Effect of sulfate on the pitting potential of austenitic stainless steels 18Cr8Ni and 17Cr6Mn5Ni in chloride media

José Wilmar Calderón-Hernández,Rodrigo Magnabosco,Neusa Alonso-Falleiros,Duberney Hincapíe-Ladino

doi:10.1590/0370-44672017720018

Abstract

Abstract Pitting corrosion resistance of two austenitic stainless steels, 18Cr8Ni (Type 304L or UNS S30403 stainless steel) and 17Cr6Mn5Ni, was evaluated in three electrolytic solutions containing a fixed concentration of 0.6M sodium chloride and different additions of sodium sulfate, 0.06M, 0.15M or 0.6M. Cyclic potentiodynamic polarization tests were performed on as-received samples and on specimens annealed at 1010°C, 1040°C, 1070°C or 1100°C. The best pitting corrosion resistance was presented by the 17Cr6Mn5Ni steel annealed at 1070°C or 1100°C, with lower delta ferrite contents, in the electrolyte with the highest sulfate concentration. It can be found that the addition of sodium sulfate inhibits pitting corrosion and has a better inhibitor effect in the high manganese steel.

Highlights

The historical problem of nickel price oscillations has propelled investigations on the use of other austenitizing elements in austenitic stainless steels, especially manganese (Charles, 2005)
These researches were executed using revealing that Mn addition reduced both electrolytic solutions based on sulfuric general and pitting corrosion resistance. acid (H2SO4), which is not appropriate for The latter was thought to be caused by studying pitting corrosion
In the 0.6M NaCl + 0.6M Na2SO4 electrolyte, 17Cr6Mn5Ni steel heat treated at 1070° C and 1100° C was there a higher pitting potential than 18Cr8Ni

Summary

Introduction

The historical problem of nickel price oscillations has propelled investigations on the use of other austenitizing elements in austenitic stainless steels, especially manganese (Charles, 2005). Some investigations on the corrosion behavior of Mn alloyed austenitic stainless steel reported that Mn promoted a negative effect on the corrosion resistance (Condylist et al, 1970; El Dim et al, 1972; Lunarska et al, 1975; Murgulesco and Radovici, 1990 and Knyazheva et al, 1965). These researches were executed using revealing that Mn addition reduced both electrolytic solutions based on sulfuric general and pitting corrosion resistance. In electrochemical tests in 0.025N NaCl, the steels used in the present investigaand anodic polarization in 0.1N H2SO4, tion, there is not expected a considerable occurrence of MnS due to low S content (10 and 20 ppm) obtained in today’s steel making practice

Results

Discussion

Conclusion