Effects of Particle Sizes on Sintering Behavior of 316L Stainless Steel Powder
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AS more than half of injection-molded and sintered components are made of stainless steel powders nowadays, understanding the densification behaviors of stainless steel powders is of great importance and interest to successful sintering processes.[1–3] Among various stainless steels, 316L stainless steel has excellent mechanical properties of high corrosion resistance, high heat resistance, and good weldability. In this regard, 316L stainless steel is one of the most widely used materials for powder injection molding (PIM) research and industrial applications such as pharmaceuticals, architectural applications, and medical implants including pins, screws, and orthopedic implants such as hip and knee replacements. In manufacturing industries, the PIM process is a productive and cost-effective net-shaping process, which combines advantages of both plastic injection molding and conventional powder metallurgy. This process has many advantages including shape complexity, tight tolerances, and material selection of metals and ceramics. Once desired materials, mold geometries, and DONG YONG PARK, Graduate Student, Department of Mechanical Engineering, and SEONG JIN PARK, Associate Professor, Department of Mechanical Engineering and Division of Advanced Nuclear Engineering, are with POSTECH, Pohang, Gyungbuk 790-784, Korea. SHI W. LEE, Assistant Professor, is with the Department of Industrial Engineering, Pusan National University, Busan 609-735, Korea. YOUNG-SAM KWON, President, is with CetaTech, Inc., Sacheon, Gyungnam 664-950, Korea. ISAMU OTSUKA, Director, is with the MP Development & Engineering Department, Epson Atmix Corporation, Hachinohe, Aomori 039-1161, Japan. Contact e-mail: [email protected] Manuscript submitted February 22, 2012. Article published online November 8, 2012 1508—VOLUME 44A, MARCH 2013
process parameters are decided, PIM is an appropriate process for the mass production. The PIM process consists of four steps: (1) mixing— producing the pelletized feedstock of the powder and organic binders; (2) molding—injecting the feedstock melt into the mold cavity, similar with thermoplastics; (3) debinding—extracting or removing the organic binders out of the injection-molded part via solvents or the thermal energy; and (4) sintering—densifying the debound part from the low initial density to the high final density, close to the full density.[4] Figure 1 shows a schematic diagram of the PIM process. Sintering, a thermally activated diffusion process, is one of the key steps in the PIM process as well as other powder metallurgy processes, which affects the density as well as other mechanical properties of the final part. Among several mechanical properties that are affected by sintering, the density can be said to be one of the most important factors to evaluate merchantability of sintered parts. The density of sintered parts is related to final dimensions as well as hardness of the part, since the pores occupying a significant portion in volume are eliminated and individual particles are bonded together int
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