A method for preparing a two-phase titanium alloy profile

Abstract

The invention discloses a method for preparing a two-phase titanium alloy profile, comprising the following steps: step 1, completely wrapping a double-layer protective cover outside a blank to be processed, the protective cover comprising an iron sheet for wrapping the surface of the blank to be processed and a copper sheet wrapping the outer side of the iron sheet; step 2, raising the blank to be processed wrapped with the double-layer protective cover to 30-50°C below the β phase transition point, keeping warm for 40-60min, and then sending it to a rolling mill for 5-12 passes of rolling to obtain a profile; step 3, heat treating the profile obtained by step 2, and then straightening the profile with temperature on a straightening machine; wherein the heat treatment process is: heating the annealing furnace to 750-850°C, and then placing the profile obtained by step 2 in a warm charging furnace, and keeping warm for 60-90min; step 4, pickling the profile after straightening in step 3, and removing the protective cover wrapped on the surface of the blank to be processed. It solves the problem of low yield of existing titanium alloy profile rolled products.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium material processing, and in particular relates to a method for preparing a two-phase titanium alloy profile. Background Art

[0002] Two-phase titanium alloy has the characteristics of good biocompatibility, excellent corrosion resistance, and low elastic modulus, and is widely used in the field of surgical implant bone plates. Bone plates are designed according to the shape of human bones and in a bionic manner, which can minimize the damage to product stress caused by bone bending, compression, and rotation. However, traditional plates have the characteristics of large plate width, uneven force during rolling, strong anisotropy, and high yield strength. This characteristic causes titanium alloy plates to break when used as bone plates. They should be continuously loaded during clinical use, which increases the tendency to break and shortens their service life. Compared with traditional plates, profiles have smaller plate widths, uniform transverse and longitudinal force during rolling, small anisotropy, and can be designed in different sizes according to different human bones. The prepared products are almost semi-finished products, and there is no need for subsequent down-cutting processes, which greatly shortens the working hours and effectively reduces production costs.

[0003] Titanium alloys have high specific strength, low specific heat capacity, and high deformation resistance. They are usually formed by hot working. However, titanium alloys have a narrow processing temperature range and are difficult to process, especially for the rolling process of titanium alloy profiles. There are many rolling passes, the rolling time is long, and the profile temperature drops quickly. In the last few rolling passes, material jamming is likely to occur, making feeding difficult, which greatly reduces the product yield. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a two-phase titanium alloy profile, so as to solve the problem of low yield of rolled products of existing titanium alloy profiles.

[0005] The present invention adopts the following technical scheme: a method for preparing a two-phase titanium alloy profile, comprising the following steps:

[0006] Step 1: completely wrap the blank to be processed with a double-layer protective cover, wherein the protective cover includes an iron sheet for wrapping the surface of the blank to be processed and a copper sheet for wrapping the outer side of the iron sheet; Step 2: raise the blank to be processed wrapped with the double-layer protective cover to 30-50°C below the β phase transition point, keep the temperature for 40-60 minutes, and then send it to a rolling mill for 5-12 passes of rolling to obtain a profile;

[0007] Step 3, heat treating the profile obtained in step 2, and then straightening the profile with temperature on a straightening machine;

[0008] The heat treatment process is as follows: the annealing furnace is heated to 750-850°C, and the profile obtained in step 2 is then placed in a warm charging furnace for 60-90 minutes;

[0009] Step 4: Pickling the profile straightened in step 3 to remove the protective cover wrapped on the surface of the blank to be processed.

[0010] Furthermore, the method of wrapping the double-layer protective cover in step one is: first wrap a layer of iron sheet on the surface of the blank to be processed, and then wrap a layer of copper sheet on the surface of the iron sheet, completely wrap the blank with the iron sheet and copper sheet, and finally fix it by welding; wherein the thickness ratio of the copper sheet to the iron sheet is (1.5-3):1.

[0011] Furthermore, in step 2, the rolling mill adopts a cross-rolling method.

[0012] Furthermore, in step 2, during the rolling process, the deformation amount per pass is controlled to be 10%-15%.

[0013] Furthermore, the pickling solution selected in step 4 is 65%-68% nitric acid solution, 40% hydrofluoric acid solution and the remainder aqueous solution.

[0014] The beneficial effects of the present invention are as follows: the preparation method of a two-phase titanium alloy profile of the present invention performs double-encapsulation treatment on the blank, so that the surface of the prepared titanium alloy profile has less oxide scale and no discontinuous surface cracks, which greatly improves the yield rate of the profile; it can also play a good heat preservation effect, effectively reduce the surface temperature drop of the profile, ensure that the rolling process is in a constant temperature state, and no rolling jamming phenomenon occurs, which effectively improves the yield rate; it can also prevent scratch defects on the surface of the profile, the production process is short, and no subsequent machining process is required. The preparation method of a two-phase titanium alloy profile of the present invention stabilizes the profile rolling process, which can effectively improve the anisotropy of the plate, and the prepared profile has uniform microstructure, small difference in transverse and longitudinal mechanical properties, reduces the tendency of cracking in subsequent service, and prolongs the service life of the parts. The profile obtained by the preparation method of the present invention can significantly reduce the yield strength of the profile and improve the machinability of the profile. The profile obtained by the preparation method of a two-phase titanium alloy profile of the present invention has good straightness, no distortion phenomenon occurs, and the profile structure is uniform. The invention discloses a method for preparing a two-phase titanium alloy profile, which adopts a double-cladding rolling process, and can effectively control the content of impurity elements in the prepared titanium alloy material, thereby ensuring the reliability of the product in surgical implantation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a metallographic microstructure diagram of Example 1 of the present invention;

[0016] Figure 2 This is a metallographic microstructure diagram of Comparative Example 1 of the present invention;

[0017] Figure 3 This is a comparison chart of the transverse and longitudinal tensile strength of the profiles of Example 1 of the present invention and Comparative Example 1;

[0018] Figure 4 This is a comparison chart of the transverse and longitudinal yield strengths of the profiles of Example 1 of the present invention and Comparative Example 1;

[0019] Figure 5 The figure is a schematic diagram of the process of wrapping the double-layer protective cover according to the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] The present invention provides a method for preparing a two-phase titanium alloy profile, comprising the following steps:

[0022] Step 1: completely wrapping the blank to be processed with a double-layer protective cover, wherein the protective cover comprises an iron sheet for wrapping the surface of the blank to be processed and a copper sheet for wrapping the outer side of the iron sheet;

[0023] Step 2, raising the temperature of the blank to be processed wrapped with a double-layer protective cover to 30-50° C. below the β phase transformation point, keeping the temperature for 40-60 minutes, and then sending it to a rolling mill for 5-12 passes of rolling to obtain a profile;

[0024] Step 3, heat treating the profile obtained in step 2, and then straightening the profile with temperature on a straightening machine;

[0025] The heat treatment process is as follows: the annealing furnace is heated to 750-850°C, and the profile obtained in step 2 is then placed in a warm charging furnace for 60-90 minutes;

[0026] Step 4: pickling the profile straightened in step 3 to remove the protective cover wrapped on the surface of the blank to be processed, so as to obtain a finished two-phase titanium alloy profile.

[0027] Cladding rolling has the functions of protecting metal, reducing pollution, reducing surface temperature drop, keeping the profile at a constant temperature during rolling, reducing deformation resistance, and improving the stress state of the plate, thereby greatly improving the fire processing rate. In the process of cladding rolling, the metal material can be repeatedly cross-rolled, and the cumulative deformation will reach the maximum value, thereby significantly reducing the difference in the transverse and longitudinal mechanical properties of the plate, which can effectively improve the structure and performance of the plate.

[0028] In some embodiments, Figure 5As shown, the method of wrapping the double-layer protective cover in step one is: first wrap a layer of iron sheet on the surface of the blank to be processed, and then wrap a layer of copper sheet on the surface of the iron sheet, completely wrap the blank with the iron sheet and the copper sheet, and finally fix it by welding; wherein the thickness ratio of the copper sheet to the iron sheet is (1.5-3):1.

[0029] According to Fourier's law of heat conduction, assuming that the temperature drops from 940℃ to room temperature, the heat conduction of 1.5-3mm thick copper is 550-1100W per unit time and per unit area, and the heat conduction of 1mm thick iron is 55W. According to the heat loss control method, it is calculated that the heat loss is the smallest when the thickness ratio of copper to iron is at least 1.5:1. As the thickness ratio of copper to iron increases, the heat loss also increases. When the thickness ratio is greater than 3:1, the heat loss hardly increases with the increase of the thickness ratio of the two, that is, when the thickness ratio of copper to iron is greater than 3:1, it has the same thermal insulation effect as the thickness ratio of 3:1. Copper and iron sheets of different thicknesses were selected for ductility experiments, and the numerical analysis model was used to calculate that when the thickness ratio of copper to iron is (1.5-3):1, the coordinated deformation capabilities of the two metals are basically consistent. The preparation method stabilizes the rolling process and can effectively improve the anisotropy of the plate. The prepared profile has uniform microstructure and small differences in transverse and longitudinal mechanical properties, which reduces the tendency of cracking in subsequent service and prolongs the service life of the parts.

[0030] Based on a large number of experiments, the numerical analysis model was used to calculate that under this ratio, the combined double jacket can have good thermal insulation performance and coordinated deformation performance. First, a layer of iron sheet is wrapped on the surface of the billet, and then a layer of copper sheet is wrapped on the surface of the iron sheet to prevent the copper sheet from directly contacting the billet to produce Ti-Cu brittle structure, and finally welded and fixed.

[0031] In some embodiments, in step 2, the rolling mill adopts a cross-rolling method, that is, after each rolling, the profile is rotated 90° for rolling, so as to make the transverse and longitudinal structures of the profile uniform.

[0032] In some embodiments, during the rolling process in step 2, the deformation amount of each pass is controlled to be 10%-15%, which can ensure that the grains are evenly broken during each deformation process.

[0033] In some embodiments, the pickling solution selected in step 4 is 65%-68% nitric acid solution, 40% hydrofluoric acid solution and the remainder aqueous solution. The pickling solution with this ratio can completely remove the double jacket wrapping the profile without reducing the size of the profile.

[0034] Example 1

[0035] This embodiment 1 provides a method for preparing a two-phase titanium alloy profile, and the preparation method includes the following steps:

[0036] Step 1: Choose a copper sheet with the dimensions of 1.0mm thickness, 250mm length, and 200mm width, and a piece of iron sheet with the dimensions of 0.5mm thickness, 250mm length, and 200mm width. First, wrap a layer of iron sheet on the surface of the blank, and then wrap a layer of copper sheet on the surface of the iron sheet, and fix them by welding. The size of the blank is Φ64×200mm.

[0037] Step 2: Raise the temperature of the double-jacketed billet to 920°C and keep it warm for 60 minutes. Adjust the rolling mill pass to a single-pass deformation of 10%, feed the heated billet into the rolling mill, and perform 8-pass rolling to obtain a profile.

[0038] Step 3: Heat the annealing furnace to 780°C, transfer the profile obtained in step 2 to a warm charging furnace, keep the heat treatment time for 60 minutes, then take the heat-treated profile out of the annealing furnace and perform warm straightening on a straightening machine.

[0039] Step 4: Pickle the straightened profile with a solution of 450 ml of 65% nitric acid solution, 100 ml of 40% hydrofluoric acid solution and the remainder of aqueous solution to remove the iron and copper sheets wrapped on the surface of the finished two-phase titanium alloy profile.

[0040] like Figure 1 As shown, the finished product prepared in Example 1 has the characteristics of small anisotropy, uniform microstructure and stable mechanical properties. The microstructure of the alloy conforms to 3T9 of 3T1-3T13 in EN 3114-003; Figure 3 As shown, the difference between its transverse and longitudinal tensile strength is less than 25MPa; Figure 4 As shown, the yield strength is in the range of 795-890MPa, and there is almost no oxide scale on the surface, which can be well applied to later parts processing.

[0041] Comparative Example 1

[0042] Step 1: Raise the temperature of the blank to 920°C and keep it warm for 60 minutes, wherein the size of the blank is Φ64×200 mm.

[0043] Step 2: Adjust the mill pass to a single-pass deformation of 10%.

[0044] Step 3: Feed the heated billet into the rolling mill for 8 passes of rolling.

[0045] Step 4: Heat the annealing furnace to 780°C.

[0046] Step 5: Place in a warm furnace and keep warm for 60 minutes.

[0047] Step 6: Take the heat-treated profile out of the annealing furnace and perform hot straightening on a straightening machine.

[0048] Step 7: Surface-treat the annealed two-phase titanium alloy profile on a milling machine and machine it to a specified size.

[0049] like Figure 2 As shown, in Comparative Example 1, because the blank was not double-encased, the microstructure of the two-phase titanium alloy profile prepared therefrom was uneven, with some elongated α phases present, and the microstructure conformed to 3T20 of 3T1-3T13 of EN 3114-003, and the profile had strong anisotropy. Figure 3 As shown, the difference in transverse and longitudinal tensile strength of the two-phase titanium alloy profile prepared in Comparative Example 1 is greater than 25 MPa. Figure 4 As shown, the yield strength of the two-phase titanium alloy profile prepared in Comparative Example 1 is higher than 890 MPa, which does not meet the technical requirements.

[0050] In summary, from Figure 3 It can be seen that the difference in transverse and longitudinal mechanical properties of the two-phase titanium alloy profile prepared in Example 1 is small, and the difference in tensile strength is less than 25 MPa. Figure 4 It can be seen that the yield strength of the two-phase titanium alloy profile prepared in Example 1 is less than 890 MPa, which meets the technical requirement of 795-890 MPa, while the yield strength of the two-phase titanium alloy profile prepared in Comparative Example 1 is greater than 890 MPa, which does not meet the technical requirement.

[0051] Comparative Example 2

[0052] Step 1: Raise the temperature of the blank to 920°C and keep it warm for 60 minutes, wherein the size of the blank is Φ64×200 mm.

[0053] Step 2: Adjust the mill pass to a single-pass deformation of 10%.

[0054] Step 3: Feed the heated billet into the rolling mill for 8 passes of rolling.

[0055] Step 4: Heat the annealing furnace to 780°C.

[0056] Step 5: Place in a warm furnace and keep warm for 60 minutes.

[0057] Step 6: Take the heat-treated two-phase titanium alloy profile out of the annealing furnace and perform hot straightening on a straightening machine.

[0058] In Comparative Example 2, the blank was not double-jacketed. Although the two-phase titanium alloy profile prepared therein significantly shortened the processing steps, the surface of the prepared two-phase titanium alloy profile had a large amount of oxide scale and a small amount of discontinuous cracks, which affected the mechanical properties of the material itself and created safety hazards during use.

[0059] During the rolling process of traditional two-phase titanium alloy profiles, the surface temperature drops quickly, the yield rate is low, the anisotropy of the plate after rolling is strong (the mechanical properties in the transverse and longitudinal directions are quite different), the yield strength is high, and it is easy to break during subsequent use. After the conventional profiles are heated, oxide scale is easily generated on the surface of the blank. If the oxide scale is not removed before rolling, the blank will have surface quality problems such as pitting and pitting after rolling. These surface problems cannot be removed by surface treatment methods such as sandblasting and pickling, and subsequent grinding is required, which is not only time-consuming and laborious, but also reduces the yield rate. A preparation method of a two-phase titanium alloy profile of the present invention performs double-jacketing on a blank before rolling, so that the prepared two-phase titanium alloy profile has less oxide scale on the surface and no discontinuous surface cracks, thereby greatly improving the yield rate of the profile; the double-jacketing of the blank can also prevent scratch defects from occurring on the surface of the two-phase titanium alloy profile, shorten the production process, and eliminate the need for subsequent machining steps; the double-jacketing of the blank can also insulate the blank, effectively reducing the surface temperature drop of the profile and preventing the occurrence of material jamming during rolling.

[0060] The method for preparing a two-phase titanium alloy profile of the present invention uses a stable rolling process, which can effectively improve the anisotropy of the plate. The prepared two-phase titanium alloy profile has a uniform microstructure, and the difference in transverse and longitudinal mechanical properties is small, which reduces the tendency of cracking during subsequent service and extends the service life of the parts. The two-phase titanium alloy profile obtained by the preparation method of the present invention can significantly reduce the yield strength of the profile and improve the machinability of the profile. Titanium alloy profiles are prone to defects such as cross-sectional distortion and twisting after extrusion. However, the conventional extrusion method is multi-roll straightening, which cannot be straightened. During extrusion, the flow speeds of the surface metal and the core metal are inconsistent, resulting in uneven deformation. The two-phase titanium alloy profile obtained by the method for preparing a two-phase titanium alloy profile of the present invention has good straightness, no twisting phenomenon occurs, and the profile structure is uniform.

[0061] In order to ensure that the titanium alloy material prepared by the preparation method of the two-phase titanium alloy profile of the present invention can be applied to surgical implantation, it is necessary to ensure that the titanium alloy material for surgical implantation has good performance and service life, so it is necessary to focus on controlling the content of impurity elements in the two-phase titanium alloy profile. In the prior art, two-phase titanium alloy profiles are mostly processed by hot working, and the conventional rolling process will cause cracks on the surface of the titanium alloy material, so that hydrogen enters the material from the surface cracks, thereby causing the hydrogen content inside the two-phase titanium alloy profile to increase. Titanium and hydrogen have a greater affinity. In the subsequent processing process, delayed fracture will occur under the action of stress, posing a safety hazard, thereby affecting the service life of the implanted titanium alloy material. The preparation method of the two-phase titanium alloy profile of the present invention adopts a double-jacket rolling process, which can effectively control the content of impurity elements in the obtained titanium alloy material, and ensure the reliability of the two-phase titanium alloy profile product for surgical implantation.

Claims

1. A method for preparing a two-phase titanium alloy profile, characterized in that: The following steps are involved: Step 1: completely wrapping the blank to be processed with a double-layer protective cover, wherein the protective cover comprises an iron sheet for wrapping the surface of the blank to be processed and a copper sheet for wrapping the outer side of the iron sheet; Step 2, raising the temperature of the blank to be processed wrapped with a double-layer protective cover to 30-50° C. below the β phase transformation point, keeping the temperature for 40-60 minutes, and then sending it to a rolling mill for 5-12 passes of rolling to obtain a profile; Step 3, heat treating the profile obtained in step 2, and then straightening the profile with temperature on a straightening machine; The heat treatment process is as follows: the annealing furnace is heated to 750-850°C, and the profile obtained in step 2 is then placed in a warm charging furnace for 60-90 minutes; Step 4: Pickling the profile straightened in step 3 to remove the protective cover wrapped around the surface of the blank to be processed.

2. The method for preparing a two-phase titanium alloy profile according to claim 1, characterized in that: The method of wrapping the double-layer protective cover in step 1 is: first wrap a layer of iron sheet on the surface of the blank to be processed, then wrap a layer of copper sheet on the surface of the iron sheet, completely wrap the blank with the iron sheet and copper sheet, and finally fix it by welding; wherein the thickness ratio of the copper sheet to the iron sheet is (1.5-3):

1.

3. The method for preparing a two-phase titanium alloy profile according to claim 1, characterized in that: In the step 2, the rolling mill adopts a cross rolling method.

4. The method for preparing a two-phase titanium alloy profile according to claim 1, characterized in that: In the step 2, during the rolling process, the deformation amount of each pass is controlled to be 10%-15%.

5. The method for preparing a two-phase titanium alloy profile according to claim 1, characterized in that: The pickling solution selected in step 4 is 65%-68% nitric acid solution, 40% hydrofluoric acid solution and the remainder aqueous solution.

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