CHARACTERISATION & CORROSION BEHAVIOR OF WARM MULTIAXIALLY FORCED 316L STAINLESS STEEL IN 3.5wt% NaCI

Abstract

Stainless steels are chosen primarily for their corrosion resistance. Most commonly used grades are the non-magnetic austenitic kind. Refinement of grains by severe plastic deformation leads to higher strength and weight saving for some applications. If the corrosion resistance of the severely deformed stainless steel is better or at least comparable to that of the as received steel then its use for biomedical applications, pharmaceutical machinery, and food preparation equipment is justified. The purpose of this work is to study the microstructural evolution and corrosion behavior of warm multi axially forged 316L steel, a grade that is also used in orthopedic implants. Most of the orthopedic implants fail due to pitting corrosion. Hardness testing was performed on the multiaxially forged samples. Potentiodynamic, cyclic polarization, FeCl3 immersion tests were performed and the uniform and localized corrosion of as received and multi-axially forged specimens is compared in 3.5wt % NaCl solution. Improved pitting corrosion resistance of the multiaxially forged sample is attributed to an increase in grain boundary volume and homogenization of pit inducing impurities and non-metallic phases due to severe plastic deformation. Mott Schottky analysis showed that the increase in pitting resistance can be attributed to an increase in the flat band potential. Corrosion behavior is influenced by the properties of the passive film formed on the steel having ultrafine grained structure.