Short-process recycling and smelting method for TC4 titanium alloy scraps through electron beam cold bed furnace

Abstract

The invention belongs to the technical field of TC4 titanium alloy scrap recycling and smelting, and discloses a TC4 titanium alloy scrap electron beam cold bed furnace short-process recycling and smelting method which comprises the following steps that S1, TC4 scrap-shaped return scraps with the size being 5-15 mm, aluminum shots and functional agents are prepared; s2, the three materials are mixed and then subjected to single-time cold pressing to form a blank, and then a protective layer is sprayed; s3, the pressed blank is fed into an electron beam cold bed smelting furnace to be smelted; smelting parameters are as follows: in a high-temperature melting stage, the temperature is 1800-1900 DEG C, and the electron beam power density is 2.5-3.5 kW / cm < 2 >; in the transition refining stage, the temperature is 1700-1800 DEG C, and the electron beam power density is 1-2 kW / cm < 2 >; in the low-temperature oxygen trapping stage, the temperature is 1000-1200 DEG C; the core-shell aluminum shots are added, aluminum volatilization in the smelting process is compensated, meanwhile, the aluminum shots react with oxygen, the aluminum content is controlled to be 5.50-6.75%, the oxygen content is controlled to be smaller than 0.2%, the national standard requirement is met, and efficient and low-cost recycling is achieved.

Description

Technical Field

[0001] This invention relates to the field of TC4 titanium alloy scrap recycling and smelting technology, specifically a short-process recycling and smelting method for TC4 titanium alloy scrap in an electron beam cold hearth furnace. Background Technology

[0002] TC4 titanium alloy possesses excellent comprehensive and machinability properties, and is primarily used in the manufacture of load-bearing components such as aero-engine fans, compressor disks, and blades. However, due to the unique processing technology, complex production process, and low yield of TC4 titanium alloy, a large amount of titanium alloy recyclable material is generated during processing, resulting in high costs and significant waste. Recycling and remelting recyclable titanium alloy material can significantly improve the utilization rate of titanium alloys and is one of the important ways to reduce titanium alloy costs. Melting is a crucial step in titanium alloy preparation; only high-quality melted products with uniform chemical composition and microstructure and few inclusions can be subsequently processed into batches of titanium materials with stable performance.

[0003] Currently, the commonly used method for titanium alloy smelting is still the traditional vacuum arc furnace (VAR furnace). For titanium alloy ingots used in aero-engines, three VAR furnace smelting processes are generally required to improve the uniformity of the ingot composition. VAR furnace smelting requires electrode pressing and welding. To ensure electrode strength, only a small amount of recycled material can be added to the electrodes, which has limited effect on cost reduction, and can only produce ingots with round cross-sections. Furthermore, conventional VAR furnace smelting methods for preparing titanium alloy ingots are difficult to completely remove high- and low-density inclusions from the ingots and ensure a high degree of compositional uniformity. The presence of inclusions and compositional inhomogeneity in the ingots will seriously impair the fatigue, durability, and other properties of engine components.

[0004] Compared with the VAR furnace smelting process, the electron beam cold hearth furnace (EB furnace) can recover a large amount of recycled titanium alloy materials, greatly reducing production costs; the requirements for the shape and size of the recycled materials are less stringent, and the raw materials are highly adaptable; the EB furnace can directly use raw materials such as sponge titanium, recycled materials and alloy additives, without the need to prepare electrodes, making it an all-around smelting equipment; the EB furnace can directly produce qualified ingots of various specifications from the raw materials.

[0005] However, the EB furnace melting technology is relatively difficult to operate, which is related to the complex characteristics of the EB furnace. When using an EB furnace to melt TC4 titanium alloy (Ti-6Al-4V) ingots, the TC4 titanium alloy contains the volatile element Al; and because the TC4 alloy is oxidized during high-temperature processing, the O content of the recycled TC4 alloy scrap is generally above 0.20%. Therefore, the current EB furnace recycling and melting process for TC4 alloy scrap has two key technical challenges. One challenge is controlling Al volatilization. During the EB melting process of TC4 alloy scrap, Al is easily volatilized and is affected by many factors, leading to segregation and unevenness of chemical composition. The other challenge is controlling the O content in the recycled titanium alloy ingots. Summary of the Invention

[0006] This invention aims to provide a short-process recycling and smelting method for TC4 titanium alloy scrap using an electron beam cold hearth furnace. The method employs core-shell structured aluminum briquettes to provide gradient compensation for the TC4 titanium alloy scrap, and adds composite functional agents for cold pressing. After being cold-pressed into billets, the billets are fed into an electron beam cold hearth furnace (EB furnace) for smelting. Based on the aluminum volatilization characteristics of the EB furnace, the process parameters are strictly controlled. The core-shell structured aluminum briquettes compensate for aluminum volatilization during the smelting process and react with oxygen to control oxygen content, achieving efficient recycling. This solves the problems in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A short-process recycling and smelting method for TC4 titanium alloy scrap in an electron beam cold hearth furnace includes the following steps:

[0009] S1. Raw material processing:

[0010] Prepare TC4 scrap recycled material, core-shell aluminum granules, and composite functional agents; among them, the core-shell aluminum granules are made of pure aluminum as the core and coated with TC4 titanium alloy on the outside; the size of the scrap recycled material is 5-15mm;

[0011] S2, pressing and forming:

[0012] The TC4 scrap return material, core-shell aluminum granules and functional agents are mixed and cold-pressed into a billet in one go, and then a protective layer is sprayed on the surface to obtain the pressed billet;

[0013] S3, Electron Beam Melting:

[0014] The pressed billet is fed into an electron beam cooling hearth furnace for melting to obtain a smelted ingot; the melting parameters are as follows:

[0015] High-temperature melting stage: temperature 1800-1900℃, electron beam power density 2.5-3.5kW / cm² 2 ;

[0016] Transitional refining stage: temperature 1700-1800℃, electron beam power density 1-2kW / cm² 2 ;

[0017] Low-temperature oxygen capture stage: temperature is 1000-1200℃.

[0018] Furthermore, in S1, the mass percentage concentration of O in the TC4 shavings return material is 0.30 wt%, and the mass percentage concentration of Al is 6.2 wt%; the particle size of the core-shell aluminum granules is Φ1.5-2.5 mm.

[0019] Furthermore, in S1, the types and mass percentage concentrations of the composite functional agents are: 0.5wt% NH4HCO3 and 0.3wt% Y2O3.

[0020] Furthermore, in S2, the core-shell aluminum bead achieves a three-dimensional gradient distribution in the compact: radial gradient: 5wt% in the central region to 3wt% in the edge region; axial gradient: 2wt% in the upper part to 5wt% in the lower part; the protective layer is TiN with a coating thickness of 3-5μm.

[0021] Furthermore, in S2, the cold pressing pressure is 300-380 MPa; the density of the resulting compact is 3-4 g / cm³. 3 .

[0022] Furthermore, in S3, the smelting parameters are:

[0023] High-temperature melting stage: temperature 1800℃, electron beam power density 3kW / cm² 2 ;

[0024] Transitional refining stage: temperature 1700℃, electron beam power density 1.5kW / cm² 2 ;

[0025] Low-temperature oxygen capture stage: The temperature is 1200℃, and a Ti-35Nb collector is used.

[0026] The principles and beneficial effects of the technical solution are as follows:

[0027] This invention provides a short-process recycling and smelting method for TC4 titanium alloy scrap using an electron beam cold hearth furnace. The method employs a core-shell structure aluminum briquettes for gradient compensation of the TC4 titanium alloy scrap, and adds composite functional agents for cold pressing. After cold pressing into billets, the billets are fed into an EB furnace for smelting. Strict control of EB furnace process parameters is maintained. The core-shell structure aluminum briquettes compensate for aluminum volatilization during smelting and react with oxygen to control oxygen content, achieving efficient and low-cost recycling of TC4 titanium alloy scrap. Tests have shown that the Al content deviation is <±0.1wt%, achieving aluminum content control at 5.50-6.75% and oxygen content reduced to below 0.2wt%, meeting the requirements of national standard GB / T3620.1-2016. Furthermore, the use of 100% scrap recycled material significantly reduces costs and further improves the recycling rate, achieving a cost reduction of over 40% compared to traditional processes. The aluminum briquette utilization rate is >92%, the sintering process is eliminated, and the smelting cycle is shortened by 40%.

[0028] Specifically, the aluminum bead has a pure aluminum core, coated with a TC4 titanium alloy (Ti-6Al-4V). The Ti-6Al-4V shell provides alloying elements (Al and V), and the uniformity of the compact composition is controlled by a gradient distribution. The core-shell interface has high bonding strength, preventing the shell from falling off during pressing. At the same time, the core and shell aluminum bead achieve a three-dimensional gradient distribution in the compact, namely: radial gradient (component cross-section): central region: aluminum bead content 5wt% (high concentration), compensating for alloying element segregation in the central region; edge region: aluminum bead content 3wt% (low concentration), avoiding over-alloying at the edges; axial gradient (component height direction): upper part: aluminum bead content 2wt% (low concentration), matching the characteristics of lower pressure and lower density in the upper part during pressing; lower part: aluminum bead content 5wt% (high concentration), compensating for alloying element aggregation caused by high pressure in the lower part. During the compaction process, a dynamic compensation system based on laser-induced breakdown spectroscopy (LIBS) real-time monitoring (using pulsed lasers to bombard the compact surface, exciting atomic emission spectra, and analyzing the concentration distribution of elements such as Al and V in the compact in real time) is used to intelligently compensate for the aluminum briquettes. This system achieves high detection accuracy (Al element ±0.1wt%) and a short response time. The raw materials are uniformly distributed in the compact, which is beneficial for the uniform chemical composition of the ingot. Furthermore, the compact has a regular shape and high density, resulting in higher melting efficiency compared to feeding loose scrap. The addition of composite functional agents creates pores and refines grains, acting as a binder and facilitating the smooth compaction process. The TiN protective layer significantly improves the overall performance of the compact. Based on the gradient compensation of the aluminum briquettes, process parameters such as the temperature of the EB furnace and the power density of the electron beam are strictly controlled to precisely control aluminum volatilization, achieving the target aluminum content control. Simultaneously, the aluminum reacts with oxygen, resulting in an oxygen content of less than 0.2%, meeting national standards. Attached Figure Description

[0029] Figure 1 This is a diagram of the pressed billet of the shaving-like TC4 titanium alloy return material in Embodiment 2 of the present invention;

[0030] Figure 2 This is a diagram of the EB furnace ingot of shaving-like TC4 titanium alloy return material in Embodiment 2 of the present invention;

[0031] In the figure, (a) is the drawing of ingot No. 1, and (b) is the drawing of ingot No. 2;

[0032] Figure 3 This is a longitudinal Al element distribution diagram of the ingot circumferential section in Embodiment 2 of the present invention;

[0033] In the figure, (a) is the longitudinal Al element distribution diagram of the circumferential section of ingot No. 1, and (b) is the longitudinal Al element distribution diagram of the circumferential section of ingot No. 2. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments:

[0035] Melting is a crucial step in titanium alloy production. Only high-quality melted ingots with uniform chemical composition and microstructure, and minimal inclusions, can be subsequently processed into batches of titanium materials with stable performance. Ingot composition uniformity has two aspects: first, it requires a uniform distribution of alloying elements across all regions of a single ingot; second, it requires stable and controllable compositional content across batches of ingots. Compared to VAR furnace melting, EB furnace melting includes a "refining" process and isolates the raw materials from the ingot, preventing high- and low-density inclusions from directly entering the ingot. EB furnace melting is significantly superior to VAR furnace melting in controlling high-density inclusions (HDI) and low-density inclusions (LDI), making it the optimal melting method for researching and producing high-performance, multi-component, high-purity titanium alloys and Ti-Al intermetallic compounds. It is also an effective method for recycling titanium alloy scrap. EB furnaces can recycle large quantities of recycled titanium alloy materials, significantly reducing production costs. The shape and size requirements for recycled materials are relatively relaxed, making them highly adaptable. EB furnaces can directly use sponge titanium, recycled materials, and alloy additives, eliminating the need for electrode preparation, making them a versatile smelting device. EB furnaces can directly produce qualified ingots of various specifications from raw materials. Studies show that when recycled materials are added at normal levels, EB furnace smelting can save approximately 37% in raw material costs compared to VAR furnace smelting. Furthermore, when the amount of recycled materials added is the same, producing sheet metal from flat ingots smelted in EB furnaces can reduce processing costs by approximately 43% compared to producing sheet metal from round ingots smelted in VAR furnaces.

[0036] However, the EB furnace melting technology is relatively difficult to operate, which is related to the complex characteristics of the EB furnace. When using an EB furnace to melt TC4 titanium alloy (Ti-6Al-4V) ingots, the TC4 titanium alloy contains the volatile element Al, resulting in uneven composition distribution in the ingots, making it difficult to control the ingot composition. Controlling the volatilization of different alloying elements during the cold hearth furnace melting process to ensure the accuracy of the final alloy composition has always been a key constraint on the preparation of complex titanium alloy ingots using the EB furnace. The EB furnace recycling and melting process for TC4 alloy return materials has two key technical challenges. One challenge is controlling Al volatilization. During the EB melting process of TC4 alloy return materials, Al is easily volatilized and influenced by many factors, leading to chemical composition segregation and unevenness. It is necessary to master the aluminum volatilization law of a given EB furnace, accurately compensate for aluminum, strictly control the EB furnace process parameters, control aluminum volatilization, and achieve the target of controlling aluminum content. The other challenge is controlling the O content in the recycled titanium alloy ingots. GB / T3620.1—2016 stipulates: (1) Main elements: Al content controlled at 5.5% to 6.75%, V content controlled at 3.5% to 4.5%; (2) Impurity elements: Fe content ≤ 0.25%, C content ≤ 0.08%; N content ≤ 0.05%; H content ≤ 0.015%; O content ≤ 0.20%; other elements combined ≤ 0.30%. It is worth noting that the TC4 alloy for aviation requires an O content in the range of 0.13% to 0.20% to obtain good yield strength and tensile strength properties. However, because TC4 alloy is oxidized during high-temperature processing, the O content of recycled TC4 alloy scrap is generally above 0.20%.

[0037] The EB furnace recycling and smelting process for TC4 alloy return material requires precise control over the state and chemical composition of the TC4 alloy return material, which is one of the key technologies of the project. On the one hand, the oxygen content of return material varies significantly depending on its state, and the process measures for controlling the oxygen content differ. On the other hand, the subsequent feeding methods of different states (blocks, scraps) in the electron beam cold hearth furnace, along with the distribution of compensating aluminum and functional agents, and in the feeding mechanism, also differ. Scrap TC4 alloy return material must be mixed and pressed into billets. This ensures two things: first, the raw materials (TC4 alloy return material, compensating aluminum, functional agents) are evenly distributed, which is beneficial for the uniform chemical composition of the ingot; second, the billet has a regular shape and high density, resulting in higher smelting efficiency compared to the feeding method of loose scraps.

[0038] Example 1

[0039] To address the aforementioned problems, this invention provides a short-process recycling and smelting method for TC4 titanium alloy scrap in an electron beam cold hearth furnace, comprising the following steps:

[0040] S1. Raw material processing:

[0041] Prepare TC4 scrap recycled material with a size of 5-15mm, core-shell aluminum pellets, and composite functional agents; wherein, the core-shell aluminum pellets have pure aluminum as the core and are coated with TC4 titanium alloy, i.e., Al core / Ti-6Al-4V shell, with a particle size of Φ1.5-2.5mm; wherein, the mass percentage concentration of O in the TC4 scrap recycled material is 0.30wt%, and the mass percentage concentration of Al is 6.2wt%; the types and mass percentage concentrations of the composite functional agents are 0.5wt% NH4HCO3 and 0.3wt% Y2O3;

[0042] S2, pressing and forming:

[0043] TC4 scrap recycled material, core-shell aluminum briquettes, and functional agents are mixed and cold-pressed in a single pass at 350 MPa. A TiN protective layer is then plasma-sprayed onto the surface to obtain a compact with a density of 3-4 g / cm³. 3 The core-shell aluminum granules achieve a three-dimensional gradient distribution in the compact: radial gradient: 5wt% in the central region to 3wt% in the edge region; axial gradient: 2wt% in the upper part to 5wt% in the lower part; the protective layer is TiN with a coating thickness of 3-5μm.

[0044] S3, Electron Beam Melting:

[0045] (1) Feed the billet into the feeding zone of the electron beam cold bed melting furnace, close the furnace door, start the vacuum pump system, and evacuate the furnace to a high vacuum; (2) Turn on the electron gun, gradually increase the filament current to the rated value, and generate a high-energy electron beam; focus the electron beam through the electromagnetic lens, and control the scanning path of the electron beam on the surface of the raw material through the scanning coil; specifically, in the high-temperature melting stage: the electron beam bombards the billet in the feeding zone, causing it to melt and form a molten pool; in the transition refining stage: the molten pool flows slowly through the water-cooled copper cold bed, and the electron beam continues to heat and maintain the liquid state, and impurities (such as high-energy electron beams) are removed. Density inclusions and low density inclusions float or sink due to density differences, separating from the titanium liquid. The high vacuum environment promotes the evaporation and removal of volatile impurities and functional agents. In the low-temperature oxygen trapping stage, a Ti-35Nb trap is used to further remove oxygen impurities. Subsequently, the alloying elements are fully dissolved and homogenized in the cold bed, and then the alloy liquid flows into the water-cooled crystallizer and is slowly pulled down by the bottom ingot rod to form an ingot. (3) Gradually reduce the electron beam power, and turn off the electron gun and vacuum pump after the molten pool solidifies. Inert gas (such as argon) is introduced, and the ingot is taken out after cooling to room temperature. The melting parameters are: high temperature melting stage: temperature is 1800℃, electron beam power density is 3kW / cm 2 Transitional refining stage: temperature 1700℃, electron beam power density 1.5kW / cm² 2 Low-temperature oxygen capture stage: The temperature is 1200℃, and a Ti-35Nb trap is used.

[0046] Example 2

[0047] The following experiments were conducted according to the above method: First, the chemical composition of the recycled TC4 alloy chips was randomly sampled and tested. The results of the chemical composition sampling test are shown in Table 1:

[0048] Table 1. Sampling inspection of chemical composition (%) of recycled TC4 alloy chips

[0049]

[0050] Using the aforementioned low-O scrap TC4 titanium alloy recycled material, and following the smelting and recycling method of Example 1, the total weight of the raw materials was 50 kg. Based on the Al element volatilization model, the aluminum volatilization rate was calculated to be 21%, resulting in the required amount of Al briquettes to be added. Specifically, the amount of aluminum briquettes was 0.7 kg, and the amount of functional agent was 0.4 kg. After the compensating aluminum briquettes were uniformly mixed with 100% scrap TC4 titanium alloy recycled material, a 2000-ton press was used to press a billet. The billet dimensions were 310 x 200 x 85 mm, the billet weight was 17.1 kg, and the billet density was approximately 3.2 g / cm³. 2 The compacted billets possess a certain degree of compactness and strength, improving the charging rate and smelting efficiency. Welding the billets together during feeding ensures smooth and continuous feeding. The smelting power is 100kW, the smelting rate is 100kg / h, and the smelting time is approximately 30 minutes. See the example of shaving-like TC4 titanium alloy return material compacts. Figure 1 As shown.

[0051] According to step S3 of Example 1, the shavings of TC4 titanium alloy return material billet is placed in the EB furnace for melting. Two ingots, numbered 1 and 2, are cast from the shavings of TC4 titanium alloy return material billet in the EB furnace. See Figure 2 As shown.

[0052] Chemical composition was tested by taking samples from three locations on the machine rings of TC4 titanium alloy return ingots No. 1 and No. 2 at the head (50mm), middle, and tail (100mm). The test results are shown in Tables 2 and 3, respectively. The longitudinal Al element distribution is shown in Table 3. Figure 3 As shown, all elements comply with the requirements of GB3620.1-2016.

[0053] Table 2. Environmental analysis of chemical composition of No. 1 ingot of TC4 titanium alloy scrap.

[0054]

[0055] Table 3. Environmental analysis of chemical composition of No. 2 ingot of TC4 titanium alloy scrap.

[0056]

[0057] In summary, the present invention provides a short-process recycling and smelting method for TC4 titanium alloy scrap in an electron beam cold hearth furnace. This method utilizes core-shell structured aluminum briquettes to provide gradient compensation for TC4 titanium alloy scrap, and adds composite functional agents for cold pressing. After cold pressing, the scrap is smelted in an electron beam cold hearth furnace (EB furnace). Strict control of EB furnace process parameters is achieved. The core-shell structured aluminum briquettes compensate for aluminum volatilization during the smelting process and react with oxygen to control oxygen content, thus realizing efficient and low-cost recycling of TC4 titanium alloy scrap. Experiments have shown that the Al content deviation is <±0.1wt%, the Al recovery rate is 96%, and the oxygen content is reduced to 0.14-0.16wt%. Furthermore, the use of 100% scrap return material significantly reduces costs and further improves the recovery rate, achieving a cost reduction of over 40% compared to traditional processes. The aluminum briquette utilization rate is >92%, the sintering process is eliminated, and the smelting cycle is shortened by 40%, from 150 minutes in the traditional method to 90 minutes.

[0058] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific technical solutions or characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A short-process recycling and smelting method for TC4 titanium alloy scrap in an electron beam cold hearth furnace, characterized in that, Includes the following steps: S1. Raw material processing: Prepare TC4 scrap recycled material, core-shell aluminum granules, and composite functional agents; among them, the core-shell aluminum granules are made of pure aluminum as the core and coated with TC4 titanium alloy on the outside; the size of the scrap recycled material is 5-15mm; S2, pressing and forming: The TC4 scrap return material, core-shell aluminum granules and functional agents are mixed and cold-pressed into a billet in one go, and then a protective layer is sprayed on the surface to obtain the pressed billet; S3, Electron Beam Melting: The pressed billet is fed into an electron beam cooling hearth furnace for melting to obtain a smelted ingot; the melting parameters are as follows: High-temperature melting stage: temperature 1800-1900℃, electron beam power density 2.5-3.5kW / cm² 2 ; Transitional refining stage: temperature 1700-1800℃, electron beam power density 1-2kW / cm² 2 ; Low-temperature oxygen capture stage: temperature is 1000-1200℃.

2. The method for short-process recycling and smelting of TC4 titanium alloy scrap in an electron beam cold hearth furnace according to claim 1, characterized in that: In S1, the mass percentage concentration of O in the TC4 scrap return material is 0.30 wt%, and the mass percentage concentration of Al is 6.2 wt%; the particle size of the core-shell aluminum granules is Φ1.5-2.5 mm.

3. The method for short-process recycling and smelting of TC4 titanium alloy scrap in an electron beam cold hearth furnace according to claim 1, characterized in that: In S1, the types and mass percentage concentrations of the composite functional agents are: 0.5wt% NH4HCO3 and 0.3wt% Y2O3.

4. The method for short-process recycling and smelting of TC4 titanium alloy scrap in an electron beam cold hearth furnace according to claim 1, characterized in that: In S2, the core-shell aluminum granules achieve a three-dimensional gradient distribution in the compact: radial gradient: 5wt% in the central region to 3wt% in the edge region; axial gradient: 2wt% in the upper part to 5wt% in the lower part; the protective layer is TiN with a coating thickness of 3-5μm.

5. The method for short-process recycling and smelting of TC4 titanium alloy scrap in an electron beam cold hearth furnace according to claim 1, characterized in that: In S2, the cold pressing pressure is 300-380 MPa; the density of the resulting compact is 3-4 g / cm³. 3 .

6. The method for short-process recycling and smelting of TC4 titanium alloy scrap in an electron beam cold hearth furnace according to claim 1, characterized in that: In S3, the smelting parameters are: High-temperature melting stage: temperature 1800℃, electron beam power density 3kW / cm² 2 ; Transitional refining stage: temperature 1700℃, electron beam power density 1.5kW / cm² 2 ; Low-temperature oxygen capture stage: The temperature is 1200℃, and a Ti-35Nb collector is used.

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