Effect of microstructure on the pitting susceptibility of a martensitic-ferritic stainless steel: A corrosion-metallurgical study.

The relationship between microstructure, composition and the localized corrosion resistance of a low carbon Cr-Ni-Mo martensitic-ferritic stainless steel was investigated. Four heat treatments were selected to examine the effect of varying tempered Martensitic-Ferritic microstructures on localized corrosion susceptibility. The pitting potential for each heat treatment was determined in deaerated 192 g/L NaCl electrolyte saturated with CO 2 (pH: 3.8) at 65 °C. Austenite reversion and other microstructural transformations associated with tempering had a detrimental effect on the pitting potential. The resulting chemical and structural inhomogeneities decreased the pitting potential. [Display omitted] • A complex MFSS was assessed as a function of heat treatment producing variations in steel microstructure. • Pitting potential was detrimentally affected by austenite reversion during tempering process. • For materials tempered at higher temperatures, pitting initiation occurred at previously reversed areas depleted in Cr/Mo. • In the as quenched condition pitting initiation occurred at lath boundaries and prior austenite grain boundaries. • Low tempering temperature led to initiation sites corresponding to the as quenched condition and inside reversed areas [ABSTRACT FROM AUTHOR]