Corrosion behavior of nickel-free high nitrogen austenitic stainless steel in simulated biological environments

The corrosion resistance of the nickel-free high nitrogen austenitic stainless steel without manganese, Fe-23Cr-2Mo-1.5N (mass%) (HNS) as biomaterials, was evaluated by the polarization test in various electrolytes: 0.9%NaCl solution (saline), phosphate buffered saline (PBS(-)), Hanks' solution (Hanks) and Eagle's minimum essential medium (E-MEM). Conventional austenitic stainless steel, 316L, was also polarized for comparison. The both alloys were spontaneously passivated in all electrolytes. The HNS didn't show pitting corrosion in the polarization range in all electrolytes although the 316L showed pitting corrosion. Passive current densities of the HNS in all electrolytes were lower than those of 316L. Therefore, the HNS shows higher passivity and resistance to pitting corrosion than 316L. The passive current density in Hanks of HNS was lower than that in saline, indicating that the protectiveness of surface oxide film increased with the existence of inorganic ions such as phosphate and calcium ions. On the other hand, the passive current density in E-MEM was higher than that in Hanks, but was lower than that in saline. Consequently, the HNS must show high corrosion resistance in vivo and be a promising biomaterials.