Localized corrosion resistance of duplex stainless steels:methodology and properties; a review paper

Abstract

Increasing interest in duplex stainless steels is due to their ability to combineelevated mechanical properties (strength, fatigue...) and an optimal resistance to manytypes of corrosion like Stress Corrosion Cracking or Intergranular Sensitization. Givenhigh chromium content of the standard and super-duplex steels along with molybdenum andnitrogen alloying additions, they also exhibit an excellent resistance to pitting andcrevice corrosion in halide-containing media generally equivalent to austenitic andsuper-austenitic with similar Pitting Resistance Equivalent. Further aspects of thequestion are reviewed in introduction of the present paper including passive film andmetallurgical features such as two-phase microstructure, presence of non metallicinclusions, precipitates or intermetallic phases. Then, this work addresses the problemsof corrosion testing of duplex stainless steels. It is intended in particular to shedlight on some points of practical importance regarding electrochemical characterizationbest practices. Thus, a reliable ranking of materials, including new lean grades, requiresa relevant choice of corrosion criteria and polarization methods. The determination ofboth pitting potentials and critical pitting temperatures is achieved by using acombination of several electrochemical tests based on potentiodynamic, potentiostatic aswell as galvanostatic experiments together with a statistical analysis when needed.