5. Conclusions
Fretting fatigue behaviour was studied in air and in PBS(-) for Ni-free high-nitrogen steel (HNS) with a yield strength of about800MPa.Forcomparison,SUS316L(CR)withasimilar yield strength was also studied. The results obtained are as follows.
1. The plain fatigue limit of HNS was slightly lower than that of SUS316L(CR) both in air and in PBS(-), although the former steel has a higher tensile strength than the latter. 2. ThefrettingfatiguelimitofHNSwassignificantlyhigher than that of SUS316L(CR) both in air and in PBS(-) as a result of an obviously smaller decrease in fatigue limit of HNS by fretting than that of SUS316L(CR). 3. The crack-initiation life of HNS was longer than that of SUS316L(CR)bothinairandinPBS(-)underthefatigue stresses giving the same fatigue life. 4. The corrosion potentials and passive current densities of both steels were approximately equal. The resistance of HNS to pitting is significantly higher than that of SUS316L(CR) and no pitting of HNS was observed up to oxygen evolution potential. 5. HNS showed the highest fretting fatigue limit in air and in PBS(-) among the conventionally used metallic biomaterials such as SUS316L(CR), Ti–6Al–4V alloy and Co–Cr alloy.
Consequently, it can be said that HNS is a potential metallic biomaterial that has higher fretting fatigue strength and corrosion resistance than conventional materials.