Corrosion Fatigue Investigations of CrNiMoN Austenitic Stainless Steels

CrNiMoN austenitic stainless steels are a common material for applications in corrosive environments, especially chloride containing environments. Steels of this type stand out through their ability to passivate, their good mechanical properties and high ductility. Previous investigation on a solution annealed and cold worked superaustenitic CrNiMoN27-30-3-0.3 showed that the fatigue limit is just slightly decreased in 43 wt% CaCl₂ solution compared to inert glycerine. In this paper a conventional austenitic stainless steel with 14 wt% Ni and 18 wt% Cr has been investigated in solution annealed and cold worked condition and the results are compared with the superaustentic stainless steel. Stress versus number of cycle curves have been recorded in 43 wt% CaCl₂ solution and inert glycerine at 120°C. A stress ratio of 0.05 was chosen to avoid destruction of the fracture surfaces. To allow corrosion to take place a frequency of 20 Hz was used. Fracture surfaces of specimens which failed after relatively short time and close to the fatigue limit have been excessively investigated in a high resolution SEM and evaluated as a function of the medium, applied stress and cold worked state. The effect of the medium and cold deformation on crack initiation and propagation is critically discussed. Additionally electrochemical investigations and immersion tests have been performed.

Key Words: corrosion fatigue, austenitic stainless steel, fracture surface, chloride media