HEAT TREATMENT INFLUENCE ON LOCALIZED AND SELECTIVE CORROSION RESISTANCE IN A 21 Cr 1 Ni DUPLEX STAINLESS STEEL

Abstract

Duplex stainless steels offer a good combination of mechanical properties and corrosion resistance compared to standard austenitic grades. They are widely used in chemical, petrochemical, fertilizer and cellulose industries. These steels solidify liquid + ferritic field and it is during cooling of the solid that a partial ferrite transformation into austenite takes place. The amount of austenite and ferrite phases depends on chemical composition and cooling rate. The best combination of mechanical properties and corrosion resistance is obtained with a á /ã volume ratio near to 1. In this work, localized corrosion resistance of a rolled duplex stainless steel 21 Cr 1 Ni was investigated by means of Double Loop Electrochemical Potentiodynamic Reactivation (DL-EPR) and potentiostatic tests performed using a computer controlled system (0.5 M H2SO4 + 0.01 M KSCN aqueous solution). This procedure was optimized to investigate the austenitic stainless steels intergranular corrosion susceptibility, but it was found to be useful also for other localized corrosion mechanisms (e.g. pitting, stress corrosion cracking). Furthermore, in order to identify the main localized corrosion morphologies, specimens surfaces were investigated by means of a light optical microscope. Finally, results were compared with the localized corrosion resistance of two 22 Cr 5 Ni stainless steels (characterized by different á /ã ratios).