A method for recovering titanium from titanium residue to produce titanium alloy ingot

Abstract

The present application relates to the field of residual titanium recycling, and specifically discloses a method for preparing titanium alloy ingot from residual titanium, which comprises the following steps: collecting residual titanium alloy materials with the same brand, and cleaning the surface of the residual titanium; smelting the residual titanium to form titanium alloy cast bar, sampling the cast bar, testing the composition of the sample, and then performing linear interpolation to obtain the composition distribution of the entire cast bar in the longitudinal direction; preparing electrode blocks from sponge titanium and intermediate alloy according to a specially designed composition sequence; combining the electrode blocks and the titanium alloy cast bar into coaxial composite electrodes; loading the composite electrodes into a vacuum consumable arc furnace, and performing twice vacuum consumable arc smelting to obtain titanium alloy ingot. The present application adjusts and matches the composition of the electrode blocks according to the composition of the ingot recovered from the cold bed furnace or the skull furnace, and then performs vacuum consumable arc smelting to prepare titanium alloy recycled ingot, which has the effect of significantly improving the product quality, and can improve the uniformity of the composition of the ingot, especially the composition stability of the batch ingot.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material processing, in particular to a method for preparing titanium alloy ingot with uniform and stable composition from residual titanium. BACKGROUND

[0002] Titanium alloy has excellent properties such as high specific strength, corrosion resistance, and high and low temperature resistance, and is widely used in the fields of aviation, aerospace, shipbuilding, and chemical industry. Due to the processing characteristics of titanium material, the final yield is generally less than 50%, and a large amount of residual titanium is generated during the entire production process. Therefore, increasing the recycling of titanium alloy residues has great social and economic benefits.

[0003] Currently, there are two main methods for recycling titanium alloy residues: ① block-shaped residual titanium alloy is washed with acid and alkali and welded into a whole electrode, or scrap residual titanium alloy is cleaned and crushed, then mixed with sponge titanium and intermediate alloy to press into electrode blocks, which are then welded into a whole electrode, and the electrode is melted in a vacuum consumable arc furnace for 2 times to prepare a titanium alloy ingot; ② block-shaped residual titanium alloy is washed with acid and alkali, or scrap residual titanium alloy is cleaned and directly pressed into electrode blocks, and the blocks (usually additional electrode blocks pressed from sponge titanium and intermediate alloy are also added) are placed in an electron beam cold hearth furnace, a plasma beam cold hearth furnace, or a vacuum consumable arc skull furnace to be melted into an ingot, which is then melted in a vacuum consumable arc furnace for 1-2 times to prepare a final titanium alloy ingot. The advantage of scheme ① is that the equipment is simple and the cost is relatively low; the advantage of scheme ② is that high-density inclusions in residual titanium can be removed by sedimentation due to the presence of a cold hearth / skull. Therefore, scheme ② can eliminate customers' concerns about metallurgical defects in titanium alloy. Generally, titanium alloy has poor processability and is prone to mix or embed high-density inclusions such as broken hard alloy tools during processing, and such inclusions cannot be removed by vacuum consumable arc melting, which can become a major hidden danger in titanium alloy parts. It should be further pointed out that the electron beam cold hearth furnace in scheme ② is the most popular titanium alloy melting and recycling scheme at present due to its relatively simple equipment structure and high production efficiency; however, the biggest disadvantage of the electron beam cold hearth furnace is that, compared to all other melting methods, the required vacuum degree is extremely high due to the presence of an electron beam during melting, resulting in the maximum volatilization of molten alloy elements, among which Al and other elements can volatilize by 5-20 wt.%, therefore, the element content control during this process is the most difficult, and the volatilization of common alloy elements during normal melting of the other several methods is very small (generally <2 wt.%).

[0004] However, the above two mainstream methods have the following problems:

[0005] The composition uniformity within a single batch of ingot is poor, and the composition stability between multiple batches of ingots is very poor. This is mainly due to the large amount of residual titanium raw materials required for single ingot smelting, and the composition of single block residual titanium is difficult to control, so it is difficult to accurately design the composition allocation of the whole ingot, resulting in very poor composition stability of multiple batches, and it is also difficult to design uniform distribution of different smelting parts of a single ingot, resulting in poor composition uniformity of a single ingot. There are two main reasons for this: first, residual titanium mainly comes from the riser, bottom sheet, surface scraps of titanium alloy ingot, head, bottom, edge and corner of bar and forged parts, etc. The composition of the residual titanium is very different from that of the mother ingot, and the composition fluctuation of the residual titanium in different areas is also very large, so it is difficult to test the composition of each or each area to grasp the true composition status. Second, residual titanium can come from different ingot numbers, even different manufacturers' materials, but the residual titanium is generally large in number but small in size, and it is difficult to manage, so it is difficult to know the true composition through traceability, and it is also difficult to know the true composition status through chemical composition test due to the large number. In addition, if the electron beam cold bed smelting recycling route is adopted, the extremely high vacuum in the electron beam smelting environment leads to high volatilization of smelting elements, which aggravates the composition control problem.

[0006] The block-shaped waste, as the main source of waste, relies too much on alkali and acid washing. The surface of the block-shaped residual titanium usually contains surface oxides in addition to oil stains, and usually needs to be treated by acid washing and alkali washing. Otherwise, the oxygen content brought by the residual titanium oxide to the recycled ingot cannot be known, which may cause the oxygen content of the ingot to exceed the range specified in the national standard GB3620.1 or the range expected by the customer (Note: Oxygen itself is a kind of alloying element of titanium alloy, and the oxygen content of titanium alloy generally has a range, and too high or too low is not in line with the standard). Related investment is usually difficult to pass environmental evaluation to build a factory, and the equipment system investment is large, which hinders the treatment of residual titanium and thus hinders the recycling of titanium alloy. In fact, since the oxygen content of sponge titanium is very low, usually ≤0.04 wt.%, and the oxygen content required for titanium alloy ingot is generally 0.10-0.20 wt.%, TiO2 oxide is added as a raw material in the production of titanium alloy. Therefore, compared with the block-shaped substrate, the relatively thin surface oxide layer formed on the surface of the titanium alloy during hot working does not have a high total oxygen content in the material, and has the potential to be used as a raw material for alloy ingot.

[0007] Due to the inability to fully grasp the composition of the raw materials or the difficulty in controlling the smelting process (if electron beam cold bed smelting is adopted) each time, this production method with poor composition uniformity and poor batch composition stability seriously aggravates the customers' concerns about the quality of titanium alloy recycling products, reduces the value of residual titanium recycling, and obviously hinders the development of the residual titanium recycling industry. SUMMARY

[0008] In view of the problems existing in the prior art in recycling and remelting titanium alloy, the purpose of the present application is to provide a method for recycling and preparing titanium alloy ingot from residual titanium, which is not only environmentally friendly, but also can prepare titanium alloy ingot with uniform and stable composition.

[0009] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0010] A method for recycling and preparing titanium alloy ingot from residual titanium, characterized in that it comprises the following steps:

[0011] Step 1), collect titanium alloy residual materials of the same grade, and clean the surface of the residual titanium, which is specifically surface cleaning with conventional environmentally friendly oil removal solvents and water in sequence;

[0012] Step 2), use an electron beam cold bed furnace or a plasma beam cold bed furnace or a vacuum consumable arc shell furnace to melt the residual titanium of step 1), and then solidify it into a round titanium alloy cast bar;

[0013] Step 3), sample the part of the titanium alloy cast bar obtained in step 2) within 300 mm from the head end face and the bottom end face in the longitudinal direction, and sample every 200-1000 mm in the remaining part of the titanium alloy cast bar, then test the composition of the sampled samples, and obtain the composition distribution of the entire titanium alloy cast bar in the longitudinal direction by linear interpolation;

[0014] Step 4), weigh, mix and press the sponge titanium and the intermediate alloy one by one according to a specially designed composition sequence to form an electrode block with a circular center hole, then stack and weld the electrode block in order, and before or after welding, insert the titanium alloy cast bar obtained in step 2) into the circular center hole of the electrode block in the preset head-bottom direction to form a coaxial composite electrode; then put the composite electrode into a vacuum consumable arc melting furnace, weld and fix it with the same grade auxiliary electrode, perform the first vacuum consumable arc melting, and use direct current stirring current in the melting process, the setting value of the direct current stirring current is determined by the stirring magnetic field intensity generated by it, and the magnetic field intensity is 4-6 mT; then turn over the composite electrode to perform the second vacuum consumable arc melting, and use alternating current stirring current in the melting process, and finally obtain a titanium alloy ingot; wherein the specially designed composition sequence needs to meet: in the longitudinal direction of the composite electrode, taking the length of a single electrode block as a unit, the composition of each unit corresponding to the titanium alloy cast bar part and the composition of the electrode block are weighted and averaged, and the composition of each unit should be consistent. That is, the average composition C of the whole composite electrode = the average composition C of any unit i = (the composition C of any electrode block block-i × the weight of any electrode block mblock-i + the composition C of the cast bar part corresponding to the unit bar-i× the weight m of the casting rod section bar-i ) / (the weight m of any electrode block block-i + the weight m of the casting rod section corresponding to the unit bar-i )。

[0015] Further, the length of the single electrode block (i.e. the length in the longitudinal direction of the composite electrode) is 200-600 mm.

[0016] Further, the AC stirring magnetic field strength during the second vacuum self-consumption arc melting is 1-3 mT, and the stirring period is 4-12 s.

[0017] Further, the shape of the electrode block is circular or regular octagonal.

[0018] Further, the diameter of the central hole of the electrode block is 110-640 mm; and when producing the same ingot, the diameter of the casting rod used is 10-40 mm smaller than the diameter of the central hole of the electrode block, and the difference between the length of the casting rod and the total length of the electrode block is ≤10 mm. When the diameter of the casting rod is 10-20 mm smaller than the diameter of the central hole of the electrode block, the casting rod is inserted into the central hole before welding the electrode block; and when the diameter of the casting rod is 20-40 mm smaller than the diameter of the central hole of the electrode block, the casting rod is inserted into the central hole after welding the electrode block.

[0019] Further, the length of the casting rod is 2000-6000 mm, and the difference between the length of the casting rod and the total length of the electrode block is ≤10 mm.

[0020] Further, the outer diameter (the diameter of the circumscribed circle or the diameter of the circumscribed circle) of the electrode block is 420-880 mm, and the pressing density of the electrode block is 3.2-3.6 g / cm 3 .

[0021] Further, in the composite electrode, the weight of the casting rod accounts for 8-60 wt.% of the total weight of the composite electrode.

[0022] Further, in the titanium alloy residual material (i.e. residual titanium) in step 1), the content of titanium element is ≥ 70 wt.%.

[0023] Further, in step 2), the power of a single electron gun during electron beam cold hearth furnace melting is 300-500 kW; the power of a single plasma gun during plasma beam cold hearth furnace melting is 300-800 kW; the melting current / voltage of the vacuum self-consumption arc skull furnace is set to 25-55 kA / 25-40 V, and a self-consumption electrode of the same grade and similar target composition is used during melting.

[0024] Further, the diameter of the auxiliary electrode used during the first vacuum self-consumption arc melting is greater than the diameter of the casting rod and smaller than the outer diameter of the composite electrode.

[0025] Further, the smelting current / voltage is 12-20 kA / 22-28 V in the first vacuum self-consumption arc smelting, and the smelting current / voltage is 15-30 kA / 24-35 V in the second vacuum self-consumption arc smelting.

[0026] Further, the crucible diameter used in the first vacuum self-consumption arc smelting is 520-980 mm, and the crucible diameter used in the second vacuum self-consumption arc smelting is 600-1080 mm.

[0027] Further, the diameter of the titanium alloy ingot after 2 times of vacuum self-consumption arc smelting is 600-1080 mm, and the weight is 2000-12000 Kg.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] 1. Due to the large number of residual titanium alloy block scraps, the composition of each unit is determined, and the process control is difficult, it is difficult to prepare a high-quality titanium alloy recycling ingot with uniform and stable composition. However, the present application can bring the following main benefits:

[0030] ① The composition of the recycling ingot is not uniform in the longitudinal direction. Through the composition adjustment of the electrode block, the entire composite electrode is uniform in the longitudinal direction, and a titanium alloy ingot with more uniform composition is prepared, and the uniformity of the composition of a single titanium alloy ingot is improved. It should be noted that in the process of vacuum self-consumption arc smelting, the molten pool is lifted layer by layer and solidified layer by layer. In short, when the head is smelted, the bottom has already solidified. Therefore, if the present application is not used, it is difficult to eliminate the composition difference in the longitudinal direction of the ingot by multiple vacuum self-consumption arc smelting;

[0031] ② Each time the ingot is produced, the composition can be accurately controlled. This not only better controls the target composition of a single ingot, but also greatly improves the composition stability between batches of multiple ingots because each ingot is in a controlled state;

[0032] ③ Since the composition of the ingot after cold bed or skull furnace smelting can be tested, the surface oxide skin no longer needs to be removed by acid and alkali washing, which not only reduces the processing cost, but also reduces the environmental pressure. In the high-temperature environment of the cold bed / skull smelting, titanium oxide will be decomposed and dissolved into the molten pool, and since the size of the oxygen atom is extremely small, it can be uniformly distributed in the molten pool as a solid solution oxygen element;

[0033] (4) The insertion of the casting rod into the center hole of the electrode block and the round or near-round (regular octagon) design of the casting rod and the electrode block can ensure the consistency of the overall composition of the composite electrode in the longitudinal direction;

[0034] 2. Due to the unevenness of the residual titanium composition, the composition of the casting rod is not only uneven in the longitudinal direction, but also uneven in the transverse direction. The present application further ingeniously utilizes the horizontal stirring characteristics of the vacuum arc consumable furnace (the main function of the vertical magnetic field generated by the stirring design of the vacuum arc consumable furnace equipment is to bring the rotation of the molten pool in the horizontal plane), and applies a certain strength of direct current stirring magnetic field during the first melting process to make the molten pool rotate at high speed in the horizontal plane, so that the composition of the molten droplets generated by the synchronous melting of the electrode block and the casting rod has certain differences, which can be fully and uniformly mixed in the molten pool after dropping into the molten pool, thereby preparing a titanium alloy ingot which is uniform in both longitudinal and transverse compositions. If other non-center hole structural designs are used, or a certain strength of direct current stirring magnetic field is not used, it is difficult to ensure uniform mixing. At the same time, during the coaxial coupling, the use of the inner and outer double circular or near-circular composite electrode structure has more advantages, which is conducive to the homogeneous distribution of the composition in the circumference and the uniform mixing of the molten pool during melting. If a square or other design with lower circularity is used, the overall stability of the molten pool will be poor, which will weaken the composition uniformity. In addition, in the subsequent second vacuum arc consumable melting, the present application uses alternating current stirring current to obtain a relatively stable molten pool, the main purpose of which is to obtain stable solidification structure and small macro and micro segregation (thus generally cannot be strongly stirred), thereby obtaining high-quality titanium alloy ingot. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The cross-sectional and longitudinal cross-sectional schematic diagrams of the assembled composite electrode of the present application are shown in (I) and (II). DETAILED DESCRIPTION

[0036] The technical solutions of the present application are further described in detail below in combination with specific embodiments. The present application can be realized in many different forms and is not limited to the embodiments described herein. It should be understood that the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0038] The following examples are intended to illustrate the present application but not to limit the scope of the present application. The following specific examples are provided to describe the method of the present application, and other preparation parameters not mentioned in each example are kept consistent in all examples.

[0039] Example One (TC4 alloy recycled ingot with a diameter of Φ880 mm and a nominal composition of Ti-6.0Al-4.0V-0.18O)

[0040] The TC4 titanium alloy bulk scrap was collected, and the residual titanium was sequentially cleaned with a conventional environmentally friendly degreasing solvent and water. After drying, the residual titanium was placed in an electron beam cold hearth furnace bin, and three single electron guns with a power of 350 kW were used for material scanning, cold hearth melting, and crystallization melting, respectively, to prepare a circular titanium alloy casting rod with a diameter of 350 mm and a length of 4800 mm. The composition of the casting rod was tested every 400 mm from the head to the bottom, and the composition was additionally tested at a distance of 200 mm from the head end surface and a distance of 200 mm from the bottom end surface. The composition distribution in the longitudinal direction of the casting rod was obtained by linear interpolation. The composition sequence of the electrode block was designed according to the composition distribution, so that the composition of the composite electrode after compounding was consistent with the nominal composition. The mixed material was automatically mixed by a mixing machine. The 1 / 2 circular electrode block with a pressing length (electrode axial length) of 400 mm was pressed, the number of electrode blocks was 24, the outer diameter of the electrode block was 680 mm, the diameter of the center hole was 360 mm, the weight of a single electrode block was 173 Kg, and the pressing density of the electrode block was 3.3 g / cm 3 ; The electrode blocks were stacked and pressed in order (two 1 / 2 circular electrode blocks in each layer were combined into one electrode block), and the titanium alloy casting rod with a preset head-bottom direction was inserted into the center hole to become a composite electrode, which was welded into a welded electrode by a vacuum plasma welding box. The composite electrode was loaded into a vacuum consumable arc melting furnace. A Φ400 mm diameter auxiliary electrode of the same grade was placed at the head of the vertical composite electrode, and the composition was similar. The auxiliary electrode and the composite electrode were arc welded to fix the two components of the composite electrode to the auxiliary electrode, and then the first vacuum consumable arc melting was performed. The first melting crucible had a diameter of 780 mm, the melting current / voltage was 15 kA / 23 V, and the direct current stirring magnetic field intensity was set to 5.0 mT (the corresponding stirring current of a certain type of ALD vacuum consumable arc melting furnace used in the test was set to 20 A) during the melting. Then the second vacuum consumable arc melting was performed, the melting crucible had a diameter of 880 mm, the melting current / voltage was 22 kA / 28 V, and the alternating current stirring magnetic field intensity / period was set to 2.5 mT / 10 S (the corresponding stirring current was set to 10 A) during the melting. Finally, a titanium alloy ingot was obtained.

[0041] The obtained titanium alloy ingot was sampled at the head (200 mm from the head end face), 1 / 4 part, middle part, 3 / 4 part, and bottom (200 mm from the bottom end face) for a total of 5 positions, and 4 samples were taken at 90° intervals on the circumference at each position, for a total of 20 samples for chemical composition testing. At the same time, 10 batches were continuously produced in the same way. Finally, the test data results of all the ingots showed that the element composition of the ingots met the requirements of the national standard GB3620.1, the main Al, V, and O elements fluctuated around the nominal composition, and the maximum ingot-to-ingot difference of Al element was 1200 ppm, the maximum ingot-to-ingot difference was 1900 ppm; the maximum ingot-to-ingot difference of V element was 900 ppm, the maximum ingot-to-ingot difference was 1500 ppm; the maximum ingot-to-ingot difference of O element was 80 ppm, and the maximum ingot-to-ingot difference was 150 ppm.

[0042] Example Two (TC18 alloy recycled ingot with a diameter of Φ680 mm and a nominal composition of Ti-5.0Al-5.0Mo-5.0V-1.0Cr-1.0Fe-0.12O)

[0043] The TC18 titanium alloy block scrap was collected, and the scrap titanium was sequentially cleaned on the surface with conventional environmentally friendly degreasing solvents and water. After drying, it was placed in the melting crucible of the vacuum consumable skull furnace. The same brand self-consumption electrode with similar target composition was used in the melting process, and the melting current / voltage was 40 kA / 35 V. After the melting was completed, the melt was poured into a crystallizer to prepare a casting rod with a diameter of 250 mm and a length of 4000 mm. The casting rod was sampled every 500 mm from the head to the bottom, and additional samples were taken at a distance of 250 mm from the head end face of the casting rod and at a distance of 250 mm from the bottom end face of the casting rod. The composition distribution of the casting rod was calculated by linear interpolation method; the composition sequence of the electrode block was designed according to the distribution so that the composition of the composite electrode in the longitudinal direction was consistent with the nominal composition; the mixed material machine was used to automatically mix and prepare 1 / 2 round electrode blocks with a length (axial length of electrode) of 400 mm, the number of electrode blocks was 20, the outer diameter of the electrode block was 480 mm, the diameter of the center hole was 280 mm, the weight of a single electrode block was 81 Kg, and the pressing density of the electrode block was 3.4 g / cm 3The electrode blocks are stacked and pressed in order, and are welded into a welding electrode in a vacuum plasma welding box. The electrode is loaded into a vacuum consumable arc melting furnace, the cast bar is inserted into the center hole in the preset head bottom direction to become a composite electrode, the Φ350 mm diameter auxiliary electrode of the same grade is placed at the vertical head of the composite electrode, and the auxiliary electrode and the composite electrode are arc welded to fix the two components of the composite electrode with the auxiliary electrode. The first vacuum consumable arc melting is carried out, the melting crucible diameter is 580 mm, the melting current / voltage is 17 kA / 25 V, and the direct current stirring magnetic field intensity is set to 4.5 mT (corresponding to the stirring current setting of 18 A of a certain type of ALD vacuum consumable arc melting furnace used in the test) during melting. Then the second vacuum consumable arc melting is carried out, the melting crucible diameter is 680 mm, the melting current / voltage is 24 kA / 28 V, and the alternating current stirring magnetic field intensity / period is set to 2.0 mT / 6S (stirring current setting is 8 A) during melting. Finally, the titanium alloy cast ingot is obtained.

[0044] The cast ingot is sampled at the head (200 mm away from the head end face), 1 / 4 part, middle part, 3 / 4 part and bottom (200 mm away from the bottom end face) for a total of 5 positions, and 4 samples are taken at 90° intervals on the circumference at each position, for a total of 20 samples for chemical composition testing. At the same time, 10 batches are continuously produced by the same method. Finally, the test data of all the cast ingots show that the element composition of the cast ingot meets the requirements of the national standard GB3620.1, the main Al, Mo, V, Cr, Fe and O elements fluctuate around the nominal composition, and the maximum ingot-to-ingot difference of Al element of all the cast ingots is 1200 ppm, the maximum ingot-to-ingot difference is 1900 ppm; the maximum ingot-to-ingot difference of Mo element is 1500 ppm, the maximum ingot-to-ingot difference is 1800 ppm; the maximum ingot-to-ingot difference of V element is 1200 ppm, the maximum ingot-to-ingot difference is 1600 ppm; the maximum ingot-to-ingot difference of Cr element is 400 ppm, the maximum ingot-to-ingot difference is 900 ppm; the maximum ingot-to-ingot difference of Fe element is 500 ppm, the maximum ingot-to-ingot difference is 1100 ppm; the maximum ingot-to-ingot difference of O element is 70 ppm, the maximum ingot-to-ingot difference is 130 ppm.

[0045] Example Three (TA15 alloy recycled ingot with a diameter of Φ780 mm and a nominal composition of Ti-6.5Al-1.0Mo-1.0V-2.0Zr-0.13O)

[0046] The TA15 titanium alloy bulk scrap is collected, and the residual titanium is sequentially cleaned on the surface by using conventional environmental protection oil removal solvent and water. After being dried, the residual titanium is placed into an electron beam cold hearth furnace charging box. Three electron guns with a single electron beam power of 350 kW are used to scan the material, cold hearth smelting and crystallization smelting respectively, so as to prepare a titanium alloy casting rod with a diameter of Φ350 mm and a length of 4800 mm. The composition of the casting rod is tested every 400 mm from the head to the bottom. The composition is tested by increasing sampling at a distance of 200 mm from the head end face of the casting rod and at a distance of 200 mm from the bottom end face of the casting rod. The composition distribution of the titanium alloy casting rod is obtained by linear interpolation method. According to the distribution, the composition sequence of the electrode block is designed so that the composition of the composite electrode in the longitudinal direction is consistent with the nominal composition. The mixed material machine is used to automatically mix the material by portion. The 1 / 2 regular octagonal electrode block with a pressing length (electrode axial length) of 400 mm is pressed. The number of electrode blocks is 24. The diameter of the circumscribed circle of the electrode block is 580 mm, the diameter of the center hole is 360 mm, the weight of a single electrode block is 103 Kg, and the pressing density of the electrode block is 3.5 g / cm 3 . The electrode blocks are stacked and pressed in order, and the titanium alloy casting rod in the preset head-bottom direction is inserted into the center hole to become a composite electrode. The vacuum plasma welding box is used for welding to become a welded electrode. The electrode is loaded into a vacuum consumable arc furnace. The Φ400 mm diameter auxiliary electrode with the same grade is placed at the head of the vertical composite electrode. The auxiliary electrode and the composite electrode are arc welded to fix the two components of the composite electrode to the auxiliary electrode. Then, the first vacuum consumable arc smelting is carried out. The smelting crucible diameter is 680 mm, the smelting current / voltage is 18kA / 25V, and the direct current stirring magnetic field intensity is set to 5.0 mT (corresponding to the stirring current setting of 20 A of a certain type of ALD vacuum consumable arc smelting furnace used in the test). Then, the second vacuum consumable arc smelting is carried out. The smelting crucible diameter is 780 mm, the smelting current / voltage is 24kA / 27V, and the alternating current stirring magnetic field intensity / period is set to 2.5mT / 10S (corresponding to the stirring current setting of 10 A). Finally, the titanium alloy ingot is obtained.

[0047] The titanium alloy ingots were sampled at five locations: the head (200 mm from the head end), 1 / 4, middle, 3 / 4, and bottom (200 mm from the bottom end). Four samples were taken at 90° intervals around each location, for a total of 20 samples for chemical composition testing. Ten batches were produced continuously using the same method. Finally, the test data results of all ingots showed that the elemental composition of the ingots met the requirements of the national standard GB3620.1, and the main Al, Mo, V, Zr, and O elements all fluctuated around the nominal composition. The maximum difference of Al element in the same ingot of all ingots was 1300ppm, and the maximum difference between ingots was 2000ppm; the maximum difference of Mo element in the same ingot was 800ppm, and the maximum difference between ingots was 1100ppm; the maximum difference of V element in the same ingot was 700ppm, and the maximum difference between ingots was 1000ppm; the maximum difference of Zr element in the same ingot was 1100ppm, and the maximum difference between ingots was 1600ppm; the maximum difference of O element in the same ingot was 80ppm, and the maximum difference between ingots was 140ppm.

[0048] Comparative Example 1

[0049] Except for the following differences, the rest is the same as Example 1:

[0050] Residual titanium and pressed electrode blocks of the same weight and source as in Example 1 were evenly placed in the charge bin of an electron beam cooling hearth furnace. A small amount of material with a composition close to the target was added to serve as the bottom charge of the cooling hearth furnace. Electron beam cold hearth melting was then performed to directly produce cast rods with a diameter of 680 mm. The composition of the electrode blocks was designed based on the estimated content of each element in the residual titanium and empirically estimated volatilization of each element during electron beam melting (here, the volatilization loss of Al was estimated to be 10 wt.%, and the volatilization loss of V was estimated to be 4 wt.%). The composition of the electrode blocks was designed based on these two estimates and the target nominal composition. The cast rods were then melted twice directly in a vacuum consumable arc melting furnace. Ten batches were produced continuously using the same method. Finally, the test data results of all ingots showed that the elemental composition of the ingots met the requirements of the national standard GB3620.1, and the main Al, V, and O elements fluctuated around the nominal composition. The maximum difference of Al element in the same ingot of all ingots was 2500ppm, and the maximum difference between ingots was 5600ppm; the maximum difference of V element in the same ingot was 1900ppm, and the maximum difference between ingots was 3800ppm; the maximum difference of O element in the same ingot was 180ppm, and the maximum difference between ingots was 560ppm.

[0051] Comparative Example 2

[0052] Except for the following differences, the rest is the same as Example 2:

[0053] The same residual titanium and pressed electrode block as in Example 2 were directly provided to a vacuum consumable arc skull melting furnace, and the pressed electrode block was uniformly placed in a melting crucible of the skull melting furnace to conduct melting and pouring to prepare a Φ480 mm diameter cast rod. The composition of the electrode block was consistent, and the method for designing the composition of the electrode block was as follows: the content of each element in the residual titanium was estimated, and the composition of the electrode block was designed in combination with the nominal composition of the target ingot. The prepared cast rod was directly subjected to 2 times of melting in a vacuum consumable arc melting furnace. At the same time, 10 batches were continuously produced by the same method. Finally, the test data of all the ingots showed that the element composition of the ingots met the requirements of the national standard GB3620.1, and the main Al, Mo, V, Cr, Fe and O elements fluctuated around the nominal composition. The maximum ingot-to-ingot difference of Al element was 1900 ppm, and the maximum ingot-to-ingot difference was 4300 ppm. The maximum ingot-to-ingot difference of Mo element was 2100 ppm, and the maximum ingot-to-ingot difference was 3600 ppm. The maximum ingot-to-ingot difference of V element was 1900 ppm, and the maximum ingot-to-ingot difference was 3700 ppm. The maximum ingot-to-ingot difference of Cr element was 900 ppm, and the maximum ingot-to-ingot difference was 2400 ppm. The maximum ingot-to-ingot difference of Fe element was 1000 ppm, and the maximum ingot-to-ingot difference was 2600 ppm. The maximum ingot-to-ingot difference of O element was 110 ppm, and the maximum ingot-to-ingot difference was 450 ppm.

[0054] Comparative Example Three

[0055] Except for the following differences, the rest was the same as in Example Three:

[0056] The shape of the pressed electrode block was inner circle and outer square, and the outer edge was 1 / 2 of a regular quadrilateral. The composition test results of the finally produced ingots were as follows: the maximum ingot-to-ingot difference of Al element was 1600 ppm, and the maximum ingot-to-ingot difference was 2500 ppm. The maximum ingot-to-ingot difference of Mo element was 900 ppm, and the maximum ingot-to-ingot difference was 1500 ppm. The maximum ingot-to-ingot difference of V element was 1000 ppm, and the maximum ingot-to-ingot difference was 1800 ppm. The maximum ingot-to-ingot difference of Zr element was 1300 ppm, and the maximum ingot-to-ingot difference was 1900 ppm. The maximum ingot-to-ingot difference of O element was 90 ppm, and the maximum ingot-to-ingot difference was 200 ppm.

[0057] Comparative Example Four

[0058] Except for the following differences, the rest was the same as in Example One:

[0059] The shape of the pressed electrode block was inner circle and outer square, and the outer edge was 1 / 2 of a regular octagon. The composition test results of the finally produced ingots were as follows: the maximum ingot-to-ingot difference of Al element was 1300 ppm, and the maximum ingot-to-ingot difference was 2100 ppm. The maximum ingot-to-ingot difference of V element was 1100 ppm, and the maximum ingot-to-ingot difference was 1600 ppm. The maximum ingot-to-ingot difference of O element was 90 ppm, and the maximum ingot-to-ingot difference was 150 ppm.

[0060] Comparative Example Five

[0061] The rest is the same as Example One except the following differences:

[0062] After multi-point sampling of the cast rod, the average composition of the cast rod is obtained by using the average method instead of the linear interpolation method. According to the average composition, the electrode block with uniform composition is configured. The test results of the composition of the finally produced cast ingot are as follows: the maximum ingot-to-ingot difference of Al element is 3100 ppm, the maximum ingot-to-ingot difference is 5200 ppm; the maximum ingot-to-ingot difference of V element is 2500 ppm, the maximum ingot-to-ingot difference is 3800 ppm; the maximum ingot-to-ingot difference of O element is 240 ppm, the maximum ingot-to-ingot difference is 460 ppm.

[0063] Comparative Example Six

[0064] The rest is the same as Example One except the following differences:

[0065] The assembly and coupling of the titanium cast rod and the electrode block do not use the coaxial center hole mode, but the electrode block is pressed into a structure with a semicircular groove with a diameter of 360 mm on the surface, and the cast rod is placed in the groove, and the two form an eccentric coupling structure. The test results of the composition of the finally produced cast ingot are as follows: the maximum ingot-to-ingot difference of Al element is 2100 ppm, the maximum ingot-to-ingot difference is 2500 ppm; the maximum ingot-to-ingot difference of V element is 1800 ppm, the maximum ingot-to-ingot difference is 2500 ppm; the maximum ingot-to-ingot difference of O element is 160 ppm, the maximum ingot-to-ingot difference is 230 ppm.

[0066] Comparative Example Seven

[0067] The rest is the same as Example One except the following differences:

[0068] The direct current stirring magnetic field intensity set in the first vacuum arc melting is 2.0 mT (the corresponding stirring current is set to 8 A). The test results of the composition of the finally produced cast ingot are as follows: the maximum ingot-to-ingot difference of Al element is 1900 ppm, the maximum ingot-to-ingot difference is 2400 ppm; the maximum ingot-to-ingot difference of V element is 1500 ppm, the maximum ingot-to-ingot difference is 1800 ppm; the maximum ingot-to-ingot difference of O element is 120 ppm, the maximum ingot-to-ingot difference is 180 ppm.

[0069] Comparative Example Eight

[0070] The rest is the same as Example One except the following differences:

[0071] The collected residual titanium is washed with acid and alkali. The test results of the composition of the finally produced cast ingot are as follows: the maximum ingot-to-ingot difference of Al element is 1300 ppm, the maximum ingot-to-ingot difference is 1800 ppm; the maximum ingot-to-ingot difference of V element is 900 ppm, the maximum ingot-to-ingot difference is 1500 ppm; the maximum ingot-to-ingot difference of O element is 70 ppm, the maximum ingot-to-ingot difference is 140 ppm.

[0072] Comparative Example Nine

[0073] The rest is the same as Comparative Example One, except the following differences:

[0074] The collected residual titanium was washed with acid and alkali. The test results of the composition of the finally produced ingot are as follows: the maximum ingot-to-ingot difference of Al element is 2600ppm, the maximum ingot-to-ingot difference is 5500ppm; the maximum ingot-to-ingot difference of V element is 1800ppm, the maximum ingot-to-ingot difference is 3800ppm; the maximum ingot-to-ingot difference of O element is 150ppm, the maximum ingot-to-ingot difference is 440ppm.

[0075] As can be seen from Example One and Comparative Example One, Example Two and Comparative Example Two, the use of the technical route can significantly reduce the ingot-to-ingot difference of the composition of the ingot, especially the ingot-to-ingot difference. That is, the technical route can significantly improve the uniformity and stability of the composition of the ingot.

[0076] As can be seen from Example One and Comparative Example Four, Example Three and Comparative Example Three, whether the pressed electrode block is circular or near-circular also has a certain influence. In the process of industrial production of pressed electrodes, in addition to circular shape, common electrode block shapes include (near) octagonal shape, (near) quadrangular shape. Therefore, for common industrial scenarios, the present application designs three shapes, namely circular, regular octagonal and regular quadrangular, for comparison and research. The results show that the closer the shape is to a circle, the better the homogenization effect, and the farther the shape deviates from a circle, the worse the uniformity of the ingot. Therefore, the present application preferably adopts a circular shape or a regular octagonal shape closest to a circle. Although other near-circular shapes such as regular dodecagonal shape or approximate shapes such as slightly chamfered regular octagonal shape are not exhaustively listed, they should be considered to fall within the protection scope of the present application.

[0077] As can be seen from Example One and Comparative Example Five, if linear interpolation is not used and the composition of the recycled ingot rod prepared by default is uniform, it will obviously deviate from the actual situation, resulting in a significant increase in the ingot-to-ingot difference of the elements of the finally produced ingot, and the corresponding ingot-to-ingot difference also increases.

[0078] As can be seen from the comparison between Example One and Comparative Example Six, the design of the composite structure has an influence on the composition uniformity. Among them, whether the coaxial center hole assembly coupling method has a great influence on the composition uniformity. Without the coaxial center hole assembly, the ingot itself is difficult to homogenize, resulting in a significant increase in the ingot-to-ingot difference of the elements of the ingot. Therefore, the non-coaxial center hole assembly should not be adopted.

[0079] From the comparison of Example 1 and Comparative Example 7, it can be seen that the direct current stirring magnetic field strength of the first vacuum consumable arc smelting also has a certain influence on the composition uniformity after assembly by the coaxial center hole method. Only sufficient horizontal stirring can better enable the composite structure to obtain better mixing effect in smelting. Of course, the magnetic field strength cannot be increased blindly, because under the condition of this size, excessive stirring will make the smelting process unstable. Therefore, there is an upper limit of the optimized setting value.

[0080] From the comparison of Example 1 and Comparative Example 8, Comparative Example 1 and Comparative Example 9, it can be seen that the acid-base washing treatment of residual titanium has obvious influence on the batch stability of O element of the traditional route recycled ingot (because the acid-base washing can more accurately estimate the whole ingot matching value of O element), and has less influence on the composition uniformity and stability control (especially for O element) of the ingot produced by the technical route. Even if the acid-base washing is not performed, the technical route can still obtain obvious uniformity and stability of O element of the ingot better than the traditional route. Therefore, considering the cost and process, the residual titanium recovered by the technical route generally does not need to be subjected to acid-base washing. Of course, if the customer has special requirements, such as requiring to produce recycled ingot with lower oxygen content, the block-shaped residual titanium can also be subjected to acid-base washing and then subjected to the technical route to continue producing ingot.

[0081] From all the above cases, it can be seen that by exploring the composition of the cold hearth furnace or the skull furnace recycled ingot, and then using the electrode block composition to adjust and match, and then performing vacuum consumable arc smelting to prepare titanium alloy recycled ingot, the product quality can be obviously improved, the composition uniformity of the ingot can be improved, and especially the composition stability of the batch ingot can be improved. The process follows the cold hearth furnace or skull furnace process for recycling material, has no metallurgical defect risk, has uniform and stable composition, and has great market value.

[0082] The technical features of the above-described embodiments can be combined arbitrarily. In order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present disclosure.

[0083] The above-described embodiments only express several implementation manners of the present application, facilitate specific and detailed understanding of the technical solutions of the present application, but cannot be understood as a limitation on the patent protection scope of the present application. It should be noted that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. It should be understood that, on the basis of the technical solutions provided by the present application, the technical solutions obtained by logical analysis, reasoning or limited experiments of those skilled in the art all belong to the protection scope of the appended claims of the present application. Therefore, the patent protection scope of the present application should be subject to the contents of the appended claims, and the description and drawings can be used to explain the contents of the claims.

Claims

1. A method for recovering residual titanium to prepare titanium alloy ingots, characterized in that: The steps include: Step 1) collecting titanium alloy residues of the same grade and cleaning the surface of the residual titanium. Specifically, the surface cleaning is carried out by using a conventional environmentally friendly degreasing solvent and water in sequence; Step 2) using an electron beam cooling hearth furnace, a plasma beam cooling hearth furnace, or a vacuum consumable arc skull furnace to melt the residual titanium from step 1) and then solidify it into a round titanium alloy casting rod; Step 3) Sampling the titanium alloy cast rod obtained in step 2) longitudinally within 300 mm of the head end face and the bottom end face, sampling the remaining parts of the titanium alloy cast rod at intervals of 200-1000 mm, and then performing composition testing on the sampled samples to obtain the composition distribution of the entire titanium alloy cast rod in the longitudinal direction by linear interpolation; Step 4) Weigh, mix and press the titanium sponge and the intermediate alloy into an electrode block with a circular center hole according to a specially designed component sequence. Then stack and weld the electrode blocks in order. Before or after welding, insert the titanium alloy cast rod obtained in step 2) into the circular center hole of the electrode block in a preset head-bottom direction to form a coaxial composite electrode. Then, place the composite electrode in a vacuum consumable arc melting furnace, use the same brand auxiliary electrode to weld and fix it to the composite electrode, and perform the first vacuum consumable arc melting. DC stirring current is used during melting. DC stirring current The setting value is determined by the intensity of the stirring magnetic field it generates, which is 4-6mT. The composite electrode is then turned around for a second vacuum consumable arc melting, and an AC stirring current is used during the melting to finally obtain a titanium alloy ingot. Among them, the specially designed composition sequence needs to meet the following requirements: in the longitudinal direction of the composite electrode, with the length of a single electrode block as a unit, the average value obtained by weighted averaging the composition of the titanium alloy casting rod portion corresponding to each unit and the composition of the electrode block should be consistent among all units, that is, the average composition C of the entire composite electrode = the average composition C of any unit i = (Any electrode block component C block-i ×Weight of any electrode block mblock-i + Composition C of the cast rod part corresponding to this unit bar-i ×The weight of the cast rod m bar-i ) / (weight of any electrode block m block-i +The weight of the cast rod corresponding to this unit m bar-i ).

2. The method for preparing titanium alloy ingots by recycling residual titanium according to claim 1, characterized in that: The length of a single electrode block is 200-600 mm.

3. The method for preparing titanium alloy ingots by recycling residual titanium according to claim 1, characterized in that: During the second vacuum consumable arc melting, the AC stirring magnetic field intensity is 1-3 mT and the stirring period is 4-12 s.

4. The method for preparing titanium alloy ingots by recycling residual titanium according to claim 1, characterized in that: The outer shape of the electrode block is circular or regular octagonal.

5. The method for preparing titanium alloy ingots by recycling residual titanium according to claim 1, characterized in that: The diameter of the center hole of the electrode block is 110-640 mm; and when producing the same ingot, the diameter of the cast rod used is 10-40 mm smaller than the diameter of the center hole of the electrode block; the length of the cast rod is 2000-6000 mm, and the difference between the cast rod length and the total length of the electrode block is ≤10 mm.

6. The method for preparing titanium alloy ingots by recycling residual titanium according to claim 1, characterized in that: The outer diameter of the electrode block is 420-880 mm, and the pressing density of the electrode block is 3.2-3.6 g / cm 3 .

7. The method for preparing titanium alloy ingots by recycling residual titanium according to claim 1, characterized in that: In the above composite electrode, the weight of the cast rod accounts for 8-60 wt.% of the weight of the entire composite electrode.

8. The method for preparing titanium alloy ingots by recycling residual titanium according to claim 1, characterized in that: In the above step 2), the power of a single electron gun during electron beam cold hearth furnace melting is 300-500 kW; the power of a single plasma gun during plasma beam cold hearth furnace melting is 300-800 kW; the melting current / voltage of the vacuum consumable arc skull furnace is set at 25-55 kA / 25-40 V, and consumable electrodes of the same brand and similar composition to the target are used during melting; in the above step 4), the melting current / voltage during the first vacuum consumable arc melting is 12-20 kA / 22-28 V; and the melting current / voltage during the second vacuum consumable arc melting is 15-30 kA / 24-35 V.

9. The method for preparing titanium alloy ingots by recovering residual titanium according to claim 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8, characterized in that: The titanium alloy ingot finally obtained has a diameter of 600-1080 mm and a weight of 2000-12000 kg.

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