Corrosion Resistance of AISI 316L after Short Holding Time of High Temperature Gas Nitriding (HTGN)

Abstract

Stainless steel AISI 316L is widely used as biomaterial due to its high corrosion resistance. However this property decreases in highly stressed and oxygen depleted environments. Several methods have been developing to increase the corrosion resistance such as low and high temperature gas nitriding. High temperature gas nitriding (HTGN) produces more depth effect than low temperature gas nitriding. Unfortunately HTGN for long holding time results on grain coarsening which reduce its tensile strength. The objective of this research is to determine the effect of HTGN at short holding time on the corrosion resistance, hardness and grain coarsening of AISI 316L.

Specimens were made from as rolled 1 mm thickness AISI 316L plate. Before HTGN process, the specimens were rinsed using ultrasonic cleaner in acetone medium. HTGN process was conducted at temperature 1050^oC, 1100^oC and 1200^oC for short period holding time i.e. 15 and 30 minutes. Micro hardness, microstructure and corrosion tests were conducted in the simulated body fluid (SBF) to evaluate the process.

The results show that hardness and corrosion resistance were increased significantly after HTGN process. Moreover, hardness for holding time of 30 minutes was higher than 15 minutes, however the corrosion resistance were decreased. In addition HTGN process also results on grain coarsening at 30 minutes holding time, however for holding time 15 minutes and temperature 1050^oC and 1100^oC did not give significant grain coarsening. Therefore, the HTGN process parameters must be optimized for compromise between hardness and corrosion resistance.

Keywords: high temperature gas nitriding, corrosion resistance, grain coarsening, AISI 316L