Effect of titanium nitride (TiN) on the corrosion behavior of a supermartensitic stainless steel

This study evaluates the effect of high N, Ni, and Ti contents on the microstructure and corrosion properties of a supermartensitic stainless steel when immersed in a 3.5% NaCl solution. Tempering procedure at several temperatures resulted in a martensitic microstructure composed of grains ranging from 60 to 70 mu m, TiN microparticles, and austenite. The sample treated at 610 degrees C showed better corrosion resistance due to the lower current density of the anodic polarization curve and less negative pitting potential, which was thoroughly influenced by the content of austenite (6.2 vol%). Anodic curves presented current fluctuation attributed to the presence of passive film instability, due to micro-galvanic corrosion between TiN particles and matrix. Impedance analysis on the sample tempered at 610 degrees C confirmed that 6.2 vol% of austenite assists the protective film by making it thicker and more protective in chloride media.