Corrosion behaviour of superferritic and austenitic stainless steel for food application

The food industry makes extensive use of conventional stainless steels, AISI 304 and AISI 316, for their high corrosion resistance in several aggressive environments, especially in the stage of cleaning and sanitizing. In this paper, among the possible alternatives available in the market, superferritic stainless steels are studied comparing them with the more common austenitic grades. The characterization work aimed at defining, through corrosion tests carried out in the specific operating conditions, if some ferritic / superferritic stainless steels may represent, from the perspective of resistance to corrosion, possible substitutes to the austenitic grade. For any selected materials, two different surface finishes were characterized. Potentiodynamic tests were carried out at room temperature in 0.5M NaCl and in alkaline foaming cleanser; at a temperature of 55°C in alkaline detergent; at a temperature of 70° C in an environment of 35% hydrogen peroxide. In addition, crevice tests have been performed. The tests allowed to define the corrosion limits and applications of ferritic/superferritic steels and to define operating conditions for which they can be considered substitutes equivalent of austenitic steels.