XPS depth profiling analysis of passive surface layers formed on austenitic AISI 304L and AISI 316L SS after high-current-density electropolishing

• High current-density electropolishing (HDEP) at 1000 A/dm2 of two austenitic steel (304L and 316L) results are presented.
• Two different electrolytes (80 vol.% H3PO4 and 20 vol.% H2SO4 as well as 20 vol.% of H3PO4 and 80 vol.% of H2SO4) were applied.
• XPS results of HDEP (EP1000) and a standard electropolishing EP50 are compared.
• Significant differences in the chemical structure and composition of passive layers are displayed.

In this paper, the XPS depth profiling results of passive surface layers formed on nickel–chromium AISI 304L and nickel–chromium–molybdenum AISI 316L austenitic stainless steels after a standard electropolishing at current density of 50 A/dm2 (EP50), and after a high current density electropolishing at 1000 A/dm2 (EP1000) in the mixture of sulfuric/orthophosphoric acids electrolyte in the following proportions H3PO4:H2SO4 = 1:4 and 4:1 are presented. The results have shown, that in case of nickel–chromium austenitic stainless steel (AISI 304L) there were no detected significant differences in the chemical composition of the passive layer formed after EP50 and EP1000 electrochemical treatments. In the passive layer of nickel–chromium–molybdenum austenitic stainless steel, the chromium and molybdenum enrichment was noted after EP1000 electropolishing, but was not observed after EP50 operation.