Electropolishing of iron chromium alloys

This study investigates the electropolishing of ferritic iron-chromium alloys (Fe-13Cr and Fe-24Cr) and austenitic type 304 stainless steel in phosphoric acid-sulphuric acid electrolytes using rotating disk electrodes. The objective is to understand the electrochemical behavior and conditions favoring electropolishing of these alloys. Based on experimental results, it is found that the electropolishing of stainless-steel-type alloys occurs in the transpassive region and is mass transport controlled, significantly influenced by elevated temperatures. The anodic polarization behavior of the Fe-Cr alloys in 65% H3PO4–20% H2SO4–15% H2O shows insensitivity to the elemental composition of the alloys, mirroring that of type 304 stainless steel. Notably, at temperatures around 70 °C, electropolishing is viable for a broad concentration range of the acid mixture, whereas in the absence of phosphoric acid, iron passivity hinders electropolishing conditions. These findings contribute to the understanding of the electrochemistry involved in electropolishing processes for iron and steel alloys.