PRE-S - A New Formalism to Rank the Pitting Corrosion Resistance of Stainless Steels Depending on the Actual Functional Surface Properties

摘要

The calculation of the PREN (pitting resistance equivalent) from the content of the alloying elements chromium, molybdenum and nitrogen is a widely used formalism to rank the resistance to pitting corrosion of stainless steels. However, there are other factors like mechanical and chemical surface treatments which largely influence the functional properties of the metal surfaces and thereby the corrosion resistance. These influences were evaluated in a systematic study and correlated to the critical pitting potential measured in 3 % NaCl-solution. Based on these results a new formula, named PRE-S (Pitting Resistance Equivalent Surface) was developed which can be used to characterize the actual corrosion behavior of parts according to their functional surface properties. This PRE-S formula includes the traditional PREN together with terms for surface roughness, chemical treatment and air-passivation.