The electropolishing of iron, the ferritic iron-chromium alloys, Fe-13Cr and Fe-24Cr, and austenitic type 304 stainless steel has been investigated in H3PO4-H2SO4 electrolytes using rotating disk electrodes. The electropolishing of stainless-steel-type alloys takes place in the transpassive region and is mass transport controlled. It is favoured by high temperatures. The anodic polarization of the Fe-Cr alloys in 65% H3PO4-20% H2SO4-15% H2O is insensitive to the elemental composition of the alloy and is the same as for the austenitic type 304 stainless steel. At 70°C electropolishing is obtained for a wide concentration range of H3PO4-H2SO4, but in the absence of H3PO4, iron passivity prevents the establishment of electropolishing conditions.
L. Ponto, Dr. Madhav Datta, and Landolt, D., “Electropolishing of iron-chromium alloys in phosphoric acid-sulphuric acid electrolytes”, Surface and Coatings Technology, vol. 30, pp. 265–276, 1987.