Effect of alloyed molybdenum on corrosion behavior of plasma immersion nitrogen ion implanted austenitic stainless steel

• The paper discusses role of Mo on the surface of plasma immersion ion implantation (PIII) modified stainless steels.
• Mo suppress α′ formation and increases corrosion and pitting resistance.
• Mo containing steel shows three passive film characteristics.
• 250 °C and 380 °C implantation temperatures enhance pitting and corrosion resistance.
• Corrosion resistance of the alloys deteriorates, when implanted at 500 °C.

Plasma immersion ion implantation (PIII) of nitrogen has been performed on two austenitic stainless steels (with and without Mo addition) at three different temperatures namely, 250, 380 and 500 °C for 3 h. Grazing angle X-ray diffraction (GXRD) was carried out on the surface of the steels (both PIII treated and untreated). GXRD results suggest that PIII is more effective in Mo containing stainless steel (SS). The electrochemical corrosion studies examined through both by DC polarization and EIS technique in 3.5 wt.% NaCl reveals that, 3 h N-implantation at 250 and 380 °C improves the corrosion and pitting resistance of both the austenitic stainless steels under investigation. The effect N implantation on pitting resistance is seen more in the presence of Mo, than when it is not present in the SS. It is further emphasized that the pitting resistance of the alloys significantly deteriorates, when they are implanted at 500 °C.