Nickel Release Rate of Several Nickel-containing Stainless Steels for Jewelries

Nickel-containing stainless steels have been widely applied in watch and jewelry production, and their responses to the Nickel Directive become a universal concern in the industry. The nickel release rates and corrosion behaviors of types 316L, 304, 303 and 201 stainless steels under the conditions of solid solution and mirror polishing were studied by artificial sweat soaking and electrochemical methods. The results show that the weekly nickel release rates in artificial sweat do not strictly correspond to the nickel contents, which present a descending order as 303 stainless steel of 2. 06 mu g/cm(2), 201 stainless steel of 1. 51 mu g/cm(2), 304 stainless steel of 0. 08 mu g/cm(2) and 316L stainless steel of 0. 02 mu g/cm(2). Both the nickel release rates of type 303 and 201 stainless steels significantly exceed the threshold values regulated in EN1811 : 2011; therefore, they should be avoided to be used as watch and jewelry materials owing to the risk of nickel sensitization. The nickel release rates of 316L and 304 stainless steels meet the requirements of the standard. Sulfide inclusions in stainless steel become the sources of pitting and exacerbate the damage of the passivation membrane, which is the significant cause to enhance the nickel release rates.