CN101440436A - Purified smelting technique for high-temperature superalloy - Google Patents

Abstract

The invention belongs to the field of vacuum metallurgy, and specifically relates to a purified smelting process for high-temperature alloy return materials. The present invention uses a traditional MgO crucible, adopts a smelting method different from general smelting superalloys for purified smelting, and the purified smelting process can be simply described as a dideoxy double-cooling smelting process, specifically including: melting early stage, melting period, Refining period, pouring period. By adopting the purified smelting process of the present invention, the vacuum induction smelting high-temperature alloy return material can reduce the O and N contents of the high-temperature alloy return material to below 10 ppm. The invention realizes the ultra-low content of O and N in the high-temperature alloy return material after purification and smelting, and is suitable for the purification and smelting of nickel-based high-temperature alloys that need to reduce the O and N content after repeated use and high O and N content. needs.

Description

A Purified Smelting Process for High-temperature Alloy Return Materials

technical field

The invention belongs to the field of vacuum metallurgy, and specifically relates to a purified smelting process for high-temperature alloy return materials.

Background technique

The yield of superalloy precision castings is usually 20% to 30%, and some parts with complex shapes are even only 10%, that is, more than 70% of superalloy products are made of material heads, runners, risers, scrapped parts and chips. Exist in other forms, collectively referred to as superalloy return material.

Recycling of superalloy return materials will produce significant economic benefits. However, with the increase of the addition ratio of return materials, the nitrogen content in superalloys increases significantly, resulting in coarse dendrite structure and obvious loose tendency, which is the main reason for the change of alloy mechanical properties. Compared with the virgin alloy, the high temperature endurance and creep life of the returned alloy are significantly reduced, the main reason is that the strain rate is significantly accelerated, and due to the higher N content in the returned alloy, there are more microporosity, which accelerates the strain rate. The durability life and creep life of the superalloy show a downward trend with the increase of the ratio of the return material.

In my country, there are few researches on high-temperature alloy return materials, and a large number of high-temperature Taiwan metal return materials have not been fully utilized, and the backlog of return materials is relatively serious. Chinese invention patent application (publication number CN1786228A) discloses a vacuum smelting process of a hafnium-containing nickel-based cast superalloy K488 return material alloy. The method of adding rare earth elements is used to purify the return material alloy. After multiple return smelting, the N content is lower than 100ppm. Its main disadvantage is that the smelting method of the superalloy return material uses rare earth as the final deoxidation element. Due to the limited deoxidation ability of the rare earth element, it cannot fully deoxidize, and the denitrification effect is closely related to the oxygen content of the surface active element. Only after deoxidation can denitrification be carried out to the maximum extent. Therefore, the remelting of the superalloy return material using the return material remelting method of the Chinese invention patent application (publication number CN1786228A) cannot reduce nitrogen to below 10PPm, and the superalloy return material remelting method described in this invention can only be used with Use after matching new materials.

Contents of the invention

The purpose of the present invention is to provide a purified smelting process for high temperature alloy return material, which realizes the ultra-low content of O and N in the high temperature alloy return material after purification and smelting.

Technical scheme of the present invention is:

A purification smelting process for high-temperature alloy return materials, using traditional MgO crucibles for purification smelting, so that the O and N content of the alloy is reduced to below 10ppm; the specific steps of purification smelting are as follows:

(1) Early stage of melting: Add 0.01-0.015% of C, which accounts for the weight ratio of the returned material, to the bottom of the crucible in the early stage of melting, and vacuumize until the vacuum degree is below 3Pa, and then send power. At this time, low-power power transmission is required, and the power is 10 ~30kw, depending on the capacity of the vacuum induction furnace, to fully exhaust the returned material and fully react C and O to facilitate carbon deoxidation; until the returned material turns red completely, it will enter the melting period, at this time Power transmission until the melting is complete;

(2) Refining period: vacuumize until the vacuum degree is below 1Pa, the temperature is 1530°C±10°C, and the refining time is 10-20 minutes, depending on the capacity of the vacuum induction furnace;

(3) The first freezing period: After the refining period is over, it enters the cold storage in the later stage of refining. At this time, the vacuum pump continues to work, and the power transmission is stopped, so that the alloy is cooled until it solidifies;

(4) Final deoxidation period: After the alloy is completely solidified, the alloy is re-melted by power transmission, and pure metal calcium is added for final deoxidation;

(5) The second freezing period: after the final deoxidation of the alloy, the power is cut off, so that the alloy is naturally solidified in a high vacuum state, and the deoxidized products, nitrides and free oxygen and nitrogen dissolved in the alloy are reduced in solubility as the temperature drops. Under the circumstances, separate out and discharge;

(6) Casting of the alloy: After the metal is completely solidified, the alloy is completely melted by power transmission, and the temperature is measured to 1380°C±10°C, and the charge is poured.

The final deoxidation period is to add the pure metal calcium that has been divided into fine particles at the moment when the alloy is just cleared, divide it into several additions, and increase the power after each addition to stir, and the amount of pure metal calcium accounts for 50% of the weight percentage of the returned material. 0.05-0.2%, the particle size is 5-10mm, and the number of additions is 3-6 times.

The purified smelting process of the present invention can be simply described as a smelting process of dideoxidation and double cooling, which specifically includes: the early melting period, the melting period, the refining period, and the pouring period. Add a small amount of C into the crucible in the early stage of melting, and evacuate until the vacuum degree is below 3Pa, and then send electricity. At this time, low-power electricity transmission is required (taking a 50 kg furnace as an example, the power is generally about 30 kilowatts) until the returned material is completely transformed. After red, turn to the melting period. At this time, high-power power can be sent until the melting is completed. The purpose of low-power power transmission is to fully exhaust the return material and fully react C and O to facilitate carbon deoxidation. The refining period is selected at 1530°C±10°C. Considering metallurgical kinetics and thermodynamics, the refining time should not be too long. Taking a 50 kg furnace as an example, 10-13 minutes is appropriate. After the refining period is over, it enters the cold storage in the later stage of refining. At this time, the vacuum pump continues to work, and the power transmission is stopped, so that the alloy is cooled until it solidifies. After the alloy is completely solidified, send electricity to re-melt the alloy, add the pure metal calcium that has been divided into fine particles at the moment when the alloy is just cleared, divide it into several additions, and increase the power after each addition to stir, and use the metal calcium to deoxidize When finished, move on to the next freezing period. After the metal is completely solidified, send electricity to completely melt the alloy, measure the temperature to 1380°C±10°C, and pour. Power is always supplied during the pouring process, but the power should not be too high. By adopting the purified smelting process, the content of O and N in the alloy can be reduced to below 10ppm.

The beneficial effects of the present invention are:

1. The present invention uses a traditional MgO crucible, adopts a smelting method different from the general smelting superalloy to carry out purified smelting, and adopts the purified smelting process of the present invention to vacuum induction smelt the superalloy return material, which can make the O, N of the superalloy return material The content is reduced to below 10ppm.

2. The present invention is suitable for the purification and smelting of nickel-based superalloys that have high O and N content after repeated use and need to reduce O and N content.

3. The high-temperature alloy obtained after smelting high-temperature alloy returned material by the present invention can completely reach the level of new material.

4. The present invention uses ultra-pure smelting technology to purify cast superalloy alloy return materials, and uses K417 and other superalloy return materials to prepare high-purity, high-quality, high-performance superalloy master alloys to improve resource utilization, especially strategic Resources nickel and cobalt. The high-purity master alloy preparation technology developed by the invention can also provide high-quality superalloy master alloy for the manufacture of aero-engines.

5. Compared with the Chinese invention patent application (publication number CN1786228A), the present invention is characterized in that it utilizes 100% superalloy return material, and after purification and smelting, the O and N content reaches the level of new material, and can be reduced to below 10PPm. The purification smelting process uses two freezing times, the first freezing is at the end of the refining period, the purpose is to denitrify, after the first freezing and remelting, strong deelemental calcium is used as a deoxidizer, and the addition of calcium is divided into several times Adding, after each addition, carry out high-power (60-80 kW) stirring for 30 seconds to 1 minute, so that the deoxidized product can be fully floated and removed to achieve the purpose of sufficient deoxidation. The second freezing is also to use the sequential solidification of the alloy to remove inclusions substances to achieve the purpose of deep deoxidation and denitrification. However, the Chinese invention patent application (publication number CN1786228A) uses rare earth as the deoxidizer, and its twice freezing is for alloying and smelting with the new material, and the purpose of the returning material smelting process is to remelt with the new material, not for 100 % superalloy return materials are purified and smelted to reach the level of new materials and put into use again.

Description of drawings

Fig. 1 is the smelting process curve of the superalloy return material of the present invention.

Detailed ways

There are many kinds of refractory materials for vacuum metallurgy. The well-known CaO and spinel refractory materials have low vapor pressure, high alkalinity and good thermodynamic stability, but the problem of pulverization of large crucibles has not been completely solved. , so the large-scale vacuum induction crucible used in large quantities is still a magnesia crucible. Therefore, the present invention selects the magnesia crucible as the experimental crucible and cooperates with the correct purification smelting process to obtain better results. After the purified smelting, the O and N contents of the returned material will be as low as below 10 ppm.

The present invention is described in detail below by way of examples and accompanying drawings.

Example

As shown in Figure 1, the process flow of the present invention for smelting superalloy return materials is: charging→pre-melting→melting period→refining period→first freezing period→final deoxidation period→second freezing period→pouring. The specific operations are as follows:

(1) Adding the return material: first clean the crucible, add 0.015% of the weight ratio of the return material to the bottom of the crucible, and then add the return material blade that has been removed from the ceramic core to the crucible naturally. Be careful not to Man-made code materials, to avoid bridging hazards caused by man-made code materials.

(2) The early stage of alloy melting: After feeding, vacuumize, and when the vacuum degree is below 3 Pa, send electricity with low power (taking a 50 kg furnace as an example, the power is generally about 30 kW), until the returned material blade turns red completely, and then slowly Increase power delivery. Low-power power transmission is for sufficient degassing (gas adsorbed in the return material blade), and to achieve good carbon deoxidation during the melting period. (The time spent in the early stage of melting depends on the capacity of the vacuum induction furnace. Taking a 50 kg vacuum induction furnace as an example, it usually takes about 15 minutes)

(3) Melting period: when the return material in the crucible turns red completely, and when molten steel appears at the bottom of the crucible, increase the power transmission power without splashing, generally 30-50 kilowatts, and maintain a high vacuum state at the same time , within 3Pa, which is conducive to the full progress of carbon deoxidation.

(4) Refining period of the alloy: when the alloy is completely melted, raise the temperature to raise the temperature of the alloy liquid to 1530°C and enter the refining period. The vacuum degree in the refining period must be below 1Pa (that is, a higher vacuum degree than the melting period). Vacuum induction furnaces with a refining time of less than 500 kg generally take 15 minutes, while vacuum induction furnaces with a capacity of more than 500 kg can appropriately extend the refining time. Maintaining a high vacuum during the refining period is to create good conditions for carbon deoxidation, and to fully float and remove oxide and nitride inclusions in the returned material. Refining time should not be too long because there are a lot of active elements in the returned material, such as titanium, tantalum, etc. If they are in contact with the crucible for a long time, they will have a replacement reaction with the magnesium oxide in the crucible to increase the inclusion content in the molten steel.

(5) The first freezing period: After the alloy is refined, the power is cut off, so that the alloy is naturally solidified in a high vacuum state, the purpose is to make the oxides, nitrides and free oxygen and nitrogen dissolved in the alloy increase in solubility When it is reduced, it will be precipitated and discharged. The time of the first freezing period is generally 15-30 minutes after the alloy in the crucible is completely conjunctivated.

(6) Final deoxidation period: After the first freezing, the alloy is melted by power transmission. As soon as the alloy is completely melted, the previously processed calcium metal is divided into several times and added to the molten steel. Increase the power to stir the molten steel to float and remove the deoxidized product. The amount of pure metallic calcium generally accounts for 0.05-0.2% by weight of the returned material, the particle size is 5-10mm, and the addition frequency is generally 3-6 times.

(7) The second freezing period: the alloy is powered off after the final deoxidation, so that the alloy is naturally solidified in a high vacuum state. The purpose is to make the deoxidized products, nitrides and free oxygen and nitrogen dissolved in the alloy. When it is reduced, it will be precipitated and discharged. The second freezing period is generally 15-30 minutes after the alloy in the crucible is completely conjunctival.

(8) Casting of the alloy: After the second freezing, the temperature of the molten steel is adjusted to 1380°C by power transmission and pouring is charged. Power is always supplied during the pouring process, but the power should not be too high, generally 10-20 kilowatts.

Blades such as K417, DZ125, DZ17G and other cast superalloy return materials are smelted by the present invention, and the O and N contents of the capacity from 10 kg to 200 kg are all reduced to below 10 ppm. The results are shown in Table 1.

Table 1. Experimental data of O and N content treated by superalloy return material purification smelting process

Table 2 Experimental data of high temperature tensile properties of K417 superalloy returned material treated by purified smelting process

Explanation: One-time refers to one-time return master alloy, which is an alloy ingot made by casting parts of new material K417 master alloy, pouring the remaining riser and scrap parts and remelting it, and the second return material is to use the first-time return material to re-melt Casting parts, the remaining riser runners are smelted into the master alloy, and so on, smelting to the fourth return master alloy; purification smelting refers to the fourth superalloy smelted by the return material purification smelting process Master alloy formed by returning material.

The results of the examples show that the purified smelting process of the present invention can smelt the superalloy return material in batches, and realize the goal of ultra-low content of O and N in the superalloy return material after purification and smelting, and the high temperature of the return material after purification smelting treatment The performance index has also reached the new material level, fully meeting the technical index requirements.

Claims (2)

1. A purified smelting process for high-temperature alloy return material, characterized in that: the traditional MgO crucible is used to carry out purified smelting, so that the O and N content of the alloy is reduced to below 10 ppm; the specific steps of purified smelting are as follows: (1) Early stage of melting: Add 0.01-0.015% of C, which accounts for the weight ratio of the returned material, to the bottom of the crucible in the early stage of melting, and vacuumize until the vacuum degree is below 3Pa, and then send power. At this time, low-power power transmission is required, and the power is 10 ~30kw, depending on the capacity of the vacuum induction furnace, to fully exhaust the returned material and fully react C and O to facilitate carbon deoxidation; until the returned material turns red completely, it will enter the melting period, at this time Power transmission until the melting is complete; (2) Refining period: vacuumize until the vacuum degree is below 1Pa, the temperature is 1530°C±10°C, and the refining time is 10-20 minutes, depending on the capacity of the vacuum induction furnace; (3) The first freezing period: After the refining period is over, it enters the cold storage in the later stage of refining. At this time, the vacuum pump continues to work, and the power transmission is stopped, so that the alloy is cooled until it solidifies; (4) Final deoxidation period: After the alloy is completely solidified, the alloy is re-melted by power transmission, and pure metal calcium is added for final deoxidation; (5) The second freezing period: after the final deoxidation of the alloy, the power is cut off, so that the alloy is naturally solidified in a high vacuum state, and the deoxidized products, nitrides and free oxygen and nitrogen dissolved in the alloy are reduced in solubility as the temperature drops. Under the circumstances, separate out and discharge; (6) Casting of the alloy: After the metal is completely solidified, the alloy is completely melted by power transmission, and the temperature is measured to 1380°C±10°C, and the charge is poured. 2. According to the purification smelting process of high-temperature alloy return material according to claim 1, it is characterized in that: the final deoxidation period is to add the pure metal calcium that has been divided into fine particles at the moment when the alloy is just cleared, and add it in several times , and increase the power to stir after each addition, the addition of pure metal calcium accounts for 0.05-0.2% of the weight percentage of the returned material, its particle size is 5-10mm, and the number of additions is 3-6 times.