Method for removing surface oxide of titanium cast ingot

Abstract

The invention discloses a method for removing surface oxides from a titanium cast ingot, and belongs to the technical field of titanium metal casting and forging processing. According to the method, CO gas and TiO2 on the surface of the titanium cast ingot (forge piece) are subjected to a reduction reaction for 0.5-6 hours in a vacuum atmosphere of CO (carbon monoxide) with the pressure of 1 * 10 <-2 >-10 Pa and under the high-temperature conditions of 550-750 DEG C, 800-980 DEG C and 990-1220 DEG C, so that a titanium oxide layer with the thickness of 50-10 mm on the surface of the cast ingot (forge piece) is converted into a titanium layer with the thickness of about 50-10 mm and the oxygen element is removed, and the oxygen content of the layer is smaller than 1.5% by weight. Compared with the prior art, a large amount of manpower needed by grinding wheel polishing adopted at present is overcome, meanwhile, air pollution caused by grinding wheel ash is reduced, and weight loss of titanium in the smelting (forging) process at present is reduced.

Description

Technical Field

[0001] This invention relates to a method for removing surface oxides from titanium ingots. Specifically, it involves using CO (carbon monoxide) gas at high temperature under vacuum to reduce TiO2 on the surface of the titanium ingot, generating Ti and transforming the titanium oxide layer into a titanium layer. This method overcomes the large amount of manpower required for grinding with grinding wheels, reduces air pollution caused by grinding wheel dust, and lowers the weight loss of titanium during smelting (forging). This invention provides a novel method for removing oxide scale from the surface of titanium ingots (forgings). It belongs to the field of titanium metal smelting, casting, and forging processing technology. Background Technology

[0002] Arc melting and forging of titanium are key processes in the processing of titanium and titanium alloys. The process primarily involves melting electrodes pressed from sponge titanium using an electric arc discharge in a vacuum environment to form titanium or titanium alloy ingots. Depending on product requirements, the ingots heated in an atmospheric high-temperature heat treatment furnace can also be forged. During these processes, due to the high reactivity of titanium and the relatively low vacuum level of the vacuum arc furnace (or heating in an atmospheric heat treatment furnace), oxygen in the atmosphere reacts with the high-temperature titanium ingots, forming a thick oxide layer (mainly TiO2, with small amounts of Ti2O3, TiO, and other low-valence oxides) on the surface of the ingot (forging). This oxide film directly affects the surface quality and product performance of the titanium in subsequent processing steps such as forging and rolling. Therefore, this oxide layer, with a thickness of 10μm-10mm, needs to be removed. Currently, mechanical, chemical, and high-temperature decomposition methods are widely used in industry. Mechanical removal methods involve directly peeling off the surface oxide layer using external force. These methods primarily include grinding with a grinding wheel, sandblasting, shot peening, turning and milling, and high-pressure water jetting. These methods are suitable for thick oxide layers and offer advantages such as simple operation and low cost. However, they can generate surface mechanical stress or micro-scratches, result in significant loss of titanium material, and produce dust pollution. Chemical removal methods, on the other hand, remove the oxide layer by reacting chemical reagents with the oxide. Their advantages include the ease of removing thin oxide layers and good treatment uniformity. However, they require wastewater treatment and have stringent environmental protection requirements. The main methods include: acid washing (HF-HNO3 system, HF-H2SO4 system), alkaline washing (sodium hydroxide (NaOH) + sodium nitrate (NaNO3), etc.). These methods are suitable for thin oxide layers, with the advantage of a bright surface, but the disadvantage of environmental pollution. High-temperature decomposition methods utilize the thermodynamic instability of oxides at high temperatures to remove the oxide layer through decomposition. These mainly include vacuum degradation, hydrogen reduction, and salt bath deoxidation. Vacuum annealing involves heating the titanium ingot to 700-900℃ under high vacuum, causing TiO2 to decompose into Ti and O2. The advantage of this method is no surface damage and it can simultaneously eliminate internal stress in the ingot. The disadvantage is that it is only suitable for thin oxide layers (<20μm). Hydrogen reduction involves heating the titanium ingot to 800-1000℃ in a hydrogen atmosphere (H2 purity > 99.99%), resulting in the reaction TiO2 + H2 → Ti + The H2O reaction occurs, and the H2O is expelled with the gas flow. The advantage of this method is thorough reduction, making it suitable for thick oxide layers; the disadvantages are the risk of hydrogen explosion and embrittlement of the titanium matrix due to hydrogen absorption. The salt bath deoxidation method involves heating titanium to 700-850℃ in a molten salt (such as a NaCl-KCl-NaF system). The oxides react with the salt to form soluble salts (such as Na2TiO3), which are then removed with the salt bath. Its advantages are high efficiency and suitability for complex-shaped ingots; its disadvantages are the volatility of the salt bath and potential environmental pollution.

[0003] To address the problems existing in current methods such as grinding to remove the thick oxide film layer generated during the titanium ingot and forging process, a method has been invented that uses CO gas to reduce titanium oxide at high temperature, converting titanium oxide into metallic titanium. This method achieves the goal of removing the thick oxide layer on the surface of titanium ingots and titanium forgings, thereby improving the quality of titanium and titanium alloys. Summary of the Invention

[0004] The primary objective of this invention is to provide a method for removing surface oxides from titanium ingots.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: The theoretical basis of this invention is the basic reaction in which CO (carbon monoxide) gas reacts with titanium oxide at high temperature to generate Ti + CO2.

[0006] Right now:

[0007] Based on the scientific foundation of the basic theory, and utilizing this scientific theory to meet the industrial need for removing oxides from the surface of titanium ingots (forgings), this invention analyzes the physical properties of oxides on the surface of titanium ingots (forgings), studies the diffusion behavior of CO gas in oxides, and invents a method for removing oxides from the surface of titanium ingots (forgings) using high-temperature CO gas.

[0008] The specific invention is as follows: Analysis revealed that, due to changes in processing conditions, the oxides on the surfaces of titanium ingots and forgings not only included Ti... 4+ TiO2, and also contains a relatively large amount of Ti 3+ Ti2O3, and a small amount of Ti 2+ According to thermodynamic calculations, the reaction conditions and times for TiO2 with CO differ depending on the valence state. To achieve energy savings and cost reduction by creating a thick titanium oxide layer at a shorter time and lower temperature, this invention comprises three processes: (1) Place the titanium ingot (forging) with a titanium oxide film on its surface into a vacuum heat treatment furnace, and evacuate the vacuum level in the furnace to 5×10 -3 Pa, heat the titanium ingot (forging) to 550-750℃, and introduce 99.995% high-purity CO gas to maintain the vacuum level of the vacuum chamber at 1×10⁻⁶. -1 When the pressure is 10 Pa for 2 to 6 hours, TiO2 in the titanium oxide on the surface of the titanium ingot (forging) is converted into Ti2O3.

[0009] (2) Continue to raise the temperature of the titanium ingot (forging) to 800-980℃, and continue to introduce 99.995% high-purity CO gas to maintain the vacuum degree of the vacuum chamber at 1×10 -2Hold at 1-5 Pa for 1-4 hours. The Ti2O3 in the titanium oxide on the surface of the titanium ingot (forging) is converted to TiO.

[0010] (3) Continue to raise the temperature of the titanium ingot (forging) to 990-1220℃, and continue to introduce 99.995% high-purity CO gas to maintain the vacuum degree of the vacuum chamber at 1×10 -2 Pa~8×10 -1 Pa, heat for 0.5–2 hours. TiO in titanium oxide on the surface of titanium ingots (forgings) is converted to Ti.

[0011] The following is a description of the specific process for removing oxides from the surface of titanium ingots, illustrated with the accompanying drawings: A method for removing surface oxides from titanium ingots, such as... Figures 1-2 As shown, a titanium ingot (forging) 1 with a TiO2 film layer 12 on its surface is placed into a vacuum heat treatment furnace 3 heated by a graphite heating element 2, and the vacuum degree inside the furnace is evacuated to 5×10⁻⁶ by the exhaust system 4. -3 Pa, heating the titanium ingot (forging) 1 to a furnace temperature of 550-750℃ as detected by the temperature detection system 6, and then introducing 99.995% high-purity CO gas through the gas filling system 5 to maintain the vacuum degree of the vacuum heat treatment furnace 3 at 1×10 -1 After holding at ~10 Pa for 2-6 hours, the temperature of heat treatment furnace 3 is further increased to 800-980℃. High-purity CO gas (99.995%) is introduced to maintain the vacuum level inside the furnace 3 at 1×10⁻⁶. -2 The pressure is maintained at ~5 Pa for 1 to 4 hours. The temperature of vacuum heat treatment furnace 3 is then further increased to 990 to 1220°C. High-purity CO gas (99.995%) is introduced to maintain the air volume inside the furnace at 1×10⁻⁵. -2 ~8×10 -1 Pa, hold at that temperature for 0.5–2 hours, then stop heating and replace the CO gas with 99.995% high-purity argon gas. Cool the furnace with the ingot until the temperature of the vacuum heat treatment furnace 3 is below 100°C. Remove the titanium ingot (forging) 1 from the vacuum heat treatment furnace 3. In this way, the original oxide 12 on the surface of the titanium ingot (forging) 1 is transformed into a metallic titanium layer 13 on the surface of the titanium ingot (forging) 1 (such as... Figure 3 (As shown). Through the above treatment, a titanium oxide layer 12 with a thickness of 50 μm to 10 mm can be removed from the surface of the titanium ingot (forging) to obtain a titanium layer 13 with a thickness of approximately 50 μm to 10 mm, wherein the oxygen weight percentage in the titanium layer 13 is less than 2%.

[0012] The present invention has the following beneficial effects: This invention involves a three-stage high-temperature reaction between oxides on the surface of titanium ingots (forgings) under vacuum and high-temperature conditions and highly reducing CO gas, thereby reducing the Ti content in titanium carbide. 4+ Ti 3+Ti 2+ Plasma gradually reduces the titanium atoms to zero valence, thus removing the oxide layer from the surface of titanium ingots (forgings).

[0013] This invention achieves this through 1×10 -2 In a vacuum atmosphere of ~10 Pa CO (carbon monoxide) and at high temperatures of 550–750℃, 800–980℃, and 990–1220℃, CO gas undergoes a reduction reaction with TiO2 on the surface of titanium ingots (forgings) for 0.5–6 hours. This transforms a 50 μm–10 mm thick titanium oxide layer on the surface of the ingot (forgings) into an oxygen-free titanium layer of approximately 50 μm–10 mm thickness, with an oxygen content of less than 1.5% by weight. This method overcomes the large amount of manpower required for current grinding wheel polishing, while also reducing air pollution caused by grinding wheel dust and lowering the weight loss of titanium during smelting (forging). Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of a titanium ingot (forging) with a TiO2 film on its surface; Figure 2 This is a schematic diagram of the structure of a vacuum heat treatment furnace; Figure 3 This is a schematic diagram of the structure of a titanium ingot (forging) whose original TiO2 film layer on the surface is transformed into a surface metallic titanium layer; Figure 4 These are electron microscope images and elemental analysis diagrams of the original TiO2 film on the surface of Example 4; Figure 5 These are electron microscope (EM) images and elemental analysis diagrams of titanium ingots (forgings) with a surface metallic titanium layer after conversion in Example 4. Detailed Implementation

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Example 1

[0016] like Figures 1-3 As shown, a method for removing surface oxides from a titanium ingot involves placing a titanium ingot (forging) 1 with a TiO2 film layer 12 on its surface into a vacuum heat treatment furnace 3 heated by a graphite heating element 2, and evacuating the vacuum level inside the furnace to 5 × 10⁻⁶ using an exhaust system 4. -3 Pa, heating the titanium ingot (forging) 1 until the furnace temperature reaches 550℃ (detected by the temperature detection system 6), then introducing 99.995% high-purity CO gas through the gas filling system 5 to maintain the vacuum degree of the vacuum heat treatment furnace 3 at 1×10 -1After holding at this temperature for 2 hours, the temperature of heat treatment furnace 3 is further increased to 800℃. High-purity CO gas (99.995%) is then introduced to maintain the vacuum level inside the furnace 3 at 1×10⁻⁶. -2 At a constant temperature of 1 Pa, the temperature of the vacuum heat treatment furnace 3 is further increased to 990℃. This is achieved by introducing 99.995% high-purity CO gas to maintain the air volume inside the furnace 3 at 1×10⁻⁶. -2 Pa, after holding at this temperature for 0.5 hours, heating is stopped, and the CO gas is replaced with 99.995% high-purity argon gas. The gas is then cooled in the furnace until the temperature of the vacuum heat treatment furnace 3 is below 100°C. The titanium ingot (forging) 1 is then removed from the vacuum heat treatment furnace 3. In this way, the original 50μm oxide 12 on the surface of the titanium ingot (forging) 1 is transformed into a metallic titanium layer 13 with a thickness of approximately 50μm on the surface of the titanium ingot (forging) 1, in which the oxygen weight percentage in the titanium layer 13 is 1.32%. Example 2

[0017] A method for removing surface oxides from titanium ingots involves placing a titanium ingot (forging) 1 with a TiO2 film layer 12 on its surface into a vacuum heat treatment furnace 3 heated by a graphite heating element 2, and evacuating the vacuum level inside the furnace to 5 × 10⁻⁶ using an exhaust system 4. -3 The titanium ingot (forging) 1 is heated to 750°C, as detected by the temperature detection system 6. 99.995% high-purity CO gas is then introduced through the gas filling system 5 to maintain the vacuum degree of the vacuum heat treatment furnace 3 at 10 Pa. After holding at this temperature for 6 hours, the temperature of the heat treatment furnace 3 is further increased to 980°C. 99.995% high-purity CO gas is then introduced to maintain the vacuum degree of the vacuum heat treatment furnace 3 at 5 Pa. After holding at this temperature for 4 hours, the temperature of the vacuum heat treatment furnace 3 is further increased to 1220°C. 99.995% high-purity CO gas is then introduced to maintain the vacuum degree of the vacuum heat treatment furnace 3 at 8 × 10⁻⁶ Pa. -1 Pa, after holding at this temperature for 2 hours, heating is stopped, and the CO gas is replaced with 99.995% high-purity argon gas. The furnace is cooled to below 100°C in the vacuum heat treatment furnace 3. The titanium ingot (forging) 1 is then removed from the vacuum heat treatment furnace 3. In this way, the original 10mm oxide 12 on the surface of the titanium ingot (forging) 1 is transformed into a metallic titanium layer 13 with a thickness of about 10mm on the surface of the titanium ingot (forging) 1, in which the oxygen weight percentage in the titanium layer 13 is 1.68%. Example 3

[0018] A method for removing surface oxides from titanium ingots involves placing a titanium ingot (forging) 1 with a TiO2 film layer 12 on its surface into a vacuum heat treatment furnace 3 heated by a graphite heating element 2, and evacuating the vacuum level inside the furnace to 5 × 10⁻⁶ using an exhaust system 4. -3The titanium ingot (forging) 1 is heated to 600℃, as detected by the temperature detection system 6. 99.995% high-purity CO gas is then introduced through the gas filling system 5 to maintain the vacuum degree of the vacuum heat treatment furnace 3 at 5 Pa. After holding at this temperature for 4 hours, the temperature of the heat treatment furnace 3 is further increased to 880℃. 99.995% high-purity CO gas is then introduced to maintain the vacuum degree of the vacuum heat treatment furnace 3 at 5 × 10⁻⁶ Pa. -1 At a constant temperature of 2 Pa, the temperature of the vacuum heat treatment furnace 3 is further increased to 1000℃. This is achieved by introducing 99.995% high-purity CO gas to maintain the air volume inside the furnace 3 at 2 × 10⁻⁶. -1 Pa, after holding at this temperature for 1.5 hours, heating is stopped, and the CO gas is replaced with 99.995% high-purity argon gas. The gas is then cooled in the furnace until the temperature of the vacuum heat treatment furnace 3 is below 100°C. The titanium ingot (forging) 1 is then removed from the vacuum heat treatment furnace 3. In this way, the original 1mm oxide 12 on the surface of the titanium ingot (forging) 1 is transformed into a metallic titanium layer 13 with a thickness of about 1mm on the surface of the titanium ingot (forging) 1, wherein the oxygen weight percentage in the titanium layer 13 is 1.35%. Example 4

[0019] A method for removing surface oxides from titanium ingots involves surface titanium oxide with a thickness of 5 mm and an average oxygen content of 25.66% by weight (e.g., ...). Figure 4 The titanium ingot (forging) 1 (as shown) is placed in a vacuum heat treatment furnace 3 heated by a graphite heating element 2, and the vacuum level inside the furnace is evacuated to 5 × 10⁻⁶ by the exhaust system 4. -3 The titanium ingot (forging) 1 is heated to 720°C, as detected by the temperature detection system 6. 99.995% high-purity CO gas is then introduced through the gas filling system 5 to maintain the vacuum level of the vacuum heat treatment furnace 3 at 1 Pa. After holding at this temperature for 2 hours, the temperature of the heat treatment furnace 3 is further increased to 900°C. 99.995% high-purity CO gas is then introduced to maintain the vacuum level of the vacuum heat treatment furnace 3 at 1 Pa. After holding at this temperature for 2 hours, the temperature of the vacuum heat treatment furnace 3 is further increased to 1100°C. 99.995% high-purity CO gas is then introduced to maintain the vacuum level of the vacuum heat treatment furnace 3 at 5 × 10⁻⁶ Pa. -1 Pa, after holding at this temperature for 1 hour, heating is stopped, and the CO gas is replaced with 99.995% high-purity argon gas. The furnace is then cooled to below 100°C in the vacuum heat treatment furnace 3. The titanium ingot (forging) 1 is then removed from the vacuum heat treatment furnace 3. This process transforms the original 5mm oxide layer 12 on the surface of the titanium ingot (forging) 1 into a 5mm thick metallic titanium layer 13, in which the oxygen weight percentage is 1.49% (e.g., ...). Figure 5 (As shown). Example 5

[0020] A method for removing surface oxides from titanium ingots involves placing a titanium ingot (forging) 1 with a TiO2 film layer 12 on its surface into a vacuum heat treatment furnace 3 heated by a graphite heating element 2, and evacuating the vacuum level inside the furnace to 5 × 10⁻⁶ using an exhaust system 4. -3 Pa, heating the titanium ingot (forging) 1 until the furnace temperature reaches 700℃ (detected by the temperature detection system 6), then introducing 99.995% high-purity CO gas through the gas filling system 5 to maintain the vacuum degree of the vacuum heat treatment furnace 3 at 8×10 -1 After holding at this temperature for 3 hours, the temperature of heat treatment furnace 3 is further increased to 880℃. High-purity CO gas (99.995%) is then introduced to maintain the vacuum level inside the furnace 3 at 8 × 10⁻⁶. -1 At a holding temperature of 3 Pa, the temperature of the vacuum heat treatment furnace 3 is further increased to 1050℃. This is achieved by introducing 99.995% high-purity CO gas to maintain the air volume inside the furnace 3 at 5 × 10⁻⁶. -1 Pa, after holding at this temperature for 0.5 hours, heating is stopped, and the CO gas is replaced with 99.995% high-purity argon gas. The furnace is then cooled to below 100°C in the vacuum heat treatment furnace 3. The titanium ingot (forging) 1 is then removed from the vacuum heat treatment furnace 3. In this way, the original 500μm oxide 12 on the surface of the titanium ingot (forging) 1 is transformed into a titanium metal layer 13 with a thickness of approximately 500μm on the surface of the titanium ingot (forging) 1, in which the oxygen weight percentage in the titanium layer 13 is 1.30%.

[0021] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0022] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0023] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for removing surface oxides from titanium ingots, characterized in that, Includes the following steps: Step 1: Place the titanium ingot with a TiO2 film on its surface into a vacuum heat treatment furnace, and evacuate the furnace to a vacuum level of 5 × 10⁻⁶. -3 Pa, heat the titanium ingot to 550-750℃, and introduce high-purity CO gas to maintain the vacuum level of the vacuum chamber at 1×10⁻⁶. -1 Pa~10Pa, keep warm for 2~6 hours; Step two: Continue to raise the temperature of the titanium ingot to 800~980℃, and continue to introduce high-purity CO gas to maintain a vacuum of 1×10⁻⁶. -2 Pa~5Pa, keep warm for 1~4 hours; Step 3: Continue to raise the temperature of the titanium ingot to 990–1220°C, and continue to purge with high-purity CO gas to maintain a vacuum of 1×10⁻⁶. -2 Pa~8×10 -1 Pa, keep warm for 0.5 to 2 hours and then stop heating; Step four: Replace the high-purity CO gas with high-purity argon gas, cool the furnace to below 100°C, and remove the titanium ingot from the vacuum heat treatment furnace to obtain the final product.

2. The method according to claim 1, characterized in that, The heating element of the vacuum heat treatment furnace is made of 99.999% high-purity graphite.

3. The method according to claim 1, characterized in that, Titanium ingots include forgings.

4. The method according to claim 1, characterized in that, In the TiO2 film, the average oxygen content is ≥25.66% by weight.

5. The method according to claim 1, characterized in that, The purity of high-purity CO gas is ≥99.995%.

6. The method according to claim 1, characterized in that, The purity of high-purity argon gas is ≥99.995%.

7. The method according to claim 1, characterized in that, The thickness of the TiO2 film is 50 μm to 10 mm. The above method converts the TiO2 film with a thickness of 50 μm to 10 mm into a titanium layer with a thickness of 50 μm to 10 mm.

8. The method according to claim 7, characterized in that, The oxygen content of the titanium layer is less than 1.5% by weight.

9. The titanium ingot obtained by the method according to any one of claims 1 to 8.

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