Vacuum consumable melting method for preparing Ti-45Nb titanium alloy cast ingot based on strong stable arc

Abstract

The invention discloses a vacuum consumable melting method for preparing a Ti-45Nb titanium alloy cast ingot based on a strong stable arc, and belongs to the technical field of high-quality titanium alloy materials, the vacuum consumable melting method is adopted for conducting three-time melting on a Ti-45Nb titanium alloy consumable electrode, direct current is adopted for the first-time melting and the second-time melting to control the stability of the melting arc, and the high-quality titanium alloy is obtained. And the third-time smelting adopts a step-by-step current reducing mode for smelting. According to the method, full alloying of titanium and niobium is achieved through high power and strong arc stabilization, precise control over the titanium alloy smelting process is achieved in combination with Meltflow simulation, reliable technological parameters are provided for ingot casting smelting, the development period is shortened, the production cost is reduced, and the method has guiding significance for smelting production of large-specification refractory ingots with high segregation risks.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-quality titanium alloy materials, and relates to the manufacturing of a Ti-45Nb titanium alloy, in particular to a vacuum self-consumption smelting method for preparing Ti-45Nb titanium alloy ingots based on strong stable arc. BACKGROUND

[0002] Ti-45Nb alloy is one of commonly used titanium alloy engineering materials, has good plasticity, self-ignition resistance and corrosion resistance, low elastic modulus and excellent biocompatibility. Researches show that the oxidation heat of the Nb element is low and the diffusion rate of O2 is high, so that the Nb element has excellent fire resistance and has become the first choice material for many hydrometallurgy autoclave applications. Compared with pure titanium, the Ti-45Nb alloy has good cold working forming performance, higher shear strength and tensile strength, and lower deformation resistance. The Ti-45Nb alloy is matched with the Ti-6Al-4V alloy to form a double-metal rivet, which has been widely used in Airbus and Boeing aircraft, and the Ti-45Nb alloy fastener has replaced the pure titanium fastener in the field of aerospace. In addition, the Ti-45Nb alloy has an elastic modulus and strength (i.e. mechanical compatibility) more suitable for bones, and excellent corrosion resistance, and the Nb element is non-toxic (i.e. biocompatibility), so the Ti-45Nb alloy is more and more widely used in the field of biomedical devices.

[0003] Although the melting point of the Ti-45Nb alloy after alloying (about 1800℃) is not significantly different from that of titanium (about 1670℃), the melting point of niobium (2469℃) is much higher than that of titanium. The traditional vacuum arc smelting process cannot guarantee long-time high temperature and stirring mixing, and after the droplets enter the molten pool, solidification occurs before the mixing with the molten pool is completed and evolution, resulting in undissolved Nb particles in the ingot. At the same time, due to the large difference in density between titanium and niobium, they are easily quickly sunk into the two-phase paste zone at the bottom of the molten pool due to the action of gravity, resulting in composition segregation or uneven smelting.

[0004] The above problems are more prominent in the smelting of large-size Ti-45Nb ingots, because in the smelting process of large-size, due to the increase of the size of the crystallizer, the heat conduction distance of the material from the core to the side wall is large and the thermal conductivity of the titanium alloy is low, the depth of the molten pool increases during smelting, the paste zone range expands, and the solidification speed of the solid-liquid interface slows down, resulting in sufficient time for the Nb element in the solid-liquid phase to segregate and diffuse, causing obvious macro-segregation of the composition. Therefore, in addition to the insufficient flow of the melt, the conventional electromagnetic stirring is difficult to cover the large-size molten pool, resulting in the difficulty in avoiding macro-segregation. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a vacuum self-consumption smelting method for preparing Ti-45Nb titanium alloy ingot based on strong stable arc, which solves the technical problems that the traditional vacuum arc smelting process cannot guarantee long-time high temperature and stirring mixing, leading to incomplete dissolution of niobium to realize alloying and form unmelted Nb particles, and the density difference between titanium and niobium is large, so they are easily quickly sunk into the bottom of the molten pool due to gravity, leading to composition segregation or uneven smelting.

[0006] In order to solve the above technical problems, the technical scheme is adopted as follows:

[0007] A vacuum self-consumption smelting method for preparing Ti-45Nb titanium alloy ingot based on strong stable arc, which adopts the vacuum self-consumption smelting method to smelt the Ti-45Nb titanium alloy consumable electrode for three times, the stability of the smelting arc is controlled by direct current in the first and second smelting, and the third smelting is carried out by gradually reducing the current.

[0008] The present application also includes the following technical features:

[0009] Specifically, the method comprises the following steps:

[0010] Step one, design the ingot smelting parameters:

[0011] Step 1.1, establish the ingot model by using Meltflow software: set the ingot diameter, ingot length and ingot type of three smelting respectively; specifically, the ingot diameter of the first smelting is set to 380mm, the ingot diameter of the second smelting is set to 460mm, and the ingot diameter of the third smelting is set to 520mm; the ingot length of the first smelting is set to 1.3m, the ingot length of the second smelting is set to 1.64m, and the ingot length of the third smelting is set to 1.27m; the ingot type of three smeltings is set to one ingot with two branches, the second smelting electrode is composed of two one-time ingots butt joint, and the third smelting electrode is one two-time ingot (211 ingot type).

[0012] Step 1.2, optimize the smelting process parameters: according to the ingot type set in step one, set different smelting parameter combinations in the simulation software, including current, voltage, stable arc magnetic field intensity and stable arc period, etc. key process parameters; then simulate and analyze the smelting process under each group of parameters, and select the parameter combination with the lowest composition segregation degree, the best impurity removal effect, the most stable molten pool morphology and the least riser defect as the optimal process scheme through systematic comparison and analysis of the simulation results; the optimal simulation composition result of the first smelting is iterated to the second smelting, and the optimal simulation composition result of the second smelting is iterated to the third smelting.

[0013] Step two, preparation of consumable electrode:

[0014] The consumable electrode is welded by using the combination of niobium rod and sponge titanium electrode block; the welding parameters are as follows: the vacuum plasma welding mode is used, the welding current is 450A-650A, preferably 550A; the vacuum degree is 1.0Pa-10.0Pa, preferably 3.0Pa; the air leakage rate is 0.1Pa / min-0.5Pa / min, the air leakage rate is 0.33Pa / min; the cooling time is 30-60min; the feeding weight is 1600kg.

[0015] Step three, the consumable electrode obtained in step two is subjected to three times of melting to obtain a titanium alloy ingot:

[0016] The vacuum consumable furnace is used for melting, the current of primary melting is controlled to be 10-13KA, the steady arc current is direct current 10-15A, and the voltage is 30-35V; the current of secondary melting is controlled to be 10-20KA, the steady arc current is direct current 8-15A, and the voltage is 30-40V; the three times of melting is carried out by using the step-by-step current reduction mode, the current in the middle stage of melting is 18-22KA, the steady arc current is alternating current 8-15A, the period is 10-30s, and the voltage is 25-40V; the stable molten pool should be rapidly established in the initial stage of melting to avoid that the rapid cooling of the pad bottom leads to repeated melting and solidification of the molten pool; the step-by-step current reduction mode is used in the middle and later stages of melting to reduce the latent heat of crystallization, stabilize the molten pool and avoid the segregation of elements; the supplement shrinkage stage is started at 100-200kg in the later stage of melting, the supplement shrinkage adopts the small current mode, the length of the riser is reduced, the yield is improved, and the cooling time after melting is not less than 7h.

[0017] The beneficial technical effects of the present application compared with the prior art are as follows:

[0018] (I) The present application realizes the full alloying of titanium and niobium by high power and strong arc stabilization, realizes the precise control of the titanium alloy melting process by combining Meltflow simulation, provides reliable process parameters for ingot melting, shortens the development cycle and production cost, has guiding significance for the melting production of large-size refractory ingots with high segregation risk.

[0019] (II) The application adopts Meltflow simulation to optimize smelting process parameters, direct current is used in primary smelting and secondary smelting stages, and full alloying of titanium and niobium is realized through high power and strong arc stabilization. The high power input can significantly improve the energy of the electrode front end arc, improve the droplet superheat, and ensure the full melting of the high melting point Nb element. Strong arc and high current produce strong tangential Lorentz force, thermal buoyancy, gravity and other forces along the molten pool, which control the flow field of solutes with different densities in the molten pool to realize full stirring of the molten pool and achieve the purpose of full alloying of niobium and titanium. The third smelting adopts step-by-step current reduction for smelting, reduces the influence of latent heat of crystallization on the depth of the molten pool and the local solidification time, stabilizes the molten pool morphology and depth, and avoids element segregation.

[0020] (III) The Ti-45Nb titanium alloy ingot prepared by the application has uniform composition and good metallurgical quality. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a binary alloy phase diagram of Ti and Nb.

[0022] Figure 2 is the sampling result of the side wall of the pre-optimized ingot.

[0023] Figure 3 is a macroscopic picture of the ingot after rolling after the smelting process is optimized.

[0024] Figure 4 (a)-(c) are simulation results of the secondary smelting process before optimization.

[0025] Figure 5 is the composition of the head 9 points and the tail 9 points after the ingot is cut off (50mm) before optimization.

[0026] Figure 6 (a)-(i) are respectively the results of primary smelting, secondary smelting and third smelting after Meltflow simulation optimization.

[0027] Figure 7 (a), (b) and (c) are respectively the ingot surface pictures after primary smelting, secondary smelting and third smelting.

[0028] Figure 8 is the side wall sampling result.

[0029] Figure 9 is the composition of the head 9 points and the tail 9 points after the ingot is cut off (55mm).

[0030] Figure 10 is a macroscopic detection picture of the ingot and after rolling.

[0031] The technical solutions of the present application are further described below in combination with examples. DETAILED DESCRIPTION

[0032] It should be noted that all the materials used in the present application are known in the art unless otherwise specified. For example, Ti-45Nb titanium alloy is an alloy known in the prior art, and the specific composition is: Nb is 45wt.%, Ti is 55wt.%.

[0033] In accordance with the above technical solutions, the following specific examples of the present application are given. It should be noted that the present application is not limited to the following specific examples, and any equivalent variations made on the basis of the technical solutions of the present application fall within the scope of protection of the present application.

[0034] Example 1

[0035] The present embodiment provides a vacuum consumable melting method for preparing Ti-45Nb titanium alloy ingot based on strong arc stabilization, which comprises the following steps:

[0036] Step one, design the ingot melting parameters:

[0037] Step 1.1, establish the ingot model using Meltflow software: set the ingot diameter, ingot length and ingot type for three times of melting respectively; in this embodiment, the ingot diameter for the first time of melting is set to 380mm, the ingot diameter for the second time of melting is set to 460mm, and the ingot diameter for the third time of melting is set to 520mm; the ingot length for the first time of melting is set to 1.3m, the ingot length for the second time of melting is set to 1.64m, and the ingot length for the third time of melting is set to 1.27m; the ingot type for the three times of melting is set to two branches for the first ingot, the second melting electrode is composed of two branches of the first ingot butt-welded, and the third melting electrode is a branch of the second ingot (i.e. 211 ingot type).

[0038] Step 1.2, optimize the process parameters for melting: according to the ingot type set in step one, set multiple different combinations of melting parameters in the simulation software, including current, voltage, arc stabilization magnetic field strength and arc stabilization period, etc. key process parameters; then simulate and analyze the melting process under each group of parameters, and through systematic comparison and analysis of the simulation results, select the parameter combination with the lowest composition segregation degree, the best impurity removal effect, the most stable molten pool morphology and the least riser defects as the optimal process scheme; iterate the simulation composition results of the optimal first melting to the second melting, and iterate the simulation composition results of the optimal second melting to the third melting; wherein the arc current in the first and second melting processes is direct current, and the third melting is carried out in a step-by-step current reduction mode.

[0039] Step two, prepare the consumable electrode:

[0040] The consumable electrode is welded by using a niobium rod and a sponge titanium electrode block; the welding parameters are as follows: the vacuum plasma welding mode is used, the welding current is 550 A, the vacuum degree is 3.0 Pa, the air leakage rate is 0.33 Pa / min, the cooling time is 30 min, and the feeding weight is 1600 kg.

[0041] Step three, the consumable electrode obtained in step two is subjected to three times of melting to obtain a titanium alloy ingot:

[0042] The vacuum consumable furnace is used for melting, the current of the first melting is controlled to be 10-13 KA, the steady arc current is direct current 10-15 A, and the voltage is 30-35 V; the current of the second melting is controlled to be 10-20 KA, the steady arc current is direct current 8-15 A, and the voltage is 30-40 V; the third melting is subjected to step-by-step current reduction mode, the current in the middle stage of melting is 18-22 KA, the steady arc current is alternating current 8-15 A, the period is 10-30 s, and the voltage is 25-40 V; a stable molten pool should be rapidly established in the initial stage of melting to avoid repeated melting and solidification of the molten pool due to rapid cooling of the pad; the step-by-step current reduction mode is used in the middle and late stages of melting to reduce the latent heat of crystallization, stabilize the molten pool, and avoid segregation of elements; the feeding stage is started at 100-200 kg in the late stage of melting, small current mode is used for feeding, the length of the riser is reduced, and the yield is improved, and the cooling time after melting is not less than 7 h.

[0043] Comparative example 1

[0044] This comparative example provides a VAR method for preparing a Ti-45Nb titanium alloy ingot before optimization, which is different from example 1 in that: no direct current strong steady arc melting mode is used in the three times of melting, and the melting power is relatively low. The method comprises the following steps:

[0045] Step one, preparing a consumable electrode:

[0046] The consumable electrode is welded by using a niobium rod and a sponge titanium electrode block; the welding parameters are as follows: the vacuum plasma welding mode is used, the welding current is 550 A, the vacuum degree is 3.0 Pa, the air leakage rate is 0.33 Pa / min, the cooling time is 30 min, and the feeding weight is 1600 kg.

[0047] Step two, the consumable electrode obtained in step one is subjected to three times of melting to obtain a titanium alloy ingot:

[0048] The vacuum consumable furnace is used for smelting, the current of primary smelting is controlled at 8-10 KA, the stable arc current is AC 8-10 A, the period is 10-30 s, and the voltage is 30-35 V; the current of secondary smelting is controlled at 8-10 KA, the stable arc current is AC 10-25 A, the period is 10-30 s, and the voltage is 25-35 V; the current of tertiary smelting is controlled at 8-10 KA, the stable arc current is AC 8-15 A, the period is 10-30 s, and the voltage is 25-35 V; a stable molten pool should be rapidly established in the initial smelting stage to avoid repeated melting and solidification of the molten pool due to rapid cooling of the base; in the later stage, 100-200 kg enters the feeding stage, the feeding adopts a small current mode, the length of the riser is reduced, the yield is improved, and the cooling time after smelting is not less than 7 h.

[0049] Comparative Example 2

[0050] The present comparative example provides a vacuum consumable smelting method for preparing a Ti-45Nb titanium alloy ingot before optimization, which is different from that of Example 1 in that although strong stable arc is used for primary smelting, the power is low, and neither secondary smelting nor tertiary smelting uses strong stable arc and the relative power is low. The method comprises the following steps:

[0051] Step 1, preparing a consumable electrode

[0052] The consumable electrode is welded in the form of a niobium rod and a titanium electrode block; the welding parameters are as follows: vacuum plasma welding is used, the welding current is 550 A, the vacuum degree is 3.0 Pa, the air leakage rate is 0.33 Pa / min, the cooling time is 30 min, and the feeding weight is 1600 kg.

[0053] Step 2, performing three times of smelting on the consumable electrode obtained in Step 1 to obtain a titanium alloy ingot

[0054] The vacuum consumable furnace is used for smelting, the current of primary smelting is controlled at 8-10 KA, the stable arc current is AC 8-10 A, the period is 10-30 s, and the voltage is 30-35 V; the current of secondary smelting is controlled at 8-10 KA, the stable arc current is AC 10-25 A, the period is 10-30 s, and the voltage is 25-35 V; the current of tertiary smelting is controlled at 8-10 KA, the stable arc current is AC 8-15 A, the period is 10-30 s, and the voltage is 25-35 V; a stable molten pool should be rapidly established in the initial smelting stage to avoid repeated melting and solidification of the molten pool due to rapid cooling of the base; in the later stage, 100-200 kg enters the feeding stage, the feeding adopts a small current mode, the length of the riser is reduced, the yield is improved, and the cooling time after smelting is not less than 7 h.

[0055] Effect verification of Comparative Example 1

[0056] Figure 2is the upper, middle and lower component detection results of the ingot produced by the smelting process before optimization. The results show that the Nb content is lower than the target value and the upper, middle and lower components are uneven. The reason is that the arc current intensity and power of the smelting process are low, which makes the element alloying insufficient, and the step-by-step current reduction method is not used in the three times of smelting, which has the risk of metallurgical segregation.

[0057] Effect verification of Comparative Example 2:

[0058] Figure 3 is the macroscopic picture of the ingot after rolling produced by the smelting process before optimization. The obvious "black spots" can be observed, and the Nb content in this area is obviously enriched (about 75%) through EDS energy spectrum detection. The reason is that the smelting power is low and the arc intensity is not enough, which causes the Nb droplets to drop into the molten pool due to insufficient superheat or insufficient stirring, and cannot fully alloy with titanium to form Nb-rich segregation.

[0059] Figure 4 is the simulation result of the secondary smelting process before optimization, (a), (b) and (c) are the component distribution of Nb content, the position of particulate matter in the smelting process and the path of the smelting process. When alternating current is used in secondary smelting, the element distribution is in the range of 40-46 wt..%, and the Nb content at the riser is obviously low. In addition, the stirring area of the molten pool under the alternating current short-period stirring current is small, which will cause the Nb droplets that drop into the molten pool due to insufficient superheat to still not fully mix under the action of gravity, and deposit at the bottom of the molten pool to form local segregation.

[0060] Figure 5 is the sampling position and component of the head 9 points and tail 9 points after cutting off the riser (50mm) of the three times of ingot. The overall component is low, and the head and tail distribution is uneven, between 41.9-44.80wt..%.

[0061] Effect verification of Example 1:

[0062] Figure 6 are the results of the primary smelting, secondary smelting and tertiary smelting after optimization by Meltflow simulation. The results show that the Nb element content is between 40-45wt.%, the Nb element distribution is between 39-46wt.% after secondary smelting, and the component distribution is uniform (43-46wt.%) except for the low Nb content (41wt.%) at the riser position after three times of smelting. The uniformity of the finished ingot is significantly improved.

[0063] Figure 6 (a), (b) and (c) are the surface pictures of the ingot after primary smelting, secondary smelting and tertiary smelting, respectively. The surface quality of the ingot is good, and there is no obvious cold separation, oxidation, porosity, air hole, crack and other defects.

[0064] Figure 8 For the side wall sampling results, the Nb content of the head and tail side walls were 45.59wt.%, 45.73wt.% and 45.36wt.% respectively. The composition distribution was uniform.

[0065] Figure 9 For the head 9-point and tail 9-point sampling positions and composition after the ingot was cut off the head (55mm), the composition distribution of the head and tail was uniform, and was between 44.31wt.% and 45.81wt.%.

[0066] Figure 10 For the macroscopic detection pictures of the ingot and after rolling, the macroscopic showed uniform structure, and no metallurgical defects such as niobium particles were found.

[0067] From the above results, it can be seen that the present application adopts the strategy of simulation and actual process optimization, the first two times of smelting are realized by high power and strong arc to realize the full alloying of titanium and niobium, and the third time of smelting is carried out by gradually reducing the current. The composition uniformity and metallurgical quality of the ingot are significantly improved, and a reliable technical scheme is provided for the industrial production of high-performance Ti-45Nb alloy. The problems of composition segregation and un-melted niobium particles and other metallurgical defects commonly encountered in the preparation process of Ti-45Nb alloy are effectively improved.

[0068] The above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A vacuum arc melting method for preparing a Ti-45Nb titanium alloy ingot based on strong arc, characterized in that, The Ti-45Nb titanium alloy consumable electrode is melted three times by using vacuum self-consumption melting method, the stability of the melting arc is controlled by using direct current in the first melting and the second melting, and the third melting is carried out by using step-by-step current reduction mode; The process parameters of the first melting include: current is 10-13KA, stable arc current is direct current 10-15A, and voltage is 30-35V; The process parameters of the second melting include: current is 10-20KA, stable arc current is direct current 8-15A, and voltage is 30-40V; The process parameters of the third melting include: the melting is carried out by using step-by-step current reduction mode, the current in the middle of the melting is 18-22KA, the stable arc current is alternating current 8-15A, the period is 10-30s, and the voltage is 25-40V.

2. The vacuum arc remelting method for producing a Ti-45Nb titanium alloy ingot according to claim 1, wherein The cooling time after the third melting is at least 7h.

3. The vacuum arc remelting method for producing a Ti-45Nb titanium alloy ingot according to claim 1, wherein The ingot model is established by using Meltflow software, and the process parameters of the melting are optimized.

4. The vacuum arc remelting method for producing a Ti-45Nb titanium alloy ingot according to claim 3, wherein The ingot model is established by using Meltflow software, which includes: setting the ingot diameter, ingot length and ingot type of the three times of melting respectively.

5. The vacuum arc remelting method for producing a Ti-45Nb titanium alloy ingot according to claim 3, wherein The ingot type of the three times of melting is set as follows: there are two primary ingots, the electrode of the second melting is composed of two primary ingots which are butt welded after turning over, and the electrode of the third melting is a secondary ingot which is turned over.

6. The vacuum arc remelting method for producing a Ti-45Nb titanium alloy ingot according to claim 3, wherein The optimization of the process parameters of the melting includes: setting multiple groups of different melting parameter combinations in the Meltflow software, including current, voltage, stable arc current and stable arc period; then simulating and analyzing the melting process under each group of parameters, comparing and analyzing the simulation results, and screening the optimal process scheme; the simulation composition result of the optimal first melting is iterated to the second melting, and the simulation composition result of the optimal second melting is iterated to the third melting.

7. The vacuum arc remelting method for producing a Ti-45Nb titanium alloy ingot according to claim 1, wherein The Ti-45Nb titanium alloy consumable electrode is prepared by using vacuum plasma welding.

8. The vacuum arc remelting method for producing a Ti-45Nb titanium alloy ingot according to claim 7, wherein The welding current is 450A-650A.

9. The vacuum arc remelting method for producing a Ti-45Nb titanium alloy ingot according to claim 7, wherein The vacuum degree during welding is 1.0Pa-10.0Pa; the air leakage rate is 0.1Pa / min-0.5Pa / min.

10. The vacuum arc remelting method for producing a Ti-45Nb titanium alloy ingot according to claim 7, wherein The cooling time after welding is 30-60min.

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