Abstract
Austenitic stainless steels are frequently subjected to high chloride containing solutions and cyclic mechanical loading at the same time. Therefore, it is of vital interest to gain knowledge about the crack growth behavior and the corrosion fatigue mechanism.
In the current work a superaustenitic CrNiMoN stainless steel in different conditions (solution annealed and cold worked) is characterized in inert glycerin and 43 wt% CaCl2 at 120°C regarding its crack growth and corrosion fatigue behavior.
Crack growth is thereby described by determining crack propagation rate curves and corrosion fatigue is studied by recording S/N curves at a stress ratio of 0.05. Using this stress ratio the destruction of the fracture surfaces is avoided as there is only tensile stress applied. The results of these experiments are correlated to observations on the fracture surface of selected tested specimens using scanning electron microscopy and electron dispersive X-ray spectroscopy. Additionally, cyclic polarization curves are recorded and immersion tests are performed to evaluate the electrochemical behavior.
Results of S-N curves show a moderate decrease of the fatigue limit in the corrosive media. Furthermore, as expected, the threshold cyclic stress intensity factor ΔKth in the corrosive media is lower compared to the inert media. However, surprisingly, a pronounced slowdown of the crack propagation rate is observed in the Paris region in the corrosive media compared to glycerin.
Possible explanations like e.g.: oxide induced crack closure effects will be critically discussed in this paper.
