A titanium alloy scrap pelletizing and consumable electrode preparation method based on vacuum sintering

Abstract

This invention discloses a method for granulating titanium alloy scrap and preparing consumable electrodes based on vacuum sintering, comprising: S1, pre-treating recycled titanium alloy scrap; S2, cold-pressing the pre-treated titanium alloy scrap into a mold to obtain a pre-formed scrap block; S3, vacuum sintering and granulating the scrap block: placing the pre-formed scrap block into a concave hole of a heat-resistant partition coated with a release agent; then feeding it into a vacuum sintering furnace, evacuating the furnace to a vacuum degree ≤0.05Pa, and raising the furnace temperature to 850-950℃ at a heating rate of 5-10℃ / min; holding at this temperature and then cooling in the furnace, naturally forming titanium alloy scrap agglomerates, which are subsequently used in the preparation of consumable electrodes. The advantages of this invention are: reducing the difficulty of cold-pressing titanium alloy scrap, improving the strength of the electrode block, preventing cracking of the consumable electrode during subsequent vacuum welding, increasing the scrap addition ratio, and simultaneously achieving stress relief, degassing, densification, and agglomeration granulation using a single vacuum sintering process, thereby improving production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal metallurgy and material recycling technology, and particularly relates to a method for granulating titanium alloy processing scrap using vacuum sintering technology and using it to prepare consumable electrodes for vacuum consumable arc melting. Background Technology

[0002] Titanium alloys generate a large amount of irregularly shaped scrap during machining, which accounts for 30% to 50% of the raw material input. Currently, the mainstream recycling process for titanium alloy scrap involves mixing the cleaned titanium scrap with sponge titanium, pressing and welding it into consumable electrodes, and then remelting it into ingots through vacuum consumable arc remelting.

[0003] However, this process is limited by the inherent properties of titanium alloy chips and has many drawbacks: First, it has poor cold-pressing formability. The irregular shape of titanium alloy scrap and the large internal stress generated during machining make it difficult to cold press when mixed with sponge titanium. At the same time, the irregular scrap will aggravate the wear of the mold during the cold pressing process, and may even easily cause problems such as electrode block delamination and cracking, and difficulty in demolding, which will significantly increase production costs and the risk of production abnormalities.

[0004] Second, the strength of the formed electrode blocks is insufficient. In traditional processes, the mixed raw materials rely solely on the mechanical interlocking of the cold pressing process, resulting in low overall strength of the electrode blocks. During electrode block handling and vacuum welding of multiple blocks, breakage is highly likely, compromising the integrity of the consumable electrode. This can lead to decreased stability in the smelting process and affect metallurgical quality, or even directly cause smelting accidents and reduce the yield.

[0005] Third, the proportion of scrap added is limited, resulting in low resource utilization. Due to constraints on formability and electrode strength, in order to ensure the stability of the vacuum consumable melting process, the proportion of titanium alloy scrap added in traditional recycling processes can usually only be controlled below 30%. Most of the titanium scrap cannot be effectively utilized, resulting in low resource recycling rate and increasing the overall cost of titanium alloy recycling production.

[0006] Fourth, production efficiency is low. The loose density of the pretreated titanium alloy scrap is low, resulting in small batch sizes and difficulty in controlling the uniformity of the mixing process. This leads to low overall production efficiency and cannot meet the capacity requirements of large-scale industrial recycling. Summary of the Invention

[0007] The purpose of this invention is to solve the problems of difficult molding and cracking, low electrode strength, limited addition ratio and low production efficiency in existing titanium alloy scrap recycling processes. It provides a titanium alloy scrap granulation method and consumable electrode preparation method based on vacuum sintering, so as to achieve efficient recycling of titanium alloy scrap and stable and high-quality production of consumable electrodes.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In one aspect, a method for granulating titanium alloy scrap based on vacuum sintering is provided, including pretreatment of titanium alloy scrap, cold pressing preforming of scrap, and vacuum sintering granulation of scrap blocks; specifically, the pretreated scrap is loaded into a mold and cold pressed to obtain scrap preformed blocks, the scrap preformed blocks are placed in the recesses of a heat-resistant partition coated with a release agent, and then the partition is sent into a vacuum sintering furnace, the furnace is evacuated to a vacuum degree ≤0.05Pa, the furnace temperature is raised to 850-950℃ at a heating rate of 5-10℃ / min, held at the temperature for 1-2 hours, and then cooled with the furnace; after the sintered blocks are removed from the furnace and cooled, titanium alloy scrap clumps are naturally formed.

[0009] The above steps simultaneously achieve four major functions through the vacuum sintering process: First, stress relief: eliminates the internal stress generated inside the scrap material during the cold pressing preforming process; Second, degassing: removes gaseous impurities such as O, N, and H adsorbed on the surface of the titanium alloy scrap material; Third, densification and agglomeration: under high temperature, the scrap material particles diffuse and bond together, greatly improving the overall strength and forming stable sintered agglomerates; Fourth, natural granulation: after cooling, regularly sized scrap material agglomerates can be obtained directly without additional crushing and grading.

[0010] In conjunction with the first aspect, in some implementations of the first aspect, during the cold pressing preforming of the scrap, the pre-treated titanium alloy scrap is loaded into a cold pressing mold for pressing, with the pressing pressure controlled at 300–800T and the holding time ≥1min, ultimately obtaining a density of 2.0–3.0 g / cm³. 3 Preformed blocks of scrap material.

[0011] This invention achieves preliminary shaping solely through cold pressing, reducing the target density of the cold-pressed preform to 2.0–3.0 g / cm³. 3 The lower range can significantly reduce the difficulty of cold pressing irregularly shaped scraps, fundamentally avoiding electrode delamination and cracking and demolding difficulties caused by high-density cold pressing. It also reduces wear on the mold caused by irregular scraps, thereby reducing mold wear and production costs.

[0012] In conjunction with the first aspect, in some implementations of the first aspect, the release agent is boron nitride or yttrium oxide.

[0013] This invention uses boron nitride or yttrium oxide as a release agent, which can effectively prevent the titanium alloy from sticking to the partition during high-temperature sintering and ensure the quality of the clumps during demolding.

[0014] In conjunction with the first aspect, in some implementations of the first aspect, the heat-resistant partition holes are evenly distributed in an array on the partition, and their size is (D35±10)×(40~50)mm, where 40~50mm is the depth of the holes.

[0015] This invention employs natural granulation, relying on the size limitation of the concave holes in the heat-resistant partition, and can directly obtain cylindrical scrap pellets with regular size after cooling.

[0016] In conjunction with the first aspect, in some implementations of the first aspect, the particle size of the titanium alloy scrap agglomerates obtained after vacuum sintering is 25±10mm.

[0017] In conjunction with the first aspect, in some implementations of the first aspect, in the pretreatment of titanium alloy scrap, the titanium alloy scrap is crushed to control the size of the crushed scrap to ≤10mm, and then subjected to alkaline washing, acid washing, rinsing and drying in sequence. Finally, the ferromagnetic impurities mixed in the scrap are removed by magnetic separation process, and finally clean, dry and impurity-free titanium alloy scrap is obtained.

[0018] In summary, the titanium alloy scrap granulation method of the present invention integrates four major processes—stress relief of titanium scrap, degassing of impurities, densification of the blank, and scrap granulation—into a single vacuum sintering step through the design of "low-density cold pressing preforming + vacuum sintering granulation," thereby improving production efficiency. At the same time, after vacuum sintering, the titanium scrap particles form a metallurgical bond through diffusion bonding, which greatly improves the strength of the agglomerates and makes them less prone to breakage during handling, splicing, and welding, thus improving the quality of the granulated finished product.

[0019] Secondly, a method for preparing consumable electrodes using the aforementioned titanium alloy scrap agglomerates is provided, including consumable electrode batching and mixing, consumable electrode pressing and welding, and vacuum consumable arc melting; specifically, the titanium alloy scrap agglomerates obtained in the above granulation method are mixed with primary sponge titanium with a particle size of 0.83-25.4 mm and intermediate alloys required for titanium alloy melting in a preset ratio; the uniformly mixed material is fed into a mold and cold-pressed to obtain electrode blocks of uniform specifications; then multiple electrode blocks are stacked and spliced, and sent into a vacuum argon-filled plasma welding box for welding to obtain an integral consumable electrode; finally, the welded integral consumable electrode is placed in a vacuum consumable arc furnace for melting to obtain a titanium alloy ingot with uniform chemical composition and dense structure.

[0020] In conjunction with the second aspect, in some implementations of the second aspect, the mass percentage of titanium alloy scrap clumps in the consumable electrode is 30% to 60%.

[0021] The titanium alloy scrap agglomerates modified by the present invention have high density and good flowability, and their shape is similar to that of conventional sponge titanium. Therefore, the mass proportion of titanium alloy scrap agglomerates in the ingredients can reach 30% to 60%, breaking through the addition ratio limitation of traditional processes. Attached Figure Description

[0022] Figure 1This is a flow chart of the titanium alloy scrap granulation and consumable electrode preparation process of the present invention; Figure 2 This is a schematic diagram showing the comparison before and after vacuum sintering granulation in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the concave hole structure of the heat-resistant partition of the present invention. Detailed Implementation

[0023] Example 1

[0024] To make the present invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates a method for granulating titanium alloy scrap and preparing consumable electrodes based on vacuum sintering. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0025] In this embodiment, taking 2000 kg of TC4 titanium alloy milling waste chips as an example, a method for granulating titanium alloy chips based on vacuum sintering is provided. The specific steps are as follows: S1, Pre-treatment of titanium alloy scrap: The recycled TC4 scrap was crushed and screened to obtain qualified scrap with a size of <10mm. The scrap was then screened, alkali washed to remove oil, ultrasonic cleaned, acid washed with HF+HNO3 mixture to remove oxide scale, rinsed with pure water to remove residual acid, and centrifuged to dehydrate. The dehydrated scrap was then placed in a 110℃ oven to dry for 4 hours. Finally, a magnetic separation process was used to remove mixed ferromagnetic impurities, resulting in 1800kg of clean and dry pretreated TC4 titanium alloy scrap.

[0026] S2, Cold pressing preforming of scrap materials: The pre-treated scrap was loaded into the mold of a cold-press baler, subjected to a pressure of 400T and held for 1 minute, and pressed into a cylindrical pre-formed block with a diameter of 30mm × 30mm. The density of the pre-formed block was measured to be 2.5g / cm³. 3 It meets the requirements for low-density preforming, with no cracking during the pressing process, smooth demolding, and no obvious wear on the mold.

[0027] S3, vacuum sintering and granulation of scrap material: (1) Boron nitride suspension is pre-coated into the recesses 3a of the heat-resistant partition, and then dried to obtain the partition 3 with a release coating. In this embodiment, the partition is uniformly arranged with recesses of D35×40mm, and the arrangement is as follows. Figure 3 As shown; (2) Place the preformed scrap obtained in step S2 into the recessed hole 3a of the heat-resistant partition one by one, and then send the partition as a whole into the vacuum sintering furnace. After closing the furnace door, evacuate the furnace until the vacuum degree inside the furnace reaches 0.03Pa. Set the heating rate to 8℃ / min, and heat to 900℃ and then hold for 1.5h. (3) After the heat preservation is completed, the furnace is cooled to room temperature. The sintered billet is taken out after the furnace is opened. TC4 titanium alloy scrap clumps with a particle size of about 25 mm are naturally obtained. There is no adhesion or breakage. The qualified rate of the granulated finished product reaches 98.5%.

[0028] The comparison results of the pre-formed scrap block 1 before vacuum sintering and granulation and the granulated titanium alloy scrap clump 2 in this embodiment are as follows: Figure 2 As shown: After granulation modification according to the present invention, the titanium alloy scrap agglomerates 2 have high density, regular shape and good flowability, which can effectively improve the uniformity of mixing in high proportion addition scenarios and reduce the difficulty of subsequent consumable electrode molding; when applied to the preparation of consumable electrodes, the proportion of titanium alloy scrap added to the consumable electrode can be increased from less than 30% in the traditional process to 30%~60%, which greatly improves the resource utilization rate of titanium alloy scrap and reduces the raw material cost of recycled titanium alloy.

[0029] Furthermore, after vacuum sintering, the titanium shavings particles form a metallurgical bond through diffusion bonding. Compared with the traditional cold pressing process that relies solely on mechanical interlocking, the density of the lumps and subsequent pressed electrode blocks obtained by this invention is increased by more than 40%. They are less prone to breakage during handling, splicing, and welding, which can effectively ensure the integrity of the consumable electrode and improve the stability of the vacuum consumable melting process.

[0030] In this embodiment, the vacuum sintering process can effectively remove gaseous impurities such as O, N, and H adsorbed on the surface of titanium chips, reduce the content of gaseous impurities in the final titanium alloy ingot, improve the metallurgical quality of the recycled titanium ingot, and make the product performance more stable. Using boron nitride as a high-temperature release agent can effectively prevent the sintered block from sticking to the partition plate, prevent the sintered block from breaking, and significantly improve the qualification rate of the granulated finished product.

[0031] Example 2

[0032] See Figure 1 Based on Example 1, using the TC4 agglomerates prepared in Example 1, consumable electrode preparation and vacuum consumable arc melting were carried out, including consumable electrode batching and mixing, consumable electrode pressing and welding, and vacuum consumable arc melting, to obtain recycled TC4 titanium alloy ingots. The specific steps are as follows: S1, Ingredients: The total amount of self-consumable electrode feed is 4 tons, of which 1800 kg of TC4 scrap agglomerates prepared in Example 1 are added, accounting for 45% of the total feed mass. The remaining feed consists of primary sponge titanium with a particle size of 0.83~25.4 mm, as well as intermediate alloys required for smelting such as vanadium aluminum, aluminum briquettes, and ferrotitanium. The feed is prepared according to the specification of 200 kg per electrode block, with a total of 20 portions.

[0033] S2, Mixing: Add the prepared single portion of raw materials to the double cone mixer and mix for no less than 1 minute to ensure that all raw materials are uniform.

[0034] S3, Electrode Block Pressing: The uniformly mixed material is loaded into the press mold cavity and cold-pressed under 6000T pressure to obtain 20 self-consumable electrode blocks of 200kg each. There is no delamination or cracking during the pressing process, and the demolding is smooth.

[0035] S4, Electrode Welding: 20 electrode blocks are stacked and spliced ​​in a 2*10 manner, clamped with a fixture, and then sent into a vacuum argon-filled plasma welding box for welding to obtain an integral and complete consumable electrode. No electrode blocks are broken during the welding process, and the overall integrity of the electrode is good.

[0036] S5, Vacuum self-consuming arc melting: The welded self-consuming electrode is placed into a VAR furnace and subjected to two vacuum self-consuming arc melting processes to obtain a complete TC4 titanium alloy ingot.

[0037] S6, Composition Analysis: Samples of the smelted ingots were taken for composition analysis. The results showed that the chemical composition of the ingots fully met the requirements of GB / T3620.1 standard. The content of oxygen and hydrogen impurities was lower than that of ingots produced by traditional processes with the same proportion of scrap material, indicating better metallurgical quality. The ingot analysis results are shown in Table 1, Example 2 Ingot Analysis Table.

[0038]

[0039] To more intuitively demonstrate the technical effects of the present invention, a comparative example is also provided, as follows: The preparation and vacuum arc melting of consumable electrode, including consumable electrode batching and mixing, consumable electrode pressing and welding, and vacuum arc melting, yields a recycled TC4 titanium alloy ingot. The specific steps are as follows: S1, Batching: The total amount of self-consumable electrodes fed this time is 4 tons, TC4 scrap is 1200kg, accounting for 30% of the total feed mass, and the remaining feed is virgin sponge titanium with a particle size of 0.83~25.4mm, as well as intermediate alloys required for smelting such as vanadium aluminum, aluminum briquettes, and ferrotitanium; the feed is prepared according to the specification of 200kg per electrode block, and each electrode is prepared twice, for a total of 40 portions.

[0040] Compared to Example 2, the comparative example requires "two batches of material for each electrode, for a total of 40 parts". This is because the loose scrap has a low density and occupies a lot of space. When the addition ratio is 30%, the single batching needs to be adjusted to two batchings, which also reflects the problem of low recycling efficiency of traditional scrap.

[0041] S2, Mixing: Add the prepared single portion of raw materials to the double cone mixer and mix for no less than 1 minute to ensure that all raw materials are uniform.

[0042] S3, Electrode Block Pressing: The uniformly mixed material is loaded into the press mold cavity and fed in two batches. The first batch is pre-formed under 2000T pressure, and the second batch is cold-pressed under 6000T pressure to obtain 20 self-consumable electrode blocks of 200kg each. There is no delamination or cracking during the pressing process, and the demolding is smooth. However, due to the loose material and loose electrode edges, there are corner chipping problems.

[0043] Compared with Example 2, in the comparative example, after the loose scrap was mixed with the other raw materials, the electrode edges cracked and chipped due to high stress and weak bonding force, which also reflects the quality problems of the traditional electrode with added scrap.

[0044] S4, Electrode Welding: 20 electrode blocks are stacked and spliced ​​in a 2*10 manner, clamped with a fixture, and then sent into a vacuum argon-filled plasma welding box for welding to obtain an integral and complete consumable electrode. No electrode blocks are broken during the welding process, and the overall integrity of the electrode is good.

[0045] S5, Vacuum self-consuming arc melting: The welded self-consuming electrode is placed into a VAR furnace and subjected to two vacuum self-consuming arc melting processes to obtain a complete TC4 titanium alloy ingot.

[0046] S6, Composition Analysis: Samples of the smelted ingots were taken for composition analysis. The results showed that the chemical composition of the ingots met the requirements of GB / T3620.1 standard. The analysis results of the ingots are shown in the comparative ingot analysis table in Table 2.

[0047]

[0048] Comparing the analysis results of the comparative ingot with those of Example 2, we can conclude that: In Example 2, the measured contents of the main elements Al and V both fell within the standard requirement range, and the measured contents of impurity elements Fe, C, O, N, and H were all far below the upper limit specified in the standard, fully meeting the quality requirements of GB / T3620.1. From the beginning to the end of the casting, the compositional range of all elements was extremely small. The range represents the maximum deviation of composition from different positions in the casting. The smaller the range, the better the uniformity. The maximum deviation of the main element Al was only 0.05wt%, the maximum deviation of V was only 0.04wt%, and the maximum deviation of impurity elements did not exceed 0.01wt%, proving that the titanium alloy ingot produced by this smelting process achieved a very high level of compositional uniformity.

[0049] In terms of the extreme difference in component uniformity: the Al deviation of Example 2 was only 41.7% of that of the comparative example, the V deviation was only 40% of that of the comparative example, and the Fe deviation was 50% of that of the comparative example. Moreover, there was no detectable deviation in N and H in Example 2. It can be seen that the uniformity of Example 2 is better.

[0050] Regarding the stability of elemental content distribution: In Example 2, the Al element fluctuation range was only 0.05wt%, and the V element fluctuation range was only 0.04wt%, with almost no compositional shift from beginning to end, indicating a very stable distribution and minimal deviation in impurity elements. In contrast, the Al fluctuation in the comparative example reached 0.12wt%, and the V fluctuation reached 0.10wt%, with compositional fluctuations more than twice that of Example 2, and the deviations in N and H impurity elements were significantly greater.

[0051] Regarding the level of impurity element control: In Example 2, the N element was <0.0030wt% at all positions, and the H element was <0.0006wt% at all positions, indicating that the accuracy and uniformity of impurity control were better than those of the comparative example.

[0052] In summary, by employing the vacuum sintering and pre-forming cold pressing of this invention, the titanium scrap is stress-relieved, the billet is densified, and a higher proportion of scrap can be added. Simultaneously, the pressed electrode blocks have high density, and the appearance does not exhibit the loose, chipped edges and corner problems common with traditionally pressed electrode blocks made from loose scrap. Furthermore, using this scrap in the preparation of consumable electrodes produces titanium alloy ingots that, while meeting national standards, have lower hydrogen and other impurity content, significantly improved compositional uniformity, smaller compositional deviations, and superior process stability. This verifies the advantages of this invention's process in controlling the compositional uniformity of titanium alloy ingots.

[0053] The production results of this embodiment show that after vacuum sintering and granulation, the loose density of titanium alloy scrap is greatly improved, the amount of material fed in a single batch during the batching process is nearly doubled, the granules have good flowability, the uniformity of mixing is easier to ensure, and the overall production efficiency is more than 30% higher than that of traditional recycling processes, which is fully adapted to the requirements of large-scale industrial recycling production.

[0054] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for granulating titanium alloy scrap based on vacuum sintering, comprising titanium alloy scrap pretreatment, scrap cold pressing pre-forming, and scrap block vacuum sintering granulation, characterized in that: S1, pre-treat the recycled titanium alloy scrap to obtain pre-treated titanium alloy scrap; S2, the pre-treated titanium alloy scrap is loaded into the mold and cold-pressed to obtain a pre-formed block of scrap; S3, vacuum sintering and granulation of scrap material: S31, place the preformed chip block into the recess of the heat-resistant partition plate coated with release agent; S32, then the partition plate is sent into the vacuum sintering furnace as a whole, and the vacuum inside the furnace is evacuated to ≤0.05Pa. The furnace temperature is raised to 850-950℃ at a heating rate of 5-10℃ / min. S33, after holding at heat for 1 to 2 hours, is cooled with the furnace, and after cooling, it naturally forms a clump of titanium alloy scrap.

2. The method for granulating titanium alloy scrap based on vacuum sintering according to claim 1, characterized in that: In step S2, during the cold pressing pre-forming of the scrap, the pre-treated titanium alloy scrap is loaded into a cold pressing mold for cold pressing. The pressing pressure is 300–800T, and the holding time is ≥1min, ultimately yielding a density of 2.0–3.0 g / cm³. 3 Preformed blocks of scrap material.

3. The method for granulating titanium alloy scrap based on vacuum sintering according to claim 2, characterized in that: In step S31, the release agent is boron nitride or yttrium oxide.

4. The method for granulating titanium alloy scrap based on vacuum sintering according to claim 1 or 2, characterized in that: In step S31, the heat-resistant partition holes are evenly distributed in an array on the partition, and their size is (D35±10)×(40~50)mm, where 40~50mm is the depth of the hole.

5. The method for granulating titanium alloy scrap based on vacuum sintering according to claim 4, characterized in that: In step S33, the particle size of the titanium alloy scrap agglomerate obtained after vacuum sintering is 25±10mm.

6. The method for granulating titanium alloy scrap based on vacuum sintering according to claim 1 or 2, characterized in that: In step S1, the titanium alloy scrap is crushed to control the size of the scrap to ≤10mm. Then, it is subjected to alkaline washing, acid washing, rinsing and drying in sequence. Finally, the ferromagnetic impurities mixed in the scrap are removed by magnetic separation to obtain titanium alloy scrap.

7. A method for preparing a consumable electrode, characterized in that: (1) Consumable electrode preparation and mixing: Titanium alloy scrap lumps prepared according to the vacuum sintering-based titanium alloy scrap granulation method described in claim 1 are mixed with primary sponge titanium with a particle size of 0.83 to 25.4 mm and intermediate alloy required for titanium alloy smelting in proportion. (2) Consumable electrode pressing and welding: The uniformly mixed material is fed into the mold and cold-pressed to obtain electrode blocks of uniform specifications. Then, multiple electrode blocks are stacked and spliced, and sent into a vacuum argon-filled plasma welding box for welding to obtain an integral consumable electrode. (3) Vacuum consumable arc melting: The welded integral consumable electrode is placed in a vacuum consumable arc furnace for melting to obtain titanium alloy ingots.

8. The method for preparing a consumable electrode according to claim 7, characterized in that: In step (1), the mass percentage of titanium alloy scrap clumps in the consumable electrode is 45% to 60%.

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