Metastable pitting in 25 Cr duplex stainless steel

Evidence of metastable pitting in conventional austenitic stainless steels at room temperature is now common. Because of the small currents associated with individual events, most studies have been carried out on micro electr odes (typically 50 mu m diameter). Here in contrast, with high chromium dup lex stainless steels (DSS), metastable pitting is clearly observed on large r electrodes in tests at elevated temperatures in neutral NaCl solutions. B elow the Critical Fitting Temperature (CPT), large metastable current peaks are observed across a range of low potentials, with less activity at highe r potentials. Above the CPT, stable pits initiate at the same low potential s where metastability occurs below the CPT, usually preceded by one or two metastable events. There are evident differences between the growth of meta stable pits-and the transition from metastable to stable pitting-in high-ch romium DSS from that in single phase austenitic steels. A proposed model to explain the metastability in these highly alloyed duplex steels is describ ed. (C) 1999 Elsevier Science Ltd. All rights reserved.