Application of Low Temperature Active-Screen Plasma Nitriding and Carburizing to an Austenitic Stainless Steel Small-Diameter Thin Pipe

Abstract

Surface hardening treatments such as nitriding can improve the mechanical properties to extend the applicability of austenitic stainless steel (ASS) fine and precise machining. Improving these characteristics without changing the design and material is highly advantageous, particularly for medical and surgical instruments. In particular, an improved bending rigidity of medical injection needles is desirable because a small needle diameter reduces invasiveness. However, no method has yet been reported for improving the bending strength of ASS without reducing its corrosion resistance. It is known that the low-temperature nitriding and carburizing generated expanded austenite (S phase) that can be hardened while maintaining the corrosion resistance of austenitic stainless steel. It would be very beneficial if these techniques could be applied to thin pipes with a small diameter such as medical injection needles. In the present study, low-temperature active-screen plasma nitriding (ASPN) and active-screen plasma carburizing (ASPC) are applied to improve the bending rigidity of an ASS pipe with a small diameter.