test conditions were the same, and the test results were shown in Table 1-Table 4.

TABLE-US-00001 TABLE 1 Oxide particle analysis results of Ni- based superalloy samples in Example 1 Count of particles of different sizes Count 30- of 0-0.5 0.5-1 1-2 2-5 5-30 100 >100 Oxide type particles m m m m m m m Total oxide 78 0 0 33 24 20 1 0 Silicate 51 0 0 17 15 18 1 0 12CaO7Al.sub.2O.sub.3 12 0 0 9 2 1 0 0 Al.sub.2O.sub.3 9 0 0 4 4 1 0 0 Oxide 3 0 0 2 1 0 0 0 SiO.sub.2 2 0 0 1 1 0 0 0 CaO 1 0 0 0 1 0 0 0

TABLE-US-00002 TABLE 2 Oxide particle analysis results of Ni- based superalloy samples in Example 2 Count of particles of different sizes Count 30- of 0-0.5 0.5-1 1-2 2-5 5-30 100 >100 Oxide type particles m m m m m m m Total oxide 74 0 0 32 23 19 0 0 Silicate 50 0 0 17 15 18 0 0 12CaO7Al.sub.2O.sub.3 11 0 0 9 2 0 0 0 Al.sub.2O.sub.3 7 0 0 3 3 1 0 0 Oxide 3 0 0 2 1 0 0 0 SiO.sub.2 2 0 0 1 1 0 0 0 CaO 1 0 0 0 1 0 0 0

TABLE-US-00003 TABLE 3 Oxide particle analysis results of Ni- based superalloy samples in Example 3 Count of particles of different sizes Count 30- of 0-0.5 0.5-1 1-2 2-5 5-30 100 >100 Oxide type particles m m m m m m m Total oxide 75 0 0 32 23 19 1 0 Silicate 50 0 0 17 15 17 1 0 12CaO7Al.sub.2O.sub.3 10 0 0 8 1 1 0 0 Al.sub.2O.sub.3 9 0 0 4 4 1 0 0 Oxide 3 0 0 2 1 0 0 0 SiO.sub.2 2 0 0 1 1 0 0 0 CaO 1 0 0 0 1 0 0 0

TABLE-US-00004 TABLE 4 Oxide particle analysis results of Ni- based superalloy samples in proportion Count of particles of different sizes Count 30- of 0-0.5 0.5-1 1-2 2-5 5-30 100 >100 Oxide type particles m m m m m m m Total oxide 115 0 0 30 47 34 4 0 Silicate 71 0 0 14 33 21 3 0 Al.sub.2O.sub.3 17 0 0 4 8 4 1 0 Oxide 10 0 0 7 3 0 0 0 SiO.sub.2 8 0 0 0 2 6 0 0 Spinel 5 0 0 5 0 0 0 0 CaO 2 0 0 0 0 2 0 0 MnO 1 0 0 0 0 1 0 0 12CaO7Al.sub.2O.sub.3 1 0 0 0 1 0 0 0

[0074] From Table 1 to Table 4, it can be seen that after adding metallic elements Ca, Ba, and Sr during the melting process, the count of oxide particles in the melt is significantly reduced, and only a small amount of inclusions enter into the melt because some inclusions accumulate with the slag to the circumferential position of the melt surface in contact with the crucible wall. For the alloy melt without metallic elements Ca, Ba, and Sr, the oxide particles all enter the alloy melt, causing a serious contamination to the alloy melt.

[0075] In particular, the technical scheme of the invention involves many parameters, and it is necessary to comprehensively consider the synergy between the various parameters in order to obtain the beneficial effect and significant progress of the invention. Moreover, the value range of each parameter in the technical scheme is obtained through a large number of tests. For each parameter and the combination of each parameter, the inventor has recorded a large number of test data, which is limited to space, and the specific test data is not disclosed here.

[0076] It is not difficult for technicians in this field to understand that the method for removing the slag during the remelting of Ni-based superalloy in this invention includes the invention content and specific implementation method part of the above-mentioned invention specification and any combination of the parts shown in the attached diagram, which is limited to space and does not describe the schemes composed of these combinations one by one in order to make the specification concise. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the invention shall be included within the scope of protection of the invention.