Medical high-nitrogen stainless steel, preparation method thereof and medical instrument

Abstract

The invention discloses medical high-nitrogen stainless steel, a preparation method thereof and a medical instrument. The medical high-nitrogen stainless steel comprises the following chemical components: C, Si, Cr, Mn, Mo, N, Cu, Ce, Mg and the balance of Fe and inevitable impurities. Wherein the content of N is 0.97 wt%-1.05 wt%, the content of Cu is 4 wt%-6 wt%, and the content of Ce is 0.11 wt%-0.3 wt%. Therefore, the defects of traditional stainless steel in the aspects of strength, corrosion resistance and antibacterial property are overcome, and the stainless steel can be widely applied to various stainless steel implantation instruments and other tools used in the medical field and has important clinical application value.

Description

Technical Field

[0001] The present application relates to the technical field of stainless steel, and in particular to a medical high-nitrogen stainless steel and a preparation method thereof, and medical devices. Background Art

[0002] The human oral cavity is a complex environment that is always in a humid state. The temperature is maintained at 36.3-37.2℃ for a long time. There are more than 400 kinds of bacteria, such as Lactobacillus, Streptococcus, Staphylococcus, Actinomyces viscous and Prevotella intermedia. These factors have put great challenges on oral materials. Taking orthodontic archwires as an example, stainless steel archwires mainly made of 302 and 304 chromium-nickel austenitic stainless steel are one of the most commonly used archwires in orthodontic clinics. Its advantages are good bending performance and corrosion resistance and low price. However, after long-term use in the oral environment, chromium-nickel stainless steel will release nickel due to corrosion and wear, which is easy to accumulate in the user's gums and cause black gums. In addition, the enrichment of nickel in the human body may not only induce toxic reactions, damage cells, and cause inflammation, but also may cause teratogenic and carcinogenic risks to the human body.

[0003] Therefore, the development of high-strength, high-corrosion-resistant, low-allergenic and antibacterial stainless steel is an urgent problem to be solved. Summary of the invention

[0004] In view of this, the present application provides a medical high-nitrogen stainless steel and a preparation method thereof, and medical equipment to solve the problem of insufficient strength, corrosion resistance and antibacterial properties of stainless steel.

[0005] According to an embodiment of one aspect of the present application, a medical high-nitrogen stainless steel is provided, the chemical composition of the medical high-nitrogen stainless steel comprising: C, Si, Cr, Mn, Mo, N, Cu, Ce, Mg, and the rest being Fe and unavoidable impurities; wherein the N content is 0.97wt% to 1.05wt%, the Cu content is 4wt% to 6wt%, and the Ce content is 0.11wt% to 0.3wt%.

[0006] Optionally, the chemical composition of the medical high nitrogen stainless steel includes 18wt% to 20wt% Cr, 14wt% to 16wt% Mn, and 3.5wt% to 4.5wt% Mo.

[0007] Optionally, the inevitable impurities in the medical high nitrogen stainless steel include Ni, and the Ni content is less than 0.05wt%;

[0008] The equivalent ratio between Cr and Ni is in the range of 0.50 to 0.70;

[0009] The Cr equivalent is the sum of the weight percentage content of Cr, the weight percentage content of Mo and the weight percentage content of Si with a preset coefficient;

[0010] The Ni equivalent is the weighted sum of the weight percentage content of Ni, the weight percentage content of C, the weight percentage content of N, the weight percentage content of Mn and / or the weight percentage content of Cu;

[0011] Optionally, the preset coefficient of Si is 1.5, the weighting coefficient of Ni is 1, the weighting coefficient of C is 30, the weighting coefficient of N is 30, the weighting coefficient of Mn is 0.5, and the weighting coefficient of Cu is 0.3.

[0012] Optionally, the pitting resistance equivalent index of the medical high nitrogen stainless steel is greater than or equal to 45;

[0013] The weight percentage content of N, the weight percentage content of Cr, and the weight percentage content of Mo satisfy the following formula: PREN = (wt.%) Cr +3.3×(wt.%) Mo +16×(wt.%) N .

[0014] Optionally, the weight percentage content of N, the weight percentage content of Cr, the weight percentage content of Mo, and the weight percentage content of Cu satisfy the following formula:

[0015] 23≤((wt.%) Cr +0.5×(wt.%) Mn -0.1×(wt.%) Cu ) / (wt.%) N ≤30.

[0016] Optionally, the C content is less than 0.02wt%; the Si content is 0.1wt% to 0.6wt%; and the Mg content is 0.002wt% to 0.005wt%.

[0017] According to another embodiment of the present application, a method for preparing medical high nitrogen stainless steel is provided, comprising:

[0018] The raw materials are configured according to the chemical composition of the medical high nitrogen stainless steel provided in the above embodiment;

[0019] Under smelting pressure, respectively adding N raw material, Si raw material, Mg raw material, and Ce raw material into a molten liquid obtained by melting Fe raw material, Cr raw material, Mo raw material, Mn raw material, and Cu raw material to obtain an alloy melt;

[0020] After a preset time interval, the alloy melt is cast under a casting pressure, and an alloy ingot is obtained after cooling and pressure relief, wherein the casting pressure is greater than the smelting pressure;

[0021] Forging the alloy ingot to obtain an alloy forging;

[0022] Heat treating the alloy forgings to obtain medical high nitrogen stainless steel;

[0023] Among them, heat treatment includes solution treatment and aging treatment.

[0024] Optionally, the smelting pressure satisfies the following formula:

[0025]

[0026] The casting pressure satisfies the following formula:

[0027] P 2 =[0.08~0.10)P 1 / P θ +(0.35~0.65)];

[0028] Where P 1 Indicates smelting pressure, P 2 Indicates casting pressure, P θ represents standard atmospheric pressure, α and β represent coefficients related to smelting temperature, and A represents a constant related to the chemical composition of medical high nitrogen stainless steel.

[0029] Optionally, the N raw material is chromium nitride, and the weight percentage of N added in the form of chromium nitride satisfies the following formula:

[0030] (wt.%) 1 =[-0.02P 1 / P θ +(0.66~0.76)]×(wt.%) N ;

[0031] Where, (wt.%) 1 Indicates the weight percentage of N added in the form of chromium nitride, P 1 Indicates smelting pressure, P θ Indicates standard atmospheric pressure, (wt.%) N Indicates the nitrogen content in the chemical composition of medical high nitrogen stainless steel.

[0032] Optionally, the temperature of the solution treatment is 1220° C. to 1230° C., the heating rate is 60° C. / h to 80° C. / h, and the time is 1 h to 2 h.

[0033] Optionally, the aging treatment temperature is 560° C. to 600° C., and the time is 2 h to 4 h.

[0034] Optionally, the alloy ingot is subjected to a forging process, including:

[0035] The alloy ingot is forged by a two-pier and two-draw method, wherein the forging ratio is in the range of 3 to 5, the forging temperature is 1220°C to 1230°C, and the final forging temperature is 1110°C to 1130°C;

[0036] After forging, the alloy forgings are water-cooled to room temperature, where the cooling rate is

[0037] 200℃ / s~300℃ / s.

[0038] According to another embodiment of the present application, a medical device is provided, which is made by a molding process using the medical high nitrogen stainless steel provided in the embodiment or the medical high nitrogen stainless steel obtained by the preparation method of the medical high nitrogen stainless steel provided in the above embodiment as a raw material.

[0039] By means of the above technical scheme, copper (Cu), cerium (Ce) and nitrogen (N) are added to stainless steel. Copper can form a uniform and dispersed antibacterial phase ε-Cu in stainless steel after heat treatment, giving stainless steel antibacterial function, and has a strong bactericidal effect on bacteria such as Escherichia coli (Ecoli), Staphylococcus aureus (S.aureus) and Salmonella (Salmonella). The cerium element reduces the content of oxygen and sulfur in steel, improves the cleanliness of steel, and helps to enhance the oxidation resistance of stainless steel. Moreover, when the solid solution cerium reaches a certain content, it can enhance the bactericidal ability of copper, so that stainless steel has a broad-spectrum antibacterial function on the basis of high strength, high corrosion resistance and low sensitization. By adding nitrogen, austenite can be stabilized, and the strength of steel can be greatly improved without significantly reducing toughness through solid solution strengthening, fine grain strengthening and precipitation strengthening. Through the synergistic effect of nitrogen and nitrogen with other alloying elements (Cr, Mo, etc.), the stability of the passivation film can be improved and the repassivation ability can be enhanced, thereby significantly improving the corrosion resistance of stainless steel. This overcomes the shortcomings of traditional stainless steel in terms of strength, corrosion resistance and antibacterial properties, making this stainless steel widely used in various stainless steel implant instruments and other tools used in the medical field, and has important clinical application value.

[0040] Furthermore, the Cu content is 4wt% to 6wt%, which can ensure the sterilization effect while preventing the problem of reduced hot working performance of stainless steel due to excessive copper content. The Ce content is 0.11wt% to 0.3wt%, thereby ensuring that the cerium element improves the sterilization ability and avoiding the formation of a large number of cerium oxide inclusions in the steel due to excessive cerium content. The N content is 0.97wt% to 1.05wt%, which can stabilize the austenite structure in stainless steel, greatly improve the strength of the steel without significantly reducing the toughness; on the other hand, it promotes the synergistic effect of nitrogen and nitrogen with other alloying elements (Cr, Mo, etc.), improves the stability of the passivation film and enhances the repassivation ability, thereby significantly improving the corrosion resistance of stainless steel. Moreover, during the preparation and processing of stainless steel, an appropriate amount of nitrogen can precipitate a small amount of nitrides as heterogeneous nucleation sites, which helps to promote the precipitation of the antibacterial phase ε-Cu, and avoids the precipitation of large-sized nitrides due to excessive nitrogen content, which reduces the hot working and cold working performance of steel, thereby greatly shortening the processing time of preparation and processing.

[0041] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0043] Figure 1 A schematic diagram of the process of producing medical high nitrogen stainless steel provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0044] The present application will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0045] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be interpreted as limiting the present application.

[0046] Those skilled in the art will appreciate that, unless expressly stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present application refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, or there may be intermediate elements. In addition, the "connection" or "connection" used herein may include wireless connection or wireless fusion. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

[0047] Now, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in a variety of different forms and should not be interpreted as being limited to the embodiments set forth herein. It should be understood that these embodiments are provided to make the disclosure of the present application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art.

[0048] In this embodiment, a medical high-nitrogen stainless steel is provided, which includes: C, Si, Cr, Mn, Mo, N, Cu, Ce, Mg, and the rest is Fe and unavoidable impurities.

[0049] Among them, the impurity elements include nickel (Ni), phosphorus (P), sulfur (S) and the like.

[0050] In this embodiment, copper (Cu), cerium (Ce) and nitrogen (N) are added to stainless steel. Copper can form a uniform and dispersed antibacterial phase ε-Cu in stainless steel after heat treatment, giving stainless steel antibacterial function, and has a strong bactericidal effect on bacteria such as Escherichia coli (Ecoli), Staphylococcus aureus (S.aureus) and Salmonella (Salmonella). By adding cerium to reduce the content of oxygen and sulfur elements in steel, improve the cleanliness of steel, and help enhance the oxidation resistance of stainless steel. Moreover, when the solid solution cerium reaches a certain content, it can enhance the bactericidal ability of copper, so that stainless steel has a broad-spectrum antibacterial function on the basis of high strength, high corrosion resistance and low sensitization. By adding nitrogen, austenite can be stabilized, and the strength of steel can be greatly improved without significantly reducing toughness through solid solution strengthening, fine grain strengthening and precipitation strengthening. Through the synergistic effect of nitrogen and nitrogen with other alloying elements (Cr, Mo, etc.), the stability of the passivation film can be improved and the repassivation ability can be enhanced, thereby significantly improving the corrosion resistance of stainless steel. This overcomes the shortcomings of traditional stainless steel in terms of strength, corrosion resistance and antibacterial properties, making this stainless steel widely used in various stainless steel implant instruments and other tools used in the medical field, and has important clinical application value.

[0051] Furthermore, the Cu content is 4wt% to 6wt%, which can ensure the sterilization effect while preventing the problem of reduced hot working performance of stainless steel due to excessive copper content. The Ce content is 0.11wt% to 0.3wt%, thereby ensuring that the cerium element improves the sterilization ability and avoiding the formation of a large number of cerium oxide inclusions in the steel due to excessive cerium content. The N content is 0.97wt% to 1.05wt%, which can stabilize the austenite structure in stainless steel, greatly improve the strength of the steel without significantly reducing the toughness; on the other hand, it promotes the synergistic effect of nitrogen and nitrogen with other alloying elements (Cr, Mo, etc.), improves the stability of the passivation film and enhances the repassivation ability, thereby significantly improving the corrosion resistance of stainless steel. Moreover, during the preparation and processing of stainless steel, an appropriate amount of nitrogen can precipitate a small amount of nitrides as heterogeneous nucleation sites, which helps to promote the precipitation of the antibacterial phase ε-Cu, and avoids the precipitation of large-sized nitrides due to excessive nitrogen content, which reduces the hot working and cold working performance of steel, thereby greatly shortening the processing time of preparation and processing.

[0052] Introducing chromium (Cr) into stainless steel can generate stable Cr on the surface of stainless steel. 2 O 3 Passivation film improves the corrosion resistance of stainless steel, and when combined with elements such as molybdenum (Mo) and nitrogen (N), it can further improve the stainless steel's resistance to pitting and crevice corrosion.

[0053] The introduction of manganese (Mn) into stainless steel can stabilize austenite with nitrogen (N) in stainless steel, which helps to enhance the mechanical properties, processing properties and corrosion resistance of stainless steel. At the same time, manganese can also significantly increase the solubility of nitrogen in steel.

[0054] The introduction of molybdenum (Mo) into stainless steel helps to promote the formation of a passivation film on the surface of stainless steel, thereby significantly improving the stainless steel's resistance to stress corrosion cracking (SCC).

[0055] It is worth mentioning that Cr, Mn, and Mo can also increase the solubility of nitrogen (N) in steel, which helps the precipitation of copper-rich phase to further enhance the antibacterial properties of stainless steel, and improve the effect of nitrogen stabilizing austenite structure, reducing the formation of martensite or ferrite, thereby improving the corrosion resistance of stainless steel.

[0056] Introducing silicon (Si) as a deoxidizer into stainless steel can reduce the oxygen content in the steel and improve the fluidity of the molten steel.

[0057] The introduction of magnesium (Mg) into stainless steel can reduce the oxygen content and help purify the molten steel. Moreover, since the size of magnesium oxide inclusions is relatively small, silicon and magnesium can be used for pre-deoxidation before adding cerium, which helps prevent the formation of coarse cerium oxide inclusions, reduce stress concentration points inside the material, and improve the strength and toughness of the stainless steel.

[0058] In one embodiment, the Cr content in the stainless steel is controlled to be 18wt% to 20wt%, so as to improve the solubility of nitrogen while preventing excessive chromium from promoting the precipitation of large-sized nitrides and intermetallic phases (such as σ phase, χ phase, etc.) and reducing the austenite phase area, thereby avoiding deterioration of the mechanical properties and corrosion resistance of the steel.

[0059] In one embodiment, the Mn content in the stainless steel is controlled to be 14wt% to 16wt%, which improves the solubility of nitrogen while avoiding the generation of a large number of MnS inclusions and reducing the cleanliness of the steel, thereby helping to improve the hot working properties, mechanical properties and corrosion resistance of the stainless steel.

[0060] In one embodiment, the Mo content in the stainless steel is controlled to be 3.5wt% to 4.5wt%, which improves the solubility of nitrogen while preventing severe molybdenum segregation and the generation of hard and brittle intermetallic phases due to excessive molybdenum content, thereby improving the hot working properties, mechanical properties and corrosion resistance of the stainless steel.

[0061] In one embodiment, the C content in the stainless steel is controlled to be less than 0.02 wt%, thereby reducing the formation of large-sized carbides (such as M 23 C 6 、M 6 C, etc.) to improve the plasticity, toughness and corrosion resistance of stainless steel.

[0062] In one embodiment, the Si content in the stainless steel is controlled to be 0.1wt% to 0.6wt%, thereby reducing the generation of a large number of inclusions and hard and brittle intermetallic phases due to excessively high silicon content, thereby avoiding deterioration of the plasticity, toughness and corrosion resistance of the steel.

[0063] In one embodiment, the Mg content in the stainless steel is controlled to be 0.002wt% to 0.005wt%, thereby ensuring that the magnesium element purifies the molten steel and inhibits the formation of cerium oxide inclusions, while preventing the mechanical properties and corrosion resistance of the steel from being reduced due to the formation of a large amount of magnesium oxide inclusions caused by excessive magnesium content.

[0064] In one embodiment, although Ni, P, and S are impurity elements, their contents still need to be controlled to avoid adverse effects. Specifically, the Ni content in stainless steel is controlled to be less than 0.05wt% to avoid the nickel element released during the use of stainless steel from being enriched in the human body and inducing toxic reactions, thereby solving the sensitization problem of stainless steel. The P content in stainless steel is controlled to be less than 0.025wt% to avoid the segregation at the grain boundary to form excessive phosphides and cause intergranular embrittlement and cold brittleness. The S content in stainless steel is controlled to be less than 0.005wt% to avoid the production of excessive low-melting-point ferrous sulfide and reduce the probability of intergranular embrittlement.

[0065] In one embodiment, the equivalent ratio between Cr and Ni is in the range of 0.50 to 0.70, which is helpful to form a stable austenite structure.

[0066] In one embodiment, the Cr equivalent is the sum of the weight percentage content of Cr, the weight percentage content of Mo, and the weight percentage content of Si with a preset coefficient.

[0067] In this embodiment, Cr equivalent is a concept of equivalent chromium content that comprehensively considers the effects of multiple elements on material properties. Thus, the content of silicon, chromium and molybdenum can more comprehensively evaluate how much chromium a material contains in certain properties.

[0068] The preset coefficient of Si is 1.5. For example, the Cr equivalent Cr eq =%Cr+%Mo+1.5×%Si. The above formula is calculated based on the weight percentage of each element.

[0069] In one embodiment, the Ni equivalent is a weighted sum of the weight percentage content of Ni, the weight percentage content of C, the weight percentage content of N, the weight percentage content of Mn and / or the weight percentage content of Cu.

[0070] In this embodiment, Ni equivalent is a concept of equivalent nickel content that comprehensively considers the effects of multiple elements on material properties. By calculating Cr and Ni equivalents, the phase composition can be determined, thereby providing a reference for the application of the alloy in different environments.

[0071] Among them, the weighting coefficient of Ni is 1, the weighting coefficients of C and N are 30, the weighting coefficient of Mn is 0.5, and the weighting coefficient of Cu is 0.3. For example, Ni equivalent

[0072] Ni eq =%Ni+30×(%C+%N)+0.5×%Mn+0.3×%Cu. The above formula is calculated based on the weight percentage of each element.

[0073] Furthermore, in order to meet medical needs, it is necessary to control the pitting resistance equivalent number (PREN) of medical high nitrogen stainless steel to be greater than or equal to 45, and further control the content of alloy elements in stainless steel through the pitting resistance equivalent number. Specifically, pitting resistance equivalent number PREN = (wt.%) Cr +3.3×(wt.%) Mo +16×(wt.%) N The higher the PREN value, the better the pitting corrosion resistance of the stainless steel.

[0074] In one embodiment, considering that chromium, manganese and copper will affect the solubility of nitrogen, in order to ensure a high nitrogen solubility, improve tissue stability, corrosion resistance and comprehensive mechanical properties, the ratio of chromium, manganese, copper and nitrogen in the antibacterial high nitrogen stainless steel is controlled so that

[0075] 23≤((wt.%) Cr +0.5×(wt.%) Mn -0.1×(wt.%) Cu ) / (wt.%) N ≤30 to meet the demand for high nitrogen solubility in this stainless steel.

[0076] In this embodiment, a method for preparing medical high nitrogen stainless steel is provided. Figure 1 As shown, the method includes:

[0077] Step 101, preparing raw materials according to the chemical composition of medical high nitrogen stainless steel.

[0078] Specifically, the chemical composition of medical high nitrogen stainless steel is as follows by weight percentage: C≤0.02; 0.1≤Si≤0.6; 18.0≤Cr≤20.0; 14.0≤Mn≤16.0; 3.5≤Mo≤4.5; 0.97≤N≤1.05;

[0079] 4.0≤Cu≤6.0; 0.11≤Ce≤0.3; 0.002≤Mg≤0.005; the balance is Fe and other inevitable impurity elements.

[0080] In a specific application scenario, the N raw material may be chromium nitride, and the weight percentage of N added in the form of chromium nitride satisfies the following formula:

[0081] (wt.%) 1 =[-0.02P 1 / P θ +(0.66~0.76)]×(wt.%) N ;

[0082] Where, (wt.%) 1 Indicates the weight percentage of N added in the form of chromium nitride, P 1 Indicates smelting pressure, P θ Indicates standard atmospheric pressure, (wt.%) N Indicates the nitrogen content in the chemical composition of medical high nitrogen stainless steel.

[0083] Step 102, under smelting pressure, respectively adding N raw material, Si raw material, Mg raw material, and Ce raw material into a melt obtained by melting Fe raw material, Cr raw material, Mo raw material, Mn raw material, and Cu raw material to obtain an alloy melt.

[0084] Among them, N raw material, Si raw material, Mg raw material, Ce raw material, Fe raw material, Cr raw material, Mo raw material, Mn raw material, and Cu raw material can be selected according to the actual process. For example, chromium nitride is used as the raw material for introducing N, iron-magnesium alloy is used as the raw material for introducing Mg, electrolytic copper is used as the Cu raw material, etc. The embodiments of the present application will not list them one by one.

[0085] Specifically, the smelting pressure satisfies the following formula:

[0086]

[0087] Where P 1 Indicates smelting pressure, P θ represents standard atmospheric pressure, α and β represent coefficients related to smelting temperature, T represents smelting temperature, A is a constant, and A is related to the chemical composition of medical high nitrogen stainless steel.

[0088] For example,

[0089] A=0.13[(wt.%) N ]+0.118[(wt.%) C ]+0.011[(wt.%) Ni ]+3.5×10 -5[(wt.%) Ni ]-0.01[(wt.%) Mo ]+7.9×10 -5 [(wt.%) Mo ] 2 -0.048[(wt.%) Cr ]+3.5×10 -4 [(wt.%) Cr ] 2 .

[0090] It is worth mentioning that when adding Si raw materials, Mg raw materials, and Ce raw materials, they can be added in the order of Si→Mg→Ce. By adding Si raw materials, Mg raw materials, and Ce raw materials in the steel in sequence, the oxygen and sulfur content in the steel can be reduced, high cleanliness can be obtained, and the formation of large-sized inclusions in the steel can be avoided.

[0091] Step 103, after a preset time interval, the alloy melt is cast under a casting pressure, and an alloy ingot is obtained after cooling and pressure relief.

[0092] Among them, the casting pressure is greater than the smelting pressure. The casting pressure satisfies the following formula:

[0093] P 2 =[(0.08~0.10)P 1 / P θ +(0.35~0.65)];

[0094] Where P 1 Indicates smelting pressure, P 2 Indicates casting pressure, P θ Indicates standard atmospheric pressure.

[0095] In this embodiment, by controlling the pressure in stages, efficient nitrogen alloying is achieved during the stainless steel smelting process, the nitrogen distribution is uniform, and the nitrogen content is precisely controlled.

[0096] Step 104, forging the alloy ingot to obtain an alloy forging.

[0097] Step 105, heat treating the alloy forging to obtain medical high nitrogen stainless steel.

[0098] Among them, the heat treatment includes solution treatment and aging treatment. The temperature of solution treatment or aging treatment can be selected according to the composition and performance requirements of the stainless steel. For example, the temperature of solution treatment is 1220℃~1230℃, the heating rate is 60~80℃ / h, and the time is 1h~2h; the temperature of aging treatment is 560℃~600℃, and the time is 2h~4h.

[0099] In this embodiment, the alloy forging is heated to a high temperature and rapidly cooled to achieve solid solution treatment of the alloy forging, so that the nitrogen-containing and copper-containing precipitates in the steel can be dissolved back, and other elements (such as carbon, chromium, nickel, etc.) can be evenly distributed in the austenite matrix in the form of solid solution. Not only does it eliminate grain boundary carbides (such as Cr 23 C 6 ), avoiding the phenomenon of chromium depletion at the grain boundary, and improving the resistance to intergranular corrosion, pitting corrosion and crevice corrosion. Furthermore, after the solution treatment, an aging treatment is carried out at a certain temperature to precipitate a small amount of chromium nitride in the matrix, and with chromium nitride as the nucleation site, sufficient copper-rich phase (ε-Cu) is precipitated and dispersed and evenly distributed in the matrix, thereby significantly improving the strength and hardness of the stainless steel.

[0100] In one embodiment, step 104 specifically includes: forging the alloy ingot by a two-pier and two-draw method; and water cooling to room temperature after forging to obtain an alloy forging.

[0101] Among them, the forging ratio is in the range of 3 to 5, the forging temperature is 1220°C to 1230°C, the final forging temperature is 1110°C to 1130°C, and then the forging is water-cooled to room temperature at a cooling rate of 200°C / s to 300°C / s.

[0102] In this embodiment, during the "two-upsetting and two-drawing" forging process, the metal alloy undergoes multiple upsetting (upsetting) and drawing (drawing) operations. During upsetting, the metal is compressed in the vertical direction, and the internal grains are flattened in the horizontal direction; while during drawing, the metal is elongated in the axial direction, and the grains are also elongated and refined, which not only makes the originally coarse grains become small and uniform, but also allows the metal fibers to be arranged in an orderly manner, which is beneficial to improving the strength and toughness of the alloy.

[0103] For example, the weight percentages of the chemical components of Examples 1-4 and Comparative Examples 1-7 are shown in Table 1, and the design parameters such as the pitting resistance equivalent index PREN, the equivalent ratio between Cr and Ni, etc. are shown in Table 2.

[0104] Table 1. Chemical composition of experimental materials (wt.%)

[0105] Serial number C Si Cr Mn Mo N Cu Ce Ni Mg Example 1 0.015 0.3 18.1 14.5 4.5 0.98 4.0 0.19 0.01 0.003 Example 2 0.012 0.5 19.9 15.0 4.4 0.98 4.8 0.11 0.01 0.003 Example 3 0.014 0.3 18.3 15.2 4.5 1.01 5.9 0.20 0.02 0.004 Example 4 0.013 0.4 18.6 14.8 4.3 1.00 4.9 0.28 0.02 0.004 Example 5 0.012 0.4 19.5 15.1 4.4 0.99 5.1 0.18 0.01 0.003 Comparative Example 1 0.012 0.4 18.5 15.6 4.2 - 4.8 0.25 0.01 0.03 Comparative Example 2 0.013 0.5 18.2 15.4 4.3 0.54 5.0 0.27 0.02 0.04 Comparative Example 3 0.013 0.2 19.2 15.0 4.5 1.00 - 0.18 0.02 0.004 Comparative Example 4 0.014 0.3 19.5 15.1 4.3 0.98 2.7 0.19 0.01 0.003 Comparative Example 5 0.015 0.4 20.1 15.2 4.3 0.99 4.7 - 0.01 0.003 Comparative Example 6 0.012 0.5 19.8 15.0 4.2 1.00 4.6 0.05 0.01 0.002 Comparative Example 7 (316L) 0.021 0.5 16.5 1.3 2.2 - - - 11.6 -

[0106] Table 2. Design parameters

[0107]

[0108] The smelting equipment is a 25kg pressurized induction furnace with a charge of 20kg and a maximum pressure of 6.0MPa.

[0109] Based on the chemical composition in Table 1 and the experimental parameters in Table 2, the manufacturing method of medical high nitrogen stainless steel includes the following steps:

[0110] (1) Smelting: Put industrial pure iron, metallic chromium, metallic molybdenum, metallic manganese and electrolytic copper into the crucible of a pressurized induction furnace. At the beginning of smelting, evacuate the pressure in the induction furnace to 7Pa, and gradually increase the power to melt the charge in the crucible. Before melting, introduce 20,000Pa of argon to form a protective atmosphere. After the charge in the crucible of the pressurized induction furnace is fully melted, fill the furnace with high-purity nitrogen with a purity of ≥99.999% to a pressure of 1.5MPa, and then add chromium nitride, industrial silicon, magnesium-iron alloy and rare earth cerium to the crucible in turn through the feeding bin for alloying. The feeding interval is 2 minutes. Fill the pressurized induction furnace with high-purity nitrogen with a purity of ≥99.999% to a pressure of 1.8MPa, then cast at 1550°C, and finally release the pressure after cooling and take out the alloy ingot.

[0111] (2) Forging: The alloy ingot is placed in a furnace at 300°C, and the temperature is raised to 1230°C at a rate of 70°C / h and kept at this temperature for 2 hours to make the temperature inside and outside the alloy ingot uniform; the alloy ingot after being kept at this temperature is forged by a two-pier and two-draw method, with a forging ratio of 3.5 and a final forging temperature of 1120°C. After forging, a water spray cooling treatment is carried out at a cooling rate of 200°C / s to obtain a forged part.

[0112] (3) Solution treatment: The surface of the forging obtained in step (2) is sprayed with a stainless steel anti-oxidation coating and dried naturally, then placed in a furnace at 300°C, heated to 1230°C at a rate of 60°C / h and kept at that temperature for 2h for solution treatment, so that the nitrogen-containing and copper-containing precipitated phases in the steel are dissolved back and other elements are evenly distributed. Then, the forging is cooled in water to obtain a solution treatment sample.

[0113] (4) Aging treatment: The solution treated sample obtained in step (3) is kept at 600°C for 3 h to allow sufficient copper-rich phase to precipitate in the matrix and disperse and evenly distribute in the matrix, and then air-cooled to room temperature to obtain the product.

[0114] The antibacterial stainless steel for oral use obtained in the embodiment was tested for antibacterial properties, and the sterilization rates of the antibacterial stainless steel and the control sample (ordinary stainless steel or other solid materials without sterilization ability) against various common bacteria in the oral cavity (Streptococcus mutans, Actinomyces viscosus, Lactobacillus and Prevotella intermedia, etc.) were calculated according to the following formula: Sterilization rate (%) = [(number of live bacteria in the control sample - number of live bacteria in the antibacterial stainless steel) / number of live bacteria in the control sample] × 100; wherein the number of live bacteria in the control sample is the number of live bacteria after bacterial culture on the control sample, and the number of live bacteria in the antibacterial stainless steel is the number of live bacteria after bacterial culture on the antibacterial stainless steel.

[0115] The antibacterial test is carried out in accordance with the standards such as "JIS Z2801-2000 "Antibacterial processed products - Antibacterial test methods and antibacterial effects" and GB / T21510-2008 "Nano-inorganic materials antibacterial performance test methods", specifically:

[0116] Take 0.3mL of the test bacterial solution and drop it on the stainless steel sample. Use sterile tweezers to cover the cover film on each sample, so that the bacterial solution evenly contacts the sample, place it in a sterile plate, and culture it in a constant temperature incubator at 37℃ and relative humidity above 90% for 24 hours. Take out the samples that have been cultured for 24 hours, add 15mL of eluent respectively, repeatedly wash the samples and the cover film, shake well, take 0.1mL and drop it on the nutrient agar medium of the plate, make three parallel samples for each sample, and spread it evenly with a sterile triangular rake, place it in a 37℃ constant temperature incubator for 48 hours, and then count the viable bacteria according to the method of GB / T4789.2. The results are shown in Table 3.

[0117] Then, the antibacterial persistence test was conducted. To simulate the oral environment, the samples and control stainless steel were wrapped with a sponge or rag soaked with artificial saliva in a 37°C incubator and then kept for 15 days. The samples were then subjected to an antibacterial test, and the results are shown in Table 3.

[0118] Table 3. Antibacterial performance comparison table (%)

[0119]

[0120] As can be seen from Table 3, the embodiments 1-4 of the present invention are effective in resisting oral bacteria and have persistent antibacterial ability. In Comparative Example 1, no N element was added, and the sterilization rate was low; in Comparative Example 2, the N element content was low, and the sterilization rate was slightly low; in Comparative Example 3, no Cu element was added, and the sterilization rate was low; in Comparative Example 4, the Cu element content was low, and the sterilization rate was slightly low; in Comparative Example 5, no Ce element was added, and the sterilization rate was low; in Comparative Example 6, the Ce element content was low, and the sterilization rate was slightly low. Through the above analysis, it can be seen that only when the contents of N element, Cu element and Ce element reach a balanced range, they complement and cooperate with each other, so that stainless steel has good antibacterial properties.

[0121] The mechanical property tests of medical stainless steel are divided into tensile and impact. The tensile specimens are finely processed into the required tensile specimen size according to the ASTM-E8 standard. The tensile test was carried out on a 200KN electronic universal testing machine. The experimental temperature was room temperature and the tensile rate was 2mm / min. Three parallel samples were selected for each group of experiments, and the average value was taken. The oscillometric impact specimens were finely processed into 10mm×10mm×55mm impact specimens, and finally processed into a V-notch with a depth of 2mm. The oscillometric impact test uses an oscillometric impact testing machine to measure the impact absorption energy of the specimen at room temperature. Three parallel samples were selected for each group of experiments, and the average value was taken.

[0122] The corrosion resistance was tested by electrochemical method. The experiment used an electrochemical workstation and a traditional three-electrode system, that is, the sample surface was the working electrode, the metal platinum electrode was the auxiliary electrode, and the saturated calomel electrode (SCE) was the reference electrode. The electrochemical experimental solution was a 3.5% NaCl solution, and the experimental temperature was controlled at 30°C by a constant temperature water bath. The dynamic potential polarization was scanned from the relative open circuit potential of -0.2V to above the overpassivation potential at a potential scanning rate of 0.333mV / s.

[0123] Tables 4 and 5 provide the results of tensile tests, impact tests and potentiodynamic polarization tests. From the data in Tables 4 and 5, it can be seen that the stainless steel prepared in Examples 1-4 exhibits better mechanical properties and corrosion resistance than the stainless steel in Comparative Examples 1-6 and the ordinary 316L austenitic stainless steel in Comparative Example 7.

[0124] Table 4. Mechanical properties comparison table

[0125]

[0126]

[0127] Table 5. Corrosion resistance comparison table

[0128] <![CDATA[Self - corrosion potential / mV SCE > <![CDATA[Pitting potential / mV SCE > Example 1 -227.2 980.5 Example 2 -241.5 948.7 Example 3 -236.4 944.3 Example 4 -230.6 968.3 Example 5 -232.6 965.4 Comparative Example 1 -362.4 590.3 Comparative Example 2 -332.4 808.5 Comparative Example 3 -180.5 1150.3 Comparative Example 4 -189.3 1032.5 Comparative Example 5 -269.4 873.8 Comparative Example 6 -255.6 902.6 Comparative Example 7 (316L) -150.4 468.7

[0129] The above serial numbers of this application are only for description and do not represent the advantages and disadvantages of the implementation scenarios. The above disclosure is only a few specific implementation scenarios of this application, but this application is not limited to them, and any changes that can be thought of by technicians in this field should fall within the scope of protection of this application.

Claims

1. A medical high nitrogen stainless steel, characterized in that: The chemical composition of the medical high nitrogen stainless steel includes: C, Si, Cr, Mn, Mo, N, Cu, Ce, Mg, the rest are Fe and unavoidable impurities; Among them, the N content is 0.97wt% to 1.05wt%, the Cu content is 4wt% to 6wt%, and the Ce content is 0.11wt% to 0.3wt%.

2. The medical high nitrogen stainless steel according to claim 1, characterized in that: Cr content is 18wt% to 20wt%; Mn content is 14wt% to 16wt%; The Mo content is 3.5wt% to 4.5wt%.

3. The medical high nitrogen stainless steel according to claim 1, characterized in that: The inevitable impurities in the medical high nitrogen stainless steel include Ni, and the Ni content is less than 0.05wt%; The equivalent ratio between Cr and Ni is in the range of 0.50 to 0.70; The Cr equivalent is the sum of the weight percentage content of Cr, the weight percentage content of Mo and the weight percentage content of Si with a preset coefficient; The Ni equivalent is the weighted sum of the weight percentage content of Ni, the weight percentage content of C, the weight percentage content of N, the weight percentage content of Mn and / or the weight percentage content of Cu; Among them, the preset coefficient of Si is 1.5, the weighting coefficient of Ni is 1, the weighting coefficient of C is 30, the weighting coefficient of N is 30, the weighting coefficient of Mn is 0.5, and the weighting coefficient of Cu is 0.

3.

4. The medical high nitrogen stainless steel according to claim 1, characterized in that: The pitting corrosion resistance equivalent index of the medical high nitrogen stainless steel is greater than or equal to 45; The weight percentage content of N, the weight percentage content of Cr, and the weight percentage content of Mo satisfy the following formula: PREN = (wt.%) Cr +3.3×(wt.%) Mo +16×(wt.%) N and / or, The weight percentage content of N, the weight percentage content of Cr, the weight percentage content of Mo, and the weight percentage content of Cu satisfy the following formula: 23≤((wt.%) Cr +0.5×(wt.%) Mn -0.1×(wt.%) Cu ) / (wt.%) N ≤30。 5. The medical high nitrogen stainless steel according to claim 1, characterized in that: C content is less than 0.02wt%; Si content is 0.1wt% to 0.6wt%; The Mg content is 0.002wt% to 0.005wt%.

6. A method for preparing medical high nitrogen stainless steel, characterized in that: The method comprises: The raw materials are configured according to the chemical composition of the medical high nitrogen stainless steel as described in any one of claims 1 to 5; Under smelting pressure, respectively adding N raw material, Si raw material, Mg raw material, and Ce raw material into a molten liquid obtained by melting Fe raw material, Cr raw material, Mo raw material, Mn raw material, and Cu raw material to obtain an alloy melt; After a preset time interval, the alloy melt is cast under a casting pressure, and an alloy ingot is obtained after cooling and pressure relief, wherein the casting pressure is greater than the smelting pressure; Forging the alloy ingot to obtain an alloy forging; heat treating the alloy forging to obtain medical high nitrogen stainless steel; Wherein, the heat treatment includes solution treatment and aging treatment.

7. The method for preparing medical high nitrogen stainless steel according to claim 6, characterized in that: The smelting pressure satisfies the following formula: The casting pressure satisfies the following formula: P2=[(0.08~0.10)P1 / P θ +(0.35~0.65)]; In the formula, P1 represents the smelting pressure, P2 represents the casting pressure, and P θ represents standard atmospheric pressure, α and β represent coefficients related to smelting temperature, and A represents a constant related to the chemical composition of the medical high nitrogen stainless steel.

8. The method for preparing medical high nitrogen stainless steel according to claim 6, characterized in that: The N raw material is chromium nitride, and the weight percentage of N added in the form of chromium nitride satisfies the following formula: (wt.%)1=[-0.02P1 / P θ +(0.66~0.76)]×(wt.%) N ; Wherein, (wt.%) 1 represents the weight percentage of N added in the form of chromium nitride, P1 represents the smelting pressure, P θ Indicates standard atmospheric pressure, (wt.%) N Indicates the N content in the chemical composition of the medical high nitrogen stainless steel; The temperature of the solution treatment is 1220°C to 1230°C, the heating rate is 60 to 80°C / h, and the time is 1h to 2h; The temperature of the aging treatment is 560° C. to 600° C., and the time is 2 h to 4 h.

9. The method for preparing medical high nitrogen stainless steel according to claim 6, characterized in that: The forging process of the alloy ingot comprises: The alloy ingot is forged by a two-pier and two-draw method, wherein the forging ratio is in the range of 3 to 5, the forging temperature is 1220° C. to 1230° C., and the final forging temperature is 1110° C. to 1130° C.; After forging, the forging is cooled to room temperature by water to obtain the alloy forging, wherein the cooling rate is 200°C / s to 300°C / s.

10. A medical device, characterized in that: The medical device is made by a molding process using the medical high nitrogen stainless steel as described in any one of claims 1 to 5 or the medical high nitrogen stainless steel obtained by the preparation method of medical high nitrogen stainless steel as described in any one of claims 6 to 9 as a raw material.

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