Sensitization phenomena on aged SAF 2205 duplex stainless steel and their control using the electrochemical potentiokinetic reactivation test

Microstructural changes and resulting properties were studied for SAF 2205( dagger) (UNS S31803) austeno-ferritic stainless steel (SS) aged between 700 degrees C and 900 degrees C for up to 2 weeks and then water-quenched. Qua ntitative metallography coupled with x-ray diffraction techniques were adop ted to follow ferrite (alpha) transformation with subsequent formation of s econdary austenite (gamma(2)) and sigma (sigma) phase. The kinetic model of a! transformation. was interpreted in the form of an Avrami-type expressio n The electrochemical potentiokinetic reactivation (EPR) test was used to e valuate the degree of sensitization of the aged specimens. Results were com pared with results from the corrosion test in boiling nitric acid (HNO3). I nfluences of the transformation of ferrite into austenite, sigma phase, and of other microstructural variations such as as chromium nitride (Cr2N) pre cipitation on stability of the passive film were shown The susceptibility t o intergranular corrosion phenomena was caused by chromium depletion caused by sigma phase precipitation, while chromium nitrides appeared less harmfu l. Results were expressed as an isocharge line diagram that allowed concise identification of sensitization and desensitization ranges.