Abstract: A method for depositing chromium and iron metals on substrates is disclosed in which the chromium hardens when heated. The electrolytic plating bath preferably includes: (a) water soluble Cr(III) produced by reducing Cr(VI) with sufficient amounts of methanol or formic acid; (b) ammonium formate; (c) a sulfate catalyst, such as sodium sulfate; (d) an inorganic iron compound, such as iron sulfate; (e) sufficient amounts of boric acid to substantially saturate the bath; and (f) a sufficient amount of sulfuric acid to provide a bath pH of from about 1.0 to about 1.5. The heat-hardenable chromium deposit allows the plated substrate to be heat tempered after plating to provide a KHN of greater than about 1200. This eliminates the necessity of removing oxidation products from an unplated heated substrate. Moreover, the amount of toxic Cr(VI) present in the bath is greatly diminished, and is replaced with a Cr(III) species that is environmentally safer.

Abstract: A method for depositing chromium on metal substrates is disclosed in which the chromium hardens when heated. The electrolytic plating bath includes water soluble Cr(III), a sulfate catalyst, a metal ion buffer, and sufficient amounts of a reducing agent such as methanol to reduce substantially all Cr(VI) to Cr(III). The heat-hardenable chromium deposit allows the plated substrate to be heat tempered after plating, which eliminates the necessity of removing oxidation products from an unplated heated substrate. Moreover, the amount of toxic Cr(VI) present in the bath is greatly diminished, and replaced with a Cr(III) species that is environmentally safer.