Powder injection molding process for nickel free high nitrogen stainless steel

 

Date：[2024/12/25]
 

Nickel free high nitrogen austenitic stainless steel is a type of stainless steel with high mechanical properties and corrosion resistance, especially it does not contain the element nickel that can cause serious allergic reactions in some people, which can effectively prevent the problem of "nickel sensitivity". Therefore, it has a wide market space in biomedical materials and is currently receiving attention from the academic and industrial circles at home and abroad.

Although new technologies and processes such as hot isostatic pressing melting, pressure induction melting, pressure plasma melting, pressure electric slag melting, and nitrogen slag removal melting have been adopted, multiple grades of nitrogen-containing stainless steel materials have been developed. However, the above production technologies all have problems such as complex equipment, high-pressure gas hazards, difficult process control, and high production costs to varying degrees, and there are certain difficulties in obtaining materials with high nitrogen content. The production of high nitrogen steel by powder metallurgy has many advantages, such as the absence of high-pressure melting facilities in production and lower costs; Fine grain strengthening, dispersion strengthening, and other strengthening methods enhance material properties. In addition, experimental evidence shows that the solid solubility of nitrogen in solid austenitic stainless steel is greater than its solubility in liquid state. Therefore, powder metallurgy solid nitriding process is an economically and technically feasible method for producing high nitrogen steel. Metal injection molding (MIM), as a product combining traditional powder metallurgy and advanced plastic injection molding processes, has unique advantages in preparing near net shape products with three-dimensional complex geometric shapes, uniform microstructure, and high performance. Moreover, this technology uses finer powder particle size, which is conducive to diffusing nitrogen into the powder particles to increase nitrogen content and ultimately obtain high nitrogen stainless steel. Currently, research on the production of nickel free high nitrogen austenitic stainless steel materials using injection molding technology is still in its preliminary stage both domestically and internationally.

The experiment used high-pressure inert gas atomization method to produce 0Cr17Mn11Mo3 stainless steel powder. It can be seen that the powder has high sphericity, small average particle size (D50=17.4 μ m), high loose density and tap density (3.67 and 4.95g · cm-3, respectively). These characteristics of the powder are conducive to improving its flowability and loading capacity during injection molding process.

The adhesive adopts a thermoplastic paraffin based adhesive system with good fluidity, with a formula of 65wt% PW+30wt% HDPE+5wt% SA. Mix stainless steel powder with an appropriate amount of binder to make feed, using a powder loading of 64%, and then test the rheological properties of the feed. The injection process is carried out on the CJ-80E injection molding machine, and the feed is injected into a rod blank with a size of  8mm × 70mm. After solvent degreasing, thermal degreasing, and 800 ℃ pre sintering, a pre sintered blank with certain strength is obtained. After sintering the pre sintered billet in high-purity nitrogen gas at different pressures in the temperature range of 1200-1350 ℃ for 1-2.5 hours, the density of the sintered body was measured using the Archimedes method (drainage method), and the nitrogen content of the sintered body was measured using the inert gas pulse infrared thermal conductivity method (QB-Q-02-1997). The sintered body is machined into a standard tensile rod of  5mm × 60mm according to national standards, and after solution treatment at 1150 ℃ for 90 minutes and water quenching, its tensile mechanical properties (such as yield, tensile strength, and elongation) are measured using an Instron universal testing machine, and compared with nitrogen free samples prepared using the same sintering process in an argon atmosphere.

1) The feed obtained by mixing 64vol% atomized 0Cr17Mn11Mo3 powder with a binder composed of 65wt% PW+30wt% HDPE+5wt% SA has good rheological properties; The optimal injection process parameters for feeding are injection pressure of 60-85MPa and corresponding injection temperature of 160-170 ℃;

Raising the sintering temperature is beneficial for increasing the density of the sintered body, but it is not conducive to obtaining high nitrogen content. Increasing the sintering nitrogen atmosphere pressure can achieve higher nitrogen content, but it is not conducive to increasing the density of the sintered body. Experiments have shown that the optimal sintering process is to sinter at 1300 ℃ for 2 hours under a nitrogen pressure of 0.1 MPa. At this time, the relative density of the sintered body can reach 99%, and the nitrogen content can reach 0.78%. After solid solution treatment at 1150 ℃ and water quenching cooling, the yield strength, tensile strength, elongation, section shrinkage, and hardness of the sintered body reached 580MPa, 885MPa, 26.0%, 29.1%, and 222HV10, respectively.

Shenzhen Yujiaxin Tech. Co., Ltd., as a leading expert in powder injection molding technology, focuses on the processing and production of nickel free high nitrogen stainless steel. With profound industry accumulation and technological innovation, the company has successfully mastered the core technology of nickel free high nitrogen stainless steel powder injection molding, providing the market with numerous high-quality and high-precision products. Nickel free high nitrogen stainless steel has shown extensive application prospects in various fields such as medical devices, food processing, chemical equipment, etc. due to its excellent corrosion resistance, high strength, and good biocompatibility. Yujia Xin Technology continuously optimizes production processes and strictly controls product quality to ensure that every product meets the stringent requirements of customers. At the same time, the company is committed to technological research and innovation, striving to make more breakthroughs in the field of nickel free high nitrogen stainless steel powder injection molding and contribute more to the development of the industry.

Yujiaxin not only focuses on the performance and quality of nickel free high nitrogen stainless steel processing, but also pays great attention to environmental protection and sustainable development. The company adopts advanced environmental protection equipment and production processes to reduce energy consumption and emissions during the production process, striving to achieve green production. In addition, Yujia Xin Technology actively communicates with customers, understands their needs, and provides customized solutions to meet the diverse needs of customers in different fields. With professional technical strength, high-quality service attitude, and environmentally friendly production concept, Yujia Xin Technology has become a leader in the field of nickel free high nitrogen stainless steel powder injection molding, winning widespread praise and trust from domestic and foreign customers.