Method for producing large-size tc18 titanium alloy ingot

Abstract

The preparation method of the large-size TC18 titanium alloy ingot comprises the following specific process: selecting and weighing raw materials; pressing the mixed raw materials into circular electrode blocks; welding the electrode blocks into a primary consumable electrode to be smelted in a plasma welding box under the protection of argon; performing three times of smelting on the primary consumable electrode in a copper crucible; starting the feeding when the residual weight of the consumable electrode is 1000kg-1500kg after the third time of smelting; and cooling and discharging after the feeding is completed to obtain the large-size TC18 titanium alloy ingot. The method solves the problem of low production efficiency of the existing large-size TC18 titanium alloy ingot.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium alloy ingot preparation, and particularly relates to a preparation method of large-specification TC18 titanium alloy ingot. BACKGROUND

[0002] Titanium alloy is widely used in various fields due to its high strength, high heat resistance, good corrosion resistance and other characteristics. The nominal composition of TC18 titanium alloy is Ti-5Al-5Mo-5V-1Cr-1Fe, which is a high-strength and high-toughness near-beta titanium alloy and can be used to manufacture key load-bearing components such as large frames, beams and landing gears of aircraft.

[0003] Vacuum arc remelting (VAR) is a widely used melting method for producing TC18 titanium alloy ingots at present, which has the characteristics of large tonnage, high melting efficiency and good composition uniformity. However, due to the multiple types of alloying elements in TC18 alloy, and the presence of easily segregated elements Fe, Cr and Mo, it is difficult to control the composition uniformity and phase transition point uniformity when preparing TC18 ingots by VAR method. Beta spots, which are abnormal structures with low alpha phase content in local areas during heat treatment below the phase transition point, are easily found in the prepared rods. Beta spots have a great impact on the tensile and fatigue properties of the rods, so they should be eliminated during the ingot production process to avoid abnormal organization and performance of the prepared rods.

[0004] To avoid composition and phase transition point inhomogeneity in ingots, production enterprises usually use low melting speed melting process to prepare alloy ingots containing easily segregated elements. However, with the increase of ingot size, only reducing the melting speed to improve the uniformity of the ingot has the disadvantage of low production efficiency. Therefore, it is urgent to develop a method suitable for high-efficiency and batch production of high-uniform TC18 titanium alloy ingots. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of large-specification TC18 titanium alloy ingot, which solves the problem of low production efficiency of existing large-specification TC18 titanium alloy ingot.

[0006] The technical solution adopted by the present application is a preparation method of large-specification TC18 titanium alloy ingot, which is implemented according to the following steps:

[0007] Step 1, selecting and weighing raw materials;

[0008] Step 2, mixing the raw materials weighed in step 1 uniformly and pressing into a circular electrode block;

[0009] Step 3, welding the electrode block pressed in step 2 into a consumable electrode to be melted in a plasma welding box under argon protection;

[0010] Step 4, the primary consumable electrode obtained in step 3 is smelted for three times in a copper crucible;

[0011] Step 5, when the remaining weight of the consumable electrode after the third smelting is 1000kg-1500kg, the top-up is started;

[0012] Step 6, after the top-up is finished, the furnace is cooled out, and the large-size TC18 titanium alloy ingot is obtained.

[0013] The application is also characterized in that,

[0014] In step 1, the raw materials are sponge titanium, MoVAl ternary intermediate alloy, CrAl binary alloy and FeAl binary alloy.

[0015] The Brinell hardness value of the sponge titanium is 80HBW-100HBW, the content of C element and N element is 0.003%-0.015%, and the content of Cl element is 0.01%-0.05%.

[0016] The particle size of the MoVAl ternary intermediate alloy, the CrAl binary alloy and the FeAl binary alloy is 2mm-5mm.

[0017] In step 2, the single weight of the electrode block is 135kg-145kg, and the electrode block density is 3.66g / cm 3 -3.93g / cm 3 .

[0018] In step 3, the size of the primary consumable electrode to be smelted is

[0019] The specific process of step 4 is as follows:

[0020] Step 4.1, the primary consumable electrode obtained in step 3 is smelted for one time in a copper crucible, the smelting current is 12kA-26kA, the smelting voltage is 25V-40V, the stable arc current is 10A-30A, and the primary ingot is obtained;

[0021] Step 4.2, after the primary ingot obtained in step 4.1 is removed from the ingot crown, it is reversed and loaded into the copper crucible for secondary smelting, the smelting current is 16kA-30kA, the smelting voltage is 28V-42V, the stable arc current is 12A-32A, and the stable arc period is 5s-15s, and the secondary ingot is obtained;

[0022] Step 4.3, after the secondary ingot obtained in step 4.2 is removed from the ingot crown, it is reversed and loaded into the copper crucible for three times of smelting, the smelting current is 12kA-26kA, the smelting voltage is 22-35V, the stable arc current is 10A-25A, and the stable arc period is 5s-15s.

[0023] The ratio of the crucible is 0.65-0.85 for once smelting, and the ratio of the crucible is 0.80-0.90 for twice and thrice smelting, wherein the ratio of the crucible is equal to the diameter of the consumable electrode to be smelted / the inner diameter of the crucible.

[0024] The specific process of step 5 is as follows: starting to top up when the remaining weight of the consumable electrode is 1000kg-1500kg, starting to reduce the current to 10kA-14kA at a current reduction rate of 0.1kA / min-0.2kA / min, then starting to top up smelting at a constant current of 10kA-14kA when the remaining weight of the consumable electrode is 500kg-800kg, and finally starting to gradually reduce the current to 3kA-5kA at a current reduction rate of 0.1kA / min-1.0kA / min when the remaining weight of the consumable electrode is 200kg-400kg.

[0025] In step 6, the cooling time is not less than 6h.

[0026] The beneficial effects of the present application are as follows:

[0027] (1) The present application can prepare large-size TC18 titanium alloy ingots with equiaxed crystal + columnar crystal structure, and the structure characteristics are as follows: the range of 120mm-150mm at the edge position is equiaxed crystal, the range of 150mm-200mm at the R / 2 position is columnar crystal, and the range of 0-50mm at the center position is mixed structure of equiaxed crystal, wherein the equiaxed crystal grain diameter is 5mm-10mm, the columnar crystal width is 5mm-10mm, the columnar crystal growth angle is 40°-60°, and especially, the range of 700mm height at the tail position is vertical columnar crystal triangle area, and the obtained ingot combines the advantages of the two structures, has smaller composition segregation tendency, and has excellent composition uniformity and phase transition point uniformity.

[0028] (2) The performance and macrostructure of the prepared rod meet the requirements of GJB2744A-2019 standard, and the rod has no beta spot after solid solution and aging heat treatment at 25℃ below the phase transition point.

[0029] (3) The preparation method has high production efficiency, and the smelting time required for preparing one 5-ton ingot is about 5h-10h, which is suitable for batch and efficient production of large-size TC18 ingots. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The microstructure diagram of the upper third (head) position of the φ720 specification TC18 titanium alloy ingot prepared by the method of the present application;

[0031] Figure 2 The microstructure diagram of the middle third (middle) position of the φ720 specification TC18 titanium alloy ingot prepared by the method of the present application;

[0032] Figure 3 Microstructure diagram of the lower third (tail) position of a φ720 specification TC18 titanium alloy ingot prepared by the method of the present application;

[0033] Figure 4 Low-magnification microstructure diagram of a bar prepared by the method of the present application after heat treatment at 25°C below the phase transition point;

[0034] Figure 5 Longitudinal section microstructure diagram of an ingot prepared by the method of the present application. DETAILED DESCRIPTION

[0035] The present application will be described in detail below in conjunction with the drawings and specific embodiments.

[0036] The method for preparing a large-specification TC18 titanium alloy ingot of the present application is implemented in accordance with the following steps:

[0037] Step 1, selecting and weighing raw materials, the raw materials being sponge titanium, MoVAl ternary intermediate alloy, CrAl binary alloy, and FeAl binary alloy;

[0038] The Brinell hardness value of the sponge titanium is 80HBW-100HBW, the content of C and N elements is 0.003%-0.015%, and the content of Cl element is 0.01%-0.05%. By reasonably controlling the hardness, C content, and N content of the sponge titanium, the influence of fluctuations in impurity elements in the raw materials on the uniformity of the phase transition point is avoided, and the performance stability of the bar is improved. By controlling the Cl content, fluctuations in the O content of the ingot caused by moisture absorption of the electrode block are avoided.

[0039] The particle size of the MoVAl ternary intermediate alloy, CrAl binary alloy, and FeAl binary alloy is 2mm-5mm, and the particle sizes of the above alloys are equal, which can further ensure the uniformity of the mixture. Mo, V, Cr, Fe, and Al elements are added in the form of ternary intermediate alloy and binary alloy.

[0040] Step 2, after the raw materials weighed in step 1 are mixed uniformly, they are pressed into a circular electrode block, the single weight of the electrode block is 135kg-145kg, and the electrode block density is 3.66g / cm 3 -3.93g / cm 3 ;

[0041] Step 3, the electrode block pressed in step 2 is welded into a primary consumable electrode with a size of in an argon gas protected plasma welding box;

[0042] Step 4, the primary consumable electrode obtained in step 3 is subjected to three times of melting in a copper crucible;

[0043] Step 4.1, the primary consumable electrode obtained in step 3 is subjected to primary melting in a copper crucible, the crucible ratio is 0.65-0.85, the melting current is 12-26 kA, the melting voltage is 25-40 V, the steady arc current is 10-30 A, and a primary ingot is obtained;

[0044] Step 4.2, after removing the ingot crown of the primary ingot obtained in step 4.1, the primary ingot is loaded into a copper crucible upside down and subjected to secondary melting, the crucible ratio is 0.80-0.90, the melting current is 16-30 kA, the melting voltage is 28-42 V, the steady arc current is 12-32 A, and the steady arc period is 5-15 s, and a secondary ingot is obtained;

[0045] Step 4.3, after removing the ingot crown of the secondary ingot obtained in step 4.2, the secondary ingot is loaded into a copper crucible upside down and subjected to tertiary melting, the crucible ratio is 0.80-0.90, the melting current is 12-26 kA, the melting voltage is 22-35 V, the steady arc current is 10-25 A, and the steady arc period is 5-15 s;

[0046] wherein the crucible ratio = diameter of the consumable electrode to be melted / inner diameter of the crucible;

[0047] The primary melting adopts a relatively small crucible ratio, which can not only make the ingot preliminarily alloyed, but also more fully remove the easily volatile impurities such as Cl element and gas; the secondary and tertiary melting need to make the composition fully homogenized, and the relatively large crucible ratio is beneficial to realize the uniform distribution of arc heat on the surface of the molten pool;

[0048] On the one hand, the third melting adopts current control, which can ensure the consistency of the actual current input and the target set value; on the other hand, the melting current value is set according to the above parameters, and appropriate voltage and steady arc stirring are adopted, which can not only ensure the production efficiency, but also obtain a moderate molten pool depth and reduce the composition segregation;

[0049] Step 5, the top-up is started when the remaining weight of the consumable electrode is 1000-1500 kg after the third melting;

[0050] The specific process is as follows:

[0051] The top-up is started when the remaining weight of the consumable electrode is 1000-1500 kg, the current is reduced to 10-14 kA at a current reduction rate of 0.1-0.2 kA / min, then when the remaining weight of the consumable electrode is 500-800 kg, the constant current top-up melting is started at 10-14 kA, and finally when the remaining weight of the consumable electrode is 200-400 kg, the current is gradually reduced to 3-5 kA at a current reduction rate of 0.1-1.0 kA / min;

[0052] First, a slow current reduction ratio melting is used, and then a constant current is maintained at a lower current. This allows the molten pool to rise gradually and slowly, further reducing the tendency of compositional segregation in the core of the ingot.

[0053] Step 6: After the feeding is completed, the furnace is cooled for no less than 6 hours to obtain a large-size TC18 titanium alloy ingot.

[0054] To better understand the key points of this invention, the following will be used as an example. The present invention is illustrated in detail using the TC18 titanium alloy ingot as an example.

[0055] Example 1

[0056] Prepare TC18 titanium alloy ingots with a diameter of φ720mm.

[0057] Step 1: Select and weigh the raw materials. The raw materials are sponge titanium, MoVAl ternary master alloy, CrAl binary alloy, and FeAl binary alloy. Weigh the raw materials according to the following ratio: Al: 5%, Mo: 5%, V: 5%, Cr: 1%, Fe: 1%, and the balance is Ti.

[0058] The Brinell hardness value of sponge titanium is 80 HBW to 100 HBW, with C and N content ranging from 0.003% to 0.015% and Cl content ranging from 0.01% to 0.05%. Since sponge titanium is produced in multiple batches in actual production, it is sufficient that its hardness value and the content of C, N, and Cl elements meet the above ranges.

[0059] The particle size of the MoVAl ternary master alloy, CrAl binary alloy, and FeAl binary alloy is 2-3 mm.

[0060] Step 2: After mixing the raw materials weighed in Step 1 evenly, press them into circular electrode blocks. The weight of a single electrode block is 135 kg, and the density of the electrode block is 3.66 g / cm³. 3 ;

[0061] Step 3: Weld the electrode blocks pressed in Step 2 into a plasma welding box protected by argon gas to form a shape with dimensions of [size missing]. The consumable electrode to be melted;

[0062] Step 4: The consumable electrode obtained in Step 3 is smelted three times in a copper crucible.

[0063] Step 4.1, place the primary consumable electrode obtained in step 3 in... A copper crucible is used for one melting process, with a melting current of 12kA to 20kA, a melting voltage of 25V to 35V, and an arc stabilization current of 10A to 30A, to obtain a first ingot.

[0064] Step 4.2, after removing the ingot crown of the primary ingot obtained in step 4.1, the primary ingot is reversed and put into a copper crucible for secondary smelting, the smelting current is 16kA-25kA, the smelting voltage is 28V-35V, the stabilizing arc current is 12A-22A, and the stabilizing arc period is 5s-15s, to obtain a secondary ingot; Step 4.3, after removing the ingot crown of the secondary ingot obtained in step 4.2, the secondary ingot is reversed and put into a copper crucible for tertiary smelting, the smelting current is 12kA-22kA, the smelting voltage is 22V-30V, the stabilizing arc current is 10A-20A, and the stabilizing arc period is 5s-15s;

[0065] Step 4.3, after removing the ingot crown of the secondary ingot obtained in step 4.2, the secondary ingot is reversed and put into a copper crucible for tertiary smelting, the smelting current is 12kA-22kA, the smelting voltage is 22V-30V, the stabilizing arc current is 10A-20A, and the stabilizing arc period is 5s-15s;

[0066] Step 5, the top-up is started when the remaining weight of the consumable electrode is 1000kg after the third smelting;

[0067] The specific process is as follows:

[0068] The top-up is started when the remaining weight of the consumable electrode is 1000kg, the current is reduced to 10kA at a current reduction rate of 0.2kA / min, then when the remaining weight of the consumable electrode is 500kg, the top-up smelting is started at a constant current of 10kA, finally when the remaining weight of the consumable electrode is 200kg, the current is gradually reduced to 3kA at a current reduction rate of 1kA / min-0.8kA / min-0.5kA / min-0.2kA / min-0.1kA / min;

[0069] Step 6, after the top-up is completed, the furnace is cooled for not less than 6h, and then the φ820mm specification TC18 titanium alloy ingot is obtained.

[0070] Example 2

[0071] A φ820mm specification TC18 titanium alloy ingot is prepared.

[0072] Step 1, the raw materials are selected and weighed, the raw materials are sponge titanium, MoVAl ternary intermediate alloy, CrAl binary alloy, and FeAl binary alloy, and the raw materials are weighed according to the following ratio: Al: 5%, Mo: 5%, V: 5%, Cr: 1%, Fe: 1%, and the balance is Ti, the sum of the mass percentages is 100%;

[0073] The Brinell hardness value of the sponge titanium is 80HBW-100HBW, the content of C element and N element is 0.003%-0.015%, and the content of Cl element is 0.01%-0.05%;

[0074] The particle size of the MoVAl ternary intermediate alloy, the CrAl binary alloy, and the FeAl binary alloy is 4-5mm; ​​

[0075] Step 2, the raw materials weighed in step 1 are mixed uniformly and then pressed into a circular electrode block, the electrode block has a single weight of 140 kg and a density of 3.79 g / cm 3 ;

[0076] Step 3, the electrode block pressed in step 2 is welded into a consumable electrode to be smelted in a plasma welding box in an argon atmosphere, the consumable electrode has a size of ;

[0077] Step 4, the consumable electrode obtained in step 3 is smelted three times in a copper crucible;

[0078] Step 4.1, the consumable electrode obtained in step 3 is smelted once in the copper crucible, the smelting current is 14 kA-22 kA, the smelting voltage is 28 V-38 V, the steady arc current is 10 A-30 A, and a primary ingot is obtained; Step 4.2, after the primary ingot obtained in step 4.1 is removed from the ingot crown and turned over, the primary ingot is smelted twice in the copper crucible, the smelting current is 18 kA-28 kA, the smelting voltage is 30 V-40 V, the steady arc current is 14 A-25 A, and the steady arc period is 5 s-15 s, and a secondary ingot is obtained;

[0079] Step 4.3, after the secondary ingot obtained in step 4.2 is removed from the ingot crown and turned over, the secondary ingot is smelted three times in the copper crucible, the smelting current is 14 kA-24 kA, the smelting voltage is 24 V-32 V, the steady arc current is 12 A-22 A, and the steady arc period is 5 s-15 s;

[0080] Step 4.3, after the secondary ingot obtained in step 4.2 is removed from the ingot crown and turned over, the secondary ingot is smelted three times in the copper crucible, the smelting current is 14 kA-24 kA, the smelting voltage is 24 V-32 V, the steady arc current is 12 A-22 A, and the steady arc period is 5 s-15 s; Step 5, the remaining weight of the consumable electrode is 1300 kg after the third smelting, and the top-up smelting is started;

[0081] Specific process is as follows:

[0082] The top-up smelting is started when the remaining weight of the consumable electrode is 1300 kg, the current is reduced to 12 kA at a current reduction rate of 0.15 kA / min, then when the remaining weight of the consumable electrode is 700 kg, the top-up smelting is started at a constant current of 12 kA, finally when the remaining weight of the consumable electrode is 300 kg, the current is gradually reduced to 4 kA at a current reduction rate of 1 kA / min-0.7 kA / min-0.4 kA / min-0.2 kA / min-0.1 kA / min;

[0083] Step 6, after the top-up smelting is completed, the furnace is cooled for not less than 7 h, and a TC18 titanium alloy ingot is obtained;

[0084] Step 6, after the top-up smelting is completed, the furnace is cooled for not less than 7 h, and a TC18 titanium alloy ingot is obtained.

[0085] ​​Example 3

[0086] Prepare TC18 titanium alloy ingots with a diameter of φ920mm.

[0087] Step 1: Select and weigh the raw materials. The raw materials are sponge titanium, MoVAl ternary master alloy, CrAl binary alloy, and FeAl binary alloy. Weigh the raw materials according to the following ratio: Al: 5%, Mo: 5%, V: 5%, Cr: 1%, Fe: 1%, with the balance being Ti. The sum of the mass percentages is 100%.

[0088] The Brinell hardness value of sponge titanium is 80HBW to 100HBW, with C and N elements content of 0.003% to 0.015% and Cl element content of 0.01% to 0.05%.

[0089] The particle size of the MoVAl ternary master alloy, CrAl binary alloy, and FeAl binary alloy is 3-4 mm.

[0090] Step 2: After mixing the raw materials weighed in Step 1 evenly, press them into circular electrode blocks. The weight of a single electrode block is 145 kg, and the density of the electrode block is 3.93 g / cm³. 3 ;

[0091] Step 3: Weld the electrode blocks pressed in Step 2 into a plasma welding box protected by argon gas to form a shape with dimensions of [size missing]. The consumable electrode to be melted;

[0092] Step 4: The consumable electrode obtained in Step 3 is smelted three times in a copper crucible.

[0093] Step 4.1, place the primary consumable electrode obtained in step 3 in... A copper crucible is used for one melting process, with a melting current of 16kA to 26kA, a melting voltage of 30V to 40V, and an arc stabilization current of 10A to 30A, to obtain a first ingot.

[0094] Step 4.2: After removing the ingot crown from the primary ingot obtained in Step 4.1, turn it around and load it into... The copper crucible is used for secondary smelting. The smelting current is 20kA to 30kA, the smelting voltage is 32V to 42V, the arc stabilization current is 16A to 32A, and the arc stabilization period is 5s to 15s, to obtain a secondary ingot.

[0095] Step 4.3: After removing the ingot crown from the secondary ingot obtained in Step 4.2, turn it around and load it into the [unclear - possibly a container or container]. The copper crucible is used for three melting processes, with a melting current of 16kA to 26kA, a melting voltage of 26V to 35V, an arc stabilization current of 14A to 25A, and an arc stabilization period of 5s to 15s.

[0096] Step 5, when the remaining weight of the consumable electrode is 1300 kg, start to top up;

[0097] The specific process is as follows:

[0098] When the remaining weight of the consumable electrode is 1500 kg, start to top up, and start to reduce the current to 14 kA at a current reduction rate of 0.1 kA / min, and when the remaining weight of the consumable electrode is 800 kg, start to top up and smelt at a constant current of 14 kA, and finally when the remaining weight of the consumable electrode is 400 kg, start to gradually reduce the current to 5 kA at a current reduction rate of 1 kA / min-0.6 kA / min-0.3 kA / min-0.2 kA / min-0.1 kA / min;

[0099] Step 6, after the top-up is completed, the furnace is discharged after cooling for not less than 8 h, and a TC18 titanium alloy ingot with a specification of φ720 mm is obtained.

[0100] Table 1 Uniformity of composition of the φ720 mm specification TC18 ingot prepared by the present application

[0101]

[0102] Table 2 Uniformity of phase transition point of the φ720 mm specification TC18 ingot prepared by the present application

[0103]

[0104] Table 3 Properties of the φ400 mm bar prepared by the present application

[0105]

[0106] As shown in Figure 1 , Figure 2 , Figure 3 and Figure 5 , the edge position 120 mm-150 mm is equiaxed crystal (position ① in Figure 5 ), the R / 2 position 150 mm-200 mm is columnar crystal (position ② in Figure 5 ), and the core position 0-50 mm is mixed structure of equiaxed crystal (position ③ in Figure 5 ). Among them, the equiaxed crystal grain diameter is 5 mm-10 mm, the columnar crystal width is 5 mm-10 mm, the columnar crystal growth angle is 40°-60°, and in particular, the tail 700 mm height range is vertical columnar crystal triangle area (position ④ in Figure 5 ). Under this structure, the core equiaxed crystal area range is narrow, the composition segregation tendency is small, and excellent composition uniformity and phase transition point uniformity are obtained.

[0107] As shown in Figure 4As shown and shown in Table 3, the ingot prepared by the application meets the standard requirements of GJB2744A-2019 in performance and macrostructure, and there is no beta spot in the macrostructure inspection after the solid solution and aging heat treatment below 25 DEG C of the phase transition point.

[0108] By reasonably controlling the selection of raw materials and the shape of the electrode block, reasonably controlling the melting process parameters such as crucible ratio, current, voltage, arc stabilization and water cooling, the TC18 ingot organization is controlled to be mixed organization of equiaxed crystal + columnar crystal, thereby realizing high homogenization of TC18 ingot composition and phase transition point, preparing the target of beta spot-free ingot and greatly improving the production efficiency.

[0109] However, the TC18 ingot prepared by the conventional technology is mostly columnar crystal in the range of 150-200mm of the edge and equiaxed crystal organization in the range of 200-300mm of the center. Under this organization, the range of equiaxed crystal area in the center of the whole ingot is deep and wide, and the composition segregation degree is large. The prepared rod has a large risk of beta spot in the center position after the solid solution and aging heat treatment below 25 DEG C of the phase transition point.

Claims

1. A method for producing a large-size TC18 titanium alloy ingot, characterized in that, The method is implemented according to the following steps: Step 1, selecting and weighing raw materials; In step 1, the raw materials are sponge titanium, MoVAl ternary intermediate alloy, CrAl binary alloy and FeAl binary alloy; The Brinell hardness value of the sponge titanium is 80HBW~100HBW, the content of C element and N element is 0.003%~0.015%, and the content of Cl element is 0.01%~0.05%; Step 2, after the raw materials weighed in step 1 are mixed uniformly, the mixture is pressed into a circular electrode block; Step 3, the electrode block pressed in step 2 is welded into a primary consumable electrode to be smelted in a plasma welding box under the protection of argon; Step 4, the primary consumable electrode obtained in step 3 is smelted three times in a copper crucible; The specific process of step 4 is as follows: Step 4.1, the primary consumable electrode obtained in step 3 is smelted once in a copper crucible, the smelting current is 12kA~26kA, the smelting voltage is 25V~40V, the stable arc current is 10A~30A, and a primary ingot is obtained; Step 4.2, after the primary ingot obtained in step 4.1 is removed from the ingot crown, it is loaded into the copper crucible upside down for secondary smelting, the smelting current is 16kA~30kA, the smelting voltage is 28V~42V, the stable arc current is 12A~32A, and the stable arc period is 5s~15s, and a secondary ingot is obtained; Step 4.3, after the secondary ingot obtained in step 4.2 is removed from the ingot crown, it is loaded into the copper crucible upside down for three times smelting, the smelting current is 12kA~26kA, the smelting voltage is 22~35V, the stable arc current is 10A~25A, and the stable arc period is 5s~15s; The crucible ratio of the primary smelting is 0.65~0.85, and the crucible ratio of the secondary smelting and the three times smelting is 0.80~0.90, wherein the crucible ratio = diameter of the consumable electrode to be smelted / inner diameter of the crucible; Step 5, when the remaining weight of the consumable electrode is 1000kg~1500kg after the third smelting, the top-up is started; The specific process of step 5 is as follows: when the remaining weight of the consumable electrode is 1000kg~1500kg, the top-up is started, the current is reduced to 10kA~14kA at a current reduction rate of 0.1kA / min~0.2 kA / min, then when the remaining weight of the consumable electrode is 500kg~800kg, the top-up smelting is started with a constant current of 10kA~14kA, finally when the remaining weight of the consumable electrode is 200kg~400kg, the current is reduced to 3kA~5kA at a current reduction rate of 0.1kA / min~1.0 kA / min; Step 6, after the top-up is completed, the furnace is cooled to obtain a large-size TC18 titanium alloy ingot.

2. The method of producing a large size TC18 titanium alloy ingot according to claim 1, characterized by, The particle size of the MoVAl ternary intermediate alloy, the CrAl binary alloy and the FeAl binary alloy is 2mm~5mm.

3. The method of producing large size TC18 titanium alloy ingot according to claim 1, characterized in that, In step 2, the electrode block single weight is 135 kg ~ 145 kg, and the electrode block density is 3.66 g / cm 3 3.93 g / cm 3 .

4. The method of producing large size TC18 titanium alloy ingot according to claim 1, characterized in that, In step 3, the size of the primary consumable electrode to be smelted is φ420mm~φ520mm.

5. The method of producing large size TC18 titanium alloy ingot according to claim 1, wherein, In step 6, the cooling time is not less than 6h.

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