A method for producing high purity iron

Abstract

This application relates to a method for preparing high-purity iron, comprising the following steps: forming an electrode rod from pure iron raw material; subjecting the electrode rod to vacuum arc melting; the vacuum arc melting includes an arc initiation stage, a melting stage, and a feeding stage; the melting current in the arc initiation stage is 1.5 kA~3.0 kA, and the arc stabilization current is 4 A~10 A; the melting current in the melting stage is 2.5 kA~3.5 kA, the melting rate is 2.5 cm / min~5.5 cm / min, and the arc stabilization current is 8 A~20 A; the melting current in the feeding stage is 1.2 kA~3.3 kA, the melting rate is 1 cm / min~4.5 cm / min, and the arc stabilization current is 4 A~11 A. This method can effectively reduce the density and refine the size of inclusions in pure iron, while also making the inclusions dispersed in the material. The high-purity iron prepared by this method has a significantly reduced inclusion density, small inclusion size, and is in a dispersed state, which meets the manufacturing requirements of iron-based supports.

Description

Technical Field

[0001] This invention belongs to the field of pure iron preparation technology, specifically relating to a method for preparing high-purity iron. Background Technology

[0002] Vascular stents can be classified into permanent stents and absorbable stents based on their duration of stay in the blood vessel. Permanent stents are made of non-degradable materials such as 316L stainless steel, platinum-chromium alloy, nickel-titanium alloy, and cobalt-chromium alloy. These stents remain in the body for life after implantation, raising concerns about late-stage safety and effectiveness, such as late-stage thrombosis and in-stent restenosis. Absorbable stents, on the other hand, gradually degrade and are absorbed by the body until they disappear completely after implantation, making them an ideal choice for treating narrowed blood vessels.

[0003] Currently, commercially available / development-under-development absorbable stents mainly include polylactic acid (PLA) stents, magnesium-based stents, iron-based stents, and zinc-based stents. Due to the inherent limitations of their materials, magnesium-based and PLA stents require larger stent sizes to achieve sufficient support for clinical applications. Therefore, these two types of stents have relatively large wall thicknesses and limited sizes, only suitable for patients with simple lesions. Zinc-based stents still face fundamental challenges related to material strength and plasticity, mechanical stability, and biocompatibility. Iron-based stents, due to their excellent mechanical properties and good biocompatibility, are an ideal choice for absorbable stents. They are made from pure iron through further processing. The strength of iron-based stents is comparable to that of permanent cobalt-chromium alloy stents, thus providing sufficient vascular support even with a very thin wall thickness. Currently, iron-based stents are gripped onto a balloon catheter before use. Once the stent reaches the target vessel, the balloon is inflated to support the narrowed vessel. After inflation, the stent strut experiences a 30-40% deformation. If there are large, numerous, and concentrated inclusions within the stent strut, abnormal stent breakage can occur during inflation, leading to premature stent failure and compromising its safety and effectiveness. Therefore, the manufacturing of iron-based stents places high or specific requirements on the characteristics of inclusions in the material, including their size, density, and distribution.

[0004] Currently, the main methods for producing high-purity iron include zone refining, electromagnetic levitation melting, and plasma arc melting. Although existing refining methods can reduce the inclusion content in pure iron to some extent, they still cannot meet the requirements of iron-based supports for the inclusions in the material (size, density, and distribution). Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention provides a method for preparing high-purity iron. This method not only effectively reduces the density and refines the size of inclusions in pure iron, but also alters the dispersion state of inclusions in the material. The high-purity iron material prepared using this method exhibits significantly reduced inclusion density, smaller size, and a dispersed state, meeting the manufacturing requirements of iron-based support structures.

[0006] The first aspect of this invention provides a method for preparing high-purity iron, comprising the following steps: Electrode rods are made from pure iron raw materials; The electrode rod is then subjected to vacuum arc melting. The vacuum arc melting includes an arc initiation stage, a melting stage, and a feeding stage; The melting current during the arc ignition stage is 1.5 kA to 3.0 kA, and the arc stabilization current is 4 A to 10 A. The melting current during the melting stage is 2.5 kA to 3.5 kA, the melting rate is 2.5 cm / min to 5.5 cm / min, and the arc stabilization current is 8A to 20A. The melting current during the feeding stage is 1.2 kA to 3.3 kA, the melting rate is 1 cm / min to 4.5 cm / min, and the arc stabilization current is 4 A to 11 A.

[0007] The high-purity iron preparation method of this application employs vacuum arc melting. By simultaneously controlling the melting current, melting rate, and arc stabilization current within specific ranges during the arc initiation, melting, and feeding stages of the melting process, the density of inclusions in pure iron can be effectively reduced, the size of inclusions can be refined, and the inclusions can be dispersed throughout the pure iron material. High-purity iron material prepared using this method, when used to manufacture iron-based supports, can significantly reduce the risk of support fracture, thereby effectively avoiding early failure caused by abnormal fracture and ensuring the long-term effectiveness and high reliability of the support.

[0008] Therefore, the inclusion size, density, and dispersion state of the high-purity iron material prepared in this application all meet the manufacturing requirements of iron-based supports.

[0009] In some embodiments, the melting current, melting rate, and arc stabilization current during the feeding stage are gradually reduced.

[0010] In some embodiments, the smelting current during the feeding stage is successively 2.3 kA ~ 3.3 kA, 1.7 kA ~ 2.5 kA, 1.4 kA ~ 1.9 kA, and 1.2 kA ~ 1.6 kA.

[0011] In some embodiments, the melting rates during the feeding stage are successively 2.3 cm / min to 4.5 cm / min, 1.7 cm / min to 3.8 cm / min, 1.3 cm / min to 3.2 cm / min, and 1 cm / min to 2.9 cm / min.

[0012] In some implementations, the arc stabilization current during the compensation stage is successively 7A~11A, 5.7A~9.7A, 4.7A~8.7A, and 4A~8A.

[0013] In some embodiments, the feeding phase begins when the remaining mass of the electrode rod is 15% to 25% of the initial mass; and the feeding phase ends when the remaining mass of the electrode is 5% to 8% of the initial mass.

[0014] In some embodiments, the vacuum arc melting is cooled by cooling water, with the inlet temperature of the cooling water being 10°C to 15°C and the outlet temperature being 30°C to 35°C.

[0015] In some embodiments, vacuum arc melting of the electrode rod includes: placing the electrode rod in a vacuum arc furnace, the vacuum arc furnace being provided with a crucible for supporting the molten pool, placing the electrode rod above the crucible and performing arc melting; the ratio of the diameter of the electrode rod to the diameter of the crucible is 0.6 to 0.85.

[0016] In some implementations, the purity of the pure iron raw material is 95% to 99.95%.

[0017] In some embodiments, the vacuum arc melting is carried out under a vacuum of ≤0.5 Pa.

[0018] A second aspect of the present invention provides a high-purity iron, which is prepared by the aforementioned method for preparing high-purity iron, wherein the inclusion density of the high-purity iron is ≤5 inclusions / mm². 2 The maximum inclusion size is ≤15μm; the shortest straight-line distance between any two inclusions is ≥100μm.

[0019] The third aspect of the present invention provides the application of the high-purity iron described above in the preparation of luminal stents, wherein the luminal stents include vascular stents, airway stents, esophageal stents, biliary stents, intestinal stents, urethral stents, nerve stents, or pancreatic stents; wherein the vascular stents include heart valve stents, coronary stents, pulmonary artery stents, renal artery stents, cone artery stents, covered stents, or peripheral stents.

[0020] Beneficial effects of this invention: The high-purity iron preparation method of this application employs a vacuum arc melting method. Vacuum arc melting sequentially proceeds through an arc initiation stage, a melting stage, and a feeding stage. By controlling the melting current, melting rate, and arc stabilization current within specific ranges at each stage, the content and density of inclusions in pure iron can be effectively reduced, and the size of inclusions can be refined. Simultaneously, the inclusions are dispersed throughout the material. High-purity iron materials prepared using this method significantly reduce the risk of support fracture when manufacturing iron-based stents, thereby effectively avoiding early failure caused by abnormal fracture and ensuring the long-term effectiveness and high reliability of the stent. Therefore, the high-purity iron material prepared in this application meets the manufacturing standards for iron-based stents.

[0021] This application, by controlling the melting current, melting rate, and the magnitude and reduction method of the arc-stabilizing current during the feeding stage, can effectively reduce the content and density of inclusions in pure iron, refine the size of inclusions, and ensure that inclusions are dispersedly distributed in the material. It also reduces the loss rate of pure iron material. Furthermore, by controlling the inlet and outlet temperatures of the cooling water, this application can further reduce the density and size of inclusions and optimize their distribution. Detailed Implementation

[0022] Exemplary embodiments of the present invention will now be described in more detail. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0023] The technical solution of this application provides a method for preparing high-purity iron, including the following steps: S100: Electrode rods are made from pure iron raw materials; S200: The electrode rod is subjected to vacuum arc melting, the vacuum arc melting including an arc initiation stage, a melting stage and a feeding stage; The melting current during the arc ignition stage is 1.5 kA to 3.0 kA, and the arc stabilization current is 4 A to 10 A. The melting current during the melting stage is 2.5 kA to 3.5 kA, the melting rate is 2.5 cm / min to 5.5 cm / min, and the arc stabilization current is 8A to 20A. The melting current during the feeding stage is 1.2 kA to 3.3 kA, the melting rate is 1 cm / min to 4.5 cm / min, and the arc stabilization current is 4 A to 11 A.

[0024] The high-purity iron preparation method of this application employs a vacuum arc melting method. Vacuum arc melting sequentially proceeds through an arc initiation stage, a melting stage, and a feeding stage. By controlling the melting current, melting rate, and arc stabilization current within specific ranges at each stage, the content and density of inclusions in pure iron can be effectively reduced, and their size refined, while simultaneously ensuring a dispersed distribution of inclusions within the material. The high-purity iron material prepared using this method significantly reduces the risk of support fracture when manufacturing iron-based supports, thereby effectively avoiding early failure caused by abnormal fracture and ensuring the long-term effectiveness and high reliability of the support. Therefore, the high-purity iron material prepared in this application meets the manufacturing requirements for iron-based supports.

[0025] In the arc-starting stage of this application, the melting current is controlled at 1.5 kA to 3.0 kA, and the arc-stabilizing current is controlled at 4A to 10A. In some other embodiments, the melting current is 2.1 kA to 3 kA, and the arc-stabilizing current is 7.5 A to 10A. In still other embodiments, the melting current is 2.5 kA to 3 kA, and the arc-stabilizing current is 8A to 10A. In specific examples, the melting current in the arc-starting stage includes, but is not limited to, 1.5 kA, 1.55 kA, 1.6 kA, 1.7 kA, 1.8 kA, 1.9 kA, 2 kA, 2.2 kA, 2.5 kA, 2.8 kA, or 3 kA. The arc-stabilizing current in the arc-starting stage includes, but is not limited to, 4A, 4.5A, 5A, 5.6A, 6A, 6.5A, 7A, 7.5A, 8A, 8.6A, 9A, 9.5A, or 10A. Understandably, this application controls the arc-starting current to be 1.5 kA ~ 3.0 kA and the arc-stabilizing current to be 4 A ~ 10 A for melting. After the molten pool stabilizes, the melting current is adjusted to 2.5 kA ~ 3.5 kA to continue melting.

[0026] In the melting stage of this application, the melting current is controlled at 2.5 kA to 3.5 kA, the melting rate is 2.5 cm / min to 5.5 cm / min, and the arc-stabilizing current is 8 A to 20 A. In other embodiments, the melting current in the melting stage is 2.9 kA to 3.5 kA, the melting rate is 2.5 cm / min to 3.2 cm / min, and the arc-stabilizing current is 14 A to 20 A. In still other embodiments, the melting current in the melting stage is 3.2 kA to 3.5 kA, the melting rate is 2.5 cm / min to 2.8 cm / min, and the arc-stabilizing current is 17 A to 20 A. In specific examples, the melting current during the melting stage includes, but is not limited to, 2.5 kA, 2.6 kA, 2.7 kA, 2.8 kA, 2.85 kA, 2.9 kA, 3.0 kA, 3.1 kA, 3.2 kA, 3.3 kA, 3.4 kA, or 3.5 kA. The melting rate during the melting stage includes, but is not limited to, 2.5 cm / min, 2.85 cm / min, 3 cm / min, 3.2 cm / min, 3.5 cm / min, 3.8 cm / min, 4 cm / min, 4.5 cm / min, 4.8 cm / min, 5 cm / min, or 5.5 cm / min. The stabilizing current during the melting stage includes, but is not limited to, 8 A, 8.5 A, 9 A, 9.6 A, 10 A, 10.5 A, 11 A, 11.5 A, 12 A, 12.3 A, 12.7 A, 13 A, 15 A, 15.5 A, 16 A, 17 A, 18 A, 19 A, or 20 A. Selecting melting current, melting rate, and stabilizing current within a specific range during the melting stage can effectively promote the removal of low-melting-point harmful impurities and inclusions, reduce the content and density of inclusion particles, and refine the size of inclusions, thereby effectively improving the purity of pure iron. It can also optimize the distribution of inclusions, allowing them to be dispersed.

[0027] The smelting current during the feeding stage of this application is 1.2 kA to 3.3 kA, the smelting rate is 1 cm / min to 4.5 cm / min, and the arc-stabilizing current is 4 A to 11 A. Excessive or insufficient smelting current, smelting rate, and arc-stabilizing current during the feeding stage will affect the inclusion content, density, size, and distribution. This application precisely controls the parameters of the feeding stage, keeping them within a specific range, thereby resulting in high-purity iron with lower inclusion content, density, smaller inclusion size, and more dispersed distribution characteristics. In specific examples, the smelting current during the feeding stage includes, but is not limited to, 1.2 kA, 1.5 kA, 1.6 kA, 1.8 kA, 2.0 kA, 2.2 kA, 2.5 kA, 2.8 kA, 3.0 kA, 3.1 kA, 3.2 kA, or 3.3 kA. The melting rate during the feeding stage includes, but is not limited to, 1 cm / min, 1.5 cm / min, 2 cm / min, 2.2 cm / min, 2.5 cm / min, 2.8 cm / min, 3 cm / min, 3.2 cm / min, 3.5 cm / min, 3.8 cm / min, 4 cm / min, 4.2 cm / min, 4.3 cm / min, or 4.5 cm / min. The arc-stabilizing current during the feeding stage includes, but is not limited to, 4 A, 4.4 A, 5 A, 5.8 A, 6 A, 6.4 A, 7 A, 7.5 A, 8 A, 8.7 A, 9 A, 9.5 A, 10 A, 10.5 A, or 11 A.

[0028] It should be noted that the parameters of the arc initiation, melting, and feeding stages of the vacuum arc melting process in this application all affect the content, density, size, and distribution of inclusions in the purified high-purity iron to a certain extent. When any parameter in any stage is outside the aforementioned range, the content, density, and size of inclusions in the pure iron material cannot be effectively reduced, nor can the distribution of inclusions be optimized. Consequently, the prepared pure iron material cannot meet the manufacturing standards and requirements for iron-based stents. Therefore, when the high-purity iron prepared in this way is used to fabricate stents, the probability of large-sized, numerous, or concentrated inclusions in the stent struts increases significantly. This increases the risk of abnormal fracture during stent expansion, which not only reduces the pass rate of stent production and increases the safety risks during clinical use but also significantly affects the effectiveness of the stent.

[0029] In some embodiments, the purity of the pure iron raw material used for the electrode rod in step S100 is 95% to 99.95%, further, the purity of the pure iron raw material is 98% to 99.95%, and even further, the purity of the pure iron raw material is 99% to 99.95%.

[0030] It should be noted that the apparatus used for vacuum arc melting is a commonly used vacuum arc melting furnace in this field, which will not be described in detail here.

[0031] In some embodiments, vacuum arc melting of the electrode rod includes: placing the electrode rod in a vacuum arc furnace, the vacuum arc furnace being provided with a crucible for supporting the molten pool, placing the electrode rod above the crucible, and performing vacuum arc melting.

[0032] In some implementations, the crucible used in vacuum arc melting is a copper crucible.

[0033] In some embodiments, the ratio of the diameter of the electrode rod to the diameter of the crucible in vacuum arc melting is 0.6 to 0.85. In other embodiments, the ratio is 0.6 to 0.7. In specific examples, the ratio is 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, or 0.85. By controlling the ratio of the electrode rod diameter to the crucible diameter within this range, this embodiment can obtain a product with a smooth cross-section.

[0034] In some embodiments, the feeding stage is performed during vacuum arc melting when the remaining mass of the electrode is 15% to 25% of the initial mass.

[0035] In some embodiments, the melting current, melting rate, and arc stabilization current during the feeding stage are gradually reduced. In this application, the melting current, melting rate, and arc stabilization current during the feeding stage are gradually reduced with a certain gradient, which can effectively improve the surface quality of the electrode tip, further reduce the content, density, and size of electrode inclusions, and optimize the inclusion distribution, so that the high-purity iron prepared has smaller inclusion density and size and more dispersed inclusion distribution.

[0036] In some embodiments, the smelting current during the feeding stage is successively 2.3 kA~3.3 kA, 1.7 kA~2.5 kA, 1.4 kA~1.9 kA, and 1.2 kA~1.6 kA. In other embodiments, the smelting current during the feeding stage is successively 2.8 kA~3.3 kA, 2 kA~2.5 kA, 1.7 kA~1.9 kA, and 1.4 kA~1.6 kA. In still other embodiments, the smelting current during the feeding stage is successively 3.1 kA~3.3 kA, 2.3 kA~2.5 kA, 1.8 kA~1.9 kA, and 1.5 kA~1.6 kA.

[0037] In some embodiments, the melting rates during the feeding stage are successively 2.3 cm / min to 4.5 cm / min, 1.7 cm / min to 3.8 cm / min, 1.3 cm / min to 3.2 cm / min, and 1 cm / min to 2.9 cm / min. In other embodiments, the melting rates during the feeding stage are successively 2.3 cm / min to 3 cm / min, 1.7 cm / min to 2.3 cm / min, 1.3 cm / min to 2.1 cm / min, and 1 cm / min to 1.8 cm / min. In still other embodiments, the melting rates during the feeding stage are successively 2.3 cm / min to 2.5 cm / min, 1.7 cm / min to 2.0 cm / min, 1.3 cm / min to 1.6 cm / min, and 1 cm / min to 1.4 cm / min.

[0038] In some embodiments, the stabilizing current during the shrinkage stage is successively 7 A ~ 11 A, 5.7 A ~ 9.7 A, 4.7 A ~ 8.7 A, and 4 A ~ 8 A. In other embodiments, the stabilizing current during the shrinkage stage is successively 9.1 A ~ 11 A, 8.2 A ~ 9.7 A, 7 A ~ 8.7 A, and 6.2 A ~ 8 A. In still other embodiments, the stabilizing current during the shrinkage stage is successively 10.8 A ~ 11 A, 9.6 A ~ 9.7 A, 8.3 A ~ 8.7 A, and 7.8 A ~ 8 A. The stabilizing current during the shrinkage stage decreases step by step in this gradient, which not only facilitates the removal of inclusions and reduces their size, but also optimizes the distribution of inclusions, making their distribution more diffuse.

[0039] In this application, the melting current, melting rate, and arc-stabilizing current in the feeding stage are gradually reduced in the aforementioned gradient. This not only reduces the inclusion content, density, and size of the electrodes and optimizes the inclusion distribution, but also reduces the loss rate of pure iron material. If the reduction gradient of the melting current, melting rate, and arc-stabilizing current in the feeding stage is too high or too low, it will not effectively reduce the inclusion content, density, and size in the pure iron material, nor will it effectively optimize the inclusion distribution. Consequently, the prepared pure iron material will not meet the manufacturing standards and requirements for iron-based stents. Therefore, the high-purity iron prepared in this way, when used to fabricate stents, has a significantly increased probability of large-sized, numerous, or concentrated inclusions in the stent struts. This increases the risk of abnormal fracture during stent expansion, reducing the stent production yield, increasing the safety risks during clinical use, and significantly affecting the stent's effectiveness. In some embodiments, during the vacuum arc melting process, the feeding stage is completed when the remaining mass of the electrode is 5% to 8% of the initial mass.

[0040] It should be noted that there is no specific limit to the melting time of each gradient in the feeding stage. The time can be the same or different, or the time can be gradually reduced. The melting current, melting rate and arc stabilization current in the feeding stage are gradually reduced according to the above gradient until the remaining mass of the electrode is 5% to 8% of the initial mass, and the feeding stage is completed.

[0041] In some embodiments, vacuum arc melting employs cooling water, with an inlet water temperature of 10°C to 15°C and an outlet water temperature of 30°C to 35°C. In other embodiments, the inlet water temperature is 12.3°C to 15°C, and the outlet water temperature is 30°C to 33.5°C. In still other embodiments, the inlet water temperature is 12.3°C to 15°C, and the outlet water temperature is 30°C to 31.4°C. In specific examples, the inlet water temperature includes, but is not limited to, 10°C, 11°C, 12°C, 13°C, 14°C, or 15°C; the outlet water temperature includes, but is not limited to, 30°C, 31°C, 32°C, 33°C, 34°C, or 35°C. By introducing cooling water into the crucible within the vacuum arc melting furnace, the crucible is effectively cooled. By controlling the inlet and outlet water temperatures within the aforementioned ranges, this embodiment can further reduce the content and density of inclusions, refine their size, and optimize their distribution. If the inlet water temperature of the cooling water is too high, it will lead to insufficient cooling of the crucible, and may even cause the crucible wall to melt through; conversely, it will lead to excessive cooling, resulting in problems such as insufficient removal of impurities, excessively large inclusions, and concentrated inclusions.

[0042] In some embodiments, the vacuum arc melting is performed at a vacuum level of ≤0.5 Pa. Further, the vacuum arc melting is performed at a vacuum level of 0.2~0.5 Pa. Controlling the vacuum level of the vacuum arc melting within this range in this embodiment is more conducive to the removal of inclusions. In specific examples, the vacuum level of the vacuum arc melting can be 0.5 Pa, 0.48 Pa, 0.45 Pa, 0.4 Pa, 0.35 Pa, 0.3 Pa, or 0.2 Pa.

[0043] In some implementation methods, after the vacuum arc melting and feeding process is completed, step S300 is also included: cooling the ingot obtained by vacuum arc melting, breaking the void, removing the ingot, and obtaining a high-purity iron ingot.

[0044] This application involves vacuum arc melting of pure iron electrode rods. The vacuum arc melting process sequentially includes an arc initiation stage, a melting stage, and a feeding stage. By controlling the melting current, melting rate, and arc stabilization current within specific ranges at each stage of the vacuum arc melting process, this application effectively reduces the content and density of inclusions in pure iron and refines the size of inclusions, while simultaneously ensuring a dispersed distribution of inclusions within the material. In this application, the melting current, melting rate, and arc stabilization current in the feeding stage are gradually reduced with a certain gradient. This effectively reduces the content and density of inclusions in the pure iron material, as well as the size of inclusions, and also reduces the loss rate of the pure iron material. The high-purity iron prepared by this method has a low loss rate and low and small inclusion content. Furthermore, this application further reduces the density and size of inclusions and optimizes their distribution by controlling the inlet and outlet temperatures of the cooling water. The high-purity iron material prepared by this method fully meets the manufacturing requirements of iron-based supports.

[0045] It should be noted that the parameters of the arc initiation stage, melting stage, feeding stage, and cooling water in the vacuum arc melting process of this application all affect the content, density, size, and distribution of inclusions in high-purity iron to a certain extent. When any parameter in any stage is outside the above range, the content, density, and size of inclusions in the pure iron material cannot be reduced effectively, nor can the distribution of inclusions be optimized. As a result, the probability of large-sized, numerous, or concentrated inclusions appearing in the stent struts of the high-purity iron prepared in this way increases significantly after the stent is fabricated. This increases the risk of abnormal fracture of the stent during expansion, which not only reduces the pass rate of stent production and increases the safety risks of stents in clinical use, but also greatly affects the effectiveness of the stent.

[0046] Another aspect of the technical solution of this application provides high-purity iron prepared by the above-described method for preparing high-purity iron, wherein the inclusion rate of the high-purity iron is ≤5 inclusions / mm. 2 The maximum inclusion size is ≤15μm; the shortest straight-line distance between any two inclusions is ≥100μm.

[0047] Another aspect of the technical solution of this application provides the use of the aforementioned high-purity iron to prepare luminal stents, which include vascular stents, airway stents, esophageal stents, biliary stents, intestinal stents, urethral stents, nerve stents, or pancreatic stents; the vascular stents include heart valve stents, coronary stents, pulmonary artery stents, renal artery stents, cone artery stents, covered stents, or peripheral stents.

[0048] The high-purity iron prepared in this application was used to fabricate iron-based lumen stents. The resulting iron-based lumen stents were expanded to their nominal diameter using a balloon, and no breakage occurred during the expansion process. The nominal diameter can be varied according to the application scenario, and can range from 2 mm to 40 mm. Specific examples include, but are not limited to, 2 mm, 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 12 mm, 15 mm, 20 mm, 25 mm, 30 mm, and 35 mm.

[0049] It should be noted that "nominal diameter" refers to the diameter of the stent when it is fully expanded under nominal pressure, "nominal pressure" refers to the pressure required to fully expand the stent in clinical practice, and "full expansion" refers to the state when the stent is expanded to match the diameter of the lumen to which it is applied.

[0050] Test methods 1. Density and size of inclusions Peel the sides of the purified ingot (3-5mm removal per side), remove the riser and base, and cut approximately 2cm from the top and bottom of the purified ingot. Take a 1cm thick circular piece from the top, middle, and bottom of the purified ingot. Then, take a rectangular sample with an area of ​​approximately 2cm × 1cm from the center, halfway from the center, and the edge in any diameter direction. Seal the samples with resin and polish them sequentially with 180, 320, 600, and 1200 grit sandpaper for 400, 300, 400, and 600 seconds, respectively. Then, switch to a cloth polishing disc and polish again for 400 seconds, 400 seconds, and 400 seconds with 6-micron and 3-micron diamond suspensions and 1-micron alumina suspension, respectively. After polishing, the sample was first rinsed with clean water, then the polished surface was cleaned with anhydrous alcohol, and finally dried with a hair dryer before being placed on the scanning electron microscope (SEM) stage. Twenty 500x lower field-view measurements were taken at each of the four corners and the center of the polished surface to observe and record the size and number of inclusions. If the inclusion size was not uniform, the distance between the two longest points on the inclusion outline was taken as the inclusion size. The inclusion density was calculated by dividing the total number of inclusions by the area being examined, with units of inclusions / mm². 2 .

[0051] 2. The distance between any two inclusions In all fields of view of the observed sample, the shortest straight-line distance connecting the edges of two inclusions is called the distance between any two inclusions. If, in all fields of view of a purified ingot being examined, no more than one inclusion is found in any field, then the inclusion spacing of this purified ingot is recorded as being greater than or equal to the length of the examination field. The following describes a method for preparing high-purity iron with specific embodiments. Those skilled in the art will understand that the preparation method described in this application is merely an example, and any other suitable preparation method is within the scope of this application.

[0052] Example 1 The method for preparing high-purity iron in this embodiment includes the following steps: S100: Electrode rods are made from pure iron with a purity of 99.95%; S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.2 Pa, the inlet temperature of the cooling water is 15 ℃, the outlet temperature of the cooling water is 30 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.6.

[0053] Arc ignition stage: Melting is carried out with an arc ignition current of 3 kA and an arc stabilization current of 10 A. After the molten pool stabilizes, the melting stage begins.

[0054] Melting stage: Melting current is 3.5 kA, melting rate is 2.5 cm / min, and arc stabilization current is 20 A.

[0055] Feeding stage: When the remaining mass of the electrode rod is 25% of the initial mass, the feeding stage begins until the remaining mass of the electrode is 5% of the initial mass.

[0056] The melting currents during the feeding stage were 3.3 kA, 2.5 kA, 1.9 kA, and 1.6 kA, respectively; the melting rates were 2.3 cm / min, 1.7 cm / min, 1.3 cm / min, and 1 cm / min, respectively; and the arc stabilization currents during the feeding stage were 11 A, 9.7 A, 8.7 A, and 8 A, respectively.

[0057] S300: After the vacuum arc melting and feeding process is completed, the ingot obtained by vacuum arc melting is cooled, the air is broken, and the ingot is removed to obtain a high-purity iron ingot.

[0058] The inclusion density of the high-purity iron prepared in this embodiment is 1.67 inclusions / mm². 2 The maximum inclusion size is 4.83 μm, and the shortest straight-line distance between any two inclusions is ≥250 μm.

[0059] The high-purity iron prepared in this embodiment was used to prepare nitrided iron alloy coronary stents. The prepared nitrided iron alloy coronary stents were expanded with balloons to nominal diameters of 2 mm, 2.5 mm, 3 mm and 4 mm, respectively. During the expansion process of their respective nominal diameters, no failure phenomena such as breakage occurred.

[0060] Example 2 The method for preparing high-purity iron in this embodiment includes the following steps: S100: Electrode rods are made from pure iron with a purity of 99.6%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting; the specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.3 Pa, the inlet temperature of the cooling water is 12.3℃, the outlet temperature of the cooling water is 31.4℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.65.

[0061] Arc ignition stage: Melting is carried out with a melting current of 2.5 kA and an arc stabilization current of 8 A. After the molten pool stabilizes, the melting stage begins.

[0062] Melting stage: Melting current is 3.2 kA, melting rate is 2.8 cm / min, and arc stabilization current is 17 A.

[0063] Feeding stage: When the remaining mass of the electrode rod is 25% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 6% of the initial mass.

[0064] The melting currents during the feeding stage were 3.1 kA, 2.3 kA, 1.8 kA, and 1.5 kA, respectively; the melting rates were 2.5 cm / min, 2.0 cm / min, 1.6 cm / min, and 1.4 cm / min, respectively; and the arc stabilization currents during the feeding stage were 10.8 A, 9.6 A, 8.3 A, and 7.8 A, respectively. S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0065] The inclusion density of the high-purity iron prepared in this embodiment is 2 inclusions / mm². 2 The maximum inclusion size is 5.29 μm, and the shortest straight-line distance between any two inclusions is ≥250 μm.

[0066] The high-purity iron prepared in this embodiment was used to prepare nitrided iron alloy peripheral vascular stents. The prepared nitrided iron alloy peripheral vascular stents were expanded with balloons to nominal diameters of 5 mm, 8 mm, 10 mm, and 15 mm. During the expansion process to the above nominal diameters, no failure phenomena such as breakage occurred.

[0067] Example 3 The method for preparing high-purity iron in this embodiment includes the following steps: S100: Electrode rods are made from pure iron with a purity of 99.6%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.25 Pa, the inlet temperature of the cooling water is 12.5 ℃, the outlet temperature of the cooling water is 33 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.7.

[0068] Arc ignition stage: Melting is carried out with a melting current of 2.2 kA and an arc stabilization current of 7.5 A. After the molten pool stabilizes, the melting stage begins.

[0069] Melting stage: Melting current is 3 kA, melting rate is 3.2 cm / min, and arc stabilization current is 14 A.

[0070] Feeding stage: When the remaining mass of the electrode rod is 25% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 6% of the initial mass.

[0071] The melting currents during the feeding stage were 2.9 kA, 2.2 kA, 1.7 kA, and 1.4 kA, respectively; the melting rates were 2.9 cm / min, 2.2 cm / min, 2.1 cm / min, and 1.8 cm / min, respectively; and the arc stabilization currents during the feeding stage were 9.1 A, 8.2 A, 7 A, and 6.2 A, respectively. S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0072] The inclusion density of the high-purity iron prepared in this embodiment is 3.33 inclusions / mm². 2 The maximum inclusion size is 8.09 μm, and the shortest straight-line distance between any two inclusions is ≥250 μm.

[0073] The high-purity iron prepared in this embodiment was used to prepare nitrided iron alloy aortic endovascular stent grafts. The prepared nitrided iron alloy aortic endovascular stent grafts were expanded with balloons to nominal diameters of 20 mm, 25 mm, 30 mm, and 40 mm, respectively. During the expansion process to the above nominal diameters, no failure phenomena such as breakage occurred.

[0074] Example 4 The method for preparing high-purity iron in this embodiment includes the following steps: S100: Electrode rods are made from pure iron with a purity of 99.6%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.35 Pa, the inlet temperature of the cooling water is 14.2 ℃, the outlet temperature of the cooling water is 33.5 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.7.

[0075] Arc ignition stage: The melting current is 2.1 kA and the arc stabilization current is 8 A for melting. After the molten pool stabilizes, the melting stage begins.

[0076] Melting stage: Melting current is 2.9 kA, melting rate is 3 cm / min, and arc stabilization current is 16 A.

[0077] Feeding stage: When the remaining mass of the electrode rod is 25% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 6% of the initial mass.

[0078] The melting currents during the feeding stage were 2.8 kA, 2 kA, 1.7 kA, and 1.4 kA, respectively; the melting rates were 3 cm / min, 2.3 cm / min, 1.9 cm / min, and 1.6 cm / min, respectively; and the arc stabilization currents during the feeding stage were 10 A, 8.7 A, 7.9 A, and 7.3 A, respectively. S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0079] The inclusion density of the high-purity iron prepared in this embodiment is 3 inclusions / mm². 2 The maximum inclusion size is 6.27 μm, and the shortest straight-line distance between any two inclusions is ≥250 μm.

[0080] The high-purity iron prepared in this embodiment was used to prepare nitrided iron alloy coronary stents. The prepared nitrided iron alloy coronary stents were expanded with balloons to nominal diameters of 2 mm, 2.5 mm, 3 mm and 4 mm, respectively. During the expansion process of their respective nominal diameters, no failure phenomena such as breakage occurred.

[0081] Example 5 The method for preparing high-purity iron in this embodiment includes the following steps: S100: Electrode rods are made from pure iron with a purity of 99.6%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.4 Pa, the inlet temperature of the cooling water is 13.5℃, the outlet temperature of the cooling water is 34.7℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.7.

[0082] Arc ignition stage: Melting is carried out with a melting current of 1.8 kA and an arc stabilization current of 5 A. After the molten pool stabilizes, the melting stage begins.

[0083] Melting stage: Melting current is 2.85 kA, melting rate is 2.9 cm / min, and arc stabilization current is 12.9 A.

[0084] Feeding stage: When the remaining mass of the electrode rod is 20% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 6% of the initial mass.

[0085] The melting currents during the feeding stage were 2.85 kA, 2.1 kA, 1.6 kA, and 1.4 kA, respectively; the melting rates were 2.9 cm / min, 2.3 cm / min, 2.0 cm / min, and 1.8 cm / min, respectively; and the arc stabilization currents during the feeding stage were 8 A, 7.4 A, 6.7 A, and 6 A, respectively. S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0086] The high-purity iron prepared in this embodiment has an inclusion density of 4 inclusions / mm². 2 The maximum inclusion size is 13.89 μm, and the shortest straight-line distance between any two inclusions is ≥100 μm.

[0087] The high-purity iron prepared in this embodiment was used to prepare nitrided iron alloy coronary stents. The prepared nitrided iron alloy coronary stents were expanded with balloons to nominal diameters of 2 mm, 2.5 mm, 3 mm and 4 mm, respectively. During the expansion process of their respective nominal diameters, no failure phenomena such as breakage occurred.

[0088] Example 6 The method for preparing high-purity iron in this embodiment includes the following steps: S100: Electrode rods are made from pure iron with a purity of 99.6%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.32 Pa, the inlet temperature of the cooling water is 13.3 ℃, the outlet temperature of the cooling water is 32.6 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.8.

[0089] Arc ignition stage: Melting is carried out with a melting current of 2 kA and an arc stabilization current of 6 A. After the molten pool stabilizes, the melting stage begins.

[0090] Melting stage: Melting current is 2.8 kA, melting rate is 3.1 cm / min, and arc stabilization current is 11 A.

[0091] Feeding stage: When the remaining mass of the electrode rod is 25% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 6% of the initial mass.

[0092] The melting currents during the feeding stage were 2.7 kA, 2.2 kA, 1.8 kA, and 1.4 kA, respectively; the melting rates were 3 cm / min, 2.3 cm / min, 2.0 cm / min, and 1.7 cm / min, respectively; and the arc stabilization currents during the feeding stage were 8.5 A, 7.9 A, 7 A, and 6.2 A, respectively. S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0093] The inclusion density of the high-purity iron prepared in this embodiment is 3 inclusions / mm². 2 The maximum inclusion size is 12.41 μm, and the shortest straight-line distance between any two inclusions is ≥159 μm.

[0094] The high-purity iron prepared in this embodiment was used to prepare nitrided iron alloy peripheral vascular stents. The prepared nitrided iron alloy peripheral vascular stents were expanded with balloons to nominal diameters of 5 mm, 8 mm, 10 mm, and 15 mm. During the expansion process to the above nominal diameters, no failure phenomena such as breakage occurred.

[0095] Example 7 The method for preparing high-purity iron in this embodiment includes the following steps: S100: Electrode rods are made from pure iron with a purity of 95%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.45 Pa, the inlet temperature of the cooling water is 11.6 ℃, the outlet temperature of the cooling water is 30.8 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.68.

[0096] Arc ignition stage: Melting is carried out with a melting current of 1.6 kA and an arc stabilization current of 4.5 A. After the molten pool stabilizes, the melting stage begins.

[0097] Melting stage: Melting current is 2.7 kA, melting rate is 4.5 cm / min, and arc stabilization current is 9 A.

[0098] Feeding stage: When the remaining mass of the electrode rod is 20% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 6% of the initial mass.

[0099] The melting currents during the feeding stage were 2.5 kA, 1.8 kA, 1.5 kA, and 1.3 kA, respectively; the melting rates were 4.2 cm / min, 3.5 cm / min, 3.2 cm / min, and 2.8 cm / min, respectively; and the arc stabilization currents during the feeding stage were 7.5 A, 6.7 A, 5.7 A, and 5 A, respectively. S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0100] The inclusion density of the high-purity iron prepared in this embodiment is 4.67 inclusions / mm². 2 The maximum inclusion size is 10.28 μm, and the shortest straight-line distance between any two inclusions is ≥250 μm.

[0101] The high-purity iron prepared in this embodiment was used to prepare nitrided iron alloy aortic endovascular stent grafts. The prepared nitrided iron alloy aortic endovascular stent grafts were expanded with balloons to nominal diameters of 20 mm, 25 mm, 30 mm, and 40 mm, respectively. During the expansion process to the above nominal diameters, no failure phenomena such as breakage occurred.

[0102] Example 8 The method for preparing high-purity iron in this embodiment includes the following steps: S100: Electrode rods are made from pure iron with a purity of 98%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.5 Pa, the inlet temperature of the cooling water is 10 ℃, the outlet temperature of the cooling water is 35 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.85.

[0103] Arc ignition stage: Melting is carried out with a melting current of 1.5 kA and an arc stabilization current of 4 A. After the molten pool stabilizes, the melting stage begins.

[0104] Melting stage: Melting current is 2.5 kA, melting rate is 5.5 cm / min, and arc stabilization current is 8 A.

[0105] Feeding stage: When the remaining mass of the electrode rod is 15% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 8% of the initial mass.

[0106] The melting currents during the feeding stage were 2.3 kA, 1.7 kA, 1.4 kA, and 1.2 kA, respectively; the melting rates were 4.5 cm / min, 3.8 cm / min, 3.2 cm / min, and 2.9 cm / min, respectively; and the arc stabilization currents during the feeding stage were 7 A, 5.7 A, 4.7 A, and 4 A, respectively. S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0107] The high-purity iron prepared in this embodiment has an inclusion density of 5 inclusions / mm². 2 The maximum inclusion size is 13.69 μm, and the shortest straight-line distance between any two inclusions is ≥100 μm.

[0108] The high-purity iron prepared in this embodiment was used to prepare nitrided iron alloy coronary stents. The prepared nitrided iron alloy coronary stents were expanded with balloons to nominal diameters of 2 mm, 2.5 mm, 3 mm and 4 mm, respectively. During the expansion process of their respective nominal diameters, no failure phenomena such as breakage occurred.

[0109] Comparative Example 1 The method for preparing high-purity iron in this comparative example includes the following steps: S100: Electrode rods are made from pure iron with a purity of 99.9%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.2 Pa, the inlet temperature of the cooling water is 12 ℃, and the flow rate of the cooling water is 28 ℃; the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.6.

[0110] Arc ignition stage: Melting is carried out with a melting current of 1 kA and an arc stabilization current of 3 A. After the molten pool stabilizes, the melting stage begins.

[0111] Melting stage: Melting current is 2 kA, melting rate is 2.3 cm / min, and arc stabilization current is 6 A.

[0112] Compensation phase: When the remaining mass of the consumable electrode is 25% of the initial mass, the compensation phase begins until the remaining mass of the electrode is 5% of the initial mass.

[0113] The melting currents during the feeding stage were 1.9 kA, 1.5 kA, 1.2 kA, and 1.0 kA, respectively; the melting rates were 2 cm / min, 1.5 cm / min, 1.1 cm / min, and 0.9 cm / min, respectively; and the arc stabilization currents during the feeding stage were 5 A, 4.7 A, 3.6 A, and 3 A, respectively.

[0114] S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0115] The inclusion density of the high-purity iron prepared in this comparative example was 40 inclusions / mm². 2 The maximum inclusion size is 36.23 μm, and the shortest straight-line distance between any two inclusions is ≥20.46 μm.

[0116] The high-purity iron prepared in this comparative example was used to prepare nitrided iron alloy coronary stents. The prepared nitrided iron alloy coronary stents were expanded with balloons to nominal diameters of 2 mm, 2.5 mm, 3 mm, and 4 mm, respectively. During the expansion process to their respective nominal diameters, the stents all experienced failure phenomena such as fracture.

[0117] Comparative Example 2 The method for preparing high-purity iron in this comparative example includes the following steps: S100: Electrode rods are made from pure iron with a purity of 99.6%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.3 Pa, the inlet temperature of the cooling water is 12 ℃, the outlet temperature of the cooling water is 27 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.65.

[0118] Arc ignition stage: Melting is carried out with a melting current of 5 kA and an arc stabilization current of 15 A. After the molten pool stabilizes, the melting stage begins.

[0119] Melting stage: Melting current is 4.5 kA, melting rate is 7 cm / min, and arc stabilization current is 22 A.

[0120] Feeding stage: When the remaining mass of the electrode rod is 25% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 6% of the initial mass.

[0121] The melting currents during the feeding stage were 4 kA, 3 kA, 2 kA, and 1.8 kA, respectively; the melting rates were 5 cm / min, 3.9 cm / min, 3.3 cm / min, and 3.0 cm / min, respectively; and the arc stabilization currents during the feeding stage were 12 A, 10.5 A, 9.7 A, and 8.5 A, respectively.

[0122] S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0123] The inclusion density of the high-purity iron prepared in this comparative example was 21.33 inclusions / mm². 2 The maximum inclusion size is 30 μm, and the shortest straight-line distance between any two inclusions is ≥32.24 μm.

[0124] The high-purity iron prepared in this comparative example was used to prepare nitrided iron alloy peripheral vascular stents. The prepared nitrided iron alloy peripheral vascular stents were expanded with balloons to nominal diameters of 5 mm, 8 mm, 10 mm, and 15 mm. During the expansion process to the above nominal diameters, the stents all experienced failure phenomena such as fracture.

[0125] Comparative Example 3 The method for preparing high-purity iron in this comparative example includes the following steps: S100: Electrode rods are made from pure iron with a purity of 98%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.5 Pa, the inlet temperature of the cooling water is 10 ℃, the outlet temperature of the cooling water is 35 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.85.

[0126] Arc ignition stage: The melting current is 1.5 kA and the arc stabilization current is 4 A for melting. After the molten pool stabilizes, the melting stage begins.

[0127] Melting stage: Melting current is 1.8 kA, melting rate is 2.3 cm / min, and arc stabilization current is 6 A.

[0128] Feeding stage: When the remaining mass of the electrode rod is 15% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 8% of the initial mass.

[0129] The melting currents during the feeding stage were 1.8 kA and 1 kA, respectively; the melting rates were 2.0 cm / min and 0.9 cm / min, respectively; and the arc stabilization currents during the feeding stage were 5 A and 3 A, respectively.

[0130] S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0131] The inclusion density of the high-purity iron prepared in this comparative example was 37.33 inclusions / mm². 2 The maximum inclusion size is 32 μm, and the shortest straight-line distance between any two inclusions is ≥24.58 μm.

[0132] The high-purity iron prepared in this comparative example was used to prepare nitrided iron alloy coronary stents. The prepared nitrided iron alloy coronary stents were expanded with balloons to nominal diameters of 2 mm, 2.5 mm, 3 mm, and 4 mm, respectively. During the expansion process to their respective nominal diameters, the stents all experienced failure phenomena such as fracture.

[0133] Comparative Example 4 The method for preparing high-purity iron in this comparative example includes the following steps: S100: Electrode rods are made from pure iron with a purity of 99.6%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting; the specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.3 Pa, the inlet temperature of the cooling water is 12 ℃, the outlet temperature of the cooling water is 21 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.65.

[0134] Arc ignition stage: The melting current is 2.5 kA and the arc stabilization current is 8 A for melting. After the molten pool stabilizes, the melting stage begins.

[0135] Melting stage: Melting current is 3.2 kA, melting rate is 2.8 cm / min, and arc stabilization current is 17 A.

[0136] Feeding stage: When the remaining mass of the electrode rod is 25% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 6% of the initial mass.

[0137] The melting currents during the feeding stage were 2.0 kA, 1.6 kA, 1.3 kA, and 1.0 kA, respectively; the melting rates were 2 cm / min, 1.5 cm / min, 1.1 cm / min, and 0.9 cm / min, respectively; and the arc stabilization currents during the feeding stage were 6 A, 5.2 A, 4.3 A, and 3.5 A, respectively.

[0138] S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0139] The inclusion density of the high-purity iron prepared in this comparative example was 16 inclusions / mm².2 The maximum inclusion size is 20.34 μm, and the shortest straight-line distance between any two inclusions is ≥38.15 μm.

[0140] The high-purity iron prepared in this comparative example was used to prepare nitrided iron alloy peripheral vascular stents. The prepared nitrided iron alloy peripheral vascular stents were expanded with balloons to nominal diameters of 5 mm, 8 mm, 10 mm, and 15 mm. During the expansion process to the above nominal diameters, the stents all experienced failure phenomena such as fracture.

[0141] Comparative Example 5 The method for preparing high-purity iron in this comparative example includes the following steps: S100: Electrode rods are made from pure iron with a purity of 98%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.5 Pa, the inlet temperature of the cooling water is 5 ℃, the outlet temperature of the cooling water is 35 ℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.85.

[0142] Arc ignition stage: The melting current is 1.5 kA and the arc stabilization current is 4 A for melting. After the molten pool stabilizes, the melting stage begins.

[0143] Melting stage: Melting current is 2.5 kA, melting rate is 5.5 cm / min, and arc stabilization current is 8 A.

[0144] Feeding stage: When the remaining mass of the electrode rod is 15% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 8% of the initial mass.

[0145] The melting currents during the feeding stage were 2.3 kA, 1.7 kA, 1.4 kA, and 1.2 kA, respectively; the melting rates were 4.5 cm / min, 3.8 cm / min, 3.2 cm / min, and 2.9 cm / min, respectively; and the arc stabilization currents during the feeding stage were 7 A, 5.7 A, 4.7 A, and 4 A, respectively.

[0146] S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0147] The inclusion density of the high-purity iron prepared in this comparative example was 12.67 inclusions / mm². 2 The maximum inclusion size is 23.36 μm, and the shortest straight-line distance between any two inclusions is ≥42.26 μm.

[0148] The high-purity iron prepared in this comparative example was used to prepare nitrided iron alloy coronary stents. The prepared nitrided iron alloy coronary stents were expanded with balloons to nominal diameters of 2 mm, 2.5 mm, 3 mm, and 4 mm, respectively. During the expansion process to their respective nominal diameters, the stents all experienced failure phenomena such as fracture.

[0149] Comparative Example 6 The method for preparing high-purity iron in this comparative example includes the following steps: S100: Electrode rods are made from pure iron with a purity of 98%. S200: The electrode rod is placed in a vacuum arc melting furnace for vacuum arc melting. The specific parameters for vacuum arc melting are as follows: The vacuum degree is 0.5 Pa, the inlet temperature of the cooling water is 12℃, the outlet temperature of the cooling water is 45℃, and the ratio of the diameter of the electrode rod to the diameter of the copper crucible is 0.85.

[0150] Arc ignition stage: The melting current is 1.5 kA and the arc stabilization current is 4 A for melting. After the molten pool stabilizes, the melting stage begins.

[0151] Melting stage: Melting current is 2.5 kA, melting rate is 5.5 cm / min, and arc stabilization current is 8 A.

[0152] Feeding stage: When the remaining mass of the electrode rod is 15% of the initial mass, the feeding stage begins until the remaining mass of the electrode rod is 8% of the initial mass.

[0153] The melting currents during the feeding stage were 2.3 kA, 1.7 kA, 1.4 kA, and 1.2 kA, respectively; the melting rates were 4.5 cm / min, 3.8 cm / min, 3.2 cm / min, and 2.9 cm / min, respectively; and the arc stabilization currents during the feeding stage were 7 A, 5.7 A, 4.7 A, and 4 A, respectively.

[0154] S300: After vacuum arc melting is completed, the ingot obtained by vacuum arc melting is cooled, broken, and removed from the ingot to obtain a high-purity iron ingot.

[0155] The inclusion density of the high-purity iron prepared in this comparative example is 10 inclusions / mm². 2 The maximum inclusion size is 20.89 μm, and the shortest straight-line distance between any two inclusions is ≥46.39 μm.

[0156] The high-purity iron prepared in this comparative example was used to prepare nitrided iron alloy coronary stents. The prepared nitrided iron alloy coronary stents were expanded with balloons to nominal diameters of 2 mm, 2.5 mm, 3 mm, and 4 mm, respectively. During the expansion process to their respective nominal diameters, the stents all experienced failure phenomena such as fracture.

[0157] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Rather, any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity iron, characterized in that, Includes the following steps: Electrode rods are made from pure iron raw materials; The electrode rod is then subjected to vacuum arc melting. The vacuum arc melting includes an arc initiation stage, a melting stage, and a feeding stage; The melting current during the arc ignition stage is 1.5 kA to 3.0 kA, and the arc stabilization current is 4 A to 10 A. The melting current during the melting stage is 2.5 kA to 3.5 kA, the melting rate is 2.5 cm / min to 5.5 cm / min, and the arc stabilization current is 8 A to 20 A. The melting current during the feeding stage is 1.2 kA to 3.3 kA, the melting rate is 1 cm / min to 4.5 cm / min, and the arc stabilization current is 4 A to 11 A.

2. The method for preparing high-purity iron according to claim 1, characterized in that, During the feeding stage, the melting current, melting rate, and arc stabilization current gradually decrease.

3. The method for preparing high-purity iron according to claim 1 or 2, characterized in that, The smelting current during the feeding stage is 2.3 kA ~ 3.3 kA, 1.7 kA ~ 2.5 kA, 1.4 kA ~ 1.9 kA, and 1.2 kA ~ 1.6 kA, respectively. The melting rates during the feeding stage are 2.3 cm / min to 4.5 cm / min, 1.7 cm / min to 3.8 cm / min, 1.3 cm / min to 3.2 cm / min, and 1 cm / min to 2.9 cm / min, respectively. The arc stabilization current during the compensation stage is 7A ~ 11A, 5.7A ~ 9.7A, 4.7A ~ 8.7A, and 4A ~ 8A, respectively.

4. The method for preparing high-purity iron according to claim 1, characterized in that, The feeding stage begins when the remaining mass of the electrode rod is 15% to 25% of the initial mass; the feeding stage ends when the remaining mass of the electrode is 5% to 8% of the initial mass.

5. The method for preparing high-purity iron according to claim 1, characterized in that, The vacuum arc melting process uses cooling water for cooling. The inlet temperature of the cooling water is 10℃~15℃, and the outlet temperature of the cooling water is 30℃~35℃.

6. The method for preparing high-purity iron according to claim 1, characterized in that, The process of vacuum arc melting the electrode rod includes: placing the electrode rod in a vacuum arc furnace, the vacuum arc furnace being equipped with a crucible for supporting the molten pool, placing the electrode rod above the crucible and performing vacuum arc melting; the ratio of the diameter of the electrode rod to the diameter of the crucible is 0.6 to 0.

85.

7. The method for preparing high-purity iron according to claim 1, characterized in that, The purity of the pure iron raw material is 95%~99.95%.

8. The method for preparing high-purity iron according to claim 1, characterized in that, The vacuum arc melting is carried out under a vacuum of ≤0.5 Pa.

9. A high-purity iron, prepared by the method for preparing high-purity iron according to any one of claims 1 to 8, wherein the inclusion density of the high-purity iron is ≤5 inclusions / mm². 2 The maximum inclusion size is ≤15 μm; the shortest straight-line distance between any two inclusions is ≥100 μm.

10. The application of high-purity iron according to claim 9 in the preparation of luminal stents, wherein the luminal stents include vascular stents, airway stents, esophageal stents, biliary stents, intestinal stents, urethral stents, nerve stents, or pancreatic stents; The vascular stents include heart valve stents, coronary stents, pulmonary artery stents, renal artery stents, cone artery stents, covered stents, or peripheral stents.