CoCr-based alloy pipe and method for manufacturing the same

Abstract

The application relates to the alloy processing technical field, in particular to a CoCr-based alloy pipe blank and a preparation method thereof. The preparation method of the CoCr-based alloy pipe blank comprises the following steps: performing bottom argon blowing on CoCr-based alloy liquid after high-temperature refining treatment to remove inclusions, then performing vacuum horizontal continuous casting to obtain a continuous casting blank; and then performing punching forming to obtain the CoCr-based alloy pipe blank; wherein, in the bottom argon blowing, the argon bubble diameter is 3-6 mm; and the argon flow Q satisfies: d max = 0.35 (Q 2 / g) 0.2 The application adopts the vacuum horizontal continuous casting bottom casting technology to perform purification treatment on the high-temperature melt, and is supplemented with bottom argon blowing in the smelting process, so that the inclusions are fully floated and captured; the purified alloy liquid is continuously cast and formed into a high-purity mother alloy continuous casting blank in a water-cooled crystallizer; and finally, the high-quality CoCr-based alloy pipe blank is prepared through machining and punching.

Description

Technical Field

[0001] This invention relates to the field of alloy processing technology, and in particular to a CoCr-based alloy tube blank and its preparation method. Background Technology

[0002] CoCr-based alloys are commonly used medical metallic materials in clinical practice. Due to their good biocompatibility and corrosion resistance, they are particularly suitable for fabricating long-term implants with stringent in vivo load-bearing conditions, such as cardiovascular stents, knee and hip joint replacement prostheses, etc. Seamless CoCr-based alloy tubes used for cardiovascular stents typically have a specified outer diameter. With a wall thickness of 0.05–0.3 mm and small dimensions, the presence of inclusions has a more significant impact on the performance of seamless tubes than ordinary seamless tubes. Inclusions larger than 50 μm can often cause penetrating defects during tube wall formation, leading to localized stress concentration and tube manufacturing failure. These inclusions often originate from the master alloy billet used and persist throughout the product's lifecycle, severely degrading the final product's performance. Therefore, standards for surgical implant CoCr-based alloys, such as ASTM F90 and ISO 5832-5, clearly specify inclusion content: according to the inclusion rating standard ASTM E45, the content of different types of non-metallic inclusions in medical CoCr-based alloys must not exceed grade 0. Furthermore, since the main inclusion types in CoCr-based alloys are CrN, Cr2O3, and SiO2, and these inclusions form at low temperatures (precipitation temperatures around 1100–1200℃), the high viscosity of the alloy liquid at low temperatures makes it difficult for inclusions to float, further increasing the difficulty of preparing high-purity CoCr-based alloy billets. Therefore, in order to improve the purity of alloys, a number of new technologies have been developed in recent years for purification smelting, including: duplex / triplex smelting process, EBCHR electron beam cold hearth furnace technology, and CaO / Y2O3 novel crucible melting technology, etc. However, these technologies have problems such as complex operation processes and high preparation costs.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] One objective of this invention is to provide a method for preparing CoCr-based alloy tube blanks, thereby solving the technical problems existing in the prior art, such as the difficulty in preparing high-purity CoCr-based alloy tube blanks.

[0005] Another object of the present invention is to provide a CoCr-based alloy tube blank that can be used for the subsequent finishing of seamless tubes for cardiovascular stents.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] The preparation method of CoCr-based alloy tube blank includes the following steps:

[0008] The CoCr-based alloy liquid after high-temperature refining is subjected to bottom blowing argon to remove inclusions, and then vacuum horizontal continuous casting is performed to obtain a continuous casting billet; then it is punched and shaped to obtain a CoCr-based alloy tube billet.

[0009] In the bottom-blown argon, the argon bubble diameter is 3-6 mm; the argon flow rate Q satisfies:

[0010] d max =0.35(Q) 2 / g) 0.2 ;d max ρ is the maximum diameter of the bubble after growth in the alloy melt, and g is the gravitational acceleration of 9.8 m / s². 2 .

[0011] In the preparation method of this invention, based on the purification of vacuum horizontal continuous casting, further purification is achieved by bottom blowing argon. Certain bottom blowing argon parameters are used: on the one hand, small-diameter bubbles are employed to increase the probability of the bubbles capturing inclusion particles; on the other hand, a larger argon flow rate is used to increase the swirling flow field distribution in the alloy melt, promoting the floating of inclusions.

[0012] In a specific embodiment of the present invention, the argon flow rate in the bottom-blown argon is 21-25 L / min.

[0013] In a specific embodiment of the present invention, d max Satisfy: d b =0.25d max ;d b This represents the diameter of the argon gas bubble. Specifically, d max It is 12-24mm.

[0014] In a specific embodiment of the present invention, in the bottom-blown argon, the diameter d of the air inlet hole of the permeable brick is... b.in satisfy: Where, σ st D represents the surface tension of the alloy liquid. n Q is the diameter of the permeable brick. g ρ is the argon flow rate. st Let g be the density of the molten alloy, and g be the acceleration due to gravity, which is 9.8 m / s². 2 Furthermore, the diameter D of the permeable brick n The thickness is 45–55 mm, such as 50 mm; the density ρ of L605 alloy liquid is between 1450–1500℃. st It is 7.2 g / cm 3 .

[0015] In a specific embodiment of the present invention, in the bottom-blown argon, the diameter d of the air inlet hole of the permeable brick is... b.in <rmax ; where r max = 2σcosθ / (ρgH); σ is the surface tension of the alloy liquid, θ is the wetting angle of the alloy liquid on the permeable brick, ρ is the density of the alloy liquid, H is the depth of the alloy liquid, and g is the acceleration due to gravity 9.8 m / s². 2 .

[0016] In a specific embodiment of the present invention, the bottom blowing argon time is 20-30 minutes, followed by a heat preservation time of 5-6 minutes. This is to ensure that inclusions in the alloy melt float to the surface sufficiently.

[0017] In a specific embodiment of the present invention, in the vacuum horizontal continuous casting, the continuous casting temperature, the billet pulling speed and the cooling rate are adjusted so that the surface temperature of the continuously cast billet at the crystallizer outlet is 1150 to 1200°C.

[0018] In a specific embodiment of the present invention, during the vacuum horizontal continuous casting, the continuous casting process parameters are dynamically adjusted according to the surface condition of the continuously cast billet. The adjustment principle is as follows: after entering the continuous casting stage, as the internal ambient temperature of the crystallizer increases, to avoid steel leakage, the billet pulling speed is reduced and the cooling water volume is increased, and the surface temperature of the continuously cast billet at the crystallizer outlet is controlled between 1150 and 1200°C. Specifically, it is reduced to 90% of the initial casting pulling speed and gradually increased to 1.5 times the cooling water volume during the initial casting stage.

[0019] In a specific embodiment of the present invention, within 5 to 10 minutes before the end of the continuous casting stage, the continuous casting speed is appropriately increased or the cooling water volume is reduced according to the temperature of the continuously cast billet, in order to avoid a significant drop in the temperature of the continuously cast billet.

[0020] In a specific embodiment of the present invention, the diameter of the continuously cast billet is 50-60 mm.

[0021] In a specific embodiment of the present invention, the CoCr-based alloy is L605 alloy. Furthermore, in the vacuum horizontal continuous casting, the casting temperature is 1400–1480°C, the circulating cooling water is 5–10 t / h, and the billet pulling speed is 0.6–1.4 m / min.

[0022] In a specific embodiment of the present invention, the temperature of the alloy liquid during bottom blowing of argon is 1450-1500°C.

[0023] The present invention also provides a CoCr-based alloy tube blank prepared by any of the above-described methods.

[0024] In a specific embodiment of the present invention, the straightness of the CoCr-based alloy tube blank is ≤5mm / 500mm, and the concentricity is less than 0.2mm.

[0025] In a specific embodiment of the present invention, the content of inclusions with a size greater than 50 μm in the CoCr-based alloy tube blank is less than 2 mg / 10 kg.

[0026] In a specific embodiment of the present invention, the inclusion content of the CoCr-based alloy tube blank reaches level 0.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) The present invention uses vacuum horizontal continuous casting bottom casting technology to purify the high temperature melt, and bottom blowing argon is used in the smelting process to allow the inclusions to float and be captured. The purified alloy liquid is continuously cast into a high-purity master alloy continuous casting billet in a water-cooled crystallizer, and finally high-quality CoCr-based alloy tube billet is prepared by machining and drilling.

[0029] (2) The CoCr-based alloy tube blank prepared by this invention has an inclusion content of 0, which meets the standard requirements of ISO 5832-5 for inclusion content of surgical implantable metal materials and can be used for further finished product processing of seamless tubes for cardiovascular stents. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the vacuum continuous casting + bottom blowing argon process provided in an embodiment of the present invention;

[0032] Figure 2 Metallographic analysis images of inclusions in L605 tube blanks prepared in Example 1 of this invention (scale bars are all 100 μm);

[0033] Figure 3 This is a photograph of the L605 tube blank prepared in Example 1 of the present invention;

[0034] Figure 4 The image shows an intermediate tube obtained by using the L605 tube blank prepared according to Example 1 of the present invention. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0036] The preparation method of CoCr-based alloy tube blank includes the following steps:

[0037] The CoCr-based alloy liquid after high-temperature refining is subjected to bottom blowing argon to remove inclusions, and then vacuum horizontal continuous casting is performed to obtain a continuous casting billet; then it is punched and shaped to obtain a CoCr-based alloy tube billet.

[0038] In the bottom-blown argon, the argon bubble diameter is 3-6 mm; the argon flow rate Q satisfies:

[0039] d max =0.35(Q) 2 / g) 0.2 ;d max ρ is the maximum diameter of the bubble after growth in the alloy melt, and g is the gravitational acceleration of 9.8 m / s². 2 .

[0040] This invention utilizes vacuum horizontal continuous casting technology to allow low-density and large-sized inclusions in the smelting process to float to the surface of the molten alloy under buoyancy. For small-sized or high-density inclusions in the molten alloy, bottom-blowing argon technology is employed in conjunction with vacuum horizontal continuous casting. This allows the inclusions to float under the circulation of the molten alloy and the adhesion of argon bubbles, overcoming the difficulties in floating small-sized or high-density inclusions in traditional smelting processes. The fully purified molten alloy is then bottom-cast at the bottom of the molten pool and continuously solidified into a master alloy rod in a water-cooled crystallizer. Further machining and drilling are then used to obtain high-purity CoCr-based alloy billets. A schematic diagram of the specific process principle can be found in [reference needed]. Figure 1 .

[0041] In the preparation method of the present invention, certain bottom-blowing argon parameters are used. On the one hand, small-diameter bubbles are used to increase the probability of bubbles capturing inclusion particles; on the other hand, a larger argon flow rate is used to increase the distribution of the swirling flow field in the alloy liquid, which promotes the floating of inclusions.

[0042] Since the inclusions in CoCr-based alloys are mainly CrN, Cr2O3, and SiO2, these inclusions differ from high-melting-point inclusions such as Al2O3 and TiO2. They form at low temperatures, making it difficult for them to float on their own. This invention promotes their floating by bottom-blowing argon. Comparative analysis of inclusion content in large-sample electrolytic castings shows that if only vacuum horizontal continuous casting is used, the inclusion content in the billet is 3.67 mg / 10 kg. However, by adding bottom-blowing argon purification, the inclusion content in the billet can be reduced to below 2 mg / 10 kg, demonstrating a significant purification effect.

[0043] During bottom-blowing argon, on the one hand, more and finer bubbles should be obtained in the alloy melt to increase the probability of bubble capture of inclusions. However, smaller is not always better, because the rising rate of bubbles increases with increasing bubble diameter, and excessively small bubbles are unlikely to rise in the alloy melt. On the other hand, increasing the argon flow rate increases the swirling flow field distribution in the alloy melt, promoting the rise of inclusions. However, when the flow rate exceeds a certain value, as the flow rate further increases, the bubble diameter increases, the number decreases, and the probability of capturing inclusions actually decreases. Based on the inclusion movement trajectory calculation, the effective bubble diameter for inclusion removal is determined to be 3–6 mm. Further, the argon flow rate is determined according to the relationship between bubble diameter and argon flow rate in the above formula to promote inclusion rise, increase the probability of inclusion capture, and thus improve purity.

[0044] In a specific embodiment of the present invention, the argon flow rate in the bottom-blown argon is 21-25 L / min.

[0045] In different implementations, the argon flow rate can be 21 L / min, 22 L / min, 23 L / min, 24 L / min, 25 L / min, etc.

[0046] In a specific embodiment of the present invention, d max Satisfy: d b =0.25d max ;d b This represents the diameter of the argon gas bubble. Specifically, d max It is 12-24mm.

[0047] In a specific embodiment of the present invention, in the bottom-blown argon, the diameter d of the air inlet hole of the permeable brick is... b.in satisfy: Where, σ st D represents the surface tension of the alloy liquid. n Q is the diameter of the permeable brick. g ρ is the argon flow rate. st Let g be the density of the molten alloy, and g be the acceleration due to gravity, which is 9.8 m / s². 2 Furthermore, the diameter D of the permeable brickn The thickness is 45–55 mm, such as 50 mm; the density ρ of L605 alloy liquid is between 1450–1500℃. st It is 7.2 g / cm 3 .

[0048] Based on the relationship between the diameter of the air inlet hole of the permeable brick, the physical properties of the alloy liquid, and the argon flow rate, the diameter of the bottom-blown argon inlet hole is determined.

[0049] In a specific embodiment of the present invention, the air inlet of the permeable brick is located at 1 / 2 of the radius of the bottom of the crucible.

[0050] By adopting the above-mentioned configuration, the distribution of the swirling flow field in the molten alloy can be further increased, which will cause the inclusions to float to the surface and increase the probability of the inclusions being captured.

[0051] In a specific embodiment of the present invention, in the bottom-blown argon, the diameter d of the air inlet hole of the permeable brick is... b.in <r max ; where r max = 2σcosθ / (ρgH); σ is the surface tension of the alloy liquid, θ is the wetting angle of the alloy liquid on the permeable brick, ρ is the density of the alloy liquid, H is the depth of the alloy liquid, and g is the acceleration due to gravity 9.8 m / s². 2 .

[0052] Because the conditions for using permeable bricks are quite harsh, in the actual application of permeable bricks, due to the depth of the alloy liquid of about 0.8 to 1.2m, the high static pressure, and the high stirring intensity of the alloy liquid, cold steel slag often forms on the surface of the permeable bricks and is difficult to clean, which can easily lead to bottom blowing failure. By meeting the above-mentioned design requirements for the diameter of the air inlet, it can be ensured that the permeable bricks have a strong resistance to molten steel penetration and that molten steel will not rush into the pores.

[0053] In a specific embodiment of the present invention, the bottom-blowing argon time is 20-30 minutes, followed by a heat preservation period of 5-6 minutes to ensure sufficient flotation of inclusions in the alloy melt. Furthermore, the heat preservation temperature is 1450-1500°C.

[0054] In a specific embodiment of the present invention, in the vacuum horizontal continuous casting, the continuous casting temperature, the billet pulling speed and the cooling rate are adjusted so that the surface temperature of the continuously cast billet at the crystallizer outlet is 1150 to 1200°C.

[0055] Research has found that the key to the success of continuous casting lies in whether the solidified billet shell can be guaranteed to have a certain strength and the continuity of the central liquid core. Since the continuously cast billet is always in motion during the solidification process, in order to obtain a dense, crack-free continuously cast billet, it is necessary to dynamically adjust and control the continuous casting process parameters.

[0056] In a specific embodiment of the present invention, during the vacuum horizontal continuous casting, the continuous casting process parameters are dynamically adjusted according to the surface condition of the continuously cast billet. The adjustment principle is as follows: after entering the continuous casting stage, as the internal ambient temperature of the crystallizer increases, to avoid steel leakage, the billet pulling speed is reduced and the cooling water volume is increased, and the surface temperature of the continuously cast billet at the crystallizer outlet is controlled between 1150 and 1200°C. Specifically, it is reduced to 90% of the initial casting pulling speed and gradually increased to 1.5 times the cooling water volume during the initial casting stage.

[0057] In a specific embodiment of the present invention, within 5 to 10 minutes before the end of the continuous casting stage, the continuous casting speed is increased or the cooling water volume is decreased according to the temperature of the continuously cast billet, in order to avoid a significant drop in the temperature of the continuously cast billet.

[0058] In a specific embodiment of the present invention, the diameter of the continuously cast billet is 50-60 mm.

[0059] In a specific embodiment of the present invention, the CoCr-based alloy is L605 alloy. Further, in the vacuum horizontal continuous casting, the casting temperature is 1400–1480°C, the circulating cooling water flow rate is 5–10 t / h, the cooling water temperature is 30–45°C, and the billet pulling speed is 0.6–1.4 m / min.

[0060] In different embodiments, the continuous casting temperature in the vacuum horizontal continuous casting can be 1400℃, 1410℃, 1420℃, 1430℃, 1440℃, 1450℃, 1460℃, 1470℃, 1480℃, etc.; the amount of circulating cooling water can be 5t / h, 6t / h, 7t / h, 8t / h, 9t / h, 10t / h, etc.; and the billet pulling speed can be 0.6m / min, 0.7m / min, 0.8m / min, 0.9m / min, 1m / min, 1.1m / min, 1.2m / min, 1.3m / min, 1.4m / min, etc.

[0061] In actual operation, under the horizontal traction of the billet dragging system, the diameter The continuously cast billet is continuously pulled out of the crystallizer. The billet dragging system consists of two pressure rollers rotating in opposite directions. The friction between these rollers and the billet drives the billet forward. During this continuous movement, the driving force overcomes the frictional resistance and suction resistance caused by the static pressure of the molten steel, the frictional resistance caused by the billet's own weight, the frictional resistance of the roller conveyor, and the viscous resistance of the solidified molten steel. Furthermore, as the billet length increases, the frictional resistance between the billet and the roller conveyor increases. To prevent slippage, the continuously cast billet is cut online according to product size requirements. The cutting machine is controlled by a synchronous motor, maintaining the same speed and direction as the horizontal movement of the billet.

[0062] In a specific embodiment of the present invention, the preparation of the alloy liquid includes: according to the alloy element composition, increasing the power to 150-200kW for rapid melting under a vacuum degree of less than 5Pa; after complete melting, raising the temperature to 1550-1580℃ for heat preservation and refining, adding trace elements during the refining period, and stirring evenly; then raising the temperature to 150-200℃ above the alloy melting point, lowering the vacuum degree to below 3Pa, adding a deoxidizer, and carrying out a displacement reaction to form oxide slag.

[0063] In practice, raw materials for smelting are selected based on the alloy composition, with a purity greater than 99.9%. Before loading into the furnace, the surface of the raw materials is mechanically polished and ultrasonically cleaned to remove surface oxide scale and impurities. Alloying is carried out according to the elemental composition ratio. After the raw materials are loaded into the furnace, vacuum is applied and then electric heating is initiated. When the vacuum degree is below 50 Pa, a holding power of 50-100 KW is used to prevent oxidation of the raw material surface. When the vacuum degree in the furnace is below 5 Pa, the holding power is increased to 150-200 KW to rapidly melt the alloy material and complete the alloying process. After complete melting, the alloy liquid is heated to 1550-1580℃ and held at that temperature to begin refining. During the refining stage: First, active and trace elements are added a second time, and online composition detection ensures that the composition of the high-temperature melt meets the technical requirements of the alloy elements. Second, harmful gases and impurities are removed. Usually, during the refining stage, the alloy liquid is heated to 150-200℃ above the alloy melting point, and the vacuum degree is reduced to below 3Pa, so that the dissolved (O, N) in the melt volatilizes and is discharged through supersaturation to generate O2 and N2. Then, a deoxidizer is added. Through the substitution chemical reaction between the alloy elements and the deoxidizer, the content of harmful gas elements (O, N, S) in the alloy is reduced, and the purity of the alloy liquid is improved.

[0064] In a specific embodiment of the present invention, the temperature of the alloy liquid during bottom blowing of argon is 1450-1500°C.

[0065] In practice, the CoCr-based tube blanks are formed by machining according to their specifications. After forming, the purity of the tube blanks is evaluated by large-scale electrolysis and metallographic analysis to determine the inclusion content.

[0066] The present invention also provides a CoCr-based alloy tube blank prepared by any of the above-described methods.

[0067] In a specific embodiment of the present invention, the straightness of the CoCr-based alloy tube blank is ≤5mm / 500mm, and the concentricity is less than 0.2mm.

[0068] In a specific embodiment of the present invention, the content of inclusions with a size greater than 50 μm in the CoCr-based alloy tube blank is less than 2 mg / 10 kg.

[0069] In a specific embodiment of the present invention, the inclusion content of the CoCr-based alloy tube blank reaches level 0.

[0070] Example 1

[0071] This embodiment provides a method for preparing L605 alloy tube blanks, which is carried out on an 800kg vacuum horizontal continuous casting machine. The master alloy is then used to prepare L605 tube blanks through machining and drilling. The alloy composition and inclusion content of the machined tube blanks are then analyzed, specifically including the following steps:

[0072] (1) Raw material selection: Based on the elemental composition of L605 alloy, raw materials Co, Cr, Ni and W with a purity greater than 99.9% are selected and placed in the crucible. Trace raw materials C, Mn and other trace materials are placed in the secondary feeding hopper and added in the later stage of smelting.

[0073] (2) Alloying: After the crucible is loaded, a small power of 50KW is used to supply power and start vacuuming. As the vacuum level increases, the heat preservation power is continuously increased to 100KW. When the vacuum level is less than 5Pa, the heat preservation power is increased to 150-200KW to rapidly melt the alloy material. Alloying is completed when the liquid level reaches 100%.

[0074] (3) High-temperature refining: First, trace elements such as C and Mn are added during the refining period through the secondary feeding funnel of the vacuum furnace, and the elements are evenly distributed by high-power stirring. Second, harmful gases and impurities in the alloy melt are removed by raising the temperature of the alloy melt to 150-200°C above the alloy melting point and reducing the vacuum degree to below 0.5 Pa, thereby reducing the solid solubility of harmful gas elements O and N in the melt, causing them to become supersaturated and precipitate. In addition, some deoxidizers with strong affinity for O, N, and S, such as Mg, Ba, and Ca, are added to form oxide slag through displacement reaction, and further, the oxides and nitrides in the melt are floated to the surface by electromagnetic stirring.

[0075] (4) Bottom-blown argon: After refining, the temperature is lowered to between 1450 and 1500℃ to begin bottom-blown argon purification. Based on the movement trajectory of inclusions in the alloy liquid, the effective bubble size diameter for removing inclusions in the alloy liquid is 3 to 6 mm (controlled by the inlet diameter, argon flow rate, etc.). Based on formulas (1) and (2) between the argon bubble diameter and the argon flow rate, the bottom-blown argon flow rate range Q is determined to be between 21 and 25 L / min. Then, the argon flow rate Q and the diameter Dn of the permeable brick are substituted into formula (3) to estimate the diameter of the inlet of the permeable brick.

[0076] d b =0.25d max (1)

[0077] d max =0.35(Q) 2 / g) 0.2 (2)

[0078]

[0079] In the formula: d b Argon gas bubbles are 3-6 mm in diameter, d max The maximum diameter of bubbles after growth in the alloy melt is 12-24 mm, Q and Q g σ represents the argon gas flow rate; st D represents the surface tension of the alloy liquid. n For breathable bricks with a diameter of 50mm, ρ st The density of the alloy melt is approximately 7.2 g / cm³ at temperatures between 1450 and 1500°C. 3 g is the acceleration due to gravity, 9.8 m / s². 2 d b.in This refers to the diameter of the air inlet hole in the breathable brick.

[0080] To ensure that the permeable brick leaks air but not steel during bottom blowing argon, the diameter of the air inlet hole of the permeable brick should be set such that the static pressure P_static of the molten steel is greater than the additional pressure P_attached (i.e., capillary tension) exerted on the molten steel by the slit of the permeable brick. Therefore, the size of the air inlet hole of the permeable brick should satisfy formula (4). For molten steel with a depth of 800 mm, the maximum diameter of the air inlet hole of the bottom blowing argon permeable brick should not exceed 0.2 mm. However, as the depth of the molten steel further increases, the maximum pore diameter r max Smaller.

[0081] r max =2σcosθ / (ρgH) (4)

[0082] In the formula: σ is the surface tension of the alloy liquid, θ is the wetting angle of the alloy liquid on the permeable brick, ρ is the density of the alloy liquid, H is the depth of the alloy liquid, and g is the gravitational acceleration 9.8 m / s². 2 .

[0083] After determining the above bottom-blowing argon process parameters, bottom-blowing argon purification is carried out. After continuous argon blowing for 20 to 30 minutes, the temperature is held at 1450 to 1500℃ for 5 minutes to achieve full floating of inclusions in the alloy liquid.

[0084] (5) Adjustment and control of continuous casting process parameters: After thorough purification, the alloy liquid solidifies and forms through the water-cooled crystallizer at the bottom of the crucible. The key to successful continuous casting is whether the solidified billet shell can be guaranteed to have a certain strength and the continuity of the central liquid core. Based on the solidification characteristics of L605 alloy, its continuous casting process parameters are determined as follows: continuous casting temperature 1400~1480℃, circulating cooling water 5~10t / h, cooling water temperature 30~45℃ (e.g. 35℃), billet pulling speed 0.6~1.4m / min for continuous billet output. Since the continuously cast billet is constantly changing, it needs to be dynamically adjusted and controlled in real time according to the surface condition of the billet. The principle for adjusting the continuous casting process parameters is as follows: After entering the continuous casting stage, as the internal ambient temperature of the crystallizer rises, in order to avoid steel leakage, the billet pulling speed is reduced (reduced to 90% of the initial casting pulling speed), and the cooling water volume is increased (gradually increased to 1.5 times the cooling water volume of the initial casting stage). During this stage, the surface temperature of the continuously cast billet at the crystallizer outlet is controlled between 1150 and 1200℃, and the status parameters of the continuous casting process are monitored in real time. If there is a large fluctuation, remedial measures such as stopping the billet and restarting should be taken immediately. At the end of the continuous casting stage (5 to 10 minutes before the end of the continuous casting stage), the continuous casting speed is appropriately increased or the cooling water volume is reduced according to the billet temperature to avoid a significant drop in the billet temperature.

[0085] (6) Billet dragging method and continuous casting billet size control: The solidified continuous casting billet moves forward under the frictional force generated between the billet and the two counter-rotating pressure rollers of the billet dragging system, and is moved out of the crystallizer at a certain billet dragging speed. As the billet length increases, the frictional resistance between the billet and the roller table increases. In order to prevent the billet from slipping, the continuous casting billet is cut online according to the product size requirements. The cutting machine needs to be controlled by a synchronous motor to keep the horizontal movement speed and direction of the billet consistent.

[0086] (7) Machining: The obtained high-quality L605 alloy continuous casting billet is machined and drilled according to the specifications of medical CoCr base tube billet. The specifications of the machined L605 alloy tube billet are: outer diameter The wall thickness is 5-10mm, the length is 500±5mm, and the straightness of the pipe is ≤5mm / 500mm.

[0087] The preparation process of high-quality L605 tube blank was completed, and the composition of the obtained L605 tube blank is shown in Table 1. The main element composition meets the international standard requirements of ISO 5832-5 for CoCrW alloy for surgical implant metal materials, and has a low content of harmful and impurity elements.

[0088] Table 1. Elemental content (wt%) of L605 tube blank

[0089] Technical Requirements 0.05～0.15 1～2 ≤0.2 ≤0.04 ≤0.03 19～21 Measured value 0.11 1.59 0.025 ＜0.001 0.0009 20.06 element Ni W Fe O Co Technical Requirements 9～11 14～16 ≤3 ≤0.001 Remain Measured value 10.16 14.83 ＜0.5 0.0004 Remain

[0090] The inclusion content of the prepared L605 tube blank was detected by large-sample electrolysis. The results are shown in Table 2. By adopting vacuum horizontal continuous casting technology and bottom blowing argon purification smelting measures, the inclusions in the melt were fully floated to the surface under the action of buoyancy and alloy liquid circulation. The content of inclusions with a size greater than 50μm in the tube blank was less than 2mg / 10kg.

[0091] Table 2 Electrolytic inclusion content of L605 tube blank samples

[0092]

[0093] For the inclusion content of small-sized inclusions (less than 50 μm) in L605 tube blanks, metallographic observation was used to examine the inclusion content of tube blanks numbered 1# to 5#. The results are as follows: Figure 2 As shown: the maximum size of the inclusion is 2.5 μm, therefore it is rated as fine based on the inclusion width; the inclusions are almost entirely oxides, including Al, Mg, Ca, and Si, therefore, they are rated as oxides and silicates respectively when distinguishing inclusion categories. The inclusion content of the tube blank was rated according to the evaluation method of inclusion content in steel in ASTM E45-1997, and the rating results are shown in Table 3: the inclusion content of L605 tube blank obtained by using this invention reaches grade 0, which meets the standard requirements of ISO 5832-5 for inclusion content of tube blanks in surgical implant metal materials.

[0094] Table 3 Metallographic Analysis of Inclusion Content in L605 Tube Blanks

[0095] level Level 0 Level 0 Level 0 Level 0 Level 0

[0096] The L605 tube blank prepared by the method of the present invention (taking tube blank #3 as an example) is as follows: Figure 3 As shown: Outer diameter The wall thickness is 7±0.3mm, the length is 500±5mm, the straightness of the pipe is ≤5mm / 500mm, and the concentricity is less than 0.2mm. After more than 10 rolling deformation passes, an intermediate pipe with an outer diameter of 8mm and a wall thickness of 0.5mm is obtained. Figure 4 As shown: Room temperature mechanical properties of the intermediate tube (σ) b 1227MPa; σ 0.2 (σ: 632MPa; δ: 57.5%), far exceeding the mechanical property requirements for tube blanks in the ISO5832-5 2005 standard for surgical implant metal materials. b ≥860MPa; σ 0.2 ≥310MPa; δ≥30%, meeting the requirements for final cardiovascular stent preparation.

[0097] Comparative Example 1

[0098] Comparative Example 1 follows the method of Example 1, except that the bottom-blowing argon parameters are different.

[0099] The bottom-blown argon parameters for Comparative Example 1 are as follows: After refining, the temperature was lowered to 1460±10℃ to begin bottom-blown argon purification. The diameter of the bottom-blown argon permeable brick was 50mm, and the diameter of the inlet hole was controlled at 0.16mm. By controlling the argon flow rate at 20L / min, argon bubbles of 2mm size were obtained. Under the above bottom-blown argon process parameters, the largest size of small inclusions smaller than 50μm in the L605 tube blank prepared in Comparative Example 1 was 3.8μm. According to the evaluation method of inclusion content in steel in ASTM E45-1997, the inclusion content of the tube blank reached grade 0.5, which does not meet the standard requirements of ISO 5832-5 for inclusion content in tube blanks for surgical implant metal materials.

[0100] Comparative Example 2

[0101] Comparative Example 2 follows the method of Example 1, except that the vacuum horizontal continuous casting parameters are different.

[0102] The vacuum horizontal continuous casting parameters for Comparative Example 2 were as follows: continuous casting temperature 1490℃, circulating cooling water 4t / h, and billet drawing speed 0.8m / min for continuous billet output. Because the continuous casting temperature was high and the cooling water volume was low in Comparative Example 2, the L605 billet obtained during the solidification process was insufficiently cooled, resulting in significant porosity. Due to the lack of internal density, the prepared billet could not meet the metallurgical quality requirements for direct rolling deformation. During further rolling deformation, the billet was prone to rolling cracks and even breakage.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing CoCr-based alloy tube blanks, characterized in that, Includes the following steps: The CoCr-based alloy liquid after high-temperature refining is subjected to bottom blowing argon to remove inclusions, and then vacuum horizontal continuous casting is performed to obtain a continuous casting billet; then it is punched and shaped to obtain a CoCr-based alloy tube billet. In the bottom-blown argon, the argon bubble diameter is 3~6mm; the argon flow rate Q satisfies: ;d max ρ is the maximum diameter of the bubble after growth in the alloy melt, and g is the gravitational acceleration of 9.8 m / s². 2 ; In the bottom-blown argon process, the argon flow rate is 21~25 L / min; d max satisfy: ;d b The diameter of the argon gas bubble; In the bottom-blown argon process, the diameter d of the air inlet hole in the permeable brick is... b.in satisfy: ; where σ st D represents the surface tension of the alloy liquid. n Q is the diameter of the permeable brick. g ρ is the argon flow rate. st Let g be the density of the molten alloy, and g be the acceleration due to gravity, which is 9.8 m / s². 2 .

2. The method for preparing CoCr-based alloy tube blanks according to claim 1, characterized in that, The diameter D of the permeable brick n It is 45~55mm.

3. The method for preparing CoCr-based alloy tube blanks according to claim 1, characterized in that, In the bottom-blown argon process, the diameter d of the air inlet hole in the permeable brick is... b.in <r max ;in, σ represents the surface tension of the alloy liquid, θ represents the wetting angle of the alloy liquid on the permeable brick, ρ represents the density of the alloy liquid, H represents the depth of the alloy liquid, and g represents the gravitational acceleration of 9.8 m / s². 2 .

4. The method for preparing CoCr-based alloy tube blanks according to claim 1, characterized in that, The bottom blowing argon time is 20-30 minutes, and the temperature is maintained for 5-6 minutes after bottom blowing argon.

5. The method for preparing CoCr-based alloy tube blank according to claim 4, characterized in that, The insulation temperature is 1450~1500℃.

6. The method for preparing CoCr-based alloy tube blanks according to claim 1, characterized in that, In the aforementioned vacuum horizontal continuous casting, the continuous casting temperature, billet pulling speed, and cooling rate are adjusted to ensure that the surface temperature of the continuously cast billet at the crystallizer outlet is between 1150 and 1200°C.

7. The method for preparing CoCr-based alloy tube blanks according to claim 1, characterized in that, The CoCr-based alloy is L605 alloy.

8. The method for preparing CoCr-based alloy tube blank according to claim 7, characterized in that, In the aforementioned vacuum horizontal continuous casting, the continuous casting temperature is 1400~1480℃, the circulating cooling water is 5~10t / h, and the billet pulling speed is 0.6~1.4m / min.

9. The method for preparing CoCr-based alloy tube blank according to claim 7, characterized in that, During bottom blowing with argon, the temperature of the alloy liquid is 1450~1500℃.

10. A CoCr-based alloy tube blank prepared by the preparation method of any one of claims 1 to 9.

11. The CoCr-based alloy tube blank according to claim 10, characterized in that, The straightness of the CoCr-based alloy tube blank is ≤5mm / 500mm, and the concentricity is less than 0.2mm; And / or, the content of inclusions with a size greater than 50 μm in the CoCr-based alloy tube blank is less than 2 mg / 10 kg; And / or, the inclusion content of the CoCr-based alloy tube blank is grade 0.

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