A grain refinement preparation process for improving the fatigue strength of titanium alloy bar for medical instruments
Patent Information
- Application Number
- CN202610869706.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-16
- Publication Date
- 2026-07-24
Smart Images
Figure CN122446103A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of grain refinement technology in the plastic processing of medical titanium alloys, and in particular to a grain refinement preparation process for improving the fatigue strength of titanium alloy bars for medical devices. Background Technology
[0002] Titanium alloys are widely used in aerospace, chemical, and industrial fastener fields due to their high strength, light weight, and corrosion resistance. Another major advantage of titanium alloys is their biocompatibility, which also makes them widely used in the medical field. For example, titanium alloy rods can be used for artificial joints, spinal fixation screws, and intramedullary nails; titanium alloy wires can be used for dental implants, bone wires, and sutures. Medical implant-grade titanium materials must meet medical standards such as GB / T13810. Medical standards, compared to industrial standards for titanium alloys, have higher requirements for grain size, microstructure uniformity, fatigue strength, and biocompatibility. Industrial titanium alloys typically do not require metallographic microstructure rating, while the metallographic microstructure of conventional medical titanium rods is below grade E, and medical titanium rods with ultrafine grains must reach grade A.
[0003] Currently available grain refinement processes for titanium alloys include offline quenching, furnace holding quenching, air cooling, wind cooling, liquid nitrogen cryogenic cooling, and segmented post-heat treatment quenching. For thin bars with a diameter of less than 20mm, traditional processes require high-temperature rolling followed by offline transfer, heat treatment in a water bath, and quenching. These processes are fragmented and time-consuming. During the waiting period, the high-temperature austenitic β phase is prone to grain coarsening, disordered crystal orientation, and uneven microstructure, resulting in finished product grains larger than 20μm, metallographic properties only reaching grade C or above, significantly reduced fatigue strength, poor implantation safety, low medical compliance rate, high scrap rate, and high cost, hindering large-scale application. Even with shorter offline transfer times, slow core cooling leads to rapid grain growth within the internal structure, resulting in coarse grains, decreased performance, and reduced fatigue strength. This affects the lifespan of medical devices within the body, increases the risk of pin breakage, and can lead to medical accidents.
[0004] Existing technologies cannot achieve rapid water cooling, directional grain refinement, and suppression of secondary growth at critical phase transition temperatures, thus failing to stably mass-produce metallographic grade A ultrafine-grained medical titanium alloy rods. This results in medical titanium alloy rods having poorer fatigue performance compared to foreign products.
[0005] Application content
[0006] To address the aforementioned problems, this application aims to provide a grain refinement process for improving the fatigue strength of titanium alloy bars used in medical devices. This process overcomes the shortcomings of existing technologies, such as fragmented processes, coarsening of grains, uneven microstructure, low fatigue strength, poor medical-grade compliance, and high costs. It provides an integrated rolling + online instant water quenching process that directly and rapidly water-cools the bars at the critical phase transformation temperature at the end of rolling, eliminating the need for transfer, secondary heating, and time intervals. This achieves directional grain refinement, inhibits secondary grain growth, and reshapes crystal orientation, stably producing ultrafine-grained medical titanium alloy bars with a grain size ≤7μm, metallographic grade A, and theoretical fatigue strength analysis (calculation) ≥500MPa. This eliminates the need for costly secondary heat treatment and liquid nitrogen cooling, significantly improving medical safety and mass production efficiency.
[0007] To achieve the above objectives, the technical solution adopted in this application is as follows: A grain refinement preparation process for improving the fatigue strength of titanium alloy bars for medical devices, comprising the following steps:
[0008] S1. The titanium alloy coarse bar material, after being heated in the furnace, is continuously rolled into finished fine bars with a diameter ≤Ø20mm through a multi-roll mill and output at an output temperature of 920~950℃.
[0009] S2. A water quenching tank is provided on one side of the multi-roll mill. The water quenching tank is arranged along the output direction of the finished thin bar and is corresponding to the axial direction of the finished thin bar. The length of the water quenching tank is such that the finished thin bar enters the water quenching tank and moves continuously to cool down to the temperature at which the grains no longer grow. The temperature is ≤80℃.
[0010] S3. After the finished thin bar is output from the multi-roll mill, its end immediately enters the water quenching tank to start water quenching, with a water temperature of <25℃; and the finished thin bars subsequently output from the multi-roll mill also continuously enter the water quenching tank for water quenching until all the finished thin bars that have been rolled are submerged in the water quenching tank for water quenching.
[0011] S4. The finished thin rods are water-quenched to ≤80℃ and then taken out of the water quenching tank. At this point, the grain refinement of the titanium alloy rods is completed.
[0012] Preferably, the water quenching tank has an inlet on one side and an outlet on the other side, so that the water quenching tank is filled with flowing water.
[0013] Preferably, the water inlet is located away from the multi-roll mill, while the water outlet is close to the multi-roll mill, so that the water flow direction in the water quenching tank is opposite to the output direction of the finished fine bar.
[0014] Preferably, the water quenching tank has a V-shaped cross-section structure, with sealing end plates at both ends.
[0015] Preferably, the sealing end plate near the outlet of the water pipe has a through hole that is directly opposite to the output of the finished thin rod. A plug plate is hinged to the inner side of the sealing end plate, and the plug plate can seal the through hole.
[0016] Preferably, the width of the water quenching tank gradually increases from the water inlet to the water outlet.
[0017] Preferably, the water quenching tank is provided with support rollers at intervals, which cause the finished thin bar to roll forward.
[0018] Preferably, a stacking trough is provided on one side of the water quenching tank. The stacking trough is composed of an inclined plate and a vertical baffle on one side of the inclined plate. The other side of the inclined plate is connected to the top edge of one side of the water quenching tank.
[0019] Preferably, a retrieval rope is distributed between adjacent support rollers. One end of the retrieval rope is connected to the junction of the inclined plate and the water quenching tank, and the other end hangs down to the outside of the water quenching tank, while the middle part of the retrieval rope falls naturally into the water quenching tank.
[0020] The beneficial effects of this application are as follows: The grain refinement preparation process disclosed in this application realizes an integrated process of rolling and online instant water quenching. The grains are directly immersed in the water quenching tank at a high temperature at the end of rolling, without transfer, secondary heating, or time interval. After the rolling process is completed, the grains are not offline or reheated, but are quenched online in real time. The grains are refined by rapid water cooling at the critical phase transformation temperature (grain size reaches ≤7μm, while the grain size of traditional processes is usually greater than 25μm). The crystal growth direction is precisely controlled to achieve directional grain refinement, inhibit secondary grain growth, reshape crystal orientation, and achieve a significant improvement in grain size. The fatigue strength theoretical analysis is ≥500 MPa. The implants have high safety and low risk of breakage, meeting the stringent requirements of high-end medical implants.
[0021] The titanium alloy rods prepared by the preparation process disclosed in this application can achieve the A-level metallographic rating of GB / T13810 standard after high magnification microstructure testing. Compared with the conventional CE-level rating, it has objective performance improvements (grain uniformity, crystal orientation consistency, material mechanical (fatigue strength) properties, implantation safety), significantly reduced scrap rate, and significantly improved economy.
[0022] This application uses V-theory analysis (calculation) to design a water quenching tank, "forced" water cooling with opposing water flow, support rollers to assist in the water quenching movement of the bar, and water quenching tank slope design to reduce pushing and extrusion deformation, thereby shortening the water quenching time, inhibiting grain growth conditions, and solving production problems such as bar swaying, bending, and deformation during water quenching, thus achieving high industrial production value.
[0023] The preparation process disclosed in this application is simple, has low mass production cost, high yield of finished products meeting medical standards, and its effects far exceed those of traditional processes. It can be mass-produced industrially and continuously generate economic and medical industry value.
[0024] The preparation process disclosed in this application changes the industry's inherent processing model, abandoning high-cost secondary heat treatment, liquid nitrogen cooling and other methods. Attached Figure Description
[0025] Figure 1 This is a schematic diagram of a multi-roll mill structure.
[0026] Figure 2 This diagram illustrates the process of rolling titanium alloy coarse bars into finished fine bars using a multi-roll mill.
[0027] Figure 3 This is a diagram showing the output of continuous rolling of finished fine bars.
[0028] Figure 4 This is a front view structural diagram of the water quenching tank in this application.
[0029] Figure 5 This is a top view of the water quenching tank in this application.
[0030] Figure 6 This is a side sectional view of the water quenching tank in this application.
[0031] Figure 7 This diagram illustrates the interaction between the finished thin bar stock and the water in the water quenching tank.
[0032] Figure 8 The illustration shows the finished thin bar stock being submerged in water during water quenching, as per this application.
[0033] Figure 9 This diagram illustrates the principle of the mixing of cold and hot water during the water quenching process in this application.
[0034] Figure 10 This diagram illustrates the mixing of hot and cold water around the finished thin bar during the water quenching process of this application.
[0035] Figure 11 This diagram illustrates the connection setup between the water quenching tank and the multi-roll mill in this application.
[0036] Figure 12 For this application Figure 11 Enlarged view of the structure at point A (the finished thin bar stock swaying after output).
[0037] Figure 13 The diagram illustrates the function of the guide tube in preventing the bar from swaying in this application.
[0038] Figure 14 This application provides a perforation diagram for the sealing end plate.
[0039] Figure 15 This is a diagram showing the hinged installation of a blocking plate on the inner side of the blocking end plate in this application.
[0040] Figure 16 This is a drawing showing the top (opening) of the end plate in the finished thin bar stock of this application.
[0041] Figure 17 A diagram showing a water quenching tank with increasing groove width is provided for this application.
[0042] Figure 18 For this application Figure 17 Diagram showing the distribution of water quenching capacity in the water quenching tank.
[0043] Figure 19 This diagram shows the locations of the output section and the water-quenching section for the finished fine bar stock of this application.
[0044] Figure 20 For this application Figure 19 Enlarged view of the structure at point B (the output section and water-quenched section of the finished thin bar are squeezed and enlarged by the pushing action).
[0045] Figure 21 A diagram showing the support rollers installed in the water quenching tank of this application.
[0046] Figure 22 The water quenching tank is shown in the slope diagram for this application.
[0047] Figure 23 A diagram showing an accumulation tank set on one side of the water quenching tank in this application.
[0048] Figure 24 This illustration shows the retrieval of the finished thin rod using a retrieval rope, as per this application.
[0049] Figure 25 A physical illustration shows the connection between the water quenching tank and the multi-roll mill in this application.
[0050] Figure 26 This is a water-quenching scene illustration of the finished fine bar stock of this application.
[0051] Figure 27 The second illustration shows the water quenching process of the finished fine bar stock of this application.
[0052] Figure 28 This is a test report for the titanium alloy bar prepared in Example 1 of this application.
[0053] Figure 29 This is an enlarged image of 99051-z-200.JPG from the test report of Example 1 of this application.
[0054] Figure 30 This is a test report for the titanium alloy bar prepared in Example 3 of this application.
[0055] Figure 31This is a test report for the titanium alloy bar prepared in Example 6 of this application.
[0056] Figure 32 Test report for the titanium alloy bar prepared for Comparative Example 1.
[0057] Figure 33 This is an enlarged view of test result 39282-1 from Comparative Example 1's test report.
[0058] Figure 34 Test report for the titanium alloy bar prepared for Comparative Example 3.
[0059] Figure 35 Test report for the titanium alloy bar prepared for Comparative Example 5.
[0060] Figure 36 This is a diagram of a traditional offline water quenching process (Comparative Example 2-3: Offline transport and water quenching method after rolling).
[0061] In the diagram: 1-Multi-roll mill; 11-Rolling roll; 1a-Rolling chamber; 21-Titanium alloy coarse bar; 22-Finished fine bar; 3-Water quenching tank; 3a-Water inlet; 3b-Water outlet; 31-Sealing end plate; 31a-Perforation; 32-Blocking plate; 33-Bracket; 4-Supporting roller; 5-Accumulation trough; 51-Inclined plate; 52-Vertical baffle; 6-Retrieving rope; 7-Guide pipe. Detailed Implementation
[0062] To enable those skilled in the art to better understand the technical solutions of this application, the technical solutions of this application will be further described below in conjunction with the accompanying drawings and embodiments.
[0063] See attached document Figures 1-35 The grain refinement process for improving the fatigue strength of titanium alloy bars for medical devices, as shown, includes the following steps:
[0064] S1. The titanium alloy coarse bar 21 (TC4, widely used in the manufacture of titanium bone nails, is selected in this application, but forged square bar can also be used) after being heated in the furnace is continuously rolled into a finished fine bar 22 with an outer diameter of 16mm through a multi-roll mill 1. The output temperature is usually 920~950℃. The heating temperature is usually 1000~1200℃. In this process, the temperature is heated to 1150~1200℃. This is because the outer diameter of the final finished fine bar 22 is small, the rolling time is long, and the temperature drop of the output bar after rolling is not too large. At this temperature, the coarse bar is fully β-formed and does not burn.
[0065] The reason why the rolling output temperature is controlled at 920~950℃ in this process is that: below 920℃, the phase transformation driving force is insufficient, and the grains are difficult to refine; above 950℃, the β grains coarsen rapidly, and subsequent water quenching cannot effectively refine them. Therefore, this application limits the rolling output temperature to serve as the basis for the final water quenching grain refinement. The furnace exit temperature of the titanium alloy coarse bar 21 is usually constant to avoid changes in the properties of the titanium alloy due to excessively high temperatures. The rolling output (final) temperature is related to changes in ambient temperature, but it cannot be lower than 920℃, otherwise the rolling effect will be affected.
[0066] Multi-roll mill 1 Figure 1-2 The structure shown comprises multiple sets of rolling rolls 11 forming rolling cavities 1a with progressively decreasing rolling apertures. Heated coarse bar stock is rolled sequentially from the largest rolling cavity 1a to the smallest rolling cavity 1a into finished fine bar stock 22. The rolling process is as follows: Figure 2 As shown.
[0067] S2, such as Figure 4 , 11 As shown, a water quenching tank 3 is provided on one side of the multi-roll mill 1, with a support 33 at its bottom. The water quenching tank 3 is arranged along the entire length of the finished thin bar 22 in the output direction and corresponds to the axial direction of the finished thin bar 22. The length of the water quenching tank 3 is designed to allow the finished thin bar to move continuously within the water quenching tank 3 and be cooled to a temperature at which grain growth ceases. This temperature is preferably ≤80℃ in this process. After the finished thin bar 22 is output from the multi-roll mill 1, it enters the water quenching tank 3 from one end. The continuous output of the finished thin bar 22 allows it to move continuously forward in the water quenching tank 3 for water quenching until the temperature at which grain growth ceases is reached.
[0068] Titanium alloys can achieve a cooling rate of >100℃ / s during the high-temperature stage of rolling output. The water used for quenching is room temperature water, but the water temperature is not higher than 25℃. If the temperature is higher than 25℃, refrigeration is required. The cooling rate at the end of the cooling process can also reach 50℃ / s. Therefore, based on the requirement of water quenching to ≤80℃ and water quenching time of 10~15s, the length of the water quenching tank 3 in this application is set to be greater than about 25m according to the output speed of the multi-roll mill. The length can meet the water quenching requirements. When the finished thin bar 22 enters from one end of the water quenching tank 3 to the other end, it is water quenched to the temperature at which the grains no longer grow (≤80℃).
[0069] Based on the above conditions, the output speed of the multi-roll mill and the length of the water quenching tank 3 are set according to the condition that the finished thin bar 22 is cooled to ≤80℃ in a water quenching time of 10~15s.
[0070] S3, such as Figure 11As shown, after the finished thin bar 22 is output from the multi-roll mill 1, its end immediately enters the water quenching tank 3 to begin water quenching. The finished thin bars 22 subsequently output from the multi-roll mill 1 also continuously enter the water quenching tank 3 for water quenching until all the finished thin bars 22 that have been rolled are submerged in the water quenching tank 3 for water quenching.
[0071] S4. After the finished fine bar 22 is completely submerged for a certain period of time, it is rapidly cooled from the rolling high temperature to below 80°C (below this temperature, grain growth and coarsening will no longer occur), and then it is taken out of the water quenching tank 3. At this point, the grain refinement of the titanium alloy bar is completed.
[0072] The grain refinement process disclosed in this application integrates rolling and water quenching into a single process, enabling uninterrupted online water quenching after rolling and changing the current offline processing mode. In this integrated structure, the rolling discharge temperature reaches the phase transformation refinement temperature, and the finished fine bar 22 immediately enters a water bath for rapid water cooling. This locks in rolling deformation, refines the microstructure, inhibits grain recrystallization and growth, and regulates disordered crystal orientation, achieving ordered crystal orientation and extremely refined grains. This process is particularly suitable for preparing medical titanium alloy bars with a diameter of 20 mm or less.
[0073] The phase transformation rolling temperature of titanium alloys is greater than 900℃. During rapid cooling via water quenching, the quenching water is immediately heated, causing its temperature to rise rapidly. This rapid temperature rise in the quenching water affects the rapid cooling of the finished thin bar 22. Therefore, if... Figure 4-5 As shown, the water quenching tank 3 has an inlet 3a on one side and an outlet 3b on the other side. By continuously supplying cooling water, the water quenching tank 3 is made to flow water, so that the water quenching water will not continue to heat up, ensuring the rapid water cooling effect of the finished fine bar 22 and effectively inhibiting the growth of grains.
[0074] When rolling titanium alloy coarse bars into finished thin bars 22 with an outer diameter of less than 20 mm, the length of the finished thin bars 22 is usually 50-60 m or more. Therefore, the finished thin bars 22 enter the water quenching tank 3 from the end to the tail end for continuous water quenching, and are also water quenched for a certain period of time after being completely submerged. Therefore, in order to further improve the water quenching effect and production efficiency (without affecting subsequent continuous rolling + water quenching), such as... Figure 4 , 11 As shown, the water inlet 3a is located away from the multi-roll mill 1, while the water outlet 3b is close to the multi-roll mill. This structural orientation ensures that the water flow direction in the water quenching tank 3 is opposite to the output direction of the finished fine bar 22. That is, the water newly added to the water quenching tank 3 through the water inlet 3a comes into contact with the finished fine bar 22, achieving a certain "forced" water quenching effect, thereby increasing the water quenching effect of the finished fine bar 22 and increasing production efficiency.
[0075] like Figures 5-6 As shown, the water quenching tank 3 has a V-shaped cross-section structure, with sealing end plates 31 at both ends. The purpose of designing the water quenching tank 3 with a V-shaped cross-section is as follows: the high rolling temperature of the finished thin bar 22, upon contact with the water quenching water, rapidly heats the water, ensuring the finished thin bar 22 is completely submerged during water quenching, thus placing it at the bottom of the water quenching tank 3, meaning the heated water quenching water is also primarily located at the bottom. Figure 9 As shown, based on the fluidity of cold and hot water, the water at the bottom of the tank will flow upwards and mix with the cold water. The mixing efficiency will affect the water quenching effect (a slow mixing rate will cause the hot water around the finished thin bar 22 to heat up further, preventing it from cooling down quickly to below the temperature where grain growth ceases, resulting in some degree of grain growth; a fast mixing rate will prevent the hot water around the finished thin bar 22 from heating up quickly, achieving effective water quenching and cooling, lowering its temperature to below the temperature where grain growth ceases). Therefore, if... Figure 10 As shown, by setting the water quenching tank 3 into a V-shaped cross-section structure, the width of the tank gradually increases from bottom to top. This accelerates the upward flow of hot water around the finished thin bar 22 and its mixing with cold water, ensuring a rapid water quenching cooling effect and preventing grain regrowth. At the same time, the enlarged opening also facilitates heat dissipation of the quenching water, preventing the continuous accumulation of water temperature.
[0076] If the overall rolling length of the finished fine bar 22 is greater than the length of the water quenching tank 3, and there is no space in the workshop to install a longer water quenching tank 3, after the front end of the finished fine bar 22 reaches the sealing end plate 31 at the outer end of the water quenching tank 3 during the water quenching process, the end of the finished fine bar 22 can be manually guided out of the outside of the water quenching tank 3, so that the rear part of the finished fine bar 22 can still be continuously output and water quenched. The length of the water quenching tank 3 should be sufficient to allow the finished fine bar 22 to be cooled to a temperature at which grain growth ceases within the length of water quenching from one end to the other. Thus, even if the overall length of the finished fine bar 22 is greater than the water quenching tank 3, the portion of the finished fine bar 22 extending out of the water quenching tank 3 will also achieve the water quenching effect of preventing grain growth.
[0077] The finished thin bar stock 22 produced by rolling will show Figure 12 The wobbling in the middle prevents it from quickly entering the water quenching tank 3 for water quenching. Therefore, to solve this problem, such as... Figure 13 As shown, a guide tube 7 is provided on the multi-roll mill 1. The inner end of the guide tube 7 is connected to the rolling chamber 1a from which the finished fine bar 22 is output, and the other end extends into the water quenching tank 3, so that the output finished fine bar 22 can quickly enter the water quenching tank 3 for water quenching, thus avoiding grain growth.
[0078] like Figure 13As shown, after the water quenching tank 3 is blocked on both sides by the sealing end plates 31, the rolled finished thin bar 22 needs to enter the water quenching tank 3, making the water quenching tank 3 lower than the output height of the finished thin bar 22. The finished thin bar 22, after being output from the multi-roll mill 1, bends downwards under gravity and falls into the water quenching tank 3 for water quenching. This causes the output finished thin bar 22 to bend, affecting its straightness accuracy. Therefore, to solve this problem, such as... Figure 14 As shown, the sealing end plate 31 near the water outlet 3b has a through hole 31a directly opposite the output of the finished thin bar 22, allowing the rolled finished thin bar 22 to enter the water quenching tank 3 in a straight line for water quenching (the guide tube 7 can also be set as a straight cylinder structure), solving the problem of gravity bending and ensuring the high-precision processing requirements of medical titanium alloy bars. In actual production, this can eliminate or speed up the subsequent straightening process and reduce processing costs.
[0079] When the length of the finished thin bar 22 rolled above is greater than the length of the water quenching tank 3, and it is necessary to take out the part of the finished thin bar 22 that extends out of the water quenching tank 3, since the part of the finished thin bar 22 that extends out of the water quenching tank 3 has been water quenched to the temperature at which the grains no longer grow, even if the part taken out is not at the same height as the part that is being water quenched, under the combined effect of the current temperature, the plate with an outer diameter of less than 20 mm processed in this application, and the relatively shallow water quenching tank 3, the front section of the finished thin bar 22 will not be bent (even if there is a slight bend, a straightening operation is usually performed later).
[0080] During the interval when the finished thin bar 22 does not enter the water quenching tank 3 through the piercing hole 31a (during the rolling of two adjacent finished thin bars 22), the quenching water will flow out through the piercing hole 31a, resulting in insufficient replenishment during subsequent water quenching. Therefore, to solve this problem, such as Figures 15-16 As shown, a blocking plate 32 is hinged to the inner side of the blocking end plate 31. When the finished thin bar 22 has not entered the water quenching tank 3, it rotates under gravity and adheres to the inner wall of the blocking end plate 31 to block the perforation 31a. The water quenching water also provides a pressing effect, preventing the rapid loss of the quenching water. When the finished thin bar 22 enters the perforation 31a, it pushes the blocking plate 32 to open and enter the water quenching tank. The finished thin bar 22 achieves a certain degree of "blocking" of the opened perforation 31a (the diameter of the perforation 31a is preferably slightly larger than the outer diameter of the finished thin bar 22. The quenching water flowing out from the gap between the two can be replenished by increasing the flow rate through the water inlet 3a until the water level can cover the finished thin bar 22). After the finished thin bar 22 has completely entered the water quenching tank 3, the blocking plate 32 seals the perforation 31a by gravity. Preferably, a torsion spring (not shown in the figure) is provided at the hinge of the blocking plate 32, and the torsion spring mechanically drives the blocking plate 32 to seal the perforation 31a.
[0081] The finished thin bar 22 experiences the greatest temperature drop upon initial contact with the quenching water. Therefore, the water temperature on the outlet 3b side is consistently higher than that on the inlet 3a side. The temperature of the finished thin bar 22 continuously decreases from the outlet 3b side towards the inlet 3a side. To prevent the water temperature on the outlet 3b side from accumulating and increasing, such as... Figure 17-18 As shown, the width of the water quenching tank 3 gradually increases from the inlet 3a towards the outlet 3b. This structure increases the cross-sectional area of the water quenching tank 3 near the outlet 3b, allowing it to hold more quenching water. Combined with the mixing of hot and cold water, the increased amount of cold water in the quenching water further enhances the mixing and displacement with the hot water, ensuring sufficient water quenching and cooling of the rolled high-temperature finished fine bar 22 and preventing the water temperature from accumulating and rising on that side. The increased tank width also enlarges the opening of the water quenching tank 3 on the outlet 3b side, accelerating the dissipation of water temperature.
[0082] Furthermore, the sidewall of the water quenching tank 3 can also achieve a certain heat dissipation effect. Therefore, in this application, the wall thickness of the water quenching tank 3 is progressively thinner towards the water outlet 3b (not shown), which accelerates the dissipation of water temperature on the water outlet 3b side. Thus, this application achieves the overall guarantee of the water quenching effect of the finished fine bar 22 through the opposing water flow, the V-shaped groove, the increase in groove width towards the water outlet 3b side, and the decrease in wall thickness towards the water outlet 3b side, avoiding the problem of grain regrowth caused by the cumulative increase in water temperature.
[0083] Currently, the length of finished thin bars 22 with an outer diameter of less than 20mm can reach 50-60m or more. From the moment the front end exits the multi-roll rolling mill until its tail end enters the water quenching tank 3, the pushing length of the finished thin bar 22 continuously increases. That is, the tail end of a 50-60m long finished thin bar 22 needs to push a section approximately less than 50-60m long. In other words, the length of the pushing body of a single finished thin bar 22 increases consistently from the start of rolling output. This increased length leads to an increased pushing weight, and simultaneously increases the friction between the pushing body and the inner wall of the water quenching tank 3. After the finished thin bar 22 is rolled and detached from the rolling chamber 1a but before water quenching, it is in a high-temperature phase transformation state and is in a suspended, un-water-quenched, soft state. This results in a corresponding increase in the pushing force as the front end length increases, making the high-temperature rolled portion detached from the rolling chamber 1a and unquenched highly susceptible to problems such as extrusion bending and enlarged bulges. Figures 19-20 As shown, for example, the finished thin bar 22 with an outer diameter of 20mm has a slightly larger outer diameter, so the extrusion bending and expansion parts are located in the rear section; while for bars with an outer diameter of less than 10mm, the extrusion bending and expansion parts are located in the front section of the bar, which affects the consistency of the outer diameter of the bar.
[0084] Although this application includes a guide tube 7 between the output and water quenching stages to straighten the bar stock, the pushing force of the bar stock itself causes the high-temperature portion within the guide tube 7 to still expand and become compressed, resulting in jamming on the outer wall of the guide tube 7 and affecting the rolling output of the bar stock. Therefore, to solve the above problems, such as Figure 21 As shown, the water quenching tank 3 is equipped with support rollers 4 at intervals. These support rollers 4 can receive the output finished thin bars 22 and roll forward under the output pushing action. This effectively overcomes the problem of contact friction with the inner wall of the water quenching tank 3 and the problem of continuously increasing pushing resistance, that is, it avoids the problem of extrusion, bending and enlargement of the finished thin bars 22 at the rear. Furthermore, a drive motor (not shown in the figure) can be installed on the support rollers 4. The drive motor pulls the finished thin bars 22 to move, which can further avoid the problem of extrusion and enlargement.
[0085] After passing through the aforementioned support roller 4, the pushing friction of the finished thin bar 22 is effectively reduced. However, during continuous horizontal pushing, the length of the finished thin bar 22 increases, and its pushing weight also continuously increases, resulting in an increase in the pushing force. Therefore, to further solve this problem, such as... Figure 22 As shown, the water quenching tank 3 is inclined, with the inlet pipe 3a side lower and the outlet pipe 3b side higher, forming a slope. This slope is preferably no greater than 5°. The specific setting is based on the overall length of the finished thin bar 22 and the length of the water quenching tank 3. The setting is required to ensure that the quenching water does not overflow from the outlet pipe 3b side, while simultaneously covering the finished thin bar 22 placed on the support roller 4. With this inclined structure, compared to the horizontal pushing of the finished thin bar 22, the force of gravity in the inclined state is also inclined downwards. Combined with the rolling of the support roller 4, this significantly reduces the pushing force on the bar, thus solving the problem of increased compression between output and water quenching.
[0086] Similarly, the water quenching tank 3 can be kept horizontal, while the height of the support rollers 4 can be set to a slope to achieve the same effect. This setting is not shown in the diagram.
[0087] Bar rolling is typically a continuous production process (each furnace requires heating several titanium alloy rough bars 21). Once one bar is rolled, the next is rolled immediately. Therefore, the finished thin bars 22, after water quenching, need to be retrieved from the water quenching tank 3. However, when retrieving finished thin bars 22 longer than 10m from one end, it is inconvenient to place them in the production workshop. Furthermore, when placed on the ground, their excessive length causes localized bending due to gravity, which is difficult to reverse if the bending is too large. Therefore, to solve this problem, such as... Figure 23As shown, a stacking trough 5 is provided on one side of the water quenching tank 3. The stacking trough 5 is composed of an inclined plate 51 and a vertical baffle 52 on one side of the inclined plate 51. The other side of the inclined plate 51 is connected to the top edge of one side of the water quenching tank 3. After water quenching, the finished thin bars 22 are driven up the side wall of the water quenching tank 3 at multiple positions to the inclined plate 51, and then roll down the inclined surface of the inclined plate 51 to the vertical baffle 52 to accumulate, realizing rapid removal after water quenching without affecting the subsequent water quenching process of the finished thin bars 22.
[0088] The finished thin bar stock 22, after water quenching, still has a relatively high temperature compared to the human body. Therefore, to avoid burns from high temperatures, such as... Figures 23-24 As shown, a retrieval rope 6 (which can be a thin steel wire rope and may have a rubber pull ring at the lifting end) is distributed between adjacent support rollers 4. One end of the retrieval rope 6 is connected to the junction of the inclined plate 51 and the water quenching tank 3, while the other end hangs down to the outside of the water quenching tank 3. The middle part of the retrieval rope 6 falls naturally into the water quenching tank 3. After water quenching is completed, the retrieval rope 6 is lifted, causing the finished thin bar 22 to be lifted up and roll into the accumulation tank 5.
[0089] Based on the above processes and specific implementation methods, the process and results of this application's preparation by multiple water quenchings and reverse (comparative) preparation are compared as shown in Table 1 below:
[0090]
[0091]
[0092] Table 1
[0093] Note: The correspondence between metallographic rating and grain size is based on Table 2 below:
[0094]
[0095] Table 2
[0096] Fatigue strength = tensile strength × fatigue coefficient. The fatigue coefficient values for different metallographic ratings are based on Table 3 below:
[0097]
[0098] Table 3
[0099] The basic principle of this application is as follows: a water quenching tank 3 forming an integral structure is set on one side of the multi-roll mill 1. After the finished fine bar 22 is rolled out, it immediately enters the water quenching tank 3 for rapid cooling. The length of the water quenching tank 3 is sufficient to completely submerge the rolled fine bar 22 for water quenching. After water quenching to the temperature at which no more grain growth occurs, it is retrieved and stacked in the side accumulation tank 5. Then, the water quenching operation of the next finished fine bar 22 is carried out.
[0100] The foregoing has shown and described the basic principles, main features, and advantages of this application. Various changes and modifications may be made to this application without departing from its spirit and scope of protection, and all such changes and modifications fall within the scope of protection claimed in this application.
Claims
1. A grain refinement process for improving the fatigue strength of titanium alloy bars for medical devices, characterized in that, Includes the following steps: S1. The titanium alloy coarse bar material after being heated in the furnace is continuously rolled into finished fine bars with a diameter ≤Ø20mm through a multi-roll mill and output at an output temperature of 920~950℃. S2. A water quenching tank is provided on one side of the multi-roll mill. The water quenching tank is arranged along the output direction of the finished thin bar and is corresponding to the axial direction of the finished thin bar. The length of the water quenching tank is such that the finished thin bar enters the water quenching tank and moves continuously to cool down to the temperature at which the grains no longer grow. The temperature is ≤80℃. S3. After the finished thin bar is output from the multi-roll mill, its end immediately enters the water quenching tank to start water quenching, with a water temperature of <25℃; and the finished thin bars subsequently output from the multi-roll mill also continuously enter the water quenching tank for water quenching until all the finished thin bars that have been rolled are submerged in the water quenching tank for water quenching. S4. The finished thin rods are water-quenched to ≤80℃ and then taken out of the water quenching tank. At this point, the grain refinement of the titanium alloy rods is completed.
2. The grain refinement preparation process according to claim 1, characterized in that: The water quenching tank has an inlet on one side and an outlet on the other side, so that the water quenching tank is filled with flowing water.
3. The grain refinement preparation process according to claim 1, characterized in that: The water inlet is located away from the multi-roll mill, while the water outlet is close to the multi-roll mill, so that the water flow direction in the water quenching tank is opposite to the output direction of the finished fine bar.
4. The grain refinement preparation process according to claim 2 or 3, characterized in that: The water quenching tank has a V-shaped cross-section structure, with sealing end plates at both ends.
5. The grain refinement preparation process according to claim 4, characterized in that: The sealing end plate near the outlet of the water pipe has a through hole that is directly opposite to the output of the finished thin rod. A plug plate is hinged to the inner side of the sealing end plate, and the plug plate can seal the through hole.
6. The grain refinement preparation process according to claim 4, characterized in that: The width of the water quenching tank gradually increases from the water inlet to the water outlet.
7. The grain refinement preparation process according to claim 5 or 6, characterized in that: The water quenching tank is provided with support rollers at intervals, which cause the finished thin bar to roll forward.
8. The grain refinement preparation process according to claim 7, characterized in that: A stacking trough is provided on one side of the water quenching tank. The stacking trough is composed of an inclined plate and a vertical baffle on one side of the inclined plate. The other side of the inclined plate is connected to the top edge of one side of the water quenching tank.
9. The grain refinement preparation process according to claim 8, characterized in that: A retrieval rope is distributed between adjacent support rollers. One end of the retrieval rope is connected to the junction of the inclined plate and the water quenching tank, while the other end hangs down to the outside of the water quenching tank, and the middle part of the retrieval rope falls naturally into the water quenching tank.