Enhanced corrosion resistance of Cr-Mn ASS by low temperature salt bath nitriding technique for the replacement of convectional Cr-Ni ASS

Abstract

Purpose The purpose of this paper is to enhance the corrosion resistance of Cr-Mn austenitic stainless steel (ASS) via low temperature salt bath nitriding and to replace the convectional Cr-Ni ASS with newly developed enhanced corrosion resistive Cr-Mn ASS. Design/methodology/approach The low temperature salt bath nitriding was performed on Cr-Mn ASS at 450°C for 3 h in potassium nitrate salt bath. Findings The present paper compares the corrosion resistance of salt bath nitrided Cr-Mn ASS with convectional Cr-Ni ASSs (316 L and 304 L ASSs) in 3.5 per cent NaCl by electrochemical techniques. The electrochemical impedance spectroscopy result shows the increase in film resistance and potentiodynamic polarization results show the enhanced corrosion resistance of nitrided Cr-Mn ASS, which is almost equivalent to that of 316 L and 304 L ASSs. This is attributed to the formation of nitrogen supersaturated dense nitride layer. The present results therefore suggest that the nitrided Cr-Mn ASS may replace costly convectional Cr-Ni ASSs for commercial and industrial applications. Originality/value Ever-increasing price of nickel (Ni) is driving the industries to use Ni-free or low-Ni austenitic stainless steels (ASSs). But its corrosion resistance is relatively poor as compared to conventional Cr-Ni ASSs. However, its corrosion resistance can be improved by nitriding. The low temperature salt bath nitriding of Cr-Mn ASS and its electrochemical behavior in 3.5 per cent NaCl has not been studied. The present research paper is beneficial for industries to use low cost Cr-Mn, enhance its corrosion resistance and replace the use of costly conventional Cr-Ni ASSs.

Effect of Heat Input on the Microstructural, Mechanical, and Corrosion Properties of Dissimilar Weldment of Conventional Austenitic Stainless Steel and Low-Nickel Stainless Steel

“…6. In Bode plots, the impedance modulus at low-frequency region signifies the resistance to corrosion, while the higher impedance values at high-frequency region signify the passive film compactness [31,32]. Similar to the Nyquist plots, the higher impedance values can be seen for 316L BM, while the least can be observed for 201 austenitic SS BM.…”

“…It has been reported that higher the E pit values, higher is the corrosion resistance. Hence, the better corrosion resistance of 316L austenitic SS can be attributed to the higher alloying elements (Mo and Ni) as more compared to 201 austenitic SS [31]. Interestingly, it can be noticed from Table 4 that the E pit values for LHI FZ and HHI FZ are higher than the 201 austenitic SS BM.…”

“…4 that the diameter of Nyquist plot of 316L austenitic SS BM is more, while the diameter of Nyquist plot of 201 austenitic SS BM is the least. This can be attributed to the higher alloying elements (Mo and Ni) in 316L austenitic SS BM, and FZs are more compared to 201 austenitic SS [31]. Moreover, the LHI FZ shows a higher diameter of the Nyquist plot as compared to that of HHI FZ.…”

Solutions of Critical Raw Materials Issues Regarding Iron-Based Alloys

“…On one hand, the use of Ni is preferable compared to Mn not only in terms of an austenitic phase stabilizer, but also due to its contribution to increasing the corrosion resistance of SSs, especially in acidic environments. On the other hand, nickel’s high and fluctuating price cannot be neglected, consequently influencing that of SSs; thus, new strategies in the development of new alloys containing Mn are proposed [ 46 ] and could be promoted.…”

“…A promising strategy in the direction of saving Cr and maintaining the corrosion performances of the most common SSs is that which considers the development of new Fe-based alloys. They have a low-Cr content in the bulk (e.g., low-alloyed common steels or some ferritic SSs), whereas the surface has a Cr-rich coating [ 21 ] and/or other protective coating solutions [ 47 ], containing in the bulk Mn [ 46 ] in place of Ni. Through laser and plasma technologies or ion implantation, a surface alloying of Cr or Cr, C, N, etc.-rich surfaces can be obtained as reported by the following examples.…”