ELECTROLYTIC TREATMENT OF CHROMIUM-CONTAINING ALLOYS AND ELECTROLYTES FOR USE THEREIN

1377079 Electrolytic hardening of porous films on Fe-Cr surfaces INTERNATIONAL NICKEL Ltd 27 Oct 1972 [3 Nov 1971 12 Oct 1972] 51164/71 and 47047/72 Heading C7B The hardness of a porous film formed on the surface of a chromium containing iron alloy, e.g. stainless steel, by treatment in an aqueous solution of chromic and sulphuric acids is increased by electrodeposition of an oxide deposit in the pores thereof by cathodic reduction of ions derived from a soluble salt containing a metallic element, e.g. Al, Ti, V, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Sn or Si, present in the electrolyte and/or a rise in pH in the pores brought about by the electrolysis; the conditions of treatment being such that no oxide deposit is formed on the surface of the porous film.