Effect of precipitated phases on the pitting corrosion of Z3CN20.09M cast duplex stainless steel

Abstract

The effect of precipitated phases on the pitting corrosion of a Z3CN20.09M cast duplex stainless steel (CDSS) which has been widely used in primary coolant pipes of nuclear power plants was investigated by using isothermal aging treatment and potentiodynamic anodic polarization methods. It was found that M23C6 carbide and · phase precipitated at the ferrite/austenite boundaries and in ferrite of the aged steel. The pitting potentials of the specimens aged at 700°C decreased with increasing of the precipitates content. The experimental results indicated that even a few percent of precipitates (about 1.0 vol%) in this steel could also worsen its pitting resistance. The pitting of the aged Z3CN20.09M specimens developed at the ferrite/austenite phase boundaries where precipitates formed often. These effects could be directly attributed to the presence of secondary austenite at the ferrite/austenite phase boundaries, which was found to be poor in Cr by energy dispersive X-ray (EDX). © 2013 The Japan Institute of Metals and Materials.