Method for Removing Slag During Remelting of Ni-Based Superalloy

The invention belongs to the field of Ni-based superalloy melting and refining technology, and specifically relates to a method for removing the slag during the remelting of Ni-based superalloy.

It is well-known that the application of Ni-based superalloys is of great importance and significance, providing a key material basis for the modern engineering technology. Ni-based superalloys exhibit the excellent performance in high-temperature, high-pressure, and corrosive environments, and can be widely used in aero-engines, gas turbines, chemical reactors, and nuclear reactors. The high-temperature resistance, oxidation resistance, mechanical properties, and corrosion resistance of Ni-based superalloy make it possible to promote the progress of high-temperature processes and technology, prolong the service life of equipment, improve work efficiency, reduce energy consumption and environmental impact, thus promoting the sustainable development of modern society.

The purity level of Ni-based superalloy is one of the important parameters to evaluate its excellent performance, and it is also one of the important indexes to measure the manufacturing level of Ni-based superalloy. The existence and distribution of inclusions in Ni-based superalloys directly damage the high-temperature application and structural stability of the alloy. Therefore, it is of great significance to study the purification technology of Ni-based superalloys to improve the stability and performance of alloys.

The purification of Ni-based superalloys is achieved during its melting stage. In order to prepare a Ni-based superalloy, the master Ni-based superalloy is prepared first, and then the master Ni-based superalloy is remelted to obtain Ni-based superalloy. For the preparation of Ni-based superalloy, the alloy purification is mainly achieved by deoxidization and desulfurization. For the remelting of master Ni-based superalloy, the alloy purification is mainly achieved by removing the slag generated during the remelting process. Regarding the remelting of master superalloy (i.e., the remelting of Ni-based superalloys), during the vacuum induction melting, Ni-based superalloy melt is in direct contact with the refractory crucible. Due to the erosion of the refractory crucible by the alloy melt, the refractory will be dissolved into the alloy melt, and the oxygen decomposed by the refractory will form an oxide with the active elements in the alloy melt. During the melting process, due to the electromagnetic stirring, the oxide is floated and mixed with the melt to form a metal film with a predetermined thickness, and the metal film is the slag.

At present, in order to remove the generated slag during the remelting process, the melting temperature is generally increased and the electromagnetic stirring is accelerated, so that the alloy melt is rapidly stirred to destroy the slag, and then the slag is dissolved into the alloy melt, which undoubtedly aggravates the interaction between the alloy melt and the crucible refractory, prolongs the processing time of the alloy melting, and increases the risk of inclusion contamination in the alloy melt. Therefore, it is necessary to develop a method for removing the generated slag during the remelting of Ni-based superalloy, so that the Ni-based superalloys can be efficiently and rapidly purified during the remelting process.

Invention No. CN117385214 A discloses a method of deoxidization and desulfurization of Ni-based superalloy based on a non-calcium refractory crucible, the non-calcium refractory crucible is used to melt Ni-based superalloy by the vacuum induction melting furnace, at the same time, metal elements are added to realize deoxidization and desulfurization, including the following steps: the non-calcium refractory crucible was put into a vacuum induction melting furnace, and the superalloy was put into the non-calcium refractory crucible; the furnace chamber was vacuumed to a predetermined vacuum degree, the furnace chamber was heated to the melting temperature, and then the melting and refining were carried out. In the process of vacuum, melting, or refining, the metal element Y was added to the Ni-based superalloy, in the refining process, the metal elements Ba and Ca were added to the superalloy, the deoxidization and desulfurization of the superalloy were completed after the refining. The technical scheme realized the deoxidation and desulfurization of the superalloy by adding metal element Y in the melting process and adding metal elements Ba and Ca in the refining process. This technical scheme was suitable for the deoxidation and desulfurization of the master superalloys, and was not suitable for the removal of slag during the remelting of the superalloy.

The invention patent No. CN117383950A disclosed a non-calcium refractory crucible and preparation method for the desulfurization of Ni-based superalloys, the non-calcium crucible is made of non-calcium refractory, the non-calcium refractory are formed by the reaction of BaO, SrO and ZrOat high temperature, and the compound formed by the reaction is BaSrZrO, the non-calcium refractory crucible was used to melt the superalloy in the vacuum induction melting furnace to achieve the desulfurization, including the following steps: the non-calcium refractory crucible was placed in the vacuum induction melting furnace, and the superalloy was placed in the non-calcium refractory crucible. The vacuum induction melting furnace was closed, and the furnace chamber was vacuumed to 1×10˜10 Pa vacuum degree; under the condition of maintaining the vacuum degree, the furnace chamber is heated to the melting temperature, and then the superalloy is melted and refined. After the refining is completed, the desulfurization of the superalloy can be completed. The technical scheme realizes the desulfurization of superalloys through the non-calcium refractory crucibles. Ba, Ca, and Sr elements are added when preparing non-calcium refractory crucibles, not during the alloy melting process. Therefore, the technical scheme is not suitable for the efficient and rapid removal of slag during the melting of the superalloy.

SUMMARY

In order to solve the problems existing in the existing technology, the invention provides a method for removing the slag during the remelting of Ni-based superalloy, the removal method includes the following steps in order:

Preferably, in Step, oxygen content in the master Ni-based superalloy does not exceed 10 ppm and a sulfur content does not exceed 5 ppm; the crucible consists of the 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, a vacuum degree in the furnace chamber does not exceed 20 Pa.

In any of the above schemes, preferably, in Step, 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, heat preservation is performed for 30-60 s, 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 heat preservation is performed for 30-60 s, the master Ni-based superalloy is completely melted at this time.

In any of the above schemes, preferably, in Step, in the melting 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.

In any of the above schemes, preferably, in Stepand Step, 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.

In any of the above schemes, preferably, in Stepand Step, 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.

In any of the above schemes, preferably, in Step, the mass of the metallic element of Ca added to the alloy melt is 30-50% of the total mass of the metallic element of Ca.

In any of the above schemes, preferably, in Step, the mass of the metallic element Ca added to the alloy melt is 50-70% of the total mass of the metallic element of Ca.

In any of the above schemes, preferably, in Stepand Step, the metallic elements Ca, Ba, and Sr added in the alloy melt are blocky or filamentous.

The vacuum induction melting furnace, vacuum pump, crucible, etc. used in the invention can be selected according to the actual use, and the existing equipment can be selected according to the actual use. There is no special requirement for the equipment model. The pouring equipment and pouring process used in subsequent pouring can be used by a traditional technology. In this invention, the addition time, addition amount, and addition sequence of metallic elements Ca, Ba, and Sr are very important. Combined with the synergistic effect of other process parameters, the efficient and rapid removal of the slag in the remelting process of the superalloy is finally realized.

In Step, when the temperature in the furnace chamber reaches 850° C., a part of the metallic element Ca needs to be put in, because a melting point of Ca is 842° C., adding a part of metallic element Ca at 850° C. in advance, the melted Ca can be used to form a liquid, covering a contact area between the alloy and the crucible, which can effectively control the contact between the alloy and the crucible matrix at the moment of the melting in advance. Ca will instantly participate in the interaction between the alloy melt and the crucible, thereby inhibiting the reaction between them.

In addition, before the metallic element Ca is put into the furnace chamber, argon gas needs to be introduced into the furnace chamber first since the metallic element Ca has a strong volatility under the vacuum, the introduction of argon gas is beneficial to inhibit the volatilization of metallic element Ca and promote the participation of metallic element Ca in the interface reaction between the alloy melt and the crucible.

In Step, in the melting stage, metallic elements Ca, Ba, and Sr need to be added to the alloy melt. The reaction between the alloy melt and the crucible is mainly based on the physical dissolution of the crucible, and the dissolved O will rapidly react with Ca, Ba, and Sr to form oxides, these oxides react with the impurity phase AlOin the alloy to form a low melting point slag phase, which makes the impurities float on the liquid surface rapidly, at the same time, under the action of electromagnetic stirring, it attaches to the inner wall of the crucible and plays a role in rapidly removing the slag.

The method for removing slag during Ni-based superalloy remelting has the following beneficial effects:

(1) The invention adds three alkaline earth metals Ca, Ba, and Sr to the superalloy melt, these three alkaline earth metals have low vapor pressure and volatilize rapidly on the surface of the liquid, which destroys the surface 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 alloy melt, which are adsorbed on the inner wall of the crucible during the melting of the superalloy, or the composite oxides formed by the stirring are adsorbed to the edge of the contact between the crucible and the alloy melt to form a slag line, thus reducing the amount of the slag in the alloy melt and the inclusions in the alloy melt.

(2) The invention does not introduce the new slag removal equipment and means, which reduces the introduction of the solid phase and gas phase impurities. Compared with the slag removal method of refining the alloy melt, the invention can rapidly remove the slag, reduce the possibility of the slag entering the alloy melt and causing contamination, and has the advantages of short time-consuming and reducing the amount of the slag contamination. The production cost of Ni-based superalloy is reduced, and the production quality and efficiency of Ni-based superalloy are improved.

(3) In order to solve the technical problem that the interface between the crucible refractory and the alloy melt causes the slag to be involved in the alloy melt during the melting of Ni-based superalloy in the existing technology, the invention uses the addition of metallic elements Ca, Ba, Sr to reduce the amount of the slag in the melting process of Ni-based superalloy, improve the purity of the melted alloy, and make the produced superalloy meet the requirements of special environmental service. (4) The invention solves the technical problems that hinder the melting of Ni-based superalloys, and lays a foundation for the efficient preparation of high-quality Ni-based superalloys, the slag removal method is especially suitable for DD series and DZ series Ni-based superalloys.

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

As shown in, 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:

In Step, 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.

In Step, 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.

In Step, 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.

In Stepand Step, 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.

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

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

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.

In Step, 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.

In Step, 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 AlOin 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.

The process of removing slag in this example was shown in, 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 fromthat 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.

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.

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:

In Step, 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.

In Step, 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 withins. 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.

In Step, 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.

In Stepand Step, 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.

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

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

The process of removing slag in this example is shown in, 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 fromthat 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.

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:

In Step, 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.

In Step, 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.

In Step, 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.