Method for removing impurities from titanium alloy excess materials through hydrogen-argon circulating smelting

Abstract

The invention discloses a hydrogen-argon circulating smelting impurity removal method for a titanium alloy excess material. Belongs to the field of metal impurity removal smelting. The problems that in the prior art, helium depends on an inlet, the gas utilization rate is low, and the purity of titanium alloy does not reach the standard due to the fact that reaction products pollute the smelting atmosphere are solved. The method comprises the steps that the titanium alloy excess materials are placed in a plasma arc cold bed smelting furnace, hydrogen and argon mixed gas is introduced, the hydrogen and argon mixed gas is the mixed gas of 10 vol.%-30 vol.% of hydrogen and 90 vol.%-70 vol.% of argon, in the smelting process, the power is 120 kW-180 kW, the pressure is 0.06 MPa-0. 1 MPa, the gas circulates at a certain time interval, and molecular sieve regeneration is started every time of circulation. According to the method, the hydrogen-argon mixed gas with better cost is used for replacing traditional helium, and the closed cycle design is combined, so that the gas utilization rate is greatly increased, and the cost of single ton of gas for titanium alloy smelting is effectively reduced. According to the method, the partial pressure of gas impurities is less than or equal to 0.1 Pa, and finally, the content of oxygen and nitrogen impurities in a titanium alloy product meets strict industrial standards.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of metal impurity removal smelting, and particularly relates to a hydrogen-argon circulation smelting impurity removal method for titanium alloy scrap. BACKGROUND

[0002] Titanium alloy is a key material in the fields of aerospace, marine engineering, etc. In the hydrogen-containing plasma arc cold bed remelting process of titanium alloy, the selection of the protective gas directly relates to the production cost and industrial independence. At the same time, the price of helium is high, which leads to a gas cost of more than 20,000 yuan per ton of titanium alloy in traditional plasma arc cold bed smelting (PACHM), which is much higher than the cost of hydrogen-argon mixed gas. Relevant industry estimates show that the smelting cost of titanium is 5 times that of stainless steel, and the high proportion of helium further aggravates the cost pressure, which seriously restricts the wide application of titanium alloy in the middle and low-end fields, and there is a large gap between the development needs of green energy saving and cost control of the titanium alloy industry.

[0003] The recycling efficiency of the protective gas is another core factor restricting the economy of titanium alloy smelting. The current traditional gas path system lacks effective recycling design, and the hydrogen-argon mixed gas is directly discharged after participating in the reaction, with a gas utilization rate of less than 40%. Research shows that although large PACHM furnaces need to be equipped with inert gas recovery devices to reduce costs, the existing recovery technology still has problems such as incomplete purification and high energy consumption. The exhaust gas without purification treatment contains water vapor, methane and other reaction products generated during the smelting process, and if it is directly discharged, it not only causes resource waste, but also has potential impact on the environment. More importantly, if the gas without purification is introduced into the smelting system again, it will cause the partial pressure of impurity gas in the furnace to rise (such as oxygen partial pressure > 10 Pa), which will destroy the stability of the smelting atmosphere, and then affect the removal efficiency of oxygen and nitrogen impurities in the titanium alloy melt, making it difficult to meet the high-purity production requirements of titanium alloy (oxygen content ≤700 ppm, nitrogen content ≤100 ppm).

[0004] In the smelting process of titanium alloy, the gas purity is closely related to the quality of the ingot and the recycling rate of the waste material. The recycling gas without purification function in the existing technology is easy to cause the composition of the titanium alloy ingot to be uneven, which affects the subsequent precision casting and powder production. Data shows that the final material yield of titanium processing is generally less than 50%, and a large amount of residual titanium is generated during the production process. However, due to the fact that the traditional smelting technology cannot effectively control the purity of the gas, the problems of high oxygen content limit the recycling of titanium alloy waste, and the proportion of titanium alloy waste mixed with new material is usually not more than 30%. This not only causes resource waste, but also further increases the production cost, which restricts the industrialization of the remelting purification and purification technology of titanium alloy. SUMMARY

[0005] To address the problems of existing technologies, such as reliance on imported helium, low gas utilization, and reaction products contaminating the smelting atmosphere, leading to substandard titanium alloy purity, this invention provides a method for impurity removal through hydrogen-argon circulating smelting of titanium alloy scrap. This invention achieves closed-loop circulation of the hydrogen-argon mixture, efficient purification of reaction products, and precise control of atmosphere parameters, thereby reducing the remelting cost of titanium alloys, improving product purity and waste utilization, and ensuring stable and compliant titanium alloy purification. To achieve the aforementioned technical problems, this invention adopts the following technical solution: The purpose of this invention is to provide a method for removing impurities from titanium alloy scrap through hydrogen-argon cyclic melting, comprising the following steps: The titanium alloy scrap is placed in a plasma arc cold hearth melting furnace, and a hydrogen-argon mixture is introduced. The hydrogen-argon mixture is a mixture of 10 vol.%-30 vol.% hydrogen and 90 vol.%-70 vol.% argon. During the melting process, the power is 120 kW-180 kW and the pressure is 0.06 MPa-0.1 MPa. The gas is circulated at certain intervals, and molecular sieve regeneration is started after each cycle. The molecular sieve regeneration process involves filtering the hydrogen-argon mixture to remove molten splash powder, then condensing water vapor and cooling it to below 50°C. Subsequently, the mixture is vacuum activated by the molecular sieve to remove carbides, pressurized, and stored in a high-pressure storage tank for recycling. The entire purification process ensures that the gas purity is ≥99.999%.

[0006] Further specified, the titanium alloy scrap is TC4 scrap, TA15 scrap, or titanium alloy scrap with initial oxygen >1500ppm and nitrogen >200ppm.

[0007] Furthermore, the gas flow rate is controlled between 50 L / min and 70 L / min.

[0008] Furthermore, the particle size of the titanium alloy scrap is specified to be 3 mm-10 mm.

[0009] Further specified, vacuum activation is performed at 300℃-350℃ and a vacuum degree of 0.001Pa-0.005Pa. Further specifying, the molecular sieve is one or both of 13X molecular sieve and 5A molecular sieve.

[0010] Further specifying, the plasma gun performs three-dimensional electric scanning.

[0011] Furthermore, the gas is circulated once every 20-30 minutes.

[0012] Furthermore, the pulling speed of the crystallizer is specified as 1.2 mm / s.

[0013] Further specifying, after the smelting is completed, the titanium alloy melt is solidified in a crystallizer.

[0014] Based on the above method, this invention provides efficient smelting solutions for TC4 titanium alloy scrap, TA15 titanium alloy scrap, and high-impurity titanium alloy scrap, respectively. The specific technical solutions are as follows: First aspect: Method for removing impurities from TC4 titanium alloy scrap through hydrogen-argon cycle melting. This approach is suitable for TC4 blocky residues (particle size 5-10mm) with an initial oxygen content of 1200-1500ppm. The specific steps are as follows: In the hydrogen-argon gas mixing stage, a stainless steel gas mixing module is used, including a pressure-resistant mixing cylinder (50L volume, 10MPa pressure resistance), a mass flow meter (Krohne OPTIFLUX 4300, range 0-100L / min, accuracy ±0.2%), and an electromagnetic shut-off valve. The hydrogen-argon volume ratio is set to 10:90 (H2:Ar), and the flow rate is 50L / min. This ratio is based on the oxygen impurity removal requirements of TC4 alloy. Too high a hydrogen content can easily lead to hydrogen embrittlement, while too low a content will result in insufficient oxygen removal.

[0015] In the circulating purification stage, the gas after the reaction first passes through a powder filter (filtration accuracy 0.1μm) to remove melt splash powder, then enters a water-cooled cooler (water temperature 25℃) to condense water vapor (reducing the temperature to below 50℃), and then passes through a 13X molecular sieve adsorption trap (vacuum activated at 300℃ for 2h) to adsorb carbides such as methane and carbon monoxide. Finally, it is pressurized to 0.8MPa by a diaphragm compressor (outlet pressure 1.0MPa, flow rate 50L / min) and stored in a high-pressure gas storage tank (volume 100L, pressure resistance 2.0MPa) for recycling. The entire purification process ensures that the gas purity is ≥99.999%.

[0016] In the hydrogen-containing plasma arc melting stage, the hydrogen-argon mixture output from the gas distribution module is introduced into the hydrogen-containing plasma arc cold bed melting furnace. The cold bed adopts a square water-cooled copper crucible (260mm×180mm×80mm), the plasma gun power is 120kW (3 guns, three-dimensional electric scanning), and the furnace pressure is maintained at 0.08MPa (close to positive pressure to suppress Ti and Al volatilization). During the melting process, the gas circulation interval is 30min, and the molecular sieve regeneration is started once after each circulation (300℃×1h) to ensure that the partial pressure of impurities in the circulating gas is ≤0.1Pa. After the melting is completed, the titanium alloy melt is solidified in a crystallizer (water-cooled copper, 150mm in diameter) and cooled for 60min to obtain TC4 ingots.

[0017] During the safety control phase, the system is equipped with an explosion-proof cabinet (protection level IP54), a hydrogen leak detector (detection limit 0.1% LEL), and an emergency shut-off valve. When the hydrogen concentration is >1% LEL, the gas supply is automatically cut off and an audible and visual alarm is triggered. The gas distribution cabinet and circulation module are set up independently and use 316L stainless steel pipelines (pressure resistant 1.5MPa) to avoid gas leakage and pipeline corrosion.

[0018] The second aspect: the method of removing impurities from TA15 titanium alloy scrap through hydrogen-argon cycle melting. This approach is applicable to TA15 residues (particle size 3-8mm) with an initial nitrogen content of 160-200ppm. The specific steps are as follows: In the hydrogen-argon gas mixing stage, based on the high nitrogen characteristics of TA15 alloy, the hydrogen-argon volume ratio is adjusted to 20:80, and the flow rate is 60L / min. The gas flow fluctuation is monitored in real time (≤±0.5%) using a mass flow meter to ensure that sufficient hydrogen participates in the reaction of nitrogen impurities (forming NH3 gaseous products).

[0019] In the circulation purification stage, a secondary molecular sieve adsorption trap is added to the conventional "filtration-cooling-adsorption" process to enhance the adsorption effect on nitrogen; the cooler water temperature is reduced to 20℃ to improve the water vapor condensation efficiency and avoid the introduction of additional oxygen impurities by the reaction of water vapor with the titanium alloy melt; the gas circulation interval is shortened to 25 minutes and the regeneration temperature is increased to 320℃ to ensure that the nitrogen partial pressure in the circulating gas is ≤0.08Pa.

[0020] During the hydrogen-containing plasma arc melting stage, a round water-cooled copper crucible (260mm inner diameter, flat bottom structure) is used as the cooling bed, the plasma gun power is 150kW, and the furnace pressure is 0.06MPa. During the melting process, the pressure of the circulation system is monitored in real time by a pressure sensor. When the pressure is <0.05MPa, the diaphragm compressor is triggered to automatically increase the pressure (to 0.08MPa). When the TA15 melt solidifies, the crystallizer pulling speed is controlled at 1.2mm / s to avoid nitrogen impurities remaining due to excessively rapid solidification.

[0021] Thirdly: Methods for removing impurities from high-impurity titanium alloy scraps through hydrogen-argon cycle melting. This approach is suitable for high-impurity titanium alloy scraps (such as crushed scrap titanium components) with initial oxygen >1500ppm and nitrogen >200ppm. The specific steps are as follows: In the hydrogen-argon gas mixing stage, the hydrogen-argon volume ratio is increased to 30:70, the flow rate is 70L / min, and the electromagnetic shut-off valve is controlled by PLC (Siemens S7-1200) to achieve dynamic fine adjustment of the hydrogen ratio.

[0022] During the circulation purification stage, a backflushing function for the powder filter is added (backflushing once every 20 minutes at a pressure of 0.2 MPa) to prevent excessive powder from clogging the filter during the smelting of high-impurity residue. The molecular sieve adsorption trap adopts a "heating-vacuuming" regeneration mode (350℃×1.5h, vacuum degree 0.001Pa) to completely desorb the adsorbed impurity gases. A gas component analyzer (Pfeiffer QMG 220) is added to the gas circulation system to monitor the O2 and N2 concentrations in the circulating gas in real time, and automatically switch to the backup gas storage tank when the concentrations exceed the limits.

[0023] During the hydrogen-containing plasma arc melting stage, the plasma gun power was increased to 180kW, and the cold bed melting time was extended to 80min to ensure that hydrogen and impurities reacted fully. The furnace pressure was maintained at 0.1MPa to suppress the volatilization of highly reactive elements. In the later stage of melting, the concentration of reaction products was monitored by a residual gas analyzer. When H2O < 300ppm and N2 < 80ppm, the hydrogen ratio was reduced to 20:80 to avoid over-hydrogenation.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly improved economic efficiency: Replacing traditional helium with a more cost-effective hydrogen-argon mixture and combining it with a closed-loop design significantly improves gas utilization and effectively reduces the gas cost per ton in titanium alloy smelting.

[0025] 2. Product purity is controllable and reliable: After three-stage purification, the partial pressure of gas impurities is ensured to be ≤0.1Pa, ultimately ensuring that the oxygen and nitrogen impurity content (oxygen ≤650ppm, nitrogen ≤98ppm) in the titanium alloy products meets strict industrial standards.

[0026] 3. Wide process compatibility and applicability: This technology can be widely applied to hydrogen-containing plasma arc cold hearth furnaces of different specifications, supporting the smelting and production of various titanium alloy grades, including TC4 and TA15, as well as high-impurity scrap materials. Detailed Implementation

[0027] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0028] Raw materials: TC4 titanium alloy scrap (Liaoning Ansteel, initial oxygen 1200ppm, nitrogen 180ppm, carbon 350ppm); TA15 titanium alloy scrap (initial oxygen 1100ppm, nitrogen 160ppm); high-impurity titanium alloy scrap (initial oxygen 1500ppm, nitrogen 200ppm), all crushed to 5-10mm; System equipment: Gas distribution module (Krohne OPTIFLUX 4300 mass flow meter), circulation and purification module (13X molecular sieve adsorption trap), storage and pressurization module (100L high-pressure gas storage tank), safety control module (hydrogen leak detector with a detection limit of 0.1% LEL); Testing equipment: Oxygen, nitrogen and hydrogen analyzer (LECO ONH836, accuracy ±1ppm), gas flow meter (accuracy ±0.2%), scanning electron microscope (ZEISS Sigma 300).

[0029] Example 1: Hydrogen-argon cycle melting of TC4 titanium alloy scrap (1) Raw material preparation: Take 20kg of TC4 residue (particle size 5-10mm), dry it at 80℃ for 2 hours in advance to remove surface oil stains; (2) System debugging: The volume partial pressure ratio of H2:Ar in the gas distribution module is set to 10:90 and the flow rate is 50L / min; in the circulation purification module, the molecular sieve is vacuum activated at 300℃ for 2h and the cooler water temperature is 25℃; the gas storage tank pressure is pre-charged to 0.8MPa; (3) Melting process: Add the TC4 residue to a square water-cooled copper crucible (size 260mm×180mm×80mm), evacuate the furnace to 2.5Pa (leakage rate 0.5Pa / min), and introduce a hydrogen-argon mixture to 0.08MPa; the plasma gun power is 120kW, melt for 60min, and start molecular sieve regeneration once every 30min; the melt is solidified in a crystallizer (diameter 150mm) and cooled for 60min.

[0030] Results: Oxygen 280ppm, Nitrogen 85ppm, Carbon 250ppm, Total gas consumption 120m³ 3 The utilization rate was 86.5%.

[0031] Example 2: Hydrogen-argon cycle melting of TA15 titanium alloy scrap (1) Raw material preparation: 20kg TA15 residue (particle size 3-8mm), initial nitrogen 160ppm; (2) System debugging: The volume partial pressure ratio of H2:Ar is 20:80, and the flow rate is 60L / min; the secondary molecular sieve (13X+5A) is activated, and the water temperature of the water-cooled cooler is controlled at 20℃; (3) Melting process: The cooling bed is a round water-cooled copper crucible (inner diameter 260mm, flat bottom structure), the furnace pressure is 0.06MPa, the plasma gun power is 150kW, the melting time is 70min, the gas circulation interval is 25min; the pulling speed of the crystallizer is 1.2mm / s. Results: Oxygen content in the ingot was 320 ppm, nitrogen content was 90 ppm, and gas consumption was 135 m³ / h. 3 The utilization rate was 84.2%.

[0032] Example 3: Hydrogen-argon cycle melting of high-impurity titanium alloy scrap (1) Raw material preparation: 20kg of high-impurity residue (initial oxygen 1500ppm, nitrogen 200ppm), crushed to 5-8mm; (2) System debugging: The volume partial pressure ratio of H2:Ar is 30:70, and the flow rate is 70L / min; the molecular sieve (using 5A molecular sieve) is regenerated at 350℃ for 1.5h, and the filter is backflushed every 20min; (3) Melting process: furnace pressure 0.1MPa, plasma gun power 180kW, melting for 80min, PLC dynamically fine-tunes hydrogen ratio (when oxygen > 800ppm + 2% H2). (4) Results detection: Oxygen 650ppm, nitrogen 98ppm, gas consumption 150m³ 3 The utilization rate was 82.1%.

[0033] Comparative Example 1: Traditional one-time helium melting system (1) Raw materials: 20kg of TC4 residue from Example 1; (2) Process: Helium flow rate 50L / min, one-time discharge, no circulation; smelting parameters are the same as in Example 1; Results: Oxygen content in the ingot was 300 ppm, nitrogen content was 88 ppm, and gas consumption was 500 m³ / s. 3 The utilization rate was 35.8%.

[0034] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A method for removing impurities from titanium alloy scrap through hydrogen-argon cyclic melting, characterized in that, Includes the following steps: The titanium alloy scrap is placed in a plasma arc cold hearth melting furnace, and a hydrogen-argon mixture is introduced. The hydrogen-argon mixture is a mixture of 10 vol.%-30 vol.% hydrogen and 90 vol.%-70 vol.% argon. During the melting process, the power is 120 kW-180 kW and the pressure is 0.06 MPa-0.1 MPa. The gas is circulated at certain intervals, and molecular sieve regeneration is started after each cycle. The molecular sieve regeneration process involves filtering the hydrogen-argon mixture to remove molten splash powder, then condensing water vapor and cooling it to below 50°C. Subsequently, the mixture is vacuum activated by the molecular sieve to remove carbides, pressurized, and stored in a high-pressure storage tank for recycling. The entire purification process ensures that the gas purity is ≥99.999%.

2. The method according to claim 1, characterized in that, The titanium alloy scrap is TC4 scrap, TA15 scrap, or titanium alloy scrap with initial oxygen >1500ppm and nitrogen >200ppm.

3. The method according to claim 1, characterized in that, The gas flow rate is controlled between 50L / min and 70L / min.

4. The method according to claim 1, characterized in that, The particle size of the titanium alloy scrap is 3 mm-10 mm.

5. The method according to claim 1, characterized in that, Vacuum activation at 300℃-350℃ and a vacuum degree of 0.001Pa-0.005Pa.

6. The method according to claim 1, characterized in that, The molecular sieve is one or both of 13X molecular sieve and 5A molecular sieve.

7. The method according to claim 1, characterized in that, A plasma gun performs three-dimensional electric scanning.

8. The method according to claim 1, characterized in that, The gas is circulated once every 20-30 minutes.

9. The method according to claim 1, characterized in that, The crystallizer's pulling speed is 1.2 mm / s.

10. The method according to claim 1, characterized in that, After smelting, the titanium alloy melt solidifies in a crystallizer.