Effect Of Thermochemical an‎d Mechanical Surface Treatments On Metallographic Of Biomaterial Stainless Steel Grad 316l

This work aims to study the effect of the thermochemical (nitro-carburizing) and mechanical (ultrasonic shot peening USP) surface treatment on surface characteristics such as hardness, roughness, residual stress, microstructure and corrosion behavior of biomaterial stainless steel grade 316 L. Nitro-carburizing process was done in temperatures 580 oC at 90 minutes and carry with ultrasonic shot peening process using shot ball from hard steel with diameter of 0.4 mm in different times at 30 and 60 min. Corrosion test was done in corrosion cell content on sea water (3.5% NaCl solution) by using potentostat instrument. The result shows that thermochemical process was formation of compost from nitro-carburizing layer (white layer) with thickness 10 µm by diffusion inner in metal layer. Also we found that the mechanical treatment by ultrasonic shot peening has cause produce of compressive residual stresses in surface layer of metal which officiates to increase the hardness of stainless steel surface. Thermochemical and mechanical processes had caused to form of carbides of NiCrMo and NiCr which hard surface layer. It was shown that both processes caused increase in surface roughness and hardness with increases the time of ultrasonic shot peening. Also the corrosion results noticed that the nitro-carburizing and ultrasonic shot peening caused a decrease in pitting corrosion resistance for all samples after thermochemical and mechanical surface processes.