Effect of Cold Working on Corrosion Fatigue Behavior of Austenitic Stainless Steel in Acidified Chloride medium

Abstract

Nitrogen is one of the most important alloying elements in alloy steels and even in small amounts can improve their properties. Because of its favorable properties, high performance nitrogen containing austenitic stainless steels are currently being developed for an advanced application that requires high strength along with better corrosion and wear resistance. The present study investigate the effects of cold work (CW) on the microstructure and corrosion fatigue (CF) resistance of AISI Type 316 LN stainless steel containing 0.11 wt. % nitrogen using microscopic, electrochemical and surface analytical methods. Potentiodynamic anodic polarization experiments were carried out in two chloride concentrations (1 M NaCl) and (5 M NaCl + 0.15 M Na2SO4) indicated that pitting potential (Epit) and passivity range drastically decreased with increase in chloride concentration and increased deformation from 0 to 20% CW. In 5 M NaCl + 0.15 M Na2SO4, corrosion resistance (Rp) decreases with an increase in cold work due to increased susceptibility of the passive film towards dissolution due to increase in dislocation density. CF behaviour of AISI Type 316LN SS with 0.11 wt.% nitrogen was studied in acidified 5 M NaCl + 0.15M Na2SO4 solution at a stress ratio (R) of 0.5 and a frequency (η) of 0.1 Hz with varying mean stress (σmean) and open circuit potential was monitored throughout till the failure of the specimen occur. Based on in-situ electrochemical measurements during corrosion fatigue tests, the shift in potential indicates the crack initiation process. The S-N curve of fatigue life (Nf) vs. stress amplitude was also generated. This study showed that the CF resistance increases with an increase in cold work and the number of cycles to failure and critical cracking potential decreases with increasing mean stress. The crack initiation and propagation show a transgranular mode in all the tested conditions.