Characterisation of microstructural damage due to corrosion fatigue in AISI type 316 LN stainless steels with different nitrogen contents

Abstract

Corrosion fatigue (CF) behaviour of AISI type 316 LN stainless steels (SS) with three different nitrogen contents was evaluated in a boiling aqueous solution of 5 M NaCl+0·15 M Na₂SO₄+2·5 ml l⁻¹ HCl at a stress ratio of 0·5 and a frequency of 0·1 Hz. After the CF tests, the specimens were observed under a field emission gun scanning electron microscope (FEG-SEM) as well as an atomic force microscope (AFM) to understand the deformation mechanism which led to the failure. Slip character could be explained based on the surface deformation features observed using FEG-SEM and AFM. A slip irreversibility relation has been proposed which when applied could explain the CF behaviour of these steels with varying nitrogen contents. Increase in the nitrogen content increased the slip reversibility up to 0·14 wt-% nitrogen; however, further increase in nitrogen content had no beneficial effect on the slip reversibility.