METHOD FOR PRODUCING A CHROMIUM COATING ON A METAL SUBSTRATE

In the method for producing a trivalent chromium based coating on a metal substrate,a layer of nickel phosphorus alloy is deposited on a metal substrateanda trivalent chromium layer is electroplated on the Ni-P layer. The coated metal substrate is subjected to one or more heat treatments to harden the coating and to produce multiphase layers including at least one layer containing crystalline Ni and crystalline Ni 3 P, and at least one layer containing crystalline Cr and crystal- line CrNi.By using this method it is possible to pro- duce coatings having a Vickers microhardness value higher than 2000 HV.