Effectiveness of using low-temperature coolants in machining to enhance durability of AISI 316L stainless steel for reusable biomedical devices

Austenitic stainless steels are currently used for the manufacture of reusable medical instruments, thanks to their combination of elevated strength, corrosion resistance, biocompatibility and low cost. However, during their service life, they are subjected to repeated sterilization cycles, which lead to the loosening of the surface oxide stability and, thus, decrease their durability. In the present study, the influence of different machining cooling conditions on the in-service corrosion behaviour of the AISI 316L stainless steel is investigated with the aim of increasing its resistance to the sterilization cycles. In particular, the effects of low-temperature coolants, namely Liquid Nitrogen (LN2) and gaseous Nitrogen (N2) cooled by LN2 to -100 degrees C, were investigated and compared to those of dry and wet cutting. The machined surface integrity was characterized in terms of microstructure, hardness, residual stresses and surface roughness. Electrochemical studies, making use of potentiodynamic and cyclic polarization tests, were carried out to evaluate the corrosion resistance of the machined surfaces. It was found that the AISI 316L microstructure near the machined surface was significantly affected by the machining cooling strategies The effectiveness of using low-temperature coolants in machining of stainless steels for the manufacture of reusable medical devices was therefore demonstrated.