Method for improving grain size and component uniformity of solidification structure in titanium alloy EB furnace smelting process through ultrasonic treatment

Abstract

The invention discloses a method for improving the grain size and component uniformity of a solidification structure in the smelting process of a titanium alloy EB furnace through ultrasonic treatment, and belongs to the technical field of titanium alloy smelting. In order to solve the problems of non-uniform cast ingot components, serious grain boundary segregation, coarse structure grains and the like in the existing EB furnace smelting process, the invention provides a method for improving the solidification structure grain size and component uniformity in the titanium alloy EB furnace smelting process through ultrasonic treatment, which comprises the following steps: high-temperature titanium alloy melt flows into a crystallizer for solidification and ingot dummy; after ingot dummy is started, an ultrasonic radiation rod is inserted into a titanium alloy melt molten pool on the upper portion of the crystallizer; and when the cast ingot is close to a solidification end point, removing the ultrasonic radiation rod to obtain the titanium alloy cast ingot. According to the method, the ultrasonic radiation rod is inserted, the insertion depth and the ultrasonic frequency are controlled, and ultrasonic vibration and cavitation are utilized, so that grains of a titanium alloy solidification structure are refined, alloy components are uniform, the machining performance of a titanium cast ingot is improved, and efficient production of the high-quality titanium alloy is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy smelting, and particularly relates to a method for improving the grain size and component uniformity of solidified structure of titanium alloy in an EB furnace smelting process by ultrasonic treatment. Background Art

[0002] Titanium alloy has low density, high specific strength, strong corrosion resistance, good high and low temperature mechanical properties, and is regarded as the most promising metal material. It is widely used in aviation, aerospace, ocean, chemical industry, medicine and other fields. At present, the smelting process of titanium alloy mainly includes vacuum consumable arc melting (VAR) and electron beam cold hearth furnace melting (EB) technology. VAR furnace has poor impurity removal and degassing effects, and is prone to inclusions and segregation, which limits its application in the field of high-quality titanium alloys. EB furnace can effectively remove high and low density inclusions in titanium and titanium alloys, and is an advanced technology for smelting titanium and titanium alloys at this stage. However, during the EB furnace smelting process, the high-temperature titanium and titanium alloy melt has low flow force and slow solidification speed, which makes it face serious problems such as uneven ingot composition, severe grain boundary segregation, and coarse grain structure.

[0003] Ultrasound is a metal-assisted melting technology that has received much attention in recent years. It uses high-frequency vibration to form ultrasonic waves that act on liquid metal. On the one hand, it can trigger the formation and collapse of microbubbles in the liquid, forming strong local high temperature and high pressure and liquid flow, which is conducive to the melting and floating of oxides and impurities in the metal melt; on the other hand, the introduction of ultrasonic waves can effectively reduce the surface tension of the metal melt, thereby promoting the uniform distribution of alloy elements in the melt. Ultrasonic technology has been applied in the melting and casting processes of metal materials such as aluminum alloys and magnesium alloys. Practice has proved that it helps to avoid defects such as stratification and pores that may occur during the melting and solidification process, thereby improving the density and mechanical properties of castings.

[0004] CN118685628 provides a method and device for purifying cast aluminum alloy melt, which puts the aluminum alloy melt in an ultrasonic field, an electromagnetic field and a negative pressure vacuum field, and effectively improves the purification effect of the aluminum alloy under the synergistic effect, so as to achieve the ultra-cleanliness, ultra-fine grains, and ultra-uniformity of the aluminum alloy melt, thereby improving the comprehensive performance of the aluminum alloy material. CN96218695.3 discloses a power ultrasonic melting furnace for manufacturing silicon carbide particle reinforced aluminum alloy composite materials, which is composed of a furnace body and a power ultrasonic chamber. The power ultrasonic radiator can be inserted into the molten aluminum liquid through a lifter for ultrasonic stirring, thereby obtaining a SiCp / Al composite material with excellent performance. CN107900315A discloses a technical method for frequency conversion ultrasound assisted ceramic and titanium alloy composite casting. During the casting process, it reduces the solidification segregation of the titanium alloy, increases the fine grain area, reduces the formation of developed dendrites, and forms a good combination between the molten titanium alloy melt and the ceramic matrix, thereby forming a titanium alloy-ceramic composite material with excellent performance.

[0005] However, to date, there is almost no relevant literature reporting the application of ultrasonic technology in titanium alloy smelting and EB furnace process. The ultrasonic-assisted process parameters suitable for titanium alloy EB furnace smelting process have not been systematically studied and clarified. The ultrasonic processes of CN118685628 and CN107900315A are difficult to apply to EB furnace smelting of titanium alloys. Summary of the invention

[0006] In order to solve the problems of the prior art, the present invention inserts an ultrasonic radiation rod into the EB furnace smelting pool to refine the grains of the titanium alloy solidification structure and make the alloy composition uniform through ultrasonic vibration and cavitation, thereby improving the processing performance of the titanium ingot and achieving efficient and high-quality production of titanium alloy.

[0007] To achieve the above object, the present invention provides a method for improving the grain size and composition uniformity of the solidified structure of titanium alloy during EB furnace smelting by ultrasonic treatment, which comprises the following steps:

[0008] A. Solidification and ingot drawing: The high-temperature titanium alloy melt flows into the crystallizer, and solidification and ingot drawing begin when the melt level is less than 30 mm from the upper edge of the crystallizer;

[0009] B. Ultrasonic treatment: applying an ultrasonic vibration system to the titanium alloy melt pool at the top of the crystallizer, starting the ultrasonic vibration system while starting the ingot, inserting the ultrasonic radiation rod into the titanium alloy melt pool at the top of the crystallizer, the ultrasonic radiation rod is immersed in the melt to a depth of 50 to 200 mm, and the ultrasonic frequency is 30 to 120 kHz; the ultrasonic vibration system includes an ultrasonic power supply, a connecting line and an ultrasonic radiation rod;

[0010] C. End of smelting: When the titanium ingot solidifies by 90% to 95%, the ultrasonic vibration system stops working, and the titanium ingot continues to descend and move out of the crystallizer; inert gas is filled into the EB furnace, and after the titanium ingot is cooled, a titanium alloy ingot is obtained.

[0011] Among them, in the above-mentioned method of improving the grain size and composition uniformity of the solidified structure of titanium alloy EB furnace smelting process by ultrasonic treatment, in step A, the ingot guiding speed is dynamically adjusted according to the liquid level of the titanium alloy melt so that its distance from the upper edge of the crystallizer is maintained at 30±10mm.

[0012] Among them, in the above-mentioned method of ultrasonic treatment to improve the grain size and composition uniformity of the solidified structure of titanium alloy EB furnace smelting process, in step B, before the ultrasonic vibration system is applied, the ultrasonic radiation rod is preheated, and the preheating temperature is not less than 800°C.

[0013] Among them, in the above-mentioned method for improving the grain size and composition uniformity of the solidified structure of titanium alloy during EB furnace smelting by ultrasonic treatment, in step B, the ultrasonic radiation rods are evenly distributed and immersed in the titanium alloy melt. In the present invention, the arrangement of the ultrasonic radiation rods includes various methods such as annular arrangement and transverse arrangement, and more than one ultrasonic radiation rod can be used.

[0014] Among them, in the above-mentioned method of improving the grain size and composition uniformity of the solidified structure of titanium alloy EB furnace smelting process by ultrasonic treatment, in step B, the ultrasonic radiation rod is vertically inserted into the melt from top to bottom.

[0015] In the present invention, the ultrasonic vibration system includes an ultrasonic power supply, a connecting line and an ultrasonic radiation rod. The ultrasonic power supply is used to emit a high-frequency alternating current signal; the connecting line transmits the high-frequency alternating current signal to the ultrasonic radiation rod; the ultrasonic radiation rod converts the high-frequency alternating current signal into a corresponding mechanical vibration and transmits it to the melt, thereby realizing continuous ultrasonic treatment of the titanium alloy melt.

[0016] In the present invention, the high-temperature titanium alloy melt can be prepared by conventional methods in the art. For example, in the embodiment of the present invention, according to the composition requirements of the titanium alloy ingot, a certain amount of sponge titanium, residual titanium material and titanium dioxide are taken, and they are evenly mixed and passed through a 10,000-ton hydraulic press to make several electrode blocks with specifications of 400*400*100mm; the sponge titanium meets the requirements of grade 1 sponge titanium in GB / T 2524-2019, and the particle size is 0.83-25.4mm; the residual titanium is a pure titanium chip-type residual material, and the composition meets the composition requirements of TA2 in GB / T 3621; the titanium dioxide additive meets the requirements of GB / T1706-2006. Then the electrode blocks are evenly placed in the EB furnace silo, and the EB furnace is closed; the vacuum unit is turned on to perform vacuum operation, so that the vacuum degree in the EB furnace is <2Pa, and the air leakage is <0.3Pa / min. Then start the electron gun with a current of 7 to 11A, so that it emits a high-energy electron beam to bombard the electrode block in the EB furnace silo; the electron kinetic energy is converted into thermal energy, and the electrode block is melted into a high-temperature titanium alloy melt and flows into the cooling bed. At this time, under the action of gravity, the high-density inclusions in the titanium liquid sink to the bottom of the cooling bed and are solidified and bonded, and the low-density inclusions float to the surface of the titanium liquid and are melted and adsorbed. The high-temperature titanium alloy melt in the cooling bed then flows into the crystallizer through the overflow port.

[0017] Beneficial effects of the present invention:

[0018] The present invention introduces ultrasonic technology into the titanium alloy EB furnace smelting process, inserts an ultrasonic radiation rod into the EB furnace smelting pool, and through ultrasonic vibration and cavitation, refines the grains of the titanium alloy solidification structure and makes the alloy composition uniform in a simple and low-cost manner, thereby achieving efficient and high-quality production of high-quality titanium alloys, and providing a new method for improving the quality of titanium alloy ingots. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the device for ultrasonic melting of titanium alloy in an EB furnace of the present invention.

[0020] Figure 2 It is a low-magnification microstructure diagram of the ingots obtained in the comparative example and the embodiment. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0022] Comparative Example 1

[0023] Step 1, electrode block preparation: Take a certain amount of titanium sponge, residual titanium material and titanium dioxide, mix them evenly and use a 10,000-ton hydraulic press to form several electrode blocks of 400*400*100mm. Titanium sponge meets the requirements of grade 1 titanium sponge in GB / T 2524-2019, with a particle size of 0.83-25.4mm; residual titanium is pure titanium chip-type residual material, and its composition meets the composition requirements of TA2 in GB / T 3621; titanium dioxide additives meet the requirements of GB / T1706-2006. Electrode block composition: 99.73% Ti, 0.12% Fe, 0.15% O.

[0024] Step 2, charging and vacuuming: evenly stack the electrode blocks in the EB furnace silo and seal the EB furnace; start the vacuuming unit to perform vacuuming operation, so that the vacuum degree in the EB furnace is <2Pa and the air leakage is <0.3Pa / min.

[0025] Step 3, cold bed smelting: start the electron gun with a current of 7 to 11A to emit a high-energy electron beam to bombard the electrode block in the EB furnace silo; the electron kinetic energy is converted into thermal energy, and the electrode block is melted into titanium liquid and flows into the cooling bed. At this time, under the action of gravity, high-density inclusions in the titanium liquid sink to the bottom of the cooling bed and are solidified and bonded, and low-density inclusions float to the surface of the titanium liquid and are melted and adsorbed.

[0026] Step 4, solidification and ingot guiding: the titanium liquid in the cooling bed flows into the crystallizer through the overflow port. The crystallizer is a water-cooled copper structure with cooling circulating water on the outside. The titanium liquid in the lower part of the crystallizer solidifies into a titanium ingot because the cooling circulating water takes away the heat, and the liquid level in the upper part of the crystallizer rises with the continuous inflow of titanium liquid. When the titanium liquid level is less than 30mm from the upper edge of the crystallizer, the ingot guiding begins to slowly lower the titanium ingot. The ingot guiding speed is dynamically adjusted according to the height of the titanium liquid level to keep its distance from the upper edge of the crystallizer at 30±10mm.

[0027] Step 5, end smelting: when the titanium ingot solidifies 90% to 95%, the electron gun stops working; the titanium ingot continues to descend and moves out of the crystallizer; argon is filled into the EB furnace, and the titanium ingot is cooled to 200°C before the furnace is opened and the titanium ingot is taken out.

[0028] Comparative Example 2

[0029] Step 1, electrode block preparation: Take a certain amount of titanium sponge, residual titanium material and titanium dioxide, mix them evenly and use a 10,000-ton hydraulic press to form several electrode blocks of 400*400*100mm. Titanium sponge meets the requirements of grade 1 titanium sponge in GB / T 2524-2019, with a particle size of 0.83-25.4mm; residual titanium is pure titanium chip-type residual material, and its composition meets the composition requirements of TA2 in GB / T 3621; titanium dioxide additives meet the requirements of GB / T1706-2006. Electrode block composition: 99.73% Ti, 0.12% Fe, 0.15% O.

[0030] Step 2, charging and vacuuming: evenly stack the electrode blocks in the EB furnace silo and seal the EB furnace; start the vacuuming unit to perform vacuuming operation, so that the vacuum degree in the EB furnace is <2Pa and the air leakage is <0.3Pa / min.

[0031] Step 3, cold bed smelting: start the electron gun with a current of 7 to 11A to emit a high-energy electron beam to bombard the electrode block in the EB furnace silo; the electron kinetic energy is converted into thermal energy, and the electrode block is melted into titanium liquid and flows into the cooling bed. At this time, under the action of gravity, high-density inclusions in the titanium liquid sink to the bottom of the cooling bed and are solidified and bonded, and low-density inclusions float to the surface of the titanium liquid and are melted and adsorbed.

[0032] Step 4, solidification and ingot guiding: the titanium liquid in the cooling bed flows into the crystallizer through the overflow port. The crystallizer is a water-cooled copper structure with cooling circulating water on the outside. The titanium liquid in the lower part of the crystallizer solidifies into a titanium ingot because the cooling circulating water takes away the heat, and the liquid level in the upper part of the crystallizer rises with the continuous inflow of titanium liquid. When the titanium liquid level is less than 30mm from the upper edge of the crystallizer, the ingot guiding begins to slowly lower the titanium ingot. The ingot guiding speed is dynamically adjusted according to the height of the titanium liquid level to keep its distance from the upper edge of the crystallizer at 30±10mm.

[0033] Step 5, ultrasonic treatment: while starting the ingot, start the ultrasonic vibration system, insert the ultrasonic radiation rod preheated to 850°C into the titanium liquid pool at the top of the crystallizer, the ultrasonic radiation rod is immersed in the melt to a depth of 30mm, and the ultrasonic frequency is 40kHz.

[0034] Step 6, end of smelting: when the titanium ingot solidifies 90% to 95%, the electron gun and ultrasonic vibration system stop working; the titanium ingot continues to descend and move out of the crystallizer; argon is filled into the EB furnace, and the titanium ingot is cooled to 200°C before the furnace is opened and the titanium ingot is taken out.

[0035] Comparative Example 3

[0036] Step 1, electrode block preparation: Take a certain amount of titanium sponge, residual titanium material and titanium dioxide, mix them evenly and use a 10,000-ton hydraulic press to form several electrode blocks of 400*400*100mm. Titanium sponge meets the requirements of grade 1 titanium sponge in GB / T 2524-2019, with a particle size of 0.83-25.4mm; residual titanium is pure titanium chip-type residual material, and its composition meets the composition requirements of TA2 in GB / T 3621; titanium dioxide additives meet the requirements of GB / T1706-2006. Electrode block composition: 99.73% Ti, 0.12% Fe, 0.15% O.

[0037] Step 2, charging and vacuuming: evenly stack the electrode blocks in the EB furnace silo and seal the EB furnace; start the vacuuming unit to perform vacuuming operation, so that the vacuum degree in the EB furnace is <2Pa and the air leakage is <0.3Pa / min.

[0038] Step 3, cold bed smelting: start the electron gun with a current of 7 to 11A to emit a high-energy electron beam to bombard the electrode block in the EB furnace silo; the electron kinetic energy is converted into thermal energy, and the electrode block is melted into titanium liquid and flows into the cooling bed. At this time, under the action of gravity, high-density inclusions in the titanium liquid sink to the bottom of the cooling bed and are solidified and bonded, and low-density inclusions float to the surface of the titanium liquid and are melted and adsorbed.

[0039] Step 4, solidification and ingot guiding: the titanium liquid in the cooling bed flows into the crystallizer through the overflow port. The crystallizer is a water-cooled copper structure with cooling circulating water on the outside. The titanium liquid in the lower part of the crystallizer solidifies into a titanium ingot because the cooling circulating water takes away the heat, and the liquid level in the upper part of the crystallizer rises with the continuous inflow of titanium liquid. When the titanium liquid level is less than 30mm from the upper edge of the crystallizer, the ingot guiding begins to slowly lower the titanium ingot. The ingot guiding speed is dynamically adjusted according to the height of the titanium liquid level to keep its distance from the upper edge of the crystallizer at 30±10mm.

[0040] Step 5, ultrasonic treatment: start the ultrasonic vibration system at the same time as the ingot is started, insert the ultrasonic radiation rod preheated to 850°C into the titanium liquid pool at the top of the crystallizer, the ultrasonic radiation rod is immersed in the melt to a depth of 100mm, and the ultrasonic frequency is 20kHz.

[0041] Step 6, end of smelting: when the titanium ingot solidifies 90% to 95%, the electron gun and ultrasonic vibration system stop working; the titanium ingot continues to descend and move out of the crystallizer; argon is filled into the EB furnace, and the titanium ingot is cooled to 200°C before the furnace is opened and the titanium ingot is taken out.

[0042] Example 1

[0043] Step 1, electrode block preparation: Take a certain amount of titanium sponge, residual titanium material and titanium dioxide, mix them evenly and use a 10,000-ton hydraulic press to form several electrode blocks of 400*400*100mm. Titanium sponge meets the requirements of grade 1 titanium sponge in GB / T 2524-2019, with a particle size of 0.83-25.4mm; residual titanium is pure titanium chip-type residual material, and its composition meets the composition requirements of TA2 in GB / T 3621; titanium dioxide additives meet the requirements of GB / T1706-2006. Electrode block composition: 99.73% Ti, 0.12% Fe, 0.15% O.

[0044] Step 2, charging and vacuuming: evenly stack the electrode blocks in the EB furnace silo and seal the EB furnace; start the vacuuming unit to perform vacuuming operation, so that the vacuum degree in the EB furnace is <2Pa and the air leakage is <0.3Pa / min.

[0045] Step 3, cold bed smelting: start the electron gun with a current of 7 to 11A to emit a high-energy electron beam to bombard the electrode block in the EB furnace silo; the electron kinetic energy is converted into thermal energy, and the electrode block is melted into titanium liquid and flows into the cooling bed. At this time, under the action of gravity, high-density inclusions in the titanium liquid sink to the bottom of the cooling bed and are solidified and bonded, and low-density inclusions float to the surface of the titanium liquid and are melted and adsorbed.

[0046] Step 4, solidification and ingot guiding: the titanium liquid in the cooling bed flows into the crystallizer through the overflow port. The crystallizer is a water-cooled copper structure with cooling circulating water on the outside. The titanium liquid in the lower part of the crystallizer solidifies into a titanium ingot because the cooling circulating water takes away the heat, and the liquid level in the upper part of the crystallizer rises with the continuous inflow of titanium liquid. When the titanium liquid level is less than 30mm from the upper edge of the crystallizer, the ingot guiding begins to slowly lower the titanium ingot. The ingot guiding speed is dynamically adjusted according to the height of the titanium liquid level to keep its distance from the upper edge of the crystallizer at 30±10mm.

[0047] Step 5, ultrasonic treatment: start the ultrasonic vibration system at the same time as the ingot is started, insert the ultrasonic radiation rod preheated to 850°C into the titanium liquid pool at the top of the crystallizer, the ultrasonic radiation rod is immersed in the melt to a depth of 100mm, and the ultrasonic frequency is 40kHz.

[0048] Step 6, end of smelting: when the titanium ingot solidifies 90% to 95%, the electron gun and ultrasonic vibration system stop working; the titanium ingot continues to descend and move out of the crystallizer; argon is filled into the EB furnace, and the titanium ingot is cooled to 200°C before the furnace is opened and the titanium ingot is taken out.

[0049] Through the above comparative examples and embodiments, titanium ingots under different ultrasonic processes were obtained. The ingot was split in half along the axial direction to detect its chemical composition and grain structure. Five equidistant sampling points were used for chemical composition detection. The samples were named P1 to P5, where P1 was close to the bottom of the ingot that solidified first, and P5 was close to the top of the ingot that solidified later. The results are shown in Tables 1 and Figure 2 .

[0050] Table 1 Fe and O contents of the ingots obtained in the comparative examples and examples

[0051]

[0052]

[0053] from Figure 2It can be seen that the outer columnar crystal zone of the titanium ingot obtained in the embodiment is significantly shorter, the core equiaxed crystal zone is significantly enlarged, and its grain size is much lower than that of Comparative Examples 1 to 3. As can be seen from Table 1, the composition ranges of Fe and O elements of the titanium ingot obtained in Comparative Example 1 are 0.029 and 0.015, respectively, the composition ranges of Fe and O elements of the titanium ingot obtained in Comparative Example 2 are 0.027 and 0.015, respectively, and the composition ranges of Fe and O elements of the titanium ingot obtained in Comparative Example 3 are 0.025 and 0.011, respectively; while the composition ranges of Fe and O elements of the titanium ingot obtained in the embodiment are 0.007 and 0.002, respectively, and its element segregation is less than that of Comparative Examples 1 to 3. The above results show that the present invention can significantly improve key indicators such as the grain size and composition uniformity of the titanium alloy ingot structure by introducing ultrasonic technology into the titanium alloy EB furnace smelting process and using appropriate ultrasonic process parameters, thereby improving the quality of the titanium alloy ingot obtained by the EB furnace process.

Claims

1. A method for improving the grain size and composition uniformity of the solidified structure of titanium alloy during EB furnace smelting by ultrasonic treatment, characterized in that: The following steps are involved: A. Solidification and ingot drawing: The high-temperature titanium alloy melt flows into the crystallizer, and solidification and ingot drawing begin when the melt level is less than 30 mm from the upper edge of the crystallizer; B. Ultrasonic treatment: applying an ultrasonic vibration system to the titanium alloy melt pool at the top of the crystallizer, starting the ultrasonic vibration system while starting the ingot, inserting the ultrasonic radiation rod into the titanium alloy melt pool at the top of the crystallizer, the ultrasonic radiation rod is immersed in the melt to a depth of 50 to 200 mm, and the ultrasonic frequency is 30 to 120 kHz; the ultrasonic vibration system includes an ultrasonic power supply, a connecting line and an ultrasonic radiation rod; C. End of smelting: When the titanium ingot solidifies by 90% to 95%, the ultrasonic vibration system stops working, and the titanium ingot continues to descend and move out of the crystallizer; inert gas is filled into the EB furnace, and after the titanium ingot is cooled, a titanium alloy ingot is obtained.

2. The method for improving the grain size and composition uniformity of the solidified structure of titanium alloy during EB furnace smelting by ultrasonic treatment according to claim 1, characterized in that: In step A, the ingot drawing speed is dynamically adjusted according to the liquid level of the titanium alloy melt so that the ingot drawing speed is kept 30±10 mm from the upper edge of the crystallizer.

3. The method for improving the grain size and composition uniformity of the solidified structure of titanium alloy during EB furnace smelting by ultrasonic treatment according to claim 1, characterized in that: In step B, before the ultrasonic vibration system is applied, the ultrasonic radiation rod is preheated, and the preheating temperature is not less than 800°C.

4. The method for improving the grain size and composition uniformity of the solidified structure of titanium alloy during EB furnace smelting by ultrasonic treatment according to claim 1, characterized in that: In step B, the ultrasonic radiation rods are evenly distributed and immersed in the titanium alloy melt.

5. The method for improving the grain size and composition uniformity of the solidified structure of titanium alloy during EB furnace smelting by ultrasonic treatment according to any one of claims 1 to 4, characterized in that: In step B, the ultrasonic radiation rod is vertically inserted into the melt from top to bottom.

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