Titanium strip for deep drawing and heat treatment process thereof

Abstract

The invention provides a titanium strip for deep drawing and a heat treatment process thereof, and relates to the technical field of metal heat treatment processes. An oxide layer is formed on the surface of the titanium strip for deep drawing in a heat treatment process. According to the method, the oxidation layer can be formed on the surface of the titanium belt for deep drawing in the mode that the compressed air is continuously introduced, oxygen in the compressed air serves as an oxidizing agent to provide active oxygen atoms, nitrogen in the compressed air serves as a diluent, the oxidation rate can be decreased, the gradient oxidation layer composed of TiO, Ti2O3 and TiO2 is formed, and the bonding strength is improved. And moreover, the flowability of the gas can be enhanced in the heat treatment equipment by introducing the compressed air, so that a uniform oxide layer can be formed on the surface of the titanium belt for deep drawing.

Description

Technical Field

[0001] The present application relates to the technical field of metal heat treatment technology, and in particular to a titanium strip for deep drawing and a heat treatment process thereof. Background Art

[0002] As an important metal plastic processing method in modern manufacturing, stamping technology is widely used in aerospace, automobile manufacturing, precision instruments and other fields. Titanium alloy has the characteristics of high strength and low density, which can reduce the weight of the structure while providing sufficient strength.

[0003] Titanium strips for stamping have good plasticity and toughness, and can withstand complex stamping deformation without breaking easily. However, when used for stamping with large deformation, high breakage rate and surface wire drawing still occur, thus limiting the application of titanium strips for stamping. Summary of the invention

[0004] In order to improve the problems of high breakage rate and surface wiredrawing in current titanium strips for stamping when used for stamping with large deformation, the present application provides a titanium strip for deep drawing and a heat treatment process thereof.

[0005] In a first aspect, the present application provides a heat treatment process for a titanium strip for deep drawing, which adopts the following technical solution: A heat treatment process for a titanium strip for deep drawing, wherein an oxide layer is formed on the surface of the titanium strip for deep drawing during the heat treatment process.

[0006] The present application forms a uniform oxide layer on the surface of the titanium strip for deep drawing, the main component of which is TiO2, which can form a crystal form or agglomerate similar to a layered structure. This layered structure makes it relatively easy for the TiO2 oxide layer to slide between layers during the friction process, thereby reducing the friction between the layers. In addition, the TiO2 particles have a large specific surface area and abundant surface active sites, and can be adsorbed on the tiny depressions and protrusions on the friction surface. This adsorption effect can fill the microscopic roughness of the surface, making the friction surface smoother, thereby further reducing friction. During the stamping process, the TiO2 particles can be broken to form a thin film with lubricating properties, making the workpiece easier to flow in the mold, avoiding rupture when the friction between the workpiece and the mold deepens to the limit, and having a higher yield rate.

[0007] Optionally, the oxide layer is formed on the surface of the titanium strip for deep drawing by continuously introducing compressed air.

[0008] In this application, an oxide layer can be formed on the surface of the titanium strip for deep drawing by continuously introducing compressed air. Among them, oxygen in the compressed air serves as an oxidant to provide active oxygen atoms, and nitrogen in the compressed air serves as a diluent to slow down the oxidation rate, forming a gradient oxide layer composed of TiO→Ti2O3→TiO2, thereby enhancing the bonding strength. Moreover, introducing compressed air can enhance the gas fluidity in the heat treatment equipment, so that a uniform oxide layer can be formed on the surface of the titanium strip for deep drawing.

[0009] Optionally, the heat treatment process of the titanium strip for deep drawing is specifically as follows: Place the titanium strip for deep drawing in a closed heat treatment equipment, first introduce an inert gas into the heat treatment equipment, and then introduce the compressed air into the heat treatment equipment.

[0010] Optionally, the inert gas is argon.

[0011] In this application, when heat treating, the method of first introducing argon and then introducing compressed air is adopted. As an inert gas, argon can not only block the direct reaction of titanium with active gases such as O2 and N2, avoid uncontrolled oxidation or nitridation, but also remove impurity gases in the heat treatment equipment, establish a high-purity inert substrate environment, and provide a uniform gas flow field for subsequent oxidation. When compressed air is introduced, there is only inert gas in the heat treatment equipment, and the entry of compressed air can promote the mixing and circulation of the two, so that a uniform oxide layer can be formed on the surface of the titanium strip for stamping.

[0012] Optionally, the flow rate of the inert gas introduced is 5-10 m³ / h, and the introduction time is 1-2 h.

[0013] Optionally, the flow rate of the compressed air introduced is 5-10 m³ / h, and the introduction time is 0.5-1 h.

[0014] Optionally, the temperature of the heat treatment process is 740-780 °C.

[0015] In this application, by separately controlling the flow rate of the inert gas and the compressed air introduced, the introduction time, and the temperature of the heat treatment process, an oxide layer can be formed on the surface of the titanium strip for deep drawing, thereby improving the stamping performance of the titanium strip for deep drawing.

[0016] Optionally, when introducing the compressed air, the water vapor content in the heat treatment equipment is controlled below 10%.

[0017] In this application, by controlling the water vapor content, it is possible to avoid water vapor dropping on the surface of the titanium strip for deep drawing during the formation of the oxide layer, thereby affecting the formation of the oxide layer and resulting in non-uniformity of the oxide layer on the surface of the titanium strip for deep drawing.

[0018] Optionally, the titanium strip for deep drawing is subjected to degreasing treatment before the heat treatment process.

[0019] The present application can fully clean the oil stains on the surface of the titanium strip for deep drawing through degreasing and degreasing treatment, so as to ensure the uniform formation of the oxide layer and the aesthetics of the surface of the titanium strip after heat treatment.

[0020] Optionally, the raw material of the deep-drawing titanium strip has an oxygen content of no more than 0.04% and an iron content of no more than 0.04%.

[0021] The present application controls the impurity content in the raw material of the titanium strip for deep drawing, thereby ensuring that a titanium strip with excellent deep drawing performance can be obtained after a heat treatment process.

[0022] In a second aspect, the present application provides a titanium strip for deep drawing, which is prepared according to the heat treatment process.

[0023] The titanium strip for deep drawing obtained in the present application has excellent deep drawing performance, and the oxide layer it possesses plays a certain lubricating role during stamping, making the material less prone to damage and having a higher yield rate.

[0024] In summary, the present application includes at least one of the following beneficial effects: 1. The present application forms an oxide layer on the surface of the deep-drawing titanium strip by continuously introducing compressed air, wherein the oxygen in the compressed air acts as an oxidant to provide active oxygen atoms, and the nitrogen in the compressed air acts as a diluent to slow down the oxidation rate, forming a gradient oxide layer composed of TiO→Ti2O3→TiO2, thereby improving the bonding strength. Moreover, the introduction of compressed air can enhance the fluidity of the gas in the heat treatment equipment, thereby forming a uniform oxide layer on the surface of the deep-drawing titanium strip.

[0025] 2. The deep-drawing titanium strip obtained in the present application has excellent deep-drawing performance, and its oxide layer plays a certain lubricating role during stamping, making the material less likely to be damaged and having a higher yield rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a surface image of a titanium strip sample of the present application which has not been subjected to a heat treatment process; Figure 2 is a surface image of the titanium strip subjected to the heat treatment process in Example 1 of the present application; Figure 3 This is a surface image of the titanium strip obtained in Example 1 after stamping. DETAILED DESCRIPTION

[0027] Traditional titanium strips are prone to cracking during the stamping process, mainly due to the excessive frictional force between the material surface and the die. This frictional force will increase sharply in the later stage of stamping deformation. When it exceeds the material's bearing limit, it will cause two typical failures: one is that the material surface is torn hard to form wire-drawing scars, and the other is that local stress concentration causes internal crack propagation until overall fracture. The fundamental contradiction lies in the vicious cycle formed by the plastic deformation ability of the titanium alloy itself and the external frictional constraint.

[0028] The applicant's research found that if a uniform oxide layer is formed on the surface of the titanium strip, the special crystal structure of this oxide layer shows a layered arrangement characteristic similar to fish scales at the micro level: when the material contacts and rubs against the die, each layer of crystals can relatively slip along a specific direction, thus converting the original rigid friction directly acting on the titanium alloy matrix into interlayer flexible sliding, and converting the original antagonistic frictional constraint into cooperative deformation assistance, which will greatly improve the ultimate depth of stamping forming, and thus this invention is formed.

[0029] In this invention, in the heat treatment process, by continuously introducing compressed air, an oxide layer is formed on the surface of the titanium strip for deep drawing, and the aerodynamic design is used to guide the preferential growth of the oxide layer crystals to form a layered arrangement structure beneficial to slip. Different from the disordered structure formed by natural oxidation, the oxide layer controlled by the process has obvious crystallographic orientation advantages.

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of this invention with reference to the accompanying drawings in the embodiments of this invention. Obviously, the described embodiments are part of the embodiments of this invention, rather than all of the embodiments.

[0031] First, perform preliminary pretreatment on the titanium strip, including the following steps: S1. Provide raw materials: Select a titanium strip with low impurity content as the raw material, where the oxygen element content ≤ 0.04% and the iron element content ≤ 0.04%; S2. Hot rolling treatment: Perform hot rolling treatment on the above-mentioned titanium strip, and then perform pickling treatment. The pickling removal amount is controlled between 2.0% and 3.5% of the titanium strip thickness to remove the oxide scale and other impurities generated during the hot rolling process; S3. Cold rolling forming: Perform cold rolling treatment on the pickled titanium strip. Through multiple passes of cold rolling, the total reduction rate of the titanium strip reaches 70% - 80%; S4. Surface treatment: Perform degreasing treatment on the cold-rolled formed titanium strip to make the surface of the titanium strip free of visible water stains, oil prints and other surface dirt. After passing the 35# dyno pen test, the titanium strip is used for the following examples and comparative examples for heat treatment.

[0032] Example 1: Take a sample of the pre-treated titanium strip above and place it in an annealing furnace. Keep the temperature of the annealing furnace at 780 °C, seal the wool felt at the entrance of the annealing furnace, slightly lift the wool felt at the exit, introduce argon into the annealing furnace, with a flow rate of 10 m³ / h and an introduction time of 1 h. Control the water vapor content in the annealing furnace to be below 10%. Then introduce compressed air, with a flow rate of 10 m³ / h and an introduction time of 0.5 h. Thus, the heat treatment of the titanium strip is completed.

[0033] Figure 1 is the surface diagram of the titanium strip sample without heat treatment process. Figure 2 is the surface diagram of the titanium strip after heat treatment process in Example 1 of this application. From Figure 1 and Figure 2 comparison, it can be seen that after the heat treatment process of Example 1, a uniformly colored black oxide layer should be formed on the surface of the titanium strip.

[0034] Example 2: Example 2 is basically the same as Example 1, except that the flow rate of the compressed air introduced is 5 m³ / h and the introduction time is 1 h.

[0035] Example 3: Example 3 is basically the same as Example 1, except that the flow rate of the compressed air introduced is 10 m³ / h and the introduction time is 1 h.

[0036] Example 4: Example 4 is basically the same as Example 1, except that the flow rate of the argon introduced is 5 m³ / h and the introduction time is 2 h.

[0037] Example 5: Example 5 is basically the same as Example 1, except that the temperature of the heat treatment equipment is 740 °C.

[0038] Comparative Example 1: Take a sample of the pre-treated titanium strip above and place it in an annealing furnace. Keep the temperature of the annealing furnace at 780 °C, seal the wool felt at the entrance of the annealing furnace, slightly lift the wool felt at the exit, control the water vapor content in the annealing furnace to be below 10%, and introduce compressed air into the annealing furnace, with a flow rate of 10 m³ / h and an introduction time of 0.5 h. Thus, the heat treatment of the titanium strip is completed.

[0039] Comparative Example 2: Take a sample of the pre-treated titanium strip above and place it in an annealing furnace. Keep the temperature of the annealing furnace at 780 °C, seal the wool felt at the entrance of the annealing furnace, slightly lift the wool felt at the exit, introduce argon into the annealing furnace, with a flow rate of 10 m³ / h and an introduction time of 1 h. Control the water vapor content in the annealing furnace to be below 10%. After the argon introduction time reaches 0.5 h, add compressed air, with a flow rate of 10 m³ / h and an introduction time of 0.5 h. Thus, the heat treatment of the titanium strip is completed.

[0040] Performance testing: The titanium strip products obtained in Examples 1-5 and Comparative Examples 1-2 were subjected to performance testing. Tensile specimens were prepared in accordance with GB / T 228.1-2021 and the tensile strength, yield strength, and elongation of the titanium strip products were tested. The grain size of the titanium strip products was tested in accordance with ASTM E112, and the Vickers hardness of the titanium strip products was tested in accordance with GB / T 4340.1-2009. The specific results are shown in Table 1.

[0041] Table 1 Performance testing results of each example and comparative example Group <![CDATA[Vickers hardness (HV 1.0 )]]> Tensile strength (MPa) Yield strength (MPa) Elongation rate (%) Grain size (grade) Example 1 125 320 185 42 8 Example 2 122 315 180 40 8 Example 3 128 325 190 43 8 Example 4 120 310 178 41 8 Example 5 118 305 175 39 7 Comparative example 1 150 420 250 22 6 Comparative example 2 130 350 200 35 7 As can be seen from Table 1, the hardness of the titanium strip product in Comparative Example 1 is significantly higher than that in Examples 1-5. The reason is that in the heat treatment process of Comparative Example 1, argon was not pre-injected for environmental cleaning, resulting in an uneven oxide layer and possibly containing brittle phases, thus increasing the hardness. All the indicators of Comparative Example 2 are inferior to those of Example 1. The reason is that the simultaneous injection of argon and compressed air disrupted the orderly formation of the gradient oxide layer, resulting in a mixed oxide layer structure, incomplete grain boundary purification, and gas reaction kinetic imbalance. These process defects directly led to a decrease in elongation and grain coarsening, ultimately resulting in inferior stamping performance compared to Example 1.

[0042] The elongation of Examples 1-5 is higher than that of Comparative Examples 1-2, so it can support stamping with a large deformation amount and suppress the risk of cracking. The yield strength of Examples 1-5 is less than that of Comparative Examples 1-2, so it is beneficial for material flow during stamping and can avoid cracking when the friction between the workpiece and the die deepens to the limit. The titanium strip products of Examples 1-4 have a higher grain size, which can promote uniform deformation, suppress crack propagation, and improve stamping stability.

[0043] Figure 3 is the surface diagram of the titanium strip prepared in Example 1 after stamping treatment. From Figure 3 it can be seen that after the titanium strip prepared in Example 1 was subjected to stamping treatment, the surface of the titanium strip did not break and was intact.

[0044] The above are all the preferred embodiments of this application. The protection scope of this application is not limited by this. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A heat treatment process for a titanium strip for deep drawing, characterized in that: An oxide layer is formed on the surface of the titanium strip for deep drawing during the heat treatment process; The titanium strip for deep drawing is placed in a closed heat treatment device, an inert gas is first introduced into the heat treatment device, and then the compressed air is continuously introduced into the heat treatment device.

2. The heat treatment process of the deep drawing titanium strip according to claim 1, characterized in that: The inert gas is introduced at a flow rate of 5-10 m³ / h and for a time of 1-2 h.

3. The heat treatment process of the titanium strip for deep drawing according to claim 1, characterized in that: The compressed air is introduced at a flow rate of 5-10 m³ / h and for a time of 0.5-1 h.

4. The heat treatment process of the titanium strip for deep drawing according to claim 1, characterized in that: The temperature of the heat treatment process is 740-780°C.

5. The heat treatment process of the titanium strip for deep drawing according to claim 1, characterized in that: When the compressed air is introduced, the water vapor content in the heat treatment equipment is controlled to be below 10%.

6. The heat treatment process of the deep drawing titanium strip according to claim 1, characterized in that: The titanium strip for deep drawing is subjected to deoiling and degreasing treatment before being subjected to a heat treatment process.

7. The heat treatment process of the titanium strip for deep drawing according to claim 1, characterized in that: The raw material of the deep-drawing titanium strip has an oxygen content of no more than 0.04% and an iron content of no more than 0.04%.

8. A titanium strip for deep drawing, characterized in that: Prepared by the heat treatment process according to any one of claims 1-7.

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