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J.L. Johnson, “Corrosion Resistant Medical Instruments Produced by Metal Injection Molding,” Medical Device Materials, S. Shrivastava (ed.), ASM International, Materials Park, OH, 2004, pp. 408-413.
Medical instruments are generally produced from stainless steels because of their strength, hardness, corrosion resistance, and ease of sterilization. New instrument applications are trending toward smaller, more complex devices for minimally invasive surgery. Such devices are being designed for greater freedom of movement, which has increased the numbers of metal parts used in the assembly. Metal injection molding (MIM) is being increasingly utilized to reduce the manufacturing costs of these types of components. Common grades of MIM stainless steel include 304L, 316L, 430, 440C, and 630. Each of these materials is mixed with a thermoplastic binder and injection molded, debound, and thermally processed. The tensile properties, hardness, surface finish, and corrosion resistance of the sintered components are shown to be comparable to the specifications for their wrought and cast counterparts.
MIM can produce stainless steels with mechanical and corrosion properties that are useful for medical instruments. Austentic 316L stainless steel produced via MIM has corrosion resistance comparable to wrought 316L. Hardness values over 50 HRC can be achieved with MIM 440C for excellent wear resistance. MIM 630 provides a good combination of strength, hardness, and corrosion resistance. Besides making manufacturing of current medical devices more affordable, the MIM process can enable the cost effective production of novel designs, including microsized and functionally graded devices. Such developments may enable new solutions to current health care problems.